High-strength steel and preparation method thereof

Abstract

The present invention provides a high-strength steel and a preparation method thereof. The high-strength steel comprises a steel body and an iron oxide scale on the surface of the steel body; wherein the chemical composition and content of the high-strength steel are as follows: C is 0.065-0.105wt%, Mn is 0.9-1.65wt%, Si is 0.01-0.19wt%, Nb is 0.02-0.05wt%, V is 0.02-0.05wt%, Ti is 0.02-0.08wt%, S is ≤0.005wt%, P is ≤0.020wt%, and the remainder is Fe and other impurities; the iron oxide scale comprises Fe2O3, Fe3O4, a eutectoid structure α-Fe+Fe3O4, and FeO, wherein the mass proportion of Fe3O4 in the iron oxide scale is 60%-90%. The iron oxide scale on the surface of the high-strength steel prepared in the present invention is dense and smooth, and has excellent surface quality.

Description

Technical Field

[0001] The invention belongs to the technical field of hot-rolled high-strength steel oxide scale control, and particularly relates to high-strength steel and a preparation method thereof. Background Art

[0002] Low-carbon, high-strength steel, with its superior properties of high strength, high toughness, and weldability, is a key material for development and promotion in the steel structure sector. The rational use of high-strength steel in moving steel components can effectively reduce the weight of heavy equipment, lower energy consumption, improve efficiency, and extend the equipment's service life. The application of these materials aligns with environmental protection, energy conservation, and economic development trends. With increasingly competitive markets, steel users are demanding not only the inherent performance of these steels but also their appearance. Surface quality issues caused by iron oxide scale have become a key issue that the steel industry needs to address.

[0003] High-strength steel first forms primary scale in the heating furnace before hot rolling, followed by secondary scale during the rough rolling stage. These primary and secondary scales are typically removed using high-pressure water descaling. Tertiary scale, formed during finishing rolling and coiling, is retained at room temperature, leaving an oxide layer primarily composed of tertiary scale on the surface of the high-strength steel.

[0004] The formation process of tertiary iron oxide scale is roughly as follows: the main component of the iron oxide scale after final rolling is FeO, which undergoes phase change during the subsequent cooling to the coiling temperature, generating an oxide layer containing Fe2O3, Fe3O4, eutectoid structure α-Fe+Fe3O4 and residual FeO.

[0005] When the Fe2O3 content in the scale is high, red scale is produced, seriously affecting the corrosion resistance and coating performance of the high-strength steel surface. At the same time, high FeO content, an inadequate eutectoid structure of α-Fe+Fe3O4, and thick scale will cause powder to fall off during steel strip processing, polluting the environment and roughening the workpiece surface, seriously affecting subsequent processing.

[0006] Based on this, in order to solve the technical problem in the above-mentioned prior art that the surface quality of high-strength steel is poor and affects subsequent processing, the present invention provides a high-strength steel and a preparation method thereof. Summary of the Invention

[0007] Aiming to solve the technical problem of poor surface quality of high-strength steel in the above-mentioned prior art, which affects subsequent processing, the present invention provides a high-strength steel, comprising a steel body and iron oxide scale on the surface of the steel body;

[0008] The chemical composition and content of the steel body are as follows: C is 0.065-0.105wt%, Mn is 0.9-1.65wt%, Si is 0.01-0.19wt%, Nb is 0.02-0.05wt%, V is 0.02-0.05wt%, Ti is 0.02-0.08wt%, S≤0.005wt%, P≤0.020wt%, and the rest is Fe and other impurities;

[0009] The iron oxide scale includes Fe2O3, Fe3O4, eutectoid structure α-Fe+Fe3O4 and FeO, wherein the mass proportion of Fe3O4 in the iron oxide scale is 60% to 90%.

[0010] Furthermore, the total mass fraction of Nb, V and Ti elements in the steel body is no more than 18%.

[0011] Furthermore, the thickness of the iron oxide scale is 6 to 15 μm.

