MODE FOR CARRYING OUT THE INVENTION
[0036]
　The present invention, when spot welding a steel sheet, is one or both of the steel sheet surfaces to be a mating surface, where the steel sheets at the time of initial pressurization of spot welding come into contact with each other to form a contact portion, the contact portion Even if oil is applied to the steel plate mating surface by pre-processing a plurality of streaks (line-shaped grooves) that pass through the contact area outside the contact part and then spot welding, it is applied at the time of initial pressing. The conventional oil can be discharged from the contact portion to the outside so that the oil is prevented from being trapped in the contact portion and invading hydrogen into the welded portion. The line may be a straight line or a curved line.
[0037]
　The "steel plate" used for manufacturing the spot-welded joint in the present invention includes a cut plate cut into a size suitable for press forming, and a tailored blank material obtained by butt-welding a plurality of dissimilar steel plates. Further, it includes a "blank" in the shape of press-molding a steel plate and a member after press-molding.
[0038]
　The test leading to the present invention will be described.
[0039]
　In the assembly of automobile members by spot welding, the steel plate member is subjected to the spot welding process with oil applied. Therefore, first of all, it was investigated whether or not oil was a source of hydrogen penetration.
[0040]
　In the experiment, as test pieces, the following three types of test pieces having a size of 30 mm×30 mm were prepared. As the oil, rust preventive oil (NOX-RUST530F(60) manufactured by Parker Kosan Co., Ltd.) was used.
　-Test piece A1 in which two steel plates with a thickness of 1 mm are applied with oil on both sides of each steel plate, and
　test piece A2 with two steel plates with a thickness of 1 mm is applied (oil is not applied to both sides of each steel plate)
　・Test piece B made of steel plate with a plate thickness of 2 mm (oil is applied to both sides of the steel plate)
[0041]
　The test pieces A1 and A2 were spot-welded under the common welding conditions shown in Table 1 below while keeping the applied pressure constant and changing the welding current to form 3 mm, 4 mm, and 5 mm diameter nuggets, respectively, and immediately thereafter. It was cooled with liquid nitrogen. Then, the test piece after welding was cut into a size of 10 mm×10 mm so as to include a nugget. The amount of invading hydrogen in the test pieces A1 and A2 after welding was measured by heating the test piece to release hydrogen and measuring the released amount of hydrogen by a gas chromatograph. The temperature rising rate was 100° C./hour, the maximum temperature reached was 200° C., and the amount of hydrogen released up to 200° C. was taken as the amount of invading hydrogen. Further, the test piece B was pressed and energized in the same manner as spot welding to form nuggets having the same diameter, and the hydrogen content of the test piece B after energization was measured in the same manner. The results of the test pieces A1 and A2 are shown in FIG. a is the result of the test piece A1 and b is the result of the test piece A2.
[0042]
[table 1]

[0043]
　In the test piece A1 to which the oil was applied, as shown in FIG. 1A, the amount of hydrogen of 0.25 μg or more was detected in the nuggets of all diameters of 3 to 5 mm. In the piece A2, as shown in FIG. 1B, some hydrogen was detected at a nugget diameter of 4 mm, but hydrogen was not detected at other diameters. Further, in test piece B, hydrogen was not detected at any nugget diameter.
[0044]
　When the hydrogen concentration of the test piece A1 at the nugget diameter of 3 mm is calculated assuming that hydrogen has penetrated only into the nugget, the hydrogen concentration becomes a very high concentration of 3.8 ppm, which may cause delayed fracture. It was found to be expensive.
[0045]
　From the above results, it was found that the presence of oil between the steel sheet mating surfaces in spot welding markedly increases the amount of invading hydrogen in the steel sheet after welding. It was also found from the result of the test piece B that hydrogen did not penetrate from the surface of the steel plate on the electrode side.
[0046]
　From this test, it was confirmed that oil serves as a hydrogen penetration source, and therefore, the mechanism by which hydrogen derived from oil penetrates into the steel sheet during spot welding was investigated.
[0047]
　In the result of FIG. 1a, no relation was observed between the nugget diameter and the amount of invading hydrogen. The relationship with the amount was examined.
