Low-alloy structural steel 40MnB as well as preparation method and application thereof

Abstract

The invention provides low-alloy structural steel 40MnB as well as a preparation method and application thereof. The low-alloy structural steel 40MnB comprises the following chemical components in percentage by weight: 0.37 to 0.44 percent of C, 1.10 to 1.40 percent of Mn, 0.17 to 0.37 percent of Si, less than or equal to 0.035 percent of P, less than or equal to 0.035 percent of S, less than or equal to 0.30 percent of Cr, less than or equal to 0.15 percent of Mo, less than or equal to 0.30 percent of Cu, less than or equal to 0.30 percent of Ni, 0.01 to 0.025 percent of Als, 0.0005 to 0.0035 percent of B, 0.01 to 0.04 percent of Ti and the balance of Fe and other inevitable impurities. The carbon content is increased to improve the strength and hardness of the steel, and meanwhile, the hardenability and strength of the steel are remarkably improved by accurately controlling the content of other alloy elements such as Mn, Si and B.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of steel smelting, in particular to a low-alloy structural steel 40MnB and a preparation method and application thereof. BACKGROUND

[0002] Boron steel is a low-alloy structural steel based on Mn and B instead of Cr and Ni. Adding trace amounts of boron to steel can significantly improve hardenability, save a large amount of valuable elements, and also obtain excellent mechanical properties. China is short of Cr and Ni resources, but rich in boron resources. Therefore, the development of boron steel is of great significance. Usually, medium carbon steel or medium carbon alloy steel is used in product design, and after quenching and tempering treatment, the mechanical property indexes required by design are reached. The final use state of the metallographic structure is a tempered sorbite structure. This tempered sorbite structure has a good combination of strength, plasticity and toughness. The front axle, half axle, spline shaft, steering knuckle, engine crankshaft, connecting rod and most fasteners of the automobile are often manufactured by this process.

[0003] Chinese invention CN202310868414.5 discloses a boron-containing steel and a manufacturing method thereof. The chemical composition of the boron-containing steel includes, in mass percentage, C: 0.21-0.30%, Mn: 1.0-2.0%, Si: 0.3-0.5%, Cr: 0.2-0.5%, B: 0.0023-0.0045%, and the balance of Fe and inevitable impurities. The intergranular oxidation crack depth of the boron-containing steel is 0-5 μm. This patent controls the content of various elements, reasonably ensures the strength of the steel, avoids hot rolling intergranular oxidation, and obtains a uniform microstructure hot rolling product. At the same time, it can effectively protect the boron-containing steel from reducing the degree of oxidation, so that after subsequent hot forming process, the intergranular oxidation crack depth of the boron-containing steel is 0-5 μm, so as to obtain a uniform microstructure and crack-free hot stamping product. However, the performance of the boron-containing steel of this patent includes: yield strength of 350-400 MPa, tensile strength of 450-600 MPa, which is difficult to meet the demand of the automobile for steel strength. SUMMARY

[0004] The present application is made in view of the above problems, and aims to provide a low-alloy structural steel 40MnB and a preparation method and application thereof.

[0005] Specifically, the first aspect of the application provides a low alloy structural steel 40MnB, which has the following chemical composition by weight percentage: C: 0.37-0.44%, Mn: 1.10-1.40%, Si: 0.17-0.37%, P: ≤0.035%, S: ≤0.035%, Cr: ≤0.30%, Mo: ≤0.15%, Cu: ≤0.30%, Ni: ≤0.30%, Als: 0.01-0.025%, B: 0.0005-0.0035%, Ti: 0.01-0.04%, and the balance being Fe and other unavoidable impurities.

[0006] Further, the low alloy structural steel 40MnB has the following chemical composition by weight percentage: C: 0.40-0.43%, Mn: 1.15-1.25%, Si: 0.20-0.30%, P: ≤0.020%, S: ≤0.010%, Cr: ≤0.25%, Mo: ≤0.15%, Cu: ≤0.20%, Ni: ≤0.30%, Als: 0.01-0.025%, B: 0.0010-0.0020%, Ti: 0.01-0.04%.