[0012] The present invention also provides a method for preparing high-strength steel, comprising the steps of:

[0013] After heating the steel billet, rolling it into a first steel strip; the surface of the first steel strip has a first oxide layer; the chemical composition and content of the steel billet correspond to the steel body in any one of the above-mentioned high-strength steels;

[0014] Cooling the first steel strip to a coiling temperature in an oxygen-deficient atmosphere to obtain a second steel strip, wherein the second steel strip has a second oxide layer;

[0015] The second steel strip is coiled at a temperature of 350° C. to 550° C., and cooled to room temperature to obtain the high-strength steel.

[0016] Furthermore, the heating includes the steps of heating the steel billet to 1200-1250° C. within 120-180 minutes and keeping the temperature for 30-60 minutes.

[0017] Furthermore, the rolling includes rough rolling and finish rolling, wherein the final rolling temperature of the rough rolling is 1010-1030°C, the start rolling temperature of the finish rolling is 960-1000°C, and the final rolling temperature of the finish rolling is 840-860°C.

[0018] Furthermore, the thickness of the first steel strip is 3 to 25.4 mm.

[0019] Furthermore, when the rolling crown is 25 to 85 μm; when the thickness of the first steel strip is 20 to 25 mm, the rolling speed is 2.5 m / s to 4 m / s; when the thickness of the first steel strip is 2.0 to 3.5 mm, the rolling speed is ≥9.5 m / s.

[0020] Furthermore, cooling the first steel strip to the coiling temperature in an oxygen-deficient atmosphere comprises the steps of: blowing a protective gas onto the surface of the first steel strip to reduce the oxygen content of the surface gas atmosphere of the first steel strip to less than 20vt%, thereby forming the oxygen-deficient atmosphere;

[0021] The first steel strip is cooled to the coiling temperature in the oxygen-deficient atmosphere to obtain the second steel strip.

[0022] Wherein, the cooling method includes laminar cooling or ultra-fast cooling, and the protective gas includes argon and / or nitrogen.

[0023] Furthermore, cooling the first steel strip to a coiling temperature in an oxygen-deficient atmosphere further comprises: a cooling rate during the cooling to the coiling temperature is 10 to 60° C. / s.

[0024] Compared with the prior art, the present invention has at least the following advantages:

[0025] In the iron oxide scale on the surface of the above-mentioned high-strength steel, Fe3O4 accounts for 60% to 90% by mass. The iron oxide scale with Fe3O4 as the main component has a dense and smooth structure, is not easy to peel off, and has excellent corrosion resistance. However, the surface quality of the iron oxide scale produced by conventional technology is poor, and the surface iron oxide layer is loose and rough with poor corrosion resistance. In comparison, the iron oxide scale produced by the present invention can provide excellent surface quality and coating performance support for subsequent operations in subsequent processing, which can accelerate the progress of subsequent processes and improve processing efficiency and process cleanliness.

[0026] In addition, the present invention further refines the high-strength steel grains and improves the low-temperature toughness of high-strength steel by accurately optimizing the element ratio, so that the components can synergize and enhance each other, thereby giving the high-strength steel the excellent properties of both high plasticity and high strength. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0028] Figure 1 Schematic diagram of the changes of the oxide layer at each stage in one embodiment of the present invention.

[0029] Figure 2 This is a cross-sectional SEM image of the iron oxide scale on the surface of the high-strength steel prepared in Example 1 of the present invention at a scale of 20 microns.

[0030] Figure 3 This is a cross-sectional SEM image of the iron oxide scale on the surface of the high-strength steel prepared in Example 1 of the present invention at a scale of 4 microns.

[0031] Figure 4 This is a cross-sectional SEM image of the iron oxide scale on the surface of the high-strength steel prepared in Example 2 of the present invention at a scale of 20 microns.

[0032] Figure 5 This is a cross-sectional SEM image of the iron oxide scale on the surface of the high-strength steel prepared in Example 2 of the present invention at a scale of 4 microns.

