Technical field
[0001]
　The present invention relates to a fillet arc welded joint and a manufacturing method thereof, and is particularly suitable for the production of fillet arc welded joint of steel sheets for automobiles steel.
Background technique
[0002]
　Conventionally, in the automotive field, for environmental protection, together with an improvement in fuel efficiency through weight reduction of the vehicle body, increase collision safety has been demanded. Therefore, to optimize the vehicle body structure together with thinning using high strength steel plate, in order to improve the weight of the vehicle body and crash safety, various efforts have been made so far.
[0003]
　The high strength steel sheet to reduce the weight of the vehicle body, a large fatigue strength obtained. In particular, underbody members such as suspension arms or the sub-frame, the fatigue strength of the welded portion becomes more important. The weld stress concentration, the residual stress is present, the fatigue strength increases the strength of the base material is not increased.
[0004]
　For such problems, Patent Documents 1 and 2, remelting the weld bead in TIG arc heat or plasma heat sources, techniques to reduce the stress concentration by arranging the shape is proposed. However, these techniques it takes a skill, it is difficult to control the stable bead shape.
　Further, when remelting a weld bead in TIG arc heat or plasma heat sources, there is a problem that lowers the fatigue strength HAZ material is deteriorated because the excessive heat input is a thin plate member.
[0005]
　In Patent Document 3, by using a laser heat source, by heating the weld toe to a temperature at which the weld metal is not melted, to reduce the strain concentrates only on the weld metal is hardened weld metal side techniques have been disclosed. In Patent Document 4, by using a laser heat source, by the steel sheet is to heat the weld toe to a temperature so as not to melt, technique to improve residual stress reduction is disclosed. However, the heating temperature of the Patent Documents 3 and 4 is the temperature below the melting point of the weld metal, there is a problem that since quenching is insufficient sufficient fatigue strength improving effect on the thin plate welded joint is not obtained.
[0006]
　The manufacturing method of lap fillet arc welded joint of steel sheet disclosed in Patent Document 5 is a starting point of the weld bead toe fatigue fracture on the lower plate surface, the fatigue strength of the welded joint by its hardness There is a technique that focuses on the changes. This manufacturing method, assuming the locations toe of lap fillet weld bead is formed, in advance the position to form a molten-solidified portion by irradiating a high energy by the high-energy irradiation means such as a TIG arc after by fillet arc welding overlapped as toe overlaps the molten-solidified portion increases the weld bead toe hardness, aiming to improve the fatigue strength. However, advance even a portion corresponding to the toe portion is cured by irradiation with high-energy heat source, may toe recast during lap fillet arc welding is softened, sufficient fatigue strength improvement there is a case that can not be obtained.
[0007]
　Further, Patent Document 6, the weld bead and the steel plate by remelting with a plasma, gently form around the toe portion around the toe of the weld bead of the welded joint, stress caused by repeated stress It discloses that concentration is suppressed. However, the metal structure in the remelted portion and the vicinity thereof, in order to change before and after the re-melting, there is a possibility that fatigue properties can not be sufficiently improved.
[0008]
　Figure 1 is an enlarged cross-sectional view of a portion showing a crack initiation position can conventional lap fillet welded joints using the upper 1 and lower plate 2. The weld bead 3, because tensile residual stress caused by the shrinkage of the stress concentration and the weld metal due to the discontinuous shape is present, as shown in FIG. 1, part a crack occurs is at weld toe 3b , most of the crack 4 propagates the HAZ5. Patent Documents 1-5 are both rather intended to inhibition of crack propagation in the suppression or HAZ decrease in fatigue strength due to the HAZ of material degradation, the tensile strength using more high-strength steel sheet 780MPa sufficient effect to improve fatigue strength of the arc welded joint is not obtained.
[0009]
　In general, be organized in generation life of fatigue life crack of welded joints, since occurrence of crack in the weld joint that is determined by a change amount of penetrant and strain gauge value, the pure Without crack initiation timing can not be determined, the fatigue strength life including the propagation of cracks is evaluated. Therefore, by suppressing crack growth in the HAZ, there is a possibility to improve the practical fatigue strength of the welded joint.
