Non-normalized medium-grade non-oriented silicon steel and manufacturing method thereof

Abstract

The application provides a non-normalized medium-grade non-oriented silicon steel and a manufacturing method, and the composition is as follows: C: 0.0010%-0.0033%, Si: 1.30%-1.55%, Al: 0.25%-0.45%, Mn: 0.70%-1.10%, O: less than or equal to 0.005%, P: less than or equal to 0.004%, S: less than or equal to 0.003%, and the rest is Fe and inevitable impurities. Compared with the prior art, the application realizes the non-normalized production of the medium-grade non-oriented silicon steel with excellent performance by optimizing the alloy composition design and combining with reasonable process parameters, and the energy consumption is significantly reduced, the production efficiency is obviously improved, and the economic benefit is significantly increased. The application breaks through the traditional concept of non-oriented silicon steel production, completes the coarsening of the second phase particles and the evolution of the structure in the normalizing stage in the hot rolling stage, realizes the full recrystallization and the appropriate grain growth, and achieves the goal of the non-normalized high-efficiency green manufacturing of the medium-grade non-oriented silicon steel.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of silicon steel manufacturing, and particularly relates to a non-normalized medium-grade non-oriented silicon steel and a manufacturing method, which has the advantages of a short production process, low energy consumption, high efficiency, excellent product magnetic performance and the like. BACKGROUND

[0002] The non-oriented silicon steel is mainly used for large and medium-sized motors and generators, household motors and micro-motors, ballasts and small transformers, and is also an important material for high-efficiency industrial motors and high-performance automobile motors. In the silicon steel output, the non-oriented silicon steel accounts for more than 80%, but at present, low-grade silicon steels (50W600, 50W800, etc.) are mainly used. With the increasing requirement for energy saving and consumption reduction, the 50W470 and above medium / high-grade high-performance non-oriented silicon steel has great development potential and prospect. Therefore, the development of the green manufacturing key technology of the high-performance non-oriented silicon steel has great significance for the upgrading and transformation of traditional products in the steel industry and the realization of the high performance and greenization of steel products.

[0003] The non-oriented silicon steel is used as a functional material, and the performance indexes pursued are mainly the magnetic induction intensity (magnetic induction) and the iron loss (magnetic hysteresis loss, eddy current loss and abnormal loss) of the material. In order to pursue high magnetic induction and low iron loss, in addition to the need for strictly controlling the impurity elements and inclusions in the steel in the smelting process, the grain size and crystallographic texture of the final product are also key factors that need to be controlled in the production process of the non-oriented silicon steel. Since the small second phase particles and the grain boundaries can hinder the rotation and movement of the magnetic domains under the alternating magnetic field, thereby causing the increase of the iron loss of the material, and the second phase particles also have an adverse effect on the texture evolution, thereby causing the decrease of the magnetic induction of the material. In addition, in order to obtain lower iron loss, increasing the Si content is the most effective means, but with the increase of the Si content, the magnetic induction of the material decreases, and in addition, when the Si content is increased to more than 1.6%, the surface corrugated defects appear, thereby causing the decrease of the stacking factor of the material. Therefore, in order to solve the contradiction between the iron loss and the magnetic induction, and at the same time avoid the corrugated defects, the high-temperature normalizing means is mainly used in the industrial production of the 50W470 and above grade non-oriented silicon steel hot-rolled coil to eliminate the hot-rolled fiber structure and obtain the ideal coarse equiaxed crystal structure, so as to prepare the structure for the realization of the performance of the final product.

[0004] The normalizing process can achieve the improvement of the final product plate magnetic induction and the reduction of the iron loss through the above basic process. However, the normalizing process is a heat treatment process that requires heating and holding treatment of the hot-rolled plate, which inevitably involves energy consumption, and the oxidation of the steel coil during the heating process also inevitably causes material loss. Currently, there are few reports on the normalizing-free process system of medium / high-grade non-oriented silicon steel. Even if there are a few attempts to study the normalizing-free process of 50W470, good results have not been achieved, stable key technologies have not been formed, and the above research work has not been widely applied and promoted in industry.

[0005] Patent No. CN115198203A disclosed by Baoshan Iron & Steel Co., Ltd. on October 18, 2022, discloses a surface normalizing and intermediate annealing non-oriented electrical steel sheet and a manufacturing method thereof. By adopting reasonable chemical composition and process design, high magnetic induction (B 50 ≥1.72T) and low iron loss (P 1.5 / 50 ≤3.2W / Kg) can be obtained while ensuring low production cost. However, this technology needs to be implemented through long-time (up to 120h) holding after hot rolling, which increases energy consumption and reduces production efficiency.

[0006] Patent No. CN114990308A disclosed by Wuhan Iron and Steel Co., Ltd. on September 2, 2022, discloses a production method of high-grade non-oriented silicon steel without normalizing. The hot-rolled plate with a thickness of D1 is obtained after smelting, continuous casting, heating, hot rolling, and rough rolling. After uncoiling and conventional pickling, the first cold rolling is performed to an intermediate thickness D2. Then, the intermediate-thickness cold-rolled steel plate with a thickness of D2 is annealed and coiled, and then uncoiled for the second cold rolling to the product thickness and coiling. Although this technology has obtained magnetic properties of high-frequency (400Hz) iron loss not more than 14.5w / Kg and magnetic induction not less than 1.65T without normalizing, it needs to go through two cold rolling and intermediate annealing processes, which has a long production process, low efficiency, and unclear energy-saving effect.

[0007] Patent No. CN104404396A disclosed by Wuhan Iron and Steel (Group) Co., Ltd. on March 11, 2015, discloses a high-magnetic non-oriented silicon steel without normalizing and a thin slab production method. By reasonably designing alloy composition, reducing slab heating temperature, optimizing coiling temperature, and strictly controlling steel coil cooling rate, the magnetic properties of B 50 ≥1.78T and P 1.5 / 50 ≤5.0W / Kg of 0.50mm non-oriented silicon steel product under the condition of normalizing-free process are realized. However, this technology is aimed at low-grade non-oriented silicon steel with low Si content (≤1.0%), and is not suitable for the production of medium / high-grade silicon steel with higher Si content and better magnetic properties.

