[Title of the Invention] METHOD OF PRODUCING WELD JOINT [Technical Field of the Inventio~l] [OOOl] The present invention relates to a metliod of producing a \veld joint having weld 111etal which has high hardness and excellent abrasion resistance and does not easily cause cold cracking when a high-hardness steel plate which has excellent abrasion resista~lcea nd is used in the field of constl~~ctiomna chines and industrial machines is welded. Priority is clainled on Ir~tert~ationAalp plication No. PCT/JP2013/080242, filed on Noventber 8,2013, the content of x\~I~icihs incorporated herein by reference. [Related Art] [0002] In niany cases, a steel plate used in a coostruction nlachine for iiiine excavation or civil engineering work needs to be replaced due to wear. In order to lengthen the senrice life of the steel plate, an abrasion resistant steel to increase the hardness of the steel plate is used. The l~ardnesso f the steel plate majr vary depending on the use enviro~lmenot r purpose, and in general, abrasion resistant steel plates in the HB400 grade (from -360 to HI3440 in terms of Brinell hardness standard value, and froin HV38O to HV469 in terms of Vickers hardness standard value), in the I-IB450 grade (from I-IB410 to IlB490 in terills of Brinell hardness standard value, and from I-IV435 to HV533 in terms of Vickers hardness sta~~tlard value), in the HB500 grade (fiarn HB450 to HB550 in terms of Brinell hardness standard value, and from TIV478 to IIV585 in terms of Vickers hard~lesss tandard value), and in the HB6OO grade (from HB550 to HB65.0 in tenlis of Brine11 hardness standard value, and from HVS85 to HV693 in terms of Vickers hardtless standard value) are widely used. [0003] Most types of abrasion resistant sleel arc \wleldcd, and weld metals may also require abrasion resistance close to base metals (abrasion resistant steel). In order to illcrease the abrasion resistance of the \veld nletal, there is also a 11eed to increase the hardness thereof. Ho~veverw, hen the hardness of the meld metal is increased, cold cracking caused by l~ydmgenth at infiltrates during welding is very likely to occur. Furthennore, since abrasion resistant steel having a high hardness is used as the base metal, an increase in the binding force is also a cause of the easy occurretlce of cold cracking. [0004] In order to avoid such cold cracking, preheating is generally performed before welding. However, the hardness of the abrasion resistant steel is more easily reduced by heatulg than typical steel and thus a high preheating temperature need not be enlployed. It is preferable that the hardness of the \weld metal be at the same level as that of the base metal. For example, in a case where the abrasion resistant steel in the HB400 grade or HBS00 grade is used as the base metal, it is preferable that the hardness of the weld metal be at least HV337 (HB320) or higher, or HV380 (HB36O) or higher if possible. [OOOS] In addition, the liardness in the vicinity of the surface is important for a weld n~etazl one from the viewpoint of abrasion resistance. Durkg 11111lti-layer melditlg, weld nletal for a lower layer is re-heated in a subsequent pass and thus the hardness thereof is slightly reduced. Ho\vever, weld metal for tlie uppermost layer in tlle case of multi-layer welding or weld nietal in a case of single pass welding may have suEcient hardness in tile vicinity of the ssurlace of the weld metal. Accordingly, it is tl~oughth at a \\>eldingn icthod of forming weld metal which has a surface hardness of HV337 or Iliglier and TlV533 or lower and sufficient abrasion resistance and does not cause cold cracking even when preheating is not perfonned, or a welding method of i'onning weld metal which has a surface hardness of HV380 or higher and HV533 or lower and sufficient abrasion resistance and does not cause cold cracking even wlvhen preheating is not perfornled, is extremely useful in a weld joint which uses an abrasion resistant steel having a surface hardness of HV380 or higher and HV693 or lo\ver as the base metal. [0006] As a teclu~iqnef or suppressing cold cracking caused by hydrogen .rvhieh occurs in high-strength weld metal, for example, methods of Patent Documents 1 to 5 are proposed. In Patent Document 1, the occurrence of cold cracking is preveuted by allowing retained austenite in a steel plate used for a high-strength line pipe or the like to f~lnctiona s a hydrogen-trapping site. In Patent Document 2, the occurrence of cold cracking is also prevented by alloxving oxides in a steel plate used for a high-strength line pipe or tlie like to htictioll as a Ilydrogen-trapping site. [0007] Patent Docun~eti3t discloses a technique for preventing the occurrence of cold cracking by allowing Mo carbides in steel liaving a tensile strength of 800 MPa to 1150 MPa to fi~nctiona s a trapping site. Patent Document 4 discloses a technique for improving the cold cracking resistance of steel having a tensile strength of 880 MPa to 1 I80 MPa by appropriately mising Mg wit11 the covered material of a shielded mctal arc welding material and thus reducing the amount of diffusible hydrogen in weld metal ininmediately after wvelding to about 3.0 m1/100 g to 4.0 1111/100 g. Patent Document 5 discloses a technique for suppressing cold cracking by limiting the amount of hydrogen cotitairled in a flux-cored wire for gas-shielded arc welding. The techniques are applied to base metals and \veld metals having a strength of lower than 1200 MPa and are not teclmiques capable of inlproving the cold cracking properties of weld metal having a hardness of HV380 (about 1200 MPa in ternls of tensile strength) almtl abrasion resistance. [OOOS] Moreover, in gencral, when an austenitic stainless steel welding material is used. the infiltratiou of hydrogen into weld metal is significantly reduced and thus scnsiti\~ityto cold cracking can also be reduced. In addition, since the material has an austcnite stmcture, cracking due to reduced ductility is less likely to occur. However, the weld metal wllich uses the austenitic stainless steel welding material cannot easily increase strength, that is, hardness, and thus abrasion resistance cannot be expected. [0009] Accordingly, there is a dematld for fonning, in a \veld joint which uses an abrasion resistant steel having a high hardlless of HV380 or higher and HV693 or lowver as the base metal, \veld metal which has a surface hardness of HV337 or higher atid HV533 or lowver and excellent abrasiou resistatlce and does not easily cause cold cracking, or weld metal wvhich has a surface hardness of I4V380 or higher and IIV533 or lower and excellent abrasion resistance and does not easily cause cold cracking througl~g as-shielded arc welding [Prior Art Document] [Patent Docu~ncnt] [OO 1 01 [Patent Document 11 Japanese Unexaminetl Patent Application, First Pitblication No. 2012-176434 [Patent Document 21 Japanese Unexamined Patent Application, First Publication No. 2012-218034 [Patent Docunlent 31 Japanese Unesanlined Patent Application, First Publication No. 2005-40816 [Patent Docunlent 41 Japanese Unexaniined Patent Application, First Publication No. Hll-147196 [Patent Docunient 51 Japanese Unexamined Patent Application, First P~lblicationNo2. 009-255168 [Disclosure of the Invention] [Problems to be Solved by the invetition] [OOll] An object of the present invention is to provide a method of producing a weld joint which uses a high-hardness steel plate having a high C content and a surface hardness of I-W380 or higher and HV693 or lower as a base metal, and has \\,elti metal \~~hichlais a snrfacc hardness of HV337 or higher and HV533 or lo\ver and excellent abrasion resistance and does not easily cause cold cracking, or weld ~neta~l vhichli as a surface hardness of HV380 or higher and HV533 or lower and excellent abrasion resistance and does not easily cause cold cracking. [Means for Solving the Problem] [0012] For abrasion resistant steel according to the related art, a preheating temperature duri~igw elding was important to prevent cold cracking. Accordingly, in general, wcldit~gw as performed using a welding material for mild steel by setting a preheating temperature as the top priority. Therefore, the hardtless of the weld nietal zone \iras low and wear was very likely to occur. This is thought of as a problem. In the present invention, it is newly found that, when the hardness of tlie \veld metal zone is increased on the contrary, cracki~gis very likely to occur not in the heat-affected zone of the base metal but in the weld metal itself. Therefore, the relationship behveen the CEN of the weld metal and cracking is examined, and tllen an appropriate range of the CEN of the weld metal is obtained. [0013] Cold cracking that occurs in the weld metal during welding is affected by tlie strength of the veld metal, a joint-restricting force, and the anonnt of diffusible hydrogen in the weld metal. The inventors examined