CN115652224A - Super-grade ferrite stainless steel and preparation method thereof - Google Patents
Super-grade ferrite stainless steel and preparation method thereof Download PDFInfo
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Abstract
The invention relates to the technical field of ferrite stainless steel, in particular to super-grade ferrite stainless steel and a preparation method thereof. In order to solve the technical scheme in the prior art, the problem of inhibiting sigma-phase precipitation is not fundamentally solved, so the super-grade ferritic stainless steel is provided and comprises the following components: cr is more than or equal to 24.0 percent and less than or equal to 32.0 percent, mo is more than or equal to 1.0 percent and less than or equal to 5.0 percent, ni is more than or equal to 0.5 percent and less than or equal to 4.0 percent, al is more than or equal to 0.5 percent and less than or equal to 8.0 percent, C is less than or equal to 0.025 percent, N is less than or equal to 0.015 percent, nb is more than or equal to 0.05 percent and less than or equal to 0.65 percent, ti is more than or equal to 0.05 percent and less than or equal to 0.2 percent, mn is less than or equal to 0.6 percent, si is less than or equal to 0.7 percent, S is less than or equal to 0.015 percent, P is less than or equal to 0.015 percent, O is less than or equal to 0.004 percent, and the sum of Cr and 3.3 x Mo is more than or equal to 35 percent, and the balance of Fe and inevitable impurities. The invention fundamentally inhibits the precipitation of sigma-phase.
Description
Technical Field
The invention relates to the technical field of ferrite stainless steel, in particular to super-grade ferrite stainless steel and a preparation method thereof.
Background
Super ferritic stainless steel (high chromium and high molybdenum ferritic stainless steel) is a resource-saving high-performance material, has excellent corrosion resistance, good heat conductivity and mechanical properties, and is mainly used as a low-cost heat exchange material in a corrosive environment, such as a condenser for a coastal power station instead of a copper pipe and a titanium pipe. The high-chromium and high-molybdenum ferritic stainless steel contains Cr and Mo elements for improving the corrosion resistance of the ferritic stainless steel, and a certain amount of Ni, C, N and Nb elements are added, wherein the added C + N element is not more than 0.04 wt% and is used for reducing the intergranular corrosivity of the ferritic stainless steel; the added Ni element is used for improving the welding performance and the toughness of the ferritic stainless steel, and the added Nb and Ti elements are used for further eliminating the adverse effect of C, N. Because high Cr and high Mo are contained in the high-chromium and high-molybdenum ferritic stainless steel, the high-chromium and high-molybdenum ferritic stainless steel has excellent corrosion resistance and simultaneously has the problem of sigma-phase precipitation brittleness, and the sigma-phase precipitation brittleness temperature range is about 750 to 960 ℃.
In the prior art, in order to avoid the problem of sigma-phase precipitation brittleness, a process route of higher-temperature annealing and rapid cooling is generally adopted, process parameters are strictly controlled, but the problems of grain coarsening and texture weakening are also brought while high-temperature annealing is carried out.
Based on this, in the prior art, as the patent number 202011559796.6, the patent name is a method for preparing a high-chromium and high-molybdenum ferritic stainless steel, the problem is solved by adopting strain-induced Laves phase with higher temperature precipitation and avoiding sigma-phase precipitation, and in order to avoid sigma-phase precipitation in the hot rolling and annealing processes, the preparation method only controls the temperature, namely, avoids the material from being heated and staying for a long time in the range of 750 ℃ to 960 ℃, and does not fundamentally solve the problem of restraining sigma-phase precipitation, so that the requirement on temperature control in the preparation process is higher, and the risk of sigma-phase precipitation still exists.
Disclosure of Invention
The invention provides a novel super-grade ferrite stainless steel and a preparation method thereof, aiming at solving the problem that the technical scheme in the prior art does not fundamentally solve the problem of inhibiting sigma-phase precipitation.
The invention is realized by adopting the following technical scheme: the super-grade ferritic stainless steel comprises the following components in percentage by weight: cr is more than or equal to 24.0 percent and less than or equal to 32.0 percent, mo is more than or equal to 1.0 percent and less than or equal to 5.0 percent, ni is more than or equal to 0.5 percent and less than or equal to 4.0 percent, al is more than or equal to 0.5 percent and less than or equal to 8.0 percent, C is less than or equal to 0.025 percent, N is less than or equal to 0.015 percent, nb is more than or equal to 0.05 percent and less than or equal to 0.65 percent, ti is more than or equal to 0.05 percent and less than or equal to 0.2 percent, mn is less than or equal to 0.6 percent, si is less than or equal to 0.7 percent, S is less than or equal to 0.015 percent, P is less than or equal to 0.015 percent, O is less than or equal to 0.004 percent, and the sum of Cr and 3.3 x Mo is more than or equal to 35 percent, and the balance of Fe and inevitable impurities.