[0033] Figure 6 This is a cross-sectional SEM image of the iron oxide scale on the surface of the high-strength steel prepared in Comparative Example 1 of the present invention at a scale of 10 microns. DETAILED DESCRIPTION

[0034] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0035] Moreover, the technical solutions between the various embodiments of the present invention may be combined with each other, but this must be based on the fact that ordinary technicians in this field can implement them. When the combination of technical solutions is mutually contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0036] When numerical ranges are given in the examples, it should be understood that unless otherwise specified herein, both endpoints of each numerical range and any value between the two endpoints may be used. Unless otherwise defined, all technical and scientific terms used herein are consistent with the prior art as understood by those skilled in the art and the description of the present invention. Any prior art methods, devices, and materials similar or equivalent to those described in the examples of the present invention may also be used to implement the present invention.

[0037] The present invention provides a high-strength steel, comprising a steel body and iron oxide scale on the surface of the steel body;

[0038] The chemical composition and content of the high-strength steel are as follows: C is 0.065-0.105wt%, Mn is 0.9-1.65wt%, Si is 0.01-0.19wt%, Nb is 0.02-0.05wt%, V is 0.02-0.05wt%, Ti is 0.02-0.08wt%, S≤0.005wt%, P≤0.020wt%, and the rest is Fe and other impurities;

[0039] The iron oxide scale includes Fe2O3, Fe3O4, eutectoid structure α-Fe+Fe3O4 and FeO, wherein the mass proportion of Fe3O4 in the iron oxide scale is 60% to 90%.

[0040] The beneficial effects of limiting the content of each element in the present invention are mainly as follows:

[0041] C: In the present invention, the mass fraction of C in the high-strength steel is 0.065-0.105 wt %, which ensures that Nb and Ti are fully precipitated while avoiding the formation of pearlite.

[0042] Among them, pearlite is a tissue bead composed of alternating ferrite and cementite lamellae that is precipitated simultaneously by the eutectoid transformation of austenite. Its mechanical properties are between those of ferrite and cementite, that is, its strength and hardness are significantly higher than those of ferrite, while its plasticity and toughness are worse than those of ferrite, but much better than those of cementite.

[0043] Si: In the present invention, the mass fraction of Si in the high-strength steel is 0.01 to 0.19 wt%. Silicon is mainly added as a deoxidizer and remains to reduce the gas content and hard point AlN in the steel. While playing a deoxidizing role, it can also reduce the formation of red iron oxide scale (i.e., Fe2O3) on the surface of the high-strength steel.

[0044] Mn: In the present invention, the mass fraction of Mn in the high-strength steel is 0.9-1.65 wt%, which can play a role in solid solution strengthening and desulfurization, thereby reducing the hot brittleness of the strengthened steel.

[0045] Nb: In the present invention, the mass percentage of Nb in the high-strength steel is 0.02-0.05%, which can play the role of grain refinement strengthening and precipitation strengthening, and is beneficial to improving the strength of the steel plate.

[0046] It should be noted that phosphorus and sulfur, as harmful impurities in high-strength steel, significantly impair the cold bending and welding properties of high-strength steel. To reduce production costs and improve product quality, controlling the mass fractions of phosphorus and sulfur in high-strength steel to 0.020% and 0.005%, respectively, can effectively reduce their impact on the cold bending and welding properties of high-strength steel.

[0047] The total mass fraction of Nb, V, and Ti in the steel body can be no greater than 18%. By controlling the total mass fraction of the above three elements in the steel body, the grain refinement and precipitation strengthening effects of Nb, V, and Ti are maximized, resulting in a high-strength steel with higher strength and ductility.

[0048] The main components of iron oxide scale include Fe3O4, Fe2O3, FeO and (α-Fe+Fe3O4).

[0049] The iron oxide scale produced by the present invention, whose primary component is Fe₃O₄, is dense and durable, and resists peeling easily from the steel body. Its appearance is bluish-black or dark blue. As an ideal surface oxide layer, in existing technology, steel components typically use bluing (also known as blueing or baking) to form an Fe₃O₄ layer on the steel body. This oxide film offers both corrosion resistance and a lustrous and aesthetically pleasing appearance, further improving the surface quality of high-strength steel.

