A high surface hardness impact-resistant clad steel plate and a method of manufacturing the same

Abstract

This invention provides a high surface hardness impact-resistant composite steel plate and its manufacturing method. The high surface hardness impact-resistant composite steel plate comprises a low-carbon steel layer and a high-carbon steel layer. The low-carbon steel layer comprises: C: 0.02–0.08, Si: 0.1–0.6, Mn: 1–2, Al: 0.01–0.06, Cr: 0.01–0.8, Mo: 0.01–0.6, Ni: 0.01–1, Nb: 0.001–0.06, Ti: 0.001–0.06. The high-carbon steel layer comprises: C: 0.7–0.9, Si: 0.1–0.5, Mn: 0.2–0.8, Cr: 0.2–1, Al: 0.01–0.05, and at least one of Mo, Ni, RE, Nb, V, and Ti. The high surface hardness impact-resistant composite steel plate of this invention exhibits good wear resistance and good impact resistance.

Description

Technical Field

[0001] This invention relates to the field of metallurgical technology, specifically to a high surface hardness impact-resistant composite steel plate and its manufacturing method. Background Technology

[0002] Due to its high strength, hardness, and excellent wear resistance, high carbon steel is widely used in machinery, chemical industry, construction and other fields.

[0003] High carbon steel can be used to make liners for mechanical equipment or large saw blades. However, due to the poor toughness of high carbon steel parts, they are prone to cracking and breakage after being impacted in the workplace. Furthermore, high carbon steel parts are also prone to fatigue cracks during high-speed and long-term service, which eventually leads to cracking of the steel plate and affects the service life of high carbon steel parts.

[0004] In the current technology for manufacturing high-hardness, high-toughness high-carbon steel parts, a certain amount of elements such as Mn, W, Al, and Ni are generally added to the high-carbon steel.

[0005] Related Patent 1: Patent Application No. 201810794236.5, Heat Treatment Method and Products of Ultra-High Carbon Steel. This patent discloses an ultra-high carbon steel product with the following chemical composition: C: 1.2%–1.6%, Si: 1.2%–1.8%, Mn: 0.3%–0.8%, Cr: 1.2%–1.6%, Ni: 0.3%–0.8%, Mo: 0.2%–0.5%. After diffusion annealing and quenching treatment, a Rockwell hardness of 55 HRC or higher and an impact toughness greater than 20 J / cm² can be obtained. 2 High-carbon steel parts. However, this component has a high C content and alloy content (3.2% to 5.5%), resulting in poor weldability.

[0006] Related Patent 2: Patent Application No. 200910075788.1, Preparation Method of High-Strength, High-Toughness Nanostructured Low-Alloy High-Carbon Steel. This patent discloses a low-alloy high-carbon steel with the following chemical composition: C: 0.7%–0.9%, Si: 1.4%–1.6%, Mn: 1.2%–1.4%, Al: 1.4%–1.6%, Cr: 0.7%–0.9%, W: 0.7%–0.9%, P < 0.02%, S < 0.02%, and the room temperature impact energy of the Charpy-U notched specimen after hot rolling is 7–22 J. However, the high alloy content (5.4%–7.4%) of this composition will directly increase the manufacturing cost of high-carbon steel. Summary of the Invention

[0007] In view of this, the purpose of the present invention is to provide a high surface hardness and impact-resistant composite steel plate with low alloy element content.

[0008] The present invention also provides a method for manufacturing a high surface hardness impact-resistant composite steel plate.

[0009] According to a first aspect of the present invention, the high surface hardness impact-resistant composite steel plate includes a low carbon steel layer and a first high carbon steel layer and a second high carbon steel layer respectively laminated on the upper and lower sides of the low carbon steel layer, wherein the composition and thickness of the first high carbon steel layer and the second high carbon steel layer are independent of each other.

[0010] The low-carbon steel layer comprises, by mass percentage: C: 0.02%–0.08%, Si: 0.10%–0.60%, Mn: 1.00%–2.00%, P≤0.030%, S≤0.010%, Al: 0.010%–0.060%, Cr: 0.010%–0.80%, Mo: 0.01%–0.60%, Ni: 0.01%–1.00%, Nb: 0.001%–0.060%, and Ti: 0.001%–0.060%.