[0008] CN103266266A published by the Iron and Steel Research Institute on August 28, 2013 discloses a thin slab continuous casting and rolling process for producing low-grade non-oriented silicon steel and a preparation method thereof. The technology is mainly proposed for the technical difficulty of how to control and eliminate the corrugation defect in the process of producing low-grade non-oriented silicon steel by thin slab continuous casting and rolling with low compression ratio. The continuous casting and rolling technology itself does not have a normalizing process and is not a special normalizing-free technology. Moreover, the product produced by the technology has a high iron loss (P 1.5 / 50 >3.25W / Kg) and is not suitable for the production of non-oriented silicon steel with low iron loss and high magnetic induction.

[0009] Other disclosed normalizing-free researches not only involve many adjusted production processes, which increase the production difficulty and cost to some extent, but also do not deeply discuss the most important hot rolling deformation mechanism and control key technology and stay in the experience trial stage. On the basis of not involving (or less involving) other process adjustment, the normalizing-free treatment is mainly realized by the optimization design of synthetic components and the hot rolling process control, which has more universal application and core competitiveness and cost advantage.

[0010] As can be seen from the above, the existing technology and the research reports have problems of low efficiency, insignificant energy consumption reduction, harsh conditions and poor applicability. Therefore, it is extremely urgent to develop a normalizing-free 50W470 non-oriented silicon steel with high efficiency, low energy consumption and cost and good magnetic performance and a manufacturing method, which has important significance for energy saving and consumption reduction and environmental protection. SUMMARY

[0011] The purpose of the present application is to provide a normalizing-free medium-grade non-oriented silicon steel and a manufacturing method. By optimizing alloy components, improving heating and hot rolling processes, and adjusting cold rolling processes, the grain morphology and size of the hot rolled plate are adjusted to obtain sufficient deformation storage in the cold rolled plate, so that the cold rolled plate can fully recrystallize during annealing. A 50W470 non-oriented silicon steel product with excellent magnetic performance is developed without normalizing treatment, and a normalizing-free production process technology for medium-grade non-oriented silicon steel is formed.

[0012] The specific technical solutions of the present application are as follows:

[0013] A normalizing-free medium-grade non-oriented silicon steel comprises the following mass percentage components: C: 0.0010%-0.0033%, Si: 1.30%-1.55%, Al: 0.25%-0.45%, Mn: 0.70%-1.10%, O≤0.005%, P≤0.004%, S≤0.003%, and the rest is Fe and unavoidable impurities.

[0014] Preferably, the non-normalized medium-grade non-oriented silicon steel comprises the following mass percentage components: C: 0.0026%-0.0033%, Si: 1.42%-1.49%, Al: 0.27%-0.45%, Mn: 0.79%-0.98%, O≤0.005%, P≤0.004%, S≤0.003%, and the rest is Fe and inevitable impurities.

[0015] The components of the non-normalized medium-grade non-oriented silicon steel satisfy: Si%+Al%≤1.90%, and Mn / Si≥0.45.

[0016] Preferably, the components of the non-normalized medium-grade non-oriented silicon steel satisfy: Si%+Al%=1.76%-1.87%, and Mn / Si≥0.52.

[0017] Both Si and Al can reduce iron loss, and can be replaced with each other within a certain range, but each has its own shortcomings; the higher the content of Si+Al, the higher the grade of silicon steel; the total amount of Si+Al controlled by the application to be Si%+Al%≤1.90% is to ensure that the silicon steel grade of the application is medium-grade. Mn has the effect of expanding the austenite phase region, while Si has the effect of reducing the austenite phase region, and the ratio of Mn / Si≥0.45 is to obtain a certain amount of austenite phase at high temperature, thereby providing a basis for the occurrence of dynamic recrystallization in the subsequent hot rolling process.

[0018] The application controls the levels of low oxygen, phosphorus, sulfur and other impurity elements to be O≤0.005%, P≤0.004%, and S≤0.003%, which aims to obtain reasonable organization and ensure good magnetic properties under the premise of low cost.

[0019] The base structure of the non-normalized medium-grade non-oriented silicon steel is polygonal ferrite, and the average grain size is 50-130 μm. In the production process of the non-oriented silicon steel, the key technology lies in how to achieve appropriate coarsening of the second phase particles and reasonable growth of the grain size. The grain size is one of the important factors affecting the magnetic properties, and small or too large grain size is not conducive to the magnetic properties. It has been verified through experiments that the grain size within this range can obtain relatively optimal magnetic properties.

[0020] The magnetic induction intensity B 50 of the non-normalized medium-grade non-oriented silicon steel is greater than 1.69 T, the iron loss value P 1.5 / 50 is 3.1-3.5 W / kg, and the magnetic permeability μ 1.5 is 1250-1883.

[0021] The manufacturing method of the non-normalized medium-grade non-oriented silicon steel provided by the application comprises the following process flows: smelting, casting, forging, hot rolling, pickling, cold rolling and annealing.

[0022] The smelting equipment can be one of a vacuum induction furnace, a converter or an electric furnace.

[0023] The casting is one of continuous casting or mold casting.

[0024] The hot rolling has a heating temperature of 1050-1200℃, a holding time of 50-80min, an initial rolling temperature of 980-1080℃, a final rolling temperature of 870-920℃, a rolling pass of not less than five, a total rolling reduction of 92-95%, a reduction per pass of 33%-55%, and a hot rolled plate finished product thickness controlled at 2.5-3.0mm, which accumulates enough deformation storage energy for subsequent cold rolling to make recrystallization fully occur.

[0025] The cold rolling has a cold rolling reduction controlled at 75%-85% and a cold rolled plate thickness of 0.45-0.55mm.

