CN108277434B - Precipitation strengthening ferritic steel with yield strength of 900MPa and production method thereof - Google Patents
Precipitation strengthening ferritic steel with yield strength of 900MPa and production method thereof Download PDFInfo
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- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
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- C21D1/26—Methods of annealing
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- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
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- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
- C21D8/0226—Hot rolling
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- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
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- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C22C38/00—Ferrous alloys, e.g. steel alloys
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
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- C21D2211/005—Ferrite
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Abstract
A precipitation strengthening ferritic steel with the yield strength of 900MPa comprises the following components in percentage by weight: c: 0.105 to 0.139%, Si: 0.05-0.16%, Mn: 0.59-0.98%, P: less than or equal to 0.008 percent, S: less than or equal to 0.003 percent, Cr: 0.11 to 0.23%, Nb: 0.121-0.182%, Ti: 0.119-0.177%, Mo: 0.22-0.47%, N: less than or equal to 0.005 percent. The production method comprises the following steps: heating the casting blank after conventional smelting and casting to form a blank; two-stage hot rolling; laminar cooling; coiling; naturally cooling to room temperature and then pickling; warm rolling; annealing; and (6) cooling. The invention can ensure that the yield strength of the steel is 903-946 MPa, the tensile strength is 952-987 MPa, the elongation is more than or equal to 21%, the average grain size of ferrite is 1.9-2.4 mu m, the precipitation strengthening contribution amount is 287-323 MPa, and the invention has excellent plasticity, forming property and welding property.
Description
Technical Field
The invention relates to a low-carbon ultrahigh-strength ferrite steel and a production method thereof, which exactly belong to precipitation strengthening type ultrafine grained ferrite steel with the yield strength of 900MPa and the production method thereof, and are suitable for the fields of automobiles, transportation, engineering machinery and the like.
Background
In recent years, high-performance automobile steel is rapidly developed, is regarded as a key for automobile weight reduction, and is one of important means for realizing energy conservation and emission reduction of automobiles. The technology for researching and developing high-performance automobile steel has important significance for the development of steel and automobile industry in China. The ultrahigh-strength ferritic steel is an important development direction of high-performance automobile steel, has excellent plasticity, formability, welding performance and the like, is particularly suitable for manufacturing automobile parts with complex structures, and has simple production process and low cost. However, the strength of ferritic steel is low, and how to improve the strength becomes a key point for developing ultra-high strength ferritic automobile steel. At present, the ultra-high strength steel mainly comprises martensite steel and bainite steel, and the steel has ultra-high strength but low elongation and cannot meet the requirement of manufacturing automobile parts with complex structures. In addition, the production of the steel needs to add a large amount of alloy elements and needs to go through a complicated heat treatment process, the manufacturing flow is long, and the production cost is high, as searched:
the Chinese patent application No. 201410535894.4 discloses an 800MPa grade cold rolling dual-phase steel and a production method thereof, and the components of the steel are as follows: 0.14-0.17% of C, 0.45-0.55% of Si, 1.6-1.8% of Mn, 0.55-0.65% of Cr, less than or equal to 0.016% of P, less than or equal to 0.008% of S, 0.02-0.05% of Als, less than or equal to 0.004% of N, and the balance of Fe. The cold-rolled dual-phase steel with the tensile strength of 800-850 MPa, the yield strength of 450-550 MPa, the elongation of 15-17% and the metallographic structure of ferrite and martensite is produced through smelting, hot rolling and cold rolling continuous annealing processes. The main strengthening mechanism is the transformation strengthening of martensite, and the strength is high but the elongation is relatively low. It is difficult to meet the use requirements of automobile parts with complex structures.
The Chinese patent application No. 201210117567.8 discloses a non-quenched and tempered hot rolled strip steel with yield strength higher than 900MPa and a preparation method thereof, which adopts low-carbon component design, and the component range is as follows: 0.06-0.12% of C, 0.10-0.30% of Si, 0.80-1.20% of Mn, 0.00-0.04% of Nb0.00, 0.00-0.04% of V, 0.02-0.10% of Ti, 0.8-1.20% of Cr0.10-0.30% of Mo0.10%, 0.001-0.003% of B, less than 0.012% of P and less than 0.01% of S, and the steel strip with yield strength of not less than 900MPa, tensile strength of not less than 940MPa and elongation after fracture of 12-16% is produced by adding microalloy elements and adopting the technologies of controlled rolling and controlled cooling, controlled rolling and controlled cooling and tempering, wherein the metallographic structure of the steel strip is bainite/martensite or tempered/bainite/tempered martensite with smaller grains and a small amount of residual austenite. The yield strength of the steel reaches 900MPa, but the elongation is only 12-16%, the main strengthening mechanism is bainite/martensite phase transformation strengthening, and the steel has high strength but relatively low elongation. The use requirements of higher-level components are still not met.
