Method for controlling hardness of CrMo steel welding heat affected zone

Abstract

The invention discloses a method for controlling the hardness of a CrMo steel welding heat affected zone, which belongs to the technical field of welded joint performance control, and comprises the following steps of: preheating a base metal before welding at the preheating temperature of not lower than 200 DEG C; sequentially welding a backing weld bead, a hot weld bead, a filling weld bead and a cosmetic weld bead on the base metal; the interlayer temperature does not exceed 300 DEG C; before the cosmetic weld bead is welded, the temperature of the base metal is not lower than 260 DEG C; the base metal is subjected to postweld heat treatment, the temperature is increased to 480 DEG C at the temperature increasing speed of 80-150 DEG C / h, and heat preservation is conducted for 1-3 h; raising the temperature to 650 DEG C at the temperature raising speed of 80-150 DEG C / h, and keeping the temperature for 7-9 hours; cooling to room temperature at a cooling speed of 80-150 DEG C / h; according to the method, the preheating temperature during preheating before welding, the interlayer temperature in the welding process, the lowest temperature of base metal during cosmetic weld bead welding and the heat preservation temperature and the temperature increasing and decreasing speed of all stages of postweld heat treatment are controlled respectively, the hardness upper limit value of the CrMo steel welding heat affected zone can be effectively controlled, and the safety and reliability of a welded joint are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of welding joint performance control, and particularly to a method for controlling the hardness of the heat affected zone of CrMo steel welding. Background Art

[0002] At present, the development of offshore oil and gas energy is rapid. The development of oil and gas resources is inseparable from the support of equipment manufacturing. As a key technology in oil and gas equipment manufacturing, welding technology will face challenges of some special materials and special requirements, and there is no good solution yet.

[0003] A relatively representative problem is the control of the hardness of the heat affected zone of the welding joint of CrMo steel (a medium carbon low alloy high strength steel, forgings, heat treatment state is quenched and tempered, poor weldability, and relatively representative CrMo steel grades in the industry are 4130, 4140, 8630). The factors affecting the hardness of the heat affected zone of such welding joints mainly include the incoming conditions of raw materials (such as tissue composition, strength, heat treatment state, etc.), welding process, post-weld heat treatment process, etc.; the biggest difference between offshore oil and gas development and onshore oil and gas development is the different mining environments. There will be some corrosive media (such as H2S) in the marine environment and offshore oil and gas. The welding joint is the weakest part in oil and gas extraction equipment. The corrosive medium will have a greater impact on the welding joint. The main mechanism is that H ions will diffuse and accumulate in the welding joint, and finally cause hydrogen embrittlement failure. In severe cases, the welding joint will break, and the consequences are extremely serious.

[0004] Research shows that the higher the hardness value of the welding joint, the greater the sensitivity to this kind of damage. The industry usually limits the upper limit of the joint hardness. In order to avoid this kind of damage, relevant specifications have been drafted in the industry to limit the upper limit of the welding joint hardness. For example, ISO 15156-2 / NACE MR0175 clearly requires that the hardness of the welding joint cannot exceed 250HV10; since the higher the carbon content of the steel, the higher the strength and the higher the hardness of the welding joint, especially in the heat affected zone. Therefore, this specification is relatively easy to achieve for the welding of some ordinary strength carbon steels, but it is a major problem and extremely difficult to control for the welding of CrMo steel, a medium carbon low alloy high strength steel, which is widely used in the industry.

[0005] Therefore, it is an urgent problem to be solved at present to research and design a method that can effectively control the upper limit value of the hardness of the heat affected zone of CrMo steel welding, improve the safety and reliability of the welded joint, and promote the development of offshore gas equipment. Summary of the Invention

[0006] Regarding the problems existing in the prior art, the present invention provides a method for controlling the hardness of the heat affected zone in the welding of CrMo steel. By separately controlling the preheating temperature during pre-welding, the interpass temperature during the welding process, the minimum temperature of the base metal during the cover pass welding, and the holding temperature and the heating and cooling rates at each stage of post-weld heat treatment, the upper limit value of the hardness of the heat affected zone in the welding of CrMo steel can be effectively controlled, improving the safety and reliability of the welded joint, which is economical and effective.