[0007] Further, the low alloy structural steel 40MnB has the following chemical composition by weight percentage: P: ≤0.015%, S: ≤0.005%, Cr: ≤0.20%, Mo: ≤0.12%, Cu: ≤0.18%, Ni: ≤0.25%.

[0008] The second aspect of the application provides a preparation method of the low alloy structural steel 40MnB, which comprises the following steps: Pretreatment of molten iron: smelting according to the chemical composition; Converter: molybdenum-iron alloy is added into the converter together with scrap steel, and the tapping temperature of the converter is not more than 1650℃; LF furnace: power-on time is 20-30min, total argon blowing time is ≥40min, and white slag retention time is ≥15min; VD / RH furnace: total argon blowing time of the VD / RH furnace is ≥30min; Continuous casting: casting speed is 0.65-0.75m / min, and the average casting speed is 0.70-0.72m / min; Rolling: the temperature of the preheating section is controlled below 850℃, the temperature of the heating section is controlled between 1160-1220℃, and the temperature of the soaking section is controlled between 1160-1200℃.

[0009] Further, the converter tapping goes to the ladle to add 500-600kg / oven of pre-melted synthetic slag, adopts slag blocking ball, slag blocking cap to block slag tapping, and controls the ladle slag thickness ≤50mm.

[0010] Further, the LF furnace is fed with Si-Ca wire or Fe-Ca wire after refining, and the feeding amount is greater than or equal to 500 m.

[0011] Further, the temperature of the molten steel out of the VD / RH furnace and on the continuous casting platform should be ensured to control the tundish temperature to be less than or equal to 25 DEG C for continuous casting, and the temperature of the first casted furnace to be less than or equal to 30 DEG C.

[0012] Further, the continuous casting adopts mold electric stirring, and the current intensity is 400-450 A, and the frequency is 2.5-2.8 Hz.

[0013] Further, the rolling starting temperature is greater than or equal to 1000 DEG C, and / or the finish rolling temperature is greater than or equal to 850 DEG C.

[0014] The third aspect of the present application provides an application of the low alloy structural steel 40MnB on an automobile.

[0015] The present application has the following beneficial effects: The present application increases the carbon content to 0.37-0.44% to improve the strength and hardness of the steel, and at the same time, by accurately controlling the content of other alloying elements such as Mn, Si, B, etc., especially the addition of boron element, and adopting a specific smelting and rolling process, the hardenability and strength of the steel are significantly improved, while the good plasticity and toughness are maintained. Compared with the prior art, the low alloy structural steel 40MnB of the present application has higher yield strength and tensile strength, and at the same time has good impact toughness and welding performance.

[0016] The preparation method of the low alloy structural steel 40MnB of the present application has stable process, is easy to control, is suitable for large-scale industrial production, and has wide application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments or the prior art, the drawings needed to be used in the following embodiment or prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the drawings, and other drawings can be obtained by those skilled in the art without creative labor.

[0018] Figure 1 For low magnification tissue detection Figure One ; Figure 2 For low magnification tissue detection Figure Two .

[0019] The realization of the object of the present application, the functional features and the advantages will be further described with reference to the embodiments and the drawings. DETAILED DESCRIPTION

[0020] In order to make the purposes, technical solutions and advantages of the present application clearer, the present application will be described and illustrated in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and should not be used to limit the present application. Based on the embodiments provided by the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of the present application.

[0021] Obviously, the following description is only some examples or embodiments of the present application, and for those of ordinary skill in the art, the present application can also be applied to other similar scenarios without creative efforts. In addition, it can be understood that although the efforts made in the development process can be complex and lengthy, for those of ordinary skill in the art related to the content disclosed in the present application, some design, manufacture or production changes based on the technical content disclosed in the present application are only routine technical means and should not be understood as insufficient disclosure of the present application.

[0022] If not specifically stated, "including" and "comprising" mentioned in the present application means open or closed. For example, "including" and "comprising" can mean that other components not listed can also be included or contained, or only the listed components can be included or contained.