The Chinese patent application No. 201610713632.1 discloses a thin hot-formed steel with tensile strength more than or equal to 1100MPa directly rolled by a thin slab and a production method thereof, and the steel comprises the following components: c: 0.12-0.16%, Si: 0.15 to 0.20%, Mn: 0.7-1.0%, P is less than or equal to 0.02%, S is less than or equal to 0.008%, Als: 0.015 to 0.060%, Cr: 0.15-0.20%, Ti: 0.005-0.02% or Nb: 0.005-0.02% or V: 0.005-0.02% or a mixture of two or more thereof at an arbitrary ratio, B: 0.0005-0.0020% and N is less than or equal to 0.005%. The method adopts hot rolling raw materials produced by continuous casting and rolling of sheet billets to heat and austenitize; and then, stamping and forming by using a die, and then quenching to finally obtain the hot forming steel with the tensile strength of more than or equal to 1100MPa, wherein the elongation rate is not more than 9%, and the quenched finished product structure is martensite which is mainly strengthened by martensite phase transformation, so that the strength is high, but the elongation rate is relatively low.
However, the existing ferritic steel can meet the requirement on elongation, but the strength is lower, and the yield strength of the existing ferritic steel is generally less than 700 MPa. How to increase the strength grade of ferritic steel becomes the key to the development of ultra-high strength ferritic steel. The ferritic steel has excellent plasticity, formability, welding performance and the like, is particularly suitable for manufacturing automobile parts with complex structures, and has simple production process and low cost. Ultra-high strength ferritic steels are an important development direction for high performance automotive steels.
The invention mainly adopts Ti-Nb-Mo composite microalloying technology and adopts the conventional modes of hot rolling, warm rolling and annealing to obtain the precipitation strengthening type ultrafine grained ferrite steel with the yield strength ranging from 903 to 946MPa, the tensile strength ranging from 952 to 987MPa, the elongation rate ranging from 21.2 to 23.4 percent, the average grain size of ferrite ranging from 1.9 to 2.4 mu m and the precipitation strengthening contribution amount ranging from 287 to 323 MPa. The invention is mainly characterized in that hot rolling, warm rolling and annealing processes are combined, the precipitation strengthening effect is fully exerted while the grain size of ferrite is refined, and the ultrahigh strengthening of ferrite steel is realized.
Disclosure of Invention
The invention aims to overcome the defects of the existing ferritic steel and provides the precipitation-strengthened ferritic steel and the production method thereof, wherein the yield strength of the steel is 903-946 MPa, the tensile strength is 952-987 MPa, the elongation of the steel is more than or equal to 21%, the average grain size of ferrite is 1.9-2.4 mu m, the precipitation strengthening contribution amount is 287-323 MPa, and the precipitation-strengthened ferritic steel has excellent plasticity, formability, welding performance and the like.
The measures for realizing the aim are as follows:
a precipitation strengthening ferritic steel with the yield strength of 900MPa comprises the following components in percentage by weight: c: 0.105 to 0.139%, Si: 0.05-0.16%, Mn: 0.59-0.98%, P: less than or equal to 0.008 percent, S: less than or equal to 0.003 percent, Cr: 0.11 to 0.23%, Nb: 0.121-0.182%, Ti: 0.119-0.177%, Mo: 0.22-0.47%, N: less than or equal to 0.005 percent, and the balance of Fe and inevitable impurities; the metallographic structure is full ferrite; mechanical properties: the yield strength range is 903-946 MPa, the tensile strength range is 952-987 MPa, and the elongation rate range is 21.2-23.4%; the ferrite has an average grain size of 1.9 to 2.4 μm.
Preferably: the content of C is 0.113-0.136 wt%.
Preferably: the Mn content is 0.66-0.95 wt%.
Preferably: the Cr content is 0.12-0.19 wt%.
Preferably: the Nb content is 0.131-0.166 wt%.
Preferably: the Ti content is 0.132-0.163 wt%.
Preferably: the weight percentage content of Mo is 0.25-0.45%.
