Method for gas shielded welding of martensitic ballistic steel of hardness 600 HBW

Abstract

The present application belongs to the technical field of steel material and steel material welding, and proposes a gas shielded welding method for a martensitic bulletproof steel with a hardness of 600HBW. The method adopts a shielded metal arc welding method, a direct current reverse polarity power supply, and a rich argon mixed protective gas. According to the low strength matching principle, a solid welding wire is selected. The same plate thickness combination butt joint is continuously welded in a multi-layer and multi-pass manner. The preheating temperature of the steel plate is 100-150 DEG C, the welding line energy is controlled at 10-15 KJ / cm, and the welding joint is slowly cooled after welding by using asbestos. The present application ensures that the welding joint meets the shaping and toughness requirements, has high yield strength and tensile strength, the yield strength of the welding joint is greater than 1300 MPa, and meets the bulletproof performance requirements after welding. For the low alloy ultra-high strength martensitic bulletproof steel with a hardness level of 580-640HBW, the welding joint and the base material do not have cracking and other problems after welding.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of steel materials and steel material welding, and particularly relates to a gas protection welding method of a martensitic bulletproof steel with a hardness of 600HBW. BACKGROUND

[0002] With the continuous development of weapons and equipment in the military field, lightening of modern weapons and equipment and improvement of the protection capability of weapons and equipment have become one of the focuses in the field of military manufacturing. The high-strength martensitic bulletproof steel has the characteristics of high strength, high hardness, low manufacturing cost and simple manufacturing process, and is widely applied in the field of weapons and equipment manufacturing. The preparation of structural parts by using the martensitic bulletproof steel to realize the thinning of the structural parts is an effective way to realize the lightening of equipment. Meanwhile, due to the high strength and high hardness of the martensitic bulletproof steel, the protection capability of the weapons and equipment is also improved to a certain extent. The components of the vehicle body and other equipment of the light armored vehicle manufactured by using the martensitic bulletproof steel can not only meet the requirements of the protection capability, but also reduce the self-weight of the equipment, reduce fuel consumption, improve the carrying capacity and maneuverability of the equipment, and improve the weapon level.

[0003] In the actual application process of the high-strength martensitic bulletproof steel, certain requirements are put forward for the welding performance of the steel plate. In the production process of special structural parts such as bulletproof parts of explosion-proof vehicles and explosion-proof doors, the bulletproof steel plate needs to be welded, and the performance of the welded joint will directly affect the application of the ultra-high-strength and ultra-high-hardness bulletproof steel. Therefore, the development of the welding process with high strength after welding significantly affects the application prospect of the martensitic bulletproof steel in the field of military industry and daily life.

[0004] The high-hardness martensitic bulletproof steel is generally alloyed by Cr, Ni, Mo and other elements, and is generally produced by using a heat treatment process of 'quenching + tempering' or a process of 'direct quenching + tempering' after rolling. The content of the alloying elements is low, the high strength and high hardness make the bulletproof performance excellent, and the steel is suitable for various working conditions. The TMCP technology can play the roles of refining grains and second-phase precipitation strengthening. In the quenching process, the alloying elements can improve the effective hardenability of the steel, so that the steel plate forms a uniform martensitic structure in the quenching process. The quenching stress is eliminated through low-temperature tempering, and the material has high strength, hardness and certain toughness through the dispersion precipitation of carbides.

[0005] In order to ensure that the martensitic bulletproof steel has sufficient hardness and strength, the carbon equivalent of the steel plate is relatively high, the hardenability is large, and the steel plate is sensitive to hydrogen-induced cracking. In the welding process, cold cracks are easily generated in the welding heat-affected coarse-grained zone and the fusion zone, which significantly reduces the toughness of the heat-affected zone. In addition, due to the change of the microstructure of the heat-affected zone in the welding process, the original fine martensitic structure is destroyed, the strength and hardness of the two-phase zone and the coarse-grained zone in the heat-affected zone decrease sharply, and the bulletproof performance of the final structural part is reduced.

