Technical field
[0001]The present invention relates to a fillet weld joint and a manufacturing method thereof, relates fillet welding technique is particularly improved welding fatigue strength while suppressing cold cracking.
BACKGROUND
[0002]Recently, a vehicle body, the use of thin high-strength steel sheet is expected as a particular purpose of the chassis lighter. The chassis member, although the fatigue strength of the member from the viewpoint of durability is important, in general, when welding the steel plates, the welding portion is reduced factor of the fatigue strength of the member becomes a stress concentration portion. Further, in the case of applying the thin high-strength steel sheet is required to increase the fatigue strength of the welded portion according to the intensity increase of the steel sheet. However, when a high strength steel sheet as the base material tend to hardness of the heat affected zone of the base metal (HAZ) is increased with respect to the weld metal, the fatigue strength of the welded portion due to the difference in hardness it may be reduced. Therefore, to apply the thin high-strength steel sheet of the vehicle body to the chassis, it is necessary to increase the weld fatigue strength of high-strength steel sheet.
[0003]Specifically, a tendency that tensile strength of the steel sheet is more than 780 MPa, the fatigue strength of the welded portion is significantly decreased. Thus, in particular, the development of tensile strength improves the fatigue strength of the welded portion of the case of using the above high-strength steel sheet 980MPa technology is desired.
[0004]As a technique having improved fatigue strength of the welded portion, following techniques are known.
CITATION
Patent Document
[0005]Patent Document 1: JP-A-11-104838
Patent Document 2: International Publication WO2017 / 018492 discloses
Patent Document 3: International Publication WO2011 / 037272 discloses
[0006]
　Discloses a structural steel welded joints in Patent Document 1. This joint is at a position within subsurface 0.5mm of weld toe, in the range of 1mm to weld metal side from fusion boundaries, and the average value A Vickers hardness was measured according to JIS Z2244, the fusion boundaries from the difference between the maximum hardness B measured in the same manner in the range of 1mm to HAZ coarse grained region side of the base material (a-B) it has been characterized in that 26 or more 39 or less. With such a feature, there is a, it is possible to stably provide a weld joint having improved fatigue strength.
[0007]
　Fillet arc welded joint is disclosed in Patent Document 2. This joint is a weld toe of the fillet arc welding, in a region including the boundary of the heat-affected zone is characterized by forming a re-melted portion by laser irradiation to a predetermined depth. With such a feature, the weld is a, the locally hardened, development of weld crack is suppressed.
[0008]
　Fillet arc welded joint is disclosed in Patent Document 3. This joint, of the steel plate and the welding wire, in particular characterized by limiting the amount of Si. With such a feature, the welding speed is 80 cm / min greater, even less, especially 110 cm / min Ultra 150 cm / min, the shape of the weld toe shape is improved, thereby improving the fatigue characteristics of the fillet arc welded joint, there is a.
Summary of the Invention
Problems that the Invention is to Solve
[0009]
　In the technique disclosed in Patent Document 1, for improving the fatigue strength of the welded portion is made higher than the hardness of the toe portion and the heat affected zone hardness of the weld metal. In general, the base metal strength increases, so also increases hardenability of the steel component, the first place becomes higher hardness of the heat affected zone had a steel sheet itself. Therefore, when the tensile strength is to use high strength steel plate as described above 980MPa, it is necessary to also use a high intensity of welding wire which is a main component of the weld metal.
[0010]
　However, welding the wire strength excessively increased, there is a risk that cold crack occurs in the weld metal is hardened weld metal. The cause of cold cracking hydrogen embrittlement, to suppress this, reduce the diffusible hydrogen penetrated into the weld metal during welding, lowering the tensile residual stresses caused by shrinkage of the weld metal, to lower the hardness of the weld metal It is effective. However, in a typical welding conditions, it is difficult to reduce the diffusible hydrogen amount and the tensile residual, prevent excessive hardening of the weld metal becomes a measure of preventing hydrogen embrittlement.
[0011]
　Further, in order to produce a welded joint the thin steel sheet as a base material, welding to be done at high speed, and the welding wire component and the base material component during solidification of the weld metal may not be uniformly mixed. Therefore, in the vicinity of toe, it becomes a region where mixing relatively low matrix component of the alloy ingredient concentration more than high welding wire relatively alloy component concentration occurs, the weld metal hardness at the region is sufficiently there can not be obtained fear.
[0012]
　Thus, in the joint weld, when the high-strength thin steel sheet, such as tensile strength is at least 980MPa used as a base material, the hardness of the weld metal at the toe portion near the cold cracking of the limitations of the weld metal there is a problem that is not sufficiently increased. As a result, the distortion caused by the loading is concentrated in the boundary region between the heat-affected zone and the weld metal, the crack is generated in the boundary area, there may not be obtained excellent weld fatigue strength.
[0013]
　In the disclosed in Patent Document 2 technology, and weld toe, into a region including a boundary of the heat affected zone, to form a re-melted portion by laser irradiation to a predetermined depth. Such laser irradiation, which are superimposed effected after the welding operation, there is a risk of increasing the capital investment and the workload for this purpose. Further, Patent Document 2, there is no description or suggestion about cold crack.
[0014]
　In the technique disclosed in Patent Document 3, of the steel plate and the welding wire, in particular by limiting the Si content, and to improve the shape of the weld toe shape, improve the fatigue properties of the fillet arc welded joint. However, Patent Document 3, or suggestion is little description on cold cracking. Specifically, Patent Document 3, because if there is a slit in the welding wire at risk of outside air (hydrogen) invasion, merely describe that no slits.
[0015]
　The present invention was made in view of the above circumstances, to provide a fillet weld joint and a manufacturing method thereof tensile strength with excellent welding fatigue strength while suppressing cold cracking in more steel 980MPa With the goal.
