CN112011746B - Steel material with yield strength of 600MPa grade after hot stamping and manufacturing method thereof - Google Patents
Steel material with yield strength of 600MPa grade after hot stamping and manufacturing method thereof Download PDFInfo
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/14—Ferrous alloys, e.g. steel alloys containing 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
- 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
- C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
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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
- 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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- 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
- 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
- C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
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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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/002—Bainite
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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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/009—Pearlite
Abstract
The invention discloses a steel material with yield strength of 600MPa after hot stamping, which comprises the following chemical elements in percentage by mass: 0.11 to 0.23% of C, 0.20 to 0.80% of Si, 1.20 to 1.90% of Mn, 0.010 to 0.060% of Ti, 0.1 to 0.6% of Mo, 0.0015 to 0.0030% of B, 0.005 to 0.015% of Al, 0.001 to 0.004% of Ca, 0.001 to 0.004% of N, and the balance of Fe and other inevitable impurities. In addition, the invention also discloses a manufacturing method of the steel material with the yield strength of 600MPa after hot stamping, which comprises the following steps: (1) smelting and casting; (2) heating; (3) rolling; (4) and (3) cooling: and cooling the steel plate to 400-500 ℃ at the speed of 40-60 ℃/s after rolling, and then coiling or air-cooling to room temperature.
Description
Technical Field
The present invention relates to a steel material and a method for producing the same, and more particularly to a steel material having a high yield strength and a method for producing the same.
Background
The axle housing is used as a key bearing part of an automobile, has higher requirements on safety and needs to meet strict component fatigue performance. In recent years, with the tightening of environmental protection policies in China, the intensity of treatment on overload of trucks is increased, the requirement for light axle housing weight is gradually increased, and more users propose to research and develop special high-strength steel products for axle housings.
At present, special axle housing steel marks such as Japanese SHP45, GW3300, Germany TL-VW1114Ti, TL-VW1128, TL-VW1206, TL-VW1490 and the like exist in the market. And China is always lack of special axle housing steel products. For example, at present, the hot stamping axle housing steel in China is mainly common C-Mn structural steel such as 16Mn, Q345C, Q420C and Q460C, however, the strength of the C-Mn steel after hot stamping is further reduced, for example, the yield strength of the Q460C after hot stamping is reduced to 400MPa, and the European heavy-duty axle is mainly made of high-strength steel with the yield strength of 460 plus 600MPa, so that the axle of the heavy-duty commercial vehicle in China is 10-15% heavier than the axle of the European main-flow commercial vehicle.
Chinese patent document with publication number CN104213019A, publication date 2014 12 months 17 days, entitled "600 MPa grade automobile axle housing steel and production method thereof" discloses 600MPa grade automobile axle housing steel and production method thereof. In the technical scheme disclosed in the patent document, the contents of V and N elements are accurately controlled, and rolling and cooling are controlled to produce the 600 MPa-grade hot-rolled strip steel for the automobile axle housing.
The Chinese patent document with the publication number of CN103422020A, the publication date of 2013, 12 months and 4 days, and the name of 'a steel plate for a press-welded axle housing and a manufacturing method thereof' discloses a steel plate with excellent 600 MPa-level hot stamping formability for heating, stamping and welding the axle housing and a manufacturing method thereof, wherein elements for ensuring the high-temperature performance of the steel, such as Nb and V, are added, the content of elements affecting the stamping performance, such as C, Si, is reduced, and the high-temperature strength is improved, the low-temperature toughness is excellent, the welding performance is improved, the fatigue strength is obviously improved, and the fatigue life of a component is prolonged by more than 50 percent while the good formability of the steel plate is fundamentally ensured through the matching of nitrogen-fixing elements, such as Ti, Al and the like.
At present, the hot stamping process production of most axle housings is as follows: plasma blanking of a steel plate, heating, hot stamping, welding of an upper half-bridge shell and a lower half-bridge shell, welding of a shaft head and welding of accessories. The strength of the domestic axle housing steel is generally reduced to below 450MPa after hot stamping.
