The metal heat treatment process is the same as other natural sciences, and it develops with the development of productivity, and is closely related to the development of other science and technology. The heat treatment process is the result of the development of ancient metallurgical technology and is a science that has gradually developed as part of metallurgical technology. In recent years, our factory often encounters some problems: In the manufacturing process, the preliminary heat treatment that should be targeted and can only be used for the parts and components is mixed with the final heat treatment of the product, which are unclear, resulting in the organization and performance of the material and the original design. The request does not match. Mainly reflected in the pressure vessel made of carbon steel and low alloy steel for quenching (plus tempering), normalizing (plus tempering) two cases; for austenitic stainless steel in solid solution (plus stabilization) .
GB150 4. 2. 4 states: “For carbon steel and low-alloy steel steel plates that need to be heat-treated during the manufacturing process of the container, the delivery status of the steel mill may not be in Table 4-1 (Steel number, standard, and use state of the steel plate) And the use state in the allowable stress at a series of temperatures." The relevant literature also emphasizes that there should be evidence that the heat treatment required by the corresponding steel specification has been carried out and passed the test. Manufacturing is based on the design of the material processing, to ensure that the material use state meets the design requirements is the basic requirements for manufacturing. Therefore, it is necessary to clarify the purpose and effect of heat treatment and the correspondence between the objects.
First, analyze the problem
Generally, the heat treatment process is divided into two categories: final heat treatment and pre-heat treatment. The purpose of the final heat treatment is to achieve the performance requirements of the part or product, and the purpose of the pre-heat treatment is to eliminate or improve the defects caused by the previous process, and to prepare for performance and organization for the subsequent work. The same heat treatment method acts on different objects, which are called final heat treatment and pre-heat treatment, respectively. For example: When the post-weld heat treatment is only for parts, it is pre-heat treated; and for the entire product, it is the final heat treatment.
Here are some of the heat treatment forms that have appeared in our factory.
Post weld heat treatment
(1) Post-weld heat treatment. Using a metal to reduce the yield strength at high temperatures, a plastic rheology occurs in a place with high stress, thereby achieving a heat treatment for eliminating welding residual stress, which is a stress relief annealing (low temperature annealing) for carbon steel and low alloy steel pressure vessels. The product is slowly heated to 500 ~ 650 ° C, kept for a certain period of time, and then evenly cooled with the furnace. Stress is the response of the elastomeric lattice to deformation.
Post-weld heat treatment can serve:
1 Improve the plasticity and toughness of welded joints and improve the resistance to stress corrosion.
2 Eliminate internal stress and cold work hardening in welded joints, and improve joint resistance to brittle fracture.
3 Stabilize the shape of the welded components to avoid deformation during post-weld machining and use.
4 Promote the outward diffusion of hydrogen from the weld.
5 Some pressure vessels have high safety requirements (such as containing extremely or highly hazardous media), and post-weld heat treatment can improve their safety margin.
Post-weld heat treatment has a variety of effects, sometimes combined with dehydrogenation treatment, recovery and improved performance heat treatment, which can eliminate residual stress after cold forming and medium temperature forming of parts such as heads and cylinders.
(2) Hydrogen elimination treatment. Immediately after welding, the weldment is heated to a higher temperature to increase the diffusion capacity of hydrogen in the steel, so that the supersaturated hydrogen atoms in the weld metal accelerate the diffusion and escape, thereby reducing the heat treatment of the container to delay the possibility of cracking. 5å°æ—¶ã€‚ Generally, the heating time is between 200 and 350 ° C, the holding time is related to the thickness of the welded joint, generally ≥ 0. 5h. Containers requiring hydrogen elimination treatment, such as post-weld stress relief heat treatment immediately after welding, can be prevented from hydrogenation after welding, but controlled at 16 to 24 hours.
Not all metal materials will produce delayed cracks when soldered. The generation of delayed cracks is related to the strength level and chemical composition of the material. This phenomenon can only occur with low alloy steels with higher strength levels. Pressure vessels that generally require hydrogen removal require post-weld heat treatment, while equipment that requires post-weld heat treatment does not necessarily require hydrogen elimination.