Means for Solving the Problems
[0016]
　The present inventors have intensively studied fillet welded joint which can achieve excellent welding fatigue strength while suppressing cold cracking. As a result, the base material having a predetermined tensile strength, as well as use the value of carbon equivalent, the relationship between the tensile strength [MPa] and carbon equivalent [wt%], the suitably selected high-strength steel sheet has a proper using the welding wire having a carbon equivalent Vickers hardness HVbond in the boundary region between the weld metal and the heat affected zone, the average value HVwmt Vickers hardness of the weld metal and the mean value of Vickers hardness of the heat affected zone HVhaz Doo is to satisfy the preferred relationship, to obtain a knowledge that it is possible to obtain a fillet welded joint which provides excellent welding fatigue strength while suppressing cold cracking. The present invention has been made based on such findings, its gist the following.
[0017]
　(1) a fillet welded joint obtained by performing fillet welding overlapping portions of the two base materials,
　the fillet weld joint, the base material comprises a weld metal and heat affected zone becomes,
　the tensile strength of the base material is not less than 980 MPa, the carbon equivalent of the base material is 0.36 to 0.60, a carbon equivalent [wt tensile strength of the base material [MPa] is the base material %] and at 1950 times or more,
　the average carbon equivalent of the weld metal is 0.45 to 0.65, higher than the carbon equivalent of the base material,
　the cross-section perpendicular to the weld line of the fillet weld joint through the position of 0.1mm or 0.3mm or less in the thickness direction of the base material from the weld toe, even on a straight line parallel to the base material surface,
　the boundary between the weld metal and the heat affected zone Vickers hardness HVbond and, 0.1 mm or more in the weld metal side from the boundary at 0 The average value HVwmt Vickers hardness of the weld metal at the following positions .3Mm, the average value of Vickers hardness of the heat affected zone of 0.1mm or 0.3mm following positions in the heat-affected portion from the boundary and HVhaz, but satisfies the following relationship, fillet weld joints, characterized in that.
　　　　　　　≦ HVwmt HVbond
　　　　　　　(1) HVbond ≧ HVhaz-50
　　　　　　　(2) HVhaz ≦ 350 (3)
[0018]
　(2) The tensile strength of the base material [MPa] is less than 2750 times the carbon equivalent [wt%] of the base material, fillet weld joint according to (1).
[0019]
　(3) The base material is, in mass%, 0.01 ≦ C ≦ 0.25,0.01 ≦ Si ≦ 2.00,0.05 ≦ Mn ≦ 3.0,0.001 ≦ Al ≦ 0. 4, containing, the balance being Fe and inevitable impurities, fillet weld joint according to (1) or (2).
[0020]
　(4) The base material is, in mass%, 0.1 ≦ Ni ≦ 3.0,0.1 ≦ Cr ≦ 2.0,0.005 ≦ Mo ≦ 0.5,0.005 ≦ Nb ≦ 0. further comprising at least one 3,0.005 ≦ V ≦ 0.3,0.005 ≦ Ti ≦ 0.3,0.0001 ≦ B ≦ 0.01, fillet welding according to (3) joint.
[0021]
　(5) the weld metal, in mass%, 0.03 ≦ C ≦ 0.25,0.01 ≦ Si ≦ 2.00,0.5 ≦ Mn ≦ 3.0,0.001 ≦ Al ≦ 0. 15, contains, the balance being Fe and inevitable impurities, fillet weld joint according to any one of the above (1) to (4).
[0022]
　(6) the weld metal, in mass%, 0.1 ≦ Ni ≦ 3.0,0.1 ≦ Cr ≦ 2.0,0.005 ≦ Mo ≦ 0.5,0.005 ≦ Nb ≦ 0. further comprising at least one 1,0.005 ≦ V ≦ 0.15,0.005 ≦ Ti ≦ 0.15,0.0001 ≦ B ≦ 0.01, fillet welding according to (5) joint.
[0023]
　(7) the thickness of the base material is less than 1.0mm 3.6mm or less, fillet weld joint according to any one of the above (1) to (6).
[0024]
　(8) In the cross-section perpendicular to the weld line of the fillet weld joint, as the position of 0.1mm or 0.3mm or less in the thickness direction of the base material from the welding route point, parallel to the base metal surface linear a top
　of the weld metal of the Vickers hardness in 0.1mm or 0.3mm following areas from the boundary in the weld metal side of the weld metal and the heat affected zone which is located below the welding route point average HVwmr satisfies the following relationship, fillet weld joint according to one any one of (7) from above (1).
　　　　　　HVwmr ≦ 350
[0025]
　(9) partially overlapping the two base material, a process for the preparation of a fillet welded joint subjected to fillet welding using a welding wire,
　the tensile strength of the base material is not less than 980 MPa, the base material carbon equivalent of is not less 0.36 0.60 or less, a tensile strength of the base material [MPa] is the carbon equivalent [wt%] of the matrix of 1950 times or more,
　the carbon equivalent of the welding wire 0 in .50 above 0.80, higher than the carbon equivalent of the base metal,
　the welding speed is less than 60cm / min or more 150 cm / min, the production method of the fillet weld, characterized in that.
The invention's effect
[0026]
　In the present invention, the base material having a predetermined tensile strength, and the value of carbon equivalent, while using suitably selected high-strength steel sheet and relationship of the carbon equivalent and tensile strength, high having the proper carbon equivalent using intensity welding wire. Therefore, according to the present invention, the boundary region between the weld metal and the heat affected zone, the weld metal, and the heat-affected zone, it is possible to suitably control the respective Vickers hardness, cold cracking of thus fillet welded joint while suppressing, it is possible to realize an excellent welding fatigue strength.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027]
[1] Figure 1 is obtained by applying a fillet weld overlapping a portion of the two sheets of the base material is a sectional view showing a fillet welded joint of the present embodiment.
FIG. 2, with respect to fillet weld joint shown in FIG. 1 is a graph showing the Vickers hardness, and a point of an imaginary line, the relationship.
FIG. 3 is a diagram for explaining a fatigue bending test.
[4] FIG. 4 is a diagram showing a welding method employed in Example.