[0006] Chinese patent CN201911286360.1, named "a medium plate armor steel laser swing welding method", although the welding process parameters are described in detail, but it belongs to the laser welding method, and it is not for the hardness 600HBW level of martensitic bulletproof steel plate, its welding process is completely different from this patent.

[0007] Chinese patent CN201610539596.1, named "a welding process for ensuring the bulletproof performance of bulletproof steel plate welding joint", belongs to the optimization of welded structure, and does not describe the welding process parameters in detail. The current domestic patent does not involve the welding process of the hardness 600HBW level of martensitic bulletproof steel plate. SUMMARY

[0008] The present application is to solve the above problems, for the HBW600 level of bulletproof steel, a gas shielded welding method of hardness 600HBW level of martensitic bulletproof steel is proposed, which can ensure that the wear-resistant steel welded joint has high tensile strength after welding, and the operation is easy to realize.

[0009] The technical scheme adopted by the present application is as follows:

[0010] The hardness 600HBW level of martensitic bulletproof steel produced by the smelting-continuous casting-controlled rolling+controlled cooling(TMCP)-quenching+tempering process has the following chemical composition by weight percentage: C: 0.34-0.42%, Si: 0.15-0.40%, Mn: 0.20-0.40%, P: ≤0.015, S≤0.003%, Cr: 0.4-0.6%, Ni: 0.9-1.8%, Mo: 0.1-0.6%, B: 0.001-0.003%, Al: 0.02-0.6%, Ti: 0.010-0.025%, V: 0.02-0.04%, and the balance is Fe and inevitable impurities. The mechanical properties of the steel plate are: tensile strength Rm≥2000MPa, elongation A≥8%, surface Brinell hardness: 580-640HBW; the thickness is 5-30mm, and the same thickness is used for splicing.

[0011] A gas shielded welding method of hardness 600HBW level of martensitic bulletproof steel, the specific steps are as follows:

[0012] Step 1. Select the hardness 600HBW level of martensitic bulletproof steel plate, the thickness of the steel plate is 5-30mm, and the same thickness is used for splicing;

[0013] Step 2. Select argon-rich mixed gas as the protective gas and yield strength ≥890MPa solid wire;

[0014] Step 3. The martensitic ballistic steel plate with hardness of 600 HBW and thickness greater than 10 mm is opened with double-sided asymmetric X-shaped groove or double-sided symmetric X-shaped groove at the joint to be welded, and the martensitic ballistic steel plate with hardness of 600 HBW and thickness less than or equal to 10 mm is opened with single V-shaped groove.

[0015] Step 4. The water, scale, rust, oil and paint and the like within the range of 50 mm on both sides of the joint to be welded are removed by mechanical or chemical method, and the dust and sundries are removed clean.

[0016] Step 5. The solid welding wire is dried before welding; the joint to be welded is preheated within the range of 150 mm on both sides of the welding seam of the martensitic ballistic steel plate with hardness of 600 HBW; the welding line energy and the interlayer temperature of the welding bead are controlled during the filling welding and the surface welding.

[0017] Step 6. The welding wire is elongated by 15-20 mm, and the multi-layer and multi-pass continuous welding is adopted; after the slag and surface spatter generated in the previous welding bead are cleaned in time, the next welding is continued.

[0018] Step 7. The joint is immediately treated for hydrogen removal after the welding is completed, and the joint is slowly cooled by using asbestos or other heat preservation materials for heat preservation.

[0019] The protective gas is argon-rich mixed gas with a volume ratio of 80% Ar + 20% CO2; the gas flow is 15-25 L / min; the purity of Ar is 99.99%, the water content is less than 15 ppm, the purity of CO2 is 99.9%, the water content is less than 40 ppm; after the gas is mixed and matched, the water content is less than 20 ppm.

