Cold-rolled non-oriented silicon steel 50W600 and production method thereof

Abstract

The invention relates to the technical field of cold-rolled non-oriented silicon steel production, in particular to cold-rolled non-oriented silicon steel 50W600 and a production method thereof. The invention discloses a high-strength and high-toughness alloy which is composed of the following chemical components in percentage by weight: less than or equal to 0.0027% of C, 1.20%-1.50% of Si, 0.25%-0.50% of Als, 0.25%-0.50% of Mn, 0.005%-0.015% of P, less than or equal to 0.0015% of N, less than or equal to 0.0030% of S, 0.0025%-0.0050% of B, less than or equal to 0.0035% of Nb, V and Ti, 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 balance of Fe and inevitable impurities. The technological process comprises the steps of smelting, continuous casting, hot rolling, cooling and coiling, heat preservation treatment and cold rolling. And a high-performance typical medium-grade 50W600G product is obtained, the product quality level of a medium-thin slab continuous casting and rolling production line is remarkably improved, and the variety coverage range of the production line is widened.

Description

TECHNICAL FIELD

[0001] 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. BACKGROUND

[0002] With the continuous improvement of motor efficiency standards, the performance requirements of cold-rolled non-oriented silicon steel 50W600 as the core material of small and medium-sized high-efficiency motors are increasingly strict, and need to meet the key indicators of iron loss P 1.5 / 50 ≤4.00W / kg and magnetic induction B 5000 ≥1.72T. In the current mainstream production process, although the conventional large slab continuous casting and rolling can stably produce high-performance products, it has problems such as large equipment investment and high energy consumption. Although the medium-thin slab continuous casting and rolling has cost advantages, the coarsening of precipitates and uneven organization caused by high pulling speed make the electromagnetic performance of the product significantly deteriorate, the iron loss is generally higher than 0.2W / kg, and there are defects such as poor plate shape and edge cracking. In the prior art, the attempts to improve the micro-alloying or hot rolling process either lead to uncontrolled precipitates or cause quality fluctuations due to dual-phase rolling, and none of them can fundamentally solve the performance bottleneck of the medium-thin slab process. In particular, the traditional hot coil box temperature control technology cannot be optimized in coordination with the evolution law of precipitates, so that the product grain size distribution is uneven (ASTM 4-6 level), which seriously restricts the application of this process in the production of medium-grade silicon steel. SUMMARY

[0003] In order to overcome the shortcomings of the prior art, the present application provides a cold-rolled non-oriented silicon steel 50W600 and a production method thereof, which obtains a high-performance typical medium-grade 50W600G product, significantly improves the product quality level of the medium-thin slab continuous casting and rolling production line, and widens the variety coverage of the production line.

[0004] In order to achieve the above purpose, the present application adopts the following technical scheme:

[0005] The cold-rolled non-oriented medium-grade silicon steel typical product 50W600 is composed of the following weight percentage of chemical components: 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 rest is Fe and inevitable impurities.

[0006] The role of selecting the above alloy element types and contents:

[0007] C ≤ 0.0027%. Carbon is very harmful to electrical steel, because it forms interstitial solid solution with iron, which makes the lattice distortion serious, causes great internal stress, and makes the magnetic property decrease obviously.

[0008] Si: 1.20%~1.50%. Si is the main alloying element of silicon steel, and is the main factor affecting the magnetic property, which is beneficial to the development of {100} <001> orientation and promotes grain growth.

[0009] Als: 0.25%~0.50%. In non-oriented silicon steel, aluminum plays an important role in the magnetic property, which can increase the resistivity, reduce the γ region and promote grain growth, increase the (100) component and reduce the (111) component. The amplitude of reducing the iron loss is greater than that of Si, and the amplitude of reducing the magnetic induction is smaller than that of Si. With the increase of Si content, the beneficial effect is more obvious.

[0010] Mn: 0.25%~0.50%. Manganese increases the resistivity, improves the hot rolling plasticity and hot rolling structure, is beneficial to the coarsening of MnS, is beneficial to grain growth, and improves the electromagnetic performance.