As known to those skilled in the art, al in conventional super ferritic stainless steel is generally added as a deoxidizer, namely, the Al is added to remove residual O elements in molten steel, but the content of the deoxidizer is generally required to be not more than 0.1%, and the applicant researches show that sigma-phase precipitation in the super ferritic stainless steel is mainly caused by segregation of Cr and Mo elements to grain boundaries and large binding energy of Cr, mo and Fe, and the invention adds a proper amount of Al element in the super ferritic stainless steel so as to fundamentally inhibit the precipitation of the sigma-phase, wherein the Al element reduces the binding energy of Cr, mo and Fe and prevents the segregation to the grain boundaries, so that the kinetics of the sigma-phase precipitation in the steel is remarkably reduced, and no sigma-phase precipitation is observed after 16 hours of isothermal temperature above 850 ℃; meanwhile, the addition of Al element also reduces the stacking fault energy of the material, the dynamic recovery kinetics of the deformed structure is reduced in the hot rolling process, more dislocations can be reserved in the deformed structure, higher deformation energy storage is formed, and larger recrystallization driving power is provided for recrystallization annealing after deformation. In addition, precipitation of a nanoscale Laves phase is promoted by adding Al, a ferrite grain boundary is pinned by using a fine Laves phase, coarsening of recrystallized grains is prevented, and a recrystallization texture is optimized.
A preparation method of super ferritic stainless steel comprises the following steps:
1) Smelting:
the smelting raw materials comprise the following elements in percentage by weight: cr is more than or equal to 24.0 percent and less than or equal to 32.0 percent, mo is more than or equal to 1.0 percent and less than or equal to 5.0 percent, ni is more than or equal to 0.5 percent and less than or equal to 4.0 percent, al is more than or equal to 0.5 percent and less than or equal to 8.0 percent (enough Al elements inhibit sigma-phase precipitation and promote Laves phase precipitation simultaneously), C is less than or equal to 0.025 percent, N is less than or equal to 0.015 percent, nb is more than or equal to 0.05 percent and less than or equal to 0.65 percent, ti is more than or equal to 0.2 percent, mn is less than or equal to 0.6 percent, si is less than or equal to 0.7 percent, S is less than or equal to 0.015 percent, P is less than or equal to 0.015 percent, O is less than or equal to 0.004 percent, and the content of Cr + 3.3XMo is more than or equal to 35 percent, and the balance of Fe and inevitable impurities;
2) Continuous casting and grinding:
continuously casting the molten steel obtained in the step 1) into a continuous casting blank, slowly cooling the continuous casting blank to 400-600 ℃ at a cooling speed of 5-10 ℃/h, and then polishing;
3) Hot rolling and curling:
heating the polished continuous casting blank obtained in the step 2) to 1050-1250 ℃, preserving heat for 0.5-2h, and then carrying out hot rolling, wherein the final hot rolling temperature is more than or equal to 850 ℃, and curling is carried out after hot rolling to form a hot rolled coil (the final hot rolling temperature is more than or equal to 850 ℃, compared with the prior technical scheme, the temperature limitation is obviously reduced, namely low-temperature hot rolling can be adopted, and the low-temperature hot rolling is realized because Al element is added into the smelting raw material, the precipitation of sigma-phase is inhibited, and the low-temperature hot rolling is beneficial to keeping hot rolling deformation tissue and improving deformation energy storage);
4) And (3) annealing:
annealing the hot-rolled coil obtained in the step 3) to obtain a hot-rolled annealed plate, wherein the heating temperature is 850-1150 ℃, and the heat preservation time is 5-120min (the purpose of low-temperature annealing is to ensure that Laves phase is separated out and utilize Laves phase to bind grain boundary to refine recrystallized grains);
5) Acid washing:
pickling the annealed plate obtained in the step 4) by using a sulfuric acid mixed solution;
6) Cold rolling:
cold rolling the annealed plate obtained in the step 5) after acid washing, wherein the cold rolling reduction rate is 30-90%;
7) Recrystallization annealing and cooling:
and (3) carrying out recrystallization annealing on the cold-rolled sheet obtained in the step 6), wherein the annealing temperature is 900-1150 ℃, and the heat preservation time is 0.5-120min (the addition of the Al element in the steel reduces the stacking fault energy and the recrystallization activation energy of the material, so that the recrystallization process can be completed at a lower temperature. In addition, the presence of the Laves phase has the functions of refining grains and optimizing texture, and further controls the formation of a structure with fine grains and sharp texture).