[0007] To achieve the above object, the technical solution adopted by the present invention is as follows: The present invention provides a method for controlling the hardness of the heat affected zone in the welding of CrMo steel, comprising the following steps: S1: Preheat the base metal before welding, and the preheating temperature is not lower than 200 °C; S2: A root pass, a hot pass, a filler pass, and a cover pass are provided on the base metal, and the root pass, the hot pass, the filler pass, and the cover pass are welded in sequence; during the welding process, the interpass temperature does not exceed 300 °C; before welding the cover pass, the temperature of the base metal is not lower than 260 °C; S3: Perform post-weld heat treatment on the base metal, raise the temperature to 480 °C at a heating rate of 80 - 150 °C / hour and hold for 1 - 3 hours; raise the temperature to 650 °C at a heating rate of 80 - 150 °C / hour and hold for 7 - 9 hours; lower the temperature to room temperature at a cooling rate of 80 - 150 °C / hour.

[0008] As a preferred technical solution, the width of the root pass is set to 5 - 7 mm and the thickness is set to 2 - 3.5 mm.

[0009] As a preferred technical solution, the width of the hot pass is set to 6 - 8 mm and the thickness is set to 3 - 4 mm.

[0010] As a preferred technical solution, the thickness of the cover pass is not greater than 3 mm.

[0011] As a preferred technical solution, when welding the root pass and the hot pass, the welding current is set to 220 - 250 A, the welding voltage is set to 12 - 14 V, the welding speed is set to 110 - 130 mm / min, the hot wire current is set to 50 A, the wire feeding speed is set to 1900 - 2300 mm / min, the oscillation width is set to 3 - 5 mm, the oscillation dwell time is set to 0.2 - 0.6 s, and the oscillation speed is set to 10 - 15 mm / s.

[0012] As a preferred technical solution, when welding the filler pass, the welding current is set to 235 - 260 A, the welding voltage is set to 12.5 - 16 V, the welding speed is set to 120 - 135 mm / min, the hot wire current is set to 50 A, the wire feeding speed is set to 2100 - 2500 mm / min, the oscillation width is set to 4 - 6 mm, the oscillation dwell time is set to 0.3 - 0.7 s, and the oscillation speed is set to 12 - 16 mm / s.

[0013] As a preferred technical solution, when welding the cover pass, the welding current is set to 200 - 230 A, the welding voltage is set to 11 - 13.5 V, the welding speed is set to 110 - 130 mm / min, the hot wire current is set to 50 A, the wire feeding speed is set to 1700 - 2200 mm / min, the oscillation width is set to 4 - 6 mm, the oscillation dwell time is set to 0.3 - 0.7 s, and the oscillation speed is set to 10 - 15 mm / s.

[0014] As a preferred technical solution, when welding the cover pass, first weld the areas of the two sides of the base material, and then weld alternately from both sides to the middle.

[0015] As a preferred technical solution, the root pass, the hot pass, the filler pass and the cover pass are all welded by the GTAW method, which can weld the CrMo steel material stably and efficiently; And / or, the welding consumable is set as a welding wire, the welding wire is set as ER100S - G, and the diameter of the welding wire is set to 1.2 mm.

[0016] As a preferred technical solution, after step S3 is completed, the welded joint is subjected to penetrant testing, ultrasonic testing, tensile test, weld impact test, heat affected zone impact test, base material impact test, bending test, weld hardness test, heat affected zone hardness test and base material hardness test.

[0017] The beneficial effects of the present invention are shown in: 1. By respectively controlling the preheating temperature during pre - welding preheating, the inter - layer temperature during welding, the minimum temperature of the base material when welding the cover pass, and the holding temperature and the heating and cooling rate at each stage of post - weld heat treatment, the present invention can effectively control the upper limit value of the hardness of the heat affected zone of CrMo steel welding, improve the safety and reliability of the welded joint, be economical and effective, solve the industry problems, promote the development of offshore oil and gas equipment, and lay a foundation for the implementation of the localization of subsea oil and gas equipment.

[0018] 2. By clarifying the specific dimensions of the root pass, the hot pass and the cover pass, and clarifying the specific welding parameters of the root pass, the hot pass, the filler pass and the cover pass, the present invention can effectively control the heat input of the heat affected zone, will not weaken the tempering effect of the subsequent pass, nor cause overheating and burning of the weld microstructure.

