JP4774850B2 - Post-weld processing method for stainless steel sheet - Google Patents

Description

  The present invention relates to a post-weld processing method and a welding apparatus for a stainless steel plate (including a steel strip), in particular, on the entry side of a pickling line for a metal plate such as a stainless steel plate and a continuous annealing pickling line. The present invention relates to a post-welding processing method and welding apparatus suitable for welding a metal plate (hereinafter referred to as a preceding material) and a subsequent metal plate (hereinafter referred to as a subsequent material). Here, the stainless steel plate refers to a steel plate containing 10 mass% or more of Cr.

  Generally, ferritic and martensitic stainless steel sheets are subjected to box annealing or continuous annealing after hot rolling and pickling. On the other hand, austenitic stainless steel sheets are pickled without being annealed.

  This is because, if the scale is still present on the surface of the stainless steel plate, the corrosion resistance inherent to the stainless steel plate cannot be exhibited, and the aesthetics are impaired.

  FIG. 6 is a diagram schematically showing the entire stainless steel hot-rolled continuous annealing pickling line 100, in which 20 is a welding machine, 30 is an entrance looper, 31 is a dispensing machine, 40 is a shot blasting facility, and 50 is An annealing furnace, 60 is a pickling tank, 70 is a bridle roll, 80 is an exit looper, 90 is a winder, and the pickling tank 60 is a pickling tank 60a filled with sulfuric acid and a pickling filled with mixed acid. It is comprised from the tank 60b.

  The stainless steel sheet after hot rolling is generally used on the entry side of the continuous annealing pickling line as described above 100 or another type of continuous pickling line, and the tail end of the preceding material and the following material. The tip is welded by a welding method such as flash butt welding or laser welding, and the entire length is pickled by continuously passing through a pickling tank filled with acid.

  Flash butt welding refers to the tail end of the preceding material and the tip of the succeeding material, current is passed in the contacted state, Joule heat generated, and arc heat generated by melting and scattering of the contact part. It is a welding method in which welding is performed by melting and pressurizing both of the preceding material and the following material (also referred to as upsetting, meaning pressing against each other).

  Laser welding means that the tail end of the preceding material and the tip of the succeeding material are abutted, and the abutting portion is irradiated with a laser beam to be melted and integrated, or depending on the case, a material (such as Inconel or SUS301S) ), The molten material is melted by a laser beam, poured into a butt portion, and melted and integrated to be welded.

  Since the laser beam has a high energy density that is input to the irradiated portion, the welding speed is high. Therefore, welding is possible with an output of 20 to 80 kW. In addition, laser welding requires less heat input to the side of the metal plate to be welded than flash butt welding, and when a molten material is used, there is less generation of oxides and good welding can be expected.

  After welding the tail end of the preceding material and the tip of the succeeding material using the welding method as described above, the welded portion is continuously processed by the continuous annealing pickling line 100 described above or another continuous pickling line. The line will be passed through.

  In the continuous processing line, for example, as can be seen in the case of the above-described continuous annealing pickling line 100, there are various rolls such as looper rolls (32 and 82) and bridle rolls (70). Each time it passes, bending strain is repeatedly applied to the weld.

  Further, when passing through the continuous processing line, a tension of 20 to 30 MPa (line tension) is applied to the metal plate to be passed, and naturally the tension acts on the welded portion, so that the welded portion Will undergo bending under the action of tensile stress.

  By the way, the method of heating a welding part is described in patent document 1 after grind-processing a welding part using said flash butt welding.

  Patent Document 1 discloses that when flash butt welding is performed on a butt stainless steel plate, the amount of upset (amount of butt and pressed) is twice or more of the plate thickness, the welded portion is heated to 850 ° C. or more, and the like. According to this, martensite generated in welds of ferritic and martensitic stainless steel sheets can be eliminated, and the toughness and mechanical properties of the welds are good. It is described that even if it passes through a continuous processing line, breakage can be suppressed.

