High hardenability high-carbon boron steel and slab continuous casting production process thereof

Abstract

The present application discloses a high hardenability high-carbon boron steel containing Fe and inevitable impurities, and further containing the following chemical elements with mass percentage as follows: C: 0.3-0.77%, B: 0.01-0.02%, Mn: 1.0-3.0%, Mo: 1.0-2.5%, W: 0.5-1.5%, Cr: 2.0-3.0%, Si: 0.2-1.2%, Ni: 1.0-3.0%, Cu: 2.0-3.0%, Ca: 0.005-0.03%, Re: 0.01-0.1%, Al: 0.05-0.2%, Mg: 0.01-0.1%, N: 0.01-0.02%. In addition, the present application further discloses a slab continuous casting production process of the high hardenability high-carbon boron steel.

Description

Technical Field

[0001] This invention relates to a metallic material and its slab continuous casting process, and more particularly to a high-carbon boron-containing steel and its slab continuous casting process. Background Technology

[0002] As is well known, boron-containing steel is a low-alloy structural steel that uses Mn and B elements as a base to replace Cr and Ni elements. B is a microalloying element; even trace amounts of boron can multiply the hardenability of steel and also achieve excellent mechanical properties. However, while improving the properties of steel, B can also bring difficulties to the continuous casting process. B and N elements in steel may combine to form BN inclusions. When the content of B and N elements in the steel exceeds a certain level, large-sized BN inclusions will precipitate. The precipitation of large-sized BN inclusions increases the susceptibility of the cast billet to cracking and easily causes surface cracks on the surface of the cast billet.

[0003] In the currently designed low-carbon boron-containing steel, the billet of low-carbon boron-containing steel has a low plasticity zone in the temperature range of 700-900℃ and above 1250℃. If the billet temperature during straightening is located in the peak temperature zone of nitride precipitation, it will cause embrittlement of the steel. Cracks are prone to occur at the trough of the vibration mark under straightening deformation.

[0004] Currently, in low-carbon boron-containing steel, surface cracks are usually distributed along grain boundaries. Under certain conditions, carbonitrides will precipitate at the austenite grain boundaries. The coarse grains at the trough of the oscillation mark will exacerbate the precipitation of carbonitrides. These precipitates, as second-phase particles in the steel matrix, are prone to stress concentration when the billet is subjected to stress, forming pores. Subsequently, the pores grow and merge to form cracks.

[0005] Therefore, when boron-containing steel billets are subjected to thermal stress or external force during casting, they are prone to transverse cracks along the bottom of the oscillation mark valley. Due to uneven cooling in the longitudinal and transverse directions, the temperature at the corner of the billet will enter the third brittle zone during the straightening process. Under the dual effects of the oscillation mark notch effect and grain boundary weakening, the corner transverse cracks will further expand and intensify.

[0006] Therefore, in order to solve the quality defects of current manganese-containing steel, this invention aims to obtain a new high hardenability high carbon boron-containing steel and its slab continuous casting production process. The slab continuous casting production process designed in this invention can not only ensure the performance of high hardenability high carbon boron-containing steel, but also effectively improve the quality of continuous casting slabs. Summary of the Invention

[0007] One of the objectives of this invention is to provide a high-hardenability high-carbon boron-containing steel, which has very high hardenability and excellent quality, with a hardenability HRC value ≥70 and an impact energy of ≥150J in the weld heat-affected zone at -20℃. The continuous casting billet prepared by this steel has good surface and center quality and has good prospects for promotion and application value.

[0008] To achieve the above objectives, the present invention provides a high-hardenability, high-carbon, boron-containing steel containing Fe and unavoidable impurity elements, and further containing the following chemical elements in the following mass percentages:

[0009] C: 0.3~0.77%, B: 0.01~0.02%, Mn: 1.0~3.0%, Mo: 1.0~2.5%, W: 0.5~1.5%, Cr: 2.0~3.0%, Si: 0.2~1.2%, Ni: 1.0~3.0%, Cu: 2.0~3.0%, Ca: 0.005~0.03%, Re: 0.01~0.1%, Al: 0.05~0.2%, Mg: 0.01~0.1%, N: 0.01~0.02%.

[0010] Furthermore, in the high hardenability high-carbon boron-containing steel described in this invention, the mass percentage content of each chemical element is as follows:

[0011] C: 0.3–0.77%, B: 0.01–0.02%, Mn: 1.0–3.0%, Mo: 1.0–2.5%, W: 0.5–1.5%, Cr: 2.0–3.0%, Si: 0.2–1.2%, Ni: 1.0–3.0%, Cu: 2.0–3.0%, Ca: 0.005–0.03%, Re: 0.01–0.1%, Al: 0.05–0.2%, Mg: 0.01–0.1%, N: 0.01–0.02%; balance Fe and unavoidable impurities.