[0026] The annealing furnace can be one of a tube furnace, a cover furnace or a continuous annealing furnace.

[0027] The annealing has an annealing treatment temperature of 950-1050℃, a time of 3-5min and an atmosphere of a mixed gas with a volume fraction of 30% H2 and 70% N2.

[0028] The design concept and principle of this invention are as follows: Starting from the purpose of normalization (improving corrugation defects, increasing grain size, and adjusting texture), the normalization effect is achieved through rational composition design and process optimization. Firstly, by adding an appropriate amount (0.70-1.10 wt%) of Mn element to expand the γ phase region, the austenite phase content in the sample at high temperatures can be increased, promoting sufficient dynamic recrystallization during hot rolling. This is because austenite has a low stacking fault energy, poor dislocation mobility, and difficulty in climb or cross-slip, limiting dynamic recovery and allowing for effective accumulation of deformation storage energy. Therefore, once the critical strain is exceeded, the driving force is large enough to induce dynamic recrystallization. Secondly, it lowers the phase transformation point, i.e., the γ→α transformation temperature is lowered, resulting in finer ferrite grains, more grain boundaries, and more nucleation sites for recrystallization, thus leading to more complete dynamic recrystallization during hot rolling. Sufficient dynamic recrystallization helps eliminate deformed structures, thereby promoting grain growth during cold rolling annealing. With low Mn content (<0.70 wt%), the increase in austenite content and the decrease in phase transformation point are not significant, resulting in limited effect on promoting dynamic recrystallization. Higher Mn content (>1.10 wt%) increases production costs and reduces the strength of favorable texture components. Secondly, Mn solid solution increases lattice distortion energy, thereby increasing the driving force for recrystallization and promoting its occurrence. Furthermore, appropriately increasing the heating and rolling temperatures during hot rolling allows for a moderate amount of re-dissolution of the second-phase particles. Higher temperatures result in poorer thermodynamic stability of the second-phase particles and a greater degree of re-dissolution, which can suppress nucleation and promote growth of the second-phase particles, achieving "epitaxial growth" during rolling. This accelerates the coarsening of the second-phase particles, reduces the hindrance to grain growth, and promotes the growth of dynamically recrystallized grains during hot rolling. Through process parameter optimization and control during rolling, the coarsening and recrystallization kinetics of the second-phase particles can be regulated. Dynamic recrystallization control can eliminate non-recrystallized structures during hot rolling, achieving complete recrystallization and texture control. Specifically, by optimizing the composition design, the phase transformation point and phase content are controlled by adjusting Si+Al≤1.90% and Mn / Si≥0.33; by optimizing the heating temperature before hot rolling (1050-1200℃), suitable grain size and second phase particle properties of the cast billet are obtained; thus, an ideal initial microstructure is obtained before hot rolling. Subsequently, during the hot rolling process, the coarsening of second phase particles and microstructure evolution in the normalization stage are completed through optimized rolling control, and ideal grain size and texture type are obtained. This provides a good microstructure basis for recrystallization in the subsequent cold rolling annealing process, achieving the goal of efficient and green manufacturing of medium-grade non-oriented silicon steel without normalization treatment.

[0029] The application breaks through the traditional concept of non-oriented silicon steel production, that is, appropriately controlling lower heating temperature to ensure that the second phase particles are not dissolved to avoid the fine and dispersed precipitation in the subsequent rolling annealing process, thereby hindering the grain growth. The application has uniqueness in alloy design, billet heating and cold rolling process parameter setting, etc.

[0030] Compared with the prior art, the application has the following technical effects: the optimized alloy component design and reasonable process parameters realize the non-normalization production of the medium-grade non-oriented silicon steel with excellent performance, the energy consumption is significantly reduced, the production efficiency is obviously improved, and the economic benefit is significantly increased. The average grain size of the non-oriented silicon steel finished plate prepared by the application is 50-130 μm, the magnetic induction intensity B 50 is greater than 1.69 T, the iron loss value P 1.5 / 50 = 3.1-3.5 W / kg, and the magnetic permeability μ 1.5 = 1250-1883. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 FIG. 1 is a metallographic structure diagram of the 950℃ annealed plate of the medium-grade non-oriented silicon steel of Example 1, which shows that the grains of the steel plate are equiaxed crystals and the sizes are relatively uniform, and the average grain size is 57 μm, which can ensure excellent magnetic properties;

[0032] Figure 2 FIG. 2 is a metallographic structure diagram of the 1000℃ annealed plate of the medium-grade non-oriented silicon steel of Example 2, which shows that the grains of the steel plate are equiaxed crystals and the sizes are relatively uniform, and the average grain size is 83 μm, which can ensure excellent magnetic properties;

[0033] Figure 3 FIG. 3 is a metallographic structure diagram of the 1050℃ annealed plate of the medium-grade non-oriented silicon steel of Example 3, which shows that the grains of the steel plate are equiaxed crystals and the sizes are relatively uniform, and the average grain size is 120 μm, which can ensure excellent magnetic properties;

[0034] Figure 4 FIG. 4 is a metallographic structure diagram of the 1050℃ annealed plate of the medium-grade non-oriented silicon steel of Example 4, which shows that the grains of the steel plate are equiaxed crystals and the sizes are relatively uniform, and the average grain size is 111 μm, which can ensure excellent magnetic properties;

[0035] Figure 5 FIG. 5 is a metallographic structure diagram of the 1000℃ annealed plate of the medium-grade non-oriented silicon steel of Example 5, which shows that the grains of the steel plate are equiaxed crystals and the sizes are relatively uniform, and the average grain size is 77 μm, which can ensure excellent magnetic properties. DETAILED DESCRIPTION

[0036] The application will be described in detail below in connection with specific embodiments, but the application is not limited to the following examples.