According to the preparation method, a proper amount of Al element is added into the super ferrite stainless steel, the Al element reduces the binding energy of Cr, mo and Fe and prevents the binding energy from deviating to grain boundaries, so that the sigma-phase precipitation kinetics in the steel is remarkably reduced, and no sigma-phase precipitation is observed after 16 hours of isothermal temperature above 850 ℃, so that the super ferrite stainless steel can be prepared by low-temperature hot rolling, and the deformation energy storage is improved by the low-temperature hot rolling; meanwhile, the addition of Al element also reduces the stacking fault energy of the material, the dynamic recovery dynamics of the deformed structure is reduced in the hot rolling process, more dislocations can be reserved in the deformed structure, and higher deformation energy storage is formed. Based on low temperature hot rolling and Al addition, the subsequent recrystallization annealing temperature can be significantly reduced to (900-1150 ℃). The low recrystallization annealing temperature and the high hot rolling deformation energy storage can obtain a structure with fine grains, thereby preparing the high-performance super-grade ferrite stainless steel. In the specific preparation method, the hot rolling finishing temperature in the step 3) is reduced to 850 ℃, the stacking fault energy of the material is reduced due to the addition of the Al element, a large amount of deformation tissues (shown in figure 1) can be reserved after hot rolling, the hot rolling deformation energy storage is remarkably improved, and a driving force and nucleation mass points are provided for recrystallization in the subsequent annealing process in the step 4). In addition, the existence of a large amount of deformed tissues can provide nucleation particles for the precipitation of the Laves phase in the low-temperature annealing process of the step 4), and promote the precipitation of the Laves phase in a sufficient amount (see figure 2). And (3) carrying out cold rolling on the annealed plate in the step 6), wherein the cold rolling reduction rate is 30-90%, deformation energy storage is formed in the cold rolling deformation process, and a large number of microstructure defects such as shear bands and the like provide nucleation particles for recrystallization in the subsequent annealing process. In addition, the nanometer Laves phase formed in the hot-rolled annealed plate can increase the cold-rolling deformation resistance, improve the deformation energy storage, increase the recrystallization driving force, further improve the recrystallization nucleation rate, promote the formation of fine recrystallization grains (see figure 3) and improve the ductility and toughness of the hot-rolled annealed plate. In the step 7), the annealing temperature of the cold-rolled sheet is further reduced to 900-1150 ℃, in the recrystallization process, the Laves phase formed at the position of the shear band inhibits the recrystallization of other oriented crystal grains such as alpha-fiber and the like and promotes the recrystallization of the gamma-fiber texture through the selective pinning effect, and finally the cold-rolled annealed sheet (shown in figure 4) with fine tissue and single gamma-fiber texture is formed, so that the forming performance of the cold-rolled annealed sheet is improved. The invention reduces the hot rolling finishing temperature, the hot rolled plate annealing temperature and the cold rolling annealing temperature, and has low manufacturing cost and uniform and fine structure.
A preparation method of super ferritic stainless steel comprises the following steps:
1) Smelting: the smelting raw materials comprise the following elements in percentage by weight: cr is more than or equal to 24.0 percent and less than or equal to 32.0 percent, mo is more than or equal to 1.0 percent and less than or equal to 5.0 percent, ni is more than or equal to 0.5 percent and less than or equal to 4.0 percent, al is more than or equal to 0.5 percent and less than or equal to 8.0 percent (enough Al elements inhibit sigma-phase precipitation and promote Laves phase precipitation simultaneously), C is less than or equal to 0.025 percent, N is less than or equal to 0.015 percent, nb is more than or equal to 0.05 percent and less than or equal to 0.65 percent, ti is more than or equal to 0.2 percent, mn is less than or equal to 0.6 percent, si is less than or equal to 0.7 percent, S is less than or equal to 0.015 percent, P is less than or equal to 0.015 percent, O is less than or equal to 0.004 percent, and the content of Cr + 3.3XMo is more than or equal to 35 percent, and the balance of Fe and inevitable impurities;
2) Forging:
forging the molten steel obtained in the step 1), wherein the forging temperature is 1150 ℃, the finish forging temperature is more than or equal to 900 ℃, and the heat preservation time is 0.5-2h;
3) Hot rolling and curling:
heating the forging stock obtained in the step 2) to 1050-1250 ℃, preserving heat for 0.5-2h, then carrying out hot rolling, wherein the hot rolling finishing temperature is more than or equal to 850 ℃, the hot rolling reduction rate is more than or equal to 70%, and cooling and curling the hot rolled plate to form a hot rolled coil;
4) Annealing:
annealing the hot-rolled coil obtained in the step 3), wherein the heating temperature is 850-1150 ℃, and the heat preservation time is 5-120min;
5) Acid washing:
pickling the annealed plate obtained in the step 4) by using a sulfuric acid mixed solution;
6) Cold rolling:
cold rolling the annealed plate obtained in the step 5) after acid washing, wherein the cold rolling reduction rate is 50-90%;
7) Recrystallization annealing and cooling:
and (3) carrying out recrystallization annealing on the cold-rolled sheet obtained in the step 6), wherein the annealing temperature is 900-1150 ℃, and the heat preservation time is 1-240min.
