A welding method for chromium-molybdenum steel and martensitic heat-resistant steel

Abstract

The present invention discloses a method for welding chromium-molybdenum steel and martensitic heat-resistant steel, comprising the following steps: first, machining the base materials of the chromium-molybdenum steel and martensitic heat-resistant steel to be welded to form a groove; using E5515-B2-V welding consumables to build up a first isolation layer at the groove of the martensitic heat-resistant steel, and performing post-weld heat treatment after the completion of the first isolation layer build-up; machining the surface of the weld layer to remove the excess after the heat treatment; using ER90S-B3 and E9018-B3 welding consumables to butt joint the first isolation layer and the chromium-molybdenum steel groove; machining to remove the root pad; performing stress relief heat treatment on the joint, and performing radiographic inspection on the weld after the heat treatment. This solves the problem of non-overlapping insulation temperatures of the base materials on both sides during stress relief heat treatment, can achieve residual stress elimination and structural transformation in the weld metal and the heat-affected zones of the base materials on both sides, and ensures that the room temperature strength, high temperature strength, plasticity and toughness, endurance performance, fatigue performance and other indicators of the dissimilar steel joint between the chromium-molybdenum steel and the martensitic heat-resistant steel meet the design requirements for use.

Description

Technical Field

[0001] The invention belongs to the technical field of nuclear power equipment welding, and in particular relates to a welding method for chromium-molybdenum steel and martensitic heat-resistant steel. Background Art

[0002] At present, for low-alloy steel, chromium-molybdenum steel, etc., a heat-affected zone will be generated during the welding process when undergoing welding heat cycles. The structure of this heat-affected zone cannot meet the operating requirements under high-temperature and high-pressure environments. Stress relief heat treatment is required during the welding process. The existing welding methods can realize the welding of homogeneous materials such as low-alloy steel and chromium-molybdenum steel, or the welding of dissimilar steels with overlapping areas of stress relief heat treatment insulation temperature of the parent materials on both sides of the weld. For the stress relief heat treatment insulation temperature ranges of the parent materials on both sides that do not overlap, such as the butt joint of F22 chromium-molybdenum steel and F91 martensitic heat-resistant steel, which have high high-temperature strength and plastic toughness requirements for the weld joint, the existing welding technology cannot meet the long-term operation requirements of nuclear power equipment under high-temperature and high-pressure environments after welding.

[0003] Therefore, a new technology is needed to solve the problem in the existing technology that chromium-molybdenum steel and martensitic heat-resistant steel cannot meet the requirements of long-term operation under high temperature and high pressure environment after welding. Summary of the Invention

[0004] To solve the above problems in the prior art, the present invention provides a method for welding chromium-molybdenum steel and martensitic heat-resistant steel. After welding, the chromium-molybdenum steel and martensitic heat-resistant steel can operate for a long time in a high temperature and high pressure environment.

[0005] The present invention adopts the following technical solutions:

[0006] A method for welding chromium-molybdenum steel and martensitic heat-resistant steel comprises the following steps:

[0007] S1. The base metals of the chromium-molybdenum steel and martensitic heat-resistant steel to be welded are machined to form a groove;

[0008] S2. Using E5515-B2-V welding consumables to weld a first insulating layer at the groove of the martensitic heat-resistant steel, and performing post-weld heat treatment after the first insulating layer is welded;

[0009] S3. Remove excess from the surface of the machined weld layer after heat treatment;

[0010] S4. Use butt joint materials between the first barrier layer and the chrome-molybdenum steel groove, including ER90S-B3 and E9018-B3;

[0011] S5. Machining to remove the root pad;

[0012] S6. Perform stress relief heat treatment on the joints and perform radiographic inspection on the welds after heat treatment.

[0013] Welding typically requires matching the base material at the weld joint. For F22 chromium-molybdenum steel, B3 consumables, such as ER90S-B3 and E9018-B3, are typically used. However, this solution utilizes E5515-B2-V, a different type of consumable, for the first overlay insulation layer. Extensive material selection testing was conducted, including chemical and mechanical property testing, including composition analysis, chemical testing, tensile testing, and impact testing. Other consumables, such as E9018-B3 and E9018-G, experience performance degradation and instability after two different heat treatments. However, E5515-B2-V meets technical requirements and offers high stability, so it was selected for the overlay.

[0014] As a further improvement of the technical solution of the present invention, in step S1, the chromium-molybdenum steel is F22, and the model is 2.25Cr1Mo.

[0015] As a further improvement of the technical solution of the present invention, in step S1, the martensitic heat-resistant steel is F91.