A method of producing a precipitation-strengthened ferritic steel having a yield strength of the 900MPa class comprising the steps of:
1) heating the casting blank after conventional smelting and casting to form a blank, wherein the temperature of the heated casting blank is controlled to be 1281-1307 ℃, and the heating time is 93-118 min;
2) carrying out two-stage hot rolling: wherein the rough rolling finishing temperature is controlled to be 1078-1092 ℃, and the accumulated reduction rate is 82-87%; controlling the finish rolling temperature to be 822-839 ℃, and controlling the accumulated reduction rate to be 92-95%;
3) carrying out laminar cooling, and cooling to the coiling temperature at the cooling speed of 55-63 ℃/s;
4) coiling, wherein the coiling temperature is controlled to be 563-582 ℃;
5) naturally cooling to room temperature and then carrying out conventional acid washing;
6) carrying out warm rolling, controlling the warm rolling temperature to be 123-237 ℃, and controlling the cumulative reduction rate to be 63-79%;
7) annealing under the protection of a full hydrogen atmosphere, controlling the annealing temperature to be 550-597 ℃, and preserving heat for 30-40 min at the temperature;
8) cooling to room temperature at a cooling rate of not less than 82 deg.C/s.
Preferably: the warm rolling temperature is 136-227 ℃, and the cumulative reduction rate is 66-73%.
Preferably: the annealing temperature is 560-589 ℃, and the heat preservation time is 32-37 min.
The action and mechanism of the main strengthening element and process in the invention
C: the low carbon design is selected to reduce the amount of cementite in the steel microstructure and inhibit the formation of pearlite. When the C content is less than 0.105%, if the carbon content is too low, it is difficult to form a nano-scale precipitate by bonding with the microalloying elements Nb, Ti, etc., and the precipitation strengthening effect is difficult to be exerted. When the C content is more than 0.139%, the welding and low temperature toughness are deteriorated rapidly, so that the C content is controlled within the range of 0.1, 05-0.139%, preferably 0.113-0.136% by weight.
Si: while the steel serves to strengthen the steel by solid solution and contains a deoxidizing element, the content of Si should be controlled to 0.05% or more, but if the content of Si is more than 0.16%, the formation of an inner rust layer is promoted, which makes descaling difficult during rolling, thereby deteriorating the surface quality of the steel strip, and if the content of Si is too high, the weldability of the steel is lowered, and thus, the content of Si is controlled to 0.05 to 0.16%.
Mn: the Mn-Mn alloy is an important toughening element in steel, improves the Mn content in the steel, can expand a gamma region, reduces the transformation temperature, expands the rolling range and promotes grain refinement, so that the toughness of the steel is improved, and the impact transformation temperature is hardly changed, so that the Mn content is more than 0.59 percent, in addition, when the Mn content is more than 0.98 percent, casting blank cracks are easily generated in the continuous casting process, and the welding performance of the steel is also reduced, so that the Mn content is controlled to be 0.59-0.98 percent, and preferably the Mn content is 0.66-0.95 percent by weight.
P: p in steel deteriorates the toughness of steel, and in particular drastically lowers the low-temperature impact toughness of steel, so that the P content is controlled to 0.008% or less.
S: MnS inclusions generated by excessively high S content in steel can cause obvious difference in longitudinal and transverse properties of steel and deteriorate low-temperature toughness. The S content should be controlled below 0.003%.
Cr: the Cr element in the steel can improve the strength and hardness of the steel, so the Cr content is controlled to be 0.12% or more, and in addition, the Cr content is controlled to be in the range of 0.11 to 0.23% in consideration of the economical efficiency of the components, and preferably the Cr content is 0.12 to 0.19% by weight.
Nb: is a strong carbonitride forming element, and trace Nb in the steel can inhibit the recrystallization of deformed austenite, prevent the growth of austenite grains, improve the recrystallization temperature of the austenite, refine the grains and improve the strength and toughness of the steel. In addition, the precipitation of Nb (CN) in the cooling process can play a role of precipitation strengthening, the mechanical property of the steel is improved, the solid solubility product of Nb and related elements in austenite and ferrite and the contents of elements such as Ti, N, S, C and the like in the steel are comprehensively considered, so the control range of the Nb content is 0.12-0.18%, if the Nb content is less than 0.12%, the Nb cannot play a role of fine-grain strengthening and precipitation strengthening, and if the Nb content is more than 0.18%, the Nb element cannot be completely dissolved, and unnecessary alloy element loss is caused. Preferably, the content of Nb is 0.131-0.166 percent by weight.