various methods to reliably suppress cold cracking using high-hardness \veld metal havi~iga surface hardness of HV337 or higher and I-IV533 or lower, or high-hardness weld metal having a surface hardness of HV380 or higher and HV533 or lower. As a result, it was concluded that the most reliable method is to sufficiently reduce the atnount of diffusible hydrogen in the weld metal and to set a CEN specified with alloy components in the weld metal to be 0.20 mass% to 0.58 mass%. [0014] FIG 1 sho\vs results of a y-groove weld-cracking test specified in JIS Z 3 158 performed on various welding lnaterials which varied in steel plates and flux compositions under various conditions. Various weld metals in which the hardnesses of the weld lnetals vary and the amounts of diffilsible hydrogen in the wed ~netalsv aly arc produced, and preheating temperature limits at ~vhichth e occurrence of cracking is suppressed are obtained. In FIG. I, the relationsliip betweell the alilount of diffilsible hydrogen in the weld rnctal and the prcl~catillgte mperature limit at \vlvhic11 the occurrence of cracking is suppressed is plotted according to the hardness levels of tl~e \veld metals. Here, as a cold-cracking test, a test based on JTS Z 3 158 (method of y-groove weld-cracking test in 1993) was performed at room temperatl~re(2 5OC), and the absence of cracking in surfaces and sections is evaluated as passing. A test for measuring the anloutlt of diffi~sibleh ydrogen was performed according to a gas chromatography method based on JIS Z 3118 (method for measurement of amount of l~ydrogene volved from steel welds in 2007). [OO 1 51 As illustrated in FIG. 1, \vllen the amount of diffiisible hydrogen in the \veld metal ilnmediately after welding is lower than 1.0 nlVlOO g, the preheating temperature limit for crack prevention at low tetnyeratme docs not significantly depend on the hardness of the \veld metal. Therefore, by allo\ring the aino~~onft d iffusible hydrogen lo be lower than 1.0 mV100 g, the sensitivity of the weld metal havitlg a hard~lesso f HV337 or higher and HV533 or lower and the weld rnctal having a hardness of HV380 or higher and HV533 or lower to cold cracking can be significantly reduced. [00 161 Howevel; reducing the amount of diffi~sibleh ydrogen in the \veld metal immediately after welding to such a level is not easily perfomled in the related art. The inventors repeated various examinations, and newly found that the amount of diffilsible hydrogen in weld llletal can be stably 1-educed to a level \i41icl1 is not easily acllieved in the rclatcd art by improving the flus composition of a flus-cored wire. Specifically, it is found that by allowing a certain atnount of fluorides including CaF2 to be contained it1 the flux components, adjusting the anloutit of oxides, and allowing the mixing ratios of fluorides anti oxides to be in predetermined ranges, the amount of difisiblc hydrogen in thc weld metal can be stably suppressed to be lo\ver than 1.0 m1/100 g. [0017] The sensitivity of the weld nletal to cold cracking significantly depends on the hardness of the weld ~iletaal nd is also affected by alloy elen~ents. The iinventors examined the relationship between various alloy compositions and the sensitivity of cold cracking (cracking suppression preheating temperatnre) for weld tnetals having a hardness of HV337 or higher and HV533 or lower and weld tnetals having a hardness of HV380 or higher aid HV533 or lo~ver. As a cold-cracking test, a test based on JIS Z 3158 (method of y-groove weld-cracking test in 1993) was perforn~cd at varying preheating temperaturcs, and the lowest preheating tetnperature at ~vliichc old cracking did not occur is referred to as a preheating temperature limit for crack prevention. During welding, flux-cored weld wires of the present invention described below are used, and all of the amounts of diffusible hydrogen in the weld metals are lower than 1.0 1111/100 g. [0018] As a result, as sho~vnin FIG. 2, it is found that when a CEN calculated by Expression 1 (refer to Welding book selections 10. "Welding of iron and steel materials" published by Sanpo Publications hicorporaled. (1999), p.163) is 0.58 ~nass%o r loiver, the preheating temperature liniit for crack prevention can be equal to or lower than room temperature (25OC), and the occurrence of cold cracking can be suppressed without preheating. CEN=[C]+(0.75+0.25xtanh(20x([C]- O.l2)))x([Si]/24+[M11]/6+[Cu]/l5+[Ni]/20+([Cr]+[Mo]+[Nb]+[V])/5+5x[R]) ...( Expression 1) Hcrc, eletnents with [] represent the amounts (mass%) olll~ceo rresponding elements. In a case ~vlvhere there are no added elements, [I is substitnted with zero. [0019] The present invention has been made based on the findings, and the summary is as follo~vs. [0020] (1) According to a first aspect of the invention, a tnethod is provided of producing a weld joint by perfortning a gas-shielded arc welding, using a flux-cored \$?ire filled with flux into a steel sheath, on any one of a steel plate having a Vickers hardness HV of 380 or higher and 514 or lower, a plate thickness of 20 mm to I00 mm, a C content of 0.120 mass% to 0.300 mass%, and a CEN calculated by the following Expression 1 0l0.20 mass% to 0.75 mass%, a steel plate having a Vickers hardness HV of higher than 514 and 565 or lower, a plate thickness of 12 mnl to 100 mm, a C content of 0.120 mass% to 0.300 mass%, and a CEN calculated by the following Expression 1 of 0.20 mass% to 0.75 mass%, and a steel plate having a Vickers hardness HV of higher than 565 and 693 or lower, a plate thickness of 6 nlm to 12 mm, a C content of 0.350 inass% to 0.450 inass%, and a CEN calcnlated by the following Expression 1 of 0.20 mass0/0 to 0.85 mass%, the method including: (a) during the gas-shielded arc welding, not perfonning a prelleating operation in a case \vhere a temperature of the steel plate is 10°C or higher, and in a case where the tenlperature of the steel plate is lower than 10°C, perfonning the preheating operation so that the tcnlperature of the steel plate is 10°C or higher, (b) whcrein the flux-cored wire contains onc or tnore of CaF2, BaF2, SrF2, and MgF2, and when a sum of amounts thereof is a, the u \\'it11 respect to a total mass of the flux-cored wire is 3.3% to 8.0% in temls olmass%, the flux-cored wire contains one or niore of Ti oxides, Si oxides, Mg oxides, and A1 oxides, and \\'hen a sum of amounts thereof is p, the fl with respect to the total mass of the flux-cored wire is 0.10% to 1 .SO% in terms of mass%, a sum of amounts of CaC03, BaCO3, SrC03, and MgCO, with respect to the total mass of the flux-cored wire is lower thru~0 .60% in ter~nso f mass%, an amount of at1 iron powder in the flux with respect to the total mass of the flux-cored wire is lower than 10.0% in terms of mass%, a ratio of the amount of CaF2 to the a is 0.90 or higher, a ratio of the a to the fl is 3.0 or higher and 80.0 or lo~ver, an amount of CaO with respect lo the total mass of the flux-cored wire is lower than 0.20% in ternis of mass%, the flux-cored wire includes chemical components excluding metal fluorides, metal oxides, and metal carbonates, with respect to the total Illass of the flus-cored wire, in terms of mass%: C: 0.010% to lower than 0.060%; Si: 0.05% to 1.80%; MI: 0.50% to 4.00%; P: 0.050% or lower; S: 0.020% or lower; Al: 0.005% to 0.150%; Cu: 0% to 0.75%; Ni: 0% to lo\vcr than 1.00%; Cr: 0% to 3.50%; Mo: 0% to 1 .SO%; Ti: 0% to 0.1 50%; Nb: 0% to 0.15%; V: 0% to 0.45%; B: 0% to 0.0500%; Mg: 0% to 2.0%; Ca: 0% to 2.0%; REM: 0% to 0.0150%; and the remainder: Fe and impurities, (c) wherein a weld rnetal of the weld joint includes as a chemical composition, in terms of mass%: C: 0.100% to 0.170%; Si: 0.05% to 0.80%; Mn: 0.20% to 2.50%; Al: 0.0050% to 0.1000%, P: 0.050% or lo\vcr; S: 0.020% or lo\jrer; N: 0.015% or lower; Cu: 0% to 0.50%; Ni: 0% to lower than 0.70%; Cr: 0% to 2.50%; Mo: 0% to 1.00%; Ti: 0% to 0.100%; Nb: 0% to 0.100%; V: 0% to 0.30%; B: 0% to 0.0100%; 0: 0% to 0.100%; Mg: 0% to 0.100%; Ca: 0% to 0.100%; MM: 0% to 0.0100%; and the remainder: Fe and impurities, a CEN of the weld metal calculated by the follo\ving Expression 1 is 0.20 mass% to 0.58 inass%, an average Vickers hardness HV of the weld metal measured at 1 mm inward from a surface of the wveld metal is 337 to 440, and all of (a) to (c) are satisfied. CEN=[C]+(0.75+0.2Sxtanh(20x([C]- 0.12)))x([Si]I24+[M11]/6+[Coi]/5l+ [Ni]l20+([Cr]+[Mo]+[Nb]+[V])/S+5x[B]) . . .