[0010]
　In particular, in the case of the high strength steel sheet, tensile the strength is high, crack growth rate increases in HAZ, since the fatigue strength of the weld toe tends to become low, HAZ eaves of improving fatigue strength by crack growth inhibition effect is considered to be large.
CITATION
Patent Literature
[0011]
Patent Document 1: JP 59-110490 Patent Publication
Patent Document 2: JP 51-90946 Patent Publication
Patent Document 3: JP-A 7-118757 Patent Publication
Patent Document 4: JP-A 10-193164 JP
Patent Document 5: JP 2011-62718 JP
Patent Document 6: JP 2014-4609 JP
Summary of the Invention
Problems that the Invention is to Solve
[0012]
　As described above, factors lowering of the fatigue strength of the welded portion of the high-strength steel sheet is considered to adverse effects on the weld fatigue strength due to the HAZ material degradation caused by the fillet arc welding. Therefore, the tensile strength is applied to the thermal cycle of welding the steel plate 440 ~ 980Mp class, compare the fatigue strength of the fatigue strength remains the base metal weld heat affected zone was investigated. The heat treatment conditions for reproducing the HAZ is the maximum temperature 1200 ℃, 1200 ℃ ~ 800 ℃, 800 ℃ ~ 500 ℃, respectively the cooling rate at 500 ° C. ~ room temperature 80 ℃ / s, 50 ℃ / s, It was 10 ℃ / s. Further, assuming a stress concentration of the weld, stress concentration factor (Kt) is provided with notches becomes 3 fatigue test piece.
[0013]
　It shows the fatigue test results in FIG. Fatigue test and the axial force fatigue test stress ratio (R) = 0.1, was determined fatigue strength (indicated by stress range) as the number of repetitions of up to 2,000,000. Fatigue strength of the base material in accordance with an increase in the tensile strength of the base metal increases, the fatigue strength of the HAZ is a tendency to decrease the boundary 590 ~ 780 MPa.
[0014]
　Thus, the high strength steel plate fatigue strength of HAZ is reduced as compared with the base material. In other words, by narrowing the area of ​​the HAZ crack it is gradually progress, it is considered possible to increase the fatigue strength of the welded portion by suppressing crack growth.
[0015]
　That is, in the present invention, can thickness direction of the heat-affected zone is a progress direction of the crack by narrowing (HAZ) region, the fillet arc welded joint and a manufacturing method thereof excellent in fatigue strength crack propagation is suppressed an object of the present invention is to provide.
Means for Solving the Problems
[0016]
　In the present invention, it was decided to utilize the laser beam to the processing of the toe portion of the fillet arc welding. As shown in FIG. 3, in the present invention, a weld toe, the corner meat arc region to include the boundaries of the heat affected zone caused by welding and then re-melted by a laser beam to put locally baked cure ( hereinafter referred to as "local quenching by laser".) makes. The present inventors have found that, by the remelting using a laser beam, it is possible to suppress cracks from fillet arc weld toe remelting area (remelted portion becomes Crack Initiation position can after laser irradiation ) 6 narrowing the HAZ6a in fusion boundary 6b in it is possible to suppress development of a crack 4, significant improvement in weld fatigue strength is found that can be achieved.
[0017]
　The present invention has been made based on the above findings and has as its gist is as follows.
[0018]
　Fillet arc welded joint of the present invention is a fillet arc welded joint formed by fillet arc welding at least two metal members, the fillet arc weld toe of the weld of at least one metal member and parts, in a region including a boundary of the HAZ said generated by fillet arc welding surface of the metal member, has a re-melted portion by laser irradiation, the remelting unit, the from the surface of the metal member a range up to 1/2 or less of the depth of the thickness of the metal member, the remelted boundary that is a boundary of the remelted portion of the surface of the metal member of 0.1mm in thickness direction of the metal member the average effective crystal grain size of the prior austenite in the heat affected zone in depth, and wherein the at 20μm or less.
[0019]
　Further, in another example of the fillet arc welded joint of the present invention, the remelting unit, may range from the surface of the metal member to 1/3 or less of the depth of the thickness of the metal member.
[0020]
　Further, in another example of the fillet arc welded joint of the present invention, the weld metal of the remelting unit, Ceq value defined by the following formula (1) may be 0.3 or more.