According to the preparation method, a proper amount of Al element is added into the super ferrite stainless steel, the Al element reduces the binding energy of Cr, mo and Fe and prevents the binding energy from deviating to grain boundaries, so that the sigma-phase precipitation kinetics in the steel is remarkably reduced, and no sigma-phase precipitation is observed after 16 hours of isothermal temperature above 850 ℃, so that the super ferrite stainless steel can be prepared by low-temperature hot rolling, and the deformation energy storage is improved by the low-temperature hot rolling; meanwhile, the addition of Al element also reduces the stacking fault energy of the material, the dynamic recovery dynamics of the deformed structure is reduced in the hot rolling process, more dislocations can be reserved in the deformed structure, and higher deformation energy storage is formed. Based on low-temperature hot rolling, the subsequent recrystallization annealing temperature can be obviously reduced to (900-1150 ℃). The low recrystallization annealing temperature and the high hot rolling deformation energy storage can obtain a structure with fine grains, thereby preparing the high-performance super-grade ferrite stainless steel. In the specific preparation method, the hot rolling finishing temperature in the step 3) is reduced to 850 ℃, the stacking fault energy of the material is reduced due to the addition of Al element, a large amount of deformation tissues (shown in figure 5) can be reserved after hot rolling, the hot rolling deformation energy storage is obviously improved, and a driving force is provided for recrystallization in the subsequent annealing process in the step 4). In addition, the existence of a large amount of deformed tissues can provide nucleation particles for the precipitation of the Laves phase in the low-temperature annealing process of the step 4), and promote the precipitation of the Laves phase in a sufficient amount (see FIG. 6). And (3) carrying out cold rolling on the annealed plate in the step 6), wherein the cold rolling reduction rate is 30-90%, deformation energy storage is formed in the cold rolling deformation process, and a large number of microstructure defects such as shear bands and the like provide nucleation particles for recrystallization in the subsequent annealing process. In addition, the nanometer Laves phase formed in the hot-rolled annealed plate can increase the cold rolling deformation resistance, improve the deformation energy storage, increase the recrystallization driving force, further improve the recrystallization nucleation rate, promote the formation of fine recrystallization grains (see figure 7) and improve the plasticity and toughness of the plate. In step 7), the annealing temperature of the cold-rolled sheet is further reduced to 900-1150 ℃. In the recrystallization process, the Laves phase formed at the position of the shear band inhibits the recrystallization of other oriented grains such as alpha-fiber and the like and promotes the recrystallization of a gamma-fiber texture through the selective pinning effect, and finally, a cold-rolled annealed plate (shown in figure 8) with a fine structure and a single gamma-fiber texture is formed, so that the forming performance of the cold-rolled annealed plate is improved. The invention reduces the hot rolling finishing temperature, the hot rolled plate annealing temperature and the cold rolling annealing temperature, and has low manufacturing cost and uniform and fine structure.
The beneficial effects produced by the invention are as follows: according to the invention, a proper amount of Al element is added into the super ferrite stainless steel, so that sigma-phase precipitation is fundamentally inhibited, and embrittlement caused by sigma-phase precipitation is reduced, and due to the addition, the requirements on temperature and cooling rate control during preparation of the super ferrite stainless steel are obviously reduced, namely low-temperature hot rolling is adopted, high temperature is not required to be adopted to avoid sigma-phase precipitation, and then based on the low-temperature hot rolling, the subsequent recrystallization annealing temperature can be obviously reduced, the low recrystallization annealing temperature is adopted, and high hot rolling deformation energy storage is added, so that a structure with fine grains can be obtained, and the high-performance super ferrite stainless steel is prepared; meanwhile, when the problem of sigma-phase precipitation brittleness is solved, the addition of a proper amount of Al element effectively promotes the pre-precipitation of a nano-level Laves phase in annealing, and a refined tissue is precipitated by utilizing the nano-level Laves phase, so that the toughness of the material is improved; in addition, the control difficulty of the process parameters is reduced by reducing the heating temperature, the manufacturing cost is obviously reduced, the strict limitations of the cooling rate and the cooling time in the cooling process after heating are further weakened, and the production is facilitated.
Drawings
FIG. 1 shows the structure of super ferritic stainless steel after low temperature hot rolling in step 3); (continuous casting method)
FIG. 2 shows the fine structure and Laves phase formed by the super ferritic stainless steel after the low temperature annealing in step 4); (continuous casting method)
FIG. 3 shows the structure of the super ferritic stainless steel of the present invention after step 7); (continuous casting method)
FIG. 4 shows the texture of the super ferritic stainless steel according to the present invention after the preparation; (continuous casting method)
FIG. 5 is a structure of super ferritic stainless steel after the low temperature hot rolling of step 3) in accordance with the present invention; (forging method)
FIG. 6 shows the fine structure and Laves phase formed by the super ferritic stainless steel after the low temperature annealing in step 4); (forging method)
FIG. 7 shows the structure of the super ferritic stainless steel of the present invention after the step 7); (forging method)
FIG. 8 shows the texture of the super ferritic stainless steel according to the present invention after the preparation; (forging method)
FIG. 9 shows the precipitation morphology of Al-free super ferritic stainless steel hot-rolled annealed plate after 850-2 h;
FIG. 10 shows the precipitation morphology of the Al-containing stainless steel hot-rolled annealed plate after 850-16 h.
Detailed Description
Example 1:
the super-grade ferritic stainless steel comprises the following components in percentage by weight: 29.0% of Cr,4.0% of Mo,3.0% of Ni,0.5% of Al,0.010% of C,0.015% of N,0.27% of Nb,0.10% of Ti,0.6% of Mn,0.7% of Si,0.015% of S,0.015% of P,0.004% of O, and the balance of Fe and unavoidable impurities.
