1. The hot stamping forming steel with the super-strong high-temperature oxidation resistance is characterized by comprising the following alloy components in percentage by mass: contains 0.2-0.4% of C, 1.0-3.0% of Si, 0.3-3.0% of Mn, 0.01-3% of Al, 0.01-3% of Cr, 0.01-1.0% of Cu, less than 0.15% of Ti, 0.0005-0.004% of B, 0.0001-0.028% of RE, not more than 0.01% of S and the balance of Fe and inevitable impurities.

2. The hot press forming steel having superior high temperature oxidation resistance according to claim 1, wherein the content of Si is 1.0-2.0%.

3. The hot press forming steel having superior high temperature oxidation resistance according to claim 1 or 2, wherein the Mn content is 1.0-2.0%.

4. A hot-stamped steel with superior high temperature oxidation resistance according to claim 1, 2 or 3, further comprising one or more of W1.0% or less, Ni 1.0% or less, and Nb 1.0% or less.

5. The hot-stamped steel with superior high temperature oxidation resistance according to claim 4, further comprising 1.0% or less of V and/or 1.0% or less of Ni.

6. The method for preparing a hot stamping steel with superstrong high temperature oxidation resistance according to any one of claims 1 to 5, wherein the method for preparing the hot stamping steel comprises the steps of steel making, continuous casting, hot rolling, pickling and cold rolling, the cold rolling and annealing processes are carried out to obtain a steel material, and the steel material is subjected to a hot stamping forming process to finally obtain a formed piece.

7. The method for preparing hot stamping forming steel with ultra-strong high temperature oxidation resistance according to claim 6, wherein the hot stamping forming process comprises the following steps: heating the steel plate for cold rolling, annealing and hot stamping forming to 880-950 ℃, preserving heat for 3-10 min to enable the steel plate to be completely austenitized, then sending the steel plate into a die with a cooling system inside for stamping forming, maintaining pressure and rapidly cooling and quenching, controlling the cooling speed at 10-300 ℃/s to enable austenite to be converted into martensite, and finally obtaining a finished product.

8. The method for preparing the hot stamping forming steel with the ultrahigh temperature oxidation resistance as claimed in claim 7, wherein the metallographic structure of the hot stamping forming steel is as follows: martensite is the main, and a small amount of ferrite, bainite or residual austenite is allowed to be contained or not contained.

Background

The hot stamping forming steel is one of the steel with the maximum strength for the automobile body structure, the tensile strength reaches 1500MPa, the hot stamping forming steel is directly processed and formed in a hot stamping mode, the hot stamping forming steel is mainly applied to the production of high-strength and difficult-to-form parts of automobiles, and the defects of difficult forming, large resilience, poor part size and shape stability and the like in cold forming can be avoided. The hot stamping of the hot stamping steel refers to heating a high-strength steel plate to 880-950 ℃, preserving heat for about 5min to ensure that the steel plate is completely austenitized, then quickly transferring the steel plate to a die with a circulating cooling system inside for stamping and forming, and maintaining the pressure for a certain time to obtain a formed part. The cooling rate must be more than 44 ℃/s to ensure that the austenite structure generates martensite transformation, the structure of the final formed piece is almost martensite, and a small amount of ferrite, bainite or residual austenite and the like can be reserved. Through the hot stamping forming process, a formed part with high precision and high strength can be obtained, meanwhile, the abrasion of materials to a die can be reduced, and the problem that high-strength steel is difficult to form is solved. However, since the hot press forming process has a high heating temperature, severe high-temperature oxidation occurs on the surface of the high-strength steel sheet to cause a large amount of scale. The hard iron scale can cause the surface of the die to be damaged, and the service life of the die is shortened. Meanwhile, the loose iron oxide scale on the surface is not beneficial to subsequent painting treatment, and the shot blasting equipment is also needed to eliminate the surface iron oxide scale, so that the shot blasting can cause the surface deformation of the part, and the production cost is further increased.