[0050] Furthermore, high Fe2O3 content in the scale produces a red, rough, and loose scale, severely impacting the surface quality of the final product and the coating properties of the steel product. Similarly, high FeO content and an inappropriate (α-Fe + Fe3O4) ratio can cause steel strip to shed during cold working, polluting the environment and roughening the workpiece surface.

[0051] The mass proportion of the eutectoid structure α-Fe+Fe 3 O 4 in the iron oxide scale may be 20-40%.

[0052] In summary, the eutectoid structure, Fe3O4 (which accounts for 60% to 90% of the mass in the iron oxide scale), and appropriate amounts of FeO and Fe2O3 work together to form high-strength steel with excellent surface quality and coating performance. The iron oxide scale has a dense and smooth structure, is not easy to peel off, and has excellent corrosion resistance.

[0053] In some embodiments, the oxide scale can have a thickness of 6 to 15 μm, which is approximately 10 to 30% thinner than the oxide scale thickness in the prior art. Compared to the prior art, due to the appropriate starting rolling temperature, faster rolling speed, and cooling in an oxygen-deficient environment, the steel body surface is provided with a dense, thin, and tough oxide scale, thereby avoiding the problem of oxide scale powdering during subsequent application and processing.

[0054] In summary, the high-strength steel produced in the present invention has the following advantages:

[0055] In the iron oxide scale on the surface of high-strength steel, Fe3O4 accounts for 60% to 90% by mass. The iron oxide scale with Fe3O4 as the main component has a dense and smooth structure, is thin and tough, is not easy to peel off and has excellent corrosion resistance. However, the surface quality of the iron oxide scale produced by conventional technology is poor, and the surface iron oxide layer is loose and rough and has poor corrosion resistance. In comparison, the iron oxide scale produced by the present invention can provide excellent surface quality and coating performance support for subsequent operations in subsequent processing technology, can accelerate the progress of subsequent processes, improve processing efficiency and process cleanliness, and can also increase sales in subsequent market outputs, which means huge economic and environmental benefits.

[0056] In addition, the present invention further refines the high-strength steel grains and improves the low-temperature toughness of high-strength steel by accurately optimizing the element ratio, so that the components can synergize and enhance each other, thereby giving the high-strength steel the excellent properties of both high plasticity and high strength.

[0057] Compared with the high cost and high equipment requirements of the conventional technology, the present invention also provides a method for preparing high-strength steel, comprising the steps of:

[0058] S1. After heating the steel billet, rolling it into a first steel strip; the surface of the first steel strip has a first oxide layer; the chemical composition and content of the steel billet correspond to the steel body in any of the high-strength steels described above.

[0059] In some embodiments, the heating may include the steps of heating the steel billet to 1200-1250° C. within 120-180 minutes and soaking and keeping the temperature for at least 30 minutes.

[0060] In other embodiments, the rolling includes rough rolling and finish rolling, wherein the final rolling temperature of the rough rolling can be 1010-1030°C, the start rolling temperature of the finish rolling can be 960-1000°C, and the final rolling temperature of the finish rolling can be 840-860°C.

[0061] To be further detailed, the rolling crown during the rolling process is 25 to 85 μm.

[0062] For example, the thickness of the first steel strip may be 3 to 25.4 mm.

[0063] As another example, when the thickness of the first steel strip is 20-25 mm, the rolling speed may be greater than 2.5 m / s and less than or equal to 4.0 m / s;

[0064] When the thickness of the first steel strip is 2.0-3.5 mm, the rolling speed may be greater than 9.5 m / s.

[0065] S2. Cooling the first steel strip to a coiling temperature in an oxygen-deficient atmosphere to obtain a second steel strip, wherein the second steel strip has a second oxide layer.