[0020] According to the low-strength matching principle, the chemical composition of the high-strength solid welding wire is as follows: C≤0.12%, Si: 0.6-0.9%, Mn: 1.6-2.1%, Cr: 0.20-0.45%, Ni: 0.6-1.3%, Mo: 0.45-0.70%, Ti≤0.10%, Zr≤0.10%, V≤0.03%, Al≤0.12%, Cu≤0.30%, P≤0.015%, S≤0.018%, and the balance is Fe and inevitable impurities. The mechanical properties of the solid welding wire are as follows: yield strength (Rp0.2) ≥ 890 MPa, tensile strength (Rm) ≥ 940 MPa, elongation (A) ≥ 19%, and impact energy at -40℃ (Akv) ≥ 47 J.

[0021] In step 3, the single V-shaped or double-sided X-shaped groove is opened on the steel plate by mechanical processing; the groove angle of the welding joint is 40-60°, the groove angle of the single-sided steel plate is 20-30°, the groove bevel height is 0-2 mm, the gap between the joint groups is 1-2 mm, and the offset of the steel plate is less than 0.1t, t being the thickness of the plate in mm.

[0022] In step 5, the solid core welding wire is dried at 200 DEG C for 2h; the preheating temperature is 100-150 DEG C.

[0023] In the multi-layer multi-pass continuous welding mode, the welding gun inclination angle is 70-80 DEG ; the temperature between welding layers is not less than the preheating temperature; when filling welding and cap welding, the temperature between welding layers is controlled at 100-200 DEG C.

[0024] In the multi-layer multi-pass continuous welding mode, when base welding, according to the principle of ensuring penetration and reducing heat input, the welding current I is 120-180 A, the arc voltage U is 18-22 V, the welding speed v is 12-30 cm / min, and the welding line energy E is controlled at 10-15 KJ / cm; when filling welding and cap welding, the welding current I is 160-260 A, the arc voltage U is 22-28 V, the welding speed v is 12-30 cm / min, and the welding line energy E is controlled at 10-15 KJ / cm.

[0025] The step 7 is specifically that, after welding, the welded joint is immediately treated for hydrogen elimination, then the welded joint is heat-insulated for slow cooling by using heat-insulating materials, or 100 DEG C heat-insulation is adopted; the heat-insulation time is T=4*t, wherein T is the time in min, and t is the plate thickness in mm, and the total heat-insulation time is not less than 1h.

[0026] The martensitic bulletproof steel and the gas shielded welding method thereof can be used for low-alloy ultra-high-strength martensitic bulletproof steel with a hardness level of 580-640 HBW.

[0027] The characteristics of the application include that, for the high-hardness bulletproof steel of HBW600 level, small line energy argon-rich mixed gas shielded welding is adopted, high-strength welding wire of a yield strength of greater than or equal to 890 MPa is selected according to the low-strength matching principle for multi-layer multi-pass continuous welding, the preheating temperature before welding and the temperature between welding layers are strictly controlled, slow cooling or low-temperature tempering treatment is adopted after welding, the toughness and plasticity of the welded joint are improved while the strength of the welded joint is ensured, the yield strength of the welded joint is greater than 1300 MPa, and the bulletproof performance of the welded joint is ensured.

[0028] The high-hardness bulletproof steel is mainly in the form of martensite, is sensitive to welding cold cracks, and is prone to cracks in the fusion zone and coarse-grained heat-affected zone of the welded joint, the main factors affecting the cracks are the martensite structure, H atoms in the steel and restraint stress, and the adoption of appropriate line energy multi-layer multi-pass welding, preheating before welding and hydrogen elimination treatment after welding can effectively avoid the occurrence of welding cold cracks.

[0029] The welding line energy is too large, the high temperature stays for a long time during welding, the austenite organization is thick, the thick martensite organization is formed during subsequent cooling process, the micro crack is easily formed and is not conducive to preventing crack propagation, the welding line energy is too small, the cooling speed is too fast, the large welding residual stress is easily formed, the cold crack is not conducive to being generated, therefore, only in the certain line energy range, the welding cold crack can be effectively avoided.

[0030] When the multi-layer multi-pass welding is carried out, the subsequent welding pass plays the tempering effect on the previous welding pass and the heat affected zone, the welding stress can be released, the cooling speed is reduced and the H atom escape is promoted.