(Expression 1) where elements with [I represent the amounts (mass%) of the corresponding elements. [0021] (2) According to a second aspect of the invention, a method is provided or produci~lga \veld joint by perfomling a gas-shielded arc wvelding, using a flux-cored wire filled with flux into a steel sheath, on any one of a steel plate having a Vickers hardness HV of 380 or higher and 514 or lower, a plate thickness of 20 tnln to 100 nun, a C content of 0.120 inass% to 0.300 mass%, and a CEN calculated by the following Expression 1 of 0.20 mass% to 0.75 mass%, a steel plate having a Vickers hardness HV of higher than 514 and 565 or lower, a plate thickness of 12 111111 to 100 IIII~, a C contcot of 0.120 mass% to 0.300 mass%, and a CEN calculated by the follovving Expression 1 of 0.20 mass% to 0.75 mass%, and a steel plate having a Vickcrs hardness HV of higher than 565 and 693 or lowirer, a plate thickness of 6 mnl to 12 mm, a C content of 0.350 mass% to 0.450 mass%, and a CEN calculated by the follo\ving Expression 1 of 0.20 mass% to 0.85 mass%, the method including: (a) during the gas-shielded arc wvelding, not perfomling a preheating operation in a case where a te~nperatureo l'the steel plate is 10°C or higher, and in a case where the temperature of the steel plate is lower than 1O0C, perfor~ning tlle preheating operation so that the te~nperatureo f the steel plate is 10°C or higher, (b) wherein the flux-cored wire contauis one or more of CaF2, BaF2, SrF2, and MgF2, and when a sum of amounts thereof is a, the a with respect to a total mass of the flux-cored wire is 3.3% to 8.0% in terms of mass%, the flux-cored wire contains one or more of Ti oxides, Si oxides, Mg oxides, and A1 oxides, and when a sun1 of arnounts thereof is P, the wit11 respect to the total Inass of the flux-cored wire is 0.10% to 1.50% in terms of mass%, a sum of amounts of CaCOx, BaC03, SrCOx, and MgC03 with respect to the total rnass of the flux-cored wire is lo\wrer than 0.60% in ternls of mass%, an amount of an iron powder in the flux with respect to the total Illass of the flux-cored wire is lower than 10.0% in terms of inass%, a ratio of the alilou~lot f CaF2 to the a is 0.90 or higher, a ratio of the a to the is 3.0 or Iiigl~era nd 80.0 or lower, an all~ounot fCaO with respect to the total nlass of the flux-cored wire is lowver than 0.20% in terms of mass%, the flux-cored wire includes chemical components excluding nletal fluorides, metal oxides, and metal carbonates, with respect to the total Inass of the flux-cored wire, in terms of mass%: C: 0.060% to 0.350%; Si: 0.05% to 1.80%; Mn: 0.50% to 4.00%; P: 0.050% or lo\ver; S: 0.020% or lower; Al: 0.005% to 0.150%; Cu: 0% to 0.75%; Ni: 0% to lower than 1.00%; Cr: 0% to 3.50%; Mo: 0% to 1.50%; Ti: 0% to 0.150%; Nb: 0% to 0.15%; V: 0% to 0.45%; B: 0% to 0.0500%; Mg: 0% to 2.0%; Ca: 0% to 2.0%; REM: 0% to 0.0150%; and the remainder: Fe and impurities, (c) wvl~erein a weld metal of tile weld joint itlcludes as a chemical composition, in terms of illass%: C: 0.120% to 0.250%; Si: 0.05% to 0.80%; Mn: 0.20% to 2.50%; Al: 0.0050% to 0.1000%; P: 0.050% or lo\w~cr; S: 0.020% or lo~ver; N: 0.015% or lower; Cu: 0% to 0.50%; Ni: 0% to lo\ver than 0.70%; Cr: 0% to 2.50%; Mo: 0% to 1.00%; Ti: 0% to 0.100%; Nb: 0% to 0.100%; V: 0% to 0.30%; B: 0% to 0.01 00%; 0: 0% to 0.100%; Mg: 0% to 0.100%; Ca: 0% to 0.100%; REM: 0% to 0.0100%; the remainder: Fe and impurities, a CEN of the weld metal calculated by the following Expression I is 0.20 mass% to 0.58 mass%, an average Vickcrs hardness HV ofthe weld metal measured at 1 mm inward froin a surface of the weld metal is 380 to 533, and all of (a) to (c) are satisfied. CEN=[C]+(O.~~+O.~~X~E~I~II(~OX([C]- O.l2)))x([Si]/24+[Mn]l6+[Cu1]/15 +[Ni]/20+([Cr]+[Mo]+[Nb]+[V])/5+5x[B]) ...( Expression 1) where elements with [I represent the aniounts (mass%) of the corresponding elements. (3) According to a third aspect of the invention, a lnetliod is provided of producing a weltl joint by perfomling a gas-shieldecl arc welding, using a flux-cored wire filled with flux into a steel sheath, on ally one of a steel plate having a Vickers hardness HV of higher than 565 atid 693 01-lo \\rer, a plate thickness of 12 mm to 20 mm, a C content of 0.350 mass% to 0.450 mass%, and a CEN calculated by the follo\ving Expression 2 of 0.20 mass% to 0.85 mass%, and a steel plate having a Vickers hardness HV of liigller than 565 and 693 or lower, a plate thickness of greater than 20 mm to 50 nlln or smaller, a C content of 0.350 mass% to 0.450 mass%, and a CEN calculated by the followi~~Egx pression 2 of 0.20 mass% to 0.85 mass%, the tnethod inclnding: (a) during the gas-shielded arc wvelding, perfor~ninga preheating opel-ation so that a temperature of the steel plate is 100°C or higher in a case where the plate thickness of the steel plate is 20 mm or smaller, and in a case where the plate thickness of the steel plate is greater than 20 nun, perfornling the preheating operation so that the temperature of the steel plate is 150°C or higher, (b) wherein the flux-cored wire contains one or more of CaFz, BaF2, SrF2, and MgF2, and when a sum of amounts thereof is a, tlie a \\it11 respect to a total Inass of the flux-cored \\?ire is 3.3% to 8.0% in ternis of mass%, the flux-cored wire cot~tainso ne or niore ofT i oxides, Si oxides, Mg oxides, and A1 oxides, and when a s~ltilo fa n110l111ttlsl ereof is 0, the 0 with respect to the total mass of the flux-cored wire is 0.10% to 1.50% in tenns of mass%, a sum of amoonts of CaC03, BaC03, SrCO3, and MgC03 with respect to the total Illass of tlie flux-cored wire is lomer t h a ~0.6 00%i n ternis ofm ass%, an amount of an iron powder in the flux wit11 respect to the total Inass of the flux-cored wire is lower than 10.0% in terms of mass%, a ratio of thc amount of CaF2 to tl~ca is 0.90 or higher, a ratio of the u to tlie 0 is 3.0 or higher and 80.0 or lower, an amount of CaO witit respect to tlie total mass of the flux-cored wire is lower than 0.20% in terms of niass%, the flux-cored wire i~~cludcehse mical components excluding metal fluorides, metal oxides, and metal carbonates, with respect to the total 111ass of the flux-cored wire, it1 terms of mass%: C: 0.060% to 0.350%; Si: 0.05% to 1.80%; Mn: 0.50% to 4.00%; P: 0.050% or lower; S: 0.020% or later; Al: 0.005% to 0.150%; Cu: 0% to 0.75%; Ni: 0% to lower than 1.00%; Cr: 0% to 3.50%; Mo: 0% to 1.50%; Ti: 0% to 0.150%; Nb: 0% to 0.15%; V: 0% to 0.45%; B: 0% to 0.0500%; Mg: 0% to 2.0%; Ca: 0% to 2.0%; REM: 0% to 0.0150%; the retnaindcr: Fe atid impurities, (c) ~\~liereiat iw eld metal of thc \veld joitit iticludes as a chemical composition, in temls of mass%: C: 0.120% to 0.250%; Si: 0.05% to 0.80%; Mn: 0.20% to 2.50%; Al: 0.0050% to 0.1000%; P: 0.050% or lower; S: 0.020% or lower; N: 0.015% or lower; Cu: 0% to 0.50%; Ni: 0% to lower thai 0.70%; Cr: 0% to 2.50%; Mo: 0% to 1.00%; Ti: 0% to 0.100%; Nb: 0% to 0.100%; V: 0% to 0.30%; B: 0% to 0.0100%; 0: 0% to 0.100%; Mg: 0% to 0.100%; Ca: 0% to 0.100%; REM: 0% to 0.0100%; and the remainder: Fe and itnpurities, a CEN of the meld ~netacl alculated by the following Expression 2 is 0.20 mass% to 0.58 mass%, an average Vickers hardness HV of the weld ntctal measured at 1 mnl inward fro111 a surface of thc wvcld ntetal is 380 to 533, and all of (a) to (c) are satisfietl. CEN=[C]+(0,75+0,25xtanh(20x([C]- 0.1 2)))x([Si]/24+[Mn]/6+[Cu]/l S+~i]/2O+([Cr]+@vfo]+~b]+[~)/5+5xp]) . ..(Expression 2) where elemetlts with [] represent the amounts (mass%) of the corresponding elenlents. [0022] (4) In the method of proditcing a ~veldjoirtdt escribed in (1) to (3), the alnount of CaO in the flux-cored wire may be 0.1 5% or lower in tertlls of mass% wit11 respect to the total Inass of the flux-cored wire. [0023] (5) In the method of producing a weld joint described in any of (I) to (4), the flux-cored wire may include the chemical components excluding the metal fluorides, metal oxides, and metal carbonates, with respect to the total mass of the flux-cored wire, in terms of mass%: Ni: 0% to 0.1%. [0024] (6) In the method of producing a weld joint described in any of (1) to (5), the flux-cored wire lllajf include the chemical components excluding the metal fluorides, metal oxides, and lnetal carbonates, with respect to the total mass of the flux-cored wire, in terms of mass%: Cu: 0% to 0.50%; Cr: 0% to 1.00%; Mo: 0% to 0.50%; Ti: 0% to 0.050%; and Nb: 0% to 0.05%. [0025] (7) In the method of producing a weld joint described in any of (1) to (6), the steel sheath of the flux-cored wire may have a slit-like gap. (8) h~ the method of producing a weld joint described in any of (1) to (6), the steel sheath of the flux-cored \\?ire may not have a slit-like gap. [0026] (9) In the method of producing a \veld joint described in any of (1) to (8), a perflnoropolyether oil may be applied to a surface of the flux-cored wire. Effects of the Invention] [0027] According to the aspects of the present invention, a weld joint which uses a high-hardness steel plate having a high C content and a surface hardness of IN380 or higher and HV693 or lo~vera s a base metal, and has weld metal which has a surface hardness of HV320 or higher and HV533 or lower and escellent abrasion resistance and does not easily cause cold cracking, or weld metal which has a surface hardness of HV380 or higher and HV533 or lower and excellent abrasion resistance and does not easily cause cold