[0012] The design principles of each chemical element in the high hardenability high-carbon boron-containing steel described in this invention are as follows:

[0013] C: In the high hardenability high-carbon boron-containing steel described in this invention, as the austenite carbon content increases, the critical cooling rate of the steel decreases significantly, its critical quenching diameter increases, and its hardenability is significantly improved. However, it should be noted that the carbon content in the steel should not be too high. Considering the crack sensitivity of hypereutectoid steel continuously cast billets, the carbon content in the steel should not exceed 0.77%. Based on this, considering the influence of carbon content on the properties of steel, in the high hardenability high-carbon boron-containing steel of this invention, the mass percentage of carbon is controlled between 0.3% and 0.77%.

[0014] Of course, in some preferred embodiments, in order to obtain better implementation results, the mass percentage content of element C can be further preferably controlled between 0.40% and 0.70%.

[0015] B: In the high hardenability high-carbon boron-containing steel described in this invention, B is the main element for improving the hardenability of the steel. Adding even a trace amount of B can significantly improve the hardenability of the steel. B dissolved in austenite can also increase hardenability. Furthermore, B tends to segregate at the interfaces of austenite grains, reducing the interfacial energy of the austenite grain boundaries and decreasing the nucleation rate during the decomposition of supercooled austenite. Therefore, adding an appropriate amount of B to the steel can effectively delay the decomposition transformation of supercooled austenite. It should be noted that the B content in the steel should not be too high. When the B content is too high, borides will appear in the steel, which will decrease the hardenability, increase brittleness, and enhance the crack sensitivity of the continuously cast billet. Therefore, to maximize the beneficial effects of B, the mass percentage of B in the high hardenability high-carbon boron-containing steel described in this invention is controlled between 0.01% and 0.02%.

[0016] Of course, in some preferred embodiments, in order to obtain better implementation results, the mass percentage content of element B can be further preferably controlled between 0.012% and 0.018%.

[0017] Mn: In the high hardenability high-carbon boron-containing steel described in this invention, Mn not only improves the hardenability of the steel, but it is also a carbide-forming element. When the Mn content in the steel exceeds 1.0%, its effect on increasing the hardenability of the steel is very significant. When austenite transforms into pearlite, alloy cementite is formed. At this time, the distribution of manganese between the ferrite and cementite phases at the austenite-pearlite interface can delay the decomposition of austenite, thus significantly increasing hardenability. Therefore, to maximize the beneficial effects of Mn, the mass percentage of Mn in the high hardenability high-carbon boron-containing steel described in this invention is controlled between 1.0% and 3.0%.

[0018] Of course, in some preferred embodiments, in order to obtain better implementation results, the mass percentage content of Mn element can be further preferably controlled between 1.5% and 2.5%.

[0019] Mo: In the high hardenability high carbon boron steel described in this invention, the addition of an appropriate amount of Mo can effectively improve the hardenability of the steel, especially in high carbon steel. Specifically, Mo can combine with elements such as C and Fe to form composite carbides M2C. M2C is a metastable carbide, which can be decomposed into two stable carbides, MC and M6C, when heated, thus improving the hot plasticity and toughness of high carbon boron steel.

[0020] Meanwhile, molybdenum and nickel have a strong interaction. During the pearlite transformation, Mo can form special carbides or alloy cementite and redistribute itself between the transformation products carbides and ferrite, thus effectively delaying the pearlite transformation. However, it should be noted that the Mo content in steel should not be too high. When the Mo content in steel is too high, excessive molybdenum is prone to forming intermetallic compounds with chromium.

[0021] Based on this, considering the influence of Mo on the properties of steel, the mass percentage of Mo in the high hardenability high carbon boron steel of the present invention is controlled between 1.0% and 2.5%.

[0022] Of course, in some preferred embodiments, in order to obtain better implementation results, the mass percentage content of Mo element can be further preferably controlled between 1.5% and 2.0%.

[0023] W: In the high hardenability high-carbon boron-containing steel described in this invention, W can combine with elements such as C and Fe to form composite carbides M6C, which precipitate as dispersed, fine carbides during subsequent heat treatments such as quenching and tempering, improving hardenability and hardening performance. Simultaneously, the carbides not dissolved in the matrix can hinder austenite grain growth, thus refining the grain size. Considering the continuous casting castability of tungsten-containing steel, the amount of tungsten added to the steel should not be too high. Therefore, to maximize the beneficial effects of tungsten, the mass percentage of W in the high hardenability high-carbon boron-containing steel described in this invention is controlled between 0.5% and 1.5%.