[0031] The slow cooling or tempering treatment is adopted after welding, the same effect of reducing the welding stress and promoting the H atom escape can also be achieved, and the higher the tempering temperature is, the greater the stress release and H atom escape promotion effect is, but as the tempering temperature increases, the strength will decrease and the tempering brittleness can be generated, therefore, the 100 DEG C tempering treatment is more appropriate.

[0032] In combination with the above points, the welding line energy is controlled in the range of 10-15 KJ / cm, the preheating temperature before welding is not less than 100 DEG C, the multi-layer multi-pass welding is adopted, the temperature between the welding passes is controlled in the range of 100-200 DEG C, the slow cooling or the low temperature tempering treatment at 100 DEG C is adopted after welding, the welding cold crack can be effectively avoided, the welded joint has good toughness and the comprehensive mechanical properties meet the design requirements.

[0033] The welding method provided by the present application solves the welding problem of the high-hardness bulletproof steel, guarantees that the strength of the welded joint meets the performance requirements, and has high bulletproof performance. The weld metal is a fine needle-shaped cellular structure, the heat affected zone is mainly tempered martensite, the different regions have high coordination deformation ability, cracks are not easily generated during cold bending, and the welded joint has high strength. The welding method has excellent welding process performance, is easy to operate, convenient to use, efficient, energy-saving, safe, and can effectively improve the application of the high-hardness bulletproof steel in various fields, especially in the military field. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figures 1-4 is a typical metallographic structure diagram of different positions in the welded joint of embodiment 3 of the present application,

[0035] Figure 1 represents the metallographic structure of the welded joint,

[0036] Figure 2 represents the metallographic structure of the weld metal WM,

[0037] Figure 3 represents the metallographic structure of the coarse grain heat affected zone CGHAZ,

[0038] Figure 4 Representative fine-grained heat-affected zone FGHAZ metallographic structure. DETAILED DESCRIPTION

[0039] In order to clearly illustrate the technical features of the process of the present application, the method of the present application will be further clearly and completely described below in combination with preferred examples. The following description is illustrative rather than limiting and should not be used to limit the scope of the present application.

[0040] Example 1: The steel plate to be welded is a martensitic ballistic steel with hardness HBW600 level, and the plate thickness combination is 8mm+8mm.

[0041] The chemical composition of the base material is: C: 0.42%, Si: 0.20%, Mn: 0.40%, P: ≤0.015%, S≤0.003%, Cr: 0.5%, Ni: 1.2%, Mo: 0.4%, B: 0.001%, Al: 0.02%, Ti: 0.025%, V: 0.03%, the balance being Fe and unavoidable impurities.

[0042] The production process of the base material is: smelting-continuous casting-thermo-mechanical control process (TMCP)-quenching+tempering.

[0043] The mechanical properties of the base material are: R p0.2 =1770MPa, R m =2150MPa, A 50 =12.5%, the average value of longitudinal impact at -40℃ is 32.5J.

[0044] The matching welding material is: T Union GM120 welding wire, diameter 1.2mm, the chemical composition and weight percentage of the deposited metal are: C≤0.12%, Si: 0.6-0.9%, Mn: 1.6-2.1%, Cr: 0.20-0.45%, Ni: 0.6-1.3%, Mo: 0.45-0.70%, Ti≤0.10%, Zr≤0.10%, V≤0.03%, Al≤0.12%, Cu≤0.30%, P≤0.015%, S≤0.018%, the balance being Fe and unavoidable impurities.

[0045] The yield strength R p0.2 of the deposited metal is ≥890MPa, the tensile strength R m is ≥940MPa, the elongation A is ≥14%, and the impact energy A kv at -40℃ is ≥47J.

[0046] The shielding gas is: 80% Ar+20% CO2 argon-rich mixed gas, and the gas flow rate is: 20L / min.

[0047] A gas shielded welding process for high-strength wear-resistant steel with high cold-bending formability of plate surface of welded joint

[0048] The welding wire is dried at 200℃ for 2h before use.