　Ceq = C + Mn / 6 + Si / 24 + Ni / 40 + Cr / 5 + Mo / 4 + V / 14 ··· Equation (1);
　In the formula (1), C, Mn, Si, Ni, Cr, Mo, V , the content of elements (wt%) indicates the case of no addition element, 0 is substituted.
[0021]
　Further, in another example of the fillet arc welded joint of the present invention, wherein the plate thickness direction of the depth of the metal member remelting unit, 1/5 or more of the plate thickness of the metal member from a surface of said metal member , and the hardness of the boundary portion between the laser remelting portion and the heat affected zone at the position below 0.1mm from the surface of the steel sheet is, be more than 1.2 times the hardness of the base material of the metal member, the boundary hardness of the metal member from the steel sheet surface in the vertical downward direction in the sheet 1/4 depth of thickness of the metal member may be a 1.1 times or less of the hardness of the base material of the metal member.
[0022]
　Further, in another example of the fillet arc welded joint of the present invention, the metal member may be a following steel sheet thickness of 4.5 mm.
[0023]
　Further, in another example of the fillet arc welded joint of the present invention, at least one part of the portion where high stress previously determined is loaded, may be re-melted portion is formed.
[0024]
　Method for producing a fillet arc welded joint of the present invention is to fillet arc welding at least two metal members, and weld toe of the fillet arc welding of at least one metal member, wherein the surface of the metal member an area including the boundary of the heat affected zone caused by the fillet arc welding melts again by laser irradiation, to form a re-melted portion from the surface of the metal member to the thickness less than 1/2 of the depth of the metal member and features.
[0025]
　Further, in another example of the manufacturing method of the fillet arc welded joint of the present invention, the effective average prior austenite in the heat affected zone from the remelted boundary at a depth of 0.1mm in the thickness direction of the metal member crystal grain size, may be 20μm or less.
[0026]
　Further, in another example of the method of manufacturing the fillet arc welded joint of the present invention, the re-melted region, ranging from the surface of the metal member to the plate than 1/3 of the depth of the thickness of said metal member it may be.
[0027]
　Further, in another example of the method of manufacturing the fillet arc welded joint of the present invention, Ceq value defined by the following equation of the metal member to which the are remelted (1) may be 0.3 or more .
　Ceq = C + Mn / 6 + Si / 24 + Ni / 40 + Cr / 5 + Mo / 4 + V / 14 ··· Equation (1);
　In the formula (1), C, Mn, Si, Ni, Cr, Mo, V , the content of elements (wt%) indicates the case of no addition element, 0 is substituted.
[0028]
　Further, in another example of the method of manufacturing the fillet arc welded joint of the present invention, the depth from the surface of the metal member of the remelted portion is 1/5 or more the thickness of the metal member, the surface of the steel sheet from the hardness at the boundary between the laser remelting portion and the heat affected zone at the position under 0.1mm in thickness direction, it is more than 1.2 times the hardness of the base material of the metal member, the vertical of the boundary hardness at a depth of 1/4 of the plate thickness of the metal member from the steel sheet surface in the downward direction, so that the following 1.1 times the hardness of the base material of the metal member may be irradiated with a laser beam.
[0029]
　Further, in another example of the manufacturing method of the fillet arc welded joint of the present invention, the metal member may be a following steel sheet thickness of 4.5 mm.
[0030]
　Further, in another example of the method of manufacturing the fillet arc welded joint of the present invention, at least one part of the portion where high stress previously determined is loaded, it may be re-melted by laser irradiation.
[0031]
　Further, in another example of the method of manufacturing the fillet arc welded joint of the present invention, the laser irradiation, the moving speed (m / min) Laser output to (kJ / sec) the ratio of 45 ~ 80 (kJ / m) it may be.
Effect of the invention
[0032]
　According to the present invention, tensile and improve fatigue strength of the weld toe of high tensile steel strength 980 MPa, it is possible to narrow the HAZ in the thickness direction. Therefore, it is possible to increase the fatigue strength of the arc welded joint of steel sheets for automobiles steel.
BRIEF DESCRIPTION OF THE DRAWINGS
[0033]
Is an enlarged partial sectional view showing the FIG. 1 Crack Initiation position can conventional lap fillet welded joint.
