CN114752861B - A kind of electric pure iron hot-rolled sheet with low yield strength ratio and its manufacturing method - Google Patents

Abstract

The invention relates to a low-yield-strength-ratio electric pure iron hot-rolled sheet. The chemical composition is calculated by weight percentage as follows: C: 0.001%-0.005%; Si≤0.01%; Mn:≤0.5%; Sr: 0.05-0.5%; Mg: 0.1～0.5%; N: 0.003%～0.020%; P≤0.015%; S≤0.01%; Mg/N≥8; Sr/S≥5; the balance is Fe and inevitable impurities. The invention does not contain Al, and uses Sr and Mg to combine deoxidation and desulfurization, and the produced electric pure iron hot-rolled sheet does not need cold rolling and magnetization annealing, the grain size is coarse, the microstructure is 0-2 grade coarse equiaxed ferrite, and the yield strength The ratio is less than 55%, the hardness is less than 90HV, and the bending and electromagnetic properties are excellent.

Description

A kind of electric pure iron hot-rolled sheet with low yield strength ratio and its manufacturing method

technical field

The invention relates to the technical field of pure iron, in particular to an electrical pure iron hot-rolled sheet with low yield strength ratio and a manufacturing method thereof.

Background technique

The difference between pure iron, steel and pig iron is mainly the carbon content in the iron. Industrial pure iron is a kind of steel, its chemical composition is mainly iron, the content is 99.50%-99.90%, the carbon content is below 0.04%, the less other elements the better. Because it is not actually pure iron, this kind of steel that is close to pure iron is called industrial pure iron. Generally, industrial pure iron has low strength, high toughness and good electromagnetic properties. Industrial pure iron is divided into: electrical pure iron, raw material pure iron, no hairline pure iron, high vacuum airtight pure iron, etc. With the development of my country's new energy vehicles, electrical component processing and other industries, the amount of electrical pure iron is increasing, and the supply is in short supply. There are two kinds of common electrical pure iron, one is as a deep-drawing material, which can be stamped into extremely complex shapes; the other is as an electromagnetic material, which has high sensitivity and low diamagnetism. It is widely used in electronic and electrical engineering. , Electrical components, magnetic materials, amorphous products, relays, sensors, automotive brakes, textile machinery, electricity meter solenoid valves and other products.

The general production process of electromagnetic pure iron steel plate: smelting - hot rolling - cold rolling - magnetization annealing. According to the magnetic properties after magnetization annealing, electromagnetic pure iron is divided into ordinary grade, high grade, special grade, super - such as DT4, DT4A, DT4E, DT4C. The minimum magnetic induction intensity BT: B200A/m～B10000A/m reaches 1.2～1.8 respectively, the maximum tensile strength is 265MPa, the minimum elongation is 25%, and the hardness is less than or equal to 195HV5. Level from low to high Maximum coercivity Hc: 96A/m～32A/m, coercive force aging increment △Hc: 9.6A/m～4A/m, maximum permeability μm: 0.0075H/m～0.0151H/ m.

The composition of electromagnetic pure iron is not clearly specified, but the general requirements are: C≤0.010%, Si≤0.10%, Mn≤0.25%, P≤0.015%, S≤0.010%, Ti≤0.02%, Cr≤0.10%, Ni≤0.05 %, Cu≤0.05%. The existing electromagnetic pure iron steel plates mainly include Baosteel's Al-free electromagnetic pure iron and Taiyuan Iron and Steel's high-Al electromagnetic pure iron. The two-component system of electromagnetic pure iron has a maximum yield strength of 300MPa and a maximum tensile strength of 400MPa.

With the development of the times and industrial progress, the requirements for the use of electrical pure iron are getting higher and higher. In addition to the magnetic properties, the shapes of the processed parts are becoming more and more complex, so the requirements for formability are higher and higher, and low yield strength is required. At the same time, it must have a higher tensile strength, that is, a lower yield-to-strength ratio is required to ensure the cold-formed performance.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is to provide a low yield ratio electrical pure iron hot-rolled sheet and a manufacturing method thereof to solve the problems of low tensile strength level, high yield ratio and poor formability of pure iron steel sheet.