[0049] The gas shielded welding is performed with symmetrical single V groove, the groove angle of the two steel plates is 60°, the groove angle of the single steel plate is 30°, the groove root face height is 1mm, the groove gap is 1.5mm, and the offset of the steel plates is less than 0.8mm. The rust, oil, paint and other impurities on the inner and outer walls and both sides of the groove are cleaned to ensure that the surface of the groove and the range of 50mm on both sides of the groove are free of defects.

[0050] The bulletproof steel plate to be welded is preheated to above 250℃, the preheating area is within 150mm on both sides of the weld, and the electric blanket or flame heating method can be used. After preheating the front surface of the steel plate, the temperature of the back surface of the steel plate is measured 2min after the preheating stops to ensure the accuracy of the preheating temperature.

[0051] The distance and mutual position of the conductive nozzle to the workpiece are adjusted, the welding wire is controlled to have an extension length of 15mm, and the welding gun has an inclination angle of 70°.

[0052] Welding process parameters: base welding: welding current: 140A, arc voltage: 20.5V, welding speed: 15cm / min, welding line energy: 11.5KJ / cm; filling welding: welding current: 220A, arc voltage: 24V, welding speed: 26cm / min, welding line energy: 12.2KJ / cm; protective gas flow: 22L / min, interlayer temperature of welding bead: 120-150℃, preheating for the next welding bead and facilitating the escape of H.

[0053] During continuous welding, the slag and surface spatter generated by the previous welding bead are cleaned in time with a sander, and then the next welding is continued.

[0054] After welding, the steel plate is covered with asbestos for slow cooling to room temperature.

[0055] The welding joint of the 600HBW grade bulletproof steel welded by the above process has good fusion, no macro welding defects, no surface cracks and root cracks.

[0056] Due to the low strength matching principle of the welding wire, the welding joint is broken at the weld, and the mechanical properties of the obtained welding joint are: tensile strength R m : 1150MPa, elongation: 11%, broken at the weld, and weld impact energy A kv35J, 18J at 2mm from fusion line, 20J at 5mm from fusion line, 22J at 10mm from fusion line. The steel plate was tempered due to too high preheating temperature, and the final welded joint tensile strength was lower than 1300MPa.

[0057] Example 2: The steel plate to be welded is a martensitic ballistic steel with hardness HBW600 grade, and the plate thickness combination is 8mm+8mm.

[0058] The chemical composition of the base material is: C: 0.42%, Si: 0.20%, Mn: 0.40%, P: ≤0.015%, S≤0.003%, Cr: 0.5%, Ni: 1.2%, Mo: 0.4%, B: 0.001%, Al: 0.02%, Ti: 0.025%, V: 0.03%, the balance being Fe and unavoidable impurities.

[0059] The production process of the base material is: smelting-continuous casting-thermo-mechanical control process (TMCP)-quenching+tempering.

[0060] The mechanical properties of the base material are: Rp0.2=1770MPa, Rm=2150MPa, A50=12.5%, -40℃ longitudinal impact average value 32.5J.

[0061] The matching welding material is: T Union GM120 welding wire, diameter 1.2mm, the chemical composition and weight percentage of the deposited metal are: C≤0.12%, Si: 0.6-0.9%, Mn: 1.6-2.1%, Cr: 0.20-0.45%, Ni: 0.6-1.3%, Mo: 0.45-0.70%, Ti≤0.10%, Zr≤0.10%, V≤0.03%, Al≤0.12%, Cu≤0.30%, P≤0.015%, S≤0.018%, the balance being Fe and unavoidable impurities.

[0062] The yield strength R p0.2 of the deposited metal is ≥890MPa, the tensile strength R m of the deposited metal is ≥940MPa, the elongation A of the deposited metal is ≥14%, and the impact energy A kv of the deposited metal at -40℃ is ≥47J.

[0063] The shielding gas is: 80% Ar+20% CO2 argon-rich mixed gas, gas flow rate: 20L / min.