In order to solve the problem of high-temperature oxidation resistance of hot stamping formed steel, two main solutions exist at present: firstly, adopting a plating technology and secondly adopting a non-plating technology. For the plating technique, the plating technique can prevent surface oxidation and decarburization during forming and can improve corrosion resistance after painting, but also increases production processes and increases production cost, and for example, U.S. Pat. No. 6296805B1 proposes a steel sheet for hot press forming coated with aluminum silicon or aluminum-silicon alloy, in which iron in the steel and aluminum in the plating layer form an iron-aluminum alloy layer at a forming heating temperature, and can protect the steel sheet from oxidation during hot forming, and thus is commercially used in large quantities. European patent EP1143029 proposes a method of manufacturing a hot press formed member using a galvanized steel sheet obtained by plating a hot rolled steel sheet with zinc or a zinc alloy, which has technical advantages over a steel sheet for hot press forming coated with aluminum silicon or an aluminum-silicon alloy in that electrochemical corrosion protection can be provided, while an aluminum silicon plating layer cannot be provided, but a zinc plating layer has a low melting point, and evaporation of zinc and melting of a zinc-iron plating layer occur during hot forming, which may cause brittleness of a liquid oil passage, reducing the strength of the steel.

For the non-coating technology, the high-temperature oxidation resistance of hot stamping forming steel is improved mainly by designing and regulating the alloy elements and the component proportion, but the research of the technology is very little at present, and the commercial application degree is not as good as that of the coating technology. In terms of non-plating technology, China CN102127675B discloses an alloy design and hot stamping forming method capable of reducing austenitizing temperature and improving hardenability, and simultaneouslyThe dense Fe is formed on the surface of the steel plate by controlling the atmosphere in the furnace or coating the surface of the steel plate₃O₄An oxide layer improves the corrosion resistance of the part, but the process is not suitable for practical production. CN109972061A discloses an anti-oxidation ultrahigh-strength steel plate for hot stamping forming and a low-temperature hot forming process, the patent technology increases the content of Mn to 6-8% by adding elements C and Mn in an austenite region, further remarkably reduces the austenitizing heating temperature, thereby reducing the high-temperature oxidation degree of the steel plate, simultaneously determines the appropriate addition amount of Cr, Si and Al alloy elements by accurate calculation and reference tests, greatly improves the high-temperature anti-oxidation performance of the steel plate while reducing the austenitizing temperature, and finally obtains the thermal shock forming steel plate with the yield strength not lower than 1400MPa, the tensile strength not lower than 1700MPa and the elongation more than 10%. However, Mn is an easily oxidizable element, and a large amount of Mn apparently lowers the oxidation resistance of the steel and is disadvantageous in the welding property. Chinese patent CN11542635A discloses a steel for hot stamping with enhanced oxidation resistance by employing a high chromium content and a high silicon content to correspondingly exclude plating and improve oxidation resistance, the high silicon not only suitably reduces the chromium content but also prevents, inhibits or reduces the formation of cementite in the final microstructure when using the quench-dispense method, without the need for pre-oxidation. The patent technology mainly adopts a high-chromium and high-silicon mode to solve the problem that pre-oxidation or plating treatment is needed currently, chromium has the functions of improving the oxidation property, the corrosion resistance and the high-temperature mechanical property, but the price of the chromium is high, and the chromium cannot be added too much. Silicon is mainly used as a reducing agent and a deoxidizing agent, is combined with molybdenum, tungsten, chromium and the like, has the effect of improving corrosion resistance and oxidation resistance, but the toughness of steel is reduced due to the excessively high silicon content, uneven black skin which is difficult to fall off is generated on the surface of a steel plate during heating, so that hot workability is influenced, and the increase of Ar3 of the steel and the instability of austenite are increased due to the excessively high silicon content, so that residual austenite is not obtained easily.

In order to overcome the respective defects of the existing hot stamping forming steel obtained by adopting a non-plating technology, the project team provides a high-temperature oxidation resistant non-plating hot stamping forming steel (CN103614640A) in 2013, the patent technology reasonably uses Cr, reduces the content of Si to be below 0.5 percent, and limits the content of Mn to be below 0.9 percent, the obtained hot stamping forming steel has the characteristics of fine grains, oxidation resistance, low critical cooling rate and the like, and the steel still has better oxidation resistance without plating treatment. However, in practical application of the prior art, the manufacturing cost is high, the high-temperature oxidation resistance cannot meet high-end requirements, and compared with similar steels, the product has no obvious advantages. Chinese patent CN111926248A discloses a Ce alloy-added hot stamping steel and a hot stamping process, which promote the rapid formation of a Si-rich oxide layer by adding Ce element, thereby realizing the improvement of the surface oxide layer structure, and strictly controlling the thickness of the oxide layer, and the obtained oxide layer is thinner. However, the patented technology can only meet the high-temperature oxidation resistance requirements of general hot stamping forming steel, and cannot meet the requirements of high-end markets.

