Vertical position welding heat treatment method for L921A high-strength steel

Abstract

The invention discloses a vertical position welding heat treatment method for L921A high-strength steel. Welding grooves of two L921A high-strength steel plates are machined into X-shaped grooves; the truncated edges of the grooves of the two pieces to be welded are aligned, and the gap between the truncated edges of the two pieces to be welded is 2-5 mm; protective gas is introduced into the front side and the back side at the same time during front side first-layer backing welding, and melting holes are formed in the front end of a weld pool during welding, so that the front side and the back side of a weld are formed during front side first-layer backing welding; and front face filling welding and cosmetic welding and back face filling welding and cosmetic welding are conducted, and after welding is completed, welding seam stress relieving heat treatment is conducted on the whole welding workpiece. According to the vertical position welding method, in the welding process, carbon gouging, back gouging and grinding are not needed to be conducted on the back face to remove a carburized layer, the problem that carbon gouging produces carburization in a welding seam can be effectively prevented, and therefore the internal quality and the welding efficiency of L921A high-strength steel welding are improved; and stress is eliminated after welding, so that deformation of the structural part after machining is avoided.

Description

Technical Field

[0001] The invention belongs to the technical field of welding butt joints of L921A steel panels, and in particular relates to a method for vertical welding heat treatment of L921A high-strength steel. Background Art

[0002] High-pressure and low-temperature shells have been widely used in recent years. Considering factors such as material consumption, high-strength steel has gradually replaced the main material of high-temperature and low-pressure shells. As we all know, high-strength steel has poor welding performance and is difficult to weld. Therefore, welding methods to improve the welding quality and welding efficiency of this material have become the main research object.

[0003] L921A steel has been successfully selected as an optional material for high-temperature and low-pressure shells due to its excellent material properties. However, this material is difficult to weld in vertical welding. At present, the traditional butt welding method of vertical welding of this material welding plate adopts the method of front welding, back carbon planing and root cleaning, and then welding the back side. There are generally the following problems:

[0004] (1) Since carbon rods are used for carbon planing and root cleaning, the carbon planing will not only damage the welded weld, but also significantly remove the main body material, which increases a lot of extra welding. Since vertical welding is difficult and the welding quality is not easy to control, it has a great impact on the welding efficiency and the internal quality of the welding.

[0005] (2) After carbon planing, there is a carburized layer on the material body and the weld. The carbon planed area needs to be manually polished to remove the carburized layer on the weld surface. In order to ensure the internal quality of the weld, non-destructive testing is also required to check for defects before welding the reverse weld. The carbon planing and polishing workload is large during the entire welding process, and the welding efficiency is low.

[0006] In addition, L921A steel structural parts are generally not subjected to stress relief heat treatment, so there are large welding residual stresses. This residual stress has little effect on welded structures without processing size requirements, but in welded structures with high interface size requirements, welding residual stress will cause the structural parts to gradually deform in size during the post-welding processing, resulting in the interface of the structural parts failing to meet the size requirements, thereby affecting the mechanical seal of the product. Summary of the invention

[0007] The invention breaks the traditional welding method of L921A high-strength steel plate vertical welding butt weld, and provides a method for L921A high-strength steel vertical welding heat treatment which improves welding efficiency and quality and reduces welding residual stress.

[0008] To achieve the above object, the present invention provides a method for heat treatment of vertical welding of L921A high-strength steel, comprising the following steps:

[0009] 1) Process the welding grooves of two L921A high-strength steel plates into X-shaped grooves;

[0010] 2) Align the blunt edges of the grooves of the two pieces to be welded, and the gap between the blunt edges of the two pieces to be welded is 2 to 4 mm;

[0011] 3) When welding the first layer of the front backing, the shielding gas is passed to both the front and back sides, and a molten hole is formed at the front end of the weld pool during welding, so that the weld is formed on both sides during the first layer of the front backing welding;

[0012] 4) Filling welding and capping welding on the front side, filling welding and capping welding on the back side;

[0013] 5) After welding is completed, the weld seam of the entire workpiece is subjected to stress relief heat treatment.

[0014] Furthermore, the step 5) of heat treatment of stress relief of weld is specifically as follows: charging the furnace below 300°C, then raising the temperature to 550-600°C at 60-100°C / h, keeping the temperature at 550-600°C for 4-6h, then cooling the furnace to below 300°C at 70-90°C / h, and cooling in still air after taking out of the furnace.

