A heat treatment method for improving the welding performance of ZG42CrMo cast steel parts

Abstract

This disclosure relates to the field of heat treatment of cast steel raw materials, and provides a heat treatment method for improving the weldability of ZG42CrMo cast steel parts. The heat treatment method for improving the weldability of ZG42CrMo cast steel parts provided by this disclosure includes the following steps: high-temperature annealing of the ZG42CrMo integral cast steel part; preheating of the local defect area of ​​the cast steel part before welding; welding repair of the defects in the cast steel part using B3 type welding materials from the Cr-Mo steel system; and quenching and tempering heat treatment of the repaired integral cast steel part, followed by tempering. The heat treatment method for improving the weldability of ZG42CrMo cast steel parts provided by this disclosure, by first performing high-temperature annealing on the integral cast steel part before welding repair, can reduce the welding risks such as cracking that may occur during the subsequent welding repair process; by using B3 type welding materials from the Cr-Mo steel system to weld repair of the defects in the cast steel part, and then performing quenching and tempering heat treatment on the integral cast steel part after welding repair, it can ensure that the cast steel part and its weld have a good balance of strength, hardness, toughness, and plasticity, thereby meeting the performance requirements.

Description

Technical Field

[0001] This disclosure relates to the field of heat treatment of cast steel raw materials, specifically a heat treatment method for improving the welding performance of ZG42CrMo cast steel parts. Background Technology

[0002] Gravity-cast steel parts, due to the material's solidification shrinkage properties, may develop inherent casting defects, such as cracks, shrinkage cavities, and porosity, both internally and externally. These defects can lead to cracking during use and even safety accidents. Therefore, welding repair of cast steel parts is a crucial step in the production process. However, high-strength, high-hardness ZG42CrMo cast steel parts have poor weldability, and the welds are prone to cracking. Low-carbon stainless steel A507 welding material is typically used for welding repairs to reduce the risk of weld cracking. However, the strength and hardness of the weld after repair are often poor, failing to meet the performance requirements of a good balance between strength, hardness, toughness, and plasticity. Summary of the Invention

[0003] In order to solve the above-mentioned technical problems, or at least partially solve the above-mentioned technical problems, this disclosure provides a heat treatment method to improve the welding performance of ZG42CrMo cast steel parts.

[0004] This disclosure provides a heat treatment method for improving the weldability of ZG42CrMo cast steel parts, including:

[0005] High-temperature annealing treatment was performed on the ZG42CrMo integral cast steel parts;

[0006] Preheating treatment is performed on the local defect areas of the cast steel part before welding;

[0007] The defects in the cast steel parts were repaired by welding using B3 type welding materials from the Cr-Mo steel system.

[0008] The welded and repaired cast steel parts are subjected to quenching and tempering heat treatment.

[0009] Optionally, the high-temperature annealing treatment of the ZG42CrMo integral cast steel part specifically includes:

[0010] The furnace temperature is less than or equal to 300℃. The cast steel part is heated to 650℃ at a heating rate of less than or equal to 110℃ / h and held at that temperature for 2 to 6 hours. Then, the cast steel part is heated to 920℃ to 960℃ at a heating rate of less than or equal to 80℃ / h and held at that temperature for 6 to 10 hours. After the holding time is completed, the furnace is cooled.

[0011] Optionally, the preheating treatment of the local defect area of ​​the cast steel part before welding specifically includes: preheating the local defect area of ​​the cast steel part at a temperature of 150°C or higher before welding, and controlling the interpass temperature of the cast steel part to within 400°C, wherein the preheating is carried out by local flame heating, and the heating range is at least 75mm around the defect.

[0012] Optionally, the welding repair of defects in the cast steel part using B3 type welding materials from the Cr-Mo steel system specifically includes:

[0013] The defects in the cast steel parts are repaired by welding using one of the following welding materials: E9018-B3, E9015-B3, or E9016-B3.

[0014] Optionally, an arc welding method can be used, in which a DC welding machine is used to weld and repair defects in the cast steel part by connecting the welding material to the positive pole and the workpiece to the negative pole.

[0015] Optionally, B3 type welding material with a diameter of 3.2mm is used, and the welding current is controlled between 80A and 140A, the welding voltage is controlled between 20V and 26V, and the welding speed is controlled between 80mm / min and 400mm / min.

[0016] Alternatively, use B3 type welding material with a diameter of 4.0mm, and control the welding current between 120A and 170A, the welding voltage between 20V and 28V, and the welding speed between 100mm / min and 400mm / min.