[0011] By mass percentage, the first high-carbon steel layer and the second high-carbon steel layer each comprise at least one of the following: C: 0.70%–0.90%, Si: 0.10%–0.50%, Mn: 0.20%–0.80%, Cr: 0.20%–1.00%, P≤0.030%, S≤0.010%, Al: 0.010%–0.050%, Mo: 0.01%–0.60%, Ni: 0.01%–1.50%, RE: 0.01%–0.08%, Nb: 0.01%–0.060%, V: 0.01%–0.60%, and Ti: 0.001%–0.060%.

[0012] According to another embodiment of the present invention, the high surface hardness impact-resistant composite steel plate includes a low carbon steel layer and a first high carbon steel layer and a second high carbon steel layer respectively laminated on the upper and lower sides of the low carbon steel layer, wherein the composition and thickness of the first high carbon steel layer and the second high carbon steel layer are independent of each other.

[0013] The low-carbon steel layer comprises, by mass percentage: C: 0.02%–0.08%, Si: 0.10%–0.60%, Mn: 1.00%–2.00%, P≤0.030%, S≤0.010%, Al: 0.010%–0.060%, Cr: 0.010%–0.80%, Mo: 0.01%–0.60%, Ni: 0.01%–1.00%, Nb: 0.001%–0.060%, Ti: 0.001%–0.060%, with the balance being Fe and unavoidable impurities;

[0014] The first high-carbon steel layer and the second high-carbon steel layer, by mass percentage, are composed of at least one of the following: C: 0.70%–0.90%, Si: 0.10%–0.50%, Mn: 0.20%–0.80%, Cr: 0.20%–1.00%, P≤0.030%, S≤0.010%, Al: 0.010%–0.050%, Mo: 0.01%–0.60%, Ni: 0.01%–1.50%, RE: 0.01%–0.08%, Nb: 0.01%–0.060%, V: 0.01%–0.60%, and Ti: 0.001%–0.060%, with the balance being Fe and unavoidable impurities.

[0015] Furthermore, the microstructure of the low-carbon steel layer consists of bainite and retained austenite, wherein the volume percentage of retained austenite is 4% to 11%.

[0016] Furthermore, the low-carbon steel layer has a Brinell hardness of 150HB or higher and a Charpy longitudinal impact energy (KV2) of 200J or higher at room temperature.

[0017] Furthermore, the thickness of the low-carbon steel layer is 2mm to 12mm.

[0018] Furthermore, the microstructures of the first high-carbon steel layer and the second high-carbon steel layer are martensite and retained austenite, respectively, wherein the volume percentage of retained austenite is 3% to 10%.

[0019] Furthermore, the Rockwell hardness of the first high-carbon steel layer and the second high-carbon steel layer are both above 55 HRC, and the Charpy longitudinal impact energy KV2 at room temperature are both 10 J to 20 J.

[0020] Furthermore, the thicknesses of the first high-carbon steel layer and the second high-carbon steel layer are 2mm to 12mm, respectively.

[0021] Furthermore, the first high-carbon steel layer and the second high-carbon steel layer are continuously cast billets with the same chemical composition and the same thickness specification.

[0022] A method for manufacturing a high surface hardness impact-resistant composite steel plate according to another embodiment of the present invention includes the following steps:

[0023] S1, according to the composition of the low carbon steel layer, the first high carbon steel layer and the second high carbon steel layer, respectively, are proportioned, smelted and cast to obtain the low carbon steel billet, the first high carbon steel billet and the second high carbon steel billet;

[0024] S2, respectively, perform surface treatment on the surfaces to be contacted of the low carbon steel billet, the first high carbon steel billet and the second high carbon steel billet in step S1;

[0025] S3, the low-carbon steel billet, the first high-carbon steel billet and the second high-carbon steel billet from step S2 are sequentially assembled and rolled to obtain the precast steel plate;

[0026] S4, the precast steel plate from step S3 is subjected to offline quenching treatment to obtain the composite steel plate;

[0027] In step S4, the quenching temperature is 850-950℃, and after water quenching to 100-300℃, tempering is performed at a temperature of 150-350℃.

