Method for stabilizing magnetic properties of welded joint of non-oriented silicon steel

Abstract

The application discloses a kind of non-oriented silicon steel welding joint magnetic property stabilization control method, belong to silicon steel processing and welding technical field.The present application uses low heat input CMT welding, heat input 3.0-4.5kJ / cm, cooperate 99.9%Ar+0.1%O2 protection and 25-30 ℃ / s rapid cooling, inhibit weld grain coarsening, make weld zone grain ≤8 μm, no coarse columnar crystal, joint permeability loss ≤5%.The present application can significantly improve the problem of silicon steel welding magnetic property sudden drop, suitable for non-oriented / oriented silicon steel coiled material, plate material welding, simple process, no special equipment, suitable for baogang silicon steel production line.

Description

Technical Field

[0001] This invention belongs to the field of silicon steel processing and welding technology, and particularly relates to a method for stabilizing and controlling the magnetic properties of non-oriented silicon steel welded joints. Background Technology

[0002] Non-oriented silicon steel is a core material for motors and transformers, requiring extremely high permeability and iron loss. Traditional MAG and plasma welding involve high heat input, leading to a sharp increase in grain size in the weld and heat-affected zone, a 15-30% decrease in permeability, and a significant increase in iron loss, which cannot meet the requirements of high-efficiency motors.

[0003] Existing technologies mostly employ laser welding, but the equipment is expensive; research on low heat input processes is insufficient, making it impossible to simultaneously guarantee penetration depth and magnetic properties. Therefore, developing welding methods with low heat input, fine grain formation, and stable magnetic properties is crucial for high-quality welding of silicon steel.

[0004] Patent application number 202411283929.X discloses a welding wire and welding method for reducing the breakage rate of normalized welds in high-silicon non-oriented silicon steel. The welding wire comprises the following chemical composition by mass percentage: C: 0.15%~0.20%, Si: ≤0.35%, Mn: 2.0~2.5%, Ni: 2.0~2.5%, Cr: 0.8~1.0%, with the remainder being Fe. The welding method includes using the above welding wire as filler material to perform laser welding on non-oriented silicon steel. This invention, through optimization of welding wire composition and welding process, controls the weld microstructure, forms a bainitic structure, strengthens ductility and toughness, achieves a 100% cupping test pass rate, and a normalized weld breakage rate ≤0.05%. The following problems exist: it only improves weld toughness and reduces normalization breakage rate, but lacks a magnetic performance control scheme, resulting in coarse weld grains and a magnetic permeability loss of 15% to 30%, which does not meet the requirements of high-efficiency motors; it requires the use of expensive laser equipment, necessitating large-scale modifications to existing CMT production lines, which are costly; it requires customized high-alloy special welding wire, resulting in high material costs, and wire replacement will delay production; it only solves the breakage problem in the normalization process, but lacks a post-weld ultra-fast cooling process, leading to continuous coarsening of grains in the heat-affected zone, and limiting its application scenarios.

[0005] Patent application number 202411383276.2 discloses a method for manufacturing high-efficiency non-oriented silicon steel for variable frequency compressors. Compared with existing technologies, this invention uses the acid continuous rolling mill stand as a leveling machine, avoiding the impact of switching emulsion systems on production efficiency. The absence of welding wire ensures weld quality, and induction heating of the strip before cold rolling is unnecessary, saving costs. Only one edge trimming is required for the finished product, improving yield and increasing production efficiency. Furthermore, the composition is simple and the cost is low. The rolling speed reaches 600-800 m / min, with longitudinal thickness fluctuation within ±3 μm and plate thickness difference ≤5 μm, meeting the requirements for stators and rotors in high-efficiency variable frequency compressors. Compared to this application, the following problems exist: it focuses on rolling and material efficiency optimization, lacks a magnetic control process for welding, and the magnetic loss of the laser self-fusion welded head is severe, making it only suitable for ordinary compressors and not for high-end high-efficiency motors; it relies on expensive laser equipment, lacks filler wire, and is prone to burn-through or incomplete penetration when welding thick and thin silicon steel, making process debugging troublesome; the process is only suitable for silicon steel in variable frequency compressors and cannot be used universally for silicon steel in new energy motors and transformers; it is naturally air-cooled after welding, without forced ultra-fast cooling, resulting in coarse grains, and there is no limitation on special protective gas, making the weld seam prone to oxidation and inclusion, further deteriorating the magnetism.