Disclosure of Invention

The invention aims to: aiming at the existing problems, the invention provides the hot stamping forming steel with super-strong high-temperature oxidation resistance and the preparation method thereof, on the basis of the original patent technology (CN103614640A), the high-temperature oxidation resistance of the hot stamping forming steel is improved by increasing the Si content, meanwhile, copper and trace rare earth element RE are introduced, the rare earth element RE can improve the oxide layer structure and control the thickness of the oxide layer, the copper and the Si element generate a synergistic effect, the copper can enable the silicon dioxide oxide layer to be more compact, the Si can solve the segregation problem caused by the copper, the cracking of the steel surface caused by the copper is avoided, under the combined effect, the high-temperature oxidation resistance of the hot stamping forming steel is obviously improved, the requirements of high-end markets are met, and the defects in the prior art are overcome.

The technical scheme adopted by the invention is as follows: the high-temperature oxidation-resistant hot-stamping formed steel is characterized by comprising the following alloy components in percentage by mass: contains 0.2-0.4% of C, 1.0-3.0% of Si, 0.3-3.0% of Mn, 0.01-3% of Al, 0.01-3% of Cr, 0.01-1.0% of Cu, less than 0.15% of Ti, 0.0005-0.004% of B, 0.0001-0.028% of RE, not more than 0.01% of S and the balance of Fe and inevitable impurities.

In the formula of the hot stamping forming steel, the main innovation points are that rare earth elements RE and Cu are introduced, and the proportion of alloy elements such as Si, Mn and the like is redesigned. Specifically, based on the purpose of how to obviously improve the high-temperature oxidation resistance of the hot stamping forming steel under the condition of obviously not increasing the cost, the invention reduces the cost by reducing the content of expensive alloy elements such as chromium, molybdenum and the like, then improves the high-temperature oxidation resistance of the hot stamping forming steel by improving the content of Si, determines the proper addition amount of other alloy elements by accurate calculation and reference tests in order to overcome the defects caused by high content of Si, and simultaneously promotes the rapid formation of a Si-rich oxide layer by adding trace rare earth element RE, thereby realizing the improvement of the surface oxide layer structure, greatly reducing the thickness of the oxide layer and further obtaining the thinner thickness of the oxide layer.

Further, in order to enable the thickness of the oxide layer of the thermal shock forming steel to meet the requirements of a high-end market, when researching how to further reduce the thickness of the oxide layer, the finding shows that when a certain amount of Cu element is introduced, Cu and Si generate a synergistic effect, Cu can be enriched to the oxide layer in the high-temperature oxidation process, and the rate of oxygen inward diffusion is slowed down or prevented, so that the density of the oxide layer is further improved, the thickness of the oxide layer is reduced, and the thickness of the oxide layer of the thermal shock forming steel meets the requirements of the high-end market. However, when the content of Cu is less than 0.2%, the antirust and heat-resistant capability is realized at high temperature, when the content of Cu exceeds 0.2%, the hot deformation processing is unfavorable, the high-temperature copper brittleness phenomenon is caused, and when the content of Cu is more than 0.7%, the aging strengthening effect is generated.

Further, in the hot press forming steel formulation of the present invention, the effects of other alloying elements are mentioned in the prior patent CN103614640A, and are not described herein. However, it should be noted that in the prior patent CN103614640A, the content of Mn is 0.2-0.9%, while the content range of Mn in the present application is wider, which overcomes the problem that when the content of Mn exceeds 0.9%, the negative effect is obvious, and the influence of Mn on the material is reduced. For Mo, different from the patented technology, based on the inventive concept of the invention, Mo has no substantial influence on the exertion of the main performance of the hot stamping forming steel of the invention, does not influence the stability of the strength performance of the material, belongs to selectable alloy elements, and can not be added at all if the cost is considered; correspondingly, Nb + V is an optional alloy element, and the high-toughness steel has good toughness even if the content of Si is increased under the condition that Nb + V is not contained, and the Nb + V does not cause substantial influence.

Further, as for the rare earth element RE introduced in the present application, as for the application of RE, it is first found in japanese patent JP2010174306A (steel sheet for die cooling) in which the oxidation resistance of hot formed steel is improved by mainly controlling the contents of RE and S to suppress the generation of black skin and to improve the adhesion of black skin. However, the technical difficulty of controlling the S content to be less than 0.001 percent is great, and domestic steel plants are difficult to meet the technical requirements. Meanwhile, experimental data can be obtained according to the examples given in the specification: the steel sheet obtained by adding only a small amount of RE had a small black skin mass after hot forming, and it was difficult to obtain uniform experimental results, compared to the steel sheet containing no RE.