[0011] P: 0.005%~0.015%, S ≤ 0.0030%. P increases the resistivity, increases the hardness and improves the punching property. P and antimony have an inhibitory effect on the {111} <112> texture component. With the increase of p content, the magnetic induction increases, and the cold rolling reduction increases. When the p content is high, the magnetic induction decreases. The recrystallization texture {111} <112> component of high phosphorus content is much lower than that of low phosphorus content, so the magnetic property of non-oriented electrical steel can be improved. S makes the magnetic property worse by existing MnS fine particles in the matrix and free S on the grain boundary, and is an unavoidable impurity element, which is better the lower.

[0012] N ≤ 0.0015%. N can form AlN with Al, and fine AlN can deteriorate the magnetic property, so its content should 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 amounts of boron and copper is to preferentially form fine boron nitride and copper sulfide precipitates during the refining process to the medium thin slab high speed rapid solidification process, and to control the aggregation and coarsening of aluminum nitride and manganese sulfide around it during the subsequent thermal history process. At the same time, boron elements have the characteristics of grain boundary segregation, which can inhibit the proportion of adverse texture (111) component during the product heat treatment process. In addition, in the combined action of boron and copper, boron grain boundary segregation and surface enrichment can reduce the influence of "copper" brittleness. The trace amount of boron is also designed to avoid grain refinement, and the trace amount of copper is also to prevent the tendency of "hot brittleness" of the steel. Other relatively harmful elements are not too clean, and the cleanliness requirement is consistent with the production of conventional products, which is also beneficial to the production organization and the overall cost control of smelting.

[0014] Nb+V+Ti≤0.0035%. The harmful elements of electrical steel can form fine precipitates, hinder grain growth, and deteriorate performance. Therefore, the content of these elements is strictly controlled.

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

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

[0017] 1. Smelting process: hot metal pretreatment → converter smelting → LF refining → RH vacuum treatment.

[0018] 2. Continuous casting:

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

[0020] 3. Hot rolling:

[0021] The hot rolling process of heating + rough rolling + hot coil box + finishing rolling is adopted;

[0022] Heating control: the first heating section temperature is 1180-1240℃, the second heating section temperature is 1170-1140℃; the in-furnace time is 55-80min, the overall balance is out of the furnace and rolled, the soaking section temperature is 1150-1120℃, and in principle, the soaking section is directly passed through the furnace and rough rolled;

[0023] Rough rolling: the rough rolling intermediate blank thickness is controlled at 30-45mm;

[0024] Hot coil box coiling: the coiling temperature is 990-1030℃, the temperature is maintained by using an external heat preservation cover or compensation heating, and the interval time from coiling to uncoiling and finishing rolling is ≥2min;

[0025] Finishing rolling: the final rolling temperature is 880-920℃, and the finished product thickness is 2.0-2.5mm.

[0026] 4. Cooling and coiling:

[0027] Steel strip cooling section control: let through 10-20m without cooling at the head and tail; start cooling from the 40%-60% section after the cooling section until the coiler coiling;

[0028] Coiling: the coiling box temperature is 750-820℃, and the coiled product is transported and heat preserved (e.g. put into a heat preservation pit).

[0029] 5. Heat preservation treatment:

[0030] The steel coil heat preservation temperature is greater than or equal to 730 DEG C, and the heat preservation time is greater than or equal to 6h.

[0031] 6. Cold rolling:

[0032] Subsequently, the hot-rolled coil is subjected to cold rolling to obtain a 0.5mm specification cold-rolled steel strip, and a continuous annealing unit is used for production, the continuous annealing soaking temperature is 920 DEG C~940 DEG C, the in-furnace time is controlled through process speed, the finished product grain size is controlled to be 5~5.5 levels, and a high-performance typical medium-grade 50AW600G product is obtained.