Based on this, it would be desirable to have a steel material that can achieve a yield strength of 600MPa after hot stamping and thus is well suited for hot forming heavy truck axle housing steel production.
Disclosure of Invention
One of the purposes of the invention is to provide a steel material with yield strength of 600MPa grade after hot stamping, and the steel material can reach the yield strength of 600MPa after hot stamping, thereby being well suitable for the production of hot-forming heavy truck axle housing steel.
In order to achieve the purpose, the invention provides a steel material with yield strength of 600MPa grade after hot stamping, which comprises the following chemical elements in percentage by mass:
0.11-0.23% of C, 0.20-0.80% of Si, 1.20-1.90% of Mn, 0.010-0.060% of Ti, 0.1-0.6% of Mo0.0015-0.0030% of B, 0.005-0.015% of Al, 0.001-0.004% of Ca, 0.001-0.004% of N, and the balance of Fe and other inevitable impurities.
In the steel material with the yield strength of 600MPa after hot stamping, the design principle of each chemical element is as follows:
c: in the steel material with the yield strength of 600MPa after hot stamping, C plays roles of solid solution strengthening and precipitation strengthening, the carbon content with the mass percentage of more than 0.11 percent can improve the strength in lower bainite, and simultaneously redundant carbon reacts with Fe to form Fe in dispersed distribution3And C, playing a role in precipitation strengthening. On the other hand, if the mass percentage of C is higher than 0.23%, the weldability of the steel sheet is not favorable. Therefore, the mass percent of C in the steel material with the yield strength of 600MPa after hot stamping is controlled to be 0.11-0.23%.
Si: in the technical scheme of the invention, more than 0.20 mass percent of Si can inhibit cementite from being precipitated at high temperature, which is beneficial to the formation of lower bainite, and simultaneously, fine cementite particles are formed in the lower bainite of the cementite, so that the strength of the lower bainite is improved. However, when the mass percentage of Si is too high, the weldability of the steel sheet deteriorates. Based on the above, the steel material with the yield strength of 600MPa after hot stamping is prepared by controlling the mass percent of Si to be 0.20-0.80%.
Mn: in the steel material with the yield strength of 600MPa after hot stamping, the Mn element with the mass percent of more than 1.20% is beneficial to promoting the formation of lower bainite, and simultaneously plays a certain role in solid solution strengthening on the lower bainite structure. In addition, the higher Mn element is beneficial to forming a thinner ferrite or bainite structure when the steel plate is hot stamped, and the strength of the steel plate after hot stamping is improved. However, when the content of Mn is too high, the weldability of the steel sheet is deteriorated, and therefore, in the technical scheme of the present invention, the mass percentage of Mn is controlled to be 1.20 to 1.90%.
Ti: in the steel material with the yield strength of 600MPa after hot stamping, trace Ti element reacts with C in the production process of a steel plate to form TiC particles with the diameter of several nanometers to dozens of nanometers, and the precipitation strengthening effect is generated. In addition, TiC can inhibit the growth of austenite grains in the hot stamping heating stage, so that the structure after hot stamping is refined, and the strength of the axle housing steel plate after hot stamping is improved. When the Ti element is too high, the Ti element is easy to react with N to form micron-sized cubic TiN large particles, and the toughness and the fatigue performance of the steel plate are deteriorated. Therefore, the mass percent of Ti in the steel material with the yield strength of 600MPa after hot stamping is controlled to be 0.010-0.060%.
Mo: in the technical scheme of the invention, in the cooling stage after the steel plate is rolled or hot stamped, a certain Mo element promotes the formation of bainite and improves the strength of the steel plate by inhibiting the diffusion of carbon. However, too high a mass percentage of the Mo element deteriorates the weldability of the steel sheet. Therefore, the mass percent of Mo in the steel material with the yield strength of 600MPa after hot stamping is controlled to be 0.1-0.6%.
