In-situ repair welding process for softening of low-rare-earth wear-resistant steel welding heat-affected zone

Abstract

The application discloses a kind of low rare-earth wear-resistant steel welding heat-affected zone softening in-situ repair welding process, using CMT+low frequency pulse composite heat source, based on thermal simulation determines critical heat input 5.57.0kJ / cm, cooperate with postweld self-tempering, realize rare earth Ce, La in-situ precipitation nano-strengthening phase, repair softening zone.Joint heat-affected zone hardness rebounds ≥25HV, tensile strength ≥700MPa, fracture toughness pit depth ≥2.2μm, softening zone width ≤0.4mm.The method does not need postweld heat treatment, welding deformation ≤1.5°, suitable for rare earth content 0.030‑05% low rare-earth wear-resistant steel plate welding, can significantly reduce welding failure rate, suitable for Baogang low rare-earth wear-resistant steel production line.

Description

Technical Field

[0001] This invention belongs to the field of rare earth wear-resistant steel welding technology, and particularly relates to an in-situ repair welding process for softening of the heat-affected zone in low rare earth wear-resistant steel welding. Background Technology

[0002] Low rare earth wear-resistant steel is a key product of Baotou Steel, with advantages such as low cost, high wear resistance, and good toughness. However, after CMT and MAG welding, this type of steel is prone to a significant softening zone in the heat-affected zone, with a hardness decrease of 20-40 HV and a tensile strength decrease of more than 10%, becoming the main source of fatigue cracking.

[0003] Existing technologies mostly employ post-weld heat treatment to improve softening, but this increases the number of processes, raises costs, and increases the risk of deformation. Simply optimizing welding parameters cannot achieve nano-precipitation strengthening, making it difficult to completely eliminate the softening problem. Failure analysis shows that over 80% of failures in low-rare-earth wear-resistant steel welded structures originate from the softening zone in the heat-affected zone. Therefore, developing a welding process that requires no heat treatment and can strengthen in situ has significant engineering value. Summary of the Invention

[0004] The purpose of this invention is to provide an in-situ repair welding process for softening of the heat-affected zone in low rare earth wear-resistant steel. This invention adopts CMT + low-frequency pulse composite welding, determines the optimal heat input window based on thermal simulation, and utilizes welding residual heat to achieve in-situ precipitation of rare earth nanophases, thereby fundamentally solving the problem of softening in the heat-affected zone.

[0005] This method achieves in-situ precipitation of rare earth Ce and La nano-reinforcing phases to repair the softened zone; the joint heat-affected zone hardness recovers by ≥25HV, tensile strength by ≥700MPa, fracture dimple depth by ≥2.2μm, and softened zone width by ≤0.4mm. This method requires no post-weld heat treatment, and welding deformation is ≤1.5°. It is suitable for welding low-rare earth wear-resistant steel plates with a rare earth content of 0.030-0.5%, significantly reducing the welding failure rate, and is compatible with Baotou Steel's low-rare earth wear-resistant steel production line.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] This invention discloses an in-situ repair welding process for softening of the heat-affected zone in low-rare-earth wear-resistant steel, comprising:

[0008] 1. Materials and Equipment

[0009] Base material: Low rare earth wear-resistant steel (RE=0.030-0.05%), plate thickness 12mm; suitable for ballast steel with RE=0.040% intermediate value low rare earth wear-resistant steel, the chemical composition by mass percentage is as follows:

[0010] C: 0.140%, Si: 0.450%, Mn: 1.320%, Cr: 0.820%, Mo: 0.210%, Nb: 0.022%, Ti: 0.028%, Al: 0.025%, Rare Earth RE (Ce+La) = 0.040% (Ce 0.027%, La 0.013%), P: 0.018%, S: 0.008%, N: 0.0045%, O: 0.0018%, with the balance being Fe, and no other harmful impurities.

[0011] Welding wire: ER50-6 modified welding wire, containing trace amounts of Ti and B; fixed composition of the base ER50-6 matrix by mass percentage:

[0012] C: 0.090%, Mn: 1.620%, Si: 0.950%, P: 0.012%, S: 0.007%, Ni: 0.010%, Cr: 0.030%, Mo: 0.010%, Cu: 0.020%; fixed values ​​for trace refining elements: Ti = 0.042%, B = 0.0028%; the remainder is Fe and impurities.

[0013] Protective gas, by volume fraction: 92%Ar + 8%CO2, flow rate 22-26L / min.

[0014] 2. Composite welding parameters

[0015] Base current: 170-200A; Pulse current: 240-260A;

[0016] Voltage: 15-17V; Thermal input: 5.5-7.0kJ / cm;

[0017] Welding speed: 5-7mm / s; Pulse frequency: 15-25Hz.

[0018] 3. In-situ self-tempering enhancement

[0019] After welding, the residual heat is used to keep the heat-affected zone at 200-300℃ for 10-15 seconds, precipitating 20-50nm Ce2O3 and La2O3 particles, pinning grain boundaries and strengthening the softened zone.

[0020] 4. Double-sided welding secondary refinement

[0021] The second heat input is reduced by 8-12%, which refines the recrystallization of the heat-affected zone from the first heat input.

[0022] Furthermore, the base current is 185A, the pulse current is 250A, the voltage is 16V, and the thermal input is 6.2kJ / cm.

[0023] Furthermore, the gas flow rate is 24 L / min, and the welding speed is 6 mm / s.

[0024] Furthermore, the second heat input is reduced by 10%.