[0037] Example 1

[0038] A non-normalized medium-grade non-oriented silicon steel includes the following mass percentage components:

[0039] C: 0.0029%, Si: 1.47%, Al: 0.30%, Mn: 0.77%, O≤0.003%, P: 0.0031%, S: 0.0027%, and the rest is Fe and inevitable impurities; wherein, Si%+Al%=1.77%, Mn / Si=0.52.

[0040] The manufacturing method of the non-normalized medium-grade non-oriented silicon steel is realized through smelting, casting, forging, hot rolling, pickling, cold rolling, and annealing processes; and the finished product plate is specifically prepared by vacuum induction furnace smelting, cast iron mold casting, forging, hot rolling, acid pickling, cold rolling, and annealing.

[0041] The cast blank is heated in a 1120℃ heating furnace for 60min, and then forged with a 45mm thickness. The forged blank is hot-rolled in 5 passes with a controlled reduction, the hot-rolling heating temperature is 1130℃ and the holding time is 65min, the initial rolling temperature is 1050℃, the hot-rolled plate is rolled to a thickness of 2.6mm, the final rolling temperature is 900℃, and the total reduction is 94.2%, and the reduction of each pass is 33.3%, 36.7%, 42.1%, 54.5%, and 48%, respectively. After the hot-rolled plate is pickled to remove the iron oxide scale, it is cold-rolled to 0.5mm. The prepared cold-rolled plate is annealed to obtain the annealed finished product plate, the annealing temperature is 950℃, the time is 5min, and the atmosphere is a mixed gas with a volume fraction of 30% H2+70% N2.

[0042] The magnetic induction intensity B of the prepared non-oriented silicon steel finished product plate is 1.701T, the iron loss value P is 3.466W / kg, and the permeability μ is 1376. 50 1.5 / 50 1.5

[0043] Example 2

[0044] A non-normalized medium-grade non-oriented silicon steel includes the following mass percentage components:

[0045] C: 0.0029%, Si: 1.47%, Al: 0.30%, Mn: 0.77%, O≤0.003%, P: 0.0031%, S: 0.0027%, and the rest is Fe and inevitable impurities; wherein, Si%+Al%=1.77%, Mn / Si=0.52.

[0046] ​​​The manufacturing method of the non-normalized medium-grade non-oriented silicon steel is realized through smelting, pouring, forging, hot rolling, pickling, cold rolling and annealing processes; specifically, the finished plate is prepared through vacuum induction furnace smelting, cast iron mold pouring, forging, hot rolling, pickling, cold rolling and annealing.

[0047] The cast blank is heated in a 1120°C heating furnace for 60 min and then forged, and the forged blank has a thickness of 45 mm. The forged blank is hot-rolled in five passes with a controlled reduction, the hot-rolling heating temperature is 1130°C and the holding time is 65 min, the initial rolling temperature is 1000°C, the hot-rolled plate has a thickness of 2.6 mm, the final rolling temperature is 880°C, the total reduction is 94.2%, and the reduction in each pass is 33.3%, 36.7%, 42.1%, 54.5% and 48%, respectively. After the hot-rolled plate is pickled to remove the iron oxide scale, it is cold-rolled to a thickness of 0.5 mm. The prepared cold-rolled plate is annealed to obtain the annealed finished plate, the annealing temperature is 1000°C, the time is 5 min, and the atmosphere is a mixed gas with a volume fraction of 30% H2+70% N2.

[0048] The magnetic induction intensity B of the prepared non-oriented silicon steel finished plate is 1.707 T, the iron loss value P is 3.441 W / kg, and the permeability μ is 1345. 50 1.5 / 50 1.5

[0049] Example 3

[0050] A non-normalized medium-grade non-oriented silicon steel includes the following components by mass percentage:

[0051] C: 0.0029%, Si: 1.47%, Al: 0.30%, Mn: 0.77%, O≤0.003%, P: 0.0031%, S: 0.0027%, and the balance being Fe and unavoidable impurities, wherein Si%+Al%=1.77%, and Mn / Si=0.52.

[0052] The manufacturing method of the non-normalized medium-grade non-oriented silicon steel is realized through smelting, pouring, forging, hot rolling, pickling, cold rolling and annealing processes; specifically, the finished plate is prepared through vacuum induction furnace smelting, cast iron mold pouring, forging, hot rolling, pickling, cold rolling and annealing.

[0053] ​​​The cast blank is heated in a heating furnace at 1120°C for 60 min, then forged, and the forged blank has a thickness of 45 mm. The forged blank is hot-rolled in 5 passes with controlled reduction, the hot-rolling heating temperature is 1130°C, the holding time is 65 min, the initial rolling temperature is 1050°C, the hot-rolled plate has a thickness of 2.6 mm, the final rolling temperature is 900°C, the total reduction is 94.2%, and the reduction in each pass is 33.3%, 36.7%, 42.1%, 54.5% and 48%, respectively. After the hot-rolled plate is pickled to remove the iron oxide scale, it is cold-rolled to a thickness of 0.5 mm. The cold-rolled plate is annealed to obtain an annealed finished plate, the annealing temperature is 1050°C, the time is 5 min, and the atmosphere is a mixed gas with a volume fraction of 30% H2+70% N2.

[0054] The non-oriented silicon steel finished plate has a magnetic induction intensity B 50 = 1.712 T, a loss value P 1.5 / 50 = 3.327 W / kg, and a permeability μ 1.5 = 1506.

[0055] Example 4

[0056] A non-normalized medium-grade non-oriented silicon steel includes the following components by mass percentage:

[0057] C: 0.0026%, Si: 1.42%, Al: 0.45%, Mn: 0.82%, O≤0.003%, P: 0.003%, S: 0.003%, and the balance being Fe and unavoidable impurities, wherein Si%+Al%=1.87%, and Mn / Si=0.58.

[0058] The manufacturing method of the non-normalized medium-grade non-oriented silicon steel includes the following steps: smelting, casting, forging, hot-rolling, pickling, cold-rolling, and annealing.