B: in the steel material with the yield strength of 600MPa after hot stamping, a trace amount of B can promote the formation of bainite, and when the B element is too high, the B brittleness problem is easy to generate, and the impact toughness of the steel plate is deteriorated. In addition, trace B element is beneficial to promoting the formation of finer ferrite or bainite in the hot stamping stage of the axle housing. The strength of the steel plate is improved. Based on the above, the mass percent of B in the steel material with the yield strength of 600MPa after hot stamping is controlled to be 0.0015-0.0030%.
Al: in the embodiment of the present invention, Al is an important deoxidizer, and a certain amount of Al is usually added. However, in the steel material with the yield strength of 600MPa after hot stamping, the strict requirement of axle housing steel on the fatigue performance is considered, so that the chain inclusion of Al oxide needs to be specially controlled, and therefore, the content of Al is controlled in an extremely low range, namely 0.005-0.015% in the technical scheme of the invention. It should be noted that in the technical solution of the present invention, the deoxidation is mainly performed by Si.
Ca: in the steel material with the yield strength of 600MPa after hot stamping, more than 0.001 percent of trace Ca element can play a role of a purifying agent in the steel smelting process, so that the toughness and the fatigue property of the steel are improved; when the mass percentage of Ca exceeds 0.004%, a large-sized Ca compound is easily formed, and the toughness is rather deteriorated. Based on the above, the mass percent of Ca in the steel material with the yield strength of 600MPa after hot stamping is controlled to be 0.001-0.004%.
N: in the technical scheme of the invention, the mass percent of N is controlled in a narrow range, because trace N can react with Ti to form TiN particles when being in a narrow range, the growth of austenite grains can be effectively inhibited when welding and hot stamping are carried out, a welding heat affected zone and a structure after hot stamping are refined, and the strength, the low-temperature toughness and the fatigue property of the heat affected zone and a hot stamping steel plate are improved. However, when the mass percentage of N is too high, the formed TiN particles are too large, which may deteriorate the low temperature toughness and fatigue property of the steel sheet. Therefore, the steel material with the yield strength of 600MPa after hot stamping controls the mass percent of N to be 0.001-0.004%.
In conclusion, through the design of the chemical elements, the steel material with the yield strength of 600MPa after hot stamping can achieve the yield strength level of 900MPa, has high plasticity, and the yield strength can reach the level of 600MPa after hot stamping.
Further, in the steel material with the yield strength of 600MPa after hot stamping, the chemical element components also meet the following requirements: Ti/N is more than or equal to 5 and/or Ca/S is more than or equal to 1.0 and less than or equal to 3.0.
In the scheme, sufficient Ti element can be reserved by controlling the Ti/N to be more than or equal to 5, so that the Ti element reacts with C to form TiC precipitation strengthening. And by controlling Ca/S to be more than or equal to 1.0 and less than or equal to 3.0, sulfides of the steel grade can be spheroidized, and the low-temperature toughness and the fatigue property of the steel are improved.
Further, in the steel material of the present invention having a yield strength of 600MPa grade after hot stamping, at least one of the following is satisfied among other inevitable impurities: p is less than or equal to 0.015 percent, S is less than or equal to 0.0020 percent, and O is less than or equal to 0.003 percent.
In the above scheme, P is an impurity element, which is easy to cause the problem of cold brittleness, therefore, the lower the content of P should be controlled as much as possible, and in the technical scheme of the invention, the mass percent of P is controlled to be less than or equal to 0.015%.
In addition, because S is easy to react with Mn to generate MnS inclusions, and the strict requirement of the axle housing steel on the fatigue performance is considered, the deep desulfurization treatment can be carried out in the steelmaking link, and the mass percent of S is controlled to be less than or equal to 0.0020 percent.
In addition, Al is easily generated due to the reaction of O with Al2O3Chain-shaped inclusions are included, and the strict requirement of axle housing steel on the fatigue performance is considered, so the mass percent of O in the steel material with the yield strength of 600MPa grade after hot stamping is controlled to be less than or equal to 0.003 percent.