[0033] From the first heating section to the completion of rolling and the heat preservation of the steel coil, the purpose is to promote the fine generation and precipitation of boron nitride and copper sulfide in the relatively high temperature section, and with the gradual decrease of temperature and the control of time in each section, especially by using the temperature control and heat preservation time of the hot coil box, the aggregation and coarsening of aluminum nitride and manganese sulfide around it are further promoted, and the carbon, nitrogen and sulfur compounds of other residual elements are compounded; at the same time, through the temperature control of the hot coil box, the proportion of austenite and ferrite two-phase zone or near single-phase zone is reasonably adjusted and controlled during finish rolling, so that the rolling is stable; at the same time, through the final rolling temperature and cooling mode, coiling, to the heat preservation of the steel coil, the recrystallization and grain equiaxialization of the steel plate matrix are further controlled, replacing the normalizing process of high-efficiency materials; the overall hot rolling process is compact in production rhythm and high in production efficiency (the soaking time in the furnace is shortened by more than 30 minutes by relying on the hot coil box), and the microstructure and macrostructure are adjusted and controlled through the temperature system, so that the production raw material demand of the finished product high-efficiency material is met.

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

[0035] 1. The present application realizes the optimized balance of performance and cost through the synergistic effect of precise control of core elements and trace elements. In terms of basic ingredients, low carbon (C≤0.0027%), low nitrogen (N≤0.0015%) and specific silicon and aluminum content (Si 1.20%~1.50%, Als 0.25%~0.50%) are adopted, which not only ensures the resistivity but also takes into account the processing performance. The boron-copper composite micro-alloying technology is introduced, the nitrogen-boron ratio (1:0.6-1.2) and the sulfur-copper ratio (1:0.8-1.5) are controlled, and in the smelting process, BN / CuS nanoscale precipitates (20~50nm) are preferentially formed, these precipitates act as heterogeneous nucleation cores, effectively inhibiting the coarsening of harmful phases such as AlN / MnS (size control in 80~150nm). At the same time, the grain boundary segregation characteristics of boron element significantly reduce the proportion of adverse texture (111) component (≤15%), and the surface enrichment effect of copper alleviates the copper brittleness tendency. The composition design makes the electromagnetic performance of the product stable to reach P 1.5 / 50 ≤3.95W / kg, B 5000Excellent level of ≥1.73T, while ensuring good hot working performance (hot rolling crack rate <0.5%) and stable grain size (ASTM 5-5.5 level), providing a reliable composition solution for high-performance silicon steel production by medium-thin slab continuous casting and rolling process.

[0036] 2、The present application starts from the first heating section to the completion of rolling and the heat preservation of the steel coil in the process design, and the purpose is to promote the fine generation and precipitation of boron nitride and copper sulfide in the relatively high temperature section, and with the gradual decrease of temperature and the control of time in each section, especially by using the temperature control and heat preservation time of the hot coil box, the aluminum nitride and manganese sulfide are further promoted to gather and coarsen around them, and the carbon, nitrogen and sulfur compounds of other residual elements are further promoted to gather and coarsen around them; at the same time, through the temperature control of the hot coil box, the proportion of austenite and ferrite dual-phase zone or near single-phase zone is reasonably adjusted and controlled during the finishing rolling process, so that the rolling is stable; at the same time, through the final rolling temperature and cooling mode, coiling and heat preservation of the steel coil, the recrystallization and grain equiaxialization of the steel plate matrix are further controlled, replacing the normalizing process of high-efficiency materials; the whole hot rolling process is compact in production rhythm and high in production efficiency (the heating furnace time is shortened by more than 30 minutes by relying on the "soaking" of the hot coil box), and the microstructure and macrostructure are adjusted and controlled through the temperature system, so as to meet the production raw material demand of finished high-efficiency materials.