DESCRIPTION OF THE INVENTION
[0028]

　present invention have found that in fillet welds of high strength thin steel sheet, improves the fatigue strength of the welded portion while suppressing cold cracking of the weld metal (including a weld metal and heat affected zone) In order, we conducted intensive research. As a result, the present inventors have found that the assumption that tension as the base material strength used thin steel above 980 MPa, suitably selecting the values of the carbon equivalent of the base material, the relationship between the carbon equivalent and tensile strength, the with the use of high strength steel sheet, using a high-strength welding wire having the proper carbon equivalent, it improves the fatigue strength of the welded portion of the toe portion neighboring region, and the weld metal, which causes cold cracking it is possible to prevent hydrogen embrittlement, to obtain a knowledge that. Fillet welded joint of the present embodiment is based on the findings as described above.
　Note that according to JIS Z 3001 (welded term), and the heat-affected zone, tissue heat welding and cutting, and (h) gold properties, such as mechanical properties occurs a change, unmelted It means the portion of the base material.
[0029]
　Fillet welded joint of the present embodiment is a joint obtained by performing fillet welding overlapping portions of the two high-strength thin steel sheet (base material), specifically, a lap joint or T-piece is a concept that includes.
[0030]
　Further, fillet welded joint of the present embodiment, the tensile strength is more than 980 MPa, has a so-called high-strength steel sheets intended for coupling to a base material. However, improvement in weld fatigue strength of the joint of the present embodiment described below the tensile strength of the base material is 1470MPa exceeds can not be sufficiently obtained. Therefore, the tensile strength of the base material is preferably not more than 1470 MPa.
[0031]
　Such under conditions fillet welded joint of the present embodiment, the carbon equivalent of the base material is 0.36 to 0.60. The carbon equivalent of the base material by 0.36 or more, the base material itself is hardened, the body, in particular obtaining a strength that can be sufficiently used as members of the chassis.
[0032]
　In contrast, by setting the carbon equivalent of the base material and 0.60 or less, without increasing the hardness of the heat affected zone excessively and hardness in the boundary region between the heat-affected zone and the weld metal, the boundary region near the heat to suppress the difference between the hardness at affected zone, it is possible to prevent the occurrence of cracks in the vicinity of the boundary area efficiently. Here, the boundary between the heat-affected zone and the weld metal, the weld was cut to the weld line and the vertical direction, it can be obtained by corroding the cross-section.
[0033]
　Incidentally, the carbon equivalent of the base material by 0.40 to 0.55, can be achieved at higher levels of each effect described above.
[0034]
　Here, the base metal, weld metal, and the welding wire carbon equivalent of [wt%] is expressed by the following equation. Carbon equivalent [wt%] = C + Si / 24 + Mn / 6 + Ni / 40 + Cr / 5 + Mo / 4 + V / 14
C in formula, Mn, Ni, Cr, Mo, V is the content in each material [wt%]. The content ratio of the elements, is measured at the portion of the welding wire without the matrix and / or plating portion does not include a plated portion.
[0035]
　Furthermore, in the fillet weld joint of the present embodiment, it has a tensile strength of the base material [MPa] or more 1950 times the carbon equivalent [wt%] of the matrix. By satisfying this requirement, structure of the base material is martensite mainly. Structure of the base material, but is subject to hot rolling conditions in the preform manufacturing, in particular, in order to secure a predetermined base material strength, with a martensitic structure increases the cooling rate during hot rolling, it is important to utilize the work hardening by rolling.
[0036]
　However, when welding with a high-strength steel sheet produced by such a rolling manner, sometimes the heat-affected zone (HAZ) is tempered back to soften. Therefore, it is preferable that the tensile strength of the base material [MPa] or less 2750 times the carbon equivalent [wt%] of the matrix. Thus, lowering the static strength of the joint with respect to the base material strength, i.e. it is possible to suppress strength reduction due to HAZ softening. Based on the tensile strength of the base material, it preferably has a specific tensile strength of the joint (tensile strength of tensile strength / base material of the joint) is 0.7 or more.
[0037]
　Figure 1 is obtained by applying a fillet weld overlapping a portion of the two sheets of the base material is a sectional view showing a fillet welded joint of the present embodiment. The cross-section is a section perpendicular to the weld line of the fillet weld joint. Fillet welded joint 10 of the present embodiment includes a two preform 12, and the weld metal 16, the heat affected zone (not shown). In Figure 1, point A is a so-called weld toe, the dotted line passes through the position of Smm (0.1 mm or 0.3mm or less) in the thickness direction of the base material from the weld toe A, the surface of the base material is a virtual line showing the parallel straight lines.
[0038]
　Relates fillet weld joint having the above configuration, point or region of the virtual line, i.e.,
　the representative point at the boundary between-weld metal 16 and (the base material 14) the heat-affected zone (HAZ) B,
　- the representative point average HVwmt, the Vickers hardness of the weld metal in the area C of 0.1mm or more 0.3mm or less in the weld metal 16 side from B
　above 0.1mm from-representative point B in the HAZ side 0.3mm following areas average HVhaz Vickers hardness of the heat affected zone in the D
consider.
　Note that the average value HVwmt and average HVhaz Vickers hardness of Vickers hardness, the region C, and each of D, and the mean value of hardness at least three arbitrary points.
[0039]
　Here, as the viewing surface of the boundary region, with picric acid corroded section. Because when etched with picric acid can be confirmed solidification form of the growth direction and the like of the dendrites, it is possible to clearly distinguish the heat-affected zone is melted and solidified weld metal portion and the transformed structure. The representative point B means a point which is determined as a boundary having no heat-affected zone of the weld metal and the organization having dendrite structure.
[0040]
　Under such assumption, fillet welded joint of the present embodiment, the Vickers hardness HVbond at the representative point B, a mean value HVwmt Vickers hardness of the weld metal in the region C, Vickers heat affected portion in the region D and hardness of the average value HVhaz, but the following relationships (a) satisfy (c).