FIG. 2 is a graph comparing the fatigue strength of the base metal and HAZ.
3 is a partial enlarged sectional view showing a crack initiation position can the welded joint subjected to laser processing in the present invention.
[4] laser hardening condition (A), it shows the (B) and (C) weld each of the cross-sectional melting shape.
FIG. 5 is the number of repetitions of a fatigue test, which is a graph showing the relationship between development of conversion and cracking of the strain.
[Figure 6A] to produce a weld specimens of varying remelting unit depth is a graph obtained experimentally the relationship between the depth and the joint fatigue strength penetration remelting unit.
FIG 6B] FIG. 6A obtained by the observation of the weld toe or laser melting end of the metal structure of the test piece used in the experiments, the average effective crystal grain size and the fatigue strength improvement rate of prior austenite in the heat affected zone is a graph showing the relationship between.
[7] by laser irradiation is a graph showing the Vickers hardness of the plate thickness direction at the weld toe of a conventional fillet arc welded joint and fillet arc welded joint of the present invention. Incidentally, the Vickers hardness is expressed as a ratio to the Vickers hardness of the base material.
[Figure 8] is an enlarged sectional view showing a portion where Vickers hardness was measured as shown in the graph of FIG. 7, (A) corresponds to the graph of "conventional" in FIG. 7, (B) is 7 corresponding to the "invention" of.
DESCRIPTION OF THE INVENTION
[0034]
　The present invention is the technique aimed at suppressing the development of a crack by narrowing the HAZ in the thickness direction by laser quenching conditions, the fatigue strength improvement effect is changed.
　So, as a preliminary evaluation, to investigate the relation between the laser irradiation conditions fatigue strength. Test material was a 980MPa grade steel sheet having a thickness of 2.3 mm, the arc welding using welding materials for 780MPa grade steel (JIS Z3312 G78A4UMN5C1M3T). Arc welding, with Parusumagu welding, a shielding gas Ar + 20% CO 2 and the welding current 190A, arc voltage 24V, and the condition of the welding speed 80 cm / min.
[0035]
　Laser irradiation conditions for laser hardening, the laser output 3 kW, and the moving speed 3m / min, aim the toe portion of the fillet arc welding, + 10 mm defocus, and the two levels of + 15 mm defocus.
[0036]
　(A) no laser irradiation in FIG. 4, showing the (B) + 10 mm defocus and (C) + 15 mm de welds sectional melt shape when being quenched by the focus. Vickers hardness of the fusion boundaries of without laser quenching has been a 250 HV, the hardness of the corresponding portion by performing laser hardening rose to 382HV. Incidentally, remelted regions (FIG. 4 (B), the A arrow indicated portion (C), the area corresponding to the re-melted portion 6 of FIG. 3), a sample cut, polished, it can be observed by etching.
[0037]
　Table 1 shows the fatigue life of the local quenching after the test piece. Incidentally, the fatigue life of the specimen was measured by performing a pulsating bending test stress amplitude 250MPa against weld toe of the test piece.
[0038]
[Table 1]

[0039]
　As can be seen from Table 1, the local hardening by laser is performed Condition No. B, In C, as compared with the case of the left welding, it can be seen that the fatigue life is improved by about 5-fold to 20-fold.
　Thus, by melting the weld toe by a laser and cured the toe portion is hardened, although the fatigue strength of the welded portions is increased, the laser irradiation conditions, i.e. greater fatigue by differences in melting shape it can be seen that the intensity difference occurs.
[0040]
　Therefore, the subject is an example of condition A ~ C of Table 1 to examine variation in the strain history of the crack in the vicinity for the number of repetitions of a fatigue test. Attaching the strain gauge to 1mm approximately away from the toe portion to measure a periodic strain amplitude due to repeated stress. When cracks are generated in the toe portion, the strain amplitude is reduced is determined by the strain gauge. All the initial strain amplitude as large normalized Satoshi in the condition A ~ C, shown in Figure 5 the relationship between the repetition number and the normalized fatigue testing the strain (amplitude). Incidentally, when classifying the condition A ~ C at the weld cross section, corresponding to the following melt-shaped.