Ti: the Ti can be preferentially combined with N to form TiN when the Ti content is low, the TiN particles are relatively large in size and cannot be dissolved under the high-temperature conditions of heating and welding, the welding performance of the steel is obviously improved, in addition, the TiN can also effectively pin austenite crystal boundaries and help to prevent the austenite crystal grains from growing large, when the Ti content is high, besides the TiN can be formed, the residual Ti in the steel can be combined with C in the steel to form TiC particles with small sizes and can play a role in precipitation strengthening, the Ti content in the steel is too low, the Ti cannot play a role in fine grain strengthening and precipitation strengthening, the Ti content is too high, the Ti cannot be completely dissolved, and unnecessary alloy element loss is caused. The solid solubility product of Ti and related elements in austenite and ferrite and the contents of Nb, N, S, C and other elements in steel are comprehensively considered, so that the content of Ti is controlled to be 0.119-0.177%, and the content of Ti in percentage by weight is preferably 0.132-0.163%.
Mo: the high-strength steel is a strong carbonitride forming element, the proper Mo content can prevent austenite grains from growing and can improve the strength of alloy steel at normal temperature, meanwhile, the Mo can improve the thermal stability of precipitated grains in a coarsening stage and can effectively inhibit the growth and coarsening of second-phase precipitated grains, so that the precipitation strengthening effect of test steel is improved, the Mo content is more than 0.22%, the Mo content is controlled to be 0.22-0.47% due to the fact that the Mo is a precious metal, and the Mo content is preferably 0.25-0.45% in percentage by weight in view of production cost.
N: nitrogen in the steel can be combined with elements such as Ti, Nb and the like at high temperature to form corresponding compounds, and the compounds can coarsen and grow at high temperature, which seriously damages the plasticity and toughness of the steel. In addition, such coarse carbonitride particles formed at high temperatures contribute little to precipitation strengthening and consume the effective Ti and Nb contents in the steel, so the content thereof is controlled to 0.005% or less.
The invention controls the warm rolling temperature to be 123-237 ℃ and the cumulative reduction ratio to be 63-79% because the common warm rolling is only suitable for steel types which are difficult to be directly cold rolled at room temperature, such as high-carbon and high-alloy steel, and is used for improving the work hardening of the steel in the cold rolling process and improving the machinability of the steel in the cold rolling process. The warm rolling process mainly aims to further refine the ferrite grain size and improve the fine grain strengthening effect at a proper rolling temperature. The warm rolling temperature is higher than 237 ℃, so that ferrite is recrystallized, the grain size is overlarge, and the fine grain strengthening effect is weakened. In addition, the warm rolling temperature is too high, which causes coarsening of second phase particles generated during the hot rolling process, resulting in a reduction in precipitation strengthening effect. When the warm rolling temperature is lower than 123 ℃ and the cumulative deformation is greater than 79%, the deformation resistance is large in the rolling process, and the rolling is difficult. When the accumulated deformation is less than 63%, the accumulated deformation is too small, so that the ferrite grain size is difficult to be further refined, and the ferrite with ultrafine grains is difficult to obtain; preferably, the warm rolling temperature is 136-227 ℃, and the cumulative reduction rate is 66-73%.
The annealing temperature is controlled to be 550 to 597 ℃, and the temperature is kept for 30 to 40 min; the annealing temperature is preferably 560-589 ℃, the heat preservation time is preferably 32-37 min, the annealing temperature is higher than 597 ℃, and the heat preservation time is more than 40min, the second phase particles can grow and coarsen, so that the precipitation strengthening effect is weakened, and the annealing temperature is lower than 550 ℃, the heat preservation time is lower than 30 min, so that the thermodynamic and kinetic conditions of the second phase particles are poor, the second phase particles are difficult to precipitate, and the precipitation strengthening effect is weakened. When the cooling rate after annealing is lower than 82 ℃/s, the second phase particles grow and coarsen in the cooling process, so that the precipitation strengthening effect is weakened. Therefore, the annealing is followed by cooling to room temperature at a cooling rate of not less than 82 ℃/s.