[0048]
　First, a pressure-sensitive paper was sandwiched between two steel plates, they were superposed, and the area of ​​the steel plate contact portion when pressures of 200 kgf and 400 kgf were applied by spot welding electrodes from both sides of the superposed steel plates was measured. Next, spot welding was performed in which the steel sheets coated with oil on the mating surface side were pressed with the same pressing force, and the amount of hydrogen in each steel sheet after welding was measured by the thermal desorption method. The results are shown in Table 2.
[0049]
　From Table 2, it was found that when the area of ​​the steel sheet portion (contact portion) that comes into contact at the time of initial pressurization of spot welding increases, the amount of hydrogen that penetrates into the steel sheet also increases.
[0050]
[Table 2]

[0051]
　From this test, it is considered that when the area of ​​the contact part becomes larger, the amount of oil trapped in the contact part also increases and the amount of hydrogen penetrating into the steel plate also increases, and there is a correlation between the nugget diameter and the amount of penetrating hydrogen. It is considered that the amount of oil retained between the steel plates contacted in the initial stage of pressurization determines the amount of invading hydrogen, since no hydrogen is observed.
[0052]
　That is, as shown in FIG. 2, when the oil 6 is applied to the mating surfaces 5 of the steel plates 3 and 4, during the initial pressurization of the steel plates 3 and 4 by the electrodes 1 and 2, the contact between the steel plates (the contact portion 7 It is considered that the amount of hydrogen penetrating into the steel sheet increases due to the fact that the oil is trapped in ), and that the trapped oil is not discharged from the contact portion to the outside even during electric heating.
[0053]
　Therefore, as a result of examining the means for discharging the oil from the inside of the steel plate contact portion to the outside when the steel sheet in the initial stage of pressurization comes into contact, a passage through which the oil can be discharged to the outside of the contact portion passes through the contact portion and is connected to the outside of the contact portion. Based on the idea of ​​forming as described above, the following tests were performed.
[0054]
　As a steel plate with a passage formed therein, the entire surface of a steel plate having a size of 30×30 mm and a plate thickness of 1 mm was polished with a polishing paper having a grain size of 80 and 400, and a large number of streaks (fine lines were formed on the surface. A steel plate having grooves) was prepared. A steel plate without polishing was also prepared for comparison.
[0055]
　A steel plate in which unpolished steel plates are laminated with oil interposed between the mating faces, and a steel plate in which the ground steel plates are laminated so that the lapping faces become overlapping faces and the oil is interposed between the mating faces A plurality of each was prepared, and the central portion of each laminated steel sheet was spot-welded under the conditions of Table 3.
[0056]
　Table 4 also shows the results of measuring the amount of hydrogen penetration of each laminated steel sheet and the rate of change from the reference value based on the hydrogen amount of the unpolished steel sheet.
[0057]
　With the steel plates whose mating surfaces were polished with No. 80 and No. 400 abrasive paper and the steel plate with the uneven streak pattern formed by the mold, the amount of penetrating hydrogen was extremely low and the oil was discharged along the streaks out of the contact area. Was inferred.
[0058]
　From the above results, it was confirmed that, in order to prevent hydrogen from entering the steel sheet due to oil, it is effective to form a passage for discharging the oil from the steel sheet contact portion to the outside.
[0059]
[Table 3]

[0060]
[Table 4]

[0061]
　As described above, the effectiveness of forming streaks with abrasive paper was confirmed, and the present invention was reached by further studying the morphology of streaks. Hereinafter, the requirements and preferable requirements constituting the present invention will be further described.
[0062]
(Range
　of forming streaks ) The range of forming streaks is a range in which the steel plates come into contact with each other at the steel plate mating surfaces at the initial stage of pressurization by the electrode for spot welding (referred to as an initial contact part. And the range exceeding it. If the streaks are not formed beyond the contact area of ​​the steel sheet, the oil cannot be discharged from the contact portion to the outside. The area of ​​the initial contact area can be evaluated by using pressure sensitive paper.
[0063]
　The streaks may be formed at each spot welding spot on the steel plate, or may be formed so as to include a plurality of spot welding spots.
[0064]
(Form of
　muscle ) It is necessary that the muscle communicates at least from the inside of the contact portion to the outside of the contact portion. It is preferable that both ends of the muscle are located outside the contact portion, that is, from the outside of the contact portion to the outside of the contact portion through the contact portion.
