CN115786804A - Low-Cr system soft magnetic stainless steel and control method of structure thereof - Google Patents
Low-Cr system soft magnetic stainless steel and control method of structure thereof Download PDFInfo
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- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
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Abstract
The invention discloses a low-Cr system soft magnetic stainless steel and a control method of the structure thereof, wherein the chromium content of the low-Cr system stainless steel is 10-15.5%, and the control method comprises the following steps: s1, hot rolling the billet at 900-1050 ℃, and cooling to obtain a fine grain structure comprising ferrite and martensite; s2, carrying out heat preservation treatment on the steel billet obtained in the step S1 at 900-1000 ℃ for 2-5 h, slowly cooling the steel billet for at least 15h to 550-650 ℃, and then cooling the steel billet; and S3, carrying out heat preservation treatment on the billet obtained in the step S2 at 700-800 ℃ for 2-5 h, and then cooling to obtain the pure ferrite stainless steel. The invention hot-rolls the billet into a fine-grained structure which takes ferrite as a matrix and martensite is uniformly distributed at a crystal boundary by a special hot rolling process. Then, the double-phase structure is completely converted into a single-phase ferrite structure through high-temperature slow cooling annealing, so that the magnetism is improved; then stress relief annealing is carried out to remove the structure stress, the structure is uniform, and the magnetism is improved again.
Description
Technical Field
The invention relates to soft magnetic ferrite, in particular to low Cr series soft magnetic stainless steel and a control method of a structure thereof.
Background
Soft magnetic materials have the characteristics of low coercive force and easy magnetization and demagnetization, so that the soft magnetic materials are widely used in the fields of radio, computers, household appliances, electrical engineering, communication and the like. Soft ferrite stainless steel is critical for the use of many electromechanical devices, which must be optimally magnetized to ensure proper output signal and response time.
Such materials are generally required to have excellent corrosion resistance in addition to excellent soft magnetic properties. In the past, materials with high chromium content are usually adopted to ensure the corrosion resistance, the components of the steel are designed to be pure ferrite tissues, and after hot rolling, only stress-relief slow cooling annealing is needed to obtain excellent magnetism. Songming in the article "development and application of chrome core-series corrosion-resistant soft magnetic alloy" states that the higher the chromium content, the lower the saturation magnetic induction, and thus, the chromium content has a certain negative correlation with the soft magnetic property. In order to obtain the soft magnetic stainless steel with excellent soft magnetic performance and corrosion resistance, the conventional method adopts a low-chromium raw material to ensure the soft magnetic performance, and then additional components such as titanium, niobium and the like are additionally added, titanium, niobium and carbon are combined to generate titanium carbide and niobium carbide, the corrosion resistance of the material is improved by the titanium carbide and the niobium carbide, the content of a carbon simple substance in the material is reduced by the generation of the titanium carbide and the niobium carbide, and the soft magnetic performance of the material is further improved. 40920 stainless steel, for example, having the composition: 0.014% of C, 0.59% of Si, 0.5% of Mn, 0.023% of P, 0.001% of S, 10.82% of Cr, 0.27% of Ni, 0.04% of Mo, 0.006% of N and 0.163% of Ti0.163% of Ti. For another patent with application publication No. CN114836684A, the component design of the patent adopts Ti element to be added to combine with C and N elements in preference to Cr element, so as to avoid local chromium deficiency and improve the corrosion resistance of the material; the patent with application publication No. CN114606440A discloses a high-performance soft magnetic stainless steel and a preparation method thereof, wherein the corrosion resistance of the stainless steel is improved by adding Mo, nb and Re elements, and the stainless steel does not rust in a salt spray test for 48 hours. In the production process of the soft magnetic stainless steel, a pure ferrite structure is generally formed during hot rolling, which has a very high requirement for refining of the preform in the early stage, resulting in a high fraction defective, and a martensite structure is easily generated during rolling, so that excellent soft magnetic properties cannot be obtained.
Disclosure of Invention
Aiming at the problem of poor soft magnetic performance of the stainless steel with the non-pure ferrite structure obtained after hot rolling, the invention provides the low Cr system soft magnetic stainless steel and the control method of the structure thereof.