[0066] In some embodiments, cooling the first steel strip to a coiling temperature in an oxygen-deficient atmosphere includes the steps of: blowing a protective gas into the surface of the first steel strip to make the oxygen content in the surface gas atmosphere of the first steel strip lower than 20vt%, thereby forming the oxygen-deficient atmosphere; and cooling the first steel strip to a coiling temperature in the oxygen-deficient atmosphere to obtain a second steel strip.

[0067] Exemplarily, the cooling method includes laminar cooling or ultra-fast cooling, and the protective gas includes argon or nitrogen.

[0068] As another example, cooling the first steel strip to the coiling temperature in an oxygen-deficient atmosphere further comprises: a cooling rate during the cooling to the coiling temperature is 10 to 60° C. / s.

[0069] In specific application: After the final finishing rolling, protective gas can be blown into the upper and lower surfaces of the first steel strip immediately, and laminar cooling water can be injected at the same time, so as to effectively control the reaction process on the surface of the first steel strip, prevent oxygen diffusion, and reduce the formation of Fe2O3, so that the composition of iron oxide scale on the surface of the steel body can be accurately controlled and the thickness is relatively thin.

[0070] The protective gas may be nitrogen or argon, and the cooling rate of the first steel strip may be 10-60° C. / s.

[0071] For example, the oxygen content of the oxygen-deficient atmosphere in which the first steel strip is located may be less than 20 vt% O2.

[0072] As another example, the oxygen content of the oxygen-deficient atmosphere in which the first steel strip is located may be less than 10vt% O2.

[0073] S3. Coiling the second steel strip at 350° C. to 550° C. and cooling it to room temperature to obtain the high-strength steel.

[0074] In some embodiments, the coiling temperature may be 350° C. to 550° C. Within this temperature range, as the temperature decreases, the iron oxide scale on the surface of the steel body can efficiently and fully undergo pro-eutectoid and eutectoid reactions to form an appropriate amount of eutectoid structure α-Fe+Fe3O4, thereby controlling powder loss on the steel coil surface and further reducing the powder loss rate of high-strength steel.

[0075] In other embodiments, the second steel strip may be cooled to room temperature in an air atmosphere to obtain high-strength steel.

[0076] It should be noted that if Figure 1 As shown, the first thing formed on the heated steel billet in the heating furnace before hot rolling is primary iron scale; the rolling process includes rough rolling and finish rolling, wherein the final rolling temperature of the rough rolling is 1010-1030°C, the start rolling temperature of the finish rolling is 960-1000°C, and the final rolling temperature of the finish rolling is 840-860°C.

[0077] Then, secondary iron oxide scale is formed in the rough rolling stage. The above-mentioned primary and secondary iron oxide scales can be removed by high-pressure water descaling technology. Tertiary iron oxide scale is formed during the finishing rolling and coiling process, and the tertiary iron oxide scale can be retained until the subsequent cooling to room temperature. Therefore, an oxide layer mainly composed of tertiary iron oxide scale is left on the surface of the hot-rolled strip. After the final finishing rolling, the tertiary iron oxide scale is mainly FeO, which undergoes a phase change during the subsequent cooling metallurgy (including cooling to the coiling temperature and natural cooling to room temperature) to generate an iron oxide scale whose main components are Fe2O3, Fe3O4, eutectic structure α-Fe+Fe3O4 and residual FeO.

[0078] To further refine the analysis, the first oxide layer is the tertiary oxide scale that has not undergone phase transformation after finishing and final rolling, and its main component is FeO. The second oxide layer is the intermediate product formed by the phase transformation of the tertiary oxide scale during the subsequent partial cooling metallurgical process (i.e., cooling to the coiling temperature).

[0079] In some embodiments, the pressure of the high-pressure water used for descaling in the above-mentioned high-pressure water descaling technology can be 18 to 20 MPa.