[0028] Given a holding time of t minutes at the tempering temperature and a composite steel plate thickness of d millimeters, the holding time and the thickness of the composite steel plate satisfy the following relationship:

[0029] t = nd, where n is 2 to 4.

[0030] Furthermore, in step S2, the rust and oxide layers on each of the surfaces to be contacted are removed by machining to a depth of 5mm to 10mm.

[0031] Further, step S3 includes:

[0032] S31, by machining, multiple bevels are formed on the four sides of each of the contact surfaces of the low-carbon steel billet, the first high-carbon steel billet and the second high-carbon steel billet in step S2, and then multiple right-angle holes are formed at each of the bevels by machining, and the multiple right-angle holes are connected to form a vacuum channel.

[0033] S32, the first high-carbon steel billet, the low-carbon steel billet, and the second high-carbon steel billet from step S31 are stacked in order from top to bottom, and then a composite billet is formed by sealing welding.

[0034] S33, Vacuum treatment is performed on the composite blank in step S32;

[0035] S34, Seal the vacuum channel on the composite billet in step S33;

[0036] S35, place the composite blank from step S34 in a heating furnace and heat it to 1000-1250℃, and keep it at that temperature for 1-3 hours;

[0037] S36, the composite billet in step S35 is subjected to vacuum hot rolling. In the vacuum hot rolling step, the initial rolling temperature is 1000-1250℃, the final rolling temperature is 850-950℃, and the reduction rate is ≥50%.

[0038] The above-described technical solution of the present invention has at least one of the following beneficial effects:

[0039] 1. The high surface hardness impact-resistant composite steel plate of this invention includes a low-carbon steel layer and a first high-carbon steel layer and a second high-carbon steel layer composited on the upper and lower sides of the low-carbon steel layer. The composition and thickness of the first and second high-carbon steel layers are independent of each other. The first and second high-carbon steel layers are located on the outer surface of the composite steel plate. The first and second high-carbon steel layers have high strength, hardness, and excellent wear resistance, thereby ensuring the strength, hardness, and wear resistance of the composite steel plate. The low-carbon steel layer is located in the middle inner layer of the composite steel plate. When the outer surface of the composite steel plate is impacted, energy is transferred from the first / second high-carbon steel layer to the low-carbon steel layer. Due to the excellent plasticity and toughness of the low-carbon steel layer, it can absorb the impact energy and improve the impact resistance of the composite steel plate.

[0040] 2. This invention, through the compositional design of a high-surface-hardness, impact-resistant composite steel plate and the optimization of its manufacturing process, specifically through the compositional design of the low-carbon steel layer in the middle of the composite steel plate, can form a microstructure of bainite and retained austenite. This low-carbon steel layer has a Brinell hardness of over 150 HB and a Charpy longitudinal impact energy (KV2) of over 200 J at room temperature, ultimately obtaining a low-carbon steel layer with good plasticity, toughness, and impact resistance. Furthermore, by designing the composition of the upper and lower surfaces of the composite steel plate, a first high-carbon steel layer and a second high-carbon steel layer with high strength, hardness, and wear resistance can be obtained, forming a... The material contains austenite and retained austenite, and the Rockwell hardness of the first high-carbon steel layer and the second high-carbon steel layer are respectively above 55 HRC and the Charpy longitudinal impact energy KV2 at room temperature are respectively 10 J to 20 J. With the optimization of manufacturing method and process parameters, the first high-carbon steel layer and the second high-carbon steel layer are respectively bonded to the upper and lower sides of the low-carbon steel layer by vacuum hot rolling. Finally, a composite steel plate with an overall surface hardness of above 56 HRC and a Charpy longitudinal impact energy KV2 at room temperature of above 100 J can be obtained. This composite steel plate has low cost, high surface hardness and excellent impact resistance. Attached Figure Description

[0041] Figure 1 This is a metallographic image of the first high-carbon steel layer of the high surface hardness impact-resistant composite steel plate according to an embodiment of the present invention.