[0024] Of course, in some preferred embodiments, in order to obtain better implementation results, the mass percentage content of W element can be further preferably controlled between 0.5% and 1.2%.

[0025] Cr: In the high hardenability high-carbon boron-containing steel described in this invention, adding an appropriate amount of Cr can effectively improve the hardenability of the steel. The hardenability effect of Cr in steel is slightly lower than that of Mn, and its effect is best in medium and high carbon steels. Cr in steel can both hinder the transformation of austenite to ferrite during pearlite transformation and delay the formation of cementite, thereby significantly increasing hardenability. Therefore, considering the influence of Cr on the properties of steel, the mass percentage of Cr in the high hardenability high-carbon boron-containing steel described in this invention is controlled between 2.0% and 3.0%.

[0026] Of course, in some preferred embodiments, in order to obtain better implementation results, the mass percentage content of Cr element can be further preferably controlled between 2.2% and 2.8%.

[0027] Si: In the high hardenability high-carbon boron-containing steel described in this invention, adding an appropriate amount of Si can effectively increase the hardenability of high-carbon austenitic steel. Si is a non-carbide-forming element, and it does not dissolve in cementite during austenite decomposition. Silicon atoms need to diffuse before cementite nucleation and growth can occur. Therefore, Si can delay the pearlite transformation of high-carbon austenite and increase hardenability. To maximize the beneficial effects of Si, the mass percentage of Si in the high hardenability high-carbon boron-containing steel described in this invention is controlled between 0.2% and 1.2%.

[0028] Of course, in some preferred embodiments, in order to obtain better implementation results, the mass percentage content of Si element can be further preferably controlled between 0.5% and 1.0%.

[0029] Ni: In the high hardenability high-carbon boron-containing steel described in this invention, Ni, like Mn, can also increase the hardenability of the steel, and there is a strong interaction between nickel and molybdenum. Therefore, to maximize the beneficial effects of Ni, the mass percentage of Ni in the high hardenability high-carbon boron-containing steel described in this invention is controlled between 1.0% and 3.0%.

[0030] Of course, in some preferred embodiments, in order to obtain better implementation results, the mass percentage content of Ni element can be further preferably controlled between 1.0% and 2.0%.

[0031] Cu: In the high hardenability high-carbon boron-containing steel described in this invention, in addition to its inherent solid solution strengthening effect, the addition of Cu alters the precipitate phase structure of the alloy, making the aged microstructure more dispersed and uniform, thereby improving both the strength and plasticity of the steel. Simultaneously, the addition of an appropriate amount of Cu to the steel also plays a positive role in its resistance to stress corrosion. However, it should be noted that the Cu content in the steel should not be too high. As the mass fraction of Cu in high-carbon steel increases, the high quenching sensitivity problem will occur. Therefore, considering the influence of Cu on the steel's properties, in this invention, the mass percentage of Cu is controlled between 2.0% and 3.0%.

[0032] Of course, in some preferred embodiments, in order to obtain better implementation results, the mass percentage content of Cu element can be further preferably controlled between 2.0% and 2.5%.

[0033] Ca: In the high hardenability high-carbon boron-containing steel described in this invention, on the one hand, the addition of an appropriate amount of Ca can interact with segregating elements such as B, Si, and Mo, which can significantly improve the hardenability of high-carbon steel; on the other hand, by controlling the nucleation of BN and (Ca,Mn)S inclusions during the welding cooling process, the microstructure of the weld heat-affected zone is refined, thereby improving the microstructure properties of the weld heat-affected zone. Based on this, in order to maximize the beneficial effects of Ca, the mass percentage of Ca in the high hardenability high-carbon boron-containing steel described in this invention is controlled between 0.005% and 0.03%.

[0034] Of course, in some preferred embodiments, in order to obtain better implementation results, the mass percentage content of Ca element can be further preferably controlled between 0.01% and 0.02%.

[0035] Re: In the high hardenability high-carbon boron-containing steel described in this invention, rare earth element Re is the most surface-active element. It preferentially segregates at grain boundaries. As the carbon content in the steel increases, the number of grain boundaries and cementite increases, making it difficult for bainite and proeutectoid ferrite to nucleate, thereby improving the hardenability of the steel. Therefore, in the high hardenability high-carbon boron-containing steel described in this invention, the mass percentage of Re element is controlled between 0.01% and 0.1%.