Further, the content of Si is 1.0-2.0%.

Further, the content of Mn is 1.0-2.0%.

As optional alloying elements, the hot-press formed steel further contains one or more of W of 1.0% or less, Ni of 1.0% or less, and Nb of 1.0% or less. The addition of these alloying elements can improve the comprehensive properties of the hot-stamping steel, and further enhance the effect.

Further, as optional alloying elements, the hot-press formed steel further contains 0.5% or less of V or/and 1.0% or less of Ni. Accordingly, V and Ni can also exert a further enhancing effect.

The invention also comprises a preparation method of the high-temperature oxidation-resistant hot stamping formed steel, wherein the preparation method of the hot stamping formed steel comprises the working procedures of steel making, continuous casting, hot rolling, acid pickling and cold rolling, steel is obtained after cold rolling and annealing, and a formed part is finally obtained after the steel is subjected to a hot stamping forming process.

Further, the hot stamping forming process comprises the following steps: heating the steel plate for cold rolling, annealing and hot stamping forming to 880-950 ℃, preserving heat for 3-10 min to enable the steel plate to be completely austenitized, then sending the steel plate into a die with a cooling system inside for stamping forming, maintaining pressure and rapidly cooling and quenching, controlling the cooling speed at 10-300 ℃/s to enable austenite to be converted into martensite, and finally obtaining a finished product.

Further, the metallographic structure of the hot press formed steel is: mainly martensite with or without small amounts of ferrite, bainite or residual austenite.

In summary, due to the adoption of the technical scheme, the invention has the beneficial effects that:

1. on the basis of the original patent technology (CN103614640A), the high-temperature oxidation resistance of the hot stamping forming steel is improved by increasing the content of Si, copper and trace rare earth elements RE are introduced, the rare earth elements RE can improve the structure of an oxidation layer and control the thickness of the oxidation layer, the copper and the Si generate synergistic action, the copper can enable a silicon dioxide oxidation layer to be more compact, the Si can solve the segregation problem caused by the copper and avoid the cracking of the steel surface caused by the copper, the high-temperature oxidation resistance of the hot stamping forming steel is obviously improved under the combined action, and the oxidation weight gain is very little, so that the thickness of the oxidation layer on the surface is extremely thin, the requirements of high-end markets are met, and the defects of the prior art are overcome;

2. in the formula of the hot stamping forming steel, the proportion of Si, rare earth, Cu and other alloy elements is redesigned, the content of Cr, Mo and other expensive alloy elements is reduced, and a better high-temperature oxidation resistance effect is achieved. Meanwhile, the invention is mainly improved in alloy proportion, the preparation process and the forming process of the invention are carried out by adopting the existing mode, the existing production equipment is not required to be greatly adjusted, shot blasting treatment is not required after forming, the input cost is not high, the production profit margin is large, and the invention is very suitable for industrial application.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

A hot press formed steel which is obtained mainly by working procedures of steel making, ingot casting, hot rolling, pickling, cold rolling and the like, for which working procedures can be realized by using existing processes, for example: smelting and casting can be carried out by adopting a 50kg vacuum induction furnace, the content of impurity elements is controlled as much as possible in the smelting process, then the steel ingot is heated to 1200 ℃, heat preservation is carried out for 2 hours, homogenization treatment is carried out, the open forging temperature is 1150 ℃, and the finish forging temperature is 850 ℃; forging the cast ingot into a long billet after multiple times of forging, then preserving heat at 1200 ℃ for 1 hour for homogenization treatment, obtaining a hot rolled plate through multiple times of hot rolling, carrying out acid washing on the hot rolled plate at the finishing rolling temperature of 800 ℃, removing surface oxide skin, and carrying out multiple times of rolling on a cold rolling mill until the thickness of the cold rolled plate is 3 mm.

In order to better implement the present invention, table 1 shows alloy compositions of some examples of the hot press forming steel of the present invention and alloy compositions of comparative examples (in the national standard "GB/T13303-:

TABLE 1 chemical composition table (mass%) of hot press formed steel of the present invention and comparative example

Note: 1. RE represents rare earth elements, mainly lanthanide series rare earth elements, and common rare earth elements are adopted;

2. of the above, the examples and comparative examples have an S content of not more than 0.01%.