cracking can be obtained. [Brief Description of the Drawings] [0028] FIG. I is a diagram sho\ving the relationship bcbveen the hardness of a base metal, the amount of diffi~sibleh ydrogen in weld metal, and a preheating ten~perature limit for crack prevention. FIG. 2 is a diagram sho~vitigth e relationship bct\vccn a CEN and a preheating temperature limit for crack prevention in weld rnetal liaving an amount of diffusible hydrogen of lower than 1.0 n11/100 g among \veld metals having a hardness of IIV337 or higher and HV533 or lower. FIG. 3A is a view S ~ I O \ V ~aI Ic~u t section of a wire. FIG. 3B is a view sho\~inga cut section of a wire. FIG. 3C is a view showing a cut section of a wire. [E~nboditnentso f the Invention] [0029] Icegarding a weld joint which uses a high-hardness steel plate as a base metal, the inventors found that when the amount of diffusible hydrogen in \veld metal immediately afier \velding is lower than 1.0 t111/100 g as described above, a prel~eating temperature limit for crack prevention at low tetnperature does not significantly depend on the hardness of the weld nietal and the sensitivity of weld metal havir~ga hardness of I-N337 or higher and NV533 or lower and weld nletal having a hardness of HV380 or higher and HV533 or lower to cold cracking call be sig~~ificantrleyd uced. [00301 Furthennore, in order to allow the atnoullt of difft~sibleh ydrogen in the weld metal immediately afier welding to be lo~verth an 1.0 1nlllO0 g, the inve~~torresp eated examination by varying the combination of flux conlponents of a flux-cored wire and the mixing ratios thereof. As a result, it is foi~ndth at flt~oridesin cluding CaF2 are particularly effective in reducing the amount of hydrogen, the amount of diffi~siblel~ ydrogenin the weld nletal can be significat~tlyre duced by allowing a certain amount of fluorides to be contained in the flux components, and the amount of diEt~sibleh ydrogen can be stably suppressed to be lower that1 1.0 m11100 g by adjusting the atnount of oxides and allowing the mixing ratios of fluorides and oxides to be in predetermined ranges. [003 11 The present inr~entionh as been made based on the cxan~i~iations.H ereinafter, an aspect of a method of producing a \veld joint according to an embodilnent will be described. The present inventio~is for a meld joint which is formed by using a higlihardness thick steel plate that is widely used as an ab~asionr esistant steel plate, has a C content of 0.12% to 0.45% hi ternls of mass%, and a liardness of HV380 or higher and HV693 or lower as a base metal, and perfor~nillga gas-shielded arc welding using the steel plate. In the present inventioti, \veld nletal has a che~llicacl ompositio~iln (I) or (2) described above. Hereinafter, the reasons that the chemical composition of the \veld tnetal is limited will be described. In the following description, " % nlealls "mass% if not particularly specified. [0032] (C: 0.100% to 0.250%) C is an elernent ~vhichtn ost affects the hardness of the weld metal. When the liardness of the base metal is HV380 or higher, it is preferable that tlie surface llarduess of the weld metal be at least HV337 or higher in order to ensure a certain degree of abrasion resistance for the weld metal. For this, the C content of the weld metal needs to be 0.100% or highel: In addition, \\!hen the hardness of the base metal is HV380 or higher, it is preferable that tlie surface liardness of tlie weld nletal be also HV380 or higher in order to ensure a similar degree of abrasion resistance to that of the base tnetal. In a case \\liere the surfacc hardness of the \veld rnetal needs to bc HV380 or highel; the C col~tctiot f the weld nietal necds to be 0.120% or higher. IIo~vever ,l i lien the C content is liigher than 0.250%, the hardness of the weld nietal becolnes higher than HV533 and thus the toughness of the weld ~lletaml ay be reduced. Therefore, the upper limit of the C content is 0.250%. In addition, typically, the C content of the weld nletal of a weld joint made by using a flux-cored wire having a C content of 0.010% to less than 0.060%, \vIiich \\ill be described later, is 0.100% to 0.170%. In order to allow the base metal to stably obtain a hardness of IN380 or higher, the lower limit of the C content nlay be 0.130% or 0.140%. In addition, in order to allow the \veld metal to stably obtain toughness, the upper limit of tlie C content niay be 0.230% or 0.210%. [0033] (Si: 0.05% to 0.80%) Si is a deoxidizing element and reduces the 0 content of the weld metal, and thus a certain amount of Si is added to the flux in order to e~lhancec leanliness. Tlierefore, the Si content in the \veld metal is also 0.05% or higher. As necessaty, the lo\ver limit of tlie Si content may be O.10%, 0.1 5%, or 0.20%. Whet1 Si is contained in a proportion of higher than 0.80%, the toughness of the weld nletal may be deteriorated, and thus 0.80% is the upper linlit of the Si content. In order to improve the toughness of the \veld metal, the upper limit of the Si content ma}1 be 0.70%, 0.65%, 0.60%, or 0.50%. [0034] (Mn: 0.20% to 2.50%) Mn forn~sM nS and thus has a1 effect of suppl-essingg rain boundaly embrittlement due to S, and thus at least 0.20% or higlier of MII is contained in the weld metal. In addition, Mn is an element which ensures tlic hardenability of the wcld metal and is thus effective in increasing strength. Therefore, in order to stably obtain hartlness, 0.50% or higher of Mn is preferably contained. In order to enhance the hardness of the \veld metal, Ute lower limit of the Mn content may be 0.60%, 0.70%, 0.80%, or 0.90%. On the other hand, when Mn is contained in a proportion of higher than 2.50%, sensitivity to grain boundary e~nbrittlententi s incl-eased,a nd thus the toughncss of the \veld metal is deteriorated. Therefore, 2.50% is the upper litnit of the Mn content. In order to ilnprove the toughness of the \veld metal, the upper limit of the Mn content ]nay be limited to 2.30%, 2.10%, 1.90%, 1.70%, or 1.50%. [0035] (Al: 0.0050% to 0.1000%) Al is a deoxidizing element and like Si, reduces the 0 content of the weld metal, and thus has an effect of enhancing the cleanliness of the \veld ntetal. Therefore, a certain amount of Al needs to be added to the flux. Typicall]; 0.0050% or higher A1 is contained in the weld metal of the weld joint made by using the fluxcored wire according to this embodiment. When the Al content is lower than 0.0050%, there is concern that the low temperature toughness of the wcld rnetal may be degraded. On the other hand, when Al is contained in a proportion of higher than 0.1000%, A1 forrns nitrides or oxides and thus deteriorates the toughness of the weld n~etal. Therefore, 0.1000% is the upper limit of the A1 content. In order to i~nprove the toughness of the \veld metal, the upper lin~iot f the Al content ntay be limited to 0.0900%, 0.0800%, 0.0700%, or 0.0600%. [0036] (P: 0.050% or lower) P is an impurity clcrnent and dctcriorates toughness. Therefore, the P content needs to be reduced as much as possible. Howwever, as a range in which all adverse effect of P on toughness is acceptable, tllc P content of the weld metal is limited to 0.050% or lo\ver. As necessary, the upper limit of the P content may be limited to 0.030%, 0.0250%, 0.0200%, or 0.0150%. TItc lower litnit of tile P conte~~t does not need to be limited. The lower limit of the P content is 0%. [0037] (S: 0.020% or lower) S is an i~npuritye lement, and xv11en an excessive aruount of S is present in the weld metal, both toughlless and ductility are deteriorated, and thus it is preferable that the S content be excessively reduced. As a range in which an adverse effect of S on toughness an$ ductility is acceptable, the S content ofthe wveld metal is litnited to 0.020% or lower. As necessary, the upper limit of tlie S content inay be limited to 0.015%, 0.010%, 0.008%, or 0.006%. The lower limit of the S content does not need to be limited. The lower litnit of the S content is 0%. 