　Condition A: when subjected only to arc welding;
　Condition B: If remelting depth by laser was set to about 1/2 of the plate thickness;
　Condition C: remelting depth by laser of thickness 1 / If it has to be in the order of 3
[0041]
　As can be seen from FIG. 5, as compared with the case of the condition A, the case of the condition B is cracking becomes slow growth rate of the crack can be seen that there is no difference. That is, the condition B is has become possible to delay the occurrence of cracks becomes hard and crack portions in the remelting by laser, HAZ comparison made of coarse tissue with the enlargement of the heat input region by laser It is thought to have spread to the specific wide range. Therefore, cracks developed in the HAZ, when crack growth rate of conventional arc welding much different without believed did not result in a sufficient improvement in the fatigue life.
[0042]
　Further, the condition C in comparison with the condition A, the generation of cracks is slow, and propagation rate of cracks also can be seen slow. As a cause of the growth rate of the crack becomes slow, crack of development path it is conceivable that became the base material consisting of a fine-grained organization instead of the HAZ. On the other hand, if even compared to the condition B hardness of cracking unit is equivalent of the condition from C, the generation of cracks is delayed, the heat input region in accordance with the reduction of the melted region due to laser reduced as a result, the tensile residual stress is considered due to a decrease.
[0043]
　For the purpose of determining the possible remelting unit depth improve fatigue strength, to produce a weld specimens of varying remelting unit depth in the same manner as in FIG. 4, arc welding alone (i.e., arc welding the fatigue strength of the left) as 1.0, to determine the relationship between the rate of improvement in depth and joint fatigue strength penetration remelted portion experimentally. The results are shown in Figure 6A. When the crack portion depth as shown in Figure 6A is larger than 1 / 2t (1/2 the thickness of the sheet thickness t), becomes as effective as when performing a TIG dressing. Further, when the penetration depth of the remelted portion is shallow, since the surface of the remelted portion becomes uneven, remelting depth is not more than 1/5 or 1 / 2t, preferably 1/5 or more 1 / 3t less.
[0044]
　Furthermore, to clarify the mechanism of improving fatigue strength in the present invention, it was observed laser melting of the heat-affected zone and its vicinity of the metal structure of the test piece used to obtain the experimental results of Figure 6A.
[0045]
　For specimens remelting is performed by laser irradiation, the boundary portion of the heat-affected zone of the remelting unit and the remelted portion on the steel sheet surface (hereinafter, referred to as. "Remelted boundary") thickness of the steel sheet from It was observed metallographic at a depth of 0.1mm in the direction. Note that the test piece of the metal structure and TIG dressing arc welding while the test piece, definitive to 0.1mm depth in the thickness direction of the boundary between the weld metal and heat affected zone in the surface of the steel sheet as a starting point, the remelting portion It was observed metal tissues except. The metal structure of the range centered on 500 [mu] m × 500 [mu] m the above-mentioned position and EBSD analysis to determine the average effective crystal grain size of crystal grains the size of prior austenite when separated by crystal orientation difference 15 °. Prior austenite to be measured of the effective crystal grain size, the rather intended to be within the remelting unit, are included in the heat-affected zone of the remelting portion by the laser irradiation.
[0046]
　It shows the relationship between the average effective crystal grain size and the fatigue strength improvement rate of prior austenite of the heat affected zone in Figure 6B. Incidentally, the fatigue strength of the arc welding alone and 1.0. Although fatigue strength with decreasing-penetration depth in FIG. 6A is increased, it can be seen that the fatigue strength is increased by a decrease in the grain size in FIG. 6B. The average effective crystal grain sizes of prior austenite in the arc welding alone was 37 [mu] m, average effective crystal grain size of the prior austenite when subjected to TIG dressing was 32 [mu] m. In contrast, in the laser processing, the fatigue strength improvement rate of over TIG dressing by an average effective crystal grain sizes of prior austenite contained in the heat-affected zone of the remelting portion by the laser treatment and 20μm or less is obtained There could be confirmed.
[0047]
　Since it 1.2 times the fatigue strength improvement rate despite the crystal grain size is relatively large in TIG dressing is obtained, which is obtained by re-melting the weld toe at a relatively large amount of heat melting It becomes smoother shape of the end portion, presumably because the stress concentration factor becomes smaller values. That is, the conventional TIG dressing and plasma treatment technique is characterized mechanism of action of reducing the stress concentration to the weld toe is crack generation unit by smoothing the shape of the melt end. In contrast, the present invention is characterized mechanisms of action that by granulating the crack generation of the metal structure can by laser processing to improve the fatigue strength, which differs from the prior art TIG dressing or the like in the technical idea it is.