[0023] The embodiments of the first aspect of the present application provide a low-alloy structural steel 40MnB, the chemical composition of which is as follows: C: 0.37-0.44%, Mn: 1.10-1.40%, Si: 0.17-0.37%, P: ≤0.035%, S: ≤0.035%, Cr: ≤0.30%, Mo: ≤0.15%, Cu: ≤0.30%, Ni: ≤0.30%, Als: 0.01-0.025%, B: 0.0005-0.0035%, Ti: 0.01-0.04%, and the balance is Fe and other unavoidable impurities.

[0024] The various chemical components in the low-alloy structural steel 40MnB described above are strictly controlled to improve the mechanical properties of the low-alloy structural steel 40MnB, wherein the content of C is 0.37-0.44%, and C is the main strengthening element in steel, which improves the strength and hardness of the steel by forming solid solution or carbide. In the low-alloy structural steel 40MnB of the present application, the content of C is controlled in the range of 0.37-0.44%, aiming to achieve a good balance between strength and toughness. This content of C not only ensures that the steel has sufficient strength to meet the demand for high-strength steel in the automotive industry, but also avoids the decrease in toughness and the deterioration of welding performance caused by excessive C content. In addition, C interacts with other alloying elements such as Mn, B, etc. in the steel, further improving the hardenability and comprehensive mechanical properties of the steel.

[0025] The content of Mn is 1.10-1.40%, and Mn is an important alloying element in steel, which significantly improves the strength and toughness of the steel through solid solution strengthening and grain refinement. In the low-alloy structural steel 40MnB of the present application, the content of Mn is controlled in the range of 1.10-1.40%, which not only effectively improves the strength of the steel, but also forms effective strengthening phases with C, B, etc. in the steel, further enhancing the hardenability and comprehensive mechanical properties of the steel. At the same time, the addition of Mn also helps to improve the welding performance and hot working performance of the steel, making the low-alloy structural steel 40MnB of the present application have better machinability and reliability in the manufacturing process of automobile parts.

[0026] The content of Si is 0.17-0.37%, and Si is a deoxidizer and strengthening element, which plays an important role in the low-alloy structural steel 40MnB of the present application. Appropriate amount of Si can improve the strength and hardness of the steel, and also helps to improve the corrosion resistance of the steel. In the low-alloy structural steel 40MnB of the present application, the content of Si is controlled in the range of 0.17-0.37%, which ensures that the steel has sufficient strength without significantly reducing the toughness. In addition, Si interacts with other alloying elements such as Mn, C, etc. in the steel, further improving the comprehensive mechanical properties of the steel.

[0027] The content of P is ≤0.020%, and the content of S is ≤0.010%, both of which are impurity elements in steel, and their content has a significant impact on the mechanical properties of the steel. In the low-alloy structural steel 40MnB of the present application, by strictly controlling the content of P and S, the non-metallic inclusions in the steel can be effectively reduced, and the purity and density of the steel can be improved, thereby further improving the strength and toughness of the steel. This control strategy makes the low-alloy structural steel 40MnB of the present application exhibit more excellent mechanical properties and reliability under complex stress and large load.

[0028] The content of Cr is ≤0.25%, and the content of elements such as Mo, Cu and Ni is also accurately controlled within a certain range. These alloying elements each play an important role, and together improve the comprehensive mechanical properties of the low-alloy structural steel 40MnB. For example, the addition of Mo can further improve the hardenability and thermal strength of the steel, Cu helps to improve the atmospheric corrosion resistance of the steel, and Ni can enhance the low-temperature toughness and fatigue resistance of the steel. Although the content of these elements in the steel is relatively small, their accurate control is crucial to achieving the purpose of the present application.

[0029] In addition, boron, as a trace element, can significantly improve the hardenability of the steel, thereby reducing the use of valuable alloying elements while ensuring the strength of the steel. In the low-alloy structural steel 40MnB of the present application, the content of boron is accurately controlled within the range of 0.0005-0.0035%, which can effectively improve the hardenability of the steel without adversely affecting the toughness of the steel. At the same time, boron interacts with other alloying elements such as C and Mn in the steel, further enhancing the comprehensive mechanical properties of the steel.

