Preparation method of high-silicon soft magnetic steel for maglev guide rail

Abstract

This invention discloses a method for preparing high-silicon soft magnetic steel for magnetic levitation guideways. The chemical composition of the steel is C=0.025%~0.035% by weight, Si=1.20%~1.60%, Mn=0.30%~0.50%, Cr=0.40%~0.60%, Ni=0.50%~0.60%, Cu=0.30%~0.40%, with the remainder being Fe and unavoidable impurities. Under a low-carbon composition system, by controlling the rolling temperature near the Ar3 phase transformation point and combining it with post-rolling cooling, a refined and fragmented rolled pearlite structure is obtained. Subsequent two-phase normalizing dissolves the pearlite structure into austenite, and finally, complete ferrite grains are obtained in the air-cooled phase transformation. The pearlite structure that deteriorates the magnetic properties is basically eliminated, and the microstructure of the high-silicon soft magnetic steel for magnetic levitation guideways is purified. The average impact energy of the finished steel plate at 1 / 4 thickness -30°C is ≥120J.

Description

Technical Field

[0001] This invention belongs to the field of steel production technology and relates to a method for preparing high-silicon soft magnetic steel for magnetic levitation guide rails. Background Technology

[0002] The high-speed maglev rail system, which "flies close to the ground," has many advantages such as high speed, safety, comfort, energy saving, and environmental protection. It is a green and environmentally friendly transportation system with broad development prospects. China has already planned and laid out six important corridors for the development of high-speed maglev trains in urban clusters such as the Yangtze River Delta, the Pearl River Delta, the Beijing-Tianjin-Hebei region, the middle reaches of the Yangtze River, and the Chengdu-Chongqing region.

[0003] High-silicon soft magnetic steel is a commonly used material for high-speed maglev guide plates. Recent news indicates that the 664-meter-long guide plate on the Qingdao 600 km / h maglev test line uses 50 tons of 28mm thick ERC430 soft magnetic steel. Reports also indicate that steel companies such as Baosteel and Nanjing Iron & Steel have successfully developed similar steel plates, with Baosteel even applying this type of steel plate to Shanghai's first maglev rail transit line; this demonstrates that Chinese steel companies have essentially mastered the production process for this type of steel plate.

[0004] Microalloying can improve the low-temperature impact toughness of hot-rolled ferritic steel. The addition of vanadium, niobium, and titanium significantly improves the mechanical properties of hot-rolled ferritic steel. Their carbonitrides not only inhibit austenite grain coarsening but also act as nucleation sites for intragranular ferrite, refining the ferrite grains and thus improving low-temperature impact toughness. However, the carbonitrides of vanadium, niobium, and titanium increase the pinning effect of magnetic domain walls and hinder their movement, negatively impacting magnetic properties.

[0005] Changing the morphology of ferrite grains is another potential way to improve low-temperature impact toughness; however, the formation of ferrite grains is inevitably accompanied by a phase transformation of pearlite structure, which deteriorates magnetic properties. This is also proven by the metallographic results disclosed in Chinese patents CN200610025124.0, CN202010579576.3, CN200410017999.7, and CN03116097.2.

[0006] Theoretically, pearlite formation can be caused by: 1) the carbon content in the chemical composition system, 2) banded pearlite produced during rolling, 3) the re-dissolution of pearlite during heat treatment, and 4) the re-phase transformation during the cooling process after heat treatment. By coupling these factors, the pearlite content can be reduced to a minimum or even completely eliminated, effectively purifying the matrix structure and improving impact and magnetic properties. Summary of the Invention

[0007] The present invention aims to provide a method for preparing high-silicon soft magnetic steel for magnetic levitation guide rails, thereby achieving purification of the microstructure of the high-silicon soft magnetic steel for magnetic levitation guide rails to ensure that the average impact energy of the finished steel plate at -30°C in both the transverse and longitudinal directions at 1 / 4 thickness is ≥120J.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing high-silicon soft magnetic steel for magnetic levitation guide rails, wherein the steel's chemical composition by weight percentage is C=0.025%~0.035%, Si=1.20%~1.60%, Mn=0.30%~0.50%, Cr=0.40%~0.60%, Ni=0.50%~0.60%, Cu=0.30%~0.40%, with the remainder being Fe and unavoidable impurities; the process steps include: 1) Smelting and continuous casting: The billet thickness is 260mm, the superheat temperature during casting is controlled to be ≤15°C, and the low magnification quality requirements of the billet are to achieve center segregation C class ≤1.5 grade and porosity ≤1.0; 2) Heating process: The 260mm cross section of the continuous casting billet is heated to 1100~1180°C, and the total furnace time is 4~8 hours; 3) Rolling process: In the rough rolling stage after exiting the furnace, the slab is subjected to 65.4% rolling deformation to the intermediate slab thickness of 90mm. In the finishing rolling stage, the total deformation is 66.7%. The surface temperature of the steel plate in the finishing rolling stage is 950~900°C, and the final thickness of the steel plate is 30mm. 4) Post-rolling cooling: After rolling, the steel plate is cooled at a cooling rate of 3~7°C / s to the surface reddening temperature of 720~690°C; 5) Heat treatment process: The steel plate cooled to room temperature is normalized at a temperature range of 790~840°C for 30~90 minutes and then air-cooled.