Furthermore, in the steel material with the yield strength of 600MPa after hot stamping, the microstructure of the steel material is lath-shaped lower bainite and pearlite, wherein the pearlite is not aggregated and is in fine dispersed distribution.
In the scheme, the lath-shaped lower bainite has higher strength, and the yield strength of the steel material with the yield strength of 600MPa grade after hot stamping is more than or equal to 900MPa by matching with the design with higher carbon content in the scheme. In order to ensure that the steel material with the yield strength of 600MPa after hot stamping has higher impact toughness and plasticity, the microstructure of the steel material can have dispersed pearlite.
Furthermore, in the steel material with the yield strength of 600MPa after hot stamping, the yield strength of the steel material is more than or equal to 900MPa, the tensile strength is more than or equal to 950MPa, the elongation A50 is more than or equal to 23 percent, and the impact energy at the temperature of minus 20 ℃ is more than or equal to 60J.
Furthermore, in the steel material with the yield strength of 600MPa after hot stamping, the yield strength of the steel material is more than or equal to 600MPa, the elongation A50 is more than or equal to 26 percent, and the impact energy at the temperature of minus 20 ℃ is more than or equal to 80J after the hot stamping step at the temperature of 830-900 ℃.
Accordingly, another object of the present invention is to provide a method for manufacturing the steel material, by which a steel material having a yield strength of 600MPa level after hot stamping can be obtained, which can achieve a yield strength of 600MPa after hot stamping, and thus can be well adapted to the production of hot formed heavy truck axle housing steel.
In order to achieve the above object, the present invention also provides a method for manufacturing the steel material, comprising the steps of:
(1) smelting and casting;
(2) heating;
(3) rolling;
(4) and (3) cooling: and cooling the steel plate to 400-500 ℃ at the speed of 40-60 ℃/s after rolling, and then coiling or air-cooling to room temperature.
In the step (4) of the manufacturing method of the present invention, the steel sheet is cooled to 400 to 500 ℃ at a rate of 40 to 60 ℃/s after rolling is controlled in order to suppress formation of a ferrite structure during cooling and to control formation of a lath-like lower bainite structure + a dispersed pearlite structure.
Further, in the manufacturing method, in the step (2), the casting blank is heated to 1180-1270 ℃, and the heat preservation time is more than or equal to 1.5 h.
In the above scheme, in the step (2), the heating temperature is controlled to be higher than 1180 ℃ and the core heat preservation time is controlled to be longer than 1.5h, so that the alloy elements can be ensured to be fully dissolved in the solid solution, but if the heating temperature exceeds 1270 ℃, the austenite grains grow excessively, so that the intercrystalline bonding force is weakened, and cracks are easily generated during rolling. In addition, the heating temperature of the steel billet is higher than 1270 ℃, so that the surface of the steel billet is easy to be decarburized, and the mechanical property of a finished product is influenced. Therefore, the heating temperature of the casting blank is controlled to be 1180-1270 ℃.
Further, in the manufacturing method of the invention, in the step (3), the casting blank is rolled to the target thickness by adopting single-frame reciprocating rolling or multi-frame hot continuous rolling, and the rolling reduction rate of the last rolling pass is more than or equal to 15%.
In the scheme, the reduction rate of the last pass of rolling is increased to be more than 15%, so that enough deformation can be accumulated before austenite is transformed into bainite, and the formation of a thinner bainite structure is promoted.
Further, in the manufacturing method of the present invention, in the step (3), the finishing temperature is controlled to be 830 to 900 ℃.
In the scheme, the rolling temperature is controlled to be 830-900 ℃, on one hand, enough deformation can be accumulated before austenite is transformed to bainite, so that a thinner bainite structure is promoted to be formed, and on the other hand, if the rolling temperature is too low, high-temperature transformation of ferrite is easy to occur, so that the strength of steel is reduced. And if the rolling temperature is too high, the deformation accumulated in the austenite is recovered, which is not beneficial to refining the structure after phase transformation. Therefore, in the technical scheme of the invention, the rolling temperature is controlled to be 830-900 ℃.