According to the invention, Ti-Nb-Mo composite micro-alloying is mainly adopted, and then a conventional hot rolling, warm rolling and annealing mode is adopted, so that the difficulty that direct cold rolling is difficult to realize due to overhigh hot rolling strength of the steel is solved, the ferrite grain size is fully refined through reasonable temperature and deformation setting, the ferrite steel with the average grain size of 1.9-2.4 mu m ultrafine grains is obtained, and the limit value of 3.0 mu m of the average grain size of the ferrite steel produced by the traditional method is broken through. The yield strength of the steel plate is 903-946 MPa, the tensile strength is 952-987 MPa, the elongation is 21.2-23.4%, the average grain size of ferrite is 1.9-2.4 mu m, and the precipitation strengthening contribution amount is 287-323 MPa. In addition, through reasonable formulation of hot rolling, warm rolling and annealing processes, fine and dispersed second-phase particles are fully separated out while ferrite grains are fully refined, the precipitation strengthening contribution amount is 287-323 MPa, the limit value of 250MPa of the precipitation strengthening contribution amount of the traditional Ti-Nb composite micro-alloy steel is broken through, and ultrahigh strengthening of the ferrite steel is realized. The steel plate produced by the invention has high strength and good plasticity.
Drawings
FIG. 1 is a metallographic structure representation of an example of the invention;
FIG. 2 is a graph of the morphology of precipitates in accordance with an embodiment of the present invention.
Detailed Description
The present invention is described in detail below:
table 1 is a list of chemical compositions for each example of the present invention and comparative example;
table 2 is a table of the main process parameters of each example of the present invention and comparative example;
table 3 is a table of the results of the performance tests of the examples of the present invention and the comparative examples.
The production of each embodiment of the invention is carried out according to the following steps:
1) heating the casting blank after conventional smelting and casting to form a blank, wherein the temperature of the heated casting blank is controlled to be 1281-1307 ℃, and the heating time is 93-118 min;
2) carrying out two-stage hot rolling: wherein the rough rolling finishing temperature is controlled to be 1078-1092 ℃, and the accumulated reduction rate is 82-87%; controlling the finish rolling temperature to be 822-839 ℃, and controlling the accumulated reduction rate to be 92-95%;
3) carrying out laminar cooling, and cooling to the coiling temperature at the cooling speed of 55-63 ℃/s;
4) coiling, wherein the coiling temperature is controlled to be 563-582 ℃;
5) naturally cooling to room temperature and then carrying out conventional acid washing;
6) carrying out warm rolling, controlling the warm rolling temperature to be 123-237 ℃, and controlling the cumulative reduction rate to be 63-79%;
7) annealing under the protection of a full hydrogen atmosphere, controlling the annealing temperature to be 550-597 ℃, and preserving heat for 30-40 min at the temperature;
8) cooling to room temperature at a cooling rate of not less than 82 deg.C/s.
TABLE 1 tabulated (wt%) chemical compositions for inventive and comparative examples
| Examples | C | Si | Mn | Ti | Mo | Nb | N | Cr | S | P |
| 1 | 0.127 | 0.08 | 0.98 | 0.152 | 0.22 | 0.182 | 0.003 | 0.13 | 0.003 | 0.007 |
| 2 | 0.139 | 0.13 | 0.72 | 0.119 | 0.46 | 0.127 | 0.005 | 0.11 | 0.002 | 0.008 |
| 3 | 0.109 | 0.16 | 0.61 | 0.169 | 0.24 | 0.171 | 0.004 | 0.15 | 0.001 | 0.005 |
| 4 | 0.113 | 0.10 | 0.95 | 0.163 | 0.45 | 0.166 | 0.005 | 0.19 | 0.003 | 0.008 |
| 5 | 0.126 | 0.06 | 0.81 | 0.158 | 0.42 | 0.157 | 0.002 | 0.12 | 0.002 | 0.004 |
| 6 | 0.121 | 0.05 | 0.86 | 0.123 | 0.27 | 0.172 | 0.003 | 0.22 | 0.003 | 0.002 |
| 7 | 0.136 | 0.07 | 0.66 | 0.132 | 0.31 | 0.131 | 0.001 | 0.15 | 0.003 | 0.006 |
| 8 | 0.119 | 0.11 | 0.75 | 0.145 | 0.25 | 0.143 | 0.004 | 0.17 | 0.002 | 0.004 |
| 9 | 0.112 | 0.09 | 0.63 | 0.177 | 0.36 | 0.129 | 0.002 | 0.21 | 0.001 | 0.005 |
| 10 | 0.105 | 0.15 | 0.59 | 0.166 | 0.47 | 0.121 | 0.005 | 0.23 | 0.002 | 0.006 |
