JP2000317642A - Flash butt welding method for high-carbon steel sheet or steel strip - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flash butt welding method for a high-carbon steel sheet or a sheet strip, by which the crack and the rupture of a weld zone can be prevented even when a tempering treatment has been performed without forcedly cooling after welding. SOLUTION: According to a carbon content, a high-carbon steel sheet or a steel strip is partitioned into >=0.30% and <0.50% C, >=0.50% and <0.80% C, and >=0.80% C. For each partition, out of the welding conditions of flash butt welding, while limiting a ratio of an upset quantity to a sheet thickness and a heat input quantity = (secondary voltage)2 × (flash time)} to a predetermined prescribed range according to an operation actual result, the flash butt welding is performed. By performing a tempering treatment to a joining part and an influence part by welding heat (HAZ) after welding in a temperature range of 600 deg.C to Ac1 transformation point, the HAZ is reduced, and nitride or oxide to be generated from a material to be welded in a flash process, is exhausted from the joining part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flash butt welding method capable of preventing deterioration of toughness due to heat received at the time of flash butt welding of a high carbon steel sheet or steel strip.

[0002]

2. Description of the Related Art Generally, when welding a steel sheet or a steel strip of high carbon steel having a C content of 0.30% or more, the entire or a part of the structure of a weld zone and a weld heat affected zone (hereinafter referred to as HAZ) depends on the amount of heat received during welding. However, it transforms into hard and brittle martensite, deteriorating the toughness of the weld and the HAZ. For this reason, in the welding of high carbon steel sheets or strips with a C content of 0.30% or more, appropriate tempering and annealing treatments are applied to the weld and HAZ to improve toughness. I have.

[0003] In the process of manufacturing a steel sheet or a steel strip, when continuously processing a steel sheet or a steel strip, as a means for continuing the processing, a tail end of a preceding material and a front end of a following material are used. Are generally performed by welding. In particular, in continuous pickling, cold rolling, continuous heat treatment, and the like, butt welding is mainly used from the viewpoint of workability.

[0004] In joining high carbon steel sheets or steel strips using flash butt welding as a means of butt welding, rapid heat quenching during welding hardens the weld and HAZ to deteriorate toughness. In the threading with deteriorated toughness, if the weld and the HAZ are bent by bridle rolls or the like at the time of threading, or if the weld or HAZ is cold-rolled,
There is a high risk of HAZ breaking. For this reason, in the case of high carbon steel sheet or steel strip, after flash butt welding, burrs on the welded part are cut, and then the welded part and HAZ are treated such as tempering and annealing, and then passed through the line. It is common to do.

[0005] For example, a method in which an electrode plate is opened after flash butt welding, and then a welding clamp is energized to heat the welded joint at a predetermined temperature and heat treated (Japanese Patent Publication No. 56-51873). Thereafter, a method of detecting the temperature of each portion of the welded portion, moving the heating electrode in the width direction of the belt-shaped member according to the temperature distribution of the welded portion, and heating the welded portion by the heating electrode (Japanese Patent Laid-Open No. 4-182075). Publication).

[0006] Further, in the heat treatment after welding of the flash butt-welded high strength steel, after heating in the air, an inert gas or a reducing atmosphere between 900 ° C and 1250 ° C, the air or water, salt water and oils and fats are heated. Cooled to the Ar3 point temperature or lower in the refrigerant, and further heated again to the _AC3 point or higher and the temperature of 1000 ° C or lower, and quenched in water, salt water or oils and fats refrigerant, and the main structure was martensite and lower bainite. Or further tempering it at a temperature of A _C1 point or lower (Japanese Patent Laid-Open No. 50-519).
No. 41), a method of obtaining a tempered martensitic structure by once forcibly cooling a weld part obtained by flash butt welding to a temperature 100 ° C. or more lower than the Ms point of the special steel immediately after welding, and then performing a post heat treatment. (Japanese Patent Publication No. 63-64501),
Heat the joint of the high strength steel by flash butt welding to a temperature range of 900 ° C or higher and 1100 ° C or lower, hold for 100 to 150 seconds, and then cool at least 800 to 500 ° C in a temperature range of 5 to 15 ° C / s. A method of cooling at a speed (Japanese Patent Laid-Open No. 1-92320) is known.