Mechanical properties (measured according to the national standard test method):

TABLE 2 Main mechanical Properties of Hot-stamped Steel products according to the invention and 22MnB5 Steel

Note: the above data are strength and elongation after quenching of the hot formed steel sheet (i.e., rapid cooling of the cold rolled steel sheet after heating at 930 ℃ for 5 min), not the sheet properties after rolling.

As can be seen from Table 2, the main mechanical properties of the hot press formed steel material of the present invention are equivalent to 22MnB5, and it is shown that the hot press formed steel material of the present invention satisfies the strength requirements of the hot press formed high strength steel.

The test method comprises the following steps:

using examples 5 to 7 as test subjects and designing three grades of 0.05%, 0.2% and 0.4% for the amount of change in Cu, 3 specimens of 30 mm. times.10 mm. times.3 mm each were prepared from the plate material obtained in examples 5 to 7 of the present invention and 22MnB5 steel, and then polished with 180#, 400#, 800#, 1500# and 2000# sandpaper in this order, washed with alcohol and dried. The dimensions of the test piece were measured with a vernier caliper, and the weight before oxidation was weighed with an electronic balance (accuracy 0.0001 g). The oxidation experiment was carried out in an air dielectric resistance furnace at 930 ℃ for 5min and 10min and 30min, respectively. The sample after oxidation was weighed again, and the oxidation weight gain per unit area of the sample was calculated in combination with the size of the sample before oxidation. The test results are as follows:

TABLE 3 Oxidation at 930 ℃ for 5min for examples 5-7 and comparative example

TABLE 4 Oxidation at 930 ℃ for 10min for examples 5-7 and comparative example

TABLE 5 Oxidation at 930 ℃ for 30min for examples 5 to 7 and comparative example

As can be seen from tables 3 to 5, when example 6 is compared with comparative example (22MnB5), when Si content is more than 1.0% and RE is introduced, the average weight increase per unit area of the hot-stamped steel is reduced by about 1/3 within 930 ℃ for plus 5min, the average weight increase per unit area of the hot-stamped steel is reduced by about 1/2 within 10min, and the average weight increase per unit area of the hot-stamped steel is reduced by about 3/5 within 30min, thereby showing that the high Si content + RE can significantly improve the high-temperature oxidation resistance of the hot-stamped steelIt is possible to reduce the thickness of the oxide layer. Comparing example 7 with comparative example (22MnB5), when only Cu is introduced, the average weight increase of the hot stamping steel per unit area is almost unchanged within 930 ℃ for plus 5min, within 10min, the average weight increase of the hot stamping steel per unit area is changed in a small range, within 30min, the average weight increase of the hot stamping steel per unit area is slightly reduced, but the technical effect advantage is not obvious, and the gain effect of high-temperature oxidation resistance is general. When high Si content + RE + Cu is adopted, the average unit area weight increase of the hot stamping steel is sharply reduced within 930 ℃ and 5min, and the average unit area weight increase is 6.275g/m²Down to 1.0g/m²About, within 10min, the average weight gain per unit area also shows a sharp decrease, and within 30min, the sharp decrease of the average weight gain per unit area is more obvious and is directly from 114.6430g/m²Down to 10.0g/m²Therefore, the high Si content + RE + Cu can obviously improve the high-temperature oxidation resistance of the hot stamping forming steel, further can obviously reduce the thickness of an oxidation layer, and meets the requirements of high-end markets.

Further, in tables 3 to 5, examples 5 to 7 were compared with each other: in examples 5 and 7, the best technical effect was obtained when the Cu content was 0.4%, thus demonstrating that, within a certain content range, the higher the high temperature oxidation resistance of the hot press formed steel as the Cu content increases; taking the case of 930 ℃ for +30min as an example, comparing examples 6 and 7, the technical effect obtained by the high-Si content + RE mode is obviously better than that obtained by the + Cu mode, and comparing examples 5, 6 and 7, the effect obtained by the high-Si content + RE + Cu mode is obviously better than that obtained by the high-Si content + RE and + Cu mode, namely, the technical effect is generated with a 'synergistic' result, thereby showing that the high-Si content and the Cu mode generate a synergistic effect between the two modes, and the technical effect of '1 +1 > 2' is obtained.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.