[0016] As a further improvement of the technical solution of the present invention, in step S2, before performing post-weld heat treatment, the welded martensitic heat-resistant steel is cooled to 80°C-100°C and kept at this temperature for 1h-2h;

[0017] The holding temperature of post-weld heat treatment is 740℃-760℃, and it is kept at this temperature for 0.5h-1h.

[0018] As a further improvement of the technical solution of the present invention, in step S2, the surfacing thickness D of the first isolation layer is ≥ 10 mm, and the surfacing welding method of the first isolation layer is arc welding;

[0019] The preheating temperature of the first insulating layer of surfacing welding is 200℃-300℃, the post-heating temperature is 300℃-350℃, the current during the process of surfacing welding the first insulating layer is 140A-200A, the voltage is 22V-32V, and the welding speed is ≥20.53cm / min.

[0020] During the cladding process of the first insulating layer, the current was 140A-200A, the voltage was 22V-32V, and the welding speed was ≥20.53cm / min. No shielding gas was used during the cladding process. The welding parameters of the E5515-B2-V welding consumable were determined based on the results of welding tests, nondestructive testing, and mechanical property tests. The final parameter range was determined by adjusting the parameters to match different current and voltage, as well as the preheating temperature range, based on the mechanical property requirements.

[0021] As a further improvement of the technical solution of the present invention, in step S3, non-destructive testing is performed after machining, and step S4 is performed after confirmation of qualification.

[0022] As a further improvement of the technical solution of the present invention, in step S4, the ER90S-B3 welding material is used as the base welding material, and the E9018-B3 welding material is used as the filling welding material.

[0023] As a further improvement of the technical solution of the present invention, the welding method of the ER90S-B3 welding material is argon arc welding, and the welding method of the E9018-B3 welding material is arc welding.

[0024] The welding parameters of ER90S-B3 and E9018-B3 welding consumables are determined based on the results of welding tests, nondestructive testing, and mechanical property tests. Based on the mechanical property requirements, the final parameter range is determined by adjusting the parameters to match different current and voltage, as well as the preheating temperature range.

[0025] As a further improvement of the technical solution of the present invention, in step S5, non-destructive testing is performed after machining, and step S6 is performed after confirmation of qualification.

[0026] As a further improvement of the technical solution of the present invention, the stress relief heat treatment temperature in step S6 is 675°C-705°C.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] E5515-B2-V welding consumables are used as the first isolation layer for cladding at the groove of martensitic heat-resistant steel. After the first isolation layer is clad, ER90S-B3 and E9018-B3 welding consumables are used as the butt joint materials with the chromium-molybdenum steel base material after cladding at the groove of the martensitic heat-resistant steel base material. This solves the problem of non-overlapping insulation temperatures of the base materials on both sides during stress relief heat treatment. This stress relief heat treatment process can eliminate residual stress and achieve microstructure transformation in the weld metal and the heat-affected zones of the base materials on both sides, so that the room temperature strength, high temperature strength, plasticity and toughness, endurance performance and fatigue performance of the dissimilar steel joints of martensitic heat-resistant steel and chromium-molybdenum steel meet the design requirements for the use of nuclear power equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The technology of the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments:

[0030] Figure 1 It is a schematic diagram of the overall structure;

[0031] Figure 2 It is a cross-sectional view of the first isolation layer structure of martensitic heat-resistant steel groove surfacing.

[0032] Reference numerals:

[0033] 1- chromium-molybdenum steel;

[0034] 2- Martensitic heat-resistant steel;

[0035] 3- first isolation layer;

[0036] 4- Docking material;

[0037] 5-Clear root line. DETAILED DESCRIPTION

[0038] The following will be combined with the embodiments and drawings to clearly and completely describe the concept, specific structure and technical effects of the present invention so as to fully understand the purpose, scheme and effect of the present invention. It should be noted that the embodiments and features in the embodiments of this application can be combined with each other unless there is a conflict. The same reference numerals used throughout the drawings indicate the same or similar parts.

[0039] It should be noted that, unless otherwise specified, when a feature is referred to as being "fixed" or "connected" to another feature, it may be directly fixed or connected to the other feature or indirectly fixed or connected to the other feature. Furthermore, terms such as "upper," "lower," "left," and "right" used in this disclosure are intended solely to describe the relative positions of the components of the disclosure as shown in the accompanying drawings.