Compared with the prior art, the steel material with the yield strength of 600MPa after hot stamping and the manufacturing method thereof have the following advantages and beneficial effects:
compared with the prior art, the steel material disclosed by the invention obtains the required microstructure by controlling the contents of Mn, Mo and B elements and combining controlled rolling and controlled cooling, so that the final steel material obtains a ferrite and bainite structure after hot stamping, thereby improving the strength. The plasticity and fatigue property of the steel material are further improved by controlling alloy elements and controlling Ti/N and Ca/S in some preferred embodiments, so that the steel material is very suitable for manufacturing commercial vehicle axle housings.
In addition, the manufacturing method combines the strict requirements of hot stamping axle housing steel on strength, impact, welding and the like, adopts special alloy design, realizes high-plasticity steel materials while finally obtaining 900MPa yield strength grade through controlled rolling and medium-low temperature final cooling, and the steel materials have good low-temperature impact performance and welding performance. After the steel material is subjected to hot stamping air cooling at 830-900 ℃ to room temperature, the yield strength is more than or equal to 600MPa, the elongation A50 is more than or equal to 26 percent, and the impact energy at-20 ℃ is more than 80J.
Drawings
FIG. 1 is a metallographic structure diagram of a steel material of example 1 of the present invention having a yield strength of 600MPa after hot stamping.
FIG. 2 is a metallographic structure diagram of a steel material of example 3 of the present invention having a yield strength of 600MPa after hot stamping.
FIG. 3 is a metallographic structure diagram of an axle housing formed by hot stamping in example 1 of the steel material with yield strength of 600MPa after hot stamping.
FIG. 4 is a metallographic structure diagram of an axle housing made of the steel material of example 3 with yield strength of 600MPa after hot stamping.
Detailed Description
The steel material with yield strength of 600MPa after hot stamping and the manufacturing method thereof according to the present invention will be further explained and illustrated with reference to the accompanying drawings and specific examples, which, however, should not be construed to unduly limit the technical solution of the present invention.
Examples 1 to 6
The steel materials of the above examples 1-6, having a yield strength of 600MPa after hot stamping, were prepared by the following steps:
(1) the smelting and casting were carried out according to the chemical compositions shown in Table 1, wherein steel was produced in a converter or a circuit and refined outside the converter (RH + LF), and the molten steel thus obtained was cast into a slab having a thickness of 200 mm.
(2) The casting blank is heated to 1180-1270 ℃, and the heat preservation time is more than or equal to 1.5 h.
(3) Rolling: and rolling the casting blank to a steel plate with a target thickness (for example 12mm) by adopting single-frame reciprocating rolling or multi-frame hot continuous rolling, wherein the rolling reduction rate of the last pass of rolling is more than or equal to 15%, and the final rolling temperature is controlled to be 830-900 ℃.
(4) And (3) cooling: and cooling the steel plate to 400-500 ℃ at the speed of 40-60 ℃/s after rolling, and then coiling or air-cooling to room temperature.
Table 1 shows the mass percentage ratio of each chemical element of the steel material of the yield strength of 600MPa grade after hot stamping of examples 1-6.
TABLE 1 (wt%, balance Fe and impurities other than P, S and O)
Table 2 lists the specific process parameters for the steel materials of examples 1-6 having a yield strength after hot stamping of the 600MPa grade.
Table 2.
The steel materials of examples 1 to 6 of the present invention, which were rated at 600MPa in yield strength after hot stamping, were subjected to the performance test, and the test results are shown in Table 3 below.
Table 3.
Note: three columns in the-20 ℃ work impact test results represent the test results for three parallel samples, respectively.
As can be seen from Table 3, the yield strength of the steel material of each example is not less than 900MPa, the tensile strength is not less than 950MPa, the elongation A50 is not less than 23%, and the impact energy at-20 ℃ is not less than 60J, that is, the steel material finally obtained by the manufacturing method can reach the 900MPa yield strength level, and simultaneously, the steel material realizes higher plasticity, and the low-temperature impact property and the welding property of the steel material are good.