100381 (N: 0.015% or lower) N is unavoidably corltai~icdin the weld metal. However, when the N content is higher than 0.015%, coarse AIN or BN is formed and thus toughness is reduced. As the upper limit at whicli the cEect of N on the weld n~etails acceptable, the N content is limited to 0.015% or lo\ver. As necessary, tlie upper limit of the N cot~tent liiay be li~nitedto 0.010%, 0.008%, or 0.006%. The lower lin~iot f tlleN content does not need to be limited. The lower liniit of the N content is 0%. [0039] (0: 0% to 0.100%) 0 is unavoidably contained in the weld metal. However, as a range in which an adverse effect of O on toughness and ductility is acceptable, tlie O content of tlie \veld riletal is limited to 0.100% or lowcn As necessary, tlie uppcr liniit of the O coutent may be 0.080%, 0.060%, 0.050%, or 0.040%. The lo\ver litnit of tlie O content does not need to be limited. The lower limit of the 0 content is 0%. [0040] (Cu: 0% to 0.50%) Cu can enhance the strength and toughness of the \veld metal and tht~sc an be contained as a selective element. However, \\rlle~ltlleC u content is Iligl~etrh an 0.50%, touglmess may be reduced. Therefore, the Cu content orthe \veld metal is 0.50% or l o e As necessary, the upper litnit of the Cu contetlt may be 0.40% or 0.30%. The lo~verli mit of tlie Cu content may not be li~nited. Therefore, the lower limit of the Cu content is 0%. On the other hand, in order to sutficiet~tlyo btain a stret~gthenitlge ffect, 0.10% or higher of Cu nlay be contauled in the ~vcldm etal. As a method of including Cu in the weld metal, there is a tilethod of adding Cu to the coating of the surface of the sheath of the wire or the flux as a sitlgle element or an alloy element, and the like. [0041] (Ni: 0% to lower than 0.70%) Ni is considered as an ele~llenet ffective in enhancing loughness and cat1 be contained as a selective element. Ho\vever, in a case where the C content is high, the effect of Ni is limited, and since Ni is all expct~sivee lement, the Ni content it1 the weld nletal is lower thm 0.70%. As necessary, the upper limit of the Ni co~ltetlitn ay be 0.60%, 0.40%, or 0.20%. The lower litnit of the Ni conteut may not be limited. Therefore, tlie lomcr liniit of tlie Ni content is 0%. On the other hand, in order to sufficiently obtain a toughness enhancing effect, 0.05% or higher of Ni maj~be contained in the weld metal. [0042] (Cr: 0% to 2.50%) Cr is an eletne~lwt hich increases hardenability and is effective in enhancing the hardness of the weld metal, and thus can be contained as a selective elen~ent. However, when Cr is excessively contained in a proportion of higher than 2.50%, toughness may be reduced. Therefore, 2.50% is the upper limit of the Cr content. As necessary, the upper limit ol'tbe Cr content may be 1.50%, 1.00%, 0.70%, or 0.40%. The lower limit of the Cr colltellt majr not be limited. Therefore, the lower limit of the Cr co;ltent is 0%. On the other hand, in a case of adding Cr for the purpose of enhancing the hardness of the weld metal, in order to obtain the effect, 0.10% or higher of Cr may be contained. 100431 (Mo: 0% to 1.00%) Mo is an element wvhich increases hardenability and is effective in enhancing the hardness of the weld metal, and thus can be contained as a selective element. Ho~veverw, hen Mo is excessively contained in a proportion of higher than 1.00%, toughness may be reduced. Therefore, 1.00% is the upper litnit of the Mo content. As necessary, the upper limit of the Mo content may be 0.70%, O.60%, 0.40%, or 0.20%. The lower limit of the Mo content may not be limited. Therefore, the lower limit of the Mo content is 0%. On the other hand, in a case of adding Mo for the putpose of enhancing the hardness, "1 order to obtain the effect, 0.05% or higher of Mo may be contained. 100441 (Ti: 0% to 0.100%) Ti is, like Al, en'ective as a deoxidizing element, has an eflect of reducing the 0 content of the weld metal, and tlios can be contained as a selective element. 111 addition, Ti is also cffcctive in fixing solid-soluted N and rclaxing an advcrse effect on to[~glmess. IIowvever, when the Ti content in the weld metal becolnes higher than 0.100% and is thus excessive, a possibility of toughness deterioration due to the formation of coarse oxides and toughness deterioration doe to excessive precipitation strengthening is increased. Therefore, the upper linlit of the Ti content is 0.100%. As necessary, the upper limit of the Ti content nlay be 0.080%, 0.050%, 0.030%, or 0.020%. The lower linlit of the Ti content majr not be limited. Therefore, the lower litnit of the Ti content is 0%. For the purpose of improving touglu~ess,0 .010% or higher of Ti may be contained. [0045] (h'b: 0% to 0.100%) Nb is solid-soluted in the weld metal tnetal and has an effect of e~lliancingth e hardness of the weld metal, and thus can be contained as a selective element. However, when Nb is contained in a proportion of liigl~etrh an 0.100%, Nb is excessively contained in the weld metal, forn~sc oarse precipitates, and t11~1s deteriorates tougl~nessw, hich is not preferable. Therefore, the upper limit of the Nb content is 0.100%. As necessary, the upper litnit of the Nb content may be 0.080%, 0.050%, 0.030%, or 0.020%. The lower limit of the Nb content may not be limited. Therefore, the lower limit of the Nb content is 0%. For thc purpose of enhancing the lia~dnesso f the \veld inetal, 0.010% or higher ofNb nlajr be contained. [0046] (V: 0% to 0.30%) V is an element \vhich increases hardenabilitj~a nd is effective in enhancing the hare limited. Therefore, the lower limit of the Cu contcnt is 0%. On thc other hand, in order to enhance the hardness of the weld n~etal,0 .10% or higllcr of Cu may be contained in the weld metal. [0072] (Ni: 0% to lowwler than 1.00%) When the Ni content in the flus-cored wire is 1.00% or higher, the Ni content of the wveld metal becomes 0.70% or higher, and the alloy cost of the wire is increased. Therefore, the Ni content in the flux-cored wire is lower thaa 1.00%. In order to prevent solidification cracking of the weld metal, the upper limit of the Ni content may be 0.50%, 0.40%, 0.30%, 0.20%, or 0.10%. The lowver limit of the Ni content Inay not be limited. Therefore, the lower litnit of the Ni content is 0%. [0073] (Cr: 0% to 3.50%) When the Cr content in the flux-cored wire is higher than 3.50%, the Cr content of the wveld ~netabl ecomes higher than 2.50%. Therefore, the Cr content in the flux-cored )\lire is 3.50% or lower. As neccssaiy, the upper lirnit of the Cr content may be 1.50%, 1.00%, 0.50%, or 0.10%. The lower liniit of the Cr content tnay not be limited. Therefore, the lower limit of the Cr content is 0%. On the other hand, in a case of adding Cr for the purpose of enhancing the hardness of the weld metal, in order to obtain the effect, 0.05% or higher of Cr tnay be contained. [0074] (Mo: 0% to 1 .SO%) When the Mo content in the flus-cored wire is higher that1 1.5096, the Mo content of the weld metal beconles higher than 1.00%. Therefore, the Mo content in the flux-cored \wire is 1.50% or lower. In order to enhance tonglmess, the upper limit of the Mo content may be 0.70%, 0.50%, 0.30%, or 0.20%. The lower linlit of the Mo content may not be limited. Therefore, tlie lo\ver litnit of the Mo content is 0%. On the otlier hand, in a case of adding Mo for the pwpose of enhancing the l~ardnesso f the xwleld metal, in order to obtain the effcct, 0.05% or higher of Mo may bc contained. [0075] (Ti: 0% to 0.150%) When the Ti content in the flux-cored wire is higher than 0.150%, the Ti content of the weld n~etabl ecomes higher tlran 0.100%. Therefore, the Ti content in the flux-cored wire is 0.150% or lower. In order to enhance toughness, the upper limit of the Ti content niajr be 0.100%, 0.080%, or 0.050%. The lower limit ofthe Ti content may not be lirnited. Therefore, the lower limit of the Ti content is 0%. For the purpose of enhancing tougluiess, 0.010% or higher of Ti may be co~~tained. [0076] (Nb: 0% to 0.15%) Wlien the Nb content in the flux-cored wire is higher than 0.15%, the Nb content of the weld metal becomes higher than 0.10%. Therefore, the Nb content in the flus-cored mire is 0.15% or lower. In order to enhance toughness, the upper limit of the Nb content may be 0.10%, 0.08%, or 0.05%. The lower lin~iot f the Nb content map not be limited. Therefore, the lower limit of theNb content is 0%. For the p~~rpoosfc e nhancing the hardness of the \veld metal, 0.01% or higher of Nb may be contained. [0077] (V: 0% to 0.45%) !-Vl~etnh e V content in tlie flus-cored \\'ire is higher than 0.45%, the V content of the weld tiletal bcco~nesh igher than 0.30%. Therefore, the V content in the fluscored wire is 0.45% or lowcr. In order to enliance toughness, tlic uppcr litnit of the V content may be 0.25%, 0.20%, or 0.15%. Tlic lowcr litnit of the V content may not be limited. Therefore, the lower limit of the V content is 0%. For the polpose of enhancing the hardness of the weld inetal, 0.01% or higher of V may be contained. [0078] (B: 0% to 0.0500%) When tlie B content in the flus-cored wire is higher than 0.0500%, the B content of the weld nletal becomes higher than 0.0100%. Thelefore, the B contelit in the flux-cored wire is 0.0500% or lower. In order to enhatlce touglu~ess,t he upper limit of the B co~itenmt ay be 0.0400%, 0.0200%, 0.0100%, or 0.0050%. The lower litnit of the B content docs not need to be litnited, and the lower lirnit of the B cotitent is 0%. [0079] (Mg: 0% to 2.0%) When the Mg content in the flux-cored wire is higher than 2.0%, the Mg content of the weld metal becomes higher than 0.10%. Thcrcfore, the Mg content in the flux-corcd wire is 2.0% or lo\ver. In order to enhance the toughness and ductility of the \\feld metal, the upper limit of the Mg content may be 1.5%, 1.0%, 0.4%, or 0.2%. The loxw~er limit of the Mg content does not need to be limited, and the lower