[0048]
　It is also necessary to prevent the HAZ is expanded by heat input of the laser. In addition, the welding becomes heat input increases a factor of the tensile residual stress increase in melt end, the crack propagation increases, only the surface layer at the weld toe, it is preferable to improve the hardness. Therefore, as shown by the graph of the "present invention" in FIG. 7, the laser irradiation, the laser irradiation intensity so as to satisfy the following the (i) and (ii), the irradiation conditions such as laser irradiation time and irradiation range it is preferable to adjust. That,
(i) the hardness of the fusion boundary is newly formed from the surface of the steel sheet by laser remelting at positions under 0.1mm in the thickness direction increased to more than 1.2 times the hardness of the base material;
(ii ) in the vertical downward direction of the fusion boundary at the position under 0.1mm in the thickness direction from the surface of the steel sheet, a hardness at about 1/4 of the depth position of the steel sheet from the surface of the steel sheet in the hardness of the matrix 1. to 1 times or less.
[0049]
　When the steel sheet surface is greater hardness of the area of ​​0.1mm thickness, can the occurrence of cracks is suppressed, and a small hardness in the region of 1/4 thickness from the steel sheet surface (i.e., when the steel is soft) , progress of the crack is suppressed. As the graph of "conventional" in FIG. 7, a conventional fillet arc welded joint, the hardness distribution, to hardness in the region of 0.1mm thickness is not increased, 1/4 thickness of a region in hardness it is not adapted to soften. On the other hand, as shown by the graph of the "present invention" in FIG. 7, the fillet arc welded joint of the present invention, the thickness direction of the distribution of the hardness, with respect to inhibition of crack, a preferred distribution.
[0050]
　Incidentally, it is shown in FIG. 8 (A) and (B) a portion of Vickers hardness shown in the graph of FIG. 7 were measured. 8 (A) is an enlarged sectional view of the arc welding part remelting portion formed by laser irradiation is not performed, FIG. 8 (B), the arc welding based on the manufacturing method of the fillet arc welded joint of the present invention is an enlarged sectional view of a portion made. In FIG. 8 (A), the boundary portion of the weld metal 3 and the heat affected zone 5 at 0.1mm below the surface of the steel sheet along the direction of the arrow in origin was measured hardness distribution in the thickness direction. In FIG. 8 (B), starting from the boundary portion of the laser remelting unit 6 and the heat affected zone 6a in 0.1mm below the surface of the steel sheet along the direction of the arrow, to measure the hardness distribution in the thickness direction.
However, the base metal hardness, FIG. 8 (A), the measured at sufficiently separated locations from the arrow lines in (B).
[0051]
　The present invention, as described above, is placed locally baked weld toe by the laser irradiation. To increase the quenching effect, it is preferable to use a steel member having a composition Ceq value defined by equation (1) becomes 0.3 or more.
　Ceq = C + Mn / 6 + Si / 24 + Ni / 40 + Cr / 5 + Mo / 4 + V / 14 ··· Equation (1);
　In the formula (1), C, Mn, Si, Ni, Cr, Mo, V , the content of elements It shows the (mass%).
[0052]
　Similarly, to enhance the effect of putting locally baked weld toe by the laser irradiation, the weld material, use those having a composition Ceq value defined by the formula (1) is 0.3 or more it is preferable.

claims.
[Claim 1]
　A fillet arc welded joint formed by fillet arc welding at least two metal members,
　and weld toe of the fillet arc welding of at least one metal member, wherein the surface of the metal member in a region including a boundary of the heat-affected zone generated by the fillet arc welding has a remelting portion by laser irradiation,
　the remelting unit, 1/2 or less of the plate thickness of the metal member from the surface of the metal member a range up to a depth of,
　prior austenite wherein in the heat affected zone from the remelted boundary which is a boundary of the remelted portion at a depth of 0.1mm in the thickness direction of the metal member on the surface of the metal member average effective crystal grain size of the fillet arc welded joint, characterized in that at 20μm or less.