Then, the steel material of each embodiment of the scheme is heated to the temperature range of 830-900 ℃ by induction heating, and after hot stamping and air cooling to room temperature, two parallel sections at two ends of the axle housing are taken to test the longitudinal tensile property and the longitudinal impact property, and the results are shown in table 4.
Table 4.
Note: three columns in the-20 ℃ work impact test results represent the test results for three parallel samples, respectively.
As can be seen from Table 4, after the hot stamping step at 830-900 ℃, the yield strength of the steel material of each example is more than or equal to 600MPa, the elongation A50 is more than or equal to 26%, and the impact energy at-20 ℃ is more than or equal to 80J, that is, the yield strength of the steel material of each example reaches 600MPa after the hot stamping, and the steel material of each example has good plasticity and low-temperature impact toughness.
FIG. 1 is a metallographic structure diagram of a steel material of example 1 of the present invention having a yield strength of 600MPa after hot stamping. FIG. 2 is a metallographic structure diagram of a steel material of example 3 of the present invention having a yield strength of 600MPa after hot stamping.
As shown in fig. 1 and 2, the metallographic structure of the steel material of examples 1 and 3 in the present application, which has a yield strength of 600 th grade after hot stamping, is lath-shaped lower bainite + pearlite, wherein the pearlite is not aggregated and is distributed in a fine dispersion manner, wherein the lath-shaped lower bainite has a high strength, and the yield strength of the steel material in the present application can be equal to or greater than 900Mpa by matching with the design of the present application with a high carbon content, and the dispersed pearlite ensures that the steel material in the present application has high impact toughness and plasticity.
FIG. 3 is a metallographic structure diagram of an axle housing made of the steel material of example 1 with yield strength of 600MPa after hot stamping. FIG. 4 is a metallographic structure diagram of an axle housing made of the steel material of example 3 with the yield strength of 600MPa after hot stamping.
As shown in figures 3 and 4, a metallographic structure of the steel material is a ferrite and bainite mixed structure after hot stamping and air cooling to room temperature, so that the yield strength of the steel material after hot stamping reaches over 600MPa, and the steel material has good plasticity and low-temperature impact toughness and is very suitable for high-strength weight reduction of a hot stamping axle housing.
In conclusion, compared with the prior art, the steel material provided by the invention has the advantages that the required microstructure is obtained by controlling the contents of Mn, Mo and B elements and combining controlled rolling and controlled cooling, so that the ferrite and bainite structures are obtained after the final steel material is subjected to hot stamping, and the strength is improved. The plasticity and fatigue property of the steel material are further improved by controlling alloy elements and controlling Ti/N and Ca/S in some preferred embodiments, so that the steel material is very suitable for manufacturing commercial vehicle axle housings.
In addition, the manufacturing method combines the strict requirements of hot stamping axle housing steel on strength, impact, welding and the like, adopts special alloy design, realizes high-plasticity steel materials while finally obtaining 900MPa yield strength grade through controlled rolling and medium-low temperature final cooling, and the steel materials have good low-temperature impact performance and welding performance. After the steel material is subjected to hot stamping air cooling at 830-900 ℃ to room temperature, the yield strength is more than or equal to 600MPa, the elongation A50 is more than or equal to 26 percent, and the impact energy at-20 ℃ is more than 80J.
It should be noted that the prior art in the protection scope of the present invention is not limited to the examples given in the present application, and all the prior art which is not inconsistent with the technical scheme of the present invention, including but not limited to the prior patent documents, the prior publications and the like, can be included in the protection scope of the present invention.
In addition, the combination of the features in the present application is not limited to the combination described in the claims of the present application or the combination described in the embodiments, and all the features described in the present application may be freely combined or combined in any manner unless contradictory to each other.
It should also be noted that the above-mentioned embodiments are only specific examples of the present invention, and it is obvious that the present invention is not limited to the above-mentioned embodiments, and many similar variations are possible. All modifications which would occur to one skilled in the art and which are, therefore, directly derived or suggested from the disclosure herein are deemed to be within the scope of the present invention.