[0080] As can be seen from the above, compared with the prior art, the present invention has at least the following advantages:

[0081] The present invention utilizes a reduced oxygen atmosphere on the surface of the first steel strip to control the compositional evolution of the oxide scale. Its main principle is as follows: When the oxygen content of the surface layer of the first steel strip is reduced to 20vt%, the oxide scale on the first steel strip undergoes a phase transformation upon cooling in the oxygen-deficient atmosphere. When the surface temperature of the oxide scale drops below 550°C, the FeO formed on the surface of the second steel strip partially transforms into Fe3O4. At this point, the oxide scale consists of Fe3O4+FeO and a small amount of Fe2O3. During the coiling process of the second steel strip, the proeutectoid and eutectoid reactions of FeO are enhanced, increasing the proportion of the resulting proeutectoid and eutectoid structures in the oxide scale. As the temperature cools to room temperature, the composition of the second oxide layer stabilizes, forming a flexible oxide scale with a dense surface structure. This invention offers a sophisticated improvement, precisely controlling the factors influencing the oxide scale composition, and efficiently synthesizing an oxide scale with an Fe3O4 mass fraction of 60% to 90%.

[0082] Those skilled in the art should be aware that the benefits of the excellent surface properties of high-strength steel to subsequent processing technology are specifically reflected in the following: the iron oxide scale produced by the invention can provide excellent surface quality and coating performance support for subsequent operations in the subsequent processing technology, which can accelerate the progress of subsequent processes, improve processing efficiency and process cleanliness, and at the same time increase sales in subsequent market outputs, which means huge economic and environmental benefits.

[0083] In order to facilitate those skilled in the art to further understand the present invention, examples are given below:

[0084] Example 1

[0085] The present invention provides a high-strength steel, comprising a steel body and iron oxide scale on the surface of the steel body, wherein the chemical components and contents thereof are as follows: C is 0.075wt%, Mn is 1.1wt%, Si is 0.109wt%, Nb is 0.02wt%, V is 0.05wt%, Ti is 0.02wt%, S is ≤0.004wt%, P is ≤0.019wt%, and the remainder is Fe and other impurities.

[0086] The iron oxide scale includes Fe2O3, Fe3O4, eutectoid structure α-Fe+Fe3O4 and FeO, wherein the mass proportion of Fe3O4 in the iron oxide scale is 80-90%, and the thickness of the iron oxide scale is 6.1um.

[0087] The present invention also provides a method for preparing the above-mentioned high-strength steel, wherein the steel billet is placed in a heating furnace, heated to 1245° C. within 180 minutes, kept warm for 30 minutes, and then rolled to obtain a first steel strip.

[0088] During the rolling process, the final rolling temperature of rough rolling was controlled at 1030°C, the start rolling temperature of finishing rolling was controlled at 1000°C, and the final rolling temperature of finishing rolling was controlled at 860°C. The rolling speed was 9.8 m / s. Immediately after finishing rolling, nitrogen was blown into the upper and lower surfaces of the first steel strip. The strip was then cooled to a coiling temperature of 450°C under laminar cooling conditions to obtain the second steel strip, which was then coiled. The laminar cooling rate was 50°C / s. The oxygen content of the oxygen-deficient atmosphere was ≤10vt% O2.

[0089] The high-strength steel is obtained by naturally cooling the second steel strip to room temperature in air.

[0090] Use a wire cutting machine to cut a sample of 10mm×10mm×15mm in size from the hot-rolled high-strength steel at 1 / 4 of the edge in the width direction, as shown in the attached figure: Figure 2 and Figure 3 The cross-sectional SEM image of the oxidized iron scale of high-strength steel in Example 1 is shown in FIG. Figure 1 As shown in the figure, the prepared high-strength steel cross-section oxide scale is mainly composed of 80% to 90% Fe3O4 in the middle layer, scattered residual FeO near the steel body, and a small amount of inconspicuous Fe2O3 in the outermost layer.

[0091] The surface morphology of the oxide layer after the bending test was statistically calculated, and the powder loss rate of the oxide scale was 7.8%.