| Comparative example 1 | 0.052 | 0.03 | 0.51 | 0.032 | 0.01 | 0.02 | 0.010 | 0.45 | 0.051 | 0.012 |
| Comparative example 2 | 0.221 | 0.24 | 1.06 | 0.012 | 0.03 | 0.06 | 0.043 | 0.01 | 0.011 | 0.029 |
| Comparative example 3 | 0.315 | 0.35 | 1.51 | 0.002 | 0.63 | 0.03 | 0.031 | 0.28 | 0.016 | 0.015 |
TABLE 2 List of the main parameters of the processes of the examples of the invention and the comparative examples
TABLE 3 Table of mechanical Properties of each example and comparative example of the present invention
As can be seen from Table 3, the steel plate of the embodiment has the yield strength ranging from 903 to 946MPa, the tensile strength ranging from 952 to 987MPa, the elongation ranging from 21.2 to 23.4%, the ferrite average grain size ranging from 1.9 to 2.4 μm, the precipitation strengthening contribution amount ranging from 287 to 323MPa, and the 180 DEG cold bending performance is all qualified, while the yield strength of the comparison sample ranges from 321 to 532MPa, the tensile strength ranges from 407 to 573MPa, the elongation ranges from 8.4 to 10.1%, the ferrite average grain size ranging from 13.6 to 16.8 μm, the precipitation strengthening contribution amount ranging from 37 to 62MPa, and the 180 DEG cold bending performance is not qualified. It can be seen that the performance indexes of the examples in this patent are all better than those of the comparative examples.
The present embodiments are merely preferred examples, and are not intended to limit the scope of the present invention.
Claims (3)
1. A precipitation strengthening ferritic steel with the yield strength of 900MPa comprises the following components in percentage by weight: c: 0.136-0.139%, Si: 0.05-0.16%, Mn: 0.59-0.98%, P: less than or equal to 0.008 percent, S: less than or equal to 0.003 percent, Cr: 0.11 to 0.23%, Nb: 0.121-0.182%, Ti: 0.119-0.177%, Mo: 0.22-0.47%, N: less than or equal to 0.005 percent, and the balance of Fe and inevitable impurities; the metallographic structure is full ferrite; mechanical properties: the yield strength range is 903-946 MPa, the tensile strength range is 952-987 MPa, and the elongation rate range is 21.2-23.4%; the average grain size of the ferrite is 1.9-2.4 μm;
the production method comprises the following steps:
1) heating the casting blank after conventional smelting and casting to form a blank, wherein the temperature of the heated casting blank is controlled to be 1281-1307 ℃, and the heating time is 93-118 min;
2) carrying out two-stage hot rolling: wherein the rough rolling finishing temperature is controlled to be 1078-1092 ℃, and the accumulated reduction rate is 82-87%; controlling the finish rolling temperature to be 822-839 ℃, and controlling the accumulated reduction rate to be 92-95%;
3) carrying out laminar cooling, and cooling to the coiling temperature at the cooling speed of 55-63 ℃/s;
4) coiling, wherein the coiling temperature is controlled to be 563-582 ℃;
5) naturally cooling to room temperature and then carrying out conventional acid washing;
6) carrying out warm rolling, controlling the warm rolling temperature to be 123-237 ℃, and controlling the cumulative reduction rate to be 63-79%;
7) annealing under the protection of a full hydrogen atmosphere, controlling the annealing temperature to be 550-597 ℃, and preserving heat for 30-40 min at the temperature;
8) cooling to room temperature at a cooling rate of not less than 82 deg.C/s.
2. A precipitation-strengthened ferritic steel of 900MPa class in yield strength as set forth in claim 1 wherein: the Mn content is 0.66-0.95 wt%.
3. A precipitation-strengthened ferritic steel of 900MPa class in yield strength as set forth in claim 1 wherein: the Nb content is 0.131-0.166 wt%.
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| CN103614629A (en) * | 2013-12-12 | 2014-03-05 | 钢铁研究总院 | 900MPa grade hot rolling non-tempering thin steel sheet and preparation method thereof |
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| CN103194676A (en) * | 2013-04-08 | 2013-07-10 | 北京科技大学 | 1,000MPa super ferritic steel and preparation method thereof |
| CN103614629A (en) * | 2013-12-12 | 2014-03-05 | 钢铁研究总院 | 900MPa grade hot rolling non-tempering thin steel sheet and preparation method thereof |
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