[0036] Of course, in some preferred embodiments, in order to obtain better implementation results, the mass percentage content of Re element can be further preferably controlled between 0.02% and 0.06%.

[0037] Al: In the high hardenability high-carbon boron-containing steel described in this invention, Al acts as a deoxidizer, effectively removing oxidation. Simultaneously, Al can combine with Nitrogen (N) to form AlN, which refines the grain size. It is important to note that the Al content in the steel should not be too high. Excessive Al content leads to the precipitation of numerous fine AlN particles along grain boundaries, reducing the austenite grain boundary strength and increasing the likelihood of grain boundary cracking under stress. Therefore, the Al content must be controlled within a reasonable range. For this reason, in the high hardenability high-carbon boron-containing steel described in this invention, the mass percentage of Al is controlled between 0.05% and 0.2%.

[0038] Of course, in some preferred embodiments, in order to obtain better implementation results, the mass percentage content of Al element can be further preferably controlled between 0.1% and 0.2%.

[0039] Mg: In the high hardenability high-carbon boron-containing steel described in this invention, Mg can not only act as pinning particles to prevent austenite grain growth, but also improve the impact toughness of the weld heat-affected zone of the high-carbon boron-containing steel. Therefore, in the high hardenability high-carbon boron-containing steel described in this invention, the mass percentage of Mg is controlled between 0.01% and 0.1%.

[0040] Of course, in some preferred embodiments, in order to obtain better implementation results, the mass percentage content of Mg element can be further preferably controlled between 0.02% and 0.05%.

[0041] N: In the high hardenability high-carbon boron-containing steel described in this invention, adding an appropriate amount of nitrogen (N) can effectively improve the processing performance of the steel. However, it should be noted that an increase in the N content in the steel can also increase the sensitivity of the continuously cast billet to transverse cracks in the continuous casting process. Furthermore, in the high hardenability high-carbon boron-containing steel described in this invention, the mass percentage of N is controlled between 0.01% and 0.02%.

[0042] Of course, in some preferred embodiments, in order to obtain better implementation results, the mass percentage content of N element can be further preferably controlled between 0.01% and 0.018%.

[0043] Furthermore, in the high hardenability high-carbon boron-containing steel described in this invention, the mass percentage content of each chemical element also satisfies the following:

[0044] 2.0% ≤ Mo + W ≤ 3.0%;

[0045] B / N≥0.8.

[0046] In the above-mentioned technical solution of the present invention, while controlling the mass percentage content of a single chemical element, the inventors further preferably controlled the mass percentage content of some elements to satisfy: "2.0% ≤ Mo + W ≤ 3.0%" and "B / N ≥ 0.8".

[0047] In this invention, the sum of the mass percentages of Mo and W elements is controlled between 2.0% and 3.0% because: if the Mo+W content is too high, the high-carbon boron-containing steel has poor thermal stability, is prone to decarburization during subsequent hot working and heat treatment, and has a narrow and difficult-to-control hot working temperature range; if the Mo+W content is too low, the number of composite carbides is small and the distribution is uneven, making it difficult to simultaneously meet the requirements for improving plasticity and hardenability. Therefore, in some preferred embodiments, to obtain better implementation effects, the mass percentages of Mo and W elements can be further preferably controlled to meet the following: 2.5% ≤ Mo+W ≤ 3.0%.

[0048] Accordingly, controlling the mass percentage content of B and N elements to satisfy "B / N≥0.8" ensures that N is mainly fixed by B, thereby avoiding excessive AlN precipitation along grain boundaries and reducing the tendency of transverse cracks at the corners of continuously cast billets. Therefore, in some preferred embodiments, to achieve even better implementation results, it is further preferable to control B / N≥1.

[0049] Furthermore, in the high hardenability high carbon boron steel described in this invention, among the unavoidable impurities, P ≤ 0.04% and S ≤ 0.02%.

[0050] In the above technical solution, P and S elements are impurity elements in the high hardenability high carbon boron steel of the present invention. When technical conditions permit, in order to obtain steel with better performance and higher quality, the content of impurity elements in the high hardenability high carbon boron steel should be reduced as much as possible.

[0051] In this invention, phosphorus and sulfur are both harmful elements, capable of forming low-melting-point brittle substances and increasing the tendency for surface cracking in the prepared continuously cast billets. Therefore, in this invention, the content of P and S elements in the steel must be strictly controlled, specifically controlled as follows: P ≤ 0.04%, S ≤ 0.02%.