[0030] In another preferred embodiment, the low-alloy structural steel 40MnB has the following chemical composition by weight percentage: C: 0.40-0.43%, Mn: 1.15-1.25%, Si: 0.20-0.30%, P: ≤0.020%, S: ≤0.010%, Cr: ≤0.25%, Mo: ≤0.15%, Cu: ≤0.20%, Ni: ≤0.30%, Als: 0.01-0.025%, B: 0.0010-0.0020%, Ti: 0.01-0.04%.

[0031] More preferably, it has the following chemical composition by weight percentage: P: ≤0.015%, S: ≤0.005%, Cr: ≤0.20%, Mo: ≤0.12%, Cu: ≤0.18%, Ni: ≤0.25%.

[0032] The low-alloy structural steel 40MnB, through careful design of the chemical composition and preparation process, ensures its excellent performance in various application scenarios. In particular, by increasing the content of C element and combining with the accurate regulation of alloying elements such as Mn, Si and B, as well as adopting a series of specific smelting and rolling processes, the prepared low-alloy structural steel 40MnB not only has high yield strength and tensile strength, but also exhibits excellent plasticity and toughness.

[0033] Embodiments of the second aspect of the present application provide a method for preparing the low-alloy structural steel 40MnB, comprising the following steps: Pretreatment of molten iron: smelting according to the chemical composition; Converter: molybdenum iron alloy is added into the converter with scrap steel, and the converter tapping temperature is not more than 1650℃; LF furnace: power-on time 20-30min, total argon blowing time ≥40min, white slag retention time ≥15min; VD / RH furnace: total argon blowing time of VD / RH furnace ≥30min; Continuous casting: casting speed 0.65~0.75m / min, typical casting speed 0.70-0.72m / min; Rolling: preheating section temperature controlled below 850℃, heating section temperature controlled between 1160~1220℃, soaking section temperature controlled between 1160~1200℃.

[0034] The preparation method of the low alloy structural steel 40MnB of the application includes various steps from molten iron pretreatment to converter smelting, LF furnace refining, VD / RH furnace vacuum degassing, continuous casting and rolling, etc., all of which adopt advanced process technology and strict quality control measures. The accurate control and mutual cooperation of these preparation steps make the prepared low alloy structural steel 40MnB have excellent organizational structure and mechanical properties.

[0035] Specifically, in the molten iron pretreatment stage, by means of adding desulfurizing agent and dephosphorizing agent, etc., the harmful impurity elements such as sulfur and phosphorus in the molten iron are effectively removed, laying a good foundation for subsequent smelting and refining. In the converter smelting stage, by accurately controlling the smelting temperature and blowing time, etc., molten steel with uniform composition and suitable temperature is obtained. In the LF furnace refining stage, by means of electric heating, argon stirring and white slag retention, etc., the inclusions and gases in the steel are further removed, and the purity and density of the steel are improved. In the VD / RH furnace vacuum degassing stage, by vacuum treatment, the hydrogen and nitrogen gases in the steel are effectively removed, further improving the quality and performance of the steel. In the continuous casting stage, by accurately controlling the casting speed and cooling system, etc., the cast billet with uniform organization and no defects is obtained. In the rolling stage, by accurately controlling the heating temperature, rolling temperature and deformation, etc., the steel product with excellent mechanical properties is obtained.

[0036] In summary, the low alloy structural steel 40MnB of the application realizes the comprehensive improvement of excellent mechanical properties such as high strength, high toughness and good welding performance by accurately controlling the chemical composition and adopting a specific preparation method. The steel has a wide application prospect in the field of automobile manufacturing, especially in the manufacturing of parts requiring high strength materials such as key parts of automobile frame, axle and transmission shaft. At the same time, the preparation method is stable and easy to control, suitable for large-scale industrial production, and has significant economic and social benefits.

[0037] In the embodiment, the molten iron is desulfurized before being poured into the converter, and the slag is removed completely before the molten iron is poured into the converter; the sulfur content of the molten iron is less than or equal to 0.010% after the treatment.