limit of the Mg content is 0%. [0080] (Ca: 0% to 2.0%) When the Ca content in the flux-cored wire is higher than 2.0%, the Ca colitent of tlie weld n~etabl ecomes higher than 0.10%. Therefore, the Ca content in the flux-cored wire is 2.0% or lower. In order to enhance the toughness and ductility of the weld metal, tlic upper limit of tlic Ca content may bc I S % , 1.0%, 0.596, or 0.3%. The lower liniit of the Ca contcnt does riot need to be limited, and the lowver limit of the Ca content is 0%. [0081] (REM: 0% to 0.01 50%) When the E M content in tlie flux-cored wire is higher tliaa 0.0150%, the REM content of thc weld ~iletabl cconies liigller than 0.0100%. Tllercfore, the REM content in the flux-cored wvire is 0.0150% or lo\ver. 111 order to enhance the tougl~l~ess and ductility of the weld metal, the upper limit of the REM content may be 0.0100%, 0.0050%, or 0.0030%. The lowver litnit of tlie REM content does not need to be limited, and tlie loiver limit of the REM contcnt is 0%. [0082] The rcasori that tlie chemical coniposition ofthe flux-cored wire according to this embodiment is limited has bee11 described a1)owre. Regarding the other chemical co~npositiono f tlie alloys of the remainder, the remainder primarily containing Fe may also contai~iln lpuritics that are incorporated during the production process and the like in a range in which the characteristics of the \veld joint according to this emboditnetit are not impeded. The Fe component contau~sF e in the steel sheath, and Fe in iron yo~vdcra rid alloy components added to tile flus. The iron powder content in the flus is lower than 10.0% in ternis of mass% with respect to the total Inass of tlie flux-cored wire. When the imn powder co~ite~isl ti ncreased, there nlay be a case ~w41eret he amount of oxygen is also increased. As necessary, the iron powder content may be lower than 5.0% or lower than 1.0%. Since the iron powder does not need to be contained, the lower limit of the iron powder content is 0%. [0083] Sabsequently, the morpllology of the flux-cored wire will be described. The flux-cored wirc is primarily divided into a seamlcss wire (that is, a wirc in \vhich the seams of the steel sheath are welded to each other) in which slit-like seams are not formed in the steel sheath, and a seamed wire in which thc sealus of the steel sheath have a slit-like gap. The present invention tnay employ any sectional structure. I-Iowever, in order to suppress the cold cracking of the weld metal, a wire without slit-like seams (seamless wire) is preferable. [OO84] Hydrogen infiltrated into the weld zone during welding is tlifft~sedi nto the weld metal and the steel side, is accutnnlated to a stress concentration zone, and acts as a cause of the occurrence of cold cracking. As the hydrogen source, moish~reh eld in the \velding material, moisture incorporated fro111 the air, rust or scales adhered to the surface of the steel, and the like are mentioned. However, during welding in which the cleanliness of the weld zone and shielding gas conditions are sufliciently managed, hydrogen contained in the wire primarily in the form of moisture beconles the main cause of difi~sibleh ydrogen that is present in the weld joint. [008S] Therefore, it is preferable that a (seamless) pipe ~vithouts lit-like seams be used as the steel sheath to suppress the infiltration of hydrogen in the air from the steel sheath to the flux until the wire is used after being produced. In a case where a (seamed) pipe with slit-like seams is used as the steel sheath, moisture in the air easily infiltrates into the flux fro111 the slit-like seams (seamed portion) of the sheath. Therefore, when such a pipe is used as it is, the infiltration of the hydroget1 source such as moishlre callnot be prevented. Therefore, in a case wl~e~a etim e period fro111 production to use is long, it is preferable that the entire wire be vacuum-packed or be stored in a container that can bc n~aintainedin a dty state. In addition, in order to enhance the transpottation performance of the wire, there niay be a case wvliere lubricating oil is applied to the sul-face of the \\fire. From the viewpoint of reducing the amount of diffi~sibleh ydrogen, as the lubricating oil applied to the surface of the wire, oil that does not contain hydrogen such as perfluoropolpetlier (PFPE) oil is preferable. [0086] The flux-cored wire used in the present invention can be produced in the same production process as that of a typical tnethod of producing a flux-cored wire. That is, first, a steel strip which is to becolne the sheath, and a flux in ~vliich tnetal fluorides, alloy components, tnetal oxides, tnetal carbonates, and an arc stabilizer are mixed to have predetern~ined contents are prepared. While the steel strip is transported in the longituditlal direction thereof, the steel strip is formed into an open pipe (U-shape) by a forming roll to be used as the steel sheath, the flux is supplied from the opening of the open pipe during the formation, and the edge faces of the opening that oppose each other are subjected to butt seam welding. A seamless pipe obtained by the welding is drawn, and is sul?iected to annealing during the drawing or after the con~pletiono f tlie drawing process, thereby obtaining a (seamless) wire having a desired wire diameter without slit-like seams. It1 addition, a (seamed) wire having slit-like seams is obtained by supplying a flux from the opening of the opeti pipe to be fornied as a seanled pipe that is not subjected to seam welding, and drawing the pipe. A cut section of the wire without slit-like gaps, which is ~iladeb y butt seam ~velding,i s illustrated in FIG. 3A. Wllen the section is polished and etched, welding traces are observed. I-Iowevel; when tlie section is not etched, \\!elding tmes are not observed. Therefore, tlie section may be called "sea~nless". On p.111 of 'New Edition of lntroductiot~t o Welding and Joir~ingT echniques" (2008) edited by "thc Japan Welding Society" and published by Sanpo Publications h~corporateda, seatnless type is described. As illustrated in FIG. 3B, \v11ell brazing is performed after butting is pcrfonned, or as illustrated in FIG. 3C, when brazing is perforlned aftcr caulking is perfolmed, wires ~vithoust lit-like gaps can also be obtained. Tn FIGS. 3B and 3C, the wires that are not subjected to brazing and are used as they are become wires having slit-like gaps. [0087] In the present invention, gas-shielded arc welding as inulti-laper welding is performed on the steel plate by using the flux-cored wire that satisfies the abovedescribed conditions to fortn weld metal that satisfies the above-described conditions, thereby acconiplishu~gth e object. The gas-shielded arc -cveldingm ethod is not particularly limited, a11d a typically used method cat1 be e~nployed. For example, as the shielding gas, as well as 100% COl gas, a rnixed gas of 3 vol% to 20 vol% of C02 gas and Ar gas, or the like can be used. The flow rate of shielding gas may be under typical conditions, that is, about 15 Lltnin to 30 1,Imin. In addition, regarding welding coliditiol~ss ucl~a s current, voltage, and the like, for example, a current of 200 Ato 350 A, a voltage of 25 V to 35 V, and the like may be employed. The welding rate tilay be controlled to allow a weld heat input to be 10 kJ/cm to 50 kJ/ctn. [008S] The shape of the produced weld joint is detennined dependiug on the applicatiot~o r the like and is not particularly lilnited. !Veld joints in which a groove is fonned, such as a typical butt joint, a corner joint, and a T joint may be applied. Therefore, the shape ofthe steel plate to be \vclded may be fornled so that at least a portion thereof where the weld joint is formed is a plate sliapc, and the slrapc may not entirely have the plate sliapc. For examplc, shaped steel rnay also bc included. In addition, the steel plate is not limitetl to various steel plates, and a single steel plate may be formed into a prcdetern~ined shape such as a pipe shape. However, a butt weld joint may also be employed. [Examples] [0089] Next, the applicability and effects of the weld joint according to this embodiment will be described with reference to Exan~ples. Steel plates having components shown in Table 1 were used as base metals. In addition, as hacking metals for welding, the satne steel plates as the base metals were used. While a steel strip was transported in the longit~ldinadl irection thereof, the steel strip was formed into an open pipe by a forniing roll, a flnx was supplied from the opening of the open pipe during the formation, and the edge faces of the opening that opposed each other were subjected to butt seam welding, thereby forming a pipe without slit-like seams. During drawing work of a wire of the formed pipe, annealing was perfonnetl, thereby producing a flux-cored wire having a final wire tlianieter of 1$1.21nm. In addition, some of the steel plates \\.ere formed into pipes