　(A) HVbond ≦ HVwmt
　(b) HVbond ≧
　HVhaz-50 (c) HVhaz ≦ 350
[0041]
　2, with respect to fillet weld joint shown in FIG. 1, the Vickers hardness is a graph showing the relationship between the virtual line region. Incidentally, the Vickers hardness shown in the figure shows a qualitative value rather than quantitative value. Hereinafter, the relationship from (a) for (c) will be described in detail.
[0042]
(A) HVbond ≦ HVwmt
　this provision is an index means to cure than the weld metal in the molten boundary regions. This provision, the components of the welding wire, and high speed welding is a feature of the sheet steel welding affects. In high speed welding, mixing of the welding wire component and the base metal component is not uniform, in particular the weld metal of the weld metal and near the boundary of the heat-affected zone (region C) is higher mixing ratio of the matrix component. Further, when the base material component is melted by welding heat, melt near the boundary for oxide inclusions in the weld metal with alloying elements due to the effect of oxidative gas atmosphere to oxidize exhaustion to promote ferrite transformation (region C) It becomes low in the weld metal hardness. Therefore, in order to prevent fatigue cracking due to the strain concentration to the weld metal softened molten near the boundary (area C), and defines the lower limit of carbon equivalent of the welding wire (higher carbon equivalent of the base material at 0.50 or higher) it is necessary to make the HVbond ≦ HVwmt Te.
[0043]
(B) HVbond ≧ HVhaz-50
　conventionally biggest reason fatigue strength is not sufficiently exhibited weld in fillet welded joint (including the weld metal and heat-affected zone) has a Vickers hardness at point B in FIG. 2 , a Vickers hardness in the region D (the average value of), because the difference is too large, was to fatigue fracture is generated from the vicinity of the toe portion a. This is because, in the boundary (the representative point B) of the heat-affected zone of the weld metal and the base metal becomes smooth solidification interface, while relatively hardness since the alloying elements of the steel components are discharged into the molten metal side is lowered, be relatively high hardness by martensitic transformation by cooling after welding in the heat affected zone (region D) was caused.
[0044]
　In contrast, this provision, in addition to the tensile strength of the base material, by a suitable choice of the relationship between tensile strength and carbon equivalent of the base material, the ratio of these points B, and hardness difference in the region D to the conventional is an index which means that can be significantly reduced in. Specifically, the carbon equivalent of the base material as 0.36 or more, by using the work hardening together promotes martensitic transformation of the base material of the base material tensile by increasing the cooling rate during the hot-rolled steel sheet manufacturing the intensity on the assumption that the above 980 MPa, for the curing inhibition of HVhaz, the carbon equivalent of the base material by 0.60 or less, is possible to suppress the hardening of the weld heat affected zone of the melt near the boundary it can. This technology is for curing due to cooling and processing in the manufacture of a plate matrix, by reducing the degree of hardening by the cooling of the heat-affected zone during welding, the heat-affected zone while ensuring the strength of the base material intended to suppress the curing, the conventional are different technologies idea. On the other hand, for softening suppression HVbond, it defines the lower limit of carbon equivalent of the welding wire (higher carbon equivalent of the base material at 0.50 or higher), while preventing the softening of the weld metal, the heat affected zone You can not increase the difference between the hardness.
[0045]
(C) HVhaz ≦ 350
　This specification, an index to prevent the decrease in melt boundary defines the hardness limit of the heat-affected zone in the vicinity of, excessive heat affected zone curing, hence weld fatigue strength associated therewith it is. The carbon equivalent of the base material by 0.60 or less, it is possible to suppress the hardening of the weld heat affected zone of the melt near the boundary.
[0046]
　Above relationship shown in (a) to (c) are combined, the fillet weld joint of the present embodiment, it is possible to realize an excellent fatigue strength of the weld (including the weld metal and heat-affected zone).
[0047]
　Incidentally, the fatigue strength is measured by the following test.
　As the fatigue test piece, prepared plane bending fatigue test piece having a shape shown in FIG. 3, to evaluate the fatigue strength of the weld toe. To determine the fatigue strength of the weld toe by Reversed bending test, after the lap fillet welding of the evaluation object, and restrain welded back side to prevent the opening of the root portion. Fatigue test and bending fatigue test of the displacement control (stress ratio R = -1), repetition frequency 25 Hz, the test termination condition 40% torque reduction or repetition rate of 2 × 10 without lowering of torque 6 reach the times and when that was.
[0048]
　Fatigue strength may be evaluated for relative reference. Based on the fatigue strength of conventional fillet welded joint, the higher the fatigue strength ratio can be regarded as excellent fatigue strength. Fatigue strength ratio according to the related art is preferably higher, it may be 1.1 or more. More preferably, the fatigue strength ratio may be 1.2 or more. More preferably, the fatigue strength ratio may be 1.3 or more. A reference, as the fatigue strength of conventional fillet welded joint, without consideration for the carbon equivalent, etc. prescribed in the present invention may be used fatigue strength of fillet weld joints and fillet welded 780MPa steel.
[0049]
　In addition, fillet welded joint of the present embodiment, the average carbon equivalent of the weld metal at 0.45 to 0.65, and higher than the carbon equivalent of the base material. By this provision, an average carbon equivalent of the weld metal at 0.45 or more, is made higher than the carbon equivalent of the base material, it is possible to prevent the softening of the weld metal, and a weld (weld metal and heat affected zone the fatigue strength of) can be further improved. On the other hand, the average carbon equivalent of the weld metal by 0.65 or less, to suppress excessive hardening of the weld metal, it is possible to prevent hydrogen embrittlement of the weld metal. Further, such carbon equivalent ranging 0.50 or more, when a 0.60 is preferable because the effect is exhibited at a high level, respectively. The average carbon content of the weld metal, the weld metal, and the average value of the average carbon content of at least three arbitrary points.
[0050]
　The fillet weld joint having such a structure, the base material and / or components, such as: the weld metal (in both mass%) can be selected from.
　First, a description will be given component of the base material. Here, the value of each component in the base material, and that measured in the base portion of the base material without the plating portion.