Furthermore, even if the welded part is heated before or during welding, it is possible to suppress breakage due to a decrease in toughness due to martensite. As the method, a method such as induction heating described in Patent Document 2 is proposed. Has been.
JP 2003-170274 A Japanese Patent No. 3492408

  According to the method described in Patent Document 1, it is possible to suppress the fracture to some extent when the welded portion passes through the continuous processing line. However, there is a problem as described below, and the welded portion breaks. This has not been completely prevented.

  In the case where the preceding material and the succeeding material are the same stainless steel type, it has been found that if the plate thickness is 3 mm or less, the method described in Patent Document 1 can also suppress the breakage, but the plate thickness is 4 mm or more. When the tail end of the preceding material and the tip of the succeeding material are welded (the welding method may be either flash bat or laser) and then heated to 850 ° C. or higher, the weld may break.

  This is due to the tensile force acting in the length direction of the surface of the metal plate, which increases as the plate thickness increases when the welded part is not grindered and is bent by various rolls in the continuous processing line. It is presumed that fine cracks that may occur in the surface layer during the welding of the metal plate develop.

  Even if the heating temperature of the welded part is 850 ° C or higher when the stainless steel types and components of the preceding and subsequent materials are different, martensite is generated during cooling or heat input during welding causes In some cases, the crystal grains of the adjacent part (welding heat affected zone) become coarse, resulting in a decrease in toughness or fracture.

  For this reason, in the case of welding of dissimilar materials (for example, welding between austenitic and ferritic stainless steel sheets) where the stainless steel types and components of the preceding material and the following material are different, it is difficult to pass through without breaking. It was.

  Although the heating method after welding described in Patent Document 1 is described as LPG or induction heating, there is no description about a specific apparatus configuration or control method, and there is room for improvement in many respects. .

  By the way, in the method of heating the welded portion by induction heating described in Patent Document 2, martensite is generated in the process of cooling at the boundary between the heating region and the non-heating region, and the generated martensite remains after that. In some cases, cracks originated from this point, leading to breakage.

  Further, the method of heating the welded portion by induction heating has a problem that the equipment becomes large. In addition, there is a problem that it takes time to reach the target temperature.

  For example, when the induction depth of the induction current generated on the butt end face of the metal plate during induction heating is induction heating of austenitic stainless steel at a frequency of 10 kHz, for example, it is 3-5 mm. Of course, if this penetration depth is to be tripled, for example, the frequency must be reduced to about 1/10, and for this purpose, the capacitor capacity of the power supply device must be increased by a factor of 100. To avoid it, even if it takes time, it has to wait for the heat to propagate.

Incidentally, the above relationship is expressed as follows.
δ = 1 / √ (πμσf) (1)
f = 1 / {2π√ (LC)} ... (2)
here,
δ: Penetration depth of induction current μ: Magnetic permeability σ: Conductivity f: Frequency L: Inductance (in the entire system including the induction heating device and the object to be heated)
C: represents the capacitor capacity of the power supply device.

The present invention has been made to solve the above problems. That is, the present invention is as follows.
1. In the post-weld processing method for stainless steel plates, where the stainless steel plates are butted and welded,
After the welded part is grindered, when the welded part is heated with gas from one or both of the upper side or the lower side of the welded part, the chemical composition of the preceding material and the subsequent material to be welded against each other is used.
The maximum heating temperature obtained by the following formula is obtained by calculation for each of the preceding material and the following material,
Among the preceding material and the following material, until the maximum heating temperature reaches the lower temperature,
A welding post-treatment method for a stainless steel sheet, wherein the welded portion after the grinder treatment is heated.
Maximum heating temperature (Tmax) (° C.) = 860−45 × C (mass%) − 2.5 × Cr (mass%) + 6.8 × Ni (mass%)
Here, C: carbon, Cr: chromium, Ni: nickel are represented.
2.1 In the post-weld processing method for a stainless steel sheet described in 2.1, the surface temperature of the welded part on the side heated by the gas or the opposite side is measured, and the gas flow rate is controlled based on the measured temperature. Post-welding method for stainless steel sheets.

  According to the present invention, even when the plate thickness is increased, the welded portion can be prevented from breaking when passing through a continuous processing line, and the stainless steel species and components of the preceding material and the following material can be suppressed. Even if they are different, they can be passed through without breaking.