[0009] Further, step 3) Rolling process: The 30mm thick finished steel plate undergoes two processes: TMCP rolling and two-phase normalizing.

[0010] Further, step 3) rolling process: using the formula Ar3=910-203C 1 / 2 The Ar3 phase transformation temperature of the steel plate is calculated to be 910°C based on the equation -30Mn+44.7Si-11Cr+31.5Mo-15.2Ni. The surface temperature of the steel plate after finishing rolling is controlled within the range of 910°C±10°C.

[0011] Furthermore, the microstructure of the finished steel plate is polygonal ferrite, the pearlite structure has basically disappeared, and the average impact energy of the steel plate at -30°C in the transverse and longitudinal directions at 1 / 4 thickness is ≥120J.

[0012] The innovations and beneficial effects of this invention are as follows: Under a low-carbon composition system, this invention obtains a refined and fragmented rolled pearlite structure by controlling the rolling temperature near the Ar3 phase transformation point and cooling after rolling. The pearlite is then dissolved into the austenite grains using two-phase normalizing. The formation of pearlite structure is avoided during subsequent air cooling. After heat treatment, the entire thickness of the finished steel plate is dominated by a uniform ferrite structure, and the pearlite structure that deteriorates the magnetic properties is basically eliminated. The average impact energy of the finished steel plate at -30°C in both the transverse and longitudinal directions at 1 / 4 thickness is ≥120J. Attached Figure Description

[0013] Figure 1 This is a micrograph of the surface layer (0.5 mm) of the steel in Example 1.

[0014] Figure 2 This is a microstructure diagram of steel with a thickness of 1 / 2 thickness from Example 1.

[0015] Figure 3 The image shows the surface microstructure of steel in Comparative Example 1, 0.5 mm thick.

[0016] Figure 4 The image shows the microstructure of steel at half its thickness as Comparative Example 1.

[0017] Figure 5 The image shows the surface microstructure of steel in Comparative Example 2, 0.5 mm thick.

[0018] Figure 6 The image shows the microstructure of steel at half its thickness in Comparative Example 2.

[0019] Figure 7 The image shows the surface microstructure of steel in Comparative Example 3, 0.5 mm thick.

[0020] Figure 8 The microstructure is shown as half the thickness of steel in Comparative Example 3. Detailed Implementation

[0021] The present invention will be further described below with reference to the embodiments and accompanying drawings.

[0022] The settings for heating, rolling, and heat treatment process parameters for each embodiment and comparative example are shown in Table 1, and the mechanical properties of the steel plates are shown in Table 2. Example 1

[0023] A method for preparing high-silicon soft magnetic steel for magnetic levitation guide rails, wherein the slab thickness is 260mm, and the chemical composition by weight percentage is C = 0.025%~0.035%, Si = 1.20%~1.60%, Mn = 0.30%~0.50%, Cr = 0.40%~0.60%, Ni = 0.50%~0.60%, Cu = 0.30%~0.40%, with the remainder being Fe and unavoidable impurities, using the formula Ar3 = 910 - 203C. 1 / 2The calculated Ar3 phase transition temperature is 910°C, derived from the equation: -30Mn + 44.7Si - 11Cr + 31.5Mo - 15.2Ni. The process steps include: 1) Smelting and continuous casting: Casting is carried out with the superheat controlled at 14°C. The billet has a center segregation of Class C 1.0 grade and porosity of 1.0 grade at low magnification. 2) Heating process: The 260mm cross section of the continuous casting billet is heated to 1120°C, with a total furnace time of 5 hours; 3) Rolling process: In the rough rolling stage after exiting the furnace, the slab is subjected to 65.4% rolling deformation to the intermediate slab thickness of 90mm. In the finishing rolling stage, the total deformation is 66.7%. The surface temperature of the finishing rolled steel plate is 950~900°C, and the final thickness of the steel plate is 30mm. 4) Post-rolling cooling: After rolling, the steel plate is cooled at a cooling rate of 3-7°C / s to the surface reddening temperature of 720-690°C; 5) Heat treatment process: The steel plate cooled to room temperature is normalized at 800°C for 60 minutes and then air-cooled.