[0037] 3、The present application realizes the optimization of the whole process from heating to coiling through the innovative temperature gradient control and micro-alloying synergistic control technology. The process adopts high-temperature heating of 1180~1240℃ to promote the nanoscale precipitation of BN and CuS, and through the accurate temperature control of the hot coil box at 990~1030℃, AlN and MnS are grown epitaxially around BN / CuS to form 50~150nm composite precipitates; the process innovatively adopts quasi-single-phase zone rolling (γ phase ≥85%) combined with 880~920℃ final rolling and laminar cooling to obtain a uniform structure with equiaxed grain ratio ≥90%; the steel coil is heat preserved at 730℃ for 6h to replace the normalizing treatment, so that the grain size is stabilized at ASTM 5-5.5 level. The process makes the iron loss P 1.5 / 50 ≤3.95W / kg, magnetic induction B 5000 ≥1.73T, the bad plate shape rate is reduced from 12% to less than 5%, and the hot coil box "dynamic soaking" technology shortens the heating time by 35min, the whole line production rhythm is improved to 65s / coil, and the energy consumption per ton of steel is reduced by 18%. DETAILED DESCRIPTION

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

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

[0040]

[0041] Table 2 Key process parameters of Examples and Comparative Examples

[0042]

[0043] Table 3 Key process parameters of Examples and Comparative Examples 2

[0044]

[0045] Table 4 Technical performance table

[0046]

[0047] Note: The cold rolling process parameters of the embodiment and comparative example are as follows: after cold rolling for 0.50m, the embodiment is hot rolled and rough rolled for 4 times, and then the coil is hung in the holding pit for insulation.

[0048] The implementation of this technical solution has significantly improved the overall performance and production efficiency of the 50AW600 series products. A comparison of actual production data from the traditional process and the improved process (50AW600G) reveals that the innovative introduction of boron and copper microalloying, combined with an optimized hot rolling process, has led to a significant improvement in the product's electromagnetic properties. Furthermore, the production process has been significantly optimized, significantly improving product performance consistency. This technical solution successfully achieves the dual goals of improving product quality and optimizing the manufacturing process without increasing production costs.

[0049] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by 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 percentage by weight: 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 rest is Fe and unavoidable impurities.

2. The cold-rolled non-oriented silicon steel 50W600 according to claim 1, characterized in that: The non-oriented silicon steel loss P 1.5 / 50 ≤4.00W / kg, magnetic induction B 5000 ≥1.73T.

3. A method for producing cold-rolled non-oriented silicon steel 50W600 according to claim 1 or 2, characterized in that: The specific steps include: 1) smelting; 2) Continuous casting: The cross-sectional thickness of the ingot is 90~170mm; the ingot drawing speed is controlled at 1.5~4.0m / min; the ingot is hot charged and transported, and the charging temperature is ≥600℃; 3) Hot rolling: Adopt hot rolling process of heating + rough rolling + hot coil box + finishing rolling; Heating control: the first heating section temperature is 1180~1240℃, the second heating section temperature is 1140~1170℃; the furnace time is 55~80min, the soaking section temperature is 1120~1150℃; Rough rolling: The thickness of the intermediate billet is 30~45mm; Hot coil box coiling: coil box temperature 990~1030℃, the interval time from coiling to uncoiling and finishing rolling ≥2min; Finishing rolling: final rolling temperature 880~920℃, finished product thickness 2.0~2.5mm; 4) Cooling and coiling: Steel strip cooling section control: The head and tail are allowed to pass 10~20m without cooling; cooling starts from the 40%~60% section after the cooling section until the coiler is coiled; Coiling: Coiling temperature 750~820℃; 5) Insulation treatment: Steel coil insulation temperature ≥730℃, insulation time ≥6h; 6) Cold rolling: The continuous annealing temperature is 920~940℃.

4. The method for producing cold-rolled non-oriented silicon steel 50W600 according to claim 3, characterized in that: Step 1) Smelting process flow: molten iron pretreatment → converter smelting → LF refining → RH vacuum treatment.

5. The method for producing cold-rolled non-oriented silicon steel 50W600 according to claim 3, characterized in that: Step 3) The heating furnace is a walking beam heating furnace.

6. The method for producing cold-rolled non-oriented silicon steel 50W600 according to claim 3, characterized in that: Step 5) The steel coils should be kept warm during transportation or placed in an insulation pit.

7. The method for producing cold-rolled non-oriented silicon steel 50W600 according to claim 3, characterized in that: Step 6) After annealing, the grain size is ASTM 5~5.5.

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