[0038] In the embodiment, the converter further comprises the following control method: the converter cannot be used for smelting when the converter condition is not good, the smoke cover appears, the oxygen lance leaks, and a large area of the converter is repaired; the end-point carbon is controlled to be not less than 0.10%, the blowing times after high-ladle-repairing blowing are not more than 2, and the C-T coordination is ensured for tapping; the ferromolybdenum alloy is added into the converter together with the scrap steel; the Mn-Fe alloy is added completely when 1 / 3 of the molten iron is tapped; 500-600 kg of pre-melted synthetic slag is added into the ladle from the converter; the tapping temperature of the converter is not more than 1650℃; the slag is blocked by the slag-blocking ball and the slag-blocking cap for tapping, and the thickness of the slag in the ladle is controlled to be less than or equal to 50 mm.

[0039] In the embodiment, the control method of the LF furnace comprises the following contents: the bottom blowing effect of the large ladle must be good, and the process conditions for entering the LF furnace are met; the white slag is made by adding CaO, CaF, calcium carbide, aluminum powder and a proper amount of submerged-arc slag for deoxidation and desulfurization, and the bottom blowing effect is good; a proper amount of alloy and carbonizer is added according to the first sample composition of the LF furnace; the molten steel is powered for 20 minutes in the LF furnace, the total argon blowing time is greater than or equal to 40 minutes, and the white slag is kept for greater than or equal to 15 minutes; the Si-Ca wire or the Fe-Ca wire is fed after the refining is completed, and the feeding amount is greater than or equal to 500 m; the soft argon blowing operation is performed on the molten steel before leaving the station, and the soft argon blowing time should be greater than or equal to 10 minutes; the heat preservative is added after the molten steel is refined and the wire is fed.

[0040] In the embodiment, the control method of the VD / RH furnace comprises the following contents: the full-range argon blowing is started when the molten steel enters the VD / RH furnace, and the temperature is measured; the total argon blowing time in the VD / RH furnace is greater than or equal to 30 minutes; the vacuum extraction target is 0.5 tor or less, and the holding time is not less than 15 minutes; the soft blowing time before the molten steel leaves the VD / RH furnace is greater than or equal to 10 minutes; the temperature of the molten steel leaving the station should be ensured to control the tundish temperature of the continuous casting furnace to be less than or equal to 25℃, and the temperature of the starting furnace to be less than or equal to 30℃.

[0041] In the embodiment, the control method of the continuous casting comprises the following contents: the equipment is carefully inspected before starting the casting, and the casting machine should be in good condition, such as the equipment cannot be used for casting production when the arc deviation is large and the roll gap precision is not high; the long nozzle is used for argon protection casting, and the long nozzle should be properly sleeved to ensure the effect; the molten steel in the crystallizer should not be exposed, and the slag should be added and the slag ring should be frequently removed; the casting speed is 0.65-0.75 m / min, and the typical casting speed is 0.70-0.72 m / min; the crystallizer electric stirring is used, the current intensity is 400-450 A, and the frequency is 2.5-2.8 Hz; at least one set of low-multiple sample is taken for each casting; the continuous casting billet should be cooled after production, and the cooling time is greater than or equal to 24 hours; and other operations are strictly performed according to the temporary process and technical operation rules of the wide and thick plate factory about the steel grade.

[0042] Further, the rolling process further includes billet acceptance: rectangular billet, square billet size, weight, appearance and surface quality, etc. The execution of the project standard Q / OHAB107-2007 "Continuous casting square billet technical conditions" is carried out.

[0043] The control method of the rolling process includes the following contents: this steel grade cannot be hot sent and hot charged, and must be cold charged; the preheating section temperature is controlled below 850 DEG C, the heating section temperature is controlled between 1160-1220 DEG C, and the soaking section temperature is controlled between 1160-1200 DEG C; internal control: 1180-1200 DEG C; the time of 300*430 square rectangular billet in the furnace is not less than 240 minutes; the rolling temperature is greater than or equal to 1000 DEG C, and the final rolling temperature is greater than or equal to 850 DEG C. The sharp corners and burrs of the rolling groove, baffle, guide, roller and the like should be polished clean; if it cannot be polished clean, it should be replaced in time; 1# high-pressure water descaling is started in the rolling process; the circular billet cannot be air-cooled on the cooling bed by using the air blower, and must be quickly lowered to the cooling bed. After the circular billet production, it enters the slow cooling pit for slow cooling, and the slow cooling time is greater than 24 hours; finishing and grinding: the operating personnel at each post must operate carefully, do not pull the bending product, and do not scratch the surface; the surface quality is checked for each root, and the defects such as ear, scratch, crack, burr and flash on the surface of the product are polished clean; two low-power samples after slow cooling for 24 hours are taken from each furnace; and other operations are carried out according to the "Temporary process technical operation rules" of the steel grade of the bar material in the second line.