[0007] Further, during cooling after flash butt welding or reheating to 900 ° C. or more after flash butt welding, during cooling after reheating, at a temperature of 700 ° C. or more, steel having a length of 10 mm in the plate longitudinal direction around the welding point at a temperature of 700 ° C. or more. Average of 4 to 50% in strip longitudinal direction
Method of applying compressive strain (Japanese Patent Laid-Open No. 5-69150), in butt welding of high carbon steel sheet or steel strip, apply laser welding, and 400 ° C. or more within 1 minute after welding completion,
A method of performing post-heat treatment in a temperature range of A _C1 point or less (JP-A-5-13
No. 2719) has been proposed.

[0008]

The method disclosed in Japanese Patent Publication No. 56-51873 and Japanese Patent Application Laid-Open No. 4-182075 is such that heating after welding is performed by energizing a welding clamp or a heating electrode. The heat treatment conditions are not specified. Further, the methods disclosed in JP-A-50-51941, JP-B-63-64501 and JP-A-1-92320 disclose an apparatus and a cooling step for forced cooling after flash butt welding such as water cooling or gas cooling. In addition, it is necessary that the C content is as high as 0.50% or more, especially in high carbon steel sheets or steel strips with high susceptibility to weld cracking, cracks occur in the weld, especially HAZ in the process from forced cooling to post heat treatment. There's a problem.

[0009] The method disclosed in Japanese Patent Application Laid-Open No. 5-69150 applies a compressive strain of 4 to 50% on the average in the longitudinal direction of the plate around the welding point during cooling after flash butt welding or during reheating cooling. It is necessary to apply compression strain after flash butt welding. Further, the method disclosed in Japanese Patent Application Laid-Open No. HEI 5-127719 applies laser welding instead of flash butt welding, and is effective because the HAZ during welding can be reduced as compared with flash butt welding. The equipment is very expensive compared to the flash butt welding equipment, and has the problem that a high-frequency heating device needs to be installed for heating the welded portion.

[0010] It is an object of the present invention to solve the above-mentioned problems of the prior art, and in flash butt welding of a steel plate or a steel strip of high carbon steel, even if a tempering treatment is performed without forcible cooling after welding, a welded portion is formed. It is an object of the present invention to provide a flash butt welding method for a high carbon steel plate or a steel strip which can prevent cracking and fracture of the steel plate.

[0011]

According to the flash butt welding method of the present invention, a high carbon steel sheet or strip of a high carbon steel can be used for high carbon steel having a carbon content of 0.30% or more, Si: 0.50% or less, and Mn: 1.00% or less. In flash butt welding of steel plate or steel strip,
In order to prevent cracking after welding, the HAZ is reduced as much as possible, and at the same time, the nitride or oxide generated in the material to be welded in the flashing process is discharged from the joint. For this reason, depending on the carbon content, the steel sheet or steel strip of high carbon steel is C: 0.30% or more and less than 0.50%, C: 0.50% or more and 0.8% or less.
Less than 0%, C: 0.80% or more, and set the relationship between the ratio of the upset amount to the plate thickness with good weld bulge evaluation and the heat input amount in advance based on the operation results for each category and input. Flash butt welding is performed with an upset amount and a heat input amount set in advance according to the carbon content and the sheet thickness to be used. Then, the joint and the HAZ are tempered in a temperature range from 600 ° C. to the AC ₁ transformation point.

[0012] As described above, in the method of the present invention, depending on the carbon content.
Welding valves based on operation results
Good upset ratio / plate thickness ratio and heat input (= (secondary
Voltage)^Two× (flash time) [V^Two・ Sec]) to a predetermined range in advance
Preset according to the carbon content and sheet thickness to be input.
Flash butt melting with the set upset amount and heat input
By contacting, the joint of the workpiece and the toughness of HAZ
Degradation and internal defects at the joint can be minimized
You. As a result, after flash butt welding,
Joint and HAZ without forced cooling of HAZ
600 ° C or more A _C1Perform tempering in the temperature range below the transformation point
It becomes possible.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The flash butt welding method of the present invention is intended to prevent the occurrence of cracks after welding of a high carbon steel plate or a steel strip having high weld crack susceptibility. Among the welding conditions of welding, the ratio of upset amount / thickness and heat input (= (secondary voltage) ²
× (flash time) [V ² · sec]) is significantly increased as compared with the conventional example as shown in FIG.

