Cold-rolled non-oriented silicon steel 50w600 and method for producing the same

Abstract

The present application relates to the technical field of cold-rolled non-oriented silicon steel production, in particular to a cold-rolled non-oriented silicon steel 50W600 and a production method thereof. The cold-rolled non-oriented silicon steel 50W600 is composed of the following chemical components with the weight percentage: C≤0.0027%, Si: 1.20%-1.50%, Als: 0.25%-0.50%, Mn: 0.25%-0.50%, P: 0.005%-0.015%, N≤0.0015%, S≤0.0030%, B: 0.0025%-0.0050%, Nb+V+Ti≤0.0035%, the molar ratio of N and B is between 1:0.6 and 1:1.2, the molar ratio of S and Cu is between 1:0.8 and 1:1.5, and the rest is Fe and inevitable impurities. The process flow is: smelting, continuous casting, hot rolling, cooling and coiling, heat preservation treatment and cold rolling. The high-performance typical medium-grade 50W600G product is obtained, the product quality level of the medium-thin slab continuous casting and rolling production line is significantly improved, and the variety coverage range of the production line is widened.

Description

Technical Field

[0001] This invention relates to the field of cold-rolled non-oriented silicon steel production technology, specifically to a cold-rolled non-oriented silicon steel 50W600 and its production method. Background Technology

[0002] With the continuous improvement of motor energy efficiency standards, cold-rolled non-oriented silicon steel 50W600, as a core material for small and medium-sized high-efficiency motors, has increasingly stringent performance requirements, needing to meet iron loss P... 1.5 / 50 ≤4.00W / kg, magnetic induction B 5000 The key indicator is ≥1.72T. Currently, while conventional large slab continuous casting and rolling can stably produce high-performance products, it suffers from high equipment investment and energy consumption. While medium-thin slab continuous casting and rolling offers cost advantages, high casting speeds lead to coarsening of precipitates and uneven microstructure, significantly degrading the electromagnetic properties of the product. Iron loss is generally higher than 0.2W / kg, and defects such as poor plate shape and edge cracks also exist. Existing technologies, such as attempts to improve the process using microalloying or hot rolling, either result in uncontrolled precipitates or quality fluctuations caused by rolling in the two-phase region, failing to fundamentally solve the performance bottleneck of medium-thin slab processes. In particular, traditional hot-rolling box temperature control technology has failed to coordinate with the precipitate evolution law for optimization, resulting in uneven grain size distribution (ASTM 4-6 grades), severely restricting the application of this process in the production of medium-grade silicon steel. Summary of the Invention

[0003] To overcome the shortcomings of the prior art, this invention provides a cold-rolled non-oriented silicon steel 50W600 and its production method, which obtains high-performance typical medium grade 50W600G products, significantly improves the product quality level of the medium and thin slab continuous casting and rolling production line, and broadens the product range of the production line.

[0004] To achieve the above objectives, the present invention employs the following technical solution:

[0005] A typical cold-rolled non-oriented medium-grade silicon steel product, 50W600, is composed of the following chemical composition by weight percentage: C≤0.0027%, Si: 1.20%~1.50%, Als: 0.25%~0.50%, Mn: 0.25%~0.50%, P: 0.005%~0.015%, N≤0.0015%, S≤0.0030%, B: 0.0025%~0.0050%, Nb+V+Ti≤0.0035%, the molar ratio of N to B is between 1:0.6 and 1:1.2, the molar ratio of S to Cu is between 1:0.8 and 1:1.5, and the remainder is Fe and unavoidable impurities.

[0006] The effect of selecting the above alloying elements and their contents:

[0007] C≤0.0027%. Carbon is an extremely harmful element in electrical steel because it forms an interstitial solid solution with iron, causing severe lattice distortion, resulting in significant internal stress and a marked decrease in magnetism.

[0008] Si: 1.20%~1.50%. Si is the main alloying element of silicon steel and a major factor affecting magnetism, which is beneficial to {100} <001> Orientation development and promotion of grain growth.

[0009] Als: 0.25%~0.50%. In non-oriented silicon steel, aluminum plays an important role in magnetism. It can increase resistivity, shrink the γ region and promote grain growth. It can increase the (100) component and decrease the (111) component. It reduces iron loss by a greater margin than Si, and reduces magnetic induction by a smaller margin than Si. The beneficial effect becomes more obvious as the Si content increases.

[0010] Mn: 0.25%~0.50%. Manganese increases resistivity, improves hot-rolled plasticity and microstructure, promotes MnS coarsening, facilitates grain growth, and enhances electromagnetic properties.