[0065]
　A typical morphology of muscle is shown in FIG. “A” indicates a case where a line which does not intersect is processed, “b” indicates a case where a line which intersects is processed, “c” indicates a case where a line is processed densely with abrasive paper, and “d” indicates a case where a curved line is processed.
[0066]
　The number of streaks is preferably 4 or more in total on the mating surfaces. If there are four or more streaks, the amount of oil removed from the entire area of ​​the initial contact portion tends to be small.
[0067]
　On the surface within the range of the initial contact portion, the maximum area of ​​the range (see b of FIG. 3) divided by the streaks and/or the outer circumference of the contact surface may be 30% or less of the area of ​​the contact portion. preferable. If it exceeds 30%, less oil tends to be removed.
[0068]
　The width of the streak and the arithmetic average height Sa that represents the roughness of the surface in the contact portion are different when the streak is applied to one or both of the steel sheet mating surfaces, and are the following conditions (a) and (b).
[0069]
　The arithmetic mean height Sa is related to the depth of the muscle (the depth of the groove), and it is preferable to satisfy the conditions specified below according to the number of muscles, because the oil can be sufficiently removed. It should be noted that when the number of streaks is large, it is possible to obtain a preferable effect only by satisfying Sa.
[0070]
(A) When four or more streaks are provided on
both steel sheet mating surfaces (a1) When the number N of streaks is 4≦N<20 on both steel sheet mating surfaces,
　　　the width of the streaks: 0.2/N (mm )
　　　Or more Arithmetic mean height Sa: −0.09×N+2 (μm) or more
(a2) When the number N of streaks is 20≦N on both steel sheet mating surfaces,
　　　the width of streak: not specified
　　　Arithmetic mean height Sa: 0.2 μm or more
[0071]
(B) When at least one of the steel plates constituting the steel plate mating surface is provided with four or more streaks,
(b1) When the number N of streaks is 4≦N<20,
　　　the width of the streaks: 0.4/N (mm) Above
　　　Arithmetic mean height Sa: -0.07×N+1.9 (μm) or more
(b2) When the number N of muscles is 20≦N
　　　Muscle width: Not specified
　　　Arithmetic mean height Sa: 0.5 μm or more
[0072]
　When four or more streaks are provided on at least one of the steel plates forming the steel plate mating surface, the other steel plate may not be streaked or may be provided with three or less streaks.
[0073]
　Sa is a surface roughness parameter defined by ISO25178. The divided range, the width of the line (groove) and Sa can be measured with a laser microscope.
[0074]
　Sa is used as a measure of surface roughness, but in the present invention, it is necessary that the surface of the steel sheet be formed with streaks serving as oil passages, and the surface is not necessarily rough. Therefore, the width and the number of lines are specified as described above.
[0075]
(Striation forming method) As a method for forming a stripe on a
　spot welded portion of a steel plate, in addition to the method of polishing the surface with the polishing paper or the polishing cloth used in the above experiment, a method of stamping with a mold is used An appropriate method such as a method of scribing a line with a scoring needle can be adopted.
[0076]
(Method of forming uneven streak pattern using die) As
　another example of the method of forming streaks, a method of forming an uneven streak pattern using a die will be described.
[0077]
　In the method of forming a streak pattern using a mold, when a steel plate is processed to obtain a steel plate member, simultaneously with the processing, a concavo-convex streak pattern is formed at a portion which will be a contact portion during initial pressure of spot welding. Specifically, it is characterized in that fine protrusions are provided on the mold and a concavo-convex streak pattern is provided at a position where a steel plate or a steel pipe, which is a workpiece, is slid in the press working.
[0078]
　The arrangement of the protrusions and the shape of the applied pattern are not particularly limited. The method of giving unevenness to the mold is not particularly limited, but it can be given by an end mill, for example. For example, consider drawing processing as shown in FIG. The steel plate 31 clamped by the blank holder 33 and the die 34 is pressed by the punch 32, so that the steel plate 31 is processed into a concave shape.
