Preheating method for gas shielded welding of high strength wear resistant steel and welding method

Abstract

This invention discloses a preheating method for gas shielded welding of high-strength wear-resistant steel, comprising the steps of: determining the time t8 for the high-strength wear-resistant steel welded joint to cool from 800℃ to 500℃ based on the maximum allowable hardness of the welded joint. / 5; Based on t8 / 5. The preheating temperature before welding is determined based on the plate thickness of the high-strength wear-resistant steel weldment; the preheating time before welding is determined based on the preheating temperature and the plate thickness of the high-strength wear-resistant steel weldment; the preheating temperature and preheating are used to perform preheating of the high-strength wear-resistant steel weldment before welding. This invention also discloses a gas-shielded welding method for high-strength wear-resistant steel. The method described in this invention can improve the welding efficiency of high-strength wear-resistant steel while obtaining good weld joint quality.

Description

Technical Field

[0001] This invention relates to a welding method, and more particularly to a gas shielded welding method. Background Technology

[0002] High-strength wear-resistant steel is a type of steel with high wear resistance, high strength, and high toughness. Its yield strength reaches 1100MPa, its tensile strength is 1400MPa, and its impact energy at -40℃ is greater than 35J. Due to its excellent wear resistance and superior comprehensive performance, it is now widely used in fields such as engineering machinery.

[0003] High-strength wear-resistant steel is primarily used for joining components in engineering applications via welding. However, its carbon equivalent is 0.497, and its cold cracking sensitivity coefficient is 0.312, making it highly susceptible to cold cracking after welding. Furthermore, the microstructure and properties of the weld and heat-affected zone differ from those of the base metal after welding, resulting in reduced strength and wear resistance. Consequently, welded structural components made of high-strength wear-resistant steel frequently crack during use, significantly impacting their service life.

[0004] Therefore, for high-strength wear-resistant steel with high carbon equivalent, large cold crack sensitivity coefficient, and easy cold cracking after welding, it is desirable to provide a welding method that can improve the service life of wear-resistant steel welded structural components in engineering machinery while ensuring high strength, toughness and wear resistance of the welded joint. Summary of the Invention

[0005] One of the objectives of this invention is to provide a preheating method for gas shielded welding of high-strength wear-resistant steel. This method can determine the preheating temperature for high-strength wear-resistant steel of different thicknesses and establish the relationship between plate thickness and different preheating times. This allows high-strength wear-resistant steel of different thicknesses to complete the preheating treatment in the shortest possible time, thereby improving the welding efficiency of high-strength wear-resistant steel and obtaining good weld joint quality.

[0006] To achieve the above objectives, the present invention provides a preheating method for gas shielded welding of high-strength wear-resistant steel, comprising the following steps: Based on the maximum allowable hardness of high-strength wear-resistant steel welded joints, the cooling time from 800℃ to 500℃ for high-strength wear-resistant steel welded joints was determined. ; based on The preheating temperature before welding is determined by the plate thickness of the high-strength wear-resistant steel welded parts. The preheating time before welding is determined based on the preheating temperature and the plate thickness of the high-strength wear-resistant steel weldment. The preheating temperature and preheating time are used to preheat the high-strength wear-resistant steel weldment before welding.

[0007] Furthermore, in the preheating method described in this invention, the following formula is used to determine... : ; ; in, What? max The value represents the maximum allowable hardness of the welded joint of high-strength wear-resistant steel, with the unit parameter being HV; C and Mn represent the mass percentage content of C and Mn elements in high-strength wear-resistant steel, respectively. This represents a coefficient related to the composition of high-strength wear-resistant steel, which can be expressed by the formula... Calculated; The martensite composition history curve represents the change in martensite composition with time t. 8 / 5 The constant for increasing the steepness ranges from 7 to 16, and within this range, the value decreases as the C and Mn contents increase. This represents the inverse error function.

[0008] Furthermore, in the preheating method described in this invention, the preheating temperature is determined based on the following formula: Where b represents the plate thickness of the high-strength wear-resistant steel welded component, with the unit parameter being mm, and T 预热 This indicates the preheating temperature, with the unit parameter being °C.