The hydrogen-removing treatment is called dehydrogenation treatment in the related literature, that is, under the condition that the workpiece structure does not change, the hydrogen in the workpiece is diffused into the atmosphere by low-temperature heating and heat preservation.
GB150 4. 2. 4 states: “For carbon steel and low-alloy steel steel plates that need to be heat-treated during the manufacturing process of the container, the delivery status of the steel mill may not be in Table 4-1 (Steel number, standard, and use state of the steel plate) And the use state in the allowable stress at a series of temperatures." The relevant literature also emphasizes that there should be evidence that the heat treatment required by the corresponding steel specification has been carried out and passed the test. Manufacturing is based on the design of the material processing, to ensure that the material use state meets the design requirements is the basic requirements for manufacturing. Therefore, it is necessary to clarify the purpose and effect of heat treatment and the correspondence between the objects.
First, analyze the problem
Generally, the heat treatment process is divided into two categories: final heat treatment and pre-heat treatment. The purpose of the final heat treatment is to achieve the performance requirements of the part or product, and the purpose of the pre-heat treatment is to eliminate or improve the defects caused by the previous process, and to prepare for performance and organization for the subsequent work. The same heat treatment method acts on different objects, which are called final heat treatment and pre-heat treatment, respectively. For example: When the post-weld heat treatment is only for parts, it is pre-heat treated; and for the entire product, it is the final heat treatment.
Here are some of the heat treatment forms that have appeared in our factory.
Post weld heat treatment
(1) Post-weld heat treatment. Using a metal to reduce the yield strength at high temperatures, a plastic rheology occurs in a place with high stress, thereby achieving a heat treatment for eliminating welding residual stress, which is a stress relief annealing (low temperature annealing) for carbon steel and low alloy steel pressure vessels. The product is slowly heated to 500 ~ 650 ° C, kept for a certain period of time, and then evenly cooled with the furnace. Stress is the response of the elastomeric lattice to deformation.
Post-weld heat treatment can serve:
1 Improve the plasticity and toughness of welded joints and improve the resistance to stress corrosion.
2 Eliminate internal stress and cold work hardening in welded joints, and improve joint resistance to brittle fracture.
3 Stabilize the shape of the welded components to avoid deformation during post-weld machining and use.
4 Promote the outward diffusion of hydrogen from the weld.
5 Some pressure vessels have high safety requirements (such as containing extremely or highly hazardous media), and post-weld heat treatment can improve their safety margin.
Post-weld heat treatment has a variety of effects, sometimes combined with dehydrogenation treatment, recovery and improved performance heat treatment, which can eliminate residual stress after cold forming and medium temperature forming of parts such as heads and cylinders.
(2) Hydrogen elimination treatment. Immediately after welding, the weldment is heated to a higher temperature to increase the diffusion capacity of hydrogen in the steel, so that the supersaturated hydrogen atoms in the weld metal accelerate the diffusion and escape, thereby reducing the heat treatment of the container to delay the possibility of cracking. 5å°æ—¶ã€‚ Generally, the heating time is between 200 and 350 ° C, the holding time is related to the thickness of the welded joint, generally ≥ 0. 5h. Containers requiring hydrogen elimination treatment, such as post-weld stress relief heat treatment immediately after welding, can be prevented from hydrogenation after welding, but controlled at 16 to 24 hours.
Not all metal materials will produce delayed cracks when soldered. The generation of delayed cracks is related to the strength level and chemical composition of the material. This phenomenon can only occur with low alloy steels with higher strength levels. Pressure vessels that generally require hydrogen removal require post-weld heat treatment, while equipment that requires post-weld heat treatment does not necessarily require hydrogen elimination.
The hydrogen-removing treatment is called dehydrogenation treatment in the related literature, that is, under the condition that the workpiece structure does not change, the hydrogen in the workpiece is diffused into the atmosphere by low-temperature heating and heat preservation.
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