In order to achieve the above object, according to one aspect of the present invention, there is provided a microstructure controlling method of a low-Cr soft magnetic stainless steel, the low-Cr soft magnetic stainless steel having a chromium content of 10 to 15.5%, the method comprising the steps of:
s1, hot rolling the billet at 900-1050 ℃, and cooling to obtain a fine grain structure comprising ferrite and martensite;
the rolling temperature is 1100-1250 ℃, the structure crystal grains obtained at the rolling temperature are usually mixed with serious crystals, except that martensite exists at the crystal boundary and small-block martensite also exists in the ferrite crystal grains, and pure ferrite cannot be obtained through phase inversion, the invention carries out hot rolling at 900-1050 ℃, can obtain fine crystal structures with uniform crystal grains, and the martensite structures are uniformly distributed at the crystal boundary, and the structures can be converted into pure ferrite in the subsequent annealing treatment, thereby ensuring the soft magnetic performance of the stainless steel;
s2, carrying out heat preservation treatment on the steel billet obtained in the step S1 at 900-1000 ℃ for 2-5 h, slowly cooling the steel billet for at least 15h to 550-650 ℃, and then cooling the steel billet;
the conventional magnetic annealing temperature is below 900 ℃, and the transition from a double-phase structure to a single-phase structure cannot be realized at the temperature, so that the annealing temperature of 900-1000 ℃ is not too high, otherwise, grains become large, the structure transition is not facilitated, the cooling time is not less than 15 hours, and otherwise, the transition is incomplete;
s3, carrying out heat preservation treatment on the steel billet obtained in the step S2 at 700-800 ℃ for 2-5 h, and then cooling to obtain pure ferrite stainless steel;
after the step S2, the martensite is transformed into the ferrite structure, and the magnetic property is improved, but there are still a small amount of retained austenite (the martensite is transformed into austenite and then into ferrite in the annealing process) and structural stress, so that the magnetic annealing treatment is required, and after the secondary magnetic annealing, the magnetic property is further improved, so as to obtain higher magnetic permeability and magnetic induction strength, and lower coercive force. The secondary magnetic annealing temperature is not higher than 800 ℃, because the secondary magnetic annealing temperature can be austenitized again, martensite is generated again during cooling, and when the secondary magnetic annealing temperature is lower than 700 ℃, the stress is not completely removed, and the magnetism cannot be improved.
The invention hot-rolls the billet into a fine-grained structure which takes ferrite as a matrix and martensite is uniformly distributed at a crystal boundary by a special hot rolling process. Then, the double-phase structure is completely converted into a single-phase ferrite structure through high-temperature slow cooling annealing, so that the magnetism is improved; and then stress relief annealing is carried out to remove the structure stress, the structure is uniform, the magnetism is improved again, and the excellent soft magnetic performance is further ensured.
Preferably, in step S1, the temperature of the hot rolling is 950 ℃.
Specifically, in the step S1, the grain size of the fine grains is more than or equal to 5 grades, and the grain size difference is less than or equal to 2 grades, so that the structure is more easily converted into pure ferrite in the subsequent annealing treatment.
Preferably, in step S2, the holding temperature is 950 ℃.
Preferably, in step S2, the steel billet is cooled after being slowly cooled to 600 ℃ for 15-20 hours after being subjected to heat preservation treatment.
Preferably, in step S3, the holding temperature is 780 ℃.
Preferably, in step S1, the cooling mode is air cooling; and/or
In the step S2, the cooling mode is air cooling; and/or
In step S3, the cooling mode is air cooling.
Preferably, the chromium content of the low-chromium stainless steel is 10.5-12.5%.
Preferably, the low chromium-based stainless steel further comprises the following components: less than or equal to 0.06 percent of carbon, less than or equal to 0.06 percent of nitrogen, less than or equal to 2 percent of silicon, less than or equal to 1.5 percent of manganese, less than or equal to 1 percent of nickel, less than or equal to 0.045 percent of phosphorus and less than or equal to 0.40 percent of sulfur.
The second aspect of the present invention provides a low Cr series soft magnetic stainless steel obtained by the above-described control method.
Through the technical scheme, the invention has the following beneficial effects:
1. according to the invention, the steel billet is hot-rolled into the dual-phase fine-grain structure comprising ferrite and martensite, the martensite structure is uniformly distributed at a crystal boundary, and then the dual-phase structure is completely converted into the pure ferrite structure through the modes of slow cooling after primary annealing and secondary annealing, so that the excellent soft magnetic property is ensured.
2. The process of the invention has no special requirement on the component design of the raw materials, can be converted even if the structure is ferrite plus martensite, and is convenient for the production of soft magnetic steel.