[0051]
　C: 0.01% to 0.25% or less
　C, for the strength of the joint securing is preferably set to 0.01% or more. Moreover, because of the uniformity of hardness distribution of the weld toe vicinity is preferably at most 0.25%.
[0052]
　Si: 0.01% to 2.00% or less
　Si is to be deoxidized, and the intensity is useful to ensure, preferably 0.01% or more. The content since impairs weldability and is added 2.00 percent is preferably at most 2.00%.
[0053]
　Mn: 0.05% to 3.0% or less
　Mn is useful as an element to increase the low cost strength, is preferably 0.05% or more for ensuring strength. The content since impairs weldability and is added 3.0 percent is preferably at most 3.0%.
[0054]
　Al: 0.001% to 0.4% or less
　Al is preferably 0.001% or more for deoxidation. Further, it is preferable that the inclusions 0.4 percent when the addition of the steel and weld metal too much, to 0.4% or less for lowering the toughness.
[0055]
　Balance: Fe and impurities
　the balance being Fe and impurities. Here, the impurities, a component to be mixed in the course of the components, or the production is contained in the raw material, refers to intentionally not were contained Ingredient in the base material. As the impurity, P, include S is. Further, it may because sometimes plating on the surface of the base material is subjected, plating components such as Zn and Al are mixed about 0.10 to 0.3 percent as unavoidable components in the base material . So as not to be affected by plating or the like, in consideration of the thickness of the plating, it is preferable to analyze the components of the base material.
[0056]
　Optionally elements: Ni,
　Cr, Mo, Nb, V, Ti, B Ni, Cr, Mo, Nb, V, Ti, B both are components to improve the joint fatigue properties, weld metal and heat affected zone it is considered that to improve the fatigue strength applied to affect the (HAZ). These ingredients in this respect is the active ingredient, the fillet weld joint of the present embodiment can be contained at least one of these components. However, excessive addition of either degrade the steel material. Thus, each, 0.1 ≦ Ni ≦ 3.0,0.1 ≦ Cr ≦ 2.0,0.005 ≦ Mo ≦ 0.5,0.005 ≦ Nb ≦ 0.3,0.005 ≦ V so it is preferably contained in the range of ≦ 0.3,0.005 ≦ Ti ≦ 0.3,0.0001 ≦ B ≦ 0.01.
[0057]
　Next, a description will be given component of the weld metal (both units are mass%).
　Components of the weld metal can be obtained by using the chips taken from the weld metal, measured in emission spectroscopy using high frequency inductively coupled plasma (ICP). Note that the collection of chips, the area of pre-weld metal by observing the cross section of the welded portion is measured, collected by cutting with a knife such as a drill from that region. Therefore, components of the weld metal is generally the average value of the weld metal central portion, it is the average value of the weld metal carbon equivalent.
[0058]
　Welding, especially in gas-shielded arc welding, oxygen and nitrogen traces from the atmosphere and shielding gas during welding is for incorporation into the molten metal, unlike the plate matrix, the weld metal contains oxide or nitride. Oxide promotes ferrite transformation of the weld metal structure, causing reduction in strength. Therefore, in the weld metal, the C and Mn is a hardenability improving element, it is necessary to increase than the base material. Meanwhile, the nitrogen reacts Al, Nb, is V, generates a nitride, a weld metal causes significantly hardened, lowering the toughness of the weld metal. Therefore, in the weld metal, the upper limit of these elements, it is necessary to limit than the base material.
　In view of the above, components of the weld metal may be defined as follows.
[0059]
　C: 0.03% to 0.25% or less
　C, for the strength of the joint securing is preferably set to 0.03% or more. C generates oxide, promotes the ferrite transformation of the weld metal structure, causing reduction in strength. Therefore, in the weld metal, the C is hardenability improving element, it has increased than the base material. Moreover, because of the uniformity of hardness distribution of the weld toe vicinity is preferably at most 0.25%.
[0060]
　Si: 0.01% to 2.00% or less
　Si is to be deoxidized, and the intensity is useful to ensure, preferably 0.01% or more. The content since impairs weldability and is added 2.00 percent is preferably at most 2.00%.
[0061]
　Mn: 0.5% to 3.0% or less
　Mn is useful as an element to increase the low cost strength, it is preferably 0.5% or more for ensuring strength. Mn generates oxide, it promotes the ferrite transformation of the weld metal structure, causing reduction in strength. Therefore, in the weld metal, the Mn is hardenability improving element, it has increased than the base material. The content since impairs weldability and is added 3.0 percent is preferably at most 3.0%.
[0062]
　Al: 0.001% or more than 0.15%
　Al is preferably 0.001% or more for deoxidation. Also, added 0.15 percent, by reaction with nitrogen to produce a nitride, a weld metal causes significantly hardened, lowering the toughness of the weld metal. Since it is preferable that 0.15% or less. Therefore, in the weld metal, the upper limit of Al, limits than the base material.
[0063]
　Balance: Fe and impurities
　the balance being Fe and impurities. Here, the impurity, elements described above, considered as components other than the optional elements will be described later. Impurities include Cu and Zn and the like. Weld metal comprises components of the welding wire and the base material. Welding the wire surface of the may Cu plating is applied to the conductive ensured, also, if also the base material is plated, because the plating components come included in the weld metal, Cu and Zn is also regarded as impurities.
[0064]
　Optionally elements: Ni,
　Cr, Mo, Nb, V, Ti, B Ni, Cr, Mo, Nb, V, Ti, B both are components to improve the joint fatigue properties, weld metal and heat affected zone it is considered that to improve the fatigue strength applied to affect the (HAZ). These ingredients in this respect is the active ingredient, the fillet weld joint of the present embodiment can be contained at least one of these components. However, excessive addition of either degrade the steel material. Thus, each, 0.1 ≦ Ni ≦ 3.0,0.1 ≦ Cr ≦ 2.0,0.005 ≦ Mo ≦ 0.5,0.005 ≦ Nb ≦ 0.1,0.005 ≦ V so it is preferably contained in the range of ≦ 0.15,0.005 ≦ Ti ≦ 0.15,0.0001 ≦ B ≦ 0.01. Incidentally, Nb and Ti reacts with nitrogen to produce a nitride, a weld metal causes significantly hardened, lowering the toughness of the weld metal. Therefore, in the weld metal, the upper limit of these elements, limiting than the base material.