[0042] Figure 2 This is a metallographic image of the low-carbon steel layer of the high surface hardness impact-resistant composite steel plate according to an embodiment of the present invention. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention are within the scope of protection of the present invention.

[0044] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms "first," "second," and similar terms used in this invention do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Similarly, the terms "an" or "a" and similar terms do not indicate a quantity limitation, but rather indicate the presence of at least one. The terms "connected" or "linked" and similar terms are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. "Up," "down," "left," "right," etc., are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship also changes accordingly.

[0045] The high surface hardness impact-resistant composite steel plate (hereinafter referred to as composite steel plate) of the present invention will be described in detail below.

[0046] The composite steel plate includes a low-carbon steel layer and a first high-carbon steel layer and a second high-carbon steel layer respectively laminated on the upper and lower sides of the low-carbon steel layer. The composition and thickness of the first high-carbon steel layer and the second high-carbon steel layer are independent of each other. By mass percentage, the low-carbon steel layer includes: C: 0.02%~0.08%, Si: 0.10%~0.60%, Mn: 1.00%~2.00%, P≤0.030%, S≤0.010%, Al: 0.010%~0.060%, Cr: 0.010%~0.80%, Mo: 0.01%~0.60%, Ni: 0.01%~1.00%, Nb: 0.001%~0.060%, Ti: 0.001%~0.060%.

[0047] By mass percentage, the first high-carbon steel layer and the second high-carbon steel layer respectively comprise: C: 0.70%–0.90%, Si: 0.10%–0.50%, Mn: 0.20%–0.80%, Cr: 0.20%–1.00%, P≤0.030%, S≤0.010%, Al: 0.010%–0.050%, and Mo: 0.01%–0.60%, Ni: 0.01%–1.50%, RE: 0.01%–0.08%, Nb: 0.01%–0.060%, V: 0.01%–0.60%, and Ti: 0.001%–0.060%.

[0048] It should be noted here that the phrase "the composition and thickness of the first high-carbon steel layer and the second high-carbon steel layer are independent of each other" means that the composition of the first high-carbon steel layer and the second high-carbon steel layer can be the same or different, and similarly, the thickness can be the same or different.

[0049] In other words, the first and second high-carbon steel layers are located on the outer surface of the composite steel plate. Through the composition design described above, the first and second high-carbon steel layers on the outer surface contain more carbon than the middle low-carbon steel layer, giving them higher strength, hardness, and excellent wear resistance, thereby improving the strength, hardness, and wear resistance of the composite steel plate. The low-carbon steel layer is located in the middle inner layer of the composite steel plate. Through the above composition design, the low-carbon steel layer has lower carbon and more manganese, giving it moderate hardness and good toughness, thereby improving the plasticity, toughness, and excellent impact resistance of the composite steel plate.

[0050] Furthermore, the high surface hardness impact-resistant composite steel plate includes a low carbon steel layer and a first high carbon steel layer and a second high carbon steel layer respectively laminated on the upper and lower sides of the low carbon steel layer. The composition and thickness of the first high carbon steel layer and the second high carbon steel layer are independent of each other.

[0051] The low-carbon steel layer, by mass percentage, comprises: C: 0.02%–0.08%, Si: 0.10%–0.60%, Mn: 1.00%–2.00%, P≤0.030%, S≤0.010%, Al: 0.010%–0.060%, Cr: 0.010%–0.80%, Mo: 0.01%–0.60%, Ni: 0.01%–1.00%, Nb: 0.001%–0.060%, Ti: 0.001%–0.060%, with the balance being Fe and unavoidable impurities; the first high-carbon steel layer and the second high-carbon steel layer, by mass percentage, comprise... The composition consists of at least one of the following: C: 0.70%–0.90%, Si: 0.10%–0.50%, Mn: 0.20%–0.80%, Cr: 0.20%–1.00%, P≤0.030%, S≤0.010%, Al: 0.010%–0.050%, Mo: 0.01%–0.60%, Ni: 0.01%–1.50%, RE: 0.01%–0.08%, Nb: 0.01%–0.060%, V: 0.01%–0.60%, and Ti: 0.001%–0.060%, with the balance being Fe and unavoidable impurities.

