Gas shielded welding method for low-alloy high-strength steel Q890D

Abstract

The invention discloses a gas shielded welding method for low-alloy high-strength steel Q890D, and belongs to the technical field of steel and iron material welding. The method comprises the following steps: the lowest preheating temperature for welding the low-alloy high-strength steel Q890D is 120 DEG C; the thickness of a Q890D steel plate subjected to gas shielded welding is 15-30 mm, the welding current is controlled to be 230-280 A, the welding voltage is controlled to be 24-31 V, the welding speed is controlled to be 33-47 cm / min, and the welding heat input is controlled to be 7.1-15.3 kJ / cm; the temperature between welding passes is controlled to be 120-190 DEG C; the highest post-welding heat treatment temperature of the low-alloy high-strength steel Q890D is not more than 400 DEG C. The joint provided by the invention has more excellent obdurability, and can achieve excellent performance matching with a base material.

Description

Technical Field

[0001] The invention belongs to the field of steel material welding, and in particular relates to a gas shielded welding method for low alloy high strength steel Q890D. Background Art

[0002] As mining machinery and engineering machinery are subjected to increasingly heavy loads, high-strength steel medium and thick plates are the preferred steel materials for hydraulic support manufacturing. The use of high-strength steel can not only reduce the weight of the steel structure itself and meet safety performance requirements, but also effectively improve the utilization efficiency of steel resources, reduce energy consumption and pollutant emissions. Low-alloy high-strength steel Q890D replaces the existing Q690 steel plate, which can save 22.5% of steel and 37.8% of welding materials, and make the hydraulic support have higher strength and toughness, which can greatly improve its comprehensive performance such as compressive strength, service life, and safety of use. Therefore, it is of great significance to develop and promote the application of higher-grade steel for hydraulic supports. For low-alloy high-strength steel Q890D, in addition to requiring it to have high strength, welding performance is an important performance indicator that affects its large-scale promotion and application.

[0003] At present, in the research of high-strength steel welding at home and abroad, in order to ensure the strength, plasticity and toughness requirements of high-strength steel, a large amount of alloying elements are added to make the carbon equivalent of the parent material higher. In the conventional arc welding process, welding cold cracks, deformation of welding workpieces, embrittlement and softening of welding joints will occur. With the increase of welding heat input, the microstructure of the coarse-grained zone shows a transformation from martensite structure to martensite and bainite mixed structure, and then to bainite and granular bainite mixed structure. Its welding heat input value can only reach 20kJ / cm. Under higher heat input conditions, its microstructure has a large number of chain-distributed MA components, which belongs to brittle fracture. When the welding heat input is high, in addition to poor impact toughness, the hardness of the heat-affected zone of the base weld will be lower than that of the weld and the parent material, and there will be post-weld softening. Therefore, its corresponding welding heat input value should be controlled in a lower range. However, when the welding heat input value is low, the cooling rate is faster, and the hydrogen content of the deposited metal is high, which will increase the sensitivity of cold cracks. Summary of the invention

[0004] The purpose of the present invention is to provide a gas shielded welding method for low alloy high strength steel Q890D. The tensile strength of the low alloy high strength steel Q890D welded joint is ≥990MPa, the yield strength is ≥920MPa, the elongation after fracture is ≥17%, the weld impact is ≥170J, the heat affected zone impact is ≥140J, the weld microstructure is bainite + ferrite, and the heat affected zone structure is bainite. The joint of the present invention has better toughness and can achieve excellent performance matching with the parent material.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0006] The invention discloses a gas shielded welding method for low alloy high strength steel Q890D. The minimum preheating temperature for welding the low alloy high strength steel Q890D is 120°C; the thickness of the Q890D steel plate for gas shielded welding is between 15 and 30 mm, the welding current is controlled between 230 and 280 A, the welding voltage is controlled between 24 and 31 V, the welding speed is controlled between 33 and 47 cm / min, and the welding heat input is controlled between 7.1 and 15.3 kJ / cm; the temperature between welding passes is controlled between 120 and 190°C; and the maximum heat treatment temperature of the low alloy high strength steel Q890D after welding should not exceed 400°C.

[0007] Furthermore, the low alloy high strength steel Q890D has C, Si, Mn, Cr, Ni, Mo, Nb and V as main alloying elements, wherein the weight percentage of chemical composition is C: 0.20%, Si: 0.30%, Mn: 1.70%, Cr: 0.40%, Ni: 0.30%, Mo: 0.27%, Nb: 0.05%, V: 0.07%, Ti: 0.02%, and the rest is Fe and impurities.

[0008] 3. The gas shielded welding method for low alloy high strength steel Q890D according to claim 1 is characterized in that the post-weld heat treatment temperature of Q890D is 250-300°C.

[0009] Furthermore, the low alloy high strength steel Q890D steel meets the following requirements: tensile strength ≥ 980MPa, yield strength ≥ 940MPa, elongation ≥ 13.5%, impact KV 2 ≥205J, the microstructure is troostite.