To achieve the above object, the present invention adopts the following technical solutions to realize:

A low-yield-strength ratio electrical pure iron hot-rolled sheet whose chemical composition is calculated by weight percentage: C: 0.001%-0.005%; Si≤0.01%; Mn:≤0.5%; Sr: 0.05-0.5%; Mg: 0.1 ～0.5%; N: 0.003%～0.020%; P≤0.015%; S≤0.01%; Mg/N≥8; Sr/S≥5; the balance is Fe and inevitable impurities.

The utility model relates to an electrical pure iron hot-rolled sheet with a low yield strength ratio. The long rod-shaped MgN inclusion phase of 50-200 nm is uniformly distributed in the structure of the steel sheet, and the area percentage is 0.008%-0.020%.

A low yield ratio electrical pure iron hot-rolled sheet, performance indicators: yield ratio less than 55%, hardness less than 90HV, tensile strength above 450MPa; C-type magnesia inclusions of grade 2 to 2.5, maximum coercivity ≤ 0A /m, the maximum permeability is ≥0.0150H/m.

The mechanism of the alloy composition, where the percent symbol % represents the weight percentage:

C: 0.001% to 0.005%

Both C and S are elements that improve coercivity. For coercive properties, the lower the content of these components, the better.

Si: ≤0.01%; Si is one of the common elements in steel. Si in solid solution form can increase the ductile-brittle transition temperature. In order to have good formability, the lower the Si content in the pure iron, the better.

Mn: ≤0.5%; Mn is one of the common elements in steel. In order to ensure magnetic properties, the lower the Mn content in the pure iron, the better.

Sr: 0.05～0.5%, Sr/S≥5; Deoxidation and desulfurization with Sr, and the solid solution of Sr in the steel can also improve the tensile strength, hinder the grain refinement, and obtain coarse ferrite grains to ensure the The invention has a tensile strength of more than 450MPa, a yield ratio of less than 55%, a hardness of less than 90HV, and excellent bending and electromagnetic properties. Sr/S≥5, can ensure the desulfurization and deoxidation effect of Sr, so that the sulfur and oxygen in the steel can fully react with Sr to produce Sr sulfides and oxides float up to form slag and precipitate from the molten steel, reducing the sulfur content in the steel after solidification to 0.01% or less. The Sr content is less than 0.5%, the desulfurization and deoxidation is insufficient, and the solid solution is insufficient, and the strength is low. The Sr content is higher than 0.5%, the strength is too high, and the brittleness is large. The solid solution of Sr can also form a large amount of dislocation density, improve the tensile strength, reduce the yield ratio, reduce the coercivity, and improve the magnetic permeability.

Mg: 0.1-0.5%, Mg/N≥8; Mg is a good deoxidizer. Mg and oxygen generate slender non-metallic inclusions to improve the magnetic induction performance. 0.1-0.5% Mg makes the C-type inclusions in the steel reach 2-2.5, reducing the coercive force and improving the magnetic permeability. On the other hand, the present invention utilizes Mg and N to generate a large number of long rod-shaped MgN inclusion phases of 50-200 nm, accounting for 0.008%-0.020% of the total area. These long rod-shaped inclusion phases can hinder recrystallization, change the texture of steel, and make magnetic The crystal anisotropy constant K1 decreases, the coercivity decreases, and the magnetic permeability increases. The C-type magnesia generated by too much Mg content is too long, and the bending cracks. If the Mg content is too small, the generated MgN is less, and the magnetic properties such as coercivity and magnetic permeability are not good. Mg/N ≥ 8 can ensure the formation of a sufficient amount of long rod-shaped nitride inclusions, accounting for 0.008% to 0.020% of the total area.

N: 0.003% to 0.020%; N can increase the strength of steel, improve steel toughness and weldability. N and Mg are used to generate long rod-shaped nitride inclusion phases of 50-200 μm, which hinders recrystallization and improves magnetic permeability. Mg/N ≥ 8 can ensure the formation of a sufficient amount of long rod-shaped nitride inclusions, hinder recrystallization, reduce coercivity ≤ 30A/m, and maximum magnetic permeability ≥ 0.0150H/m. If the N content is too high, the pure iron steel plate is brittle and easy to crack when formed. Therefore, the N content in the molten steel should be controlled to be less than 0.020%.