Example 2:
the super-grade ferritic stainless steel comprises the following components in percentage by weight: 24.5% of Cr,5.0% of Mo,4.0% of Ni,1.0% of Al,0.025% of C,0.012% of N,0.65% of Nb,0.20% of Ti,0.2% of Mn,0.15% of Si,0.010% of S,0.010% of P,0.002% of O, and the balance of Fe and unavoidable impurities.
Example 3:
the super-grade ferritic stainless steel comprises the following components in percentage by weight: 32% of Cr,4.0% of Mo,0.5% of Ni,8.0% of Al,0.015% of C,0.005% of N,0.25% of Nb,0.05% of Ti,0.1% of Mn,0.4% of Si,0.001% of S,0.005% of P,0.001% of O, and the balance Fe and unavoidable impurities.
Example 4:
the super-grade ferritic stainless steel comprises the following components in percentage by weight: 31% of Cr,1.5% of Mo,3.5% of Ni,5.0% of Al,0.005% of C,0.010% of N,0.05% of Nb,0.05% of Ti,0.5% of Mn,0.2% of Si,0.015% of S,0.015% of P,0.004% of O, and the balance of Fe and unavoidable impurities.
Example 5:
the super-grade ferritic stainless steel comprises the following components in percentage by weight: 28.0% of Cr,5.0% of Mo,0.5% of Ni,6.0% of Al,0.025% of C,0.012% of N,0.60% of Nb,0.17% of Ti,0.6% of Mn,0.7% of Si,0.015% of S,0.010% of P,0.003% of O, and the balance of Fe and unavoidable impurities.
Example 6:
the super-grade ferritic stainless steel comprises the following components in percentage by weight: 24.0% of Cr,4.0% of Mo,1% of Ni,7.0% of Al,0.020% of C,0.012% of N,0.45% of Nb,0.10% of Ti,0.3% of Mn,0.2% of Si,0.005% of S,0.013% of P,0.002% of O, and the balance Fe and unavoidable impurities.
Example 7:
a preparation method of super ferritic stainless steel comprises the following steps:
1) Smelting:
the smelting raw materials comprise the following elements in percentage by weight: 27% of Cr,4.0% of Mo,0.5% of Ni,0.5% of Al,0.010% of C,0.015% of N,0.35% of Nb,0.15% of Ti,0.6% of Mn,0.7% of Si,0.015% of S,0.015% of P,0.004% of O and the balance of Fe and inevitable impurities, and preparing raw materials according to the element proportion and then smelting to obtain molten steel;
2) Continuous casting and grinding:
continuously casting the molten steel obtained in the step 1) into a continuous casting blank, slowly cooling the continuous casting blank to 400 ℃ at a cooling speed of 5 ℃/h, and then polishing;
3) Hot rolling and curling:
heating the polished continuous casting blank obtained in the step 2) to 1120 ℃, preserving heat for 0.5h, and then carrying out hot rolling at a final hot rolling temperature of 920 ℃, and curling after hot rolling to form a hot rolled coil;
4) And (3) annealing:
annealing the hot-rolled coil obtained in the step 3) to obtain a hot-rolled annealed plate, wherein the heating temperature is 1150 ℃, the heat preservation time is 5min, and the heating rate is 100 ℃/min;
5) Acid washing:
pickling the annealed plate obtained in the step 4) by using a sulfuric acid mixed solution;
6) Cold rolling:
cold rolling the annealed plate obtained in the step 5) after acid washing, wherein the cold rolling reduction rate is 90%;
7) Recrystallization annealing and cooling:
and (3) carrying out recrystallization annealing on the cold-rolled sheet obtained in the step 6), wherein the annealing temperature is 900 ℃, the heat preservation time is 60min, and the cooling rate is 100 ℃/s.
The performance and structure indexes after cold rolling and annealing are shown in table 1:
TABLE 1
Example 8:
a preparation method of super ferritic stainless steel comprises the following steps:
1) Smelting:
the smelting raw materials comprise the following elements in percentage by weight: 24% of Cr,5% of Mo,4% of Ni,2% of Al,0.025% of C,0.012% of N,0.65% of Nb,0.2% of Ti,0.2% of Mn,0.15% of Si,0.010% of S,0.010% of P,0.002% of O and the balance of Fe and inevitable impurities, and the raw materials are prepared according to the element proportion and then smelted to obtain molten steel;
2) Continuous casting and grinding:
continuously casting the molten steel obtained in the step 1) into a continuous casting blank, slowly cooling the continuous casting blank to 600 ℃ at a cooling speed of 6 ℃/h, and then polishing;
3) Hot rolling and curling:
heating the continuous casting blank obtained in the step 2) to 1050 ℃, preserving heat for 1.5h, and then carrying out hot rolling at a finishing temperature of 860 ℃ to obtain a hot rolled coil;
4) Annealing:
annealing the hot-rolled coil obtained in the step 3) to obtain a hot-rolled annealed plate, wherein the heating temperature is 1150 ℃, the heat preservation time is 30min, and the heating rate is 200 ℃/min;
5) Acid washing:
pickling the annealed plate obtained in the step 4) by using a sulfuric acid mixed solution;
6) Cold rolling:
cold rolling the annealed plate obtained in the step 5) after acid washing, wherein the cold rolling reduction rate is 80%;
7) Recrystallization annealing and cooling:
and (3) carrying out recrystallization annealing on the cold-rolled sheet obtained in the step 6), wherein the annealing temperature is 900 ℃, the heat preservation time is 120min, and the cooling rate is 200 ℃/s.