[0092] Example 2

[0093] The present invention provides a high-strength steel, comprising a steel body and iron oxide scale on the surface of the steel body, wherein the chemical components and contents thereof are as follows: C is 0.10wt%, Mn is 1.6wt%, Si is 0.16wt%, Nb is 0.04wt%, V is 0.02wt%, Ti is 0.05wt%, S is ≤0.005wt%, P is ≤0.020wt%, and the remainder is Fe and other impurities.

[0094] The iron oxide scale includes Fe2O3, Fe3O4, eutectoid structure α-Fe+Fe3O4 and FeO, wherein the mass proportion of Fe3O4 in the iron oxide scale is 60-70%, and the thickness of the iron oxide scale is 14.8um.

[0095] The present invention also provides a method for preparing the above-mentioned high-strength steel, wherein the steel billet is placed in a heating furnace, heated to 1200° C. within 130 minutes, kept warm for 30 minutes, and then rolled to obtain a first steel strip.

[0096] During the rolling process, the final rolling temperature of rough rolling was controlled at 1016°C, the start rolling temperature of finishing rolling was controlled at 967°C, and the final rolling temperature of finishing rolling was controlled at 840°C. The rolling speed was 3.0 m / s. Immediately after finishing rolling, argon gas was blown into the upper and lower surfaces of the first steel strip. The strip was cooled to a coiling temperature of 530°C under laminar cooling conditions to obtain the second steel strip, which was then coiled. The laminar cooling rate was 15°C / s, and the oxygen-deficient atmosphere contained ≤20% O2.

[0097] The high-strength steel is obtained by naturally cooling the second steel strip to room temperature in air.

[0098] Use a wire cutting machine to cut a sample of 10mm×10mm×15mm in size from the hot-rolled high-strength steel at 1 / 4 of the edge in the width direction, as shown in the attached figure: Figure 4 and Figure 5 This is a cross-sectional SEM image of the oxide scale formed in Example 2. The oxide scale on the prepared high-strength steel is primarily composed of an intermediate layer of Fe₃O₄, scattered residual FeO near the substrate, a eutectoid structure, and an outermost layer of Fe₂O₃. Fe₃O₄ accounts for 60% to 70% of the total oxide layer. Based on statistical calculations of the oxide layer surface morphology after the bend test, the oxide scale dust loss rate was 10.8%.

[0099] Comparative Example 1

[0100] A high-strength steel includes a steel body and iron oxide scale on the surface of the steel body, wherein the chemical composition and content of the steel body are as follows: C is 0.070wt%, Mn is 1.15wt%, Si is 0.012wt%, Nb is 0.02wt%, V is 0.045wt%, Ti is 0.02wt%, S is ≤0.004wt%, P is ≤0.019wt%, and the remainder is Fe and other impurities.

[0101] The iron oxide scale includes Fe2O3, Fe3O4, a small amount of eutectoid structure α-Fe+Fe3O4 and FeO, wherein the mass proportion of Fe3O4 in the iron oxide scale is 30-50%, and the thickness of the iron oxide scale is 9.1um.

[0102] The present invention also provides a method for preparing the above-mentioned high-strength steel, wherein the steel billet is placed in a heating furnace, heated to 1235° C. within 170 minutes, kept warm for 30 minutes, and then rolled to obtain a first steel strip.

[0103] During the rolling process, the final rolling temperature of roughing was controlled at 1028°C, the start rolling temperature of finishing rolling was controlled at 1000°C, and the final rolling temperature of finishing rolling was controlled at 865°C. The rolling speed was 9.5 m / s. After finishing rolling, the first steel strip was cooled to a coiling temperature of 550°C under laminar cooling conditions in air (with an oxygen concentration of approximately 21% by volume), producing a second steel strip, which was then coiled. The laminar cooling rate was 20°C / s.

[0104] The high-strength steel is obtained by naturally cooling the second steel strip to room temperature in air.