A method for manufacturing a low-yield-strength-ratio electrical pure iron hot-rolled sheet, specifically comprising:

1 Smelting process: converter smelting, double electric furnace refining;

1) The converter adopts Sr deoxidation and desulfurization;

2) Refining by ANS-OB method, using Sr to blow oxygen to heat up, the heating rate is 4 ℃/min～10 ℃/min, when the oxygen content is 0.0050～0.010%, add Mg to adjust the chemical composition content;

3) Refining in a VD furnace, maintaining the pressure for more than 10 minutes, and adjusting the carbon content;

4) The continuous casting speed is above 1.4m/min, the superheat degree is above 25°C, and the equiaxed crystallinity rate is below 20%, which promotes the formation of columnar crystals and the micro-segregation of liquid Mg at the end, so that there is enough Mg and N at the micro-segregation of Mg for subsequent follow-up. Long rod-shaped MgN inclusions of 50-200 nm are formed during rolling;

2. Casting billet treatment process: The billets are stacked and placed off the line for more than 32 hours and heated in a heating furnace, and the temperature of the billet entering the furnace is below 300 °C;

3. Rolling process

1) Rough rolling is adopted. Rough rolling adopts double vertical rolls + double horizontal rolls, 3 to 5 passes of high temperature continuous rolling, the reduction rate of each pass is less than or equal to 20%, the rolling temperature is 1050 ° C ~ 1200 ° C, and the maximum rolling force is 50000KN , the rolling speed is 2m/s～6m/s;

2) Finish rolling adopts work roll axial movement and roll bending device, 5 to 7 passes of continuous rolling, the total reduction ratio of finishing rolling is ≤93%, the maximum rolling force is 35000KN, and the rolling speed is 10m/s～30m/s , the rolling temperature is 700 ~ 780 ℃, the ferrite is rolled, no austenite recrystallization occurs, and coarse equiaxed ferrite grains are obtained. The grain size is below grade 2, resulting in dislocation density and increased ferrite dislocations. Density, improve tensile strength and magnetic induction performance;

4. Cooling process: direct hot coiling after final rolling, and coiling by a coiler with 3 fully hydraulic rolls evenly spaced at 120 degrees. ;Hot coiling belt heating device, use the residual heat and heat it to 900～950℃ for 2～5 minutes, then put it into the slow cooling pit for slow cooling for more than 72 hours, and the cooling rate is 10℃/hour～30℃/hour.

In step 2, the thickness of the slab is 200-300 mm.

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

The invention does not contain Al, uses Sr and Mg to combine deoxidation and desulfurization, and the produced electric pure iron hot-rolled sheet does not need cold rolling and magnetization annealing, the grains are coarse, the microstructure is 0-2 grade coarse equiaxed ferrite, and the yield strength Low, the yield ratio is less than 55%, the hardness is less than 90HV, and the bending performance is excellent. When the diameter of the bending core is less than the thickness, the 180-degree cold bending will not crack. Sr solid solution strengthening and a large number of dislocation density strengthening, the tensile strength is above 450MPa; C-type magnesia inclusions are 2-2.5 grades, and there are a large number of long rod-shaped MgN inclusions with a uniform distribution of 50-200nm, and the area percentage is 0.008%-0.020%. The maximum coercivity is ≤30A/m, the maximum magnetic permeability is ≥0.0150H/m, and the electromagnetic performance is excellent.

Description of drawings

Figure 1 is a schematic diagram of long rod-like MgN inclusions in the microstructure of a low yield ratio electrical pure iron hot-rolled sheet.

Detailed ways

The specific embodiments of the present invention are further described below in conjunction with the accompanying drawings:

A low-yield-strength ratio electric pure iron hot-rolled sheet and a manufacturing method thereof, the chemical composition is calculated by weight percentage: C: 0.001%-0.005%; Si≤0.01%; Mn:≤0.5%; Sr: 0.05-0.5% ; Mg: 0.1～0.5%; N: 0.003%～0.020%; P≤0.015%; S≤0.01%; Mg/N≥8; Sr/S≥5; the balance is Fe and inevitable impurities.