[0044] The third aspect of the application provides an application of the low-alloy structural steel 40MnB in automobiles.

[0045] The low-alloy structural steel 40MnB is very suitable for application in the automobile manufacturing field due to its excellent mechanical properties and good welding performance. Specifically, it can be used to manufacture key components of automobiles that need to bear large loads and complex stress states, such as frames, axles and transmission shafts. By using 40MnB low-alloy structural steel, the strength and toughness of these components can be significantly improved, thereby enhancing the overall structural strength and safety of the automobile.

[0046] In addition, since the 40MnB low-alloy structural steel has good machinability and reliability, it can also be used to manufacture other components of automobiles, such as engine supports, suspension system components and chassis components. These components also require high strength and good toughness to ensure the stability and comfort of the automobile under various road conditions and driving conditions.

[0047] Embodiment The present disclosure is more particularly described in the following examples that are intended purely for illustrative purposes and are not intended to limit the scope of the present disclosure. Various modifications and variations will be apparent to those skilled in the art from the disclosure without departing from the scope of the present disclosure. Unless otherwise stated, all proportions, percentages, and ratios reported in the following examples are by weight. Unless otherwise stated, all reagents used in the examples are available commercially or synthesized according to conventional methods and used as received without further purification. Unless otherwise stated, all equipment used in the examples is available commercially.

[0048] Example 1 A low alloy structural steel 40MnB has the following chemical composition by weight percentage: C: 0.42%, Mn: 1.20%, Si: 0.24%, P: 0.017%, S: 0.001%, Cr: ≤0.15%, Mo: ≤0.05%, Cu: ≤0.12%, Ni: ≤0.13%, Als: 0.022%, B: 0.0018%, Ti: 0.013%.

[0049] A method for preparing the low alloy structural steel 40MnB, comprising the following steps: Pretreatment of molten iron: smelting according to the chemical composition; Converter: molybdenum iron alloy is added into the converter together with scrap steel, the converter tapping temperature is not more than 1650℃, 550kg / furnace of pre-melted synthetic slag is added into the ladle from the converter, the slag blocking ball, the slag blocking cap is used for blocking the slag tapping, and the ladle slag thickness is controlled to be 48mm; LF furnace: power-on time is 25min, total argon blowing time is 50min, white slag maintaining time is 20min, Si-Ca wire or Fe-Ca wire is fed after LF furnace refining is completed, and the feeding amount is 600m; VD / RH furnace: total argon blowing time of the VD / RH furnace is 35 minutes, the temperature of the molten steel out of the station and on the continuous casting platform should be ensured to control the tundish temperature to be 20℃, and the tundish temperature of the starting casting furnace is 25℃; Continuous casting: the casting speed is 0.68m / min, the typical casting speed is 0.70m / min, the continuous casting adopts the crystallizer electric stirring, the current intensity is 400A, and the frequency is 2.5Hz; Rolling: the preheating section temperature is controlled to be below 850℃, the heating section temperature is controlled to be between 1160~1220℃, the soaking section temperature is controlled to be between 1160~1200℃, the starting rolling temperature is 1050℃, and the final rolling temperature is 860℃.

[0050] Example 2 This example is basically the same as example 1, except that Mn: 1.23%, P: 0.014%, B: 0.0019%, Ti: 0.016%, and Als: 0.025%.

[0051] Example 3 This example is substantially the same as Example 1 except that Mn: 1.19%, Si: 0.27%, S: 0.002%, B: 0.0019%, and Als: 0.027%.

[0052] Example 4 This example is substantially the same as Example 1 except that C: 0.41%, Mn: 1.19%, P: 0.014%, Ti: 0.012%, and Als: 0.019%.