[0052] Furthermore, in the high hardenability high-carbon boron-containing steel described in this invention, the mass percentage content of each chemical element also satisfies at least one of the following conditions:

[0053] C: 0.40~0.70%,

[0054] B: 0.012~0.018%,

[0055] Mn: 1.5–2.5%,

[0056] Mo: 1.5–2.0%,

[0057] W: 0.5–1.2%,

[0058] Cr: 2.2-2.8%,

[0059] Si: 0.5–1.0%,

[0060] Ni: 1.0~2.0%,

[0061] Cu: 2.0–2.5%,

[0062] Ca: 0.01–0.02%,

[0063] Re: 0.02~0.06%,

[0064] Al: 0.1-0.2%,

[0065] Mg: 0.02–0.05%,

[0066] N: 0.01~0.018%.

[0067] Furthermore, in the high hardenability high-carbon boron-containing steel described in this invention, the mass percentage content of each chemical element also satisfies the following:

[0068] 2.5% ≤ Mo + W ≤ 3.0%;

[0069] B / N≥1.

[0070] Furthermore, in the high hardenability high carbon boron steel described in this invention, its hardenability HRC value is ≥70, and the impact energy of the weld heat-affected zone at -20℃ is ≥150J.

[0071] Accordingly, another objective of the present invention is to provide a continuous casting production process for high-hardenability high-carbon boron-containing steel slabs. This slab continuous casting production process can effectively improve the quality of high-hardenability high-carbon boron-containing steel continuous casting slabs. The continuously casting slabs produced by this process have excellent characteristics such as good surface and center quality. It can give full play to the advantages of continuous casting production, effectively suppress the generation of depressions and cracks in the slabs, significantly improve the surface and center quality of the slabs, and also realize multi-furnace continuous casting.

[0072] To achieve the above objectives, the present invention proposes a continuous casting production process for high hardenability high-carbon boron-containing steel slabs, wherein the process parameters for controlling the continuous casting process satisfy at least one of the following:

[0073] The target temperature for the second cooling zone is controlled above 1000℃;

[0074] The secondary cooling system uses a weak cooling ratio water volume control of 0.2–0.4 L / kg;

[0075] The average casting speed is controlled at 2.0–2.8 m / min.

[0076] The electromagnetic stirring current of the crystallizer is 500-700A;

[0077] The secondary cooling electromagnetic stirring current is 1500–2500A, and the stirring frequency is 2.0–4.0Hz;

[0078] The continuously cast billets are directly hot-charged and fed into the furnace at a temperature exceeding 800℃.

[0079] In the slab continuous casting process described in this invention, upon entering the secondary cooling zone, precipitates such as alloy nitrides and borides form at the austenite grain boundaries. Furthermore, considering that the austenite-to-ferrite transformation to intergranular ferrite occurs as the temperature decreases, significantly reducing the hot plasticity of the continuously cast slab, this invention aims to ensure the quality of the continuously cast slab by controlling the target temperature of the secondary cooling zone above 1000°C and controlling the amount of weak cooling water used in the secondary cooling zone between 0.2 and 0.4 L / kg.

[0080] In the slab continuous casting process designed in this invention, in some embodiments, a slab thickness × slab width of (200-300) mm × (900-2350) mm can be obtained. To meet the target temperature of over 1000℃ in the secondary cooling zone, the average casting speed must be controlled to be higher than 2.0 m / min during continuous casting. However, it should be noted that the average casting speed should not be too high. When the average casting speed is too high, the initial slab shell is thin, the slab cooling is uneven, and cracks are easily generated. Therefore, in this invention, the average casting speed is controlled between 2.0 and 2.8 m / min.

[0081] To improve the aggregation problem of precipitates such as BN during continuous casting, this invention incorporates electromagnetic stirring in the crystallizer and secondary cooling zone. If the electromagnetic stirring current in the crystallizer is below 500A and the electromagnetic stirring current in the secondary cooling zone is below 1500A, it has no effect on improving the precipitation behavior during continuous casting. However, when the electromagnetic stirring current in the crystallizer is controlled above 700A and the electromagnetic stirring current in the secondary cooling zone is controlled above 2500A, the liquid level in the crystallizer fluctuates significantly, and negative segregation is prone to occur in the cast billet. Therefore, to ensure the quality of the continuously cast billet, the inventors conducted extensive experimental verification, specifically controlling the electromagnetic stirring current in the crystallizer to 500–700A, the electromagnetic stirring current in the secondary cooling zone to 1500–2500A, and the stirring frequency to 2.0–4.0Hz.

