A gas shielded welding method for microalloyed low alloy high strength steel Q690D

Abstract

The invention discloses a gas shielded welding method for microalloyed low alloy high strength steel Q690D, including: adopting equal strength matching principle; shielding gas adopting argon-rich gas of 80% Ar+20% CO2; Q690D plate thickness of gas shielded welding is between 15-30mm, and base welding is performed; Q690D steel plate preheating temperature before welding is ≥60℃, and insulation time is ≥30min; welding pass temperature is controlled between 120-190℃; post-weld heat treatment optimal temperature is 245-255℃, and insulation time is ≥2h. The purpose of the invention is to provide a gas shielded welding method for microalloyed low alloy high strength steel Q690D, which is based on the commonly used steel composition system, performance index and welding means, and can meet the welding production needs of microalloyed low alloy high strength steel Q690D.

Description

Technical Field

[0001] The invention belongs to the technical field of steel material welding, and in particular relates to a gas shielded welding method for micro-alloyed low-alloy high-strength steel Q690D. Background Art

[0002] Q690D steel plate is a micro-alloyed low-alloy high-strength steel with a yield strength of 690MPa developed by Baosteel. It has excellent low-temperature toughness and is mainly used for engineering and mining machinery. The steel plate is supplied in a quenched and tempered state. The development of Q690D steel plates at home and abroad mainly focuses on C, Si, Mn, Cr, Ni, Mo, Nb, V, B, Ti and other main alloying elements. By optimizing the ratio of different alloying elements, different performance requirements and cost requirements are achieved. However, in order to achieve the requirement of yield strength greater than 690MPa, various steel mills are conducting a lot of research and development on alloying elements and controlled cooling, but lack relevant research and process support in the corresponding welding process.

[0003] In the research on 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 alloy elements are added to make the carbon equivalent of the parent material higher. In the conventional arc welding process, welding cold cracks, workpiece deformation, abnormal organization and other phenomena will occur. When the welding heat input is high, in addition to the obvious reduction in joint toughness, the heat-affected zone of the joint also softens. Therefore, it is very important to explore the optimal welding process window through welding tests for the corresponding steel. For the Q690D steel developed by Baotou Steel, its basic weldability is mastered, and the welding process and post-weld heat treatment process are reasonably formulated to make the performance of Q690D steel welded joints meet the use requirements of industrial and mining products. Summary of the invention

[0004] The purpose of the present invention is to provide a gas shielded welding method for micro-alloyed low-alloy high-strength steel Q690D. The invention is based on the common steel composition system, performance indicators and welding methods, and can meet the welding production needs of micro-alloyed low-alloy high-strength steel Q690D.

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

[0006] The present invention discloses a gas shielded welding method for microalloyed low alloy high strength steel Q690D, comprising:

[0007] Adopting the principle of equal strength matching, the welding material is JM-110 solid welding wire;

[0008] The shielding gas is 80% Ar+20% CO2 rich argon gas, and the gas pressure flow is controlled between 18-21L / min; X-shaped groove double-sided butt welding is adopted, the X-shaped groove angle is 30°-45°, the bluntness is 2mm, and the wire dry extension length is 15-20mm;

[0009] The thickness of Q690D plate for gas shielded welding is between 15-30mm. For base welding, the current is controlled between 230-250A, the welding voltage is controlled between 24-26V, the welding speed is controlled at about 33cm / min, and the welding heat input is controlled between 10.0-12kJ / cm; for filling welding, the welding current is controlled between 250-370A, the welding voltage is controlled between 26-40V, the welding speed is controlled between 33-47cm / min, and the welding heat input is controlled between 12-25kJ / cm;

[0010] The preheating temperature of Q690D steel plate before welding is ≥60℃, and the insulation time is ≥30min; the temperature between welding passes is controlled between 120-190℃;

[0011] The optimal temperature for post-weld heat treatment is 245-255℃, and the holding time is ≥2h.

[0012] Furthermore, the optimum temperature for post-weld heat treatment is 250°C.

[0013] Furthermore, the weight percentage of the chemical composition of the microalloyed low alloy high strength steel Q690D is C: 0.10%, Si: 0.35%, Mn: 1.70%, Cr: 0.30%, Ni: 0.10%, V: 0.07%, Nb: 0.05%, Ti: 0.02%, B: 0.002%, and the rest is Fe and impurities.

[0014] Furthermore, the micro-alloyed low-alloy high-strength steel Q690D 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.

[0015] Furthermore, the microalloyed low alloy high strength steel Q690D meets the following properties: tensile strength ≥820MPa, yield strength ≥750MPa, elongation ≥16.0%, -20°C impact (KV2) ≥120J, and the microstructure is troostite.

[0016] Furthermore, the performance of the micro-alloyed low-alloy high-strength steel Q690D joint obtained by welding meets the following requirements: joint tensile strength ≥800MPa, yield strength ≥710MPa, elongation after fracture ≥20%, and -20°C weld impact ≥150J.