[0065]
　Furthermore, in the fillet weld joint having the above structure, the plate thickness of the base material, can be less than 1.0mm 3.6mm or less. By the thickness of the base material and more 1.0 mm, prevented without dissolving the base material excessively, the welding defects of burn through failure or the like even in the longitudinal direction of the any portion of the fillet weld joint matrix can do.
[0066]
　In contrast, the thickness of the base material is set to be lower than or equal 3.6 mm, it becomes easy to deform in the plane direction of the steel sheet, reducing the weld tensile residual stresses in question in the welding of steel plate can.
[0067]
　Incidentally, when the thickness of the base material to 1.8mm or 2.6mm or less, since the the above-mentioned effect is exhibited at a high level, respectively preferable.
[0068]
　Furthermore, in the fillet weld joint having the above structure, Vickers hardness HVwmr of the weld metal of the weld root point side that defined below may satisfy the following relationship.
HVwmr ≦ 350
[0069]
　Point E in FIG. 1 is a so-called welding route point. Vickers hardness HVwmr weld root portion, as in section perpendicular to the weld line of the fillet weld joint, the position of 0.1mm or 0.3mm or less in the thickness direction of the base material 14 from the welding route point E the a on a straight line parallel to the base metal surface, (the boundary area between the weld metal and the heat affected zone which is located below the weld root point E) a boundary region between the weld metal and the heat affected zone of the weld root point side the average value of Vickers hardness of the weld metal in the region F of 0.1mm or 0.3mm or less in the weld metal side from. This will mean, in the region F, the average value of hardness at least three arbitrary points.
[0070]
　Generally, arc welding of a thin steel sheet, since the high-speed welding is performed, since the welding wire component and the base metal component is solidified without being mixed well, unevenness occurs in the components of the weld metal. As a result, while the higher the mixing ratio of the matrix components in the weld metal toe portion A near the mixing of the base material component in the region F in the vicinity of the root point E becomes less prone.
　In the present application, in order to improve the weld fatigue strength, because of the high carbon equivalent of the weld metal components than the base metal component, in comparison with the weld metal of the weld toe A near the weld metal of the root near the point (region F) It is likely to be hard hardness. Therefore, in order to prevent cold cracking of the root portion is the Vickers weld metal hardness of the root near the point (region F) as an average of three arbitrary points 350 or less (HVwmr ≦ 350) it is preferable.
　The numerical values of the Vickers hardness 350, together known as an index for the cold cracking prevention in the welding of thick steel plates, cold cracking study results for lap fillet joint steel sheets inventors have conducted consistent with the value. That is, the Vickers hardness of the weld metal of the weld root point side by 350 or less, thereby improving the effect of suppressing cold cracking.
[0071]

　Next, a detailed method for manufacturing the fillet weld joint of the present embodiment.
　Method for producing a fillet welded joint of the present embodiment, tensile strength and carbon equivalent overlapped portion of two preform is a predetermined range, using a welding wire of a given carbon equivalent, at a predetermined welding speed a method for producing a fillet welded joint subjected to fillet weld, tensile strength of the base material is not less than 980 MPa, the carbon equivalent of the base material is 0.36 to 0.60, the base material tensile strength [MPa ] to the above 1950 times the carbon equivalent [wt%] of the matrix are as described above. The resulting fillet weld joint comprises the base material, the weld metal and heat affected zone.
[0072]
　Specifically, in the manufacturing method of the fillet weld joint of the present embodiment, as the welding wire, the carbon equivalent is at least 0.50 0.80, and using a higher than the carbon equivalent of the base material. By the carbon equivalent of the welding wire and 0.50 or more, while it is possible to prevent softening of the weld metal, by 0.80 or less, to suppress excessive hardening of the weld metal, the hydrogen embrittlement of the weld metal it is possible to prevent the reduction. Further, such carbon equivalent ranging 0.55 or more, when the 0.70 or less is preferable because the effect is exhibited at a high level, respectively.
[0073]
　In the manufacturing method of the fillet weld joint of the present embodiment, for the above-mentioned base material carbon equivalent of (0.36 to 0.60), the carbon equivalent of the welding wire is set high. This, together with the alloy components of the welding wire is oxidized and consumed during welding, oxide inclusions in the weld metal by promoting intragranular transformation of the weld metal, because the fine tissue.
[0074]
　In the manufacturing method of the fillet weld joint of the present embodiment, the welding speed than 60cm / min or more 150 cm / min. The welding speed by a 60cm / min or more, mixing unevenness of the base metal component and welding the wire component of the weld metal of the toe portion near found in high speed welding is remarkable, the fatigue strength improvement effect of the present invention is exhibited easy it is for. Incidentally, the scope of such welding speed when the 80 cm / min or more is preferable because the effect is exhibited at a high level. Welding speed is one factor that determines the production efficiency of the welded structure, efficiency is good enough to set higher the speed. Therefore, as long as it does not adversely affects the fatigue strength, etc., it may not particularly define the upper limit on the welding speed. However, excessive speed, such as vigorously the movement of the molten pool, from the viewpoint of the weld bead shape, which is not preferable. Therefore, the welding speed is less 150 cm / min. Preferably, the welding speed may be less 120 cm / min.
[0075]
　Here, as a welding method applicable to the manufacturing method of the welded joint of the present embodiment, Ar and CO 2 gas shielded welding method using a mixed gas of the like. In particular, it also becomes possible to obtain a uniform weld bead shape to achieve the effect of the present invention (improvement of the welding fatigue strength while suppressing cold cracking) efficiently in high speed welding by adopting Parusumagu welding it can.