[0053] Example 5 This example is substantially the same as Example 1 except that C: 0.41%, Mn: 1.18%, Si: 0.23%, P: 0.014%, Ti: 0.011%, and Als: 0.016%.

[0054] Example 6 This example is substantially the same as Example 1 except that C: 0.40%, Mn: 1.19%, Si: 0.23%, P: 0.020%, B: 0.0017%, Ti: 0.011%, and Als: 0.015%.

[0055] Example 7 This example is substantially the same as Example 1 except that C: 0.40%, Si: 0.25%, B: 0.0015%, Ti: 0.012%, and Als: 0.016%.

[0056] Example 8 This example is substantially the same as Example 1 except that C: 0.41%, Mn: 1.18%, Si: 0.21%, B: 0.0015%, Ti: 0.012%, and Als: 0.017%.

[0057] Example 9 This example is substantially the same as Example 1 except that C: 0.41%, Mn: 1.16%, Si: 0.20%, P: 0.014%, S: 0.002%, B: 0.0017%, Ti: 0.010%, and Als: 0.017%.

[0058] Example 10 This example is substantially the same as Example 1 except that C: 0.41%, Mn: 1.16%, Si: 0.21%, P: 0.016%, S: 0.002%, B: 0.0015%, Ti: 0.013%, and Als: 0.016%.

[0059] Example 11 This embodiment is basically the same as Embodiment 1, except that C: 0.40%, Mn: 1.18%, Si: 0.23%, P: 0.012%, S: 0.002%, B: 0.0016%, Ti: 0.011%, and Als: 0.016%.

[0060] Example 12 This embodiment is basically the same as Embodiment 1, except that C: 0.43%, Mn: 1.17%, P: 0.014%, S: 0.002%, B: 0.0016%, Ti: 0.011%, and Als: 0.013%.

[0061] Example 13 This embodiment is basically the same as Embodiment 1, except that C: 0.41%, Si: 0.22%, P: 0.015%, S: 0.002%, B: 0.0017%, Ti: 0.011%, and Als: 0.016%.

[0062] The 40MnB component control of the above Examples 1-13 is shown in Table 1:

[0063] Experimental Cases 1.1 The chemical components are determined according to the internal control components specified in Table 1, and the chemical component tolerance of the round billet shall comply with the GB / T222 standard.

[0064] 1.2 Surface Quality The steel surface shall not have cracks, scabs, folding inclusions, etc. If there are such defects, they must be removed. The removal depth, calculated from the actual surface of the steel, shall not exceed the steel size tolerance, and the removal width shall not be less than 6 times the depth, and the maximum removal width on the same section shall not be more than one. It is allowed to have individual small scratches, indentation, and pinhole on the actual size, not more than half of the size tolerance.

[0065] 1.3 Macrostructure There shall be no visible shrinkage, bubbles, cracks, inclusions, peeling, white spots, and intergranular cracks on the cross-section acid immersion macrostructure specimen of the steel, and the acid immersion macrostructure shall be rated according to GB / T1979, and shall comply with the requirements of Table 2.

[0066] Table 2 Macrostructure

[0067] 1.4 Hardenability The hardenability sample is 10mm x 10 x 20mm, taken at a radius of 1 / 2, and shall comply with the requirements of Table 3.

[0068] Table 3 Hardenability

[0069] 1.5 Mechanical properties and impact energy The mechanical properties and impact energy of the product shall meet the relevant provisions of GB / T 3077-1999. After the prescribed heat treatment, the longitudinal mechanical properties of the steel are determined according to GB / T 228 and GB / T 229, and the test results shall meet the provisions of Table 4.

[0070]

[0071] The wide and thick plate 40MnB is prepared according to the method of Examples 1-13. During the preparation process, since 40MnB is a B-containing steel, BN compounds are easily generated and gathered on the surface to cause surface cracks. In order to prevent surface cracks, Ti is added to solidify N and improve surface cracks. The addition amount of Ti is controlled to be 0.01-0.02%, and the addition sequence of B-Fe and Ti-Fe is specified. At the end of LF furnace refining, 70 Kg of Ti-Fe alloy is added first, and 5-10 min later, 17-18 Kg of B-Fe alloy is added.