A method for manufacturing a low-yield-strength-ratio electrical pure iron hot-rolled sheet, specifically comprising:

1 Smelting process: converter smelting, double electric furnace refining;

1) The converter adopts Sr deoxidation and desulfurization; because Al has the effect of refining grains, the yield strength after grain refinement is high, and it is difficult to form. Therefore, the present invention does not use Al deoxidation, and the converter uses Sr deoxidation and desulfurization instead, and Sr/S ≥ 5 can ensure the desulfurization and deoxidation effect of Sr, so that the sulfur and oxygen in the steel fully react with Sr to produce Sr sulfides and oxides float up into slag Precipitation from molten steel, reducing the sulfur content in the steel after solidification to less than 0.01%. At the same time, the remaining Sr solid solution in the steel can also improve the tensile strength, hinder the grain refinement, and obtain coarse ferrite grains.

2) Refining by ANS-OB method, using Sr to blow oxygen to heat up, the heating rate is 4°C/min～10°C/min, when the oxygen content is 0.0050%～0.010%, add Mg to adjust the chemical composition content; Mg is a relatively active metal, which is easy to It reacts with oxygen. Therefore, when deoxidized to 0.0050% to 0.010% first, Mg is added, so as to ensure that there is sufficient oxygen and Mg to form large particle inclusions, and to prevent the deoxidization reaction from being too intense.

3) Adjust the carbon content in the VD furnace and maintain the pressure for more than 10 minutes; decarburization, adjust the carbon content, and provide conditions for the aggregation of Sr inclusions to form large particle inclusions;

4) Continuous casting speed is above 1.4m/min, superheat degree is above 25°C, and equiaxed crystal rate is below 20%, which promotes the formation of columnar crystals, so as to form coarse ferrite structure after rolling, reduce yield strength, and reduce coercivity. force to increase the magnetic permeability. The continuous casting pulling speed is more than 1.4m/min, which can also promote the formation of Mg liquid micro-segregation at the end of the dendrite, so that there is enough Mg and N at the Mg micro-segregation to nucleate a large amount of MgN phase during the subsequent slow cooling and rolling of the slab. During rolling, the recrystallization of austenite is hindered to obtain coarse grains, and under specific cooling conditions after rolling, the MgN phase grows to a long rod shape of 50 to 200 nm, accounting for 0.008% to 0.020% of the total area. Coercive force, improve permeability.

2. Casting billet treatment process: The billets are stacked and placed off the line for more than 32 hours and heated in a heating furnace, and the furnace temperature is below 300 °C; there is sufficient time and nucleation kinetics to promote the formation of a large number of MgN inclusions, which hinder the regeneration of austenite during rolling. Crystallization to obtain coarse grains, and a large number of MgN phases generated grow into long rods of 50-200 nm under specific cooling conditions after rolling, accounting for 0.008%-0.020% of the total area, reducing coercivity and improving magnetic permeability. Rate. The slab thickness is 200-300mm.

3. Rolling process

1) Rough rolling adopts double vertical rolls + double horizontal rolls, 3 to 5 passes of high temperature continuous rolling, the reduction rate of each pass is ≤ 20%, the rolling temperature is 1050 ° C ~ 1200 ° C, the maximum rolling force is 50000KN, and the rolling speed is 2m/s～6m/s; minimize recrystallization and avoid grain refinement.

2) Finish rolling adopts work roll axial movement and roll bending device, 5 to 7 passes of continuous rolling, the total reduction ratio of finishing rolling is ≤93%, the maximum rolling force is 35000KN, and the rolling speed is 10m/s～30m/s , the rolling temperature is 700 ~ 780 ℃, ferrite rolling, no recrystallization of austenite occurs, coarse equiaxed ferrite grains are obtained, the grain size is below grade 2, the yield strength is reduced, and the MgN phase is promoted at the same time. A large amount of dislocation density is formed under the action of Sr solid solution strengthening, which increases the tensile strength and reduces the yield ratio. .

4. Cooling process: direct hot coiling after final rolling at 700~800℃, with heating device for hot coiling, using waste heat and heating to 900~950℃ for 2~5 minutes, the grains recover and grow, reduce yield strength, reduce Small yield-strength ratio; cooling rate of 10-30°C/hour, slow cooling for more than 72 hours, promotes the growth of a large number of MgN inclusions formed in the early stage to long rods of 50-200nm, accounting for 0.008%-0.020% of the total area, reducing Coercive force, improve permeability.

Example

The chemical composition is shown in Table 1.