[0010] Further, the gas shielded welding shielding gas for low alloy high strength steel Q890D adopts argon-rich gas of 80% Ar+20% CO2, and the gas pressure flow is controlled between 15 and 20L / min; X-type groove double-sided butt welding is adopted, the X-type groove angle is 30°-45°, the bluntness is 2mm, and the wire dry extension length is 15-20mm.

[0011] Furthermore, the gas shielded welding of low alloy high strength steel Q890D adopts the principle of equal strength matching, and the welding material is BHG-5 solid welding wire. The welding wire meets the following requirements: tensile strength ≥ 985MPa, yield strength ≥ 955MPa, elongation ≥ 15%, impact KV 2 ≥90J, the diffusible hydrogen content of the deposited metal of the welding wire is 0.0258mL / g.

[0012] Furthermore, after welding, the low alloy high strength steel Q890D meets the following requirements: joint tensile strength ≥990MPa, yield strength ≥920MPa, elongation after fracture ≥17%, weld impact ≥170J, heat affected zone impact ≥140J, weld microstructure is bainite + ferrite, and heat affected zone microstructure is bainite.

[0013] Compared with the prior art, the beneficial technical effects of the present invention are:

[0014] The tensile strength of the welded joint of the low alloy high strength steel Q890D is ≥990MPa, the yield strength is ≥920MPa, the elongation after fracture is ≥17%, the weld impact is ≥170J, the heat affected zone impact is ≥140J, the weld microstructure is bainite + ferrite, and the heat affected zone structure is bainite. The joint of the present invention has better toughness and can achieve excellent performance matching with the parent material. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The present invention will be further described below in conjunction with the accompanying drawings.

[0016] Figure 1 is the microstructure of the parent material;

[0017] Figure 2 is the weld microstructure;

[0018] Figure 3 Microstructure of heat affected zone. DETAILED DESCRIPTION

[0019] A gas shielded welding method for low alloy high strength steel Q890D is invented based on the common steel composition system, performance index and welding method, which can meet most of the welding production needs of low alloy high strength steel Q890D. The specific invention is as follows:

[0020] 1. The low alloy high strength steel Q890D of the present invention uses C, Si, Mn, Cr, Ni, Mo, Nb and V as main alloying elements, wherein the weight percentage of the chemical composition is C: 0.20%, Si: 0.30%, Mn: 1.70%, Cr: 0.40%, Ni: 0.30%, Mo: 0.27%, Nb: 0.05%, V: 0.07%, Ti: 0.02%, and the rest is Fe.

[0021] 2. The low alloy high strength steel Q890D of the present invention is obtained through molten iron pretreatment, converter smelting, LF refining, RH vacuum treatment, slab continuous casting, slab heating, controlled rolling, controlled cooling, straightening and finishing.

[0022] 3. Low alloy high strength steel Q890D steel tensile strength ≥980MPa, yield strength ≥940MPa, elongation ≥13.5%, impact (KV 2)≥205J, the microstructure is troostite, such as Figure 1 shown.

[0023] 4. Gas shielded welding of low alloy high strength steel Q890D adopts the principle of equal strength matching. The welding material is BHG-5 solid welding wire. The tensile strength of the welding wire is ≥985MPa, the yield strength is ≥955MPa, the elongation is ≥15%, and the impact (KV 2 )≥90J, the diffusible hydrogen content of the deposited metal of the welding wire is 0.0258mL / g.

[0024] 5. Q890D gas shielded welding uses argon-rich gas of 80% Ar + 20% CO2 as the shielding gas, and the gas pressure flow is controlled between 15 and 20L / min; X-type groove double-sided butt welding is adopted, the X-type groove angle is 30°-45°, the bluntness is 2mm, and the wire dry extension length is 15-20mm.

[0025] 6. For Q890D steel plate, carbon equivalent CE = C + Mn / 6 + (Cu + Ni) / 15 + (Cr + Mo + V) / 5 = 0.56; cold crack sensitivity Pw = Pcm + 100HDM / 60 + h / 600 = 0.35, theoretical minimum preheating temperature T = 1440Pw-392 = 112 ° C.

[0026] 7. Combined with the actual inclined Y groove welding crack test of steel plate, it is concluded that the minimum preheating temperature for Q890D welding is 120℃.

[0027] 8. The thickness of Q890D plate for gas shielded welding is between 15-30mm, the welding current is controlled between 230-280A, the welding voltage is controlled between 24-31V, the welding speed is controlled between 33-47cm / min, and the welding heat input is controlled between 7.1-15.3kJ / cm.

[0028] 9. The temperature between welding passes is controlled between 120-190℃. The appearance of the gas shielded welding weld is well formed. After ultrasonic testing and metallographic structure observation, there are no welding defects such as pores and inclusions.

[0029] 10. The optimal temperature for post-weld heat treatment of Q890D is 250-300℃, and the maximum heat treatment temperature should not exceed 400℃.

[0030] 11. The tensile strength of the welded joint of the low alloy high strength steel Q890D is ≥990MPa, the yield strength is ≥920MPa, the elongation after fracture is ≥17%, the weld impact is ≥170J, the heat affected zone impact is ≥140J, the weld microstructure is bainite + ferrite, and the heat affected zone structure is bainite. The joint of the present invention has better toughness and can achieve excellent performance matching with the parent material.