[0059] The finished plate is obtained by smelting in a vacuum induction furnace, casting in an iron mold, forging, hot-rolling, pickling, cold-rolling, and annealing.

[0060] The cast blank is heated in a heating furnace at 1120°C for 60 min, then forged, and the forged blank has a thickness of 45 mm. The forged blank is hot-rolled in 5 passes with controlled reduction, the hot-rolling heating temperature is 1130°C, the holding time is 65 min, the initial rolling temperature is 1050°C, the hot-rolled plate has a thickness of 2.6 mm, the final rolling temperature is 900°C, the total reduction is 94.2%, and the reduction in each pass is 33.3%, 36.7%, 42.1%, 54.5% and 48%, respectively. After the hot-rolled plate is pickled to remove the iron oxide scale, it is cold-rolled to a thickness of 0.5 mm. The cold-rolled plate is annealed to obtain an annealed finished plate, the annealing temperature is 1050°C, the time is 5 min, and the atmosphere is a mixed gas with a volume fraction of 30% H2+70% N2.

[0061] The magnetic induction intensity B of the finished sheet of non-oriented silicon steel prepared 50 = 1.731 T, the iron loss value P 1.5 / 50 = 3.393 W / kg, the permeability μ 1.5 = 1359.

[0062] Example 5

[0063] A non-normalized medium-grade non-oriented silicon steel includes the following mass percentage components:

[0064] C: 0.0032%, Si: 1.49%, Al: 0.27%, Mn: 0.98%, O≤0.003%, P: 0.0039%, S: 0.0030%, the rest being Fe and unavoidable impurities, wherein Si% + Al% = 1.76%, Mn / Si = 0.66.

[0065] The manufacturing method of the non-normalized medium-grade non-oriented silicon steel is realized through smelting, casting, forging, hot rolling, pickling, cold rolling, and annealing processes, and the finished sheet is prepared by using a vacuum induction furnace for smelting, a cast iron mold for casting, forging, hot rolling, acid pickling, cold rolling, and annealing.

[0066] The cast blank is heated in a 1120°C heating furnace for 60 min, then forged, and the forged blank has a thickness of 46 mm. The forged blank is hot-rolled in five passes with controlled reduction, the hot-rolling heating temperature is 1130°C and the holding time is 65 min, the initial rolling temperature is 1000°C, the hot-rolled sheet has a thickness of 2.7 mm, the final rolling temperature is 880°C, the total reduction is 94.1%, and the reduction of each pass is 34.8%, 36.7%, 42.1%, 54.5%, and 46%, respectively. After the hot-rolled sheet is pickled to remove the iron oxide scale, it is cold-rolled to a thickness of 0.5 mm. The prepared cold-rolled sheet is annealed to obtain an annealed finished sheet, the annealing temperature is 1000°C, the time is 5 min, and the atmosphere is a mixed gas with a volume fraction of 30% H2+70% N2.

[0067] The magnetic induction intensity B of the finished sheet of non-oriented silicon steel prepared 50 = 1.774 T, the iron loss value P 1.5 / 50 = 3.457 W / kg, the permeability μ 1.5 = 1801.

[0068] Comparative Example 1

[0069] A non-normalized medium-grade non-oriented silicon steel includes the following mass percentage components:

[0070] C: 0.0027%, Si: 1.46%, Al: 0.28%, Mn: 0.51%C: 0.0027%, Si: 1.46%, Al: 0.28%, Mn: 0.45%, P: 0.0033%, S: 0.0029%, the rest is Fe and inevitable impurities, wherein, Si% + Al% = 1.74%, Mn / Si = 0.35.

[0071] The manufacturing method of the non-normalized medium-grade non-oriented silicon steel is realized through smelting, pouring, forging, hot rolling, pickling, cold rolling and annealing processes. Specifically, the finished plate is prepared through vacuum induction furnace smelting, cast iron mold pouring, forging, hot rolling, pickling, cold rolling and annealing.

[0072] The cast blank is heated in a 1120℃ heating furnace for 60min, and then is forged, with a thickness of 45mm. The forged blank is hot-rolled in 5 passes with a controlled reduction, with a hot-rolling heating temperature of 1130℃ and a holding time of 65min, an initial rolling temperature of 1050℃, a hot-rolled plate thickness of 2.6mm, a final rolling temperature of 900℃, and a total reduction of 94.2%, with a reduction of 33.3%, 36.7%, 42.1%, 54.5% and 48% in each pass, respectively. After pickling to remove the iron oxide scale, the hot-rolled plate is cold-rolled to 0.5mm. The prepared cold-rolled plate is annealed to obtain an annealed finished plate, with an annealing temperature of 950℃, a time of 5min, and a mixed gas atmosphere of 30% H2+70% N2.

[0073] The average grain size of the prepared non-oriented silicon steel finished plate is 74μm, Magnetic induction B 50 = 1.661 T, iron loss value P 1.5 / 50 = 4.063 W / kg, permeability μ 1.5 = 891.

[0074] The rolling process, annealing temperature and grain size of the steel plate of the comparative example 1 meet the requirements of the present application, but the composition does not meet the requirements of the present application, with a low Mn content; and the Mn / Si ratio is 0.35, which also does not meet the requirements of the present application, so the performance does not meet the requirements of the claim, with a low magnetic induction, high iron loss and low magnetic permeability.

[0075] Comparative example 2

[0076] A non-normalized medium-grade non-oriented silicon steel, comprising the following components by mass percentage:

[0077] C: 0.0027%, Si: 1.46%, Al: 0.28%, Mn: 0.45%, P: 0.0033%, S: 0.0029%, the rest is Fe and inevitable impurities, wherein, Si% + Al% = 1.74%, Mn: 0.51% C: 0.0027%, Si: 1.46%, Al: 0.28%, Mn: 0.45%, P: 0.0033%, S: 0.0029%, the rest is Fe and inevitable impurities, wherein, Si% + Al% = 1.74% Mn / Si = 0.35.