  An example of an embodiment of the present invention is schematically shown in FIG. FIG. 1 illustrates the entry side of a continuous treatment line (such as a continuous pickling line, a continuous annealing line, or a continuous annealing pickling line that combines continuous annealing and continuous pickling).

  FIG. 1 (a) shows the welding state of the leading end of the preceding material and the leading end of the following material, (b) shows the state where the welded portion is grindered, and (c) shows the state of gas heating.

  In the figure, 1 is a preceding material, 2 is a following material, 3 is a welded part, 4 is a laser welder, 5 is a grinder, 6 is a gas burner nozzle, 7 is a thermometer, 8 is a retractor, and 15 is a welded part heating. An apparatus 16 is a welding apparatus. The welding device 16 according to the present invention includes all of the welding part heating device 15 including the gas burner nozzle 6, the radiation thermometer 7, and the retracting device 8 in addition to the welding machine 4 such as a laser welding machine and the grinder 5. In addition, the grinder 5 can consider the thing of the system of rotating a grindstone, the system of the push-cutting which moves the fixed cutter which does not rotate different from a figure in the board width direction, etc., and is meant to include all these.

  As the preceding material 1 or the following material 2 shown in FIG. 1, for example, austenitic stainless steel SUS304: 18Cr-8Ni (numerical values are mass%, the same applies hereinafter), SUS316: 18Cr-12Ni-2.5Mo-0.6C, ferrite Stainless steel SUS430: 17Cr-0.03-0.06C, martensitic stainless steel SUS410: 13Cr-0.08C, SUS420J1: 13Cr-0.2C, SUS420J2: 13Cr-0.3C, SUS429J1: 17Cr-0. Various stainless steel plates such as 3C can be cited as examples.

  The preceding material 1 and the following material 2 are welded by the laser welding machine 4 after the tail end portion of the preceding material 1 and the leading end portion of the following material 2 are cut and butted together by a shearing machine (not shown). The plate width of the leading material 1 and the following material 2 is 700 to 1600 mm, and the plate thickness is 2 to 6 mm.

  It is preferable to use a 40-70 kW laser welder. In the case of such an output, the laser welding machine can perform welding while moving at a plate width direction speed of 1 to 2 m / min, and may use inconel of φ1 to 3 mm, SUS301S, or the like as a molten material.

  Thereafter, as shown in FIG. 1B, the welded portion is cut and processed by the grinder 5. The grinder has a grindstone having a diameter of 200 to 300 mm, and is driven by a motor at a rotational speed of 600 to 3000 rpm.

  By adjusting the distance between the grindstones, the scattered marks of the base metal, the molten material, or the molten metal that have risen in the welded portion are removed. The reason for removing the raised portion is to remove the fine cracks that may occur on the surface layer during welding of the metal plate, and to remove the crack, so that when the plate is bent by various rolls in the continuous processing line, This is to prevent the weld from being broken by the tensile force acting in the length direction of the surface of the metal plate, which increases as the thickness increases.

  In addition, there is also a reason for preventing the occurrence of scouring due to the contact between the roll and the welded portion while the continuous processing line passes through the plate.

  FIG. 2 schematically shows the situation. Here, 9 is a molten material, 10 is a weld heat affected zone, FIG. 2A shows the longitudinal cross-sectional shape of the welded portion before the grinder treatment, and FIG. 2B shows the same shape after the grinder treatment. The welding heat-affected zone 10 is a portion where mechanical properties are lowered, such as hardening due to coarsening of crystal grains by welding.

  FIG. 1 (c) schematically shows a method of heating the welded portion subjected to the grinder process. The gas burner nozzle 6 may use, for example, LPG as gas and oxygen as a combustion aid. The distance between the welded portion and the gas burner nozzle is preferably 20 to 40 mm. Even if it is less than 20 mm or exceeds 40 mm, it becomes difficult to effectively heat the welded portion.

  The pressure for supplying the gas is preferably 0.05 to 0.1 MPa for LPG and 0.1 to 0.3 MPa for oxygen. The pressure for supplying the gas is preferably adjusted according to the thickness of the preceding and subsequent materials to be welded. It is because combustion becomes difficult if it is less than this range or exceeds this range.