[0052] In other words, the low-carbon steel layer, the first high-carbon steel layer, and the second high-carbon steel layer each use Fe as the main component element. By adjusting the mass percentage of beneficial elements and controlling the content of unavoidable impurities, the surface hardness and impact resistance of the composite steel plate are improved.

[0053] Specifically, in this invention, the design principles of each chemical element in the low-carbon steel layer, the first high-carbon steel layer, and the second high-carbon steel layer are as follows:

[0054] Carbon (C): Carbon is the most basic and important element in wear-resistant steel. It promotes the formation of martensitic structure in steel through solid solution strengthening and precipitation strengthening, thereby increasing the steel's strength and hardness. If the C content in steel is too low, it cannot guarantee the formation of martensitic structure and the required mechanical and wear-resistant properties, while simultaneously increasing the steel's plasticity and toughness. If the C content in steel is too high, it will increase the tendency for segregation during continuous casting or ingot casting, leading to severe segregation in the steel plate, reducing its toughness, and causing the mechanical properties to fail to meet standards.

[0055] Therefore, in this invention, for obtaining a first high-carbon steel layer and a second high-carbon steel layer with a microstructure consisting mostly of martensite and retained austenite, the mass percentage of carbon in the first high-carbon steel layer and the second high-carbon steel layer is controlled at 0.70% to 0.90%; for obtaining a low-carbon steel layer with a microstructure consisting mostly of bainite and retained austenite, the mass percentage of carbon in the low-carbon steel layer is controlled at 0.02% to 0.08%.

[0056] Si: Appropriate Si is a beneficial deoxidizer in steel. It can form calcium aluminum silicate inclusions that are easy to float together with Ca and Al in steel, thereby improving the purity of steel. Furthermore, the solid solution strengthening effect of Si in ferrite and austenite can improve hardness and strength. However, excessive Si content will lead to a sharp decrease in the toughness of steel.

[0057] Therefore, in this invention, for obtaining a first high-carbon steel layer and a second high-carbon steel layer with a Rockwell hardness of 55 HRC or higher and a room temperature Charpy longitudinal impact energy KV2 of 10 J to 20 J, the mass percentage of Si in the first high-carbon steel layer and the second high-carbon steel layer is controlled at 0.10% to 0.50%; for obtaining a low-carbon steel layer with a Brinell hardness of 150 HB or higher and a room temperature Charpy longitudinal impact energy KV2 of 200 J or higher, the mass percentage of Si in the low-carbon steel layer is controlled at 0.10% to 0.60%.

[0058] Mn: Mn can increase the hardenability of steel, reduce the transformation temperature and critical cooling rate of steel. However, when the Mn content is high, it tends to coarsen the grains and increase the steel's temper brittleness sensitivity. It can also easily lead to segregation and cracks in the billet, reducing the performance of the steel plate.

[0059] Therefore, in this invention, for obtaining a first high-carbon steel layer and a second high-carbon steel layer with a Rockwell hardness of 55 HRC or higher and a room temperature Charpy longitudinal impact energy KV2 of 10 J to 20 J, the mass percentage of Mn in the first high-carbon steel layer and the second high-carbon steel layer is controlled at 0.20% to 0.80%; for obtaining a low-carbon steel layer with a Brinell hardness of 150 HB or higher and a room temperature Charpy longitudinal impact energy KV2 of 200 J or higher, the mass percentage of Mn in the low-carbon steel layer is controlled at 1.00% to 2.00%.

[0060] Cr: Cr can improve the hardenability of steel, as well as its strength and hardness. During tempering, Cr can prevent or slow down the precipitation and aggregation of carbides, thus improving the tempering stability of steel. Cr can also significantly improve corrosion resistance. However, excessive Cr content can impair the low-temperature toughness, impact load fracture characteristics, and bending cold workability of steel plates, especially their weldability.