[0024] The full-thickness microstructure of the steel plate produced according to the above method is as follows: Figure 1 and Figure 2 As shown, the microstructure is dominated by equiaxed and polygonal ferrite, while pearlite is almost absent.

[0025] Comparative Example 1: A method for preparing high-silicon soft magnetic steel for magnetic levitation guide rails, wherein the slab thickness is 260mm, and the chemical composition by weight percentage is C = 0.025%~0.035%, Si = 1.20%~1.60%, Mn = 0.30%~0.50%, Cr = 0.40%~0.60%, Ni = 0.50%~0.60%, Cu = 0.30%~0.40%, with the remainder being Fe and unavoidable impurities, using the formula Ar3 = 910 - 203C. 1 / 2 The calculated Ar3 phase transition temperature is 910°C, derived from the equation: -30Mn + 44.7Si - 11Cr + 31.5Mo - 15.2Ni. The process steps include: 1) Smelting and continuous casting: Casting is carried out with the superheat controlled at 14°C. The billet has a center segregation of Class C 1.0 grade and porosity of 1.0 grade at low magnification. 2) Heating process: The 260mm cross section of the continuous casting billet is heated to 1120°C, with a total furnace time of 5 hours; 3) Rolling process: In the rough rolling stage after exiting the furnace, the slab is subjected to 65.4% rolling deformation to the intermediate slab thickness of 90mm. In the finishing rolling stage, the total deformation is 66.7%. The surface temperature of the finishing rolled steel plate is 950~900°C, and the final thickness of the steel plate is 30mm. 4) Post-rolling cooling: After rolling, the steel plate is cooled at a cooling rate of 3-7°C / s to the surface reddening temperature of 720-690°C; 5) Heat treatment process: The steel plate cooled to room temperature is normalized at 900°C for 60 minutes and then air-cooled.

[0026] The full-thickness microstructure of the steel plate produced according to the above method is as follows: Figure 3 and Figure 4 As shown, the microstructure is mainly composed of equiaxed and polygonal ferrite, with a large number of fine and dispersed pearlite distributed at the boundaries of ferrite grains or at the junctions of three crystals; the mechanical properties are shown in Table 2.

[0027] A method for preparing high-silicon soft magnetic steel for magnetic levitation guide rails, wherein the slab thickness is 260mm, and the chemical composition by weight percentage is C=0.025%~0.035%, Si=1.20%~1.60%, Mn=0.30%~0.50%, Cr=0.40%~0.60%, Ni=0.50%~0.60%, Cu=0.30%~0.40%, with the remainder being Fe and unavoidable impurities, using the formula Ar3=910-203C. 1 / 2 The calculated Ar3 phase transition temperature is 910°C, derived from the equation: -30Mn + 44.7Si - 11Cr + 31.5Mo - 15.2Ni. The process steps are as follows: 1) Smelting and continuous casting: Casting is carried out with the superheat controlled at 14°C. The billet has a center segregation of Class C 1.0 grade and porosity of 1.0 grade at low magnification. 2) Heating process: The 260mm cross section of the continuous casting billet is heated to 1120°C, with a total furnace time of 4 hours; 3) Rolling process: In the rough rolling stage after exiting the furnace, the slab is subjected to 65.4% rolling deformation to the intermediate slab thickness of 90mm. In the finishing rolling stage, the total deformation is 66.7%. The surface temperature of the finishing rolled steel plate is 950~900°C, and the final thickness of the steel plate is 30mm. 4) Post-rolling cooling: Air-cool to room temperature after rolling; 5) Heat treatment process: The steel plate cooled to room temperature is normalized at 800°C for 60 minutes and then air-cooled.

[0028] The full-thickness microstructure of the steel plate produced according to the above method is as follows: Figure 5 and Figure 6 As shown, the microstructure is mainly composed of equiaxed and polygonal ferrite, with pearlite grains distributed at the boundaries of ferrite grains or at the junctions of three crystals; the mechanical properties are shown in Table 2.