[0078] The manufacturing method of the non-normalized medium-grade non-oriented silicon steel is realized through smelting, pouring, forging, hot rolling, pickling, cold rolling and annealing processes. Specifically, the finished plate is prepared through vacuum induction furnace smelting, cast iron mold pouring, forging, hot rolling, pickling, cold rolling and annealing.

[0079] The cast blank is heated at 1120℃ for 60min, then forged to a thickness of 45mm. The forged blank is hot-rolled in 5 passes with a controlled reduction, the hot-rolling temperature is 1130℃ and the holding time is 65min, the initial rolling temperature is 1050℃, the hot-rolled plate is rolled to a thickness of 2.5mm, the final rolling temperature is 900℃, the total reduction is 94.4%, and the reduction of each pass is 44.4%, 40%, 50%, 33.3%, and 50%, respectively. The hot-rolled plate is pickled to remove the iron oxide scale, then cold-rolled to a thickness of 0.5mm. The cold-rolled plate is annealed to obtain the annealed finished plate, the annealing temperature is 1050℃, the time is 5min, and the atmosphere is a mixed gas with a volume fraction of 30% H2+70% N2.

[0080] The average grain size of the finished non-oriented silicon steel plate is 122μm, Magnetic induction B 50 = 1.650 T, iron loss value P 1.5 / 50 = 3.955 W / kg , Permeability μ 1.5 = 846.

[0081] The rolling process, annealing temperature and grain size of the steel plate of Comparative Example 2 meet the requirements of the present application, but the composition does not meet the requirements of the present application, the Mn content is low; and the ratio of Mn / Si is 0.35, which also does not meet the requirements of the present application, therefore the performance does not meet the requirements of the claim, the magnetic induction is low, the iron loss is high, and the magnetic permeability is low. Under the condition that the composition does not meet the requirements of the present application, compared with Comparative Example 1, even if the annealing temperature is increased to 1050℃, the grain size of the finished steel plate is large enough, and the magnetic properties do not meet the requirements of the present application.

[0082] Comparative Example 3

[0083] A non-normalized medium-grade non-oriented silicon steel, comprising the following mass percentage components:

[0084] C: 0.0029%, Si: 1.47%, Al: 0.30%, Mn: 0.77%, O≤0.003%, P: 0.0031%, S: 0.0027%, and the balance being Fe and unavoidable impurities, wherein Si%+Al%=1.77%, Mn / Si=0.52;

[0085] The manufacturing method of the non-normalized medium-grade non-oriented silicon steel comprises the steps of smelting, casting, forging, hot-rolling, pickling, cold-rolling, and annealing, and the finished plate is obtained by using a vacuum induction furnace for smelting, a cast iron mold for casting, forging, hot-rolling, pickling, cold-rolling, and annealing.

[0086] The cast blank is heated at 1120℃ for 60min in a heating furnace, then forged to a thickness of 45mm, and the forged blank is hot-rolled in 5 passes with a controlled reduction, the hot-rolling temperature is 1130℃ and the holding time is 65min, the initial rolling temperature is 1050℃, the hot-rolled plate is rolled to a thickness of 2.6mm, the final rolling temperature is 900℃, the total reduction is 94.2%, and the reduction in each pass is 33.3%, 36.7%, 42.1%, 54.5% and 48%, respectively. After the hot-rolled plate is pickled to remove the iron oxide scale, it is cold-rolled to a thickness of 0.5mm. The cold-rolled plate is annealed to obtain an annealed finished plate, the annealing temperature is 900℃， 30% H2+70% N2 mixed gas for 5min.

[0087] The average grain size of the finished non-oriented silicon steel plate is 30 μm , the magnetic induction intensity B 50 =1.709T, Iron loss value P 1.5 / 50 = 3.785 W / kg , and the magnetic permeability μ 1.5 =1697.

[0088] The composition and the composition ratio formula of Comparative Example 3 meet the requirements of the present application, but the annealing temperature and the average grain size do not meet the requirements of the present application, resulting in a high iron loss.

[0089] Comparative Example 4

[0090] A non-normalized medium-grade non-oriented silicon steel includes the following components by mass percentage:

[0091] C: 0.0026%, Si: 1.42%, Al: 0.45%, Mn: 0.82%, O≤0.003%, P: 0.003%, S: 0.003%, and the balance of Fe and inevitable impurities, wherein Si%+Al%=1.87%, and Mn / Si=0.58.

[0092] The manufacturing method of the non-normalized medium-grade non-oriented silicon steel includes the following steps: smelting, casting, forging, hot-rolling, pickling, cold-rolling, and annealing.

[0093] The finished plate is obtained by vacuum induction furnace smelting, cast iron mold casting, forging, hot-rolling, pickling, cold-rolling, and annealing.

[0094] The cast blank is heated at 1120℃ for 60min in a heating furnace, then forged to a thickness of 47mm, and the forged blank is hot-rolled in 5 passes with a controlled reduction, the hot-rolling temperature is 1130℃ and the holding time is 65min, the initial rolling temperature is 1050℃, the hot-rolled plate is rolled to a thickness of 3.0mm, the final rolling temperature is 900℃, the total reduction is 93.6%, and the reduction in each pass is 36.2%, 36.7%, 42.1%, 54.5% and 40%, respectively. After the hot-rolled plate is pickled to remove the iron oxide scale, it is cold-rolled to a thickness of 0.5mm. The obtained cold-rolled plate is annealed to obtain an annealed finished plate, the annealing temperature is 900℃ , the time is 5min, and the atmosphere is a mixed gas with a volume fraction of 30% H2+70% N2.

[0095] The average grain size of the obtained non-oriented silicon steel finished plate is 28 μm , and the magnetic induction intensity B 50 =1.736T, Iron loss value P 1.5 / 50 = 3.727 W / kg , Permeability μ 1.5 = 2079.