[0064] The welding wire is dried at low temperature of 200℃ for 2h before use, and is used immediately after taking out.

[0065] The gas shielded welding butt joint is opened with single V groove, the groove angle of the two steel plates is 60°, the groove angle of the single steel plate is 30°, the groove root face height is 1 mm, the groove gap is 1.5 mm, and the offset of the steel plates is less than 0.8 mm. The rust, oil, paint and other impurities on the inner and outer walls and both sides of the groove are cleaned to ensure that the surface of the groove and the range of 50 mm on both sides of the groove are free of defects.

[0066] The bulletproof steel plate to be welded is preheated to 120°C, and the preheating area is within 150 mm on both sides of the weld. The preheating can be performed by using an electric blanket or a flame heating method. After the front surface of the steel plate is preheated, the temperature of the back surface of the steel plate is measured 2 minutes after the preheating is stopped to ensure the accuracy of the preheating temperature.

[0067] The distance and mutual position of the conductive nozzle to the workpiece are adjusted, the welding wire extension length is controlled to be 15 mm, and the welding gun inclination angle is 70°.

[0068] The welding process parameters are as follows: base welding: welding current is 140 A, arc voltage is 20.5 V, welding speed is 8 cm / min, and welding line energy is 21.5 KJ / cm; filling welding: welding current is 220 A, arc voltage is 24 V, welding speed is 10 cm / min, and welding line energy is 31.7 KJ / cm; the protective gas flow is 20 L / min, the inter-pass temperature of the welding bead is 100-150°C, which is preheated for the next welding bead and is beneficial to the escape of H. During the continuous welding process, the slag and surface spatters generated by the previous welding bead are cleaned in time by using a sander, and then the next welding is continued.

[0069] After welding, the steel plate is covered with asbestos for heat preservation and slow cooling to room temperature.

[0070] The bulletproof steel welded joint obtained by using the above process has good fusion, no macro welding defects, no weld surface cracks and root cracks.

[0071] Since the welding wire adopts the low-strength matching principle, the welding joint is broken at the weld, and the mechanical properties of the obtained welding joint are as follows: tensile strength R m : 1130 MPa, elongation: 9.3%, broken at the weld, weld impact energy Akv at-40°C is 35 J, impact energy at 2 mm from the fusion line is 15 J, impact energy at 5 mm from the fusion line is 18 J, and impact energy at 10 mm from the fusion line is 20 J. Due to the high welding line energy, the microstructure of the welding joint is softened, and the final tensile strength of the welding joint is lower than 1300 MPa.

[0072] Example 3: The steel plate to be welded is a martensitic bulletproof steel with a hardness of HBW600, and the plate thickness combination is 8 mm+8 mm.

[0073] C: 0.42%, Si: 0.20%, Mn: 0.40%, P: ≤0.015, S ≤0.003%, Cr: 0.5%, Ni: 1.2%, Mo: 0.4%, B: 0.001%, Al: 0.02%, Ti: 0.025%, V: 0.03%, balance Fe and inevitable impurities.

[0074] The production process of the base material is: smelting-continuous casting-thermo-mechanical control process (TMCP)-quenching + tempering.

[0075] The mechanical properties of the base material are: Rp0.2 = 1770 MPa, Rm = 2150 MPa, A50 = 12.5%, and the average value of longitudinal impact at -40°C is 32.5 J.

[0076] The matching welding material is: T Union GM120 welding wire, diameter 1.2 mm, and the chemical components and weight percentages of the deposited metal are: C ≤0.12%, Si: 0.6-0.9%, Mn: 1.6-2.1%, Cr: 0.20-0.45%, Ni: 0.6-1.3%, Mo: 0.45-0.70%, Ti ≤0.10%, Zr ≤0.10%, V ≤0.03%, Al ≤0.12%, Cu ≤0.30%, P ≤0.015%, S ≤0.018%, balance Fe and inevitable impurities.

[0077] The yield strength Rp0.2 of the deposited metal is ≥890 MPa, the tensile strength Rm is ≥940 MPa, the elongation A is ≥14%, and the impact energy Akv at -40°C is ≥47 J.