The performance and structure index after cold rolling and annealing are shown in table 2:
TABLE 2
Example 9:
a preparation method of super ferritic stainless steel comprises the following steps:
1) Smelting:
the smelting raw materials comprise the following elements in percentage by weight: preparing raw materials according to the element proportion, and then smelting to obtain molten steel, wherein the raw materials comprise 32% of Cr,1% of Mo,1.0% of Ni,8.0% of Al,0.005% of C,0.005% of N,0.05% of Nb,0.05% of Ti,0.1% of Mn,0.4% of Si,0.001% of S,0.005% of P,0.001% of O and the balance of Fe and inevitable impurities;
2) Continuous casting and grinding:
continuously casting the molten steel obtained in the step 1) into a continuous casting blank, slowly cooling the continuous casting blank to 500 ℃ at a cooling speed of 10 ℃/h, and then polishing;
3) Hot rolling and curling:
heating the continuous casting slab obtained in the step 2) to 1250 ℃, preserving heat for 2.0h, and then carrying out hot rolling, wherein the hot rolling finishing temperature is 850 ℃, and curling is carried out after hot rolling to form a hot rolled coil;
4) Annealing:
annealing the hot-rolled coil obtained in the step 3) to obtain a hot-rolled annealed plate, wherein the heating temperature is 1100 ℃, the heat preservation time is 10min, and the heating rate is 50 ℃/min;
5) Acid washing:
pickling the annealed plate obtained in the step 4) by using a sulfuric acid mixed solution;
6) Cold rolling:
cold rolling the annealed plate obtained in the step 5) after acid washing, wherein the cold rolling reduction rate is 60%;
7) Recrystallization annealing and cooling:
and (3) carrying out recrystallization annealing on the cold-rolled sheet obtained in the step 6), wherein the annealing temperature is 1150 ℃, the heat preservation time is 0.5min, and the cooling rate is 150 ℃/s.
The properties and the structure indexes after cold rolling and annealing are shown in Table 3:
TABLE 3
Example 10:
a preparation method of super ferritic stainless steel comprises the following steps:
1) Smelting:
the smelting raw materials comprise the following elements in percentage by weight: 27% of Cr,2% of Mo,1.5% of Ni,0.5% of Al,0.025% of C,0.015% of N,0.25% of Nb,0.20% of Ti,0.6% of Mn,0.7% of Si,0.015% of S,0.015% of P,0.004% of O and the balance of Fe and inevitable impurities, and the raw materials are prepared according to the element proportion and then smelted to obtain molten steel;
2) Forging:
forging the molten steel obtained in the step 1), wherein the forging temperature is 1150 ℃, the finish forging temperature is 950 ℃, and the heat preservation time is 0.5h;
3) Hot rolling and curling:
heating the forging stock obtained in the step 2) to 1080 ℃, preserving heat for 0.5h, carrying out hot rolling, cooling a hot rolled plate, and then curling to form a hot rolled coil, wherein the hot rolled final rolling temperature is 850 ℃, and the hot rolling reduction rate is 80%;
4) Annealing:
annealing the hot-rolled coil obtained in the step 3), wherein the heating temperature is 1000 ℃, the heat preservation time is 5min, and the heating rate is 50 ℃/min;
5) Acid washing:
pickling the annealed plate obtained in the step 4) by using a sulfuric acid mixed solution;
6) Cold rolling:
cold rolling the annealed plate obtained in the step 5) after acid washing, wherein the cold rolling reduction rate is 80%;
7) Recrystallization annealing and cooling:
and (3) carrying out recrystallization annealing on the cold-rolled sheet obtained in the step 6), wherein the annealing temperature is 900 ℃, the heat preservation time is 120min, and the cooling rate is 300 ℃/s.