[0079]
　At this time, the portion of the steel plate 31 held between the blank holder 33 and the die 34 receives surface pressure in the plate thickness direction by the blank holder 33 and the die 34, and slides when the steel plate 31 is deformed. In the present invention, by providing minute projections on the surface of the blank holder 33 and/or the die 34 (for example, the hatched portion in FIG. 4) where the steel plate 31 is slid, the steel plate 31 to be slid Pattern is formed on the surface of.
[0080]
　The size and arrangement of the protrusions provided on the mold can be appropriately determined according to the pattern to be formed. For example, a protrusion pattern having a height of 10 to 100 μm and an interval of 50 to 1000 μm can be formed on the surface sliding on the steel plate or the steel pipe.
[0081]
　According to this method, when the steel sheet 31 is drawn by press working, it is possible to give a regular pattern to the surface of the steel sheet 31 that slides at the same time. do not need. It is also possible to give a part of the pattern of the steel plate 31 by setting the position where the protrusion is provided on the mold to a specific position.
[0082]
　Further, in the case of providing a concave-convex streak pattern on the portion held between the blank holder 33 and the die 34, it is possible to manage the blank holder surface with a constant gap by using a distance block (not shown). An uneven streaky pattern of depth can be provided. Further, it is possible to control the surface pressure to an arbitrary value by controlling the cushion pressure.
[0083]
　A regular pattern shown in FIG. 5 was formed on the surface of the die 34, and the steel plate was pulled out under a pressing pressure of 2.9 MPa and 4.8 MPa under cushion pressure control. FIG. 6 shows the state of the surface after extraction.
[0084]
　Further, Table 5 shows Sa (arithmetic mean height: μm) and Str at the time of pulling out with no pressing, No. 80 polishing, and No. 400 abrasive with a pressing load of 2.9 MPa and 4.8 MPa. Table 5 shows the average amount of hydrogen in the weld metal when spot welding is performed with the respective surface states facing each other. The result without polishing as a reference is the same as in Table 4. From this result, it can be seen that when Str is 0.3 or less, the average hydrogen amount is significantly reduced (80% or more), and the possibility of hydrogen embrittlement cracking can be significantly reduced. Further, it is understood that the amount of penetrating hydrogen is greatly reduced if Str is small even if it is polished.
[0085]
[Table 5]

[0086]
(Structure of streak pattern) At
　least the streak pattern needs to communicate from the inside of the contact portion to the outside of the contact portion. It is preferable that both ends of the muscle are located outside the contact portion, that is, from the outside of the contact portion to the outside of the contact portion through the contact portion.
[0087]
　The uneven pattern is preferably a regular pattern in which the aspect ratio (Str) of the surface texture is 0.3 or less in order to sufficiently remove the rust preventive oil. Str is a parameter representing the isotropic property or anisotropy of the surface property defined by ISO 25178-2. When it is close to 0, there are lines, and when it is close to 1, the surface does not depend on the direction. Show. It is preferable that the number of the uneven lines is four or more in order to eliminate the rust preventive oil from the entire area of ​​the initial contact portion.
[0088]
　In the present invention, the first steel plate member having the steel plate processed by using the mold and the second steel plate member having the steel plate or the steel plate processed are overlapped and spot-welded. If the concavo-convex pattern is formed on the first steel plate member, the pattern may or may not be formed on the steel plate or the second steel plate member to be spot-welded. The number of steel plates to be overlapped is not limited to two, and may be three or more. Further, the types, component compositions, and plate thicknesses of the steel plates to be overlapped may be the same or different from each other.
[0089]
　Further, the "steel plate" that is spot-welded to the first steel plate member may be a part of the first steel plate member without being limited to the one composed of separate steel plates.
[0090]
(Other forms)
[0091]
　When the steel plate 61 is sandwiched between the punch 62 and the pad 63 for the bending process in FIG. 7, a projection portion is provided on the punch 62 and/or the pad 63 and can be slid to give an uneven pattern. .. As for the pad, as in the case of the blank holder, the constant clearance can be managed by using a distance block (not shown).
[0092]
　When the steel plate 71 is sandwiched between the upper mold 72 and the lower mold 73 as in stamping molding or restrike shown in FIG. An uneven line pattern can be formed at a position where the steel plate 71 sandwiched between the lower mold 73 and the lower mold 73 slides. Also in this case, by using a distance block (not shown), it is possible to give an arbitrary unevenness depth.