  Further, when heating with gas, the surface temperature of the welded portion on the gas heating side or the opposite side may be measured by the radiation thermometer 7, and the gas flow rate may be controlled based on the measured temperature. .

  The radiation thermometer 7 preferably calibrates the emissivity prior to the start of service or periodically such as monthly. It is preferable that the gas burner nozzle 6 and the radiation thermometer 7 can be moved in the welding direction by a retractor 8 and the speed thereof is 1 to 3 m / min.

  FIG. 3 shows a control block diagram when heating with gas. In the figure, 12 is a gas regulator, 13 is an LPG pipe when LPG is used as a gas, and 14 is an oxygen pipe.

  The temperature T0 measured by the radiation thermometer 7 is input to the control device 11, and in the control device 11, the maximum heating temperature Tmax1 determined from the data related to the components of the preceding material transmitted from the host computer (not shown), and the subsequent The Tmax2 determined from the data on the component of the material is linearly regressed with the component content (mass%) of C, Cr, Ni, for example, by the method described in the below-mentioned examples of the maximum heating temperature. It is obtained by calculation using the following formula (3) obtained.

Tmax _i = 860-45 × C (mass%)-2.5 × Cr (mass%) + 6.8 × Ni (mass%) ・ ・ ・ (3)
Here, the subscripts i = 1 and 2 mean the preceding material and the following material, respectively.
The smaller value of Tmax1 and Tmax2 obtained is set as Tmax, and the difference from the measured temperature T0 is obtained by the following equation (4).
ΔT = Tmax-T0 ... (4)
The control device 11 controls the pressure of the supplied gas by adjusting the opening of the pressure regulating valve of the regulator 12 based on ΔT and targeting Tmax. Specifically, for example, the following equation (5) may be used, and Pa may be controlled to be a target value so that the absolute value of ΔT becomes small.
Pa = P0 + a × ΔT ... (5)
here,
Pa: pressure of gas targeted for control,
P0: target gas pressure (0.05 to 0.1 MPa),
a: Proportional gain (0.0001 to 0.0005)
It is. Note that a limit may be set in advance such that Pa does not exceed 0.1 MPa. According to such a method, it can control to heat a welding part to optimal temperature.

  For example, martensite is likely to be generated in a cooling process after welding in a portion adjacent to a molten material after welding a martensitic stainless steel plate. Although martensite is high in hardness but low in toughness, it becomes a starting point of cracks, and when passing through a continuous processing line, the welded part or the weld heat-affected part tends to break.

  The inventors have found that there is an appropriate post-weld heating temperature to extinguish this martensite depending on the components it contains. Furthermore, it has also been found that when martensitic stainless steel having a high C (carbon) content is gas-heated at a high temperature of 850 ° C. or higher, martensite is generated again in the subsequent cooling process even if heated.

  In addition, even with ferritic stainless steel and austenitic stainless steel with extremely low C (carbon) content, residual stress accompanying thermal strain generated by welding is also added, so various types of materials are used when passing through a continuous processing line. Cracks may occur in the welded part or welded heat-affected zone due to repeated bending received from the roll and may break.

  In particular, as the plate thickness increases, the tensile force acting in the length direction of the surface of the metal plate also increases, so cracks are likely to occur.

  Also, when the weld is heated, the residual stress associated with the thermal strain generated by welding tends to be eliminated, but excessive heating causes the crystal grains in the weld heat affected zone to become coarser, resulting in reduced toughness and cracks. It tends to occur and may cause breakage.

  As a result of further research, the inventors have found that there is an appropriate post-weld heating temperature depending on the components contained.

  Appropriate heating temperature after welding is the above equation (3). In obtaining Equation (3) by regression, experiments as described below were performed using stainless steels having various component compositions. Here, whether or not the continuous processing line can be passed was determined by a bending test. This assumes bending by a roll when passing through a continuous processing line.