[0082] Accordingly, to prevent the re-precipitation of boron-containing steel and other precipitates during hot rolling in the furnace, it is necessary to ensure that the temperature of the boron-containing steel entering the furnace is above the A3 temperature line (the transformation temperature from austenite to ferrite). Considering issues such as non-equilibrium superheat, after multiple field tests and verifications, controlling the hot charging temperature above 800℃ can effectively avoid defects such as post-rolling surface peeling. Therefore, in this invention, the obtained continuously cast billet is directly hot-charged, and the furnace charging temperature of the hot-charged billet is controlled above 800℃.

[0083] Furthermore, in the slab continuous casting production process described in this invention, the secondary cooling water ratio is controlled at 0.25–0.35 L / kg.

[0084] Furthermore, in the slab continuous casting production process described in this invention, the average casting speed is controlled to be 2.2–2.6 m / min.

[0085] Furthermore, in the slab continuous casting production process described in this invention, the electromagnetic stirring current of the crystallizer is 550-650A.

[0086] Furthermore, in the slab continuous casting production process described in this invention, the electromagnetic stirring current of the secondary cooling system is 1600–2200 A, and the stirring frequency is 2.5–3.5 Hz.

[0087] Compared with existing technologies, the high hardenability high-carbon boron-containing steel and its slab continuous casting production process described in this invention have the following advantages and beneficial effects:

[0088] Compared with existing technologies, the continuous casting process for producing high-hardenability, high-carbon, boron-containing steel slabs developed in this invention features superior surface and center quality of the continuously cast slab. It not only fully leverages the advantages of continuous casting but also suppresses crack formation in the slab, significantly improving the surface and center quality. Furthermore, it enables continuous casting across multiple furnaces. This technology is a key technology for achieving continuous casting production and quality assurance of high-hardenability, high-carbon, boron-containing steel slabs.

[0089] In this invention, the high hardenability high carbon boron steel prepared by using the chemical composition and slab continuous casting production process designed by the inventor has very high hardenability and excellent quality. Its hardenability HRC value is ≥70, and the impact energy of the welding heat-affected zone at -20℃ is ≥150J. Its slab continuous casting does not produce longitudinal cracks or corner transverse cracks, and the surface and center quality of the continuous casting slab are good.

[0090] The slab continuous casting production process designed in this invention has excellent application value. Using this slab continuous casting production process can effectively assist enterprises in the production and experimental development of boron-containing products, and can improve enterprise capacity, reduce production costs, and enhance the overall competitiveness of enterprises. It has excellent application value. Detailed Implementation

[0091] The following will further explain and illustrate the high hardenability high carbon boron-containing steel and its slab continuous casting production process described in this invention with reference to specific embodiments. However, this explanation and illustration do not constitute an improper limitation on the technical solution of this invention.

[0092] Examples 1-6

[0093] Table 1 lists the mass percentage of each chemical element in the high hardenability high carbon boron-containing steels of Examples 1-6.

[0094] Table 1. (wt%, balance Fe and other unavoidable impurities besides P and S)

[0095]

[0096] Table 2 lists the calculated composition ratios of some elements in the high hardenability high-carbon boron-containing steels of Examples 1-6.

[0097] Table 2.

[0098]

[0099] Note: In the above formulas “Mo+W” and “B / N”, each element should be substituted with its corresponding chemical element mass percentage.

[0100] Accordingly, in this invention, the continuous casting production process of high hardenability high-carbon boron-containing steel slabs in Examples 1-6 of this invention all include the following steps:

[0101] In the continuous casting process, the target temperature of the secondary cooling zone is controlled above 1000℃, and the amount of weak cooling water used in the secondary cooling zone is controlled at 0.2-0.4 L / kg, preferably further controlled at 0.25-0.35 L / kg; when the slab thickness × slab width is (200-300) mm × (900-2350) mm, the average casting speed is controlled at 2.0-2.8 m / min, preferably further controlled at 2.2-2.6 m / min;

[0102] Electromagnetic stirring is performed in the crystallizer and the secondary cooling zone. In the electromagnetic stirring process of the crystallizer and the secondary cooling zone, the electromagnetic stirring current of the crystallizer is controlled at 500-700A, the electromagnetic stirring current of the secondary cooling zone is controlled at 1500-2500A, and the stirring frequency is 2.0-4.0Hz. Of course, in order to obtain better implementation results, the electromagnetic stirring current of the crystallizer can also be preferably controlled at 550-650A, the electromagnetic stirring current of the secondary cooling zone is controlled at 1600-2200A, and the stirring frequency is 2.5-3.5Hz.