[0061] Therefore, in this invention, for obtaining a first high-carbon steel layer and a second high-carbon steel layer with a Rockwell hardness of 55 HRC or higher and a room temperature Charpy longitudinal impact energy KV2 of 10 J to 20 J, the mass percentage of Cr in the first high-carbon steel layer and the second high-carbon steel layer is controlled at 0.20% to 1.00%; for obtaining a low-carbon steel layer with a Brinell hardness of 150 HB or higher and a room temperature Charpy longitudinal impact energy KV2 of 200 J or higher, the mass percentage of Cr in the low-carbon steel layer is controlled at 0.010% to 0.80%.

[0062] Ti: Ti is one of the strong carbide-forming elements, forming fine TiC particles with C. The small TiC particles are distributed at the grain boundaries, achieving the effect of refining the grains. The relatively hard TiC particles improve the wear resistance of steel.

[0063] Therefore, in this invention, for the first high-carbon steel layer and the second high-carbon steel layer, which are to obtain Rockwell hardness of 55HRC or higher and Charpy longitudinal impact energy KV2 of 10J to 20J at room temperature, and for the low-carbon steel layer, which are to obtain Brinell hardness of 150HB or higher and Charpy longitudinal impact energy KV2 of 200J or higher at room temperature, the mass percentage of Ti added to the first high-carbon steel layer, the second high-carbon steel layer, and the low-carbon steel layer is controlled to be 0.001% to 0.060%.

[0064] Al: Al can combine with nitrogen in steel to form fine, insoluble AlN particles, refining the steel grain structure. Al can refine the steel grain structure, fix nitrogen and oxygen in the steel, reduce the steel's sensitivity to notches, reduce or eliminate aging phenomena in the steel, and improve the steel's toughness.

[0065] Therefore, in this invention, for obtaining a first high-carbon steel layer and a second high-carbon steel layer with a Rockwell hardness of 55 HRC or higher and a room temperature Charpy longitudinal impact energy KV2 of 10 J to 20 J, the mass percentage of Al in the first high-carbon steel layer and the second high-carbon steel layer is controlled at 0.010% to 0.050%; for obtaining a low-carbon steel layer with a Brinell hardness of 150 HB or higher and a room temperature Charpy longitudinal impact energy KV2 of 200 J or higher, the mass percentage of Al in the low-carbon steel layer is controlled at 0.010% to 0.060%.

[0066] P and S: P is an impurity introduced into steel from pig iron. P can completely dissolve in ferrite, reducing the plasticity and toughness of steel. S is an impurity introduced into steel from pig iron and fuel. Sulfides formed during steel production reduce the mechanical properties of steel, and hot-working fibrous structures are formed during rolling. Therefore, in wear-resistant steel, both P and S are harmful elements, and their content must be strictly controlled.

[0067] Therefore, in this invention, the mass percentage of P in the first high-carbon steel layer, the second high-carbon steel layer, and the low-carbon steel layer is controlled to be ≤0.030%, and the mass percentage of S is controlled to be ≤0.010%.

[0068] Mo: Mo can refine grains and improve strength and toughness. Mo is an element that reduces temper brittleness and can improve tempering stability.

[0069] Therefore, in this invention, for the first high-carbon steel layer and the second high-carbon steel layer, which are to obtain Rockwell hardness of 55HRC or higher and Charpy longitudinal impact energy KV2 of 10J to 20J at room temperature, and for the low-carbon steel layer, which are to obtain Brinell hardness of 150HB or higher and Charpy longitudinal impact energy KV2 of 200J or higher at room temperature, the mass percentage of Mo in the first high-carbon steel layer, the second high-carbon steel layer, and the low-carbon steel layer is controlled at 0.01% to 0.60%.

[0070] Ni: Ni has the effect of significantly reducing the brittle transition temperature, but if the content is too high, it will make it difficult to remove the oxide scale on the surface of the steel plate, and the cost will increase significantly.

[0071] Therefore, in this invention, for the first high-carbon steel layer and the second high-carbon steel layer to obtain a microstructure consisting mostly of martensite and retained austenite, the mass percentage of Ni in the first high-carbon steel layer and the second high-carbon steel layer is controlled between 0.01% and 1.50%; for the low-carbon steel layer to obtain a microstructure consisting mostly of bainite and retained austenite, the mass percentage of Ni in the low-carbon steel layer is controlled between 0.01% and 1.00%.