[0011] P: 0.005%~0.015%, S≤0.0030%. P increases resistivity, increases hardness, and improves die-casting properties. Like antimony, P is effective against {111}. <112> Texture components have an inhibitory effect. As the phosphorus content increases, the magnetic induction intensity increases; however, with increasing cold rolling reduction, the decrease in magnetic induction is smaller when the phosphorus content is high. Recrystallization texture with high phosphorus content {111} <112> The strength of the component is much lower than that of components with low phosphorus content, thus improving the magnetic properties of non-oriented electrical steel. S, through the presence of fine MnS particles in the matrix and free S at grain boundaries, deteriorates the magnetic properties; it is an unavoidable impurity element, and lower levels are better.

[0012] N ≤ 0.0015%. N can react with Al to form AlN, and fine AlN particles can degrade magnetic properties, so its content must be strictly controlled.

[0013] The molar ratio of N to B is between 1:0.6 and 1:1.2, and the molar ratio of S to Cu is between 1:0.8 and 1:1.5. The purpose of adding trace elements of boron and copper is to preferentially form fine precipitates of boron nitride and copper sulfide during the refining process and the rapid solidification process of the medium and thin slab at high drawing speed, and to control the aggregation and coarsening of aluminum nitride and manganese sulfide around them during the subsequent thermal run. At the same time, the boron grain boundary segregation characteristics are utilized to suppress the proportion of unfavorable texture (111) components during the heat treatment of the finished product. Furthermore, in the boron-copper composite effect, the boron grain boundary segregation and surface enrichment reduce the impact of "copper" embrittlement. The boron trace element design also avoids grain refinement, and the copper trace element also prevents the tendency of steel to be "hot brittle". Other relatively harmful elements are not excessive. The cleanliness requirements are consistent with those of conventional product production, which is also conducive to production organization and overall smelting cost control.

[0014] Nb+V+Ti≤0.0035%. These elements are harmful to electrical steel, forming fine precipitates that hinder grain growth and deteriorate performance. Therefore, their content must be strictly controlled.

[0015] The above-mentioned non-oriented silicon steel loss P 1.5 / 50 ≤4.00W / kg, magnetic induction B 5000 ≥1.73T.

[0016] The production method of the above-mentioned typical product, 50W600, of non-oriented medium-grade silicon steel specifically includes the following steps:

[0017] 1. Smelting process flow: Hot metal pretreatment → Converter smelting → LF refining → RH vacuum treatment.

[0018] 2. Continuous casting:

[0019] The thickness of the billet section is 90~170mm; the billet casting speed is controlled at 1.5~4.0m / min; the billet is hot-charged and hot-delivered, and the furnace charging temperature is ≥600℃.

[0020] 3. Hot rolling:

[0021] The hot rolling process is adopted, which involves heating, rough rolling, hot coiling, and finishing rolling.

[0022] Heating control: The temperature of the first heating section is 1180~1240℃, the temperature of the second heating section is 1170~1140℃; the time in the furnace is 55~80min, the overall steel rolling rhythm is balanced, the temperature of the soaking section is 1150~1120℃, and in principle, the soaking section is skipped and the steel is directly passed through the roughing mill.

[0023] Rough rolling: The thickness of the intermediate billet in rough rolling is controlled at 30~45mm;

[0024] Hot roll box winding: winding temperature 990~1030℃, using external heat insulation cover or compensating heating to maintain a constant temperature, the interval from the start of winding to unwinding and finishing rolling is ≥2min;

[0025] Finishing rolling: final rolling temperature 880~920℃, finished product thickness 2.0~2.5mm.

[0026] 4. Cooling and winding:

[0027] Steel strip cooling section control: No cooling is allowed for the first 10-20m of the head and tail sections; cooling begins from the 40%-60% section after the cooling section and continues until the coiler winds it up.

[0028] Winding: Winding box temperature 750~820℃, transport out and keep warm (e.g., put into an insulated pit).

[0029] 5. Thermal insulation treatment:

[0030] The insulation temperature of the steel coil is ≥730℃, and the insulation time is ≥6h.

[0031] 6. Cold rolling:

[0032] The hot-rolled coil is then cold-rolled to produce 0.5mm cold-rolled steel strip, which is then produced by a continuous annealing unit. The continuous annealing temperature is 920℃~940℃. The furnace time is controlled by the process speed, and the finished product grain size is controlled to grade 5~5.5 to obtain the high-performance typical grade 50AW600G product.