[0015] Furthermore, in the step 1), the processing groove angle is 60° to 70°, and the blunt edge is 0 to 2 mm.

[0016] Furthermore, in the step 3), the first layer of the front backing welding is TIG welding, and a φ2.0mm RsWM60S-T welding wire is used, and the shielding gas is 99.999% argon; the front weld width is 4 to 6mm; the back weld thickness is 1 to 2mm and the width is 4 to 6mm.

[0017] Furthermore, in the step 3), when performing the first layer of back welding on the front side, the front side gas flow rate is 10-15 L / min, the back side gas flow rate is 8-12 L / min, the welding current is 90-120 A, the voltage is 12-15 V, and the welding speed is 6-10 cm / min.

[0018] Further, the front filling welding and capping welding in the step 4) are specifically as follows: the second layer filling welding adopts TIG welding, and adopts a φ2.0mm RsWM60S-T welding wire, and the shielding gas is 99.999% argon; the welding current is 100-110A, the voltage is 21-22V, the welding speed is 10-12cm / min, the thickness of the weld is 2-4mm, and the width is 3-5mm;

[0019] The third layer of filling welding and the fourth layer of cap welding are both pulsed MAG welding, the shielding gas is 95% Ar + 5% CO2, and the φ1.2mm brand RsWM60S welding wire is used; the gas flow rate of the third layer of filling welding and the fourth layer of cap welding is 18-25L / min, the filling current during filling welding is 150-300A, the voltage is 22-30V, and the welding speed is 15-30cm / min, and the cap current during cap welding is 150-300A, the voltage is 22-30V, and the welding speed is 15-30cm / min; the width of each single weld of pulse MAG welding is 5-10mm and the thickness is 2-4mm; during welding, the inter-pass temperature of the weld is 80-120℃.

[0020] Further, the back filling welding and capping welding in the step 4) are specifically as follows: the second layer filling welding adopts TIG welding, and adopts a φ2.0mm RsWM60S-T welding wire, and the shielding gas is 99.999% argon; the welding current is 100-110A, the voltage is 21-22V, the welding speed is 10-12cm / min, the thickness of the weld is 2-4mm, and the width is 3-5mm;

[0021] The third layer of filling welding and the fourth layer of cap welding are both pulsed MAG welding, the shielding gas is 95% Ar + 5% CO2, and the φ1.2mm brand RsWM60S welding wire is used; the gas flow rate of the third layer of filling welding and the fourth layer of cap welding is 18-25L / min, the filling current during filling welding is 150-300A, the voltage is 22-30V, and the welding speed is 15-30cm / min, and the cap current during cap welding is 150-300A, the voltage is 22-30V, and the welding speed is 15-30cm / min; the width of each single weld of pulse MAG welding is 5-10mm and the thickness is 2-4mm; during welding, the inter-pass temperature of the weld is 80-120℃.

[0022] Furthermore, the reverse sides of the two pieces to be welded are positioned and fixed by using a cama plate to ensure that the misalignment at the joint of the two pieces to be welded is not greater than 1 mm.

[0023] Furthermore, the TIG welding adopts a welding device of model WsM-400, and the pulse MAG welding adopts a welding device of model YD-500GL5HN.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1) The vertical welding method of the present invention improves welding efficiency and quality, and the weld root is well fused. Compared with the traditional welding method, the welding efficiency is increased by more than 2 times, the consumables cost is reduced by 1 times, and the labor cost is reduced by 50%;

[0026] 2) In the vertical welding method of the present invention, there is no need to perform carbon planing and root cleaning and grinding on the reverse side to remove the carburized layer during welding, which can effectively prevent the carburization problem caused by carbon planing in the weld, thereby improving the internal quality and welding efficiency of L921A high-strength steel welding;

[0027] 3) The welding heat input of the welding process is effectively controlled during the welding process, the fusion ratio of the weld is guaranteed, the interlayer temperature of the weld is strictly controlled, and the welding process of vertical welding and butt joint of L921A high-strength steel plate is formulated. The single-sided welding and double-sided forming welds are formed on both sides, and the mechanical properties such as tensile and bending are good, and meet the impact requirements of high temperature and high pressure;

[0028] 4) Stress elimination after welding avoids deformation of structural parts after processing. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 A schematic diagram of the invented jigsaw puzzle structure;

[0030] Figure 2 Schematic diagram of assembling Kama board for inventing jigsaw puzzle;

[0031] Figure 3 Weld bead layout diagram for invented welds. DETAILED DESCRIPTION

[0032] The present invention will be further described in detail in conjunction with specific embodiments and drawings to facilitate a clearer understanding of the present invention, but they do not constitute a limitation to the present invention.