[0017] Furthermore, the weld microstructure is bainite + ferrite.

[0018] Compared with the prior art, the beneficial technical effects of the present invention are:

[0019] The microalloyed low alloy high strength steel Q690D joint obtained based on the above welding process has the following characteristics: the tensile strength of the joint is ≥800MPa, the yield strength is ≥710MPa, the elongation after fracture is ≥20%, the weld impact (-20°C) is ≥150J, and the weld microstructure is bainite + ferrite. The joint of the present invention has better strength and toughness, and can achieve excellent performance matching with the parent material. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The present invention will be further described below in conjunction with the accompanying drawings.

[0021] Figure 1 is the microstructure of the parent material;

[0022] Figure 2 is the weld microstructure;

[0023] Figure 3 Microstructure of heat affected zone. DETAILED DESCRIPTION

[0024] Since the welding heat input and the temperature changes between welds will affect the welding thermal cycle process, thus affecting the microstructure and mechanical properties of the weld metal and heat-affected zone of the weld joint, the changes in the welding voltage, current and heat input of the joint are combined with the relationship with the mechanical properties of the Q690D steel welded joint during implementation to obtain the optimal welding window and process, providing a basis for formulating a reasonable welding process.

[0025] Table 1 Gas shielded welding process parameters for different embodiments

[0026]

[0027] Table 2 Mechanical properties of joints corresponding to different embodiments

[0028]

[0029] It can be seen from Table 1 and Table 2 that when the heat input of microalloyed low alloy high strength steel Q690D is within the range of 10-25 kJ / mm, as the heat input increases, the weld metal strength of the weld joint decreases, the tensile strength of the joint decreases from 840 MPa to 805 MPa, and the yield strength decreases from 789 MPa to 703 MPa. All indicators decrease, but the decrease is not large, and the -20°C impact toughness remains above 150 J. 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 interpass welding defects, is prone to inclusions at the weld, and reduces production efficiency. The microalloyed low alloy high strength steel Q690D gas shielded welded joints of Examples 1 to 4 of the present invention have better strength and toughness, match the performance of the parent material, and can meet the requirements of engineering applications.

[0030] 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 microalloyed low alloy high strength steel Q690D, characterized in that: include: Adopting the principle of equal strength matching, the welding material is JM-110 solid welding wire; The shielding gas is 80% Ar+20% CO2 rich argon gas, and the gas pressure flow is controlled between 18-21L / min; X-shaped groove double-sided butt welding is adopted, the X-shaped groove angle is 30°-45°, the bluntness is 2mm, and the wire dry extension length is 15-20mm; The thickness of Q690D plate for gas shielded welding is between 15-30mm. For base welding, the current is controlled between 230-250A, the welding voltage is controlled between 24-26V, the welding speed is controlled at about 33cm / min, and the welding heat input is controlled between 10.0-12kJ / cm; for filling welding, the welding current is controlled between 250-370A, the welding voltage is controlled between 26-40V, the welding speed is controlled between 33-47cm / min, and the welding heat input is controlled between 12-25kJ / cm; The preheating temperature of Q690D steel plate before welding is ≥60℃, and the insulation time is ≥30min; the temperature between welding passes is controlled between 120-190℃; The optimal temperature for post-weld heat treatment is 245-255℃, and the holding time is ≥2h.

2. The gas shielded welding method for microalloyed low alloy high strength steel Q690D according to claim 1, characterized in that: The optimum temperature for post-weld heat treatment is 250°C.

3. The gas shielded welding method for microalloyed low alloy high strength steel Q690D according to claim 1, characterized in that: The weight percentage of the chemical composition of the micro-alloyed low-alloy high-strength steel Q690D is C: 0.10%, Si: 0.35%, Mn: 1.70%, Cr: 0.30%, Ni: 0.10%, V: 0.07%, Nb: 0.05%, Ti: 0.02%, B: 0.002%, and the rest is Fe and impurities.

4. The gas shielded welding method for microalloyed low alloy high strength steel Q690D according to claim 3, characterized in that: The micro-alloyed low-alloy high-strength steel Q690D 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.

5. The gas shielded welding method for microalloyed low alloy high strength steel Q690D according to claim 4, characterized in that: The microalloyed low alloy high strength steel Q690D meets the following properties: tensile strength ≥820MPa, yield strength ≥750MPa, elongation ≥16.0%, -20°C impact (KV2) ≥120J, and the microstructure is sorbite.

6. The gas shielded welding method for microalloyed low alloy high strength steel Q690D according to claim 1 or 5, characterized in that: The performance of the micro-alloyed low-alloy high-strength steel Q690D joint obtained by welding meets the following requirements: joint tensile strength ≥800MPa, yield strength ≥710MPa, elongation after fracture ≥20%, and -20℃ weld impact ≥150J.

7. The gas shielded welding method for microalloyed low alloy high strength steel Q690D according to claim 1, characterized in that: The weld microstructure is bainite + ferrite.

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