The properties and the structure indexes after cold rolling and annealing are shown in Table 4:
TABLE 4
Example 11:
a preparation method of super ferritic stainless steel comprises the following steps:
1) Smelting:
the smelting raw materials comprise the following elements in percentage by weight: 24.0% of Cr,5% of Mo,4% of Ni,2% of Al,0.020% of C,0.012% of N,0.65% of Nb,0.05% of Ti,0.2% of Mn,0.15% of Si,0.010% of S,0.010% of P,0.002% of O and the balance of Fe and inevitable impurities, and preparing raw materials according to the element proportion and then smelting to obtain molten steel;
2) Forging:
forging the molten steel obtained in the step 1), wherein the forging temperature is 1150 ℃, the finish forging temperature is 900 ℃, and the heat preservation time is 2 hours;
3) Hot rolling and curling:
heating the forging stock obtained in the step 2) to 1050 ℃, preserving heat for 2.0h, and then carrying out hot rolling, wherein the final hot rolling temperature is 960 ℃, cooling a hot rolled plate and then curling the hot rolled plate, and the hot rolling reduction rate is 90% to form a hot rolled coil;
4) Annealing:
annealing the hot-rolled coil obtained in the step 3), wherein the heating temperature is 850 ℃, the heat preservation time is 120min, and the heating rate is 100 ℃/min;
5) Acid washing:
pickling the annealed plate obtained in the step 4) by using a sulfuric acid mixed solution;
6) Cold rolling:
cold rolling the annealed plate obtained in the step 5) after acid washing, wherein the cold rolling reduction rate is 90%;
7) Recrystallization annealing and cooling:
and (3) carrying out recrystallization annealing on the cold-rolled sheet obtained in the step 6), wherein the annealing temperature is 1150 ℃, the heat preservation time is 1min, and the cooling rate is 100 ℃/s.
The properties and the structure indexes after cold rolling and annealing are shown in Table 5:
TABLE 5
Example 12:
a preparation method of super ferritic stainless steel comprises the following steps:
1) Smelting:
the smelting raw materials comprise the following elements in percentage by weight: 32% of Cr,1% of Mo,0.5% of Ni,8.0% of Al,0.005% of C,0.005% of N,0.05% of Nb,0.10% of Ti,0.1% of Mn,0.4% of Si,0.001% of S,0.005% of P,0.001% of O and the balance of Fe and inevitable impurities, and preparing raw materials according to the element proportion and then smelting to obtain molten steel;
2) Forging:
forging the molten steel obtained in the step 1), wherein the forging temperature is 1150 ℃, the finish forging temperature is 1000 ℃, and the heat preservation time is 1h;
3) Hot rolling and curling:
heating the forging stock obtained in the step 2) to 1250 ℃, preserving heat for 0.5h, and then carrying out hot rolling, wherein the hot rolling finishing temperature is 850 ℃, the hot rolling reduction rate is 70%, and the hot rolled plate is cooled and then curled to form a hot rolled coil;
4) Annealing:
annealing the hot-rolled coil obtained in the step 3), wherein the heating temperature is 1150 ℃, the heat preservation time is 5min, and the heating rate is 80 ℃/min;
5) Acid washing:
pickling the annealed plate obtained in the step 4) by adopting a sulfuric acid mixed solution;
6) Cold rolling:
cold rolling the annealed plate obtained in the step 5) after acid washing, wherein the cold rolling reduction rate is 50%;
7) Recrystallization annealing and cooling:
and (3) carrying out recrystallization annealing on the cold-rolled sheet obtained in the step 6), wherein the annealing temperature is 1050 ℃, the heat preservation time is 240min, and the cooling rate is 500 ℃/s.
The properties and structure indexes after cold rolling and annealing are shown in Table 6:
TABLE 6
In order to further verify the sigma-phase inhibition effect of the super-grade ferritic stainless steel, the hot-rolled annealed plate of the super-grade ferritic stainless steel added with Al and not added with Al is subjected to isothermal aging treatment at 850 ℃. The precipitation morphology of the Al-free sample after isothermal treatment for 2 hours is shown in FIG. 9 (obvious wide range of sigma-phase occurrence); the precipitation morphology of the Al-containing sample after isothermal treatment for 16h is shown in FIG. 10 (no obvious sigma-phase). The comparison shows that the mechanical property indexes of the two steels are shown in table 7, after the Al element is added, the precipitation tendency of a brittle phase in the super ferrite stainless steel is obviously weakened, and the toughness fracture is still kept after the super ferrite stainless steel is stretched.
TABLE 7
Claims (7)
1. The super-grade ferritic stainless steel is characterized by comprising the following components in percentage by weight: cr is more than or equal to 24.0 percent and less than or equal to 32.0 percent, mo is more than or equal to 1.0 percent and less than or equal to 5.0 percent, ni is more than or equal to 0.5 percent and less than or equal to 4.0 percent, al is more than or equal to 0.5 percent and less than or equal to 8.0 percent, C is less than or equal to 0.025 percent, N is less than or equal to 0.015 percent, nb is more than or equal to 0.05 percent and less than or equal to 0.65 percent, ti is more than or equal to 0.05 percent and less than or equal to 0.2 percent, mn is less than or equal to 0.6 percent, si is less than or equal to 0.7 percent, S is less than or equal to 0.015 percent, P is less than or equal to 0.015 percent, O is less than or equal to 0.004 percent, and the sum of Cr and 3.3 x Mo is more than or equal to 35 percent, and the balance of Fe and inevitable impurities.