[0017] Alternatively, use B3 type welding materials with a diameter of 5.0mm, and control the welding current between 180A and 240A, the welding voltage between 20V and 32V, and the welding speed between 100mm / min and 400mm / min.

[0018] Optionally, during arc ignition, the end of the welding material is brought into contact with the surface of the cast steel part to form a short circuit, and then the welding material is lifted upwards by 2mm to 4mm; after the arc is ignited, segmented back welding and multi-layer multi-pass welding are used to repair the defects of the cast steel part; before the arc is interrupted and the welding is completed, the arc crater at the end is filled.

[0019] Optionally, the quenching and tempering heat treatment of the welded integral cast steel part, which involves quenching followed by tempering, specifically includes:

[0020] First, perform quenching heat treatment: the furnace temperature is less than or equal to 300℃, and the cast steel part is heated to 650℃ at a heating rate of less than or equal to 110℃ / h for uniform holding for 2 to 6 hours. Then, the cast steel part is heated to 920℃ to 960℃ at a heating rate of less than or equal to 80℃ / h for holding for 6 to 10 hours. After holding, it is quenched in polymer for cooling.

[0021] Then, tempering is performed: the furnace temperature is less than or equal to 300℃, the cast steel part is heated to 350℃ at a heating rate of less than or equal to 110℃ / h and held at that temperature for 2 to 6 hours. Then, the cast steel part is heated to 620℃ to 640℃ at a heating rate of less than or equal to 80℃ / h and held at that temperature for 8 to 12 hours. After the holding time is completed, the part is air-cooled.

[0022] Optionally, before performing preheating treatment on the local defect area of ​​the cast steel part, the method further includes:

[0023] The cast steel parts are pre-treated before welding by grinding to remove oil and rust from their surface.

[0024] Optionally, after repairing the defects in the cast steel part using B3 type welding materials from the Cr-Mo steel system, the method further includes:

[0025] Hydrogen removal treatment at 350℃ is performed after welding.

[0026] The technical solution provided in this disclosure has the following advantages compared with the prior art:

[0027] The heat treatment method for improving the weldability of ZG42CrMo cast steel parts provided in this embodiment first involves high-temperature annealing of the entire ZG42CrMo cast steel part. This high-temperature annealing utilizes the full diffusion of atoms to eliminate the inhomogeneity of chemical composition and microstructure within the cast steel part. Simultaneously, the high-temperature annealing causes the internal grain structure of the cast steel part to grow, thereby reducing the strength and hardness of the cast steel part, improving its weldability, and reducing the welding risks such as cracking that may occur during subsequent welding repair processes. Then, B3 type welding materials from the Cr-Mo steel system are used to weld repairs to the defects in the cast steel part. After welding repair, the entire ZG42CrMo cast steel part is then... The quenching and tempering heat treatment of cast steel parts first results in a good balance of strength and toughness, with both high strength and hardness, as well as excellent toughness and plasticity. Since the composition of the B3 type welding material in the Cr-Mo steel system is similar to that of the base material ZG42CrMo, the quenching and tempering heat treatment can also ensure that the weld seam of the cast steel parts has a good balance of strength, hardness, toughness, and plasticity. This ensures that the overall cast steel parts after welding repair have excellent performance, and that their strength, hardness, toughness, and plasticity all meet the performance requirements. Attached Figure Description

[0028] The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments consistent with this disclosure and, together with the description, serve to explain the principles of this disclosure.

[0029] To more clearly illustrate the technical solutions in the embodiments of this disclosure or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 This is a schematic flowchart of a heat treatment method for improving the welding performance of ZG42CrMo cast steel parts according to an embodiment of the present invention.

[0031] Figure 2 This is a graph showing the relationship between time and temperature in a high-temperature annealing heat treatment according to an embodiment of the present invention.

[0032] Figure 3 This is a graph showing the relationship between time and temperature in the quenching heat treatment according to an embodiment of the present invention.

[0033] Figure 4 This is a graph showing the relationship between the tempering heat treatment time and temperature according to an embodiment of the present invention;

[0034] Figure 5 This is a schematic diagram of the welding bevel structure according to an embodiment of the present invention. Detailed Implementation

[0035] To better understand the above-mentioned objectives, features, and advantages of this disclosure, the solutions disclosed herein will be further described below. It should be noted that, unless otherwise specified, the embodiments and features described herein can be combined with each other.