  First, a test piece having a width of 30 mm and a length of 300 mm including a welded portion subjected to laser welding and grinder treatment was cut out to obtain a test piece for bending. After the welded part was gas heated together with the test piece, bending and bending back processing was performed with a tool of r = 40 mm, and the occurrence of cracks in the welded part was observed.

  FIG. 4 schematically shows the bending and bending back process. 3 is a welding part. The plate thickness was 5 mm.

  Table 1 shows the results of experiments using each steel type as a test piece. Here, x is a crack that occurs during bending and bending back processing, and when it breaks, △ is not broken, but when a crack occurs on the surface of the welded part, ○ is when a crack only occurs It is. In this way, the highest temperature among the heating temperatures at which ◯ was obtained by bending and bending back processing was defined as the highest heating temperature (Tmax). Formula (3) was obtained by carrying out the primary regression process of the maximum heating temperature using each component content (mass%) of each steel type.

  (Example of the present invention) In the welding method shown in FIG. 1, a laser welding machine having an output of 55 kW was used, and an inconel φ1 mm was used as the molten material. The plate width direction speed was 1.5 m / min. After the excess melt was removed with a grinder, the welded portion that had been grindered by the heating method of the present invention was heated.

Supply pressure of the gas in the plate thickness of 3 mm 0.06 MPa, the flow rate is 0.110m ³ / min, in the case of 4 mm 0.07 MPa, the flow rate was targeted 0.122 m ³ / min, . The supply pressure of oxygen was constant at 0.2 MPa. The proportional gain a was set to 0.0008 to control the LPG supply pressure.

(Conventional example 1)
In Conventional Example 1, flash butt welding (output 130 kVA) described in Patent Document 1 was performed, and after the grinder treatment, the welded portion was heated to 850 ° C. or higher. It was the range of 855-900 degreeC in the measurement with a radiation thermometer. The upset amount was twice the plate thickness.

(Conventional example 2)
In Conventional Example 2, with the welding method shown in FIG. 1, a laser welding machine with an output of 55 kW was used, and a melt with Inconel φ1 mm was used. The welding speed was 1.5 m / min in the plate width direction. The excess melt was removed with a grinder, and then no heating was performed.

(1) Influence of plate thickness The present invention described above is applied to 1000 stainless steel plates having a plate thickness of 2 to 6 mm and a plate width of 700 to 1600 mm (the ratio of austenite, ferrite and martensite is 1: 6: 3). In accordance with the example and the conventional examples 1 and 2, it was passed through the continuous annealing pickling line 100 shown in FIG. In the examples of the present invention, the heating temperature after welding was controlled to 750 to 840 ° C., and no coarsening of crystal grains in the weld heat affected zone was observed.

  Table 2 shows the ratio of breakage when passing through a continuous annealing pickling line when welding under the condition that the steel grades of the preceding material and the following material are the same in the range of the plate thickness of 2 to 6 mm. %).

  In the example of the present invention, in the continuous annealing pickling line, the welded part or the weld heat-affected zone did not break, and good results were obtained. The rate has increased. According to the present invention, it can be seen that an appropriate heat treatment of the weld is performed.

(2) Influence of dissimilar material welding For 100 stainless steel plates (austenitic, ferritic, martensitic) with a plate thickness of 3 mm and a width of 700 to 1600 mm, dissimilar material welding (for example, austenitic and ferritic) is performed. In accordance with the present invention example and the conventional examples 1 and 2, the sheet was passed through the continuous annealing pickling line 100 shown in FIG.

  In the examples of the present invention, the heating temperature after welding was controlled to 750 to 840 ° C., and no coarsening of crystal grains in the weld heat affected zone was observed.

  Table 3 shows the fracture ratio (%). In the example of the present invention, in the continuous annealing pickling line, the welded part or the weld heat-affected zone did not break, and good results were obtained. The rate has increased.

  Next, it shows about the result which compared the example of this invention and the method (comparative example) which heats before welding using an induction heating apparatus. In addition, the induction heating apparatus with a frequency of 10 kHz and an output of 200 kW was used.