[0014] This increase in the upset amount causes an increase in the molten and ejected portion of the material to be extruded from the joint surface, and the HAZ after welding is completed.
And the discharge of impurities such as nitrides and oxides generated by the reaction of the material to be welded with the surrounding air during welding, particularly during the flashing process, from the joint surface is promoted. As a result, it is possible to minimize toughness deterioration of the welded portion after welding and internal defects of the joint. Since the melt-extruded portion of the material to be welded extruded from the joint surface is usually removed by flash trimming as a weld bead, there is no influence on the strength and quality of the welded portion.

[0015] The equation representing the effect of chemical components on the weld hardenability in steel welding is a carbon equivalent (Ce) expressed by the following equation (1).
q), and it is known that the weld cracking susceptibility (P _CM ) is determined by the following equation (2). Ceq = C + Mn / 6 + Si / 24 + Ni / 40 + Cr / 5 + Mo / 4 + V / 14 [%] ... Equation (1) P _CM = C + (Mn + Cr + Cu) / 20 + Si / 30 + Ni / 60 + Mo / 15 + V / 10 + 5B [%]… Equation (2) As shown in equation (2), the weld cracking susceptibility is C: 0.30% or higher for high carbon steel. , Are more affected by carbon content than Si or Mn. Therefore, in the present invention, the carbon content is empirically C: 0.30% or more and less than 0.50%, C: 0.50% or more
Less than 0.80%, C: 0.80% or more welding crack susceptibility is classified into groups close to each other, and the ratio of upset amount / thickness and heat input (= (secondary voltage ) ² × (flash time) [V ² · sec]) is set in advance based on operation results as shown in FIG.

[0016] Generally, the upset amount in flash butt welding is described on page 51, "Recent developments in cold strip equipment and manufacturing technology in Japan" issued by the Iron and Steel Institute of Japan on August 20, 1977. As described on page 52, 1.35 to 1.40 times the plate thickness at a plate thickness of 2 mm or less,
When the thickness is 2.3 mm or more, an amount of 1.2 to 1.25 times the thickness is used.

This is intended to push out nitrides and oxides generated by the material to be welded reacting with the surrounding air or the like in the flashing process at the time of upsetting from the joint surface. If the nitride or oxide is not extruded from the joint surface but remains partially, and if the amount of upset is too large, the material to be welded buckles during upset, causing defects such as steps in the welded portion. Therefore, an appropriate range of the upset amount is determined by a balance between these two.

[0018] However, C: 0.30% or more, Si: 0.50% or less, M
n: 1.00% or less, the flash butt welding of a high carbon steel sheet or steel strip composed of the balance of Fe and other unavoidable impurities has a high welding cracking susceptibility. Therefore, it is necessary to reduce the HAZ as much as possible. Also, due to the large deformation resistance compared to ordinary carbon steel, such as general cold-rolled steel sheet and steel strip (SPCC steel) specified in JIS G3141, due to the large carbon content in steel, during welding, In particular, the effect of pushing out nitrides and oxides generated by the material to be welded reacting with the surrounding air or the like in the flashing process from the joint surface during upsetting is small.

In order to solve this problem, the upset amount may be increased to 1.2 to 2.0 times the thickness of the material to be welded. However, if the upset amount alone is increased alone, the material to be welded at the time of upset is increased. Buckles, and a defect such as a step occurs in the welded portion. In general, carbon steel is known to soften with increasing temperature, and the upset amount is set to 1.
In order to prevent the material to be welded from buckling when it increases by 2 to 2.0 times, the amount of heat input during welding is increased to increase the temperature of the welded portion, and the deformation resistance during upset may be reduced. .

[0020] The heat input during welding needs to be changed according to the carbon content in steel, and the larger the carbon content in steel, the higher the heat input. On August 20, 1977, the Iron and Steel Institute of Japan issued, `` Recent developments in cold strip equipment and manufacturing technology in Japan '', page 51,
FIG. 5 shows a general relationship between the plate thickness of the material to be welded and the heat input in the conventional flash butt welding described on page 52.

The amount of heat input in the present invention is, for example, as shown in FIG. 5, increased at least 1.5 times or more the amount of heat input generally used conventionally. However, if the temperature of the welded part exceeds the melting point of the material to be welded due to excessive heat input, the material will melt and flash will not occur, so the heat input of the welded part must not exceed the melting point of the material to be welded. There is a need to.