[0036] Numerous specific details are set forth in the following description in order to provide a full understanding of this disclosure, but this disclosure may also be implemented in other ways different from those described herein; obviously, the embodiments in the specification are only some, and not all, of the embodiments of this disclosure.

[0037] The heat treatment method for improving the weldability of ZG42CrMo cast steel parts is described in detail below through specific embodiments:

[0038] Reference Figure 1 As shown, an embodiment of the present invention provides a heat treatment method for improving the welding performance of ZG42CrMo cast steel parts, comprising the following steps:

[0039] S101, high-temperature annealing treatment is performed on the ZG42CrMo integral cast steel parts;

[0040] S102, preheating treatment is performed on the local defect area of ​​the cast steel part before welding;

[0041] S103, using B3 type welding materials from the Cr-Mo steel system to weld and repair defects in cast steel parts;

[0042] S104 is a tempering heat treatment method for welded and repaired integral cast steel parts, which involves quenching followed by tempering.

[0043] In practice, the ZG42CrMo cast steel parts are first subjected to high-temperature annealing. This utilizes the full diffusion of atoms at high temperatures to improve or eliminate various structural defects and residual stresses caused during the casting process, preventing deformation and cracking. Simultaneously, high-temperature annealing causes the internal grain structure of the cast steel to grow, thereby reducing the strength and hardness of the ZG42CrMo cast steel, improving weldability, minimizing welding defects caused by subsequent welding repairs, and preparing the microstructure for the post-weld tempering heat treatment (quenching followed by tempering). Secondly, casting defects such as cracks, shrinkage cavities, and porosity are locally preheated before welding. This reduces the cooling rate of the weld joint, avoids the formation of hardened structures, reduces welding stress and deformation, and prevents welding cracks. Then, after preheating the local defect areas of the cast steel parts, the defects are repaired using B3 type welding materials from the Cr-Mo steel system. The composition of B3 type welding materials from the Cr-Mo steel system is similar to that of the base material ZG42CrMo. The composition of 42CrMo is similar. The carbon content of the B3 type welding material in the Cr-Mo steel system is higher than that of the traditional stainless steel A507 welding material. After subsequent quenching and tempering heat treatment, it can still guarantee a certain strength requirement. Finally, the integral cast steel part after welding repair undergoes quenching and tempering heat treatment, i.e., quenching and tempering heat treatment, so that the cast steel part obtains a good balance of strength and toughness, with both high strength and hardness and excellent toughness and plasticity. Since the composition of the B3 type welding material in the Cr-Mo steel system is similar to that of the base material ZG42CrMo, after quenching and tempering heat treatment, it can also ensure that the weld position of the cast steel part obtains a good balance of strength, hardness, toughness and plasticity. This ensures that the integral cast steel part after welding repair has excellent performance, and that its strength, hardness, toughness and plasticity all meet the performance requirements. This solves the problem that the weld of high-strength, high-hardness ZG42CrMo cast steel parts is prone to cracking, and the strength, hardness and other properties of the weld position after welding repair do not meet the requirements.

[0044] It should be noted that in the embodiments of this disclosure, since the welding repair is performed first, followed by quenching and tempering heat treatment, the weld is considered part of the cast steel part from a material perspective when the quenching and tempering treatment is performed after the welding repair. If the welding material used for the welding repair has a low carbon content, such as stainless steel A507 welding material or ordinary Mn-Mo steel-based welding material, the strength of the weld in the cast steel part after the quenching and tempering treatment will become lower and will not meet the strength requirements. In other words, traditional stainless steel A507 welding material and Mn-Mo steel-based welding material can no longer meet the requirements. However, since the alloy composition of B3 type welding material in Cr-Mo steel is similar to that of the base material ZG42CrMo, after quenching and tempering treatment, it can also ensure that the weld position of the cast steel part achieves a good balance of strength, hardness, toughness, and plasticity, thereby ensuring that the overall cast steel part after the welding repair has excellent performance, and that its strength, hardness, toughness, and plasticity all meet the performance requirements.

[0045] Furthermore, it should be understood that the quenching and tempering heat treatment employed in S104 of this disclosure differs from conventional post-weld heat treatment aimed at relieving stress, such as stress-relieving annealing or high-temperature tempering. Conventional post-weld heat treatment typically involves lower heating temperatures, generally between 500°C and 680°C. Conventional post-weld heat treatment processes can only partially eliminate the internal stress of cast steel parts; however, they cannot effectively overcome the performance degradation caused by excessive growth and coarsening of the internal structure of the cast steel parts due to pre-weld high-temperature annealing. Therefore, if conventional post-weld heat treatment processes are used, it is impossible to effectively guarantee that the welded cast steel parts possess excellent strength and toughness. In contrast, this disclosure effectively ensures the weldability of cast steel parts through pre-weld high-temperature annealing, and by using B3-class welding materials during welding and post-weld quenching and tempering heat treatment, it effectively ensures that the overall cast steel parts after welding possess excellent strength and toughness.