[0076]
　When you select the tensile strength and carbon equivalent of the base material as described above, the base material is a tissue plus a work-hardened martensite, heat-affected portion becomes martensite structure which is auto-tempering, the hardness it is possible to suppress an excessive increase.
[0077]
　On the other hand, the organization of the weld metal becomes martensite, bainite, ferrite mixed structure of. Oxide inclusions produced during welding becomes a starting point of the ferrite transformation in the weld metal, as a result of intragranular transformation is promoted, it is possible to show the fine structure forms a relatively high-strength weld metal.
[0078]
　Tensile strength of such a base material, the carbon equivalent of the base material, and by selection of the carbon equivalent of the welding wire, in a fillet weld joint obtained by the manufacturing method of this embodiment, the following relation (formula (4) equation (6) is satisfied from.
[0079]
　　　　　　　ＨＶbond≦ＨＶwmt 　　　　　　　　　　　　　　　　　　　　　（４）
　　　　　　　ＨＶbond≧ＨＶhaz－５０ 　　　　　　　　　　　　　　　　　　（５）
　　　　　　　ＨＶhaz≦３５０ 　　　　　　　　　　　　　　　　　　　　　　（６）
[0080]
　Therefore, by satisfying the above formulas (4) to (6), the fillet weld joint obtained by the manufacturing method of this embodiment, (including the weld metal and heat-affected zone) superior weld fatigue strength it can be realized.
[0081]
　Further, in the fillet weld joint obtained by the manufacturing method of this embodiment, the weld root portion of the Vickers hardness HVwmr can also meet the following relationship.
　　HVwmr ≦ 350
This improves the effect of suppressing cold cracking in the fillet weld joint.
Example
[0082]
　Hereinafter, detailed examples to demonstrate the effect of the present invention.
　Figure 4 is a diagram showing a welding method employed in Example. As shown in the figure, to create a fillet welded joint overlaid with two thin plates (thickness 2.6 mm). 4, reference numeral 26 denotes a weld metal, reference numeral W denotes a welding machine.
[0083]
　Welding conditions, the Parusumagu welding current 230A, voltage 26V, both the welding speed was 80 cm / min.
[0084]
　Table 1 steel (base material) used in Example illustrates the ingredients and carbon equivalent of the A-F, show the components and carbon equivalent of the welding wire a-e used in Example Table 2. Steel B with respect to the carbon equivalent of the steel material, C is (0.60 0.36 or higher) outside the scope of the present invention, the welding wire a respect carbon equivalent of the welding wire, range d is the invention (0.50 more than 0.80 or less) outside.
[0085]
[Table 1]

[0086]
[Table 2]

[0087]
　In ingredients in Table 1 to produce a steel sheet various intensity (base material), and then using these welding wire of the steel plate and Table 2, lap fillet of Comparative Examples 1-6 and Invention Examples 1 to 8 shown in Table 3 the welded joints were produced. Then, for each of these respective fillet welded joint, in cross-section perpendicular to the weld line of the fillet weld joint, as the position of 0.2mm in thickness direction of the base material from the weld toe, parallel to the surface of the base material a such straight line, and the Vickers hardness HVbond at the boundary between the weld metal and the heat affected zone, the average value HVwmt Vickers hardness of the weld metal at 0.2mm locations in the weld metal side from the boundary region, the boundary the average value HVhaz Vickers hardness of the heat affected zone at the position of 0.2mm the heat affected zone side, were investigated. It was also investigated Vickers hardness HVwmr of the weld metal of the weld root point side. The results are also shown in Table 3. A method fatigue test as the plane bending fatigue test, for determination of the fatigue strength was evaluated as acceptable if higher than the fatigue strength of 780MPa steel shown in Comparative Example 1. As for the determination of the static strength of the joint, since the strength of the hot stamped steel, which is used as the prior art is reduced to about 60% of the base material strength, "available for more than 60% of the strength of the base metal strength for more than 70% of the strength and "was" good ".
[0088]
[table 3]

[0089]
　As apparent from Table 3, all of the invention examples 1 to 8, the base material strength or more 980MPa, 0.36 ~ 0.60 (%) is the carbon equivalent of the base material, (base material tensile strength / parent material carbon eq) is 1950 or more, the carbon equivalent of the welding wire is a prerequisite that the higher carbon equivalent of the base material at from 0.50 to 0.80, satisfying the HVbond ≦ HVwmt, HVbond ≧ HVhaz-50 and HVhaz ≦ 350, There has been confirmed. And, for these these invention examples 1-8, both without causing cold cracking, excellent fatigue strength of at least 1.1 times the fatigue strength as a reference of the fatigue strength (780 MPa steel shown in Comparative Example 1 the ratio) obtained was confirmed.
[0090]
　In particular, and with (the base material tensile strength / parent material carbon equivalent) ≦ 2750 or less, for Inventive Examples 1, 2, 4 to 7, it is confirmed that it is possible to suppress a decrease in joint tensile strength due to HAZ softening It was.
[0091]
　In contrast, Comparative Examples 1 to 6, both the tensile strength of the base material, the carbon equivalent of the base material, the relationship between tensile strength and carbon equivalent of the base metal, welding wire carbon equivalent of, the Vickers hardness of at least either, because it is outside the predetermined range defined in the present invention, cold cracking, at least one superior results for the fatigue strength and static tensile strength can not be obtained has been confirmed. Predetermined More specifically, in Comparative Example 1, the tensile strength of the base material, the relationship between tensile strength and carbon equivalent of the base material, and the Vickers hardness (the relational expression (1) HVbond ≦ HVwmt) is defined in the present invention is outside the range of the tensile strength is low, the fatigue strength was 215 MPa.
　In Comparative Example 2, the carbon equivalent of the base material is out of the predetermined range defined in the present invention, below the Comparative Example 1 in which fatigue strength equivalent to conventional products.
　In Comparative Example 3, the carbon equivalent of the base material, the relationship between tensile strength and carbon equivalent of the base material, and the Vickers hardness (equation (1) to (3)) There are outside a predetermined range defined in the present invention , lower than the Comparative example 1 in which fatigue strength equivalent to conventional products.