[0040] Reference Figure 1 and Figure 2 A method for welding chromium-molybdenum steel to martensitic heat-resistant steel comprises the following steps:

[0041] S1. Machine the base materials of the chromium-molybdenum steel 1 and martensitic heat-resistant steel 2 to form grooves. The chromium-molybdenum steel 1 is American Standard F22, which is a chromium-molybdenum steel 1 forging made of 2.25Cr1Mo, primarily designated SA-336Gr.F22 Cl.1. The martensitic heat-resistant steel 2 is American Standard F91, primarily designated SA-182M F91.

[0042] S2. Using E5515-B2-V welding material to weld the first isolation layer 3 at the groove of martensitic heat-resistant steel 2. The surfacing welding method adopts arc welding, that is, arc welding is adopted for surfacing in the flat welding position. The preheating temperature of the first isolation layer 3 is 200℃-300℃, the post-heating temperature is 300℃-350℃, the current in the process of surfacing the first isolation layer 3 is 140A-200A, the voltage is 22V-32V, the welding speed is ≥20.53cm / min, and there is no protective gas in the process of surfacing the first isolation layer 3. The surfacing thickness D of the first isolation layer 3 is ≥10mm. The chemical composition of the cladding metal of the welding material E5515-B2-V used in the first isolation layer 3 requires more stringent control. The C content in the composition of the E5515-B2-V welding material is 0.05%-0.12%. Controlling the C content within this range can improve the strength, plasticity and toughness of the welded joint. The Mn content is not more than 0.90%, and the P content is not more than 0.020%. The S content is no more than 0.010%, the Si content is no more than 0.60%, and the Cr content is 0.80%-1.5%, which can improve the corrosion resistance and strength of the welded joint. The Mo content is 0.40%-0.65%, and the V content is 0.10%-0.35%. E5515-B2-V welding consumables are used as the first isolation layer 3 of the welding groove of F91 material. Its room temperature and high temperature strength, impact toughness, etc. must meet specific high temperature use requirements. At 600°C, its tensile load is ≥98MPa, and it maintains high strength without fracture within a time range of 100 hours. After the first isolation layer 3 is surfacing welded, post-weld heat treatment is performed. The welded F91 material and the first isolation layer 3 are subjected to post-weld heat treatment together. Before the post-weld heat treatment, the welded martensitic heat-resistant steel 2 is naturally cooled to T1, T1 is 80℃-100℃, and kept at T1 for 1h-2h, and then the temperature is increased to T2, T2 is 740℃-760℃. The heating rate during the temperature increase from T1 to T2 does not exceed 55℃ / h, that is, the holding temperature T2 of the post-weld heat treatment is 740℃-760℃, and the holding time at this T2 temperature is 0.5h-1h. E5515-B2-V welding material is used as the isolation layer for the first isolation layer 3 surfacing welded at the groove of the martensitic heat-resistant steel 2, which solves the problem of non-overlapping holding temperatures of the stress relief heat treatment of the parent materials on both sides.

[0043] The welding parameters for E5515-B2-V welding consumables were determined based on welding tests, nondestructive testing, and mechanical property testing. The final parameter range was determined by adjusting parameters to match different current and voltage, as well as the preheating temperature range, based on mechanical property requirements. Welding typically requires matching the base material at the weld joint. For F22 chromium-molybdenum steel 1, B3 welding consumables, such as ER90S-B3 and E9018-B3, are typically used. However, this solution utilizes E5515-B2-V welding consumables, which differ from B3 welding consumables, for the first insulation layer 3. Extensive material selection testing was also conducted, including composition analysis, chemical testing, tensile testing, and impact testing, among other chemical and mechanical property tests. Other welding materials, such as E9018-B3 and E9018-G, have decreased performance and become unstable after undergoing two different heat treatments. However, the performance of E5515-B2-V welding material can meet the technical requirements and has high stability. Therefore, E5515-B2-V welding material is selected as the first isolation layer 3.

[0044] S3. After heat treatment, remove the excess from the surface of the machined weld layer, such as the excess on the inner and outer walls. Perform non-destructive testing after machining. After passing the testing, proceed to step S4.