[0072] Nb: Nb can improve the strength and toughness of steel through grain refinement.

[0073] Therefore, in this invention, for obtaining a first high-carbon steel layer and a second high-carbon steel layer with a Rockwell hardness of 55 HRC or higher and a room temperature Charpy longitudinal impact energy KV2 of 10 J to 20 J, the mass percentage of Nb in the first high-carbon steel layer and the second high-carbon steel layer is controlled at 0.01% to 0.060%; for obtaining a low-carbon steel layer with a Brinell hardness of 150 HB or higher and a room temperature Charpy longitudinal impact energy KV2 of 200 J or higher, the mass percentage of Nb in the low-carbon steel layer is controlled at 0.001% to 0.060%.

[0074] Rare earth elements (REs) (composed of one of La, Ce, and Nd) improve the fluidity of steel, reduce non-metallic inclusions, make the steel structure denser and purer, and have good deoxidation and desulfurization effects, improving anisotropy. REs are particularly effective in high-carbon steel: they can essentially eliminate MnS and Al2O3 inclusions, forming circular or elliptical rare earth sulfides, rare earth oxysulfides, and composite inclusions with Al2O3 as the core and rare earth elements surrounding them. Rare earth elements have low solid solubility in steel and readily segregate at grain boundaries, thus suppressing the segregation of S, P, and their low-melting-point inclusions at grain boundaries. Rare earth elements combine with these inclusions to form high-melting-point composite inclusions, eliminating the harmful effects of low-melting-point inclusions agglomerating at grain boundaries. Rare earth elements can also inhibit columnar crystal growth, refine the as-cast structure, reduce dendritic and regional segregation, and improve the uniformity of the steel's chemical composition. In summary, adding RE can significantly reduce the brittleness of high-carbon steel and improve the toughness and plasticity of steel plates.

[0075] Therefore, in this invention, for obtaining a first high carbon steel layer and a second high carbon steel layer with a microstructure consisting mostly of martensite and retained austenite, the mass percentage of RE in the first high carbon steel layer and the second high carbon steel layer is controlled at 0.01% to 0.08%.

[0076] V: V exists mainly in steel in the form of carbides. Its main function is to refine the steel's microstructure and grain size, thereby reducing the steel's strength and toughness.

[0077] Therefore, in this invention, for obtaining a first high-carbon steel layer and a second high-carbon steel layer with Rockwell hardness of 55 HRC or higher and Charpy longitudinal impact energy KV2 of 10 J to 20 J at room temperature, the mass percentage of V in the first high-carbon steel layer and the second high-carbon steel layer is controlled at 0.01% to 0.60%.

[0078] This invention, through the compositional design of the aforementioned composite steel plate, enables the formation of martensite and retained austenite in the first / second high-carbon steel layer, ensuring a Rockwell hardness of 55 HRC or higher and a room-temperature Charpy longitudinal impact energy (KV2) of 10 J to 20 J. It also enables the formation of bainite and retained austenite in the low-carbon steel layer, ensuring a Brinell hardness of 150 HB or higher and a room-temperature Charpy longitudinal impact energy (KV2) of 200 J or higher. This invention effectively improves the strength, hardness, wear resistance, and impact resistance of the composite steel plate while reducing production costs.

[0079] Furthermore, the microstructure of the low-carbon steel layer consists of bainite and retained austenite, with the retained austenite having a volume percentage of 4% to 11%. In other words, through the above compositional design of the low-carbon steel layer, bainite and retained austenite can be obtained. The bainite and retained austenite with a volume percentage of 4% to 11% formed in the low-carbon steel layer can thus improve the overall impact resistance of the composite steel plate.

[0080] Furthermore, the low-carbon steel layer has a Brinell hardness of over 150 HB and a Charpy longitudinal impact energy (KV2) of over 200 J at room temperature. In other words, through the aforementioned compositional design of the low-carbon steel layer, it possesses excellent impact resistance, thereby further improving the impact resistance of the composite steel plate.

[0081] Furthermore, the thickness of the low-carbon steel layer is 2mm to 12mm. In other words, a low-carbon steel layer thickness of 2mm to 12mm can further improve the impact resistance of the composite steel plate.