[0033] 1. Material selection

[0034] The two pieces to be welded are made of high-strength steel with a grade of L921A and a thickness of 12mm. This material has high mechanical properties, especially under high temperature and high pressure conditions. However, this material has high requirements for the control of welding line energy during the welding process. The welding process is relatively complicated and the interpass temperature should be strictly controlled during the welding process.

[0035] TIG welding uses φ2.0mm RsWM60S-T welding wire with 99.999% argon, and pulse MAG welding uses φ1.2mm RsWM60s welding wire with 95% Ar+5% cO2. The linear expansion coefficient of this welding material is close to that of L921A high-strength steel. It is preheated to 80℃ before welding to remove moisture, and stress relief heat treatment is performed after welding. After the weld is formed, it has high strength, pressure resistance, high temperature resistance, and good crack resistance. Alkaline low-hydrogen welding wire is used to effectively remove harmful elements in the weld during welding, reduce the hydrogen content in the weld, and improve the welding quality of the weld.

[0036] TIG welding uses welding equipment model WsM-400, and pulse MAG welding uses welding equipment model YD-500GL5HN.

[0037] In order to improve welding efficiency and reduce material waste, the welding equipment of the present invention is selected for comparison under the same welding process conditions.

[0038] Example 1

[0039] The welding equipment selected was pulse welding (YD-500GL5HN), welding wire brand RsWM60S, diameter 1.2 mm, welding speed 15-30 cm / min, welding current 150-300 A, voltage 22-30 V, mixed shielding gas 95% Ar+5% CO2 flow rate 18-25 L / min, and three groups of test blocks were welded.

[0040] Example 2

[0041] The welding equipment selected was (NBC-500P plus), welding wire brand RsWM60S, diameter 1.2 mm, welding speed 15-30 cm / min, welding current 150-300 A, voltage 22-30 V, mixed shielding gas 95% Ar+5% CO2 flow rate 18-25 L / min, and three groups of test blocks were welded.

[0042] Example 3

[0043] The welding equipment selected was pulse welding (YD-500GL5HN), welding wire brand ER50-6, diameter 1.2 mm, welding speed 15-30 cm / min, welding current 150-300 A, voltage 22-30 V, mixed shielding gas 95% Ar+5% CO2 flow rate 18-25 L / min, and three groups of test blocks were welded.

[0044] Example 4

[0045] The welding equipment selected was (NBC-500P plus), welding wire brand ER50-6, diameter 1.2 mm, welding speed 15-30 cm / min, welding current 150-300 A, voltage 22-30 V, mixed shielding gas 95% Ar+5% CO2 flow rate 18-25 L / min, and three groups of test blocks were welded.

[0046] Table 1

[0047]

[0048] According to Table 1, with the same welding parameters, the equipment and welding parameters selected in Example 1, i.e., the present invention, all meet the requirements and are better than other solutions.

[0049] 2. Preparation before welding

[0050] like Figure 1As shown, the welding grooves of two L921A high-strength steel plates are processed into X-shaped grooves with a processing groove angle of 60° to 70° and a blunt edge of 1 to 2 mm;

[0051] Grind and align the blunt edges of the grooves of the two pieces to be welded, and the gap between the blunt edges of the two pieces to be welded is 2 to 4 mm; Figure 2 The reverse sides of the two pieces to be welded are positioned and fixed by a cama plate 1 to ensure that the misalignment at the joint of the two pieces to be welded is not greater than 1 mm.

[0052] 3. Welding process

[0053] like Figure 3 As shown, the number of front welding passes is 4 layers, the number of back welding passes is 3 layers, and the vertical butt welding process adopts the bottom-up welding method, as follows:

[0054] Before welding, preheat the welding area and surrounding areas, which can not only reduce the cooling rate of the weld, but also reduce the welding stress; fully preheat the welding gun 8 to 10 mm below the weld joint of the first layer of base welding on the front side to remove moisture on the surface of the groove.

[0055] The first layer of backing welding on the front side adopts TIG welding. During the first layer of backing welding, shielding gas is passed to both the front and back sides, and a molten hole is formed at the front end of the weld pool during welding, so that the weld is formed on both sides during the first layer of backing welding on the front side. After welding, no carbon planing is required to clean the root on the back side. Passing shielding gas to the weld pool can prevent the formation of pores and inclusions in the molten pool during the solidification process, thereby preventing defects such as cracks.