[0009] Furthermore, in the preheating method described in this invention, the preheating time T is determined based on the following formula. 总 : Where K is the heat preservation time per unit thickness of high-strength wear-resistant steel, with a unit parameter of min / mm and a value range of 1.5-3; b is the plate thickness of the welded high-strength wear-resistant steel component, with a unit parameter of mm; T 预热 The preheating temperature is expressed in °C (i.e., the preheating temperature determined in the previous step); t r v represents the current room temperature, with its unit parameter being °C; t The heating rate is expressed in °C / min.

[0010] Another objective of this invention is to provide a gas-shielded welding method for high-strength wear-resistant steel, which can improve the welding efficiency of high-strength wear-resistant steel and obtain good weld joint quality based on the determination of the preheating process.

[0011] Based on the above-mentioned objectives, the present invention also provides a gas-shielded welding method for high-strength wear-resistant steel, comprising the following steps: The high-strength wear-resistant steel welded parts were preheated using the preheating method described above. Manual welding is used for the root pass. Gas shielded welding was used for filling and capping welding.

[0012] Furthermore, in the welding method described in this invention, in the step of performing the root pass welding using manual welding, the welding current is controlled to be 140-160A and the welding voltage is 18V-21V.

[0013] In this embodiment, a lower current and voltage are used for manual welding of the root pass, which causes the molten droplets to exhibit a short-circuit transition, resulting in a root pass weld with better welding quality.

[0014] Furthermore, in the welding method described in this invention, in the steps of filling and capping welding using gas shielded welding, the droplet transfer mode is controlled to be jet transfer, the welding current is controlled to be 270-290A, and the welding voltage is controlled to be 28-30V.

[0015] In this embodiment, a large current and high voltage are used during weld filling. On the one hand, this makes the molten droplets exhibit jet transition, increasing the welding speed. On the other hand, it also increases the spreadability of the molten weld metal, resulting in a lower weld joint height, a smooth transition at the weld toe, less spatter, and no undercut or slag inclusions.

[0016] Furthermore, in the welding method described in this invention, during the steps of filling and capping welding using gas shielded welding, the interpass temperature is controlled between 150°C and 200°C.

[0017] Furthermore, in the welding method described in this invention, after the filling and cover welding steps using gas shielded welding, the method further includes the step of cooling the weld to 100°C-300°C and holding it at that temperature.

[0018] Cooling the weld to 100℃-300℃ and holding it at that temperature helps reduce hydrogen in the weld joint, decreases the occurrence of cold cracks, and improves the overall mechanical properties of the weld joint.

[0019] Furthermore, in the welding method described in this invention, the weld is cooled to 100℃-300℃ and held for 1-3 hours.

[0020] The preheating method described in this invention can be used to design specific preheating processes for high-strength wear-resistant steels of different thicknesses, thus having wider applicability.

[0021] By employing the preheating method described in this invention, the relationship between the maximum hardness and the preheating temperature can be used to design the preheating temperature before welding. This reduces the experimental content related to the maximum hardness, saves experimental costs, and allows for the rapid development of appropriate process parameters. Consequently, preheating treatment of high-strength wear-resistant steel can be completed in the shortest possible time, thereby improving the welding efficiency of high-strength wear-resistant steel.

[0022] The preheating method described in this invention can ensure that the surface and center of the high-strength wear-resistant steel welded parts are at the same temperature, while also greatly saving energy.

[0023] The welding method described in this invention can achieve good weld joint quality, with uniform weld metal spread, smooth weld toe transition, and no defects such as spatter or inclusions.

[0024] The welding method described in this invention greatly reduces cold crack sensitivity, decreases the generation of cold cracks, significantly improves the quality of welded joints, increases the plasticity reserve of welded joints, reduces the occurrence of cracking failure in high-strength wear-resistant steel during service, and improves the service life of joints or structural components. Detailed Implementation

[0025] The preheating method and welding method for gas shielded welding of high-strength wear-resistant steel described in this invention will be further explained and described below with reference to specific embodiments. However, this explanation and description do not constitute an improper limitation on the technical solution of this invention.