　In Comparative Example 4, less than the predetermined range in which the carbon equivalent of the welding wire defined in the present invention, also Vickers hardness (equation (1)) is out of the predetermined range defined in the present invention, fatigue strength conventional below the Comparative example 1 which corresponds to the goods.
　In Comparative Example 5, the carbon equivalent of the welding wire is more than the predetermined range defined in the present invention, the relationship between the Vickers hardness of the root portion is not satisfied HVwmr ≦ 350, cold cracking occurred.
　In Comparative Example 6, the Vickers hardness (equation (1) and (3)) is out of the predetermined range defined in the present invention, below the Comparative Example 1 in which fatigue strength is equivalent to the prior art.
　Therefore, in Comparative Examples, it can not be said good fatigue strength while suppressing cold cracking is achieved in the weld (including the weld metal and heat-affected zone).
DESCRIPTION OF SYMBOLS
[0092]
　10 fillet welded joint
　12, 14, 22, 24 base material
　16, 26 weld metal
　A weld toe
　representative points of B boundary
　is 0.3mm following positions than 0.1mm in the weld metal 16 side from C representative point B region of the weld metal
　D boundaries (representative point B) from the area of the heat-affected in part is a position of 0.1mm or 0.3mm or less in the HAZ side
　E welding root point
　of F welding route point side boundary (weld root point region of the weld metal is 0.3mm or less positions than 0.1mm in the weld metal side from the boundary) between the weld metal and the heat affected zone located below the E
　between S weld toe and the virtual line dimensions
　W welders

The scope of the claims
[Requested item 1]
　A fillet weld joint obtained by performing fillet welding overlapping portions of the two base materials,
　the fillet weld joint, the base material, comprises a weld metal and heat-affected zone,
　the the tensile strength of the base material is not less than 980 MPa, the carbon equivalent of the base material is 0.36 to 0.60, a tensile strength of the base material [MPa] is the carbon equivalent of [wt%] of the base material and at 1950 times or more,
　the average carbon equivalent of the weld metal is 0.45 to 0.65, higher than the carbon equivalent of the base material,
　the cross-section perpendicular to the weld line of the fillet weld joint, weld toe as the position of 0.1mm or 0.3mm or less in the thickness direction of the base material from the edge, even on a straight line parallel to the base material surface,
　located below the weld toe, and the weld metal a Vickers hardness HVbond at the boundary between the heat affected zone, said solvent from said boundary The average value HVwmt of the weld metal of the Vickers hardness in 0.3mm following positions than 0.1mm on the metal side, the heat affected at 0.1mm or 0.3mm following positions in the heat-affected portion from the boundary the average value HVhaz Vickers hardness of parts, but satisfies the following relationship, fillet weld joints, characterized in that.
　　　　　　　≦ HVwmt HVbond
　　　　　　　(1) HVbond ≧ HVhaz-50
　　　　　　　(2) HVhaz ≦ 350 (3)
[Requested item 2]
　The tensile strength of the base material is not more than 2750 times the carbon equivalent of the base material, fillet weld joint according to claim 1.
[Requested item 3]
　The base material is, in mass%, 0.01 ≦ C ≦ 0.25,0.01 ≦ Si ≦ 2.00,0.05 ≦ Mn ≦ 3.0,0.001 ≦ Al ≦ 0.4, the contained, the balance being Fe and impurities, fillet weld joint according to claim 1 or 2.
[Requested item 4]
　The base material is, in mass%, 0.1 ≦ Ni ≦ 3.0,0.1 ≦ Cr ≦ 2.0,0.005 ≦ Mo ≦ 0.5,0.005 ≦ Nb ≦ 0.3,0 .005 ≦ V ≦ 0.3,0.005 further contains at least one ≦ Ti ≦ 0.3,0.0001 ≦ B ≦ 0.01, fillet weld joint according to claim 3.
[Requested item 5]
　The weld metal contains, by mass%, 0.03 ≦ C ≦ 0.25,0.01 ≦ Si ≦ 2.00,0.5 ≦ Mn ≦ 3.0,0.001 ≦ Al ≦ 0.15, the contained, the balance being Fe and impurities, fillet weld joint according to any one of claims 1 4.
[Requested item 6]
　The weld metal contains, by mass%, 0.1 ≦ Ni ≦ 3.0,0.1 ≦ Cr ≦ 2.0,0.005 ≦ Mo ≦ 0.5,0.005 ≦ Nb ≦ 0.1,0 .005 ≦ V ≦ 0.15,0.005 further contains at least one ≦ Ti ≦ 0.15,0.0001 ≦ B ≦ 0.01, fillet weld joint according to claim 5.
[Requested item 7]
　The thickness of the base material is less than 1.0mm 3.6mm or less, fillet weld joint according to any one of claims 1 6.
[Requested item 8]
　In cross-section perpendicular to the weld line of the fillet weld joint, through the plate thickness direction to 0.1mm or 0.3mm following positions of the base material from the welding route point, a on a straight line parallel to the base material surface Te,
　wherein is located below the welding route point, the weld metal and the average value of Vickers hardness of the weld metal in the region of 0.1mm or more 0.3mm or less in the weld metal side from the boundary between the heat affected zone HVwmr satisfies the following relationship, fillet weld joint according to any one of claims 1 7.
　　　　　　HVwmr ≦ 350
[Requested item 9]
　Overlapping part of the two base materials, a process for the preparation of a fillet welded joint subjected to fillet welding using a welding wire,
　the tensile strength of the base material is not less than 980 MPa, the carbon equivalent of the base material There 0.36 to 0.60, the tensile strength of the base material [MPa] is not less the carbon equivalent [wt%] of the matrix of 1950 times or more,
　0 carbon equivalent of the welding wire is 0.50 or more .80 below higher than the carbon equivalent of the base metal,
　the welding speed is less than 60cm / min or more 150 cm / min, the production method of the fillet weld, characterized in that.