[0019] 3. The present invention fully utilizes theoretical and practical means, providing ideas for the research of welding process technology in the industry and having great reference value. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a bead layout diagram of a method for controlling the hardness of the heat affected zone of CrMo steel welding according to the present invention.

[0021] In the figure: 1 - base metal, 11 - heat affected zone, 21 - root pass, 22 - hot pass, 23 - filler pass, 24 - cover pass. DETAILED DESCRIPTION OF THE INVENTION

[0022] For the convenience of those skilled in the art to understand, the present invention will be further described below with reference to the accompanying drawings. Example 1

[0023] Please refer to Figure 1 , which is the first embodiment of a method for controlling the hardness of the heat affected zone of CrMo steel welding provided by the present invention. The width W1 of the root pass 21 is set to 5 - 7 mm, and the thickness H1 is set to 2 - 3.5 mm. The width and thickness of the bead are mutually restricted. The width of the bead can limit the swing amplitude. When welding the root pass, the larger the swing amplitude, the longer the contact time with the base metal 1 each time, the greater the heat input, and it will increase the hardenability of the root of the heat affected zone 11; if the thickness H1 is too thick, the overall heat input will be too high, increasing the hardenability of the heat affected zone 11. If the thickness H1 is too thin, the weld and the heat affected zone 11 will cool too fast, also increasing the hardenability of the heat affected zone 11. Similarly, the width W2 of the hot pass 22 is set to 6 - 8 mm, and the thickness H2 is set to 3 - 4 mm; the thickness H3 of the cover pass 24 is not greater than 3 mm.

[0024] Among them, the base metal 1 is 4130 75k material with a thickness of 45 mm, and the material specification is ASTM A519. The material technical requirements of the base metal 1 are shown in Table 1; Table 1 Material Technical Requirements

[0025] Before welding, the base metal 1 is preheated to not less than 200 °C; during welding, the interlayer temperature does not exceed 300 °C; before welding the cover pass 24, the temperature of the base metal 1 is not less than 260 °C; the welding parameters are shown in Table 2; Table 2 Welding Parameter Table

[0026] The swing width can control the relationship between the weld width and the weld layer thickness. The above swing width can obtain an appropriate thickness, which will neither weaken the tempering effect of the subsequent weld bead due to excessive thickness nor cause overheating or burning of the weld structure due to insufficient thickness. At the same time, by setting the above swing dwell time, better edge fusion can be obtained, and the arc dwell time is relatively reasonable, which can effectively control the heat input of the heat affected zone 11.

[0027] After welding the base material 1, post-weld heat treatment is carried out. The temperature is raised to 480 °C at a heating rate of 100 °C / hour and held for 2 hours; the temperature is raised to 650 °C at a heating rate of 100 °C / hour and held for 8 hours; the temperature is lowered to room temperature at a cooling rate of 100 °C / hour.

[0028] After the heat treatment is completed, the welded joint is subjected to penetrant testing, ultrasonic testing, tensile testing, weld impact testing, heat affected zone impact testing, base material impact testing, bending testing, weld hardness testing, heat affected zone hardness testing and base material hardness testing. All the test results meet the requirements; the specific test results are shown in Table 3.

[0029] Table 3 Welded Joint Test Table Example Two

[0030] Please refer to Figure 1 , the second embodiment of a method for controlling the hardness of the heat affected zone in CrMo steel welding provided by the present invention. Among them, the base material 1 is 8630 80k material with a thickness of 76 mm, and the material specification is ASTM A29. The material technical requirements of the base material 1 are shown in Table 4; Table 4 Material Technical Requirements

[0031] Before welding, the base material 1 is preheated to not less than 200 °C; during welding, the interlayer temperature does not exceed 300 °C; before welding the cover weld bead 24, the temperature of the base material 1 is not less than 260 °C; the welding parameters are shown in Table 5; Table 5 Welding Parameters

[0032] After welding the base material 1, post-weld heat treatment is carried out. The temperature is raised to 480 °C at a heating rate of 80 °C / hour and held for 2 hours; the temperature is raised to 650 °C at a heating rate of 80 °C / hour and held for 8 hours; the temperature is lowered to room temperature at a cooling rate of 80 °C / hour.