[0026] In some implementations, high-strength wear-resistant steel components can be welded using 80kg-grade welding materials, and the gas-shielded welding method may include the following steps: Step 100: Determine the cooling time of the high-strength wear-resistant steel welded joint from 800℃ to 500℃ based on the following formula. : ; ; in, What? max The value represents the maximum allowable hardness of the welded joint of high-strength wear-resistant steel, with the unit parameter being HV; C and Mn represent the mass percentage content of C and Mn elements in high-strength wear-resistant steel, respectively. The coefficients related to the composition of high-strength wear-resistant steel can be obtained through composition calculations, using the following formula: ; The martensite composition history curve represents the change in martensite composition with time t. 8 / 5 The constant for increasing the steepness ranges from 7 to 16, and within this range, the value decreases as the C and Mn contents increase. This represents the inverse error function.

[0027] Step 200: Based on Determine the preheating temperature before welding: Where b represents the plate thickness of the high-strength wear-resistant steel welded component, with the unit parameter being mm, and T 预热 The preheating temperature is indicated by a unit of °C.

[0028] Step 300: Determine the preheating time before welding based on the preheating temperature and the plate thickness of the high-strength wear-resistant steel weldment. Where K is the heat preservation time per unit thickness of high-strength wear-resistant steel, with a unit parameter of mm / mm and a value range of 1.5-3; b is the plate thickness of the welded high-strength wear-resistant steel component, with a unit parameter of mm; T 预热 The preheating temperature is expressed in °C (i.e., the preheating temperature determined in the previous step); t r v represents the current room temperature, with its unit parameter being °C; t The heating rate is expressed in °C / min.

[0029] Step 400: Preheat the high-strength wear-resistant steel weldment using the preheating temperature and preheating time determined above.

[0030] In some more specific embodiments, before preheating for welding, the high-strength wear-resistant steel weldment is machined into a single-sided 30° V-groove or a single-sided 60° X-groove. First, a grinder is used to grind within a 30mm radius of the groove until a metallic luster appears. Then, the groove and the ground area are cleaned with alcohol to remove oil and reduce the source of hydrogen in the weld joint.

[0031] Step 500: Perform the root pass welding using manual welding.

[0032] In some more specific implementations, the welding current is controlled at 140-160A, the welding voltage at 18V-21V, and the welding speed at 193mm / min.

[0033] Step 600: Use gas shielded welding with a shielding gas of 80% Ar + 20% CO2 for filling and cover welding.

[0034] In some more specific embodiments, the droplet transfer mode is controlled as jet transfer, wherein the welding current is 270-290A, the welding voltage is 28-30V, the welding speed is 490mm / min, and the interpass temperature is controlled between 150℃ and 200℃ using an infrared thermometer.

[0035] Step 700: Cool the weld to 100℃-300℃ and hold for 1-3 hours.

[0036] Cooling the weld to 100℃-300℃ and holding it at that temperature helps reduce hydrogen in the weld joint, decreases the occurrence of cold cracks, and improves the overall mechanical properties of the weld joint.

[0037] Examples 1-4 To verify the technical solution of the present invention, Tables 1-1 and 1-2 list the parameters for determining the preheating temperature and preheating time in Examples 1-4, respectively.

[0038] Table 1-1. Table 1-2. Table 2 lists the manual welding process parameters used in Examples 1-4.

[0039] Table 2. Table 3 lists the welding process parameters and post-weld treatment processes for the gas shielded welding used in Examples 1-4.

[0040] Table 3. Observations of the high-strength wear-resistant steel welded joints and welds obtained in the above four embodiments revealed that they all achieved good welding quality, with no obvious visible defects and a smooth and uniform weld toe transition.