[0046] Specifically, in S101, the integral ZG42CrMo cast steel parts undergo high-temperature annealing treatment, referring to... Figure 2As shown, the specific process includes: The initial furnace temperature is ≤300℃. The cast steel parts are heated to 650℃ at a heating rate ≤110℃ / h for uniform holding. Specifically, the heating rate is determined based on the size of the workpiece and the furnace load during production. The holding time is 2 to 6 hours. Then, the cast steel parts are heated to 920℃ to 960℃ at a heating rate ≤80℃ / h for holding for 6 to 10 hours. After holding, the parts are allowed to cool naturally in the furnace. Different furnace loads correspond to different furnace cooling times, which vary significantly. After high-temperature annealing, the ZG42CrMo cast steel parts have a more uniform chemical composition and internal structure, reduced residual stress, and increased internal grain growth, resulting in lower hardness and increased weldability. This facilitates the welding repair of defects in the ZG42CrMo cast steel parts and reduces the risk of cracking during the welding process. Furthermore, in this embodiment, the defects of the ZG42CrMo cast steel parts are repaired by welding before the ZG42CrMo cast steel parts are heat-treated. This avoids the risk that the strength and hardness of the ZG42CrMo cast steel parts will increase after the heat treatment, resulting in poor weldability and ultimately leading to weld cracking or even failure to weld.

[0047] In some embodiments, in S102, preheating the local defect area of ​​the cast steel part before welding specifically includes: preheating the local defect area of ​​the cast steel part at a temperature of 150°C or higher before welding, controlling the interpass temperature of the cast steel part below 400°C, wherein the preheating is performed by local flame heating, and the heating range is at least 75mm around the defect. Preheating the ZG42CrMo cast steel part before welding can mainly prevent cold cracks, hot cracks, and hardened structures in the heat-affected zone, which would affect the weld quality, and can also prevent crack formation. Preheating methods mainly include flame heating, furnace heating, and far-infrared heating; this disclosure does not further limit these methods, as long as they can achieve the effect of improving weld quality.

[0048] Furthermore, before performing preheating treatment on localized defect areas of the cast steel parts, the process also includes: pre-treatment of the cast steel parts by grinding to remove oil and rust from their surface. Understandably, pre-treatment also removes the effects of oil, rust, and moisture on weld quality, improves welding performance, and enhances the surface appearance of the weld.

[0049] In some embodiments, after repairing defects in the cast steel part using B3 type welding materials in the Cr-Mo steel system, the process further includes: performing a hydrogen removal treatment at 350°C post-weld. Specifically, the hydrogen removal treatment at 350°C after welding and before tempering heat treatment promotes the escape of hydrogen from the weld, prevents defects such as porosity, prevents crack formation, improves weld quality, and enhances the weldability of ZG42CrMo cast steel parts.

[0050] In some embodiments, in S103, B3 type welding consumables from the Cr-Mo steel system are used to repair defects in the cast steel parts. Specifically, this includes using E9018-B3 welding consumables to repair defects in the cast steel parts. The alloy composition of E9018-B3 welding consumables is similar to that of the base material ZG42CrMo. After quenching and tempering, it can ensure that both the base material and the weld achieve a good balance of strength and toughness, meeting the performance requirements of strength, hardness, toughness, and plasticity. Specifically, the tensile strength of E9018-B3 welding consumables is 730 MPa, the yield strength is 574 MPa, the elongation is 19%, and the impact energy is 77 J. Of course, in other implementations, the welding material can also be other B3 type welding materials in the Cr-Mo steel system besides E9018-B3 welding material, such as 9015-B3 welding material, 9016-B3 welding material, etc. In the welding material model, B3 represents alloy, 90 represents strength, and 15, 16, 18 represent coating type. The coating type does not affect the welding performance, as long as it is a high-strength B3 type welding material that can meet the strength requirements.

[0051] In one specific embodiment, a B3 type welding material with a diameter of 3.2 mm is used. Specifically, the welding material can be any one of the E9018-B3 welding material, E9015-B3 welding material, and E9016-B3 welding material listed above. Correspondingly, the welding current is controlled between 80A and 140A, the welding voltage is controlled between 20V and 26V, and the welding speed is controlled between 80mm / min and 400mm / min.