  The above-described example of the present invention and the induction heating apparatus were used for 1000 stainless steel plates having a plate thickness of 2 to 6 mm and a plate width of 700 to 1600 mm (the ratio of austenite, ferrite, and martensite is 1: 6: 3). For both the examples and the continuous annealing pickling line 100 shown in FIG.

  In Table 4, in the range of the plate thickness of 2 to 6 mm, and under the conditions that the steel types of the preceding material and the following material are the same, the rupture ratio when passing through the continuous annealing pickling line ( %).

In the example of the present invention, in the continuous annealing pickling line, the welded part or the weld heat-affected zone did not break, and good results were obtained. Then, the fracture ratio became high. According to the present invention, it can be seen that an appropriate heat treatment of the weld is performed.
On the other hand, when the induction heating apparatus was used, the fracture ratio increased when the plate thickness was thick.

  In addition, the heating time in the example of the present invention was an average of 42 seconds, whereas in the case of using the induction heating device, it was 63 seconds. In the present invention, the heating time is shorter with a simpler device. It can be seen that it can be processed.

  As described above, the present invention is not limited to the above embodiment. For example, the gas burner nozzle 6 may heat the welded portion from the lower side rather than the upper side of the welded portion, or may heat from both sides. Further, the gas burner nozzle 6 is not limited to a type that moves one nozzle in the plate width direction, but may be a type that moves a plurality of rows in the plate width direction as shown in FIG. Alternatively, a type in which a curtain wall flame burns so as to cover the entire width may be used without moving in the plate width direction.

  In addition, if the preceding material and the following material are the same material, the flow rate of the gas or oxygen or the plate of the welding machine according to the table value for each material determined empirically without necessarily depending on the calculation result in formula (3). The speed in the width direction may be determined.

  Further, a mechanism for controlling the gas flow rate based on the radiation thermometer 7 and the measured temperature is not essential, and the flow rate of the gas and oxygen according to the empirically determined table value, or the plate width direction speed of the welding machine, etc. You may decide with.

  The present invention can be applied not only to laser welding but also to a welding method in which martensite is generated in the process of being cooled at the boundary between a heating region and a non-heating region, such as induction heating. It goes without saying that martensite can be extinguished by heating the part, and is similarly effective in suppressing breakage.

The perspective view for demonstrating one embodiment of this invention Schematic diagram of the weld The control block diagram at the time of heating the welding part which concerns on embodiment of this invention with gas The figure which shows the appearance of the bending test typically The figure for demonstrating another embodiment of this invention The figure which showed the whole continuous annealing pickling line suitable for using this invention roughly.

Explanation of symbols

1: preceding material 2: following material 3: welding part 4: laser welding machine 5: grinder 6: gas burner nozzle 7: radiation thermometer 8: retracting device 9: molten material 10: welding heat affected zone 11: control device 12: Gas regulator 13: LPG pipe 14: Oxygen pipe 15: Welding part heating device 16: Welding device 20: Welding machine 30: Inlet looper 31: Dispensing machine 40: Shot blasting equipment 50: Annealing furnace 60: Pickling tank 70: Bridle Roll 80: Outlet looper 90: Winder 100: Continuous annealing pickling line

Claims (2)

In the post-weld processing method for stainless steel plates, where the stainless steel plates are butted and welded,
After the welded part is grindered, when the welded part is heated with gas from one or both of the upper side or the lower side of the welded part, the chemical composition of the preceding material and the subsequent material to be welded against each other
The maximum heating temperature obtained by the following formula is obtained by calculation for each of the preceding material and the following material,
Among the preceding material and the following material, until the maximum heating temperature reaches the lower temperature ,
A welding post-treatment method for a stainless steel sheet, wherein the welded portion after the grinder treatment is heated.
Maximum heating temperature (Tmax) (° C.) = 860−45 × C (mass%) − 2.5 × Cr (mass%) + 6.8 × Ni (mass%)
Here, C: carbon, Cr: chromium, Ni: nickel are represented.   2. The post-weld processing method for a stainless steel sheet according to claim 1, wherein the surface temperature of the welded portion on the side heated by the gas or the opposite side is measured, and the gas flow rate is controlled based on the measured temperature. Post-welding method for stainless steel sheets.

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