[0105] Use a wire cutting machine to cut a sample of 10mm×10mm×15mm in size from the hot-rolled high-strength steel at 1 / 4 of the edge in the width direction, as shown in the attached figure: Figure 6 The cross-sectional SEM image of the oxide scale of high-strength steel of comparative example 1 is shown in FIG. Figure 6 As shown in the figure, the outermost layer of the oxide scale on the cross section of the prepared high-strength steel is an incomplete thin Fe2O3 + a small amount of Fe3O4 layer, the second outermost layer is a Fe3O4 oxide layer, followed by an intermediate layer containing a uniformly distributed (α-Fe+Fe3O4) eutectoid structure, a small amount of residual FeO near the steel body, and the Fe3O4 content in the oxide scale is 30% to 50%.

[0106] According to the statistical calculation based on the surface morphology of the oxide layer after the bending test, the powder loss rate of the iron oxide scale is 35%.

[0107] It can also be observed that, compared with Example 1, the iron oxide scale on the surface of the high-strength steel in Comparative Example 1 is thicker.

[0108] The above technical solutions of the present invention are only preferred embodiments of the present invention and do not limit the patent scope of the present invention. All equivalent structural transformations made by using the contents of the present invention's description and drawings under the technical concept of the present invention, or directly / indirectly applied in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A method for preparing high-strength steel, characterized in that: Including steps: After heating the steel billet, rolling it into a first steel strip; the surface of the first steel strip has a first oxide layer; the chemical composition and content of the steel billet are: C 0.065-0.105wt%, Mn 0.9-1.65wt%, Si 0.01-0.19wt%, Nb 0.02-0.05wt%, V 0.02-0.05wt%, Ti 0.02-0.08wt%, S ≤ 0.005wt%, P ≤ 0.020wt%, and the remainder is Fe and other impurities; Cooling the first steel strip to a coiling temperature in an oxygen-deficient atmosphere to obtain a second steel strip, wherein the second steel strip has a second oxide layer; cooling the first steel strip to a coiling temperature in an oxygen-deficient atmosphere comprises the steps of: blowing a protective gas onto a surface of the first steel strip to reduce the oxygen content of the surface gas atmosphere of the first steel strip to less than 20vt%, thereby forming the oxygen-deficient atmosphere; The second steel strip is coiled at 350° C. to 550° C. and cooled to room temperature to obtain the high-strength steel; the high-strength steel includes a steel body and iron oxide scale on the surface of the steel body, wherein the chemical composition and content of the steel body correspond to those of the steel billet, and the iron oxide scale includes Fe2O3, Fe3O4, a eutectoid structure of α-Fe+Fe3O4, and FeO, wherein the mass proportion of Fe3O4 in the iron oxide scale is 60% to 90%.

2. The method for preparing high-strength steel according to claim 1, characterized in that: The thickness of the iron oxide scale is 6-15 μm.

3. The preparation method according to claim 1, characterized in that The heating comprises the steps of heating the steel billet to 1200-1250° C. within 120-180 minutes and keeping the temperature for 30-60 minutes.

4. The preparation method according to claim 1, characterized in that The rolling includes rough rolling and finish rolling, wherein the finish rolling temperature of the rough rolling is 1010-1030°C, the start rolling temperature of the finish rolling is 960-1000°C, and the finish rolling temperature of the finish rolling is 840-860°C.

5. The preparation method according to claim 1, characterized in that The thickness of the first steel strip is 3-25.4 mm.

6. The preparation method according to claim 5, characterized in that The rolling crown of the rolling is 25 to 85 μm; When the thickness of the first steel strip is 20-25 mm, the rolling speed is 2.5 m / s-4 m / s; when the thickness of the first steel strip is 2.0-3.5 mm, the rolling speed is ≥9.5 m / s.

7. The preparation method according to claim 1, characterized in that The first steel strip is cooled to a coiling temperature in the oxygen-deficient atmosphere to obtain a second steel strip, wherein the cooling method includes laminar cooling or ultra-fast cooling, and the protective gas includes nitrogen and / or argon.

8. The preparation method according to claim 7, characterized in that Cooling the first steel strip to a coiling temperature in an oxygen-deficient atmosphere further includes: a cooling rate during the cooling to the coiling temperature is 10-60° C. / s.

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