[0078] Protective gas: 80% Ar + 20% CO2 rich argon mixture, gas flow: 22 L / min.

[0079] A gas shielded welding method for a martensitic bulletproof steel with a hardness of 600 HBW level:

[0080] The welding wire is dried at a low temperature of 200°C for 2 hours before use, and is used immediately after drying.

[0081] The gas shielded welding butt joint is opened with a symmetrical single V-shaped groove, the groove angle of the welding joint of the two steel plates is 60°, the groove angle of the single side steel plate is 30°, the groove root face height is 1 mm, the groove gap is 1.5 mm, and the butt joint offset of the steel plate is less than 0.8 mm. This shape of groove can save a lot of welding material and electric energy, and is easy to process, can effectively reduce the welding deformation, and has good weldability since the welding is performed on both sides of the component.

[0082] The inside and outside walls of the groove and the impurities such as rust, oil stains and paint on the two sides of the groove are cleaned to ensure that the groove surface and the range of 50 mm on both sides of the groove are free of defects.

[0083] The bulletproof steel plate to be welded is preheated to 100℃, the preheating area is within 150mm on both sides of the weld, and the preheating can be performed by using an electric blanket or a flame heating method. After preheating the front surface of the steel plate, the temperature of the back surface of the steel plate is measured 2 minutes after the preheating is stopped, so as to ensure the accuracy of the preheating temperature.

[0084] The distance and mutual position of the conductive nozzle to the workpiece are adjusted, the welding wire extension length is controlled to be 15mm, and the welding gun inclination angle is 75°.

[0085] The welding process parameters are as follows: base welding: welding current: 140A, arc voltage: 20.5V, welding speed: 15cm / min, and welding line energy: 11.5KJ / cm; filling welding: welding current: 220A, arc voltage: 24V, welding speed: 26cm / min, and welding line energy: 12.2KJ / cm; protective gas flow: 22L / min, inter-pass temperature: 120-150℃, which is preheating for the next welding pass and is beneficial to the escape of H.

[0086] In the continuous welding process, the slag and surface spatters generated in the previous welding pass are cleaned in time by using a sander, and then the next welding pass is continued.

[0087] After welding, the steel plate is covered with asbestos for slow cooling to room temperature.

[0088] The welding joint of the 600HBW grade bulletproof steel welded by using the above process has good fusion, no macroscopic welding defects, no weld surface cracks and root cracks.

[0089] Since the welding wire adopts the low-strength matching principle, the welding joint is fractured at the weld, and the obtained welding joint mechanical properties are as follows: tensile strength Rm: 1350MPa, elongation: 11%, fracture at the weld, weld impact energy Akv at-40℃: 35J, impact energy at 2mm from the fusion line: 20J, impact energy at 5mm from the fusion line: 25J, and impact energy at 10mm from the fusion line: 27J. The comprehensive mechanical properties meet the design requirements.