[0093]
　The present invention is also applicable when the steel plate member is a steel pipe. For example, in the case of rotary drawing of a steel pipe, by providing a protrusion on the pressure die, it is possible to impart an uneven streak pattern on the surface of the steel pipe that slides on the pressure die.
[0094]
　As shown in FIG. 9, the rotary drawing of the steel pipe is performed by holding the steel pipe with a bending die 82 and a holding die 83 provided on the outer peripheral surface of the steel pipe 81, and bending the steel pipe with a pressure die 84 in the bending die direction. The mold and the grip mold are driven to rotate, and the steel pipe is bent while being stretched. At this time, since the steel pipe 81 slides with respect to the pressure die 84, by providing a projection on the surface of the pressure die 84 that contacts the steel pipe 81, it is possible to impart an uneven line pattern to the surface of the steel pipe.
[0095]
　Since the constant gap management is possible at the mold position, it is possible to provide a concave-convex streak pattern with an arbitrary groove depth. Further, since the pressure applied by a normal pressure type is about 1 to 10 MPa, it is suitable for the present invention.
[0096]
　The present invention can also be applied to the case of pipe expansion molding shown in FIG. In this case, by providing the protrusions on the punch 92, it is possible to give the uneven pattern to the position where the steel pipe 91 slides.
[0097]
(Others)
　The steel sheet used in the present invention includes a cut sheet cut into a size (for example, 1 m×1 m) suitable for press forming, and a tailored blank material obtained by butt-welding a plurality of dissimilar steel sheets. The steel sheet used in the present invention need only have a plate-shaped overlapping portion, and need not be a plate as a whole. For example, it includes a flange portion of a member press-molded into a specific shape having a hat-shaped cross section. The number of steel plates to be overlapped is not limited to two, and may be three or more. Further, the types, component compositions, and plate thicknesses of the steel plates to be overlapped may be the same or different from each other. The steel plates to be overlapped may be a plurality of steel plates butt-welded together. Further, the invention is not limited to the case where the steel plates are made of different steel plates, and one steel plate may be formed into a predetermined shape such as a tubular shape and the ends thereof may be overlapped.
[0098]
　The strength of the steel sheet is also not particularly limited. However, the problem of delayed fracture is likely to occur when spot-welding a high-strength steel sheet, so the present invention is particularly effective for a steel sheet having a tensile strength of 500 MPa or more, and further for a steel sheet having a tensile strength of 780 MPa or more.
[0099]
　Further, the timing of forming the muscle is not particularly limited. As an example, the streaks can be formed immediately before spot welding the steel plates.
[0100]
　In the case of spot welding of automobile parts, it is conceivable that a "blank" is formed into a shape in which a steel sheet is press-formed, and then the blank is formed and spot-welded. In such a case, the final spot welding position is fixed regardless of whether the steel plate is in the blank state or the blank state. Therefore, streaks may be formed at spots where spot welding is to be performed at the stage of a steel plate (including a cut plate and a tailored blank) or at the stage of forming a blank.
Example
[0101]
　A test of spot welding was performed by stacking two test pieces each having a strength of 980 MPa and having a size of 30×30 mm and a plate thickness of 1 mm. At that time, use either a die (stamping), a scoring needle, or an abrasive paper on one side (one side) or both sides (both sides) of the surface to be the mating surface of the laminated test pieces. , A plurality of streaks for letting out oil were machined in a certain width in the vicinity of the welded part. As the oil, rust preventive oil (NOX-RUST530F(60) manufactured by Parker Kosan Co., Ltd.) was used.
[0102]
　The conditions were set so that the initial contact portion at the time of spot welding had a circular shape with a diameter of 3 mm. However, for some test pieces, for comparison, the streaks were processed so as not to go out of the outer circumference of the initial contact portion.
[0103]
　The pattern of the processed lines is shown in FIG.