[0056] When welding the first layer of the front side, the front side gas flow is 10-15L / min, the back side gas flow is 8-12L / min, the welding current is 90-120A, the voltage is 12-15V, and the welding speed is 6-10cm / min; the front side weld width is 4-6mm; the back side weld thickness is 1-2mm and the width is 4-6mm.

[0057] The second layer of filling welding on the front side adopts TIG welding, and uses φ2.0mm RsWM60S-T welding wire, and the shielding gas is 99.999% argon; the welding current is 100-110A, the voltage is 21-22V, the welding speed is 10-12cm / min, the thickness of the weld is 2-4mm, and the width is 3-5mm;

[0058] The third layer filling welding and the fourth layer cap welding on the front side are both pulsed MAG welding, the shielding gas is 95% Ar + 5% CO2, and the φ1.2mm brand RsWM60S welding wire is used; the gas flow rate of the third layer filling welding and the fourth layer cap welding is 18-25L / min, the filling current during filling welding is 150-300A, the voltage is 22-30V, and the welding speed is 15-30cm / min, and the cap current during cap welding is 150-300A, the voltage is 22-30V, and the welding speed is 15-30cm / min; the single pass width of each weld of pulse MAG welding is 10-15mm and the thickness is 2-4mm; during welding, the interpass temperature of the weld is 100-120℃.

[0059] The second layer of back-side filling welding adopts TIG welding, and uses φ2.0mm RsWM60S-T welding wire, and the shielding gas is 99.999% argon; the welding current is 100-110A, the voltage is 21-22V, the welding speed is 10-12cm / min, the thickness of the weld is 2-4mm, and the width is 3-5mm;

[0060] The third layer filling welding and the fourth layer cap welding on the back side are both pulsed MAG welding, the shielding gas is 95% Ar + 5% CO2, and the φ1.2mm brand RsWM60S welding wire is used; the gas flow rate of the third layer filling welding and the fourth layer cap welding is 18-25L / min, the filling current during filling welding is 150-300A, the voltage is 22-30V, and the welding speed is 15-30cm / min, and the cap current during cap welding is 150-300A, the voltage is 22-30V, and the welding speed is 15-30cm / min; the width of each single weld of pulse MAG welding is 10-15mm and the thickness is 2-4mm; during welding, the inter-pass temperature of the weld is 100-120℃.

[0061] 4. After welding, the weld does not need slow cooling or post-heat treatment, and it can be cooled naturally in the air. Then the workpiece is subjected to stress relief heat treatment: the furnace is loaded below 300℃, and then the temperature is raised to 550-600℃ at 60-100℃ / h, kept at 550-600℃ for 4-6h, and then the furnace is cooled to below 300℃ at 70-90℃ / h, and cooled in still air after being taken out of the furnace.

[0062] 5. Welding quality inspection

[0063] The visual inspection of the front and back sides of the weld shows that the weld has good forming, without conventional defects such as undercut, pores, lack of fusion, cracks, etc. The non-destructive testing RT inspection shows that the internal quality of the weld is also good and without any defects. The radiographic inspection results show that the weld quality grade meets the requirements of NB / T47013.2 Grade I welds. According to the NB / T47014-2011 standard specification, the butt-jointed plate welds were sampled for tensile, impact, bending, macro, micro, fatigue and other mechanical property tests. The test results show that they all meet the welding process requirements of L921A high-strength steel.

[0064] The deformation of the structural parts after welding and processing was good. Ten days after processing, the flatness of the flange sealing end faces of the two workpieces with a diameter of φ4500 were measured to be 0.10mm and 0.12mm respectively, which met the flatness requirement of 0.15mm for the workpieces. After the overall manufacturing of the structural parts was completed, a 0.7MPA airtight test was carried out, and there was no pressure drop after maintaining the pressure for 15 minutes.

Claims

1. A method for heat treatment of vertical welding of L921A high-strength steel, characterized in that: The steps include: 1) Process the welding grooves of two L921A high-strength steel plates into X-shaped grooves; 2) Align the blunt edges of the grooves of the two pieces to be welded, and the gap between the blunt edges of the two pieces to be welded is 2 to 4 mm; 3) When welding the first layer of the front backing, the shielding gas is passed to both the front and back sides, and a molten hole is formed at the front end of the weld pool during welding, so that the weld is formed on both sides during the first layer of the front backing welding; 4) Filling welding and capping welding on the front side, filling welding and capping welding on the back side; 5) After welding is completed, the weld seam of the entire workpiece is subjected to stress relief heat treatment.