[0006] Patent application number 202511068018.X discloses a continuous annealing method for new energy non-oriented silicon steel, comprising: annealing in a continuous annealing furnace, firstly uncoiling and welding the cold-rolled coil, then pre-cleaning to remove oil stains and impurities from the steel strip surface, and then annealing in the annealing furnace, which is divided into a heating section (RTF), a soaking section (SF), a tube cooling section (CTF), a controlled cooling section (SJC), and a rapid cooling section (RJC). The purpose of this invention is to provide a continuous annealing method for new energy non-oriented silicon steel, and to formulate an annealing process based on the equipment conditions of the continuous annealing furnace, so as to achieve new energy non-oriented silicon steel with low iron loss, high magnetic induction, and high strength. The following problems exist: The core focus is on the annealing furnace temperature control process, which only optimizes the overall magnetic properties of the base material and does not specifically address the magnetic degradation of the weld joint. There is no low heat input welding or post-weld ultra-fast cooling crystallization control scheme, resulting in coarse weld grains and high magnetic permeability loss. It only controls the cooling throughout the annealing process and does not involve the heat input, protective atmosphere, or immediate rapid cooling after welding, which cannot suppress grain coarsening in the weld and heat-affected zone. It only improves the properties of the steel strip matrix, with welding only as a pre-process auxiliary step. There is no complete welding process specifically designed to stabilize the magnetic properties of the joint, and it cannot solve the industry pain point of the sharp drop in magnetic properties after silicon steel welding. Summary of the Invention

[0007] The purpose of this invention is to provide a method for stabilizing and controlling the magnetic properties of non-oriented silicon steel welded joints. This invention achieves fine grain formation of the weld seam through low heat input and ultra-fast cooling, thereby controlling the magnetic property loss to within 5%.

[0008] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0009] This invention discloses a method for stabilizing and controlling the magnetic properties of non-oriented silicon steel welded joints. Through low heat input and ultra-fast cooling treatment, it achieves weld grain refinement, controlling magnetic property loss to within 5%.

[0010] Low heat input welding: current 100-140A, voltage 13-15V, heat input 3.0-4.5kJ / cm;

[0011] Protective gas: 99.9% Ar + 0.1% O2, flow rate 18~22 L / min;

[0012] Welding speed: 8-12 mm / s;

[0013] Ultra-fast cooling: Immediately after welding, the temperature is cooled to 200℃ at 25-30℃ / s to inhibit grain growth.

[0014] Furthermore, after low heat input and ultra-fast cooling treatment: the weld grain size is ≤8μm, with no columnar crystals and no Widmanstätten structure.

[0015] Furthermore, CMT low heat input soldering is adopted.

[0016] Furthermore, the welding parameters are: 120A, 14V, heat input 3.8kJ / cm, speed 10mm / s.

[0017] Furthermore, the protective gas flow rate is 20 L / min.

[0018] Furthermore, ultra-fast cooling: immediately after welding, the temperature is cooled to 200°C at a rate of 28°C / s.

[0019] Furthermore, the results showed that the weld grain size was 7.2 μm and the magnetic permeability decreased by 3.8%, meeting the requirements for high-efficiency motors.

[0020] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0021] (1) The weld grain size is ≤8μm and the microstructure is uniform;

[0022] (2) Permeability decreases by ≤5%, iron loss increases by ≤6%;

[0023] (3) Stable melting depth, no porosity or cracks;

[0024] (4) Low cost and compatible with existing CMT equipment. Detailed Implementation

[0025] Example 1 (Standard Process of the Invention)

[0026] Base material: 1.0mm high-efficiency non-oriented silicon steel (its chemical composition by weight percentage is: Si: 3.20%; Al: 0.80%; Mn: 0.27%; C: 0.002%; S: 0.002%; N: 0.002%; P: 0.015%; the remainder is Fe and impurities)

[0027] Soldering method: CMT low heat input soldering

[0028] Current 120A, voltage 14V, heat input 3.8kJ / cm, welding speed 10mm / s

[0029] Protective gas: 99.9% Ar + 0.1% O2, flow rate 20 L / min

[0030] Cooling rate: 28℃ / s, cooling to 200℃

[0031] Test results: The weld grain size is 7.2 μm, with no columnar grains or Widmanstätten structure; the magnetic permeability decreased by 3.8%, and the iron loss increased by 4.2%, meeting the requirements for high-efficiency motors.