[0104]
　As for the streak pattern, the pattern without processing is set to a1, and the pattern (b1, b2) in which the streak does not intersect by processing with a die (stamping) or a scoring needle, the pattern in which the streak also intersects (c1, c2), and polishing The pattern (d1) was formed in which many streaks were formed by processing with paper. In addition, the pattern in which the streaks were formed so as not to go out of the outer circumference of the initial contact portion was defined as the pattern (e1). Here, b1 and c1 are examples where the number of muscles is small (the area of ​​the range divided by the muscles and outer circumference is large), and b2 and c2 are the number of muscles is appropriate (the area of ​​the range separated by muscles and the outer periphery is proper) ) Is an example.
[0105]
　For each test piece obtained by processing the muscle, the number of the muscles was counted and the arithmetic mean height Sa was measured. Moreover, when the number N of the streaks was less than 20, the area of ​​the maximum range among the ranges divided by the streaks and the outer circumference of the contact surface was measured.
[0106]
　Immediately after spot welding the test piece, it was cooled with liquid nitrogen. Then, the test piece after welding was cut into a size of 10 mm×10 mm so as to include a nugget. The amount of invading hydrogen was measured by raising the temperature of the test piece to release hydrogen and measuring the released amount of hydrogen by a gas chromatograph. The temperature rising rate was 100° C./hour, the maximum temperature reached was 200° C., and the amount of hydrogen released up to 200° C. was taken as the amount of invading hydrogen.
[0107]
　The results are shown in Table 5.
[0108]
　In Table 6, as the value (lower limit value) of Sa required for hydrogen reduction, when N<20, the formula (−0.09×N+2) is used for both sides, and the formula (−) is used for one side. The value (μm) calculated from 0.07×N+1.9) was used. When N≧20, 0.2 μm was used for one side and 0.5 μm for both sides.
[0109]
　As the width of the streaks required for hydrogen reduction, when N<20, the value calculated from the formula 0.2/N (mm) for both sides and the formula 0.4/N (mm) for one side. Was used, and when N≧20, no designation was made.
[0110]
　Regarding the maximum value of the divided area ratio, in the case of the pattern (e1), since there is no portion divided by the streak and the outer circumference of the contact surface, it is described as almost 100.
[0111]
　In the invention examples, the amount of penetrating hydrogen was significantly reduced compared to the standard.
　On the other hand, in the comparative example, the amount of invading hydrogen hardly decreased as compared with the standard.
[0112]
[Table 6]

Explanation of symbols
[0113]
　1, 2 Spot welding electrode
　3, 4 Steel plate
　5 Steel plate mating surface
　6 Oil
　7 Contact area
　11 Range of initial contact area
　12 Line
　13 Area divided by line or outer circumference
　21 Range of initial contact area
　22 Line
　31 Steel plate
　32 Punch
　33 Blank Holder
　34 Die
　61 　Steel plate
　62 Punch
　63 Pad
　64 Die
　71 Steel plate
　72 Upper mold
　73 Lower mold
81 Steel pipe
　82 Bending mold
　83 Gripping mold
　84 Pressure mold
　91 Steel pipe
　92 Punch
The scope of the claims
[Claim 1]
　In the method for manufacturing a spot-welded joint of steel plates that have been overlapped
　, one or both of the steel plate surfaces that are the mating surfaces of the steel plates, where the steel plates are in contact with each other during initial pressure during spot welding, A method for manufacturing a spot-welded joint, characterized in that a plurality of linear grooves, which are continuous with the outside of the contact portion and pass through the contact portion, are preliminarily processed and spot welding is performed at the contact portion.
[Claim 2]
　The number of the muscles, is 4 or more, respectively in both of the steel sheet surface as the mating surface of the steel sheet,
　the arithmetic average height Sa of the steel sheet surface width and the contact portion of the muscle,
　each of the steel sheet surface serving as mating surfaces When
　the number N of muscles is 4≦N<20, the muscle width is 0.2/N (mm) or more and the arithmetic mean height Sa: −0.09×N+2 (μm) or more,
　The
method for manufacturing a spot welded joint according to claim 1, wherein when the number N of streaks is 20≦N , a plurality of streaks are processed so that the arithmetic average height Sa is 0.2 μm or more. ..
[Claim 3]
　The method for manufacturing a spot welded joint according to claim 2, wherein an area of ​​a maximum range of the areas divided by the streaks and the outer circumference of the contact portion is 30% or less of an area of ​​the contact portion.