[0052] In another specific implementation, B3 type welding materials with a diameter of 4.0 mm are used. Specifically, any one of the E9018-B3 welding materials, E9015-B3 welding materials, and E9016-B3 welding materials listed above can be used. Correspondingly, the welding current is controlled between 120A and 170A, the welding voltage is controlled between 20V and 28V, and the welding speed is controlled between 100mm / min and 400mm / min.

[0053] In another specific embodiment, a B3 type welding material with a diameter of 5.0 mm is used. Specifically, the welding material can be any one of the E9018-B3 welding material, E9015-B3 welding material, and E9016-B3 welding material listed above. Correspondingly, the welding current is controlled between 180A and 240A, the welding voltage is controlled between 20V and 32V, and the welding speed is controlled between 100mm / min and 400mm / min.

[0054] Specifically, for defects of varying degrees in ZG42CrMo cast steel parts, different diameters of B3 type welding materials are selected as needed, and the corresponding welding current, welding voltage and welding speed are matched to repair the ZG42CrMo cast steel parts by welding.

[0055] In some embodiments, an electric arc welding method is used to repair defects in cast steel parts. Taking E9018-B3 welding material as an example, the E9018-B3 welding material and the ZG42CrMo cast steel part to be welded are used as two electrodes. The arc heat between the welding rod and the workpiece is used to melt the metal and repair the ZG42CrMo cast steel part, thereby making up for the defects in the cast steel part and reducing the scrap rate of the cast steel part.

[0056] In some embodiments, a DC welding machine is used to repair defects in cast steel parts by using a DC reverse polarity method where the welding material is connected to the positive electrode and the workpiece is connected to the negative electrode. This DC reverse polarity welding method allows the oxide film on the surface of ZG42CrMo cast steel parts to be removed under the action of the electric arc, resulting in a bright, beautiful, and well-formed weld, thereby improving the surface performance of ZG42CrMo cast steel parts after welding repair.

[0057] Specifically, during welding repair, the striking method is used when igniting the arc, where the end of the welding material contacts the surface of the cast steel part to form a short circuit. The welding material is then lifted upwards by 2mm to 4mm. After the arc is ignited, segmented back-welding and multi-layer, multi-pass welding are used to repair defects in the cast steel part, reducing the risk of deformation caused by welding stress. Before the arc is interrupted and welding is completed, the crater at the end is filled. If the arc is immediately broken at the end, a crater lower than the surface of the weldment will be formed, potentially causing crater cracks.

[0058] To ensure welding quality, the weld bevel can be referenced. Figure 5 The design shown has a weld bevel angle α greater than 5 degrees, i.e., α > 5°; in the area indicated by b in the figure, the weld bevel has no sharp corners or sudden changes in cross-section; in the area indicated by c in the figure, the bottom of the weld bevel has a smooth transition.

[0059] In some embodiments, in S104, the integral cast steel part after welding repair is subjected to quenching and tempering heat treatment, specifically, the ZG42CrMo cast steel part, including the weld, is subjected to quenching and tempering heat treatment after welding repair.

[0060] The specific heat treatment steps for tempering include: first, quenching heat treatment: the furnace temperature is less than or equal to 300℃, and the cast steel part is heated to 650℃ at a heating rate of less than or equal to 110℃ / h for uniform holding for 2 to 6 hours; then, the cast steel part is heated to 920℃ to 960℃ at a heating rate of less than or equal to 80℃ / h for holding for 6 to 10 hours; after holding, it is quenched in a polymer cooler, referring to... Figure 3 As shown.

[0061] Then, tempering is performed: the furnace temperature is less than or equal to 300℃, and the cast steel is heated to 350℃ at a heating rate of less than or equal to 110℃ / h for uniform holding for 2 to 6 hours. Then, the cast steel is heated to 620℃ to 640℃ at a heating rate of less than or equal to 80℃ / h for holding for 8 to 12 hours. After holding, it is cooled with air. (Refer to...) Figure 4 As shown.

[0062] In this embodiment, the quenching and tempering heat treatment must consider not only the material properties but also the welding characteristics. Welding stress is high, and rapid heating can cause cracking. Therefore, an equalization zone is added during heating to reduce thermal stress and minimize weld defects.