having slit-like seams that were not subjectcd to seatn welding, and the pipes were drawa, thereby producing flux-col-ed wires liaving a wire dianleter of 41.2 mm. In the case of the wire having slit-like gaps, the entire wire was vacuunl-packed and stored in a container so as to be maintained in a d ~syta te, until wclding is perfol-med. The cl~emicacl ompoaents of the produced flux-cored wire were analyzed as follo\vs. First, tlie filling flux was extracted fionl tlie flux-cored wire, and the fluxcored wire wvas separated into the stccl sheath and the flux. l'he chemical components of the stccl sheath were obtaincd by measuring the content of each of metal conlponents through chemical analysis. The chemical co~nponentso f the flux were perfomled in the following order. First, the co~~stitnennlta terials and components of the flux wet-e subjected to quantitative evaluation by X-ray diffractometty and fluorescent X-ray spectroscopy. Thereafter, the flux was separated into a slag content and an alloy content by using a separation method such as flotation or ~nagneticse paration, a ~tdhe cheniical conlpone~~tthse reof were analyzed by performing chemical analysis, gas ru~alysiso, r the like. The chenlical compositions of the produced flux-cored wires are shown in Tables 2-1-1 to 2-2, and Tables 3-1-1 to 3-2. [0090] The base metals were allowed to abut each other with a root gap of I6 mm and a groove angle of 20" by using the flux-cored wvire, and were welded by using the backing nletal under the welding conditions sho\vn in Tables 4-1-1 to 4-2-3. On the surfaces of the groove surface of the base metal and the backing metal, buttering of two or more layers and an excess weld metal height of 3 mtn or higher wvas perfortned by using the tested flux-cored wire. Here, as Ti oxides, Si oxides, Mg oxides, and A1 oxides, TiOz, SiOz, MgO, atldA1203 were respectively used. In Tables 2-2 to 2-4, the metal carbonates include CaC03, BaC03, SrC03, and MgC03. [0091] The analysis results of the chemical con~positionso f the obtained weld metals are shown in Tables 5-1-1, 5-1-2,s-2-1,5-2-2,s-2-4, and 5-2-5. Asanlple of a polished section of the wvelld metal, lw41ich is perpendicular to the welding direction, nras acquired, and the Vickers hardnesses of I0 points of the sample at a position I mm illward from the surface of the weld ntctal \\,ere measured, and werc converted into Brine11 hardnesses using the hardness conversion table from SAE J417 (1983). In addition, a No. 4 Charpy test piece (2 nnn V-~lotch)b ased on JIS 23 111 (2005) was acquired, and the Chalpp absorbed energy of the weld metal at -40°C was measured. A -40°C absorbed energy of 27 J or higher was evaluated as passing. The obtained resr~ltso f the hardnesses and the Charpy test are shown in Tables 5-1-3, 5-2-3, and 5-2-6. [0092] 111 addition, a cold-cracking test and a diffusible hydroge~al anlount-measurit~g test were performed 011 each of the \veld joit~tso btained under the same welding conditions. As the cold-cracku~gte st, a test based on JIS Z 3158 (nlethod of y-groove \veld-cracking test in 1993) was performed at roo111 temperature (2S°C), and the absence of cracking it1 surfaces atldsections was evaluated as passing. The diffusible hydrogen a~nou~lt-nleasurintegs t was performed according to a gas chromatography method based on JIS Z 3 118 (nlethod for measurement of amount of hydrogen evolved from steel \velds it1 2007). An atnourlt of diffusible hydrogen of lo~vetrh at1 1.0 n11/100 g was evaluated as passing. The results are shown in Tables 5-1-3,s-2-3, and 5-2-6. [0093] During welding, a significant level of the generation of funies or slag \\?as evaluated as poor welding workability. A lo\\,, level of the generation of fumes or slag was evaluated as good welding ~vorkability. The results are shown in 'fables 5-1-3, 5- 2-3, a ~5d-2 -6. [0094] As showti in the test results of'rable 5-1-3, the weld metals of Examples 1 to 54 wliich arc examples of the present invention were excellent in all of hardness, touglmess, cold cracking resistance, and welding workability and thus passed the tests. On the other hand, as sho~vnin the test results of Tables 5-2-3 to 5-2-6, the weld metals of Comparative Exan~ples 101 to 165 did not satisfy the requirements specified in tlle present invention and at least one of hardness, toughness, cold cracking resistance, and welding \\rorkability did not pass the tests. The underlined numbers in Conlparative Examples of 'l'ables 5-2-1 to 5-2-6 represent outside of the ranges of the present invention. [0095] [Table I] [0096] [Table 2-1-11 LO0971 [Table 2-1-21 [0098] [Table 2-21 [0099] [Table 3-1-11 [OlOO] mble 3-1-21 [OlOl] [Table 3-21 [O 1021 [Table 4-1-11 [0 1031 [Tablc 4-1 -21 [0104] [Table 4-2-11 [O 1 051 [Table 4-2-21 [0106] [Table 4-2-31 [0 1071 [Table 5-1-11 [O 1081 [Table 5-1-21 [0109] [I'able 5-1 -31 [OllO] [Table 5-2-11 [OI 1 I] [Table 5-2-21 [0112] [Tablc 5-2-31 [0113] [Table 5-24] [OI 141 [Table 5-2-51 [0115] ['Table 5-2-61 [Industrial Applicability] [0116] According to the prescnt invention, in a weld joint wvllich uses a high-hardness steel plate having a liigh C content and a surface hardness of HV380 or higher and HV693 or lower as a base metal, weld ~netawl hich has a surrace hardness of I1V337 or higller and HV533 or lower and excellent abrasion resistance or weld metal wvhich has a surface hardness of HV380 or higher and I-N533 or lower and excelle~a~btr asion resistance can be obtained without the occurrence of cold cracking even when preheating is not performed. Therefore, welding efkiciency can be significantly enllanced, and tlius such a \veld joint is extremely valuable in the indostrial field. CLAIMS 1. A method of producing a weld joint by performing a gas-shielded arc welding, using a flux-cored wire filled with flux into a steel sheath, on any one of a steel plate having a Vickers hardness HV of 380 or higlier and 514 or lower, a plate thickness of 20 mm to 100 mm, a C content of 0.120 mass% to 0.300 mass%, and a CEN calculated by the following Expression 1 of 0.20 mass%to 0.75 mass%, a steel plate having a Vickers hardness HV of higher than 514 and 565 or lower, a plate thickness of 12 mm to 100 mm, a C content of 0.120 mass% to 0.300 mass%, and a CEN calculated by the following Expression 1 of 0.20 mass% to 0.75 mass%, and a steel plate having a Vickers hardness HV of higlier than 565 and 693 or lower, a plate thickness of 6 mm to 12 mm, a C content of 0.350 mass% to 0.450 mass%, and a CEN calculated by the following Expression 1 of 0.20 mass% to 0.85 mass%, the method comprising: (a) during the gas-shielded arc welding, not performing a preheating operation in a case where a temperature of the steel plate is 10°C or higher, and in a case where the temperature of the steel plate is lower than I0°C, performing the preheating operation so that the temperature of the steel plate is 10°C or higher, (b) wherein the flux-cored wire contains one or more of CaF2, BaF2, SrF2, and MgF2, and when a sum of amounts thereof is a, the a with respect to a total mass of the flux-cored wire is 3.3% to 8.0% in terms of mass%, the flux-cored wire contains one or more of Ti oxides, Si oxides, Mg oxides, and Al oxides, and when a sum of amounts thereof is P, the p with respect to the total mass of the flux-cored wire is 0.10% to 1.50% in terms of mass%, a sum of amounts of CaCC% BaCCh, S1CO3, and MgCCh with respect to the total mass of the flux-cored wire is lower than 0.60% in terms of mass%, an amount of an iron powder in the flux with respect to the total mass of the flux-cored wire is lower than 10.0% in terms of mass%, a ratio of the amount of CaF2 to the a is 0.90 or higher, a ratio of the a to the (3 is 3.0 or higher and 80.0 or lower, an amount of CaO with respect to the total mass of the flux-cored wire is lower than 0.20% in terms of mass%, (lie flux-cored wire include as a chemical composition excluding metal fluorides, metal oxides, and metal carbonates, with respect to the total mass of the fluxcored wire, in terms of mass%: C: 0.010% to lower than 0.060%; Si: 0.05% to 1.80%; Mn: 0.50% to 4.00%; P: 0.050% or lower; S: 0.020% or lower; Al: 0.005% to 0.150%; Cu: 0% to 0.75%; Ni: 0% to lower than 1.00%; Cr: 0% to 3.50%; Mo: 0% to 1.50%; Ti:0% to 0.150%; Nb:0%to0.15%; V: 0% to 0.45%; B:0% to 0.0500%; Mg: 0% to 2.0%; Ca: 0% to 2.0%; -j>n - REM: 0% to 0.0150%; and the remainder: Fe and impurities, (c) wherein a weld metal of the weld joint includes as a chemical composition, in terms of mass%: C: 0.100% to 0.170%; Si: 0.05% to 0.80%; Mn: 0.20% to 2.50%; . Al: 0.0050% to 0.1000%; P: 0.050% or lower; S: 0.020% or lower; N: 0.015% or lower; Cu:0%to0.50%; Ni: 0% to lower than 0.70%; Cr:0%to2.50%; Mo: 0% to 1.00%; Ti:0% to 0.100%; Nb:0%to0.100%; V;0%to0.30%; B:0% to 0.0100%; O:0% to 0.100%; Mg:0% to 0.100%; Ca:0% to 0.100%; REM: 0% to 0.0100%; and the remainder: Fe and impurities, a CEN of the weld metal calculated by the following Expression 1 is 0.20 -M - mass% to 0.58 mass%, an average Vickers hardness H V of the weld metal measured at 1 mm inward from a surface of the weld metal is 337 to 440, and all of (a) to (c) are satisfied. CEN=[CJ+(0.75+0.25xtanh(20x([C]- 0.12)))x([Si]/24+|Mn]/6+[Cu]/15+[Ni]/20+([Cr]+[Mo]+[Nb]+[V])/5+5x[B]) ...