Drawings
FIG. 1 is a metallographic structure diagram of a steel slab hot-rolled in example 1 of the present invention;
FIG. 2 is a metallographic structure diagram of a soft magnetic stainless steel produced in example 1 of the present invention;
FIG. 3 is a metallographic structure diagram of a soft magnetic stainless steel prepared in comparative example 1 of the present invention;
FIG. 4 is a metallographic structure diagram of a soft magnetic stainless steel prepared in comparative example 2 of the present invention;
FIG. 5 is a metallographic structure drawing after hot rolling of a steel slab in comparative example 3 according to the invention;
FIG. 6 is a metallographic structure diagram of a soft magnetic stainless steel prepared in comparative example 3 of the present invention;
FIG. 7 is a metallographic structure graph of a steel slab of comparative example 6 of the present invention after hot rolling;
FIG. 8 is a metallographic structure drawing of a soft magnetic stainless steel according to comparative example 6 of the present invention.
Detailed Description
The following examples are provided to explain the present invention in detail. It should be understood that the detailed description and specific examples, while indicating the present invention, are given by way of illustration and explanation only, not limitation.
Example 1
S1, refining a continuous casting blank containing 0.011% of carbon, 12.16% of chromium, 0.88% of silicon, 0.58% of nickel, 0.9% of manganese, 0.028% of phosphorus, 0.015% of sulfur, 0.36% of molybdenum, 0.085% of copper, 0.008% of nitrogen and 0.147% of vanadium, wherein the refining mode adopts three-stage steelmaking: smelting waste steel, alloy, lime and the like serving as raw materials into molten iron in an electric furnace, then transferring to a converter to increase Si for removing C and O, then transferring to a VOD furnace to blow oxygen for removing C and N, and increasing needed metal for final component regulation, and then continuously casting into a 150-square continuous steel billet (the cross section of the square continuous casting billet is 150mm x 150mm);
s2, preserving the temperature of the steel billet obtained in the step S1 at 1050 ℃ for 2h, and then hot-rolling the steel billet into a straight rod, wherein the metallographic structure of the straight rod is shown in a figure 1, and the metallographic structure is a uniform fine-grained structure;
s3, completely annealing the material obtained in the step S2 by adopting a box-type furnace, wherein the annealing process comprises the following steps: preserving heat at 1000 ℃ for 3h, slowly cooling to 600 ℃ for 17h, and then discharging from the furnace for air cooling;
s4, performing magnetic annealing on the material obtained in the step S3 by using a continuous furnace, wherein the annealing process comprises the following steps: the stainless steel structure obtained after heat preservation at 780 ℃ for 2h was air-cooled as shown in FIG. 2, and as can be seen from FIG. 2, the stainless steel structure was a pure ferrite structure.
Comparative example 1
The other conditions were the same as example 1 except that step S4 was omitted, and the microstructure of the obtained material was as shown in FIG. 3, from which it was found that the microstructure had been transformed into a ferrite structure and the crystal grains were fine, but the magnetic properties were inferior to example 1.
Comparative example 2
The other conditions were the same as example 1 except that step S3 was omitted, and the material structure was obtained as shown in fig. 4, but it was found that the structure could not be transformed only by the low-temperature magnetic annealing, and that a large amount of martensite remained at the grain boundaries, and the magnetic properties were poor.
Comparative example 3
S1, refining a continuous casting blank containing 0.011% of carbon, 12.16% of chromium, 0.88% of silicon, 0.58% of nickel, 0.9% of manganese, 0.028% of phosphorus, 0.015% of sulfur, 0.36% of molybdenum, 0.085% of copper, 0.008% of nitrogen and 0.147% of vanadium, wherein the refining mode adopts three-stage steelmaking: refining in an electric furnace, a converter and VOD (same as example 1), and then continuously casting to obtain a 150-square continuous steel billet;
s2, preserving the temperature of the billet obtained in the step S1 for 2h at 1150 ℃, then hot-rolling the billet into a straight rod, wherein the metallographic structure of the straight rod is shown in figure 5, and as can be seen from the figure, the obtained structure grains are seriously mixed with crystals, except that martensite exists at the grain boundary and small-block martensite also exists in the ferrite grains;
s3, completely annealing the material obtained in the step S2 by adopting a box-type furnace, wherein the annealing process comprises the following steps: preserving heat at 1000 ℃ for 3h, slowly cooling to 600 ℃ for 17h, and then discharging from the furnace for air cooling;
s4, magnetically annealing the material obtained in the step S3 by using a continuous furnace, wherein the annealing process comprises the following steps: the stainless steel structure obtained after heat preservation at 780 ℃ for 2h was air-cooled as shown in FIG. 6, and it can be seen from the figure that the material was still a dual phase structure of ferrite and martensite, and a pure ferrite structure could not be obtained.