Claims

1. A gas-shielded welding method for martensitic bulletproof steel with a hardness of 600 HBW, characterized in that, The specific steps are as follows: Step 1. Select martensitic bulletproof steel plates with a hardness of 600HBW and a thickness of 5-30mm, and weld them together with plates of equal thickness. Step 2. Select argon-rich mixed gas as the shielding gas and solid welding wire with a yield strength ≥ 890 MPa; Step 3. For martensitic bulletproof steel plates with a thickness greater than 10mm and a hardness of 600HBW, make a double-sided asymmetrical X-shaped bevel or a double-sided symmetrical X-shaped bevel at the joint to be welded; for martensitic bulletproof steel plates with a thickness ≤10mm and a hardness of 600HBW, make a single V-shaped bevel. Step 4. Remove water, iron oxide scale, rust, oil and paint from the bevel surface and within 50mm on both sides of the area to be welded, and clean away dust and debris; Step 5. Dry the solid welding wire before welding; preheat the area within 150mm on both sides of the weld of the 600HBW grade martensitic bulletproof steel plate; control the welding heat input and interpass temperature during filler and capping welding. Step 6. Use a multi-layer, multi-pass continuous welding method. During the continuous welding process, clean the welding slag and surface spatter generated in the previous weld pass before continuing to the next weld pass. Step 7. Immediately after welding, the weld should be subjected to slow cooling treatment; The chemical composition (by weight percentage) of the 600HBW grade martensitic bulletproof steel is as follows: C: 0.34-0.42%, Si: 0.15-0.40%, Mn: 0.20-0.40%, P≤0.015%, S≤0.003%, Cr: 0.4-0.6%, Ni: 0.9-1.8%, Mo: 0.1-0.6%, B: 0.001-0.003%, Al: 0.02-0.6%, Ti: 0.010-0.025%, V: 0.02-0.04%, with the balance being Fe and unavoidable impurities. The production process is: smelting - continuous casting - controlled rolling + controlled cooling - quenching + tempering treatment. According to the principle of low strength matching, the solid welding wire is used for depositing metal, and its chemical composition by weight percentage is as follows: C≤0.12%, Si: 0.6-0.9%, Mn: 1.6-2.1%, Cr: 0.20-0.45%, Ni: 0.6-1.3%, Mo: 0.45-0.70%, Ti≤0.10%, Zr≤0.10%, V≤0.03%, Al≤0.12%, Cu≤0.30%, P≤0.015%, S≤0.018%, with the balance being Fe and unavoidable impurities.

2. The gas-shielded welding method for martensitic bulletproof steel with a hardness of 600 HBW according to claim 1, characterized in that, The protective gas is an argon-rich mixture with a volume ratio of 80% Ar + 20% CO2; gas flow rate: 15-25 L / min; Ar purity 99.99%, moisture content <15 ppm; CO2 purity 99.9%, moisture content <40 ppm; after mixing, the moisture content is <20 ppm.

3. The gas-shielded welding method for martensitic bulletproof steel with a hardness of 600 HBW according to claim 1, characterized in that, In step 3, a single V-shaped or double-sided X-shaped bevel is cut into the steel plate using a machining method; the bevel angle of the welded joint between the two steel plates is 40-60°, the bevel angle of the steel plate on one side is 20-30°, the bevel blunt edge height is 0-2mm, the joint assembly gap is 1-2mm, and the offset of the steel plate butt joint is less than 0.1t, where t is the plate thickness in mm.

4. The gas-shielded welding method for martensitic bulletproof steel with a hardness of 600 HBW according to claim 1, characterized in that, In step 5, the solid welding wire is dried at 200℃ for 2 hours; the preheating temperature is 100-150℃.

5. The gas-shielded welding method for martensitic bulletproof steel with a hardness of 600 HBW according to claim 4, characterized in that, In the multi-layer, multi-pass continuous welding method, the welding torch tilt angle is 70-80°; the lower limit of the interpass temperature is not lower than the preheating temperature; during filler and capping welding, the interpass temperature is controlled at 100-200℃.

6. The gas-shielded welding method for martensitic bulletproof steel with a hardness of 600 HBW according to claim 1, characterized in that, In the aforementioned multi-layer, multi-pass continuous welding method, during the root pass welding, based on the principle of ensuring penetration and reducing heat input, the welding current I is 120-180A, the arc voltage U is 18-22V, the welding speed v is 12-30cm / min, and the welding heat input E is controlled at 10-15KJ / cm; during the fill and cover passes welding, the welding current I is 160-260A, the arc voltage U is 22-28V, the welding speed v is 12-30cm / min, and the welding heat input E is controlled at 10-15KJ / cm.

7. The gas-shielded welding method for martensitic bulletproof steel with a hardness of 600 HBW according to claim 1, characterized in that, Step 7 specifically involves immediately after welding using insulation material to keep the welded joint warm and allow it to cool slowly, or by maintaining it at 100℃; the warming time is T=4×t, where T is the time in minutes and t is the plate thickness in mm, and the total warming time is not less than 1 hour.

Images