[0045] S4. After passing the nondestructive testing, ER90S-B3 and E9018-B3 welding consumables are used to butt-weld the first insulating layer 3 and the groove of the chromium-molybdenum steel 1. The ER90S-B3 welding consumable is used as the base welding consumable. The welding method using the ER90S-B3 welding consumable as the base welding consumable is manual argon arc welding. The ER90S-B3 welding consumable as the base welding consumable must be preheated before welding. The preheating temperature is 200°C-300°C, the post-heating temperature is 250°C-400°C, the current is 80A-200A, the voltage is 10V-20V, and the welding speed is ≥8.54cm / min. The shielding gas during welding with the ER90S-B3 base welding consumable is high-purity argon, and the gas flow rate is 7L / mm-20L / mm. The E9018-B3 welding material is a filler welding material. The diameter of the E9018-B3 welding material can preferably be 1.6 mm. The welding method of the E9018-B3 welding material is arc welding. The E9018-B3 welding material needs to be preheated before welding as a base welding material. The preheating temperature is 200°C-300°C, and the post-heating temperature is 250°C-400°C. When using E9018-B3 welding materials with a diameter of 3.2 mm, the welding current is 100A-160A, the voltage is 22V-32V, and the welding speed is ≥9.81cm / min; when using E9018-B3 welding materials with a diameter of 4.0 mm, the welding current is 140A-200A, the voltage is 22V-32V, and the welding speed is ≥12.27cm / min. No protective gas is used when welding E9018-B3 welding materials as base welding materials. Both ER90S-B3 and E9018-B3 welding materials must be preheated before butt welding. The preheating temperature is 200℃-300℃. After butt welding is completed, post-heating is required to prevent rapid cooling and eliminate the thermal stress generated by welding. The post-heating temperature is 250℃-400℃ and the post-heating time is 2h.

[0046] ER90S-B3 and E9018-B3 welding consumables are used to butt the first isolation layer 3 and the groove of the chromium-molybdenum steel 1. The ER90S-B3 welding consumable is used as the base welding consumable, and the E9018-B3 welding consumable is used as the filler welding consumable. The welding parameters of the ER90S-B3 welding consumables and the E9018-B3 welding consumables are determined based on the results of welding tests, non-destructive testing, and mechanical property tests. According to the requirements of mechanical properties, the final parameter range is determined by adjusting the parameters to match different current and voltage, as well as the preheating temperature range.

[0047] S5. The specific position of the root cleaning line 5 can be set according to the actual welding situation. The root pad is removed by machining according to the root cleaning line 5. After machining, non-destructive testing is performed. After the testing is qualified, step S6 is performed.

[0048] S6. After passing nondestructive testing, the joint undergoes stress relief heat treatment at a temperature of 675°C to 705°C (T3). This involves raising the temperature to T3 and maintaining it at this temperature for 0.5 to 1 hour. After heat treatment, the weld is then radiographed. This stress relief heat treatment eliminates residual stress and transforms the microstructure of the weld metal and the heat-affected zones of the parent metal on both sides, ensuring that the room-temperature strength, high-temperature strength, ductility, endurance, and fatigue properties of the F22 and F91 dissimilar steel joints meet design requirements.

[0049] Example 1

[0050] The above-mentioned welding method of chromium-molybdenum steel 1 and martensitic heat-resistant steel 2 is used to weld the nozzle of steam generator equipment to the main steam pipeline in a certain project.

[0051] When the nozzle of the steam generator equipment needs to be welded to the main steam pipeline, according to the design requirements and material properties, the weld cladding metal and the heat-affected zone of the parent materials on both sides need to be subjected to stress relief heat treatment to improve the metallographic structure and performance of the weld and heat-affected zone of the weld joint. Since the parent materials on both sides of the weld are chromium-molybdenum steel 1 and martensitic heat-resistant steel 2 respectively, there is no overlapping area in the stress relief heat treatment insulation temperature after the welding connection of the parent materials on both sides. If the heat treatment insulation temperature suitable for chromium-molybdenum steel 1 is used, the parent material, heat-affected zone and fusion zone on the side of martensitic heat-resistant steel 2 will not achieve the effect of high-temperature tempering, thereby failing to improve the metallographic structure of this side, failing to improve the mechanical properties such as plasticity and toughness of the weld joint, failing to effectively reduce the hardness of this side, and also making it very easy for the weld to produce defects such as cracks during operation. However, using the same holding temperature for the base metal heat treatment on the martensitic heat-resistant steel 2 side would cause the chromium-molybdenum steel 1 base metal to undergo austenite transformation, resulting in excessive grain size after cooling and carbide aggregation and growth. This would significantly reduce the mechanical properties and hardness of the base metal and heat-affected zone on this side, making it unable to meet the operating requirements of a steam generator, a primary equipment component of a certain fourth-generation nuclear power plant. Therefore, direct welding is impossible. While the materials commonly used in the current process for the first isolation layer 3 can address the issue of overlapping holding temperatures for the base metal stress relief heat treatment on both sides of the weld, they cannot effectively eliminate residual stresses and promote microstructural transformation in the weld metal and the base metal heat-affected zones on both sides, and thus fail to improve the room temperature strength, high temperature strength, ductility, endurance, and fatigue properties of the joint between the chromium-molybdenum steel 1 and the martensitic heat-resistant steel 2.