According to the method of the present invention, in flash butt welding, it is possible to suppress internal defects in the welded portion and to reduce the HAZ, and to perform tools such as a welded portion and a flash trimmer blade in the flash trimming process after welding. The cooling effect due to contact with the substrate increases. Therefore, in the method of the present invention,
Tempering can be performed without performing forced cooling after flash butt welding as is often performed in the past.

In the tempering process, the material to be welded is Ar3
Rises to a temperature above a point, then the flash trimmer is quenched by contact with the atmosphere or the like and surrounding the tool, the martensite structure which generates only needs to and tempered structure, joint and the HAZ 600 ° C. or higher A _C1 transformation 3 in the temperature range below the point
The effect of improving the toughness can be sufficiently obtained only by holding for a short time of 0 second or less.

[0024] The temperature of the tempering treatment was 600 ° C. or higher A _C1 less transformation point, is less than 600 ° C. is insufficient the effect of the joint and HAZ of martensitic tempered tissue, also, A _C1 transformation If the point is exceeded, the structure of the joint and the HAZ becomes an austenitic structure again, and a martensitic structure is again generated and hardened in the cooling process.

[0025] Heating during tempering in the present invention is generally carried out by performing flash trimming after welding with a flash butt welding machine and then applying current to a heating electrode or a welding clamp to utilize resistance heating. .

In the present invention, the chemical component of the material to be welded is C:
0.30% or more, Si: 0.50% or less, Mn: 1.0% or less, high-carbon steel sheet or steel strip consisting of the balance Fe and other unavoidable impurities, when C: less than 0.30%, especially the present invention This is because the conventional technique can be sufficiently applied without applying the method. In addition, Si content is more than 0.50%, Mn content is 1.00%
In the case of exceeding, Si and Mn in these steels undergo nitridation or oxidation reaction at the time of welding, and the generated nitrides or oxides increase, and it is impossible to sufficiently extrude from the joint surface even by applying the method of the present invention. This is because

[0027]

EXAMPLES Example 1 As shown in Table 1, C: 0.30 to 0.89%, Si: 0.50% or less, Mn:
1.00% or less, width 1 consisting of balance Fe and unavoidable impurities
Prepare two high-carbon steel sheets No. 1 to 10 with a thickness of 1.8 mm to 2.3 mm each using a 825 kw flash butt welding machine.
As shown in Tables 2 and 3, the upset amount was 1.2 to 1.9 of the plate thickness.
5 and the heat input (= (secondary voltage) ² ×
(Flush time) [V ² · sec]) the 600~3800V ² · sec varied from flush butt welded, after performing the flash trimming, weld by energizing the heating electrode and the HAZ at 700 ° C. After heating and holding for 15 seconds, it was air-cooled. After visually observing the butt weld, the butt weld is cut at a distance of 150 mm from the center line to prepare a weld sample having a width of 300 mm.

[0028] 50mm, 250m in the width direction on the welding line of this sample
Marking was performed at points of m, 500 mm, 750 mm, and 950 mm, and a bulge evaluation test was performed on the marked portion. A crack generation pressure and a crack generation portion were investigated, and a bulge evaluation of the welded portion was performed. The results are shown in Tables 4 and 5 and FIGS. The bulge test method is as follows:
Secure the weld sample so that it does not move, and a radius of 10 from the bottom.
A steel ball of mm is pressed by air pressure so that the marking portion is aligned with the center of the steel ball, and the air pressure when a crack occurs in the welded sample is measured. Regarding the evaluation method, as a result of the bulge test, a case where a crack was generated on the weld line was evaluated as x, a case where there was no crack on the weld line but had a step was evaluated as △, and a case where there was no crack on the weld line and there was no step was evaluated as ○.
It should be noted that the step of welding can be a starting point of fracture because rolling causes a notch in the thickness direction of the sheet.

[0029]

【table 1】

[0030]

[Table 2]

[0031]

[Table 3]

[0032]

[Table 4]

[0033]

[Table 5]

As shown in Tables 1 to 5 and FIGS. 1 to 3, in Test Nos. 1 to 8 using steel sheets No. 1 to 3 having a carbon content of 0.30% or more and less than 0.50%, test Nos. The bulge evaluations of .3, 6, and 8 were good, but the bulge evaluations of Test Nos. 1, 2, 4, 5, and 7 were poor. In Test Nos. 9 to 17 using steel sheets Nos. 4 to 7 having a carbon content of 0.50% or more and less than 0.80%, Test Nos. 13, 15, and 17 had good bulge evaluations. N
o. 9 to 12, 14, 16, and 18 had poor bulge evaluation. Test N using steel sheets No. 8 to 10 with a carbon content of 0.80 to 0.89
In o.18 to 28, the test Nos. 25, 26 and 28 had good bulge evaluation, but in test Nos. 18 to 24 and 27, the bulge evaluation was poor.