[0031] During the implementation process, the inclined Y groove welding crack test was used to determine the welding preheating temperature of different embodiments. The inclined Y groove welding crack test results are shown in Table 1.

[0032] Table 1 Oblique Y groove welding crack test results

[0033]

[0034] It can be seen from Table 1 that when the preheating temperature is lower than 100℃, 2% cracks appear on the weld surface; when the preheating temperature is higher than 120℃, no cracks will appear on the weld. Combined with the theoretical calculation of the preheating temperature, the minimum preheating temperature for Q890D welding is finally determined to be 120℃.

[0035] Table 2 Gas shielded welding process parameters for different embodiments

[0036]

[0037]

[0038] Table 3 Mechanical properties of joints corresponding to different embodiments

[0039]

[0040] It can be seen from Table 2 and Table 3 that when the welding heat input E is in the range of 7.1-15.3 kJ / cm, the tensile fracture position is the parent material, and various mechanical performance indicators meet the welding requirements; when the welding heat input E is greater than 16.1 kJ / cm, the fracture position is the heat-affected zone, and the tensile strength, yield strength, elongation, etc. are all reduced. Excessive line energy will cause unstable performance of the heat-affected zone, resulting in an increase in the heat-affected zone. During the tensile test, the heat-affected zone is prone to fracture, resulting in a decrease in tensile strength; too little line energy requires multiple passes of welding, which increases the risk of inter-pass welding defects, is prone to inclusions in the weld, and reduces production efficiency. The low-alloy high-strength steel Q890D gas shielded welding head of Examples 1 to 3 of the present invention has better strength and toughness, matches the performance of the parent material, and can meet the requirements of engineering applications.

[0041] Table 4 Mechanical properties of different post-weld heat treatment processes

[0042]

[0043]

[0044] It can be seen from Table 4 that when the post-weld heat treatment temperature is 400℃ or 500℃, the tensile strength and yield strength of the joint are reduced, and the joint performance is best when the heat treatment temperature is 250℃. Therefore, the post-weld heat treatment temperature of Q890D should not exceed 400℃ to ensure the mechanical properties of the base material and the welded joint.

[0045] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A gas shielded welding method for low alloy high strength steel Q890D, characterized in that: The minimum preheating temperature for welding the low-alloy high-strength steel Q890D is 120°C; the thickness of the Q890D steel plate for gas shielded welding is between 15-30mm, the welding current is controlled between 230-280A, the welding voltage is controlled between 24-31V, the welding speed is controlled between 33-47cm / min, and the welding heat input is controlled between 7.1-15.3kJ / cm; the temperature between welding passes is controlled between 120-190°C; the maximum heat treatment temperature of the low-alloy high-strength steel Q890D after welding should not exceed 400°C.

2. The gas shielded welding method for low alloy high strength steel Q890D according to claim 1, characterized in that: The low alloy high strength steel Q890D uses C, Si, Mn, Cr, Ni, Mo, Nb and V as main alloying elements, wherein the weight percentage of the chemical composition is C: 0.20%, Si: 0.30%, Mn: 1.70%, Cr: 0.40%, Ni: 0.30%, Mo: 0.27%, Nb: 0.05%, V: 0.07%, Ti: 0.02%, and the rest is Fe and impurities.

3. The gas shielded welding method for low alloy high strength steel Q890D according to claim 1, characterized in that: The post-weld heat treatment temperature of the low alloy high strength steel Q890D is 250-300°C.

4. The gas shielded welding method for low alloy high strength steel Q890D according to claim 1, characterized in that: The low alloy high strength steel Q890D meets the following requirements: tensile strength ≥ 980 MPa, yield strength ≥ 940 MPa, elongation ≥ 13.5%, impact KV2 ≥ 205 J, and the microstructure is troostite.

5. The gas shielded welding method for low alloy high strength steel Q890D according to claim 1, characterized in that: The shielding gas for gas shielded welding of low alloy high strength steel Q890D is 80% Ar + 20% CO2 argon-rich gas, and the gas pressure flow is controlled between 15 and 20L / min; X-type groove double-sided butt welding is adopted, the X-type groove angle is 30°-45°, the bluntness is 2mm, and the wire dry extension length is 15-20mm.

6. The gas shielded welding method for low alloy high strength steel Q890D according to claim 1, characterized in that: The gas shielded welding of the low alloy high strength steel Q890D adopts the principle of equal strength matching, and the welding material is BHG-5 solid welding wire. The welding wire meets the following requirements: tensile strength ≥985MPa, yield strength ≥955MPa, elongation ≥15%, impact KV2 ≥90J, and the diffusible hydrogen content of the weld metal of the welding wire is 0.0258mL / g.

7. The gas shielded welding method for low alloy high strength steel Q890D according to claim 1, characterized in that: After welding, the low alloy high strength steel Q890D meets the following requirements: joint tensile strength ≥990MPa, yield strength ≥920MPa, elongation after fracture ≥17%, weld impact ≥170J, heat affected zone impact ≥140J, weld microstructure is bainite+ferrite, and heat affected zone microstructure is bainite.

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