[0103] Finally, the obtained continuous casting billets are directly hot-charged, and the charging temperature is specifically controlled to be higher than 800℃.

[0104] Tables 3 and 4 list the specific process parameters for manufacturing the high hardenability high-carbon boron-containing steels of Examples 1-6.

[0105] Table 3.

[0106]

[0107] Table 4.

[0108]

[0109] In order to demonstrate that the slab produced by the slab continuous casting process designed in this invention has good quality, the inventors sampled the slabs of Examples 1-6 prepared by the above-mentioned slab production process and tested the quality of the slabs of Examples 1-6. The test results are listed in Table 5 below.

[0110] The relevant testing methods are as follows:

[0111] Slab quality inspection: The slabs of each embodiment were evaluated according to the low magnification performance test method of continuous casting slabs using the "YB / T 4003-2016 Low magnification microstructure defect rating chart of continuous casting steel slabs" to determine whether the slabs of each embodiment had cracks or center segregation levels.

[0112] Table 5 lists the billet quality test results of the high hardenability high carbon boron-containing steels in Examples 1-6.

[0113] Table 5.

[0114] serial number billet quality Example 1 No cracks, Class A center segregation 1.5 Example 2 No cracks, Class A center segregation 0.5 Example 3 No cracks, Class A center segregation 1.0 Example 4 No cracks, Class A center segregation 0.5 Example 5 No cracks, Class A center segregation 1.0 Example 6 No cracks, Class A center segregation 1.5

[0115] It is easy to see from the quality inspection results in Table 5 above that the slabs of Examples 1-6 prepared by the slab continuous casting production process designed in this invention all have good quality, with no obvious cracks and the center segregation level is all within the range of 1.5.

[0116] Therefore, the continuous casting production process of high hardenability high carbon boron steel slabs described in this invention can effectively improve the quality of continuous casting slabs of high hardenability high carbon boron steel. The continuous casting slabs produced have excellent characteristics such as good surface and center quality, which can give full play to the advantages of continuous casting production, effectively suppress the generation of cracks in the slab, significantly improve the surface and center quality of the slab, and also realize multi-furnace continuous casting, thereby effectively improving the production efficiency of enterprises.

[0117] Accordingly, after completing the above-mentioned billet quality inspection for Examples 1-6, in order to demonstrate that the slab continuous casting production process with optimized chemical composition designed in this invention can achieve good performance, the inventors sampled the high hardenability high carbon boron steels of Examples 1-6 and tested the hardenability and weld heat-affected zone impact energy of the high hardenability high carbon boron steels of each example. The test results are listed in Tables 6 and 7, respectively.

[0118] The relevant hardenability performance test results are as follows: The hardenability of the high hardenability high carbon boron steels in Examples 1-6 was measured according to the "End Quenching Test Method (Jominy Test) for Hardenability of Steel" in GB / T 225-2006.

[0119] The relevant test results of the impact energy performance of the weld heat-affected zone are as follows: According to GB / T 229—2020 Metallic Materials Charpy Pendulum Impact Test Method, the impact energy of the weld heat-affected zone of the high hardenability high carbon boron steel in Examples 1-6 at -20℃ was measured.

[0120] Table 6 lists the hardenability test results of the high hardenability high-carbon boron-containing steels in Examples 1-6.

[0121] Table 6.

[0122] serial number Hardness HRC Example 1 70 Example 2 83 Example 3 78 Example 4 76 Example 5 72 Example 6 74

[0123] As can be seen from Table 6, in this invention, the high hardenability high carbon boron steels of Examples 1-6 all have very high hardenability, with hardenability ≥70HRC, and specifically between 70 and 83HRC.

[0124] Table 7 lists the test results of the impact energy performance of the weld heat-affected zone of the high hardenability high carbon boron steels in Examples 1-6.

[0125] Table 7.

[0126] serial number Impact energy (J) (-20℃) Example 1 150 Example 2 170 Example 3 166 Example 4 162 Example 5 155 Example 6 159

[0127] As can be seen from Table 7, in this invention, the high hardenability high carbon boron steels of Examples 1-6 all have very high impact toughness, and the impact energy of the weld heat-affected zone at -20℃ is ≥150J, specifically between 150 and 170J.