[0052] Since the parent materials on both sides of the welded joint are divided into F22 and F91, there is no overlapping area in the stress relief heat treatment insulation temperature of the parent materials on both sides. According to the design requirements, the design temperature of the main steam nozzle is as high as 530℃, the design pressure is 17MPa, and the test pressure is 23.85MPa, which places higher high-temperature strength and plastic toughness requirements on the welded joint.

[0053] The above-mentioned welding method of chromium-molybdenum steel 1 and martensitic heat-resistant steel 2 was used to successfully weld dissimilar steels of F22 and F91 materials for pressure-bearing components of 16 sets of steam generators for nuclear power main equipment. The high-temperature and room-temperature strength, impact energy, face and back bending, hardness, Charpy transformation curve, and microcrystalline phase of the weld metal and heat-affected zone all met the design requirements for use. After welding using the welding method of this scheme, the high-temperature tensile strength of the joint and weld cladding metal at 530°C was ≥346MPa, the high-temperature tensile strength at 515°C was ≥355MPa, and the high-temperature tensile strength at 450°C was ≥365MPa. The impact absorbed energy at 25°C in the heat-affected zone on the F91 side was ≥54J, the impact absorbed energy at -20°C in the F91 / F22 heat-affected zone and cladding metal was 68J, and RTNDT was ≤-20°C. At a test temperature of 530°C, the average fracture stress of the endurance performance after 3000h was ≥142MPa, and the average fracture stress after 10000h was ≥124MPa.

[0054] The other contents of the welding method of chromium-molybdenum steel and martensitic heat-resistant steel described in the present invention can be found in the prior art and will not be described in detail here.

[0055] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Therefore, any modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A method for welding chromium-molybdenum steel and martensitic heat-resistant steel, characterized by: The following steps are involved: S1. The chromium-molybdenum steel and martensitic heat-resistant steel base materials to be welded are machined to form grooves; the chromium-molybdenum steel is F22, the main grade is SA-336Gr.F22 Cl.1; the martensitic heat-resistant steel is F91, the main grade is SA-182M F91; S2. Use E5515-B2-V welding consumables to weld the first isolation layer at the groove of martensitic heat-resistant steel. After the first isolation layer is welded, perform post-weld heat treatment. The martensitic heat-resistant steel after welding and the first isolation layer are subjected to post-weld heat treatment together. Before post-weld heat treatment, the welded martensitic heat-resistant steel is naturally cooled to T1, T1 is 80℃-100℃, and kept at T1 for 1h-2h. Then the temperature is raised to T2, T2 is 740℃-760℃. The heating rate during the heating process from T1 to T2 is No more than 55°C / h, that is, the holding temperature T2 of the post-weld heat treatment is 740°C-760°C, and the holding time at this T2 temperature is 0.5h-1h; wherein, the thickness D of the first insulating layer surfacing is ≥10mm, and the surfacing method of the first insulating layer is arc welding; the preheating temperature of the surfacing first insulating layer is 200°C-300°C, the post-heating temperature is 300°C-350°C, the current during the surfacing first insulating layer is 140A-200A, the voltage is 22V-32V, and the welding speed is ≥20.53cm / min; S3. Remove excess from the surface of the machined weld layer after heat treatment; S4. Use butt joint materials between the first barrier layer and the chrome-molybdenum steel groove, including ER90S-B3 and E9018-B3; S5. Machining to remove the root pad; S6. Perform stress relief heat treatment on the joints and perform radiographic inspection on the welds after heat treatment.

2. The method for welding chromium-molybdenum steel and martensitic heat-resistant steel according to claim 1, characterized in that: In step S3, non-destructive testing is performed after machining, and step S4 is performed after confirmation of passing.

3. The welding method of chromium-molybdenum steel and martensitic heat-resistant steel according to claim 1, characterized in that: In step S4, the ER90S-B3 welding material is used as the base welding material, and the E9018-B3 welding material is used as the filler welding material.

4. The welding method of chromium-molybdenum steel and martensitic heat-resistant steel according to claim 3, characterized in that: The welding method of the ER90S-B3 welding consumables is argon arc welding, and the welding method of the E9018-B3 welding consumables is arc welding.

5. The welding method of chromium-molybdenum steel and martensitic heat-resistant steel according to claim 1, characterized in that: In step S5, non-destructive testing is performed after machining, and step S6 is performed after confirmation of passing.

6. The method for welding chromium-molybdenum steel and martensitic heat-resistant steel according to claim 1, characterized in that: The stress relief heat treatment temperature in step S6 is 675°C-705°C.

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