[0096] The composition and the composition ratio formula of Comparative Example 4 meet the requirements of the present application, but the annealing temperature and the average grain size do not meet the requirements of the present application, resulting in a high iron loss. Under the condition that the annealing temperature and the grain size do not meet the requirements of the present application, even if the total amount of Si+Al is provided, the iron loss of the finished plate still cannot meet the requirements of the present application compared with Comparative Example 3.

[0097] Comparative Example 5

[0098] A normalizing-free medium-grade non-oriented silicon steel, comprising the following mass percentage components:

[0099] C: 0.0024%, Si: 1.69%, Al: 0.20%, Mn: 0.55% , O≤0.003%, P: 0.003%, S: 0.0029%, and the balance being Fe and unavoidable impurities, wherein, Si%+Al%=1.89%, Mn / Si = 0.33 .

[0100] The manufacturing method of the normalizing-free medium-grade non-oriented silicon steel comprises the steps of smelting, casting, forging, hot-rolling, pickling, cold-rolling, and annealing.

[0101] Specifically, the finished plate is obtained by smelting in a vacuum induction furnace, casting in an iron mold, forging, hot-rolling, pickling, cold-rolling, and annealing.

[0102] The cast billet was forged after being held at 1120℃ for 60 minutes in a furnace. The forged billet thickness was 45mm. The forged billet underwent five passes of hot rolling with controlled reduction. The hot rolling temperature was 1130℃, and the holding time was 65 minutes. The initial rolling temperature was 1050℃, and the billet was hot-rolled to a thickness of 2.7mm. The final rolling temperature was 900℃, and the total reduction rate was 94.0%. The reduction rates for each pass were 33.3%, 36.7%, 42.1%, 54.5%, and 46%, respectively. After pickling to remove iron oxide scale, the hot-rolled plate was cold-rolled to 0.5mm. The resulting cold-rolled plate was annealed to obtain the annealed finished plate. The annealing temperature was 950℃, and the annealing time was 5 minutes. The atmosphere used was a mixture of 30% H2 and 70% N2 by volume.

[0103] The average grain size of the obtained non-oriented silicon steel finished plate is 53 μm, and the magnetic induction intensity B is... 50 =1.771T, Iron loss value P 1.5 / 50 = 3.767 W / kg, permeability μ 1.5 = 2403.

[0104] The rolling process, annealing temperature, and grain size of the steel plate in Comparative Example 5 meet the requirements of this invention, but the Si, Al, and Mn compositions do not. The Si content is high, while the Al and Mn contents are low. Furthermore, the Mn / Si ratio is 0.33, which also does not meet the requirements of this invention. Therefore, the magnetic properties do not meet the requirements of this invention, and the iron loss is high.

[0105] Comparative Example 6

[0106] A non-normalizing medium-grade non-oriented silicon steel comprises the following components by weight percentage:

[0107] C: 0.0029%, Si: 1.47%, Al: 0.30%, Mn: 0.77%, O≤0.003%, P: 0.0031%, S: 0.0027%, with the remainder being Fe and unavoidable impurities; where Si%+Al%=1.77%, Mn / Si=0.52;

[0108] The manufacturing method of the non-normalized medium-grade non-oriented silicon steel is achieved through smelting, casting, forging, hot rolling, pickling, cold rolling, and annealing processes; specifically, it adopts the following steps: vacuum induction furnace smelting, cast iron mold casting, forging, hot rolling, pickling, cold rolling, and annealing to obtain the finished plate.

[0109] The billet is held at 1120℃ for 60 minutes in a furnace before forging. The billet thickness is 45mm. The forged billet then undergoes five passes of hot rolling with controlled reduction. The hot rolling heating temperature is... 1250℃The holding time was 65 min, the initial rolling temperature was 1050℃, and the hot-rolled sheet was 2.6 mm thick. The final rolling temperature was 900℃, with a total reduction rate of 94.2%. The reduction rates for each pass were 33.3%, 36.7%, 42.1%, 54.5%, and 48%, respectively. After pickling to remove iron oxide scale, the hot-rolled sheet was cold-rolled to 0.5 mm. The resulting cold-rolled sheet was annealed at 950℃ for 5 min in a mixed gas atmosphere of 30% H2 and 70% N2 by volume.

[0110] The resulting non-oriented silicon steel finished plate magnetic induction B 50 = 1.666 T, iron loss value P 1.5 / 50 = 3.675 W / kg, magnetic Conductivity μ 1.5 = 1045 .

[0111] The composition and proportion formula, hot rolling parameters, cold rolling parameters, and annealing parameters of Comparative Example 6 meet the requirements of this invention. However, the heating temperature does not meet the requirements of this invention, exceeding the upper limit of 1200℃ specified in this patent. This results in coarse grain size, reduced grain boundary quantity, and sufficient re-dissolution of second-phase particles in the billet. During hot rolling, the lack of recrystallization nucleation sites hinders the effective occurrence of dynamic recrystallization. Furthermore, because the second-phase particles are fully re-dissolved, "epitaxial growth" of the second-phase particles cannot be achieved during rolling. The precipitation kinetics are large during hot rolling, and the small size of the second-phase particles significantly hinders grain growth. Therefore, ideal equiaxed grains cannot be obtained, and the normalization-free effect cannot be achieved, thus affecting the microstructure of the final finished plate and causing the magnetic properties to fail to meet the requirements.

[0112] Comparative Example 7

[0113] A non-normalizing medium-grade non-oriented silicon steel comprises the following components by weight percentage:

[0114] C: 0.0029%, Si: 1.47%, Al: 0.30%, Mn: 0.77%, O≤0.003%, P: 0.0031%, S: 0.0027%, with the remainder being Fe and unavoidable impurities, of which Si%+Al%=1.77% and Mn / Si=0.52.