Example 2 C: 0.86%, Si: 0.20%, Mn: 0.04%, P: 0.021%, S: 0.007%, C
u: 0.06%, Ni: 0.02%, Cr: 0.15%, the balance is prepared a high-carbon steel sheet of 2.0 mm thick consisting of Fe and unavoidable impurities, using a 825kw flash butt welding machine, Table 6
After performing flash butt welding under the welding conditions shown in (1) and performing flash trimming, the welding electrode and the HAZ were heated and maintained at 690 ° C. for 15 seconds, and then air-cooled.
Then, after visually observing the butt weld, the example
The same bulge evaluation test as in 1 was performed, the crack generation pressure and the crack generation site were investigated, and the bulge evaluation of the weld was performed. Table 7 shows the results.

[0036]

[Table 6]

[0037]

[Table 7]

[0038] As shown in Tables 6 and 7, the upset amount was
In the test Nos. 34 to 36 of 1.6 times, when the heat input is less than 2733 [V ² · sec], the heat input is insufficient, so that the deformation resistance of the material to be welded is large, and a step occurs at the time of upset. In Test Nos. 31 to 33 in which the upset amount was 1.4 times or less the plate thickness, the strength of the welded portion was extremely weak because the extrusion of nitrides, oxides, and the like was not sufficient at the time of upset. 1.6 times the amount of plate thickness upset, heat input at 1.8 times 3650,2733 [V ² · s
ec] in Test Nos. 37 and 38 satisfying the conditions of the method of the present invention,
It was possible to obtain a welded portion of a high carbon steel sheet having no steps and sufficient weld strength.

[0039]

According to the flash butt welding method of the present invention, a flash butt welding method for a high carbon steel sheet or steel strip is performed according to the following conditions. Ratio and heat input, carbon content,
Flash butt welding limited to a predetermined range determined in advance based on the operation results according to the plate thickness can minimize the toughness deterioration of the joint and the HAZ of the material to be welded and the internal defect of the joint. As a result, it is possible to perform after flash butt welding joint and without the HAZ of forced cooling, tempering at the joint and HAZ a temperature range of 600 ° C. or higher A _C1 following transformation point.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the ratio of upset amount / thickness, heat input, and pass / fail of a bulge evaluation test in a steel sheet having a carbon content of 0.3% or more and less than 0.50% in Example 1.

FIG. 2 is a graph showing the relationship between the ratio of the upset amount / thickness of a steel sheet having a carbon content of 0.50% or more and less than 0.80%, the heat input, and the pass and fail of the bulge evaluation test in Example 1.

FIG. 3 is a graph showing a relationship between a ratio of upset amount / thickness, a heat input amount, and a pass / fail of a bulge evaluation test in a steel sheet having a carbon content of 0.8 to 0.89% in Example 1.

FIG. 4 is a graph showing the relationship between the ratio of the upset amount / thickness, the heat input, and the acceptable range of the bulge evaluation test for the carbon steel sheets of the prior art and the present invention.

FIG. 5 is a graph showing a relationship between a thickness of a steel sheet having a carbon content of a conventional technique and an example of the present invention, a heat input amount, and an acceptable range of a bulge evaluation test.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C22C 38/04 C22C 38/04

Claims (1)

[Claims] Claims: C: 0.30% or more, Si: 0.50% or less, containing Mn: 1.00% or less, in flash butt welding of a high carbon steel sheet or steel strip comprising the balance Fe and other unavoidable impurities, According to the carbon content, C: 0.30% or more and less than 0.50%, C: 0.50% or more and less than 0.80%, C: 0.80% or more, good weld bulge evaluation based on operation results for each category The relationship between the ratio of the upset amount to the plate thickness (upset amount / plate thickness) and the amount of heat input {= (secondary voltage) ² × (flash time)} is set in advance, and the content of carbon, depending on the plate thickness After welding with a preset upset amount and heat input, the joint and the weld heat affected zone are tempered at a temperature not lower than 600 ° C and not higher than the A _C1 transformation point. Butt welding method.