[0128] In summary, it can be seen that the high hardenability high-carbon boron-containing steel prepared by the inventor's chemical composition and slab continuous casting production process has very high hardenability and excellent quality. Its hardenability HRC value is ≥70, and the impact energy of the welding heat-affected zone at -20℃ is ≥150J. Its slab continuous casting does not produce longitudinal cracks or corner transverse cracks, and the surface and center quality of the continuous casting slab are good.

[0129] The slab continuous casting production process designed in this invention has excellent application value. Using this slab continuous casting production process can effectively assist enterprises in the production and experimental development of boron-containing products, and can improve enterprise capacity, reduce production costs, and enhance the overall competitiveness of enterprises. It has excellent application value.

[0130] It should be noted that the scope of protection of the prior art in this invention is not limited to the embodiments given in this application. All prior art that does not contradict the solution of this invention, including but not limited to prior patent documents, prior publications, prior public uses, etc., can be included in the scope of protection of this invention.

[0131] Furthermore, the combination of the technical features in this case is not limited to the combination methods described in the claims of this case or the combination methods described in the specific embodiments. All technical features described in this case can be freely combined or combined in any way, unless they contradict each other.

[0132] It should also be noted that the embodiments listed above are merely specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and similar changes or modifications made thereto are those that can be directly derived or easily conceived by those skilled in the art from the content disclosed in the present invention, and should all fall within the protection scope of the present invention.

Claims

1. A high-hardenability, high-carbon, boron-containing steel, characterized in that, Its mass percentage content of each chemical element is as follows: C: 0.3~0.77%, B: 0.01~0.02%, Mn: 1.0~3.0%, Mo: 1.0~2.5%, W: 0.5~1.5%, Cr: 2.0~3.0%, Si: 0.2~1.2%, Ni: 1.0~3.0%, Cu: 2.0~3.0%, Ca: 0.005~0.03%, Re: 0.01~0.1%, Al: 0.05~0.2%, Mg: 0.01~0.1%, N: 0.01~0.02%; the balance is Fe and unavoidable impurities. Its mass percentage content of each chemical element also meets the following requirements: 2.0%≤Mo+W≤3.0%; B / N≥0.

8.

2. The high hardenability high-carbon boron-containing steel as described in claim 1, characterized in that, In unavoidable impurities, P ≤ 0.04% and S ≤ 0.02%.

3. The high hardenability high-carbon boron-containing steel as described in claim 1, characterized in that, Its mass percentage content of each chemical element also satisfies at least one of the following conditions: C：0.40~0.70%， B：0.012~0.018%， Mn: 1.5~2.5%, Mo: 1.5~2.0%, W：0.5~1.2%， Cr：2.2~2.8%， Si: 0.5~1.0%, Ni: 1.0~2.0%, Cu: 2.0~2.5%, Ca: 0.01~0.02%, Re: 0.02~0.06%, Al：0.1~0.2%， Mg: 0.02~0.05%, N：0.01~0.018%。 4. The high hardenability high-carbon boron-containing steel as described in claim 1, characterized in that, Its mass percentage content of each chemical element also meets the following requirements: 2.5%≤Mo+W≤3.0%; B / N≥1.

5. The high hardenability high-carbon boron-containing steel as described in claim 1, characterized in that, Its hardenability HRC value is ≥70, and the impact energy of the weld heat-affected zone at -20℃ is ≥150J.

6. A continuous casting process for producing high-hardenability, high-carbon, boron-containing steel slabs as described in any one of claims 1-5, characterized in that, The process parameters for the continuous casting process must satisfy at least one of the following: The target temperature for the second cooling zone is controlled above 1000℃; The secondary cooling system uses a weak cooling ratio with a water flow rate controlled at 0.2~0.4L / kg; The average casting speed is controlled at 2.0~2.8 m / min; The electromagnetic stirring current of the crystallizer is 500~700A; The secondary cooling electromagnetic stirring current is 1500~2500A, and the stirring frequency is 2.0~4.0Hz; The continuously cast billets are directly hot-charged and fed into the furnace at a temperature exceeding 800℃.

7. The slab continuous casting production process as described in claim 6, characterized in that, The secondary cooling system uses a very weak cooling ratio with a water volume control of 0.25~0.35L / kg.

8. The slab continuous casting production process as described in claim 6, characterized in that, The average casting speed is controlled at 2.2~2.6 m / min.

9. The slab continuous casting production process as described in claim 6, characterized in that, The electromagnetic stirring current of the crystallizer is 550~650A.

10. The slab continuous casting production process as described in claim 6, characterized in that, The secondary cooling electromagnetic stirring current is 1600~2200A, and the stirring frequency is 2.5~3.5Hz.

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