[Claim 4]
　The number of the streaks is 4 or more on at least one of the steel plate surfaces serving as the mating surfaces of the steel plates, and
　the width of the streaks and the arithmetic mean height Sa of the steel plate surfaces of the contact portions are
　at least one steel plate serving as the mating surfaces. When
　the number of muscles N is 4≦N<20, the width of the muscle is 0.4/N (mm) or more and the arithmetic mean height Sa is −0.07×N+1.9 (μm). ) When
　the number N of the streaks is 20≦N or more
, a plurality of streaks are processed so that the arithmetic average height Sa: 0.5 μm or more is produced, and the spot-welded joint manufacturing according to claim 1. Method.
[Claim 5]
　The method of manufacturing a spot-welded joint according to claim 4, wherein the area of ​​the maximum range of the areas divided by the streaks and the outer circumference of the contact portion is 30% or less of the area of ​​the contact portion.
[Claim 6]
　It is a steel plate for spot welding used for the manufacturing method of the spot-welded joint according to claim 1, The
　said steel plate WHEREIN: At the location used as a contact part which contacts other steel plates at the time of initial pressurization of spot welding, this contact A steel plate for spot welding, characterized in that a plurality of streaks passing through the portion and continuing to the outside of the contact portion are formed in advance.
[Claim 7]
　When the number of the streaks is 4 or more and
　the number of the streaks N is 4≦N<20 with respect to the width of the streaks and the arithmetic mean height Sa of the steel plate surface of the contact portion , the width of the streaks: 0.2 /N (mm) or more, arithmetic average height Sa: −0.09×N+2 (μm) or more,
　and when the number of muscles N is 20≦N, arithmetic average height Sa: 0.2 μm or more
must be satisfied. The steel plate for spot welding according to claim 6, wherein.
[Claim 8]
　The steel plate for spot welding according to claim 7, wherein the area of ​​the maximum range of the areas divided by the streaks and the outer circumference of the contact portion is 30% or less of the area of ​​the contact portion.
[Claim 9]
　When the number of the streaks is 4 or more and
　the number of the streaks N is 4≦N<20 with respect to the width of the streaks and the arithmetic mean height Sa of the steel plate surface of the contact portion , the width of the streaks: 0.4. in / N (mm) or more, the arithmetic average height Sa: -0.07 × N + 1.9 ( μm) or more, when the number N is 20 ≦ N muscle, arithmetic average height Sa: more 0.5μm
to The steel plate for spot welding according to claim 6, which is satisfied.
[Claim 10]
　The steel plate for spot welding according to claim 9, wherein the area of ​​the maximum range of the areas divided by the streaks and the outer circumference of the contact portion is 30% or less of the area of ​​the contact portion.
[Claim 11]
　The method for manufacturing a spot welded joint according to claim 1, wherein Str of the contact portion where the lines that are grooves on the plurality of lines are processed is 0.3 or less.
[Claim 12]
　It is a steel plate used for the manufacturing method of the spot welded joint of Claim 1,
　Comprising: Str of the said contact part in which the streak which is the said some groove|channel was processed becomes 0.3 or less, For spot welding. Steel plate.
[Claim 13]
　The processing of the line that is the plurality of linear grooves is performed by using a mold having a protrusion on at least a part of the surface that comes into contact with the steel plate, and sliding the steel plate with respect to the mold to form the contact portion. The method for manufacturing a spot-welded joint according to claim 1, wherein a concavo-convex streak pattern passing through the contact portion and continuing to the outside of the contact portion is processed in advance.
[Claim 14]
　The method for manufacturing a spot welded joint according to claim 13, wherein Str of the contact portion where the uneven streak pattern is processed is 0.3 or less.
[Claim 15]
　It is a steel plate member used for the manufacturing method of the spot-welded joint of Claim 13 or 14,
　Comprising: At the time of initial pressurization of spot welding with a steel plate or the 2nd steel plate member by which the steel plate was processed, it contacts a steel plate or a 2nd steel plate member. A steel plate member for spot welding, which is characterized in that an uneven streak pattern is processed at the planned contact point.
[Claim 16]
　The steel plate member for spot welding according to claim 15, wherein Str of the contact portion on which the uneven line pattern is formed is 0.3 or less.
Drawing
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