[0033] After the heat treatment is completed, the welded joints are subjected to penetrant testing, ultrasonic testing, tensile testing, weld impact testing, heat affected zone impact testing, base metal impact testing, bending testing, weld hardness testing, heat affected zone hardness testing and base metal hardness testing. All the test results meet the requirements. The specific test results are shown in Table 6.

[0034] Table 6 Welded Joint Test Table

[0035] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for controlling the hardness of the heat-affected zone of CrMo steel welding, characterized in that: The following steps are involved: S1: Preheat the base material (1) before welding, the preheating temperature should not be less than 200℃; S2: A base weld (21), a hot weld (22), a filling weld (23) and a cap weld (24) are provided on the base material (1), and the base weld (21), the hot weld (22), the filling weld (23) and the cap weld (24) are welded in sequence; during the welding process, the interlayer temperature does not exceed 300° C.; before welding the cap weld (24), the temperature of the base material (1) is not lower than 260° C.; S3: performing a post-weld heat treatment on the base material (1), raising the temperature to 480°C at a heating rate of 80-150°C / hour and keeping the temperature at that temperature for 1-3 hours; raising the temperature to 650°C at a heating rate of 80-150°C / hour and keeping the temperature at that temperature for 7-9 hours; and cooling the temperature to room temperature at a cooling rate of 80-150°C / hour.

2. A method for controlling the hardness of the heat affected zone of CrMo steel welding according to claim 1, characterized in that: The base weld (21) has a width of 5-7 mm and a thickness of 2-3.5 mm.

3. The method for controlling the hardness of the heat affected zone of CrMo steel welding according to claim 1, characterized in that: The width of the hot weld (22) is set to 6-8 mm, and the thickness is set to 3-4 mm.

4. The method for controlling the hardness of the heat affected zone of CrMo steel welding according to claim 1, characterized in that: The thickness of the cover weld (24) is no more than 3 mm.

5. The method for controlling the hardness of the heat affected zone of CrMo steel welding according to claim 1, characterized in that: When welding the base weld (21) and the hot weld (22), the welding current is set to 220-250A, the welding voltage is set to 12-14V, the welding speed is set to 110-130mm / min, the hot wire current is set to 50A, the wire feeding speed is set to 1900-2300mm / min, the swing width is set to 3-5mm, the swing dwell time is set to 0.2-0.6s, and the swing speed is set to 10-15mm / s.

6. The method for controlling the hardness of the heat affected zone of CrMo steel welding according to claim 1, characterized in that: When welding the filling weld (23), the welding current is set to 235-260A, the welding voltage is set to 12.5-16V, the welding speed is set to 120-135mm / min, the hot wire current is set to 50A, the wire feeding speed is set to 2100-2500mm / min, the swing width is set to 4-6mm, the swing dwell time is set to 0.3-0.7s, and the swing speed is set to 12-16mm / s.

7. The method for controlling the hardness of the heat affected zone of CrMo steel welding according to claim 1, characterized in that: When welding the cap weld (24), the welding current is set to 200-230A, the welding voltage is set to 11-13.5V, the welding speed is set to 110-130mm / min, the hot wire current is set to 50A, the wire feeding speed is set to 1700-2200mm / min, the swing width is set to 4-6mm, the swing dwell time is set to 0.3-0.7s, and the swing speed is set to 10-15mm / s.

8. A method for controlling the hardness of the heat-affected zone of CrMo steel welding according to claim 1 or 7, characterized in that: When welding the cap weld (24), the areas of the parent material (1) on both sides are welded first, and then welded alternately from both sides to the middle.

9. The method for controlling the hardness of the heat-affected zone of CrMo steel welding according to claim 1, characterized in that: The base weld (21), the hot weld (22), the filling weld (23) and the cap weld (24) are all welded by argon arc welding; And / or, the welding material is set to welding wire, the welding wire is set to ER100S-G, and the diameter of the welding wire is set to 1.2 mm.

10. The method for controlling the hardness of the heat affected zone of CrMo steel welding according to claim 1, characterized in that: After step S3 is completed, the weld joint is subjected to penetration testing, ultrasonic testing, tensile testing, weld impact testing, heat affected zone impact testing, parent material impact testing, bending testing, weld hardness testing, heat affected zone hardness testing and parent material hardness testing.

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