[0033] From the first heating section to the completion of rolling and coil holding, the aim is to promote the fine formation and precipitation of boron nitride and copper sulfide in the relatively high-temperature section. As the temperature gradually decreases and the time is controlled in each stage, especially by utilizing the temperature control and holding time of the hot coil box, aluminum nitride and manganese sulfide are further promoted to gather and coarsen around it, and to form carbon, nitrogen, and sulfur compounds of other residual elements. At the same time, by controlling the temperature of the hot coil box, the proportion of austenite and ferrite in the two-phase region or the rolling of the near-single-phase region is reasonably adjusted during the finishing rolling process to maintain rolling stability. Meanwhile, by controlling the final rolling temperature and cooling method, coiling, and holding the coil, the recrystallization of the steel plate matrix and the equiaxed crystallization of the grains are further controlled, replacing the normalization process of high-efficiency materials. The overall hot rolling process has a compact production rhythm and high production efficiency (relying on the "uniform heating" of the hot coil box to shorten the furnace time by more than 30 minutes), and the micro and macro structure is controlled by the temperature regime to meet the raw material requirements for the production of high-efficiency finished materials.

[0034] Compared with the prior art, the beneficial effects of the present invention are:

[0035] 1. This invention achieves an optimized balance between performance and cost by precisely controlling the synergistic effect of core and trace elements. In terms of basic composition, a design employing low carbon (C≤0.0027%), low nitrogen (N≤0.0015%), and specific silicon-aluminum content (Si 1.20%~1.50%, Als 0.25%~0.50%) ensures both resistivity and processing performance. The introduction of boron-copper composite microalloying technology, controlling the nitrogen-boron ratio (1:0.6-1.2) and sulfur-copper ratio (1:0.8-1.5), preferentially forms BN / CuS nanoscale precipitates (20~50nm) during smelting. These precipitates, acting as heterogeneous nucleation cores, effectively suppress the coarsening of harmful phases such as AlN / MnS (size controlled at 80~150nm). Meanwhile, the grain boundary segregation characteristics of boron significantly reduced the proportion of unfavorable texture (111) components (≤15%), while the surface enrichment effect of copper alleviated the copper embrittlement tendency. This composition design, without increasing smelting difficulty and cost, enabled the product to stably achieve P-level electromagnetic properties. 1.5 / 50 ≤3.95W / kg, B 5000With an excellent strength of ≥1.73T, it also ensures good hot working performance (hot rolling crack rate <0.5%) and stable grain size (ASTM 5-5.5 grade), providing a reliable compositional solution for the production of high-performance silicon steel using the continuous casting and rolling process for medium and thin slabs.

[0036] 2. In terms of process design, this invention, from the first heating section to the completion of rolling and coil heat preservation, aims to promote the fine formation and precipitation of boron nitride and copper sulfide in the relatively high-temperature section. As the temperature gradually decreases and the time of each stage is controlled, especially by utilizing the temperature control and heat preservation time of the hot coil box, aluminum nitride and manganese sulfide are further promoted to gather and coarsen around it, and to form carbon, nitrogen, and sulfur compounds of other residual elements. At the same time, by controlling the temperature of the hot coil box, the proportion of austenite and ferrite in the two-phase region or the rolling of the near-single-phase region is reasonably adjusted during the finishing rolling process to maintain rolling stability. Meanwhile, by controlling the final rolling temperature and cooling method, coiling, and heat preservation of the steel coil, the recrystallization of the steel plate matrix and the equiaxed crystallization of the grains are further controlled, replacing the normalization process of high-efficiency materials. The overall hot rolling process has a compact production rhythm and high production efficiency (relying on the "uniform heating" of the hot coil box to shorten the furnace time by more than 30 minutes), and the micro and macro structure is controlled by the temperature regime to meet the raw material requirements for the production of high-efficiency finished materials.