(Expression 1) where elements with [] represent the amounts (mass%) of the corresponding elements. 2. A method of producing a weld joint by performing a gas-shielded arc welding, using a flux-cored wire filled with flux into a steel sheath, on any one of a steel plate having a Vickers hardness HV of 380 or higher and 514 or lower, a plate thickness of 20 mm to 100 mm, a C content of 0.120 mass% to 0.300 mass%, and a CEN calculated by the following Expression 1 of 0.20 mass% to 0.75 mass%, a steel plate having a Vickers hardness HV of higher than 514 and 565 or lower, a plate thickness of 12 mm to 100 mm, a C content of 0.120 mass% to 0.300 mass%, and a CEN calculated by the following Expression 1 of 0.20 mass% to 0.75 mass%, and a steel plate having a Vickers hardness HV of higher than 565 and 693 or lower, a plate thickness of 6 mm to 12 mm, a C content of 0.350 mass% to 0.450 mass%, and a CEN calculated by the following Expression 1 of 0.20 mass% to 0.85 mass%, the method comprising: (a) during the gas-shielded arc welding, not performing a preheating operation in a case where a temperature of the steel plate is 10°C or higher, and in a case where the temperature of the steel plate is lower than 10°C, performing the preheating -J59 - operation so that the temperature of the steel plate is 10°C or higher, (b) wherein the flux-cored wire contains one or more of CaF2, BaF2, SrF2, and MgF2, and when a sum of amounts thereof is a, the a with respect to a total mass of the flux-cored wire is 3,3% to 8.0% in terms of mass%, the flux-cored wire contains one or more of Ti oxides, Si oxides, Mg oxides, and Al oxides, and when a sum of amounts thereof is p, the P with respect to the total mass of the flux-cored wire is 0.10% to 1.50% in terms of mass%, a sum of amounts of CaCC>3, BaCCb, S1CO3, and MgCCb with respect to the total mass of the flux-cored wire is lower than 0.60% in terms of mass%, an amount of an iron powder in the flux with respect to the total mass of the flux-cored wire is lower than 10.0% in terms of mass%, a ratio of the amount of CaF2 to the a is 0.90 or higher, a ratio of the a to the p is 3.0 or higher and 80.0 or lower, an amount of CaO with respect to the total mass of the flux-cored wire is lower than 0.20% in terms of mass%, the flux-cored wire includes chemical components excluding metal fluorides, metal oxides, and metal carbonates, with respect to the total mass of the flux-cored wire, in terms of mass%: C: 0.060% to 0.350%; Si: 0.05% to 1.80%; Mn: 0.50% to 4.00%; P: 0.050% or lower; S: 0.020% or lower; Al: 0.005% to 0.150%; Cu: 0% to 0.75%; -.60 - Ni: 0% to lower than 1.00%; Cr:0%to3.50%; Mo: 0% to 1.50%; Ti:0% to 0.150%; Nb:0%to0.15%; V: 0% to 0.45%; B:0% to 0.0500%; Mg: 0% to 2.0%; Ca:0%to2.0%; REM: 0% to 0.0150%; and the remainder: Fe and impurities, (c) wherein a weld metal of the weld joint includes as a chemical composition, in terms of mass%: C: 0.120% to 0.250%; Si: 0.05% to 0.80%; Mn: 0.20% to 2.50%; Ai: 0.0050% to 0.1000%; P: 0.050% or lower; S: 0.020% or lower; N: 0.015% or lower; Cu: 0% to 0.50%; Ni: 0% to lower than 0.70%; Cr: 0% to 2.50%; Mo: 0% to 1.00%; Ti:0% to 0.100%; ->1 - Nb:0% to 0.100%; V: 0% to 0.30%; B:0% to 0.0100%; O:0% to 0.100%; Mg:0%to0.100%; Ca:0% to 0.100%; REM: 0% to 0.0100%; the remainder: Fe and impurities, a CEN of the weld metal calculated by the following Expression 1 is 0.20 mass% to 0.58 mass%, an average Vickers hardness HV of the weld metal measured at 1 mm inward from a surface of the weld metal is 380 to 533, and all of (a) to (c) are satisfied. CEN=[C]+(0.75+0.25xtanh(20x([C]- 0.12)))x([Si]/24+[Mn]/6+[Cu]/15+[Ni]/20+([Cr]+[Mo]+[Nb3+[V])/5+5x[B]) ...(Expression 1) where elements with [] represent the amounts (mass%) of the corresponding elements. 3. Amethod of producing a weld joint by performing a gas-shielded arc welding, using a flux-cored wire filled with flux into a steel sheath, on any one of a steel plate having a Vickers hardness HV of higher than 565 and 693 or lower, a plate thickness of 12 mm to 20 mm, a C content of 0.350 mass% to 0.450 mass%, and a CEN calculated by the following Expression 2 of 0.20 mass% to 0.85 mass%, and a steel plate having a Vickers hardness HV of higher than 565 and 693 or lower, a plate thickness of greater than 20 mm to 50 mm or smaller, a C content of 0.350 mass% to 0.450 mass%, and a CEN calculated by the following Expression 2 of 0.20 mass% to 0.85 mass%, the method comprising: (a) during the gas-shielded arc welding, performing a preheating operation so that a temperature of the steel plate is 100°C or higher in a case where the plate thickness of the steel plate is 20 mm or smaller, and in a case where the plate thickness of the steel plate is greater than 20 mm, performing the preheating operation so that the temperature of the steel plate is 150°C or higher, (b) wherein the flux-cored wire contains one or more of CaF2, BaFa, SrF?, and MgF2, and when a sum of amounts thereof is a, the a with respect to a total mass of tlie flux-cored wire is 3.3% to 8.0% in terms of mass%, the flux-cored wire contains one or more of Ti oxides, Si oxides, Mg oxides, and Al oxides, and when a sum of amounts thereof is p\ the [i with respect to the total mass of the flux-cored wire is 0.10% to 1.50% in terms of mass%, a sum of amounts of CaCOs, BaCCb, SrCC^, and MgCCb with respect to the total mass of the flux-cored wire is lower than 0.60% in terms of mass%, an amount of an iron powder in the flux with respect to the total mass of the flux-cored wire is lower than 10.0% in terms of mass%, a ratio of the amount of CaF2 to the a is 0.90 or higher, a ratio of the a to the p is 3.0 or higher and 80.0 or lower, an amount of CaO with respect to tlie total mass of the flux-cored wire is lower than 0.20% in terms of mass%, the flux-cored wire includes chemical components excluding metal fluorides, metal oxides, and metal carbonates, with respect to the total mass of the flux-cored wire, in terms of mass%: C: 0.060% to 0.350%; Si: 0.05% to 1.80%; Mn: 0.50% to 4.00%; P: 0.050% or lower; S: 0.020% or lower; Al: 0.005% to 0.150%; Cu: 0% to 0.75%; Ni: 0% to lower than 1.00%; Cr:0%to3.50%; Mo: 0% to 1.50%; Ti:0%to0.150%; Nb:0%to0.15%; V: 0% to 0.45%; B: 0% to 0.0500%; Mg:0%to2.0%; Ca: 0% to 2.0%; REM: 0% to 0.0150%; the remainder: Fe and impurities, (c) wherein a weld metal of the weld joint includes as a chemical composition, in terms of mass%: C: 0.120% to 0.250%; Si: 0.05% to 0.80%; Mn: 0.20% to 2.50%; AI: 0.0050% to 0.1000%; P: 0.050% or lower; S: 0.020% or lower; N: 0.015% or lower; Cu:0%to0.50%; Ni: 0% to lower than 0.70%; Cr: 0% to 2.50%; Mo: 0% to 1.00%; Ti:0% to 0.100%; Nb:0% to 0.100%; V: 0% to 0.30%; B: 0% to 0.0100%; O:0% to 0.100%; Mg:0% to 0.100%; Ca:0% to 0.100%; REM: 0% to 0.0100%; and the remainder: Fe and impurities, a CEN of the weld metal calculated by the following Expression 2 is 0.20 mass% to 0.58 mass%, an average Vickers hardness HV of the weld metal measured at 1 mm inward from a surface of the weld metal is 380 to 533, and all of (a) to (c) are satisfied. CEN=[C]+(0.75+0.25xtanh(20x([C]- 0.12)))x([Si]/24+[Mn]/6+[Cu]/15+[Ni]/20+([Cr]+[Mo]+[Nb]+[V[)/5+5x[B]) ...(Expression 2) where elements with [] represent the amounts (mass%) of the corresponding elements. 4. The method of producing a weld joint according to any one of Claims 1 to 3, wherein the amount of CaO in the flux-cored wire is 0.15% or lower in tenns of mass% with respect to the total mass of the flux-cored wire. 5. The method of producing a weld joint according to any one of Claims 1 to 4, wherein the flux-cored wire includes the chemical components excluding the metal fluorides, metal oxides, and metal carbonates, with respect to the total mass of the flux-cored wire, in tenns of mass%: Ni:0%to0.1%. 6. The method of producing a weld joint according to any one of Claims 1 to 5, wherein the flux-cored wire includes the chemical components excluding the metal fluorides, metal oxides, and tnetal carbonates, with respect to the total mass of the flux-cored wire, in terms of mass%: Cu: 0% to 0.50%; Cr:0%tol.00%; Mo: 0% to 0.50%; Ti: 0% to 0.050%; and Nb: 0% to 0.05%. 7. The method of producing a weld joint according to any one of Claims 1 to 6, wherein the steel sheath of the flux-cored wire does not have a si it-like gap. 8. The method of producing a weld joint according to any one of Claims 1 to 6, | wherein the steel sheath of the flux-cored wire has a slit-like gap. 9. The method of producing a weld joint according to any one of Claims 1 to 8, wherein a perfluoropofyether oil is applied to a surface of the flux-cored wire.