[Claim 2]
　The remelting unit, fillet arc welded joint according to claim 1, characterized in that in the range of from the surface of the metal member to 1/3 or less of the depth of the thickness of the metal member.
[Claim 3]
　The weld metal remelting unit, fillet arc welded joint according to claim 1 or 2 Ceq value defined by the following equation (1) is equal to or less than 0.3.
　Ceq = C + Mn / 6 + Si / 24 + Ni / 40 + Cr / 5 + Mo / 4 + V / 14 ··· Equation (1);
　In the formula (1), C, Mn, Si, Ni, Cr, Mo, V , the content of elements It shows the (mass%).
[Claim 4]
　The plate thickness direction of the depth of the metal member remelting unit, the are from the surface of the metal member and the metal member of the plate thickness 1/5 or more,
　the laser remelting portion at a position below 0.1mm from the surface of the steel sheet and the hardness of the boundary portion between the heat affected zone, said not less than 1.2 times the hardness of the base material of the metal member, the surface of the steel sheet in the vertical down direction of the boundary portion of the plate thickness of the metal member 1 / hardness of the metallic member at 4 depth, fillet arc welding according to any one of claims 1 to 3, characterized in that said at most 1.1 times the hardness of the base material of the metal member joint.
[Claim 5]
　Wherein the metal member is fillet arc welded joint according to any one of claims 1 to 4, wherein the thickness is less steel 4.5 mm.
[Claim 6]
　Advance to at least one portion of a portion obtained high stress is loaded, fillet arc welded joint according to any one of claims 1 to 5, characterized in that the remelting portion is formed.
[Claim 7]
　At least two metal members by fillet arc welding,
　and the weld toe of the fillet arc welding of at least one metal member, the fillet arc boundaries of the heat affected zone caused by welding of the surface of the metal member fillet arc welded joint manufacturing method, wherein a region including remelting by laser irradiation, to form a re-melted portion from the surface of the metal member to the thickness less than 1/2 of the depth of the metal member.
[8.]
　According to claim 7, average effective crystal grain size of the prior austenite in the heat affected zone at a depth of 0.1mm in the thickness direction of the metal member from the remelted boundary portion, and wherein the at 20μm or less method of manufacturing a fillet arc welding joints.
[Claim 9]
　The re-melted region, fillet arc welded joint according to claim 7 or 8, wherein the ranges from the surface of the metal member to 1/3 or less of the depth of the plate thickness of the metal member the method of production.
[Claim 10]
　Wherein the metal member is re-melted, fillets as claimed in any one of claims 7-9 which Ceq value defined by the following equation (1) is equal to or less than 0.3 method of manufacturing an arc welded joint.
　Ceq = C + Mn / 6 + Si / 24 + Ni / 40 + Cr / 5 + Mo / 4 + V / 14 ··· Equation (1);
　In the formula (1), C, Mn, Si, Ni, Cr, Mo, V , the content of elements It shows the (mass%).
[Claim 11]
　Wherein the depth from the surface of the metal member remelting unit is a said metal member of thickness 1/5 or more,
　the laser remelting portion and heat affected at the position under 0.1mm in the thickness direction from the surface of the steel sheet hardness at the boundary between the parts is, the be more than 1.2 times the hardness of the base material of the metal member, 1/4 depth of thickness of the metal member from the steel sheet surface in the vertical downward direction of the boundary hardness, so that the following 1.1 times the hardness of the base material of the metal member, fillet arc welding according to any one of claims 7-10, characterized in that performing laser irradiation in manufacturing method of the joint.
[Claim 12]
　Wherein the metal member, the manufacturing method of the fillet arc welded joint according to any one of claims 7 to 11, wherein the thickness is less steel 4.5 mm.
[Claim 13]
　Previously determined at least one location of the high point of stress is loaded, the production method of the fillet arc welded joint according to any one of claims 7 to 12, characterized in that remelting by laser irradiation .
[Claim 14]
　The laser irradiation, in any one of claims 7 to 13, wherein the ratio of the moving speed (m / min) Laser output to (kJ / sec) is 45 ~ 80 (kJ / m) method for producing a fillet arc welded joint according.