[0029] A method for preparing high-silicon soft magnetic steel for magnetic levitation guide rails, wherein the slab thickness is 260mm, and the chemical composition by weight percentage is C=0.025%~0.035%, Si=1.20%~1.60%, Mn=0.30%~0.50%, Cr=0.40%~0.60%, Ni=0.50%~0.60%, Cu=0.30%~0.40%, with the remainder being Fe and unavoidable impurities, using the formula Ar3=910-203C. 1 / 2 The calculated Ar3 phase transition temperature is 910°C, derived from the equation: -30Mn + 44.7Si - 11Cr + 31.5Mo - 15.2Ni. The process steps include: 1) Smelting and continuous casting: Casting is carried out with the superheat controlled at 14°C. The billet has a center segregation of Class C 1.0 grade and porosity of 1.0 grade at low magnification. 2) Heating process: The 260mm cross section of the continuous casting billet is heated to 1230°C, with a total furnace time of 4 hours; 3) Rolling process: In the rough rolling stage after exiting the furnace, the slab is subjected to 65.4% rolling deformation to the intermediate slab thickness of 90mm. In the finishing rolling stage, the total deformation is 66.7%. The surface temperature of the finishing rolled steel plate is 950~900°C, and the final thickness of the steel plate is 30mm. 4) Post-rolling cooling: After rolling, the steel plate is cooled at a cooling rate of 3-7°C / s to the surface reddening temperature of 720-690°C; 5) Heat treatment process: The steel plate cooled to room temperature is normalized at 800°C for 60 minutes and then air-cooled.

[0030] The full-thickness microstructure of the steel plate produced according to the above method is as follows: Figure 7 and Figure 8 As shown, the microstructure is mainly composed of equiaxed and polygonal ferrite, with pearlite being relatively small in size and scattered at the boundaries of ferrite grains or at the junctions of three crystals; the mechanical properties are shown in Table 2.

[0031] The process and performance results of the examples and comparative examples show that, under the premise that the chemical composition by weight percentage is C=0.025%~0.035%, Si=1.20%~1.60%, Mn=0.30%~0.50%, Cr=0.40%~0.60%, Ni=0.50%~0.60%, and Cu=0.30%~0.40%, only by heating the 260mm cross-section continuous casting billet to 1100~1180°C, cooling the steel plate after rolling at a cooling rate of 3~7°C / s to the surface reddening temperature of 720~690°C, and then normalizing it at a temperature range of 790~840°C for 30~90 minutes followed by air cooling, can pearlite, which is detrimental to improving the magnetic properties of the steel plate, be eliminated and ferrite grains be purified.

[0032] Table 1 Heating and Rolling Process Parameters

[0033] .

[0034] Table 2 Low-temperature toughness of 1 / 4 thickness at 30°C .

Claims

1. A method for preparing high-silicon soft magnetic steel for magnetic levitation guide rails, characterized in that: The steel's chemical composition by weight percentage is: C = 0.025%~0.035%, Si = 1.20%~1.60%, Mn = 0.30%~0.50%, Cr = 0.40%~0.60%, Ni = 0.50%~0.60%, Cu = 0.30%~0.40%, with the remainder being Fe and unavoidable impurities; the process steps include: 1) Smelting and continuous casting: The billet thickness is 260mm, the superheat temperature during casting is controlled to be ≤15°C, and the low magnification quality requirements of the billet are to achieve center segregation C class ≤1.5 grade and porosity ≤1.0; 2) Heating process: The 260mm cross section of the continuous casting billet is heated to 1100~1180°C, and the total furnace time is 4~8 hours; 3) Rolling process: In the rough rolling stage after exiting the furnace, the slab is subjected to 65.4% rolling deformation to the intermediate slab thickness of 90mm. In the finishing rolling stage, the total deformation is 66.7%. The surface temperature of the steel plate in the finishing rolling stage is 950~900°C, and the final thickness of the steel plate is 30mm. 4) Post-rolling cooling: After rolling, the steel plate is cooled at a cooling rate of 3~7°C / s to the surface reddening temperature of 720~690°C; 5) Heat treatment process: The steel plate cooled to room temperature is normalized at a temperature range of 790~840°C for 30~90 minutes and then air-cooled.

2. The method for preparing high-silicon soft magnetic steel for magnetic levitation guide rails according to claim 1, characterized in that... Step 3) Rolling process: The 30mm thick finished steel plate undergoes two processes: TMCP rolling and two-phase normalizing.

3. The method for preparing a pearlitic structure of high-silicon soft magnetic steel for purifying magnetic levitation guide rails according to claim 1, characterized in that... Step 3) Rolling process: using the formula Ar3=910-203C 1 / 2 The Ar3 phase transformation temperature of the steel plate is calculated to be 910°C based on the equation -30Mn+44.7Si-11Cr+31.5Mo-15.2Ni. The surface temperature of the steel plate after finishing rolling is controlled within the range of 910°C±10°C.

4. The method for preparing high-silicon soft magnetic steel for magnetic levitation guide rails according to claim 1, characterized in that: The microstructure of the finished steel plate is polygonal ferrite, and the pearlite structure has basically disappeared. The average impact energy of the steel plate at -30°C in the transverse and longitudinal directions at 1 / 4 thickness is ≥120J.

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