[0115] The manufacturing method of the non-normalized medium-grade non-oriented silicon steel is achieved through smelting, casting, forging, hot rolling, pickling, cold rolling, and annealing processes; specifically, it adopts the following steps: vacuum induction furnace smelting, cast iron mold casting, forging, hot rolling, pickling, cold rolling, and annealing to obtain the finished plate.

[0116] The cast billet is held at 1120℃ for 60 minutes in a furnace before forging. The billet thickness is 45mm. The forged billet then undergoes five passes of hot rolling with controlled reduction. The hot rolling temperature is 1130℃ and the holding time is 65 minutes. The initial rolling temperature is... 950℃ Hot rolled to a thickness of 4.0 mm Hot-rolled plate, Final rolling temperature 850°C, total reduction 91.1％ The reduction of each pass was 33.3%, 33.3%, 40%, 50%, and 33.3%, respectively. After the hot-rolled plate was pickled to remove the oxide scale, it was cold-rolled to 0.5 mm. The cold-rolled plate was annealed to obtain the annealed finished plate. The annealing temperature was 1000°C, the annealing time was 5 min, and the atmosphere was a mixed gas of 30% H2+70% N2.

[0117] The obtained non-oriented silicon steel finished plate magnetic induction B 50 = 1.676 T , Iron loss value P 1.5 / 50 = 3.733 W / kg , permeability μ 1.5 = 1273.

[0118] The composition and the composition ratio formula, the hot-rolling heating temperature and time, and the annealing parameters of Comparative Example 7 met the requirements of the present application, but the hot-rolling parameters (the initial rolling temperature, the total reduction, the hot-rolled plate thickness, and the final rolling temperature) did not meet the requirements of the present application, which resulted in that the cold-rolling reduction did not meet the requirements of the present application. The low hot-rolling temperature and the small total reduction were not conducive to the full occurrence of dynamic recrystallization in the hot-rolling process, so that the ideal hot-rolled structure could not be obtained. In addition, the large total cold-rolling reduction resulted in that the driving force for static recrystallization nucleation was large during the annealing process, and the annealed plate had a small grain size, which was not conducive to the magnetic properties. Therefore, the magnetic properties did not meet the requirements of the present application.

[0119] The above underlined data did not meet the requirements of the present application.

[0120] As can be seen from the above comparative examples, the magnetic properties of the non-oriented silicon steel obtained from the technical solutions not defined in the claims of the present application were either high iron loss or low magnetic induction, which could not achieve the effects of the technical solutions defined in the claims of the present application.

[0121] The above-described examples are only typical embodiments of the present application, and are merely illustrative but not limiting of the present application. It is understood by those skilled in the art that many changes, modifications, and even equivalents can be made to the present application within the spirit and scope defined in the claims of the present application, and all of them will fall within the protection scope of the present application.

Claims

1. A medium-grade non-oriented silicon steel that is exempt from normalization, characterized in that, The non-normalized, medium-grade non-oriented silicon steel comprises the following components by mass percentage: C: 0.0010%-0.0033%, Si: 1.30%-1.55%, Al: 0.25%-0.45%, Mn: 0.70%-1.10%, O≤0.005%, P≤0.004%, S≤0.003%, with the remainder being Fe and unavoidable impurities. The composition of the non-normalized medium-grade non-oriented silicon steel meets the following requirements: Si% + Al% ≤ 1.90%, Mn / Si ≥ 0.45; The matrix structure of the non-normalized medium-grade non-oriented silicon steel is polygonal ferrite with an average grain size of 50-130 μm. The manufacturing process of the non-normalized medium-grade non-oriented silicon steel is as follows: smelting, casting, forging, hot rolling, pickling, cold rolling and annealing. The hot rolling process involves an initial rolling temperature of 980-1080℃, a final rolling temperature of 870-920℃, at least five rolling passes, a total rolling reduction of 92-95%, a reduction of 33%-55% per pass, and a finished hot-rolled plate thickness controlled at 2.5-3.0mm.

2. The non-normalizing medium-grade non-oriented silicon steel according to claim 1, characterized in that, The non-normalized, medium-grade non-oriented silicon steel comprises the following components by mass percentage: C: 0.0026%-0.0033%, Si: 1.42%-1.49%, Al: 0.27%-0.45%, Mn: 0.79%-0.98%, O≤0.005%, P≤0.004%, S≤0.003%, with the remainder being Fe and unavoidable impurities.

3. The non-normalizing medium-grade non-oriented silicon steel according to claim 1 or 2, characterized in that, The magnetic induction intensity B of the non-oriented silicon steel of the unnormalized grade 50 >1.69T, iron loss value P 1.5 / 50 =3.1-3.5 W / kg, permeability μ 1.5 =1250-1883.

4. A method for manufacturing medium-grade non-oriented silicon steel without normalization as described in any one of claims 1-3, characterized in that, The manufacturing process is as follows: smelting, casting, forging, hot rolling, pickling, cold rolling and annealing.

5. The method for manufacturing medium-grade non-oriented silicon steel without normalization according to claim 4, characterized in that, The hot rolling process involves heating at a temperature of 1050-1200℃ and holding for 50-80 minutes.

6. The method for manufacturing medium-grade non-oriented silicon steel without normalization according to claim 4 or 5, characterized in that, The hot rolling process involves an initial rolling temperature of 980-1080℃, a final rolling temperature of 870-920℃, at least five rolling passes, a total rolling reduction of 92-95%, a reduction of 33%-55% per pass, and a finished hot-rolled plate thickness controlled at 2.5-3.0mm.

7. The method for manufacturing medium-grade non-oriented silicon steel without normalization according to claim 4, characterized in that, The cold rolling process involves a cold rolling reduction rate controlled at 75%-85% and a cold-rolled sheet thickness of 0.45-0.55 mm.

8. The method for manufacturing medium-grade non-oriented silicon steel without normalization according to claim 4, characterized in that, The annealing process is carried out at a temperature of 950-1050℃ for 3-5 minutes.

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