Claims (7)
1. A steel material with yield strength of 600MPa after hot stamping is characterized by comprising the following chemical elements in percentage by mass:
0.11-0.23% of C, 0.20-0.80% of Si, 1.20-1.90% of Mn, 0.010-0.060% of Ti, 0.1-0.6% of Mo, 0.0015-0.0030% of B, 0.005-0.015% of Al, 0.001-0.004% of Ca, 0.001-0.004% of N, and the balance of Fe and other inevitable impurities;
the microstructure of the steel material is lath-shaped lower bainite and pearlite, wherein the pearlite is not aggregated and is distributed in a fine dispersion manner;
the yield strength of the steel material is more than or equal to 900MPa, the tensile strength is more than or equal to 950MPa, the elongation A50 is more than or equal to 23 percent, and the impact energy at minus 20 ℃ is more than or equal to 60J.
2. A steel material having a yield strength of 600 MPa-grade after hot stamping according to claim 1, wherein each chemical element composition further satisfies: Ti/N is more than or equal to 5 and/or Ca/S is more than or equal to 1.0 and less than or equal to 3.0.
3. A steel material having a yield strength after hot stamping of the order of 600MPa according to claim 1, characterized in that, among other unavoidable impurities, at least one of the following is satisfied: p is less than or equal to 0.015 percent, S is less than or equal to 0.0020 percent, and O is less than or equal to 0.003 percent.
4. The steel material with the yield strength of 600MPa grade after hot stamping as claimed in claim 1, wherein the yield strength of the steel material is more than or equal to 600MPa, the elongation A50 is more than or equal to 26 percent, and the impact energy at the temperature of minus 20 ℃ is more than or equal to 80J after the hot stamping step at 830-900 ℃.
5. A method of manufacturing a steel material according to any one of claims 1-4, comprising the steps of:
(1) smelting and casting;
(2) heating;
(3) rolling: rolling the casting blank to a target thickness by adopting single-frame reciprocating rolling or multi-frame hot continuous rolling, wherein the rolling reduction rate of the last pass of rolling is more than or equal to 15 percent;
(4) and (3) cooling: and cooling the steel plate to 400-500 ℃ at the speed of 40-60 ℃/s after rolling, and then coiling or air-cooling to room temperature.
6. The manufacturing method according to claim 5, wherein in the step (2), the casting blank is heated to 1180-1270 ℃ for a holding time of not less than 1.5 hours.
7. The manufacturing method according to claim 5, wherein in the step (3), the finish rolling temperature is controlled to be 830 to 900 ℃.
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| CN114836696B (en) * | 2022-04-27 | 2023-06-20 | 鞍钢股份有限公司 | 390 MPa-level steel for automobile axle housing for hot stamping and production method thereof |
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| CN1840724A (en) * | 2005-03-30 | 2006-10-04 | 宝山钢铁股份有限公司 | Superhigh strength steel plate with yield strength more than 960Mpa and method for producing same |
| CN108588550A (en) * | 2018-01-19 | 2018-09-28 | 河钢股份有限公司承德分公司 | A kind of hot rolling press axle housing steel plate and its production method |
| CN109022733A (en) * | 2018-08-30 | 2018-12-18 | 宝山钢铁股份有限公司 | A kind of 600MPa grades high tired high-strength steel and its manufacturing method |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN1840724A (en) * | 2005-03-30 | 2006-10-04 | 宝山钢铁股份有限公司 | Superhigh strength steel plate with yield strength more than 960Mpa and method for producing same |
| CN108588550A (en) * | 2018-01-19 | 2018-09-28 | 河钢股份有限公司承德分公司 | A kind of hot rolling press axle housing steel plate and its production method |
| CN109022733A (en) * | 2018-08-30 | 2018-12-18 | 宝山钢铁股份有限公司 | A kind of 600MPa grades high tired high-strength steel and its manufacturing method |
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