Comparative example 4
Other conditions are the same as in comparative example 3 except that step S4 is omitted.
Comparative example 5
Other conditions are the same as in comparative example 3 except that step S3 is omitted.
Comparative example 6
S1, refining a continuous casting blank with the components of 0.011 percent of carbon, 12.16 percent of chromium, 0.88 percent of silicon, 0.58 percent of nickel, 0.9 percent of manganese, 0.028 percent of phosphorus, 0.015 percent of sulfur, 0.36 percent of molybdenum, 0.085 percent of copper, 0.008 percent of nitrogen and 0.147 percent of vanadium, wherein the refining mode adopts three-stage steelmaking: refining in an electric furnace, a converter and VOD (same as example 1), and then continuously casting to obtain a 150-square continuous steel billet;
s2, keeping the temperature of the steel blank obtained in the step S1 at 1250 ℃ for 2h, and rolling the steel blank into a straight rod when the rolling ratio is controlled to be less than 65%, wherein the metallographic structure of the straight rod is shown in a figure 7, and a dual-phase coarse grain structure of ferrite and martensite is obtained;
s3, completely annealing the material obtained in the step S2 by adopting a box-type furnace, wherein the annealing process comprises the following steps: preserving heat at 1000 ℃ for 3h, slowly cooling to 600 ℃ for 17h, and then discharging from the furnace for air cooling;
s4, performing magnetic annealing on the material obtained in the step S3 by using a continuous furnace, wherein the annealing process comprises the following steps: the stainless steel structure obtained after heat preservation at 780 ℃ for 2h was air-cooled as shown in FIG. 8, and it can be seen from the figure that the material was still a dual phase structure of ferrite and martensite after annealing, and a pure ferrite structure could not be obtained as well.
Comparative example 7
The other conditions were the same as in comparative example 6 except that step S4 was omitted.
Comparative example 8
The other conditions were the same as in comparative example 6 except that step S3 was omitted.
Example 2
S1, refining continuous casting blanks with the components of 0.028% of carbon, 13.8% of chromium, 1.45% of silicon, 0.20% of nickel, 0.15% of manganese, 0.004% of phosphorus, 0.007% of sulfur, 0.214% of molybdenum, 0.072% of copper and 0.05% of vanadium, wherein the refining mode adopts three-stage steelmaking: refining in an electric furnace, a converter and VOD (same as example 1), and then carrying out continuous casting to obtain a 150-square continuous casting blank;
s2, preserving the temperature of the steel blank obtained in the step S1 for 2 hours at 900 ℃, and then hot-rolling the steel blank into a straight rod;
s3, completely annealing the material obtained in the step S2 by adopting a box-type furnace, wherein the annealing process comprises the following steps: preserving heat at 900 ℃ for 5h, slowly cooling to 650 ℃ for 15h, and then discharging from the furnace for air cooling;
s4, magnetically annealing the material obtained in the step S3 by using a continuous furnace, wherein the annealing process comprises the following steps: keeping the temperature at 700 ℃ for 5h, and then cooling in air.
Example 3
S1, refining a continuous casting blank containing 0.011% of carbon, 11.13% of chromium, 0.38% of silicon, 0.95% of nickel, 0.49% of manganese, 0.021% of phosphorus, 0.001% of sulfur, 0.065% of molybdenum, 0.10% of copper, 0.012% of nitrogen and 0.06% of vanadium, wherein the refining mode adopts three-stage steelmaking: refining in an electric furnace, a converter and VOD (same as example 1), and then carrying out continuous casting to obtain a 150-square continuous casting blank;
s2, preserving the heat of the steel billet obtained in the step S1 for 2 hours at 950 ℃, and then hot-rolling the steel billet into a straight rod;
s3, completely annealing the material obtained in the step S2 by adopting a box-type furnace, wherein the annealing process comprises the following steps: preserving heat for 2 hours at 950 ℃, slowly cooling to 550 ℃ after 20 hours, discharging from the furnace and air cooling;
s4, performing magnetic annealing on the material obtained in the step S3 by using a continuous furnace, wherein the annealing process comprises the following steps: keeping the temperature at 800 ℃ for 2h and then cooling in air.