2. The method for vertical welding heat treatment of L921A high-strength steel according to claim 1, characterized in that: The step 5) weld stress relief heat treatment is specifically as follows: loading the furnace below 300°C, then controlling the temperature to rise to 550-600°C at 60-100°C / h, keeping the temperature at 550-600°C for 4-6h, then controlling the furnace to cool to below 300°C at 70-90°C / h, and cooling in still air after taking out of the furnace.

3. The method for vertical welding heat treatment of L921A high-strength steel according to claim 1, characterized in that: In the step 1), the processing groove angle is 60° to 70°, and the blunt edge is 0 to 2 mm.

4. The method for vertical welding heat treatment of L921A high-strength steel according to claim 1, characterized in that: In the step 3), the first layer of the front backing welding is TIG welding, and a φ2.0mm RsWM60S-T welding wire is used, and the shielding gas is 99.999% argon; the front weld width is 4-6mm; the back weld thickness is 1-2mm and the width is 4-6mm.

5. The method for vertical welding heat treatment of L921A high-strength steel according to claim 1, characterized in that: In the step 3), when performing the first layer of back welding on the front side, the front side gas flow rate is 10-15 L / min, the back side gas flow rate is 8-12 L / min, the welding current is 90-120 A, the voltage is 12-15 V, and the welding speed is 6-10 cm / min.

6. The method for vertical welding heat treatment of L921A high-strength steel according to claim 1, characterized in that: The front filling welding and capping welding in step 4) are specifically as follows: the second layer of filling welding adopts TIG welding, and adopts a φ2.0mm RsWM60S-T welding wire, and the shielding gas is 99.999% argon; the welding current is 100-110A, the voltage is 21-22V, the welding speed is 10-12cm / min, the thickness of the weld is 2-4mm, and the width is 3-5mm; The third layer of filling welding and the fourth layer of cap welding are both pulsed MAG welding, the shielding gas is 95% Ar + 5% CO2, and the φ1.2mm brand RsWM60S welding wire is used; the gas flow rate of the third layer of filling welding and the fourth layer of cap welding is 18-25L / min, the filling current during filling welding is 150-300A, the voltage is 22-30V, and the welding speed is 15-30cm / min, and the cap current during cap welding is 150-300A, the voltage is 22-30V, and the welding speed is 15-30cm / min; the width of each single weld of pulse MAG welding is 5-10mm and the thickness is 2-4mm; during welding, the inter-pass temperature of the weld is 80-120℃.

7. The method for vertical welding heat treatment of L921A high-strength steel according to claim 1, characterized in that: The front filling welding and capping welding in step 4) are specifically as follows: the second layer of filling welding adopts TIG welding, and adopts a φ2.0mm RsWM60S-T welding wire, and the shielding gas is 99.999% argon; the welding current is 100-110A, the voltage is 21-22V, the welding speed is 10-12cm / min, the thickness of the weld is 2-4mm, and the width is 3-5mm; The third layer of filling welding and the fourth layer of cap welding are both pulsed MAG welding, the shielding gas is 95% Ar + 5% CO2, and the φ1.2mm brand RsWM60S welding wire is used; the gas flow rate of the third layer of filling welding and the fourth layer of cap welding is 18-25L / min, the filling current during filling welding is 150-300A, the voltage is 22-30V, and the welding speed is 15-30cm / min, and the cap current during cap welding is 150-300A, the voltage is 22-30V, and the welding speed is 15-30cm / min; the width of each single weld of pulse MAG welding is 5-10mm and the thickness is 2-4mm; during welding, the inter-pass temperature of the weld is 80-120℃.

8. The method for vertical welding heat treatment of L921A high-strength steel according to claim 1, characterized in that: The reverse sides of the two pieces to be welded are positioned and fixed by a cama plate to ensure that the misalignment of the two pieces to be welded at the joint is not greater than 1 mm.

9. The method for vertical welding heat treatment of L921A high-strength steel according to claim 5, characterized in that: The TIG welding adopts a welding device of model WsM-400, and the pulse MAG welding adopts a welding device of model YD-500GL5HN.

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