Table 1: Chemical Composition, %

The production process is shown in Table 2.

Table 2:

The properties of the steel plates are shown in Table 3.

Table 3: Steel Plate Properties

The above description is only the basic principle of the present invention, and does not limit the present invention. Any equivalent changes and modifications made to it according to the present invention are all within the scope of the technical protection scheme of this patent.

Claims (5)

1. An electrical pure iron hot rolled plate with low yield ratio is characterized by comprising the following chemical components in percentage by weight: c:0.001 to 0.005 percent; si is less than or equal to 0.01 percent; mn: less than or equal to 0.5 percent; sr:0.05 to 0.5 percent; mg:0.1 to 0.5 percent; n:0.003 to 0.020 percent; p is less than or equal to 0.015 percent; s is less than or equal to 0.01 percent; mg/N is more than or equal to 8; sr/S is more than or equal to 5; the balance being Fe and unavoidable impurities.

2. The low yield ratio electrical pure iron hot-rolled plate according to claim 1, wherein the structure of the steel plate is uniformly distributed with 50-200 nm long rod-shaped MgN inclusion phase, and the area percentage is 0.008-0.020%.

3. A low yield ratio electrical pure iron hot-rolled sheet according to claim 1, wherein the low yield ratio electrical pure iron hot-rolled sheet has the following performance indexes: the yield ratio is less than 55%, the hardness is less than 90HV, and the tensile strength is more than 450 MPa; the class C magnesium oxide inclusion is 2-2.5 grade, the maximum coercive force is less than or equal to 0A/m, and the maximum magnetic conductivity is more than or equal to 0.0150H/m.

4. The method of claim 1, wherein the method comprises the steps of:

firstly, a smelting process: converter smelting and double-electric-furnace refining;

1) The converter adopts Sr to deoxidize and desulfurize;

2) ANS-OB method refining, adopting Sr oxygen blowing to raise temperature, when the temperature raising speed is 4 ℃/min-10 ℃/min and the oxygen content is 0.0050-0.010%, adding Mg to adjust the chemical component content;

3) Refining in a VD furnace, maintaining the pressure for more than 10 minutes, and adjusting the carbon content;

4) The continuous casting speed is more than 1.4m/min, the superheat degree is more than 25 ℃, the equiaxed crystal rate is less than 20%, and the formation of columnar crystals and the liquid state microsegregation of terminal Mg are promoted, so that enough Mg and N at the Mg microsegregation position generate a long rod-shaped MgN inclusion phase of 50-200 nm during subsequent rolling;

secondly, a casting blank treatment process: stacking the casting blanks off the line for more than 32 hours, and heating in a heating furnace at the temperature of below 300 ℃;

rolling process

1) The rough rolling adopts double vertical rolls and double horizontal rolls, 3-5 times of high-temperature continuous rolling is adopted, the reduction rate of each time is less than or equal to 20%, the rolling temperature is 1050-1200 ℃, the maximum rolling force is 50000KN, and the rolling speed is 2-6 m/s;

2) The finish rolling adopts a working roll axial movement and roll bending device, continuous rolling is carried out for 5-7 times, the total reduction rate of the finish rolling is less than or equal to 93 percent, the maximum rolling force is 35000KN, the rolling speed is 10-30 m/s, the rolling temperature is 700-780 ℃, ferrite rolling is carried out, austenite recrystallization does not occur, coarse equiaxed ferrite grains are obtained, the grain size is below 2 grade, the dislocation density is generated, the dislocation density of ferrite is increased, and the tensile strength and the magnetic induction performance are improved;

fourthly, cooling process: directly carrying out hot coiling after finishing rolling, and adopting a coiling machine with 3 full-hydraulic type wrapper rollers uniformly distributed at intervals of 120 degrees for coiling, wherein the maximum motor power of a coiling drum is 1500kW, and the maximum motor power of the wrapper rollers is 150kW; the hot coiling belt heating device utilizes the residual heat and heats to 900-950 ℃ for 2-5 minutes, and then enters a slow cooling pit for slow cooling for more than 72 hours at the cooling speed of 10-30 ℃/hour.

5. The method for manufacturing an electrical pure iron hot-rolled plate with a low yield ratio as claimed in claim 4, wherein the thickness of the cast slab in the second step is 200-300 mm.

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