The materials obtained in examples 1 to 3 and comparative examples 1 to 8 described above were subjected to a magnetic test by: the rods were processed into grinding rods having a diameter of R14.9mm and a length of 200-300. Magnetic measurements were carried out by means of a class A magnetic permeameter according to IEC 60404-4 standard using an AMH-DC-TB-S model apparatus from laboratory eletrofifiisco.
TABLE 1 magnetic test results
As can be seen from the above table:
(1) The soft magnetic stainless steel structures prepared in the comparative examples and comparative examples can obtain pure ferrite structures with good soft magnetic performance after annealing only when the hot rolling is carried out to obtain M + F biphase fine crystals;
(2) Compared with the comparative example 1, the pure ferrite structure can be obtained through only one-stage high-temperature slow cooling annealing, but the soft magnetic performance is poor, and the pure ferrite structure can be obtained through high-temperature slow cooling and stress relief annealing, and the soft magnetic performance is excellent;
(3) In comparative example and comparative example 2, after hot rolling to form M + F dual phase fine grains, a pure ferrite structure could not be obtained only by general stress relief annealing (700 to 900 ℃), and the soft magnetic properties of stainless steel were poor.
The preferred embodiments of the present invention have been described in detail with reference to the examples, however, the present invention is not limited to the details of the above embodiments, and various simple modifications may be made to the technical solution of the present invention within the technical idea of the present invention, and these simple modifications all fall within the scope of protection of the present invention.
It should be noted that the various technical features described in the above embodiments can be combined in any suitable manner without contradiction, and the invention is not described in any way for the possible combinations in order to avoid unnecessary repetition.
In addition, any combination of the various embodiments of the present invention can be made, and the same should be considered as the disclosure of the present invention as long as the idea of the present invention is not violated.
Claims (10)
1. A structure control method of a low Cr system soft magnetic stainless steel is characterized in that the chromium content of the low Cr system soft magnetic stainless steel is 10-15.5%, and the control method comprises the following steps:
s1, hot rolling the billet at 900-1050 ℃, and cooling to obtain a fine grain structure comprising ferrite and martensite;
s2, carrying out heat preservation treatment on the steel billet obtained in the step S1 at 900-1000 ℃ for 2-5 h, slowly cooling for at least 15h to 550-650 ℃, and then cooling;
and S3, carrying out heat preservation treatment on the billet obtained in the step S2 at 700-800 ℃ for 2-5 h, and then cooling to obtain the pure ferrite stainless steel.
2. The method for controlling a structure of a low Cr soft magnetic stainless steel according to claim 1, wherein the temperature of the hot rolling in step S1 is 950 ℃.
3. The microstructure control method of a low Cr system soft magnetic stainless steel according to claim 1, wherein in step S1, the grain size of the fine grains is not less than 5 grade, and the difference in grain size is not more than 2 grade.
4. The method for controlling a structure of a low Cr soft magnetic stainless steel according to claim 1, wherein the keeping temperature in step S2 is 950 ℃.
5. The microstructure control method of claim 1, wherein in the step S2, the steel slab is cooled to 600 ℃ after being slowly cooled for 15 to 20 hours after the heat preservation treatment.
6. The method for controlling a microstructure of a low Cr soft magnetic stainless steel according to claim 1, wherein the soaking temperature in step S3 is 780 ℃.
7. The microstructure controlling method of a low Cr soft magnetic stainless steel according to claim 1, wherein in the step S1, the cooling method is air cooling; and/or
In the step S2, the cooling mode is air cooling; and/or
In step S3, the cooling mode is air cooling.
8. A microstructure controlling method as set forth in any one of claims 1 to 7, wherein a chromium content of the low-chromium stainless steel is 10.5 to 12.5%.
9. The structure controlling method of claim 8, wherein the low-chromium-based soft magnetic stainless steel further comprises the following components: less than or equal to 0.06 percent of carbon, less than or equal to 0.06 percent of nitrogen, less than or equal to 2 percent of silicon, less than or equal to 1.5 percent of manganese, less than or equal to 1 percent of nickel, less than or equal to 0.045 percent of phosphorus and less than or equal to 0.4 percent of sulfur.
10. A low Cr-based soft magnetic stainless steel obtained by the control method according to any one of claims 1 to 9.
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