[0072] The alloy steel in Examples 1-5 is rolled with a specification of φ110 mm. The heating furnace is strictly executed according to the process specification of the steel grade. The furnace time is more than 4 h, the rolling process is smooth, no defects are found in the online surface pickling, and after rolling, all tests are qualified, as follows: 1. Macrostructure The macrostructure is uniform and compact, and Figure 1 and Figure 2 are seen.

[0073] 3. Hardenability The hardenability results are shown in Table 6.

[0074] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and embodiments having the same technical idea and playing the same role and effect within the scope of the technical solutions of the present application are all included in the technical scope of the present application. In addition, within the scope of the main idea of the present application, various modifications that can be thought of by those skilled in the art, and other ways constructed by combining part of the components of the embodiments are also included in the scope of the present application.

Claims

1. A low alloy structural steel 40MnB, characterized in that, The chemical composition weight percentage is: C: 0.37~0.44%, Mn: 1.10~1.40%, Si: 0.17~0.37%, P: ≤0.035%, S: ≤0.035%, Cr: ≤0.30%, Mo: ≤0.15%, Cu: ≤0.30%, Ni: ≤0.30%, Als: 0.01~0.025%, B: 0.0005~0.0035%, Ti: 0.01~0.04%, the balance is Fe and other inevitable impurities.

2. The low alloy structural steel 40MnB according to claim 1, characterized in that, The chemical composition weight percentage is: C: 0.40~0.43%, Mn: 1.15~1.25%, Si: 0.20~0.30%, P: ≤0.020%, S: ≤0.010%, Cr: ≤0.25%, Mo: ≤0.15%, Cu: ≤0.20%, Ni: ≤0.30%, Als: 0.01~0.025%, B: 0.0010~0.0020%, Ti: 0.01~0.04%.

3. The low alloy structural steel 40MnB according to claim 1, characterized in that, The chemical composition weight percentage is: P: ≤0.015%, S: ≤0.005%, Cr: ≤0.20%, Mo: ≤0.12%, Cu: ≤0.18%, Ni: ≤0.25%.

4. A method of producing a low alloy structural steel 40MnB according to any one of claims 1-3, characterized in that, It comprises the following steps: Pretreatment of molten iron: smelting according to the chemical composition; Converter: molybdenum iron alloy is added into the converter together with scrap steel, and the tapping temperature of the converter is not more than 1650℃; LF furnace: power-on time is 20-30min, total argon blowing time is ≥40min, and white slag maintaining time is ≥15min; VD / RH furnace: total argon blowing time of VD / RH furnace is ≥30min; Continuous casting: casting speed is 0.65~0.75m / min, and model casting is 0.70-0.72m / min; Rolling: preheating section temperature is controlled below 850℃, heating section temperature is controlled between 1160~1220℃, and soaking section temperature is controlled between 1160~1200℃.

5. The method of producing a low alloy structural steel 40MnB according to claim 4, characterized in that, The converter tapping goes to the ladle to add 500~600kg / oven of pre-melted synthetic slag, adopts slag blocking ball, slag blocking cap to block slag tapping, and controls the ladle slag thickness ≤50mm.

6. The method of producing a low alloy structural steel 40MnB according to claim 4, characterized in that, After the LF furnace refining is completed, Si-Ca wire or Fe-Ca wire is fed, and the feeding amount is ≥500m.

7. The method of producing a low alloy structural steel 40MnB according to claim 4, characterized in that, The VD / RH furnace molten steel outstation temperature on the continuous casting platform should ensure that the tundish temperature continuous casting furnace is ≤25℃, and the tundish temperature start casting furnace is ≤30℃.

8. The method of producing a low alloy structural steel 40MnB according to claim 4, characterized in that, The continuous casting adopts crystallizer electric stirring, current intensity is 400~450A, and frequency is 2.5~2.8Hz.

9. The method of producing a low alloy structural steel 40MnB according to claim 4, characterized in that, The rolling start rolling temperature is ≥1000℃, and / or the finish rolling temperature is ≥850℃.

10. The application of the low-alloy structural steel 40MnB according to any one of claims 1-3 on automobiles.

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