[0041] Furthermore, for the welded joints prepared in the above four embodiments, metallographic specimens were processed in the stable region (30mm removed from both ends of the weld). Subsequently, the specimens were polished with #180, #320, #400, #600, and #1000 SiC sandpaper, and the scratches were polished with 2.5µm diamond spray polishing agent. Finally, they were etched with 4% HNO3 alcohol to obtain the macroscopic morphology and metallographic structure of the welded joints. Notably, the coarse-grained region of the 16mm, 20mm, 25mm, and 30mm thick high-strength wear-resistant steel in Examples 1-4 all exhibited martensitic structure.

[0042] Following the cutoff point method in GB / T6394 standard, the grain size of the microstructure was measured to be between 45µm and 110µm. Subsequently, the microhardness of the coarse-grained region was measured using a weld joint area hardening characterizer. During the measurement, a loading force of 10kg was applied for 10s, yielding martensitic hardness values ​​between 380HV and 470HV. 。

[0043] In addition, tensile, impact and bending tests were performed on the welded joints of Examples 1-4, and the test results are listed in Table 4.

[0044] Table 4. As can be seen from Table 4, the welded joints of each embodiment have good comprehensive mechanical properties.

[0045] Therefore, the preheating method and welding method described in this invention can improve welding efficiency and obtain welded joints with excellent comprehensive mechanical properties.

[0046] It should be noted that the embodiments listed above are merely specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and similar changes or modifications made thereto are those that can be directly derived or easily conceived by those skilled in the art from the content disclosed in the present invention, and should all fall within the protection scope of the present invention.

Claims

1. A preheating method for gas shielded welding of high-strength wear-resistant steel, characterized in that, Including the following steps: Based on the maximum allowable hardness of high-strength wear-resistant steel welded joints, the cooling time from 800℃ to 500℃ for high-strength wear-resistant steel welded joints was determined. ; based on The preheating temperature before welding is determined by the plate thickness of the high-strength wear-resistant steel welded parts. The preheating time before welding is determined based on the preheating temperature and the plate thickness of the high-strength wear-resistant steel weldment. The preheating temperature and preheating time are used to preheat the high-strength wear-resistant steel weldment before welding. The determination is based on the following formula. : ； ； in, HV max This indicates the maximum allowable hardness of the welded joint of high-strength wear-resistant steel; C and Mn represent the mass percentage content of C and Mn elements in high-strength wear-resistant steel, respectively. This represents a coefficient related to the composition of high-strength wear-resistant steel. The martensite composition history curve represents the change in martensite composition with time t. 8 / 5 A constant that increases steepness; Represents the inverse error function; The preheating temperature is determined based on the following formula: Where b represents the plate thickness of the high-strength wear-resistant steel welded component, and T 预热 Indicates the preheating temperature; The preheating time T is determined based on the following formula. 总 : Where K is the heat preservation time per unit thickness of high-strength wear-resistant steel; b is the plate thickness of the welded high-strength wear-resistant steel component; t is the preheating temperature; r v is the current room temperature; t The heating rate is denoted as .

2. A gas-shielded welding method for high-strength wear-resistant steel, characterized in that, Including the following steps: The high-strength wear-resistant steel welded parts are preheated using the preheating method described in claim 1. Manual welding is used for the root pass. Gas shielded welding was used for filling and capping welding.

3. The welding method as described in claim 2, characterized in that, In the step of manual welding for the root pass, the welding current is controlled at 140-160A and the welding voltage is controlled at 18V-21V.

4. The welding method as described in claim 2, characterized in that, In the steps of filling and capping welding using gas shielded welding, the droplet transfer mode is controlled as jet transfer, the welding current is controlled as 270-290A, and the welding voltage is controlled as 28-30V.

5. The welding method as described in claim 2, characterized in that, In the steps of filling and capping welding using gas shielded welding, the interpass temperature is controlled between 150℃ and 200℃.

6. The welding method according to any one of claims 2-5, characterized in that, The process includes the following steps after the gas shielded welding steps for filling and covering: cooling the weld to 100°C-300°C and holding it at that temperature.

7. The welding method as described in claim 6, characterized in that, Cool the weld to 100℃-300℃ and hold for 1-3 hours.

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