[0032] Comparative Example 1: Traditional MAG welding (existing conventional silicon steel welding method)

[0033] process parameters

[0034] Base material: Same as in Example 1, 1.0mm high-efficiency non-oriented silicon steel

[0035] Welding method: Standard MAG welding

[0036] Current 160A, voltage 18V, heat input 6.2kJ / cm, welding speed 6mm / s

[0037] Protective gas: 80% Ar + 20% CO2, flow rate 22 L / min

[0038] Cooling method: Natural air cooling after welding

[0039] Test results

[0040] The weld grain size is 21.6 μm, and it contains a large number of coarse columnar grains and Widmanstätten structure.

[0041] Magnetic permeability decreased by 22.7%, while iron loss increased by 19.3%.

[0042] The weld shows visible micropores and has a wide heat-affected zone, making it unsuitable for use in high-efficiency motors.

[0043] Comparative Example 2: The process system of this application, but the parameters exceed the scope of protection of the claims (low heat input not meeting the standard + insufficient cooling rate).

[0044] process parameters

[0045] Base material: Same as in Example 1, 1.0mm high-efficiency non-oriented silicon steel

[0046] Soldering method: CMT soldering

[0047] Current 150A, voltage 16V, heat input 5.1kJ / cm (exceeding the upper limit of 3.0~4.5kJ / cm), welding speed 7mm / s (below the lower limit of 8~12mm / s)

[0048] Protective gas: 99.9% Ar + 0.1% O2, flow rate 20 L / min

[0049] Cooling rate: 18℃ / s to 200℃ (below the lower limit of 25~30℃ / s)

[0050] Test results

[0051] The weld grain size is 9.5 μm, with localized coarse dendrites.

[0052] The permeability decreased by 6.4% (exceeding the target requirement of ≤5%).

[0053] Iron loss increased by 7.8%, and the magnetic properties of the joints did not meet the standards for high-efficiency motors.

[0054] Comparison and summary:

[0055] Compared with Comparative Example 1 (traditional MAG): The low heat input + ultra-fast cooling of the present invention CMT can significantly refine the weld grain, and the magnetic performance attenuation is only about 1 / 6 of that of the traditional process, with fewer defects;

[0056] Comparative Example 2 (parameters out of range): When any parameter of heat input, welding speed, or cooling rate deviates from the range defined in the claims, the weld grains coarsen, the magnetic permeability loss exceeds the 5% threshold, and the expected effect of the invention is not achieved, proving that the parameter range of this application is unique and necessary.

[0057] 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 method for stabilizing and controlling the magnetic properties of non-oriented silicon steel welded joints, characterized in that, By using low heat input and ultra-fast cooling treatment, the weld seam is refined, and the magnetic property loss is controlled to within 5%. Low heat input welding: current 100-140A, voltage 13-15V, heat input 3.0-4.5kJ / cm; Protective gas: 99.9% Ar + 0.1% O2, flow rate 18~22 L / min; Welding speed: 8-12 mm / s; Ultra-fast cooling: Immediately after welding, the temperature is cooled to 200℃ at 25-30℃ / s to inhibit grain growth.

2. The method for stabilizing and controlling the magnetic properties of non-oriented silicon steel welded joints according to claim 1, characterized in that, After low heat input and ultra-fast cooling treatment: the weld grain size is ≤8μm, with no columnar crystals and no Widmanstätten structure.

3. The method for stabilizing and controlling the magnetic properties of non-oriented silicon steel welded joints according to claim 1, characterized in that, CMT low heat input soldering is used.

4. The method for stabilizing and controlling the magnetic properties of non-oriented silicon steel welded joints according to claim 3, characterized in that, Welding parameters: 120A, 14V, heat input 3.8kJ / cm, speed 10mm / s.

5. The method for stabilizing and controlling the magnetic properties of non-oriented silicon steel welded joints according to claim 4, characterized in that, Protective gas flow rate: 20 L / min.

6. The method for stabilizing and controlling the magnetic properties of non-oriented silicon steel welded joints according to claim 5, characterized in that, Ultra-fast cooling: immediately after welding, the temperature is cooled to 200°C at a rate of 28°C / s.

7. The method for stabilizing and controlling the magnetic properties of non-oriented silicon steel welded joints according to claim 6, characterized in that, Results: The weld grain size was 7.2 μm and the magnetic permeability decreased by 3.8%, meeting the requirements for high-efficiency motors.