[0037] 3. This invention achieves microstructure optimization throughout the entire process from heating to coiling through innovative temperature gradient control and microalloying synergistic regulation technology. The process employs high-temperature heating at 1180~1240℃ to promote the nanoscale precipitation of BN and CuS. Precise temperature control at 990~1030℃ in the hot coiling box allows AlN and MnS to epitaxially grow with BN / CuS as the core, forming 50~150nm composite precipitates. The innovative use of quasi-single-phase rolling (γ phase ≥85%) combined with final rolling at 880~920℃ and laminar flow cooling yields a uniform microstructure with an equiaxed crystal ratio ≥90%. Holding the steel coil at 730℃ for 6 hours replaces normalizing treatment, stabilizing the grain size at ASTM 5-5.5 grade. This process reduces iron loss P 1.5 / 50 ≤3.95W / kg, magnetic induction B 5000 With a capacity of ≥1.73T, the defect rate of sheet shape has been reduced from 12% to below 5%. At the same time, the "dynamic uniform heating" technology of the hot coil box has shortened the heating time by 35 minutes, and the production rhythm of the entire line has been increased to 65 seconds per coil, reducing energy consumption per ton of steel by 18%. Detailed Implementation

[0038] The chemical composition of the embodiments and comparative examples of the present invention is shown in Table 1; the key process parameters of the embodiments and comparative examples of the present invention are shown in Tables 2 and 3; the mechanical property parameters of the present invention are shown in Table 4.

[0039] Table 1. Specific chemical composition (Wt%) of the examples

[0040]

[0041] Table 2 Key process parameters for examples and comparative examples

[0042]

[0043] Table 3 Key process parameters for examples and comparative examples II

[0044]

[0045] Table 4 Technical Performance Table

[0046]

[0047] Note: The cold rolling process parameters for the examples and comparative examples are as follows: after cold rolling for 0.50m, the hot rolling process in the examples involves 4 passes of rough rolling, followed by coiling and hoisting to the insulation pit for insulation.

[0048] The implementation of this invention significantly improves the overall performance and production efficiency of the 50AW600 series products. A comparison of actual production data between the traditional and improved processes (50AW600G) shows that, in terms of chemical composition, the innovative introduction of boron and copper microalloying, combined with optimized hot rolling processes, results in a breakthrough improvement in the product's electromagnetic properties. Simultaneously, the production process is significantly optimized, leading to a marked improvement in product performance consistency. This invention successfully achieves the dual goals of product quality upgrading and manufacturing process optimization without increasing production costs.

[0049] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. Cold-rolled non-oriented silicon steel 50W600, characterized in that, It is composed of the following chemical components in weight percentage: C≤0.0027%, Si: 1.20%~1.50%, Als: 0.25%~0.50%, Mn: 0.25%~0.50%, P: 0.005%~0.015%, N≤0.0015%, S≤0.0030%, Cu: 0.0026%~0.0038%, B: 0.0025%~0.0050%, Nb+V+Ti≤0.0035%, the molar ratio of N to B is between 1:0.6 and 1:1.2, the molar ratio of S to Cu is between 1:0.8 and 1:1.5, and the remainder is Fe and unavoidable impurities; The non-oriented silicon steel loss P 1.5 / 50 ≤4.00W / kg, magnetic induction B 5000 ≥1.73T.

2. A method for producing cold-rolled non-oriented silicon steel 50W600 as described in claim 1, characterized in that, Specifically, the steps include the following: 1) Smelting; 2) Continuous casting: The thickness of the billet section is 90~170mm; the billet casting speed is controlled at 1.5~4.0m / min; the billet is hot-charged and hot-delivered, and the furnace charging temperature is ≥600℃; 3) Hot rolling: The hot rolling process is adopted, which involves heating, rough rolling, hot coiling, and finishing rolling. Heating control: First heating section temperature 1180~1240℃, second heating section temperature 1140~1170℃; furnace time 55~80min, soaking zone temperature 1120~1150℃; Rough rolling: The thickness of the intermediate billet in rough rolling is 30~45mm; Hot coil box winding: The temperature of the winding box is 990~1030℃, and the interval between winding and unwinding is ≥2min; Finish rolling: final rolling temperature 880~920℃, finished product thickness 2.0~2.5mm; 4) Cooling and winding: Steel strip cooling section control: No cooling is allowed for the first 10-20m of the head and tail sections; cooling begins from the 40%-60% section after the cooling section and continues until the coiler winds it up. Winding: Winding temperature 750~820℃; 5) Thermal insulation treatment: During transportation, steel coils should be insulated or placed in insulated pits. The insulation temperature of the steel coils should be ≥730℃ and the insulation time should be ≥6h. 6) Cold rolling: The annealing temperature is 920~940℃; the grain size after annealing is ASTM grade 5~5.

5.

3. The production method of cold-rolled non-oriented silicon steel 50W600 according to claim 2, characterized in that, In step 1), the smelting process flow is: molten iron pretreatment → converter smelting → LF refining → RH vacuum treatment.

4. The production method of cold-rolled non-oriented silicon steel 50W600 according to claim 2, characterized in that, In step 3), the heating furnace is a walking beam furnace.

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