2. A preparation method of super ferritic stainless steel is characterized by comprising the following steps:
1) Smelting:
the smelting raw materials comprise the following elements in percentage by weight: cr is more than or equal to 24.0 percent and less than or equal to 32.0 percent, mo is more than or equal to 1.0 percent and less than or equal to 5.0 percent, ni is more than or equal to 0.5 percent and less than or equal to 4.0 percent, al is more than or equal to 0.5 percent and less than or equal to 8.0 percent, C is less than or equal to 0.025 percent, N is less than or equal to 0.015 percent, nb is more than or equal to 0.05 percent and less than or equal to 0.65 percent, ti is more than or equal to 0.05 percent and less than or equal to 0.2 percent, mn is less than or equal to 0.6 percent, si is less than or equal to 0.7 percent, S is less than or equal to 0.015 percent, P is less than or equal to 0.015 percent, O is less than or equal to 0.004 percent, and the Cr +3.3 xMo is more than or equal to 35 percent, and the balance of Fe and inevitable impurities are prepared according to the element proportion, and then smelted to obtain molten steel;
2) Continuous casting and grinding:
continuously casting the molten steel obtained in the step 1) into a continuous casting blank, slowly cooling the continuous casting blank to 400-600 ℃ at a cooling speed of 5-10 ℃/h, and then polishing;
3) Hot rolling and curling:
heating the polished continuous casting blank obtained in the step 2) to 1050-1250 ℃, preserving heat for 0.5-2h, and then carrying out hot rolling, wherein the final rolling temperature of the hot rolling is more than or equal to 850 ℃, and curling the hot rolled continuous casting blank after the hot rolling to form a hot rolled coil;
4) Annealing:
annealing the hot-rolled coil obtained in the step 3) to obtain a hot-rolled annealed plate, wherein the heating temperature is 850-1150 ℃, and the heat preservation time is 5-120min;
5) Acid washing:
pickling the annealed plate obtained in the step 4) by using a sulfuric acid mixed solution;
6) Cold rolling:
cold rolling the annealed plate obtained in the step 5) after acid washing, wherein the cold rolling reduction rate is 30-90%;
7) Recrystallization annealing and cooling:
and (3) carrying out recrystallization annealing on the cold-rolled sheet obtained in the step 6), wherein the annealing temperature is 900-1150 ℃, and the heat preservation time is 0.5-120min.
3. The method for preparing super ferritic stainless steel according to claim 2, wherein the heating rate in step 4) is not less than 50 ℃/min.
4. The method for preparing super ferritic stainless steel according to claim 2, characterized in that, in step 7), the cooling rate is not less than 100 ℃/s.
5. A preparation method of super ferritic stainless steel is characterized by comprising the following steps:
1) Smelting: the smelting raw materials comprise the following elements in percentage by weight: cr is more than or equal to 24.0 percent and less than or equal to 32.0 percent, mo is more than or equal to 1.0 percent and less than or equal to 5.0 percent, ni is more than or equal to 0.5 percent and less than or equal to 4.0 percent, al is more than or equal to 0.5 percent and less than or equal to 8.0 percent, C is less than or equal to 0.025 percent, N is less than or equal to 0.015 percent, nb is more than or equal to 0.05 percent and less than or equal to 0.65 percent, ti is more than or equal to 0.05 percent and less than or equal to 0.2 percent, mn is less than or equal to 0.6 percent, si is less than or equal to 0.7 percent, S is less than or equal to 0.015 percent, P is less than or equal to 0.015 percent, O is less than or equal to 0.004 percent, and the Cr +3.3 xMo is more than or equal to 35 percent, and the balance of Fe and inevitable impurities are prepared according to the element proportion, and then smelted to obtain molten steel;
2) Forging:
forging the molten steel obtained in the step 1), wherein the forging temperature is 1150 ℃, the finish forging temperature is more than or equal to 900 ℃, and the heat preservation time is 2h;
3) Hot rolling and curling:
heating the forging stock obtained in the step 2) to 1050-1250 ℃, preserving heat for 0.5-2h, then carrying out hot rolling, wherein the final rolling temperature of the hot rolling is more than or equal to 850 ℃, the hot rolling reduction rate is more than or equal to 70%, and cooling and curling the hot rolled plate to form a hot rolled coil;
4) Annealing:
annealing the hot-rolled coil obtained in the step 3), wherein the heating temperature is 850-1150 ℃, and the heat preservation time is 5-120min;
5) Acid washing:
pickling the annealed plate obtained in the step 4) by using a sulfuric acid mixed solution;
6) Cold rolling:
cold rolling the annealed plate obtained in the step 5) after acid washing, wherein the cold rolling reduction rate is 50-90%;
7) Recrystallization annealing and cooling:
and (3) carrying out recrystallization annealing on the cold-rolled sheet obtained in the step 6), wherein the annealing temperature is 900-1150 ℃, and the heat preservation time is 1-240min.
6. The method for preparing super ferritic stainless steel according to claim 5, wherein the heating rate in step 4) is not less than 50 ℃/min.
7. The method for preparing super ferritic stainless steel according to claim 5, wherein the cooling rate in step 7) is not less than 100 ℃/s.
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