[0025] Furthermore, the self-tempering temperature is 260℃, and the holding time is 12 seconds.

[0026] Furthermore, after welding, the following properties are met: heat-affected zone hardness: 242HV; tensile strength: 718MPa; dimple depth: 2.6μm; softened zone width: 0.4mm; metallographic structure: fine lath martensite + nano-rare earth precipitates.

[0027] Furthermore, after welding, the following conditions are met: the hardness of the heat-affected zone increases by ≥25HV, and the hardness of the softened zone increases by ≥235HV; the tensile strength increases by ≥10% to ≥700MPa; the dimple depth increases by ≥2.2μm, exhibiting excellent toughness; no post-weld heat treatment is required, and deformation is minimal; rare earth elements are evenly distributed, with no abnormal inclusions.

[0028] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0029] (1) The hardness of the heat-affected zone increases by ≥25HV, and the hardness of the softened zone increases by ≥235HV;

[0030] (2) Tensile strength ≥700MPa, with an increase of ≥10%;

[0031] (3) The dimple depth is ≥2.2μm, indicating excellent toughness;

[0032] (4) No post-weld heat treatment is required, and deformation is minimal;

[0033] (5) The rare earth elements are evenly distributed and there are no abnormal inclusions. Detailed Implementation

[0034] Example 1: 12mm low rare earth wear-resistant steel

[0035] Base material: Low rare earth wear-resistant steel (plate thickness 12mm, fixed composition for specific examples, mass fraction wt.%)

[0036] Compatible with Baosteel RE=0.040% intermediate low rare earth wear-resistant steel, precise value:

[0037] C: 0.140%, Si: 0.450%, Mn: 1.320%, Cr: 0.820%, Mo: 0.210%, Nb: 0.022%, Ti: 0.028%, Al: 0.025%, Rare Earth RE (Ce+La) = 0.040% (Ce 0.027%, La 0.013%), P: 0.018%, S: 0.008%, N: 0.0045%, O: 0.0018%, with the balance being Fe, and no other harmful impurities.

[0038] 1. V-shaped bevel, angle 60°;

[0039] 2. CMT+Pulse: Base current 185A, pulse current 250A, voltage 16V, thermal input 6.2kJ / cm;

[0040] 3. Gas flow rate: 24 L / min; Welding speed: 6 mm / s;

[0041] 4. Double-sided welding reduces heat input by 10% in the second stage;

[0042] 5. Self-tempering temperature 260℃, hold for 12 seconds.

[0043] Performance results:

[0044] Heat-affected zone hardness: 242 HV; tensile strength: 718 MPa;

[0045] Dip depth: 2.6 μm; softened zone width: 0.4 mm;

[0046] Metallography: Fine lath martensite + nano-rare earth precipitates.

[0047] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A welding process for in-situ repair of softened heat-affected zone in low rare earth wear-resistant steel welding, characterized in that, include: (1) Materials and equipment Base material: Low rare earth wear-resistant steel; Welding wire: ER50-6 modified welding wire, containing trace amounts of Ti and B; Protective gas: 92% Ar + 8% CO2, flow rate 22-26 L / min; (2) Composite welding parameters Base current: 170-200A; Pulse current: 240-260A; Voltage: 15-17V; Thermal input: 5.5-7.0kJ / cm; Welding speed: 5-7mm / s; Pulse frequency: 15-25Hz; (3) In-situ self-tempering enhancement After welding, the residual heat is used to keep the heat-affected zone at 200-300℃ for 10-15 seconds to precipitate 20-50nm Ce2O3 and La2O3 particles, which pin the grain boundaries and strengthen the softened zone. (4) Double-sided welding secondary refinement The second heat input is reduced by 8-12%, which refines the recrystallization of the heat-affected zone from the first heat input.

2. The in-situ repair welding process for softening of the heat-affected zone in low rare earth wear-resistant steel welding according to claim 1, characterized in that, Base current 185A, pulse current 250A, voltage 16V, heat input 6.2kJ / cm.

3. The in-situ repair welding process for softening of the heat-affected zone in low rare earth wear-resistant steel welding according to claim 2, characterized in that, Gas flow rate 24L / min, welding speed 6mm / s.

4. The in-situ repair welding process for softening of the heat-affected zone in low rare earth wear-resistant steel welding according to claim 3, characterized in that, The second heat input is reduced by 10%.

5. The in-situ repair welding process for softening of the heat-affected zone in low rare earth wear-resistant steel welding according to claim 4, characterized in that, Self-tempering temperature 260℃, hold time 12s.

6. The in-situ repair welding process for softening of the heat-affected zone in low rare earth wear-resistant steel welding according to claim 5, characterized in that, After welding, the following requirements must be met: heat-affected zone hardness: 242 HV; tensile strength: 718 MPa; dimple depth: 2.6 μm; softened zone width: 0.4 mm. Metallography: Fine lath martensite + nano-rare earth precipitates.

7. The in-situ repair welding process for softening of the heat-affected zone in low rare earth wear-resistant steel welding according to claim 1, characterized in that, After welding, the following conditions must be met: the hardness of the heat-affected zone increases by ≥25HV, and the hardness of the softened zone increases by ≥235HV; the tensile strength increases by ≥10% to ≥700MPa; the dimple depth increases by ≥2.2μm, and the toughness is excellent; no post-weld heat treatment is required, and the deformation is small; the rare earth elements are evenly distributed and there are no abnormal inclusions.