[0063] Metallographic observation revealed that the quenched and tempered ZG42CrMo ultimately acquired a granular bainitic structure. Mechanical property tests showed that the quenched and tempered ZG42CrMo met the following requirements: tensile strength of 850-1000 MPa, yield strength ≥700 MPa, elongation ≥10%, and impact energy ≥27 J. Both strength and toughness / plasticity met the performance requirements.

[0064] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes the element.

[0065] The above are merely specific embodiments of this disclosure, enabling those skilled in the art to understand or implement this disclosure. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this disclosure. Therefore, this disclosure is not to be limited to these embodiments, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A heat treatment method for improving the weldability of ZG42CrMo cast steel parts, characterized in that, include: The ZG42CrMo integral cast steel parts are subjected to high-temperature annealing treatment. The furnace entry temperature is less than or equal to 300℃. The cast steel parts are heated to 650℃ at a heating rate of less than or equal to 110℃ / h and held at that temperature for 2 to 6 hours. Then, the cast steel parts are heated to 920℃ to 960℃ at a heating rate of less than or equal to 80℃ / h and held at that temperature for 6 to 10 hours. After the holding time is completed, the parts are furnace cooled. Preheating treatment is performed on the local defect area of ​​the cast steel part before welding. The local defect area of ​​the cast steel part is preheated at a temperature of 150°C or higher before welding, and the interpass temperature of the cast steel part is controlled within 400°C. The preheating is performed by local flame heating, and the heating range is at least 75mm around the defect. The defects in the cast steel parts were repaired by welding using B3 type welding materials from the Cr-Mo steel system. The welded integral cast steel part undergoes a quenching and tempering heat treatment, specifically quenching followed by tempering. The quenching process begins with a furnace temperature of ≤300℃, followed by heating to 650℃ at a rate of ≤110℃ / h and holding for 2-6 hours. Then, the part is heated to 920-960℃ at a rate of ≤80℃ / h and held for 6-10 hours. After holding, the part is quenched in a polymer cooler. The tempering process then follows: a furnace temperature of ≤300℃, followed by heating to 350℃ at a rate of ≤110℃ / h and holding for 2-6 hours. Then, the part is heated to 620-640℃ at a rate of ≤80℃ / h and held for 8-12 hours. After holding, the part is air-cooled.

2. The heat treatment method for improving the welding performance of ZG42CrMo cast steel parts according to claim 1, characterized in that, The specific steps of repairing defects in the cast steel parts using B3 type welding materials from the Cr-Mo steel system include: The defects in the cast steel parts are repaired by welding using one of the following welding materials: E9018-B3, E9015-B3, or E9016-B3.

3. The heat treatment method for improving the welding performance of ZG42CrMo cast steel parts according to claim 2, characterized in that, The defects in the cast steel parts are repaired by welding using an arc welding method, with the welding material connected to the positive pole and the workpiece connected to the negative pole using a DC reverse polarity method.

4. The heat treatment method for improving the welding performance of ZG42CrMo cast steel parts according to claim 3, characterized in that, Use B3 type welding material with a diameter of 3.2mm, and control the welding current between 80A and 140A, the welding voltage between 20V and 26V, and the welding speed between 80mm / min and 400mm / min. Alternatively, use B3 type welding material with a diameter of 4.0mm, and control the welding current between 120A and 170A, the welding voltage between 20V and 28V, and the welding speed between 100mm / min and 400mm / min. Alternatively, use B3 type welding materials with a diameter of 5.0mm, and control the welding current between 180A and 240A, the welding voltage between 20V and 32V, and the welding speed between 100mm / min and 400mm / min.

5. The heat treatment method for improving the welding performance of ZG42CrMo cast steel parts according to claim 3, characterized in that, When igniting the welding arc, the end of the welding material is brought into contact with the surface of the cast steel part to form a short circuit, and then the welding material is lifted upward by 2mm to 4mm; after the arc is ignited, segmented back welding and multi-layer multi-pass welding are used to repair the defects of the cast steel part. Before the arc is interrupted and the welding is completed, fill the crater at the end.

6. The heat treatment method for improving the weldability of ZG42CrMo cast steel parts according to any one of claims 1 to 5, characterized in that, Before performing preheating treatment on the local defect area of ​​the cast steel part, the procedure also includes: The cast steel parts are pre-treated before welding by grinding to remove oil and rust from their surface.

7. The heat treatment method for improving the weldability of ZG42CrMo cast steel parts according to any one of claims 1 to 5, characterized in that, After repairing the defects in the cast steel part by welding with B3 type welding material from the Cr-Mo steel system, the process further includes: Hydrogen removal treatment at 350℃ is performed after welding.

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