[0082] Furthermore, the microstructures of the first high-carbon steel layer and the second high-carbon steel layer are martensite and retained austenite, respectively, with the retained austenite having a volume percentage of 3% to 10%. In other words, through the above compositional design of the first and second high-carbon steel layers, martensite and retained austenite with a volume percentage of 3% to 10% can be obtained, thereby improving the overall strength and surface hardness of the composite steel plate.

[0083] Furthermore, the Rockwell hardness of the first and second high-carbon steel layers is above 55 HRC, and their Charpy longitudinal impact energy (KV2) at room temperature is 10 J to 20 J, respectively. In other words, through the compositional design of the first and second high-carbon steel layers, they possess the advantages of high surface hardness and high wear resistance, thereby further improving the surface hardness and wear resistance of the composite steel plate.

[0084] Furthermore, the thicknesses of the first and second high-carbon steel layers are 2mm to 12mm, respectively. In other words, when the thicknesses of the first and second high-carbon steel layers are 2mm to 12mm, the surface hardness and wear resistance of the composite steel plate can be further improved.

[0085] Furthermore, the first high-carbon steel layer and the second high-carbon steel layer are continuously cast billets with the same chemical composition and thickness. In other words, the first high-carbon steel layer and the second high-carbon steel layer have the same chemical composition and thickness, so the same manufacturing method and process parameters can be used to composite the first high-carbon steel layer and the second high-carbon steel layer onto the upper and lower surfaces of the low-carbon steel layer, which has the advantage of convenient processing and manufacturing.

[0086] This invention also provides a method for manufacturing a high surface hardness impact-resistant composite steel plate, comprising the following steps:

[0087] S1, according to the composition of the low-carbon steel layer, the first high-carbon steel layer, and the second high-carbon steel layer, respectively, the components are proportioned, smelted, and cast to obtain the low-carbon steel billet, the first high-carbon steel billet, and the second high-carbon steel billet; S2, the surfaces to be in contact of the low-carbon steel billet, the first high-carbon steel billet, and the second high-carbon steel billet in step S1 are respectively subjected to surface treatment; S3, the low-carbon steel billet, the first high-carbon steel billet, and the second high-carbon steel billet in step S2 are sequentially assembled and rolled to obtain a precast steel plate; S4, the precast steel plate in step S3 is subjected to offline quenching treatment to obtain a composite steel plate; in step S4, the quenching temperature is 850~950℃, water quenching is performed to 100~300℃ and then tempering is performed, the tempering temperature is 150~350℃; with the holding time at the tempering temperature t minutes and the thickness of the composite steel plate being d millimeters, the holding time and the thickness of the composite steel plate satisfy the following relationship: t=nd, where n is 2~4.

[0088] In other words, optimizing manufacturing process parameters further improves the surface hardness and impact resistance of composite steel plates. Specifically, setting the quenching temperature to 850–950℃ can balance the grain refinement effect of low-carbon steel billets, first high-carbon steel billets, and second high-carbon steel billets, thereby improving the strength and toughness of the composite steel plate; quenching to 100–300℃ can fully form retained austenite, improving toughness and plasticity, and avoiding excessive quenching stress caused by quenching to room temperature, which could lead to cracking of the composite steel plate; tempering at 150–350℃ can eliminate the internal stress of the composite steel plate while maintaining its strength; setting the tempering holding time to t = nd, where n is 2–4, helps the composite steel plate to be fully heated evenly, eliminates internal stress, improves the uniformity of microstructure and properties, and is beneficial for controlling the plate shape.

[0089] Furthermore, in step S2, the rust and oxide layers on each surface to be contacted are removed by machining. The machining depth can be, for example, 5mm, 6mm, 7mm, 8mm, 9mm, or 10mm. In other words, before assembling the billet, the rust and oxide layers on its surface are removed by machining to prevent impurities from being mixed into the composite billet and affecting the overall performance of the composite steel plate.

[0090] Further, step S3 includes: S31, forming multiple bevels on the four sides of each contact surface of the low-carbon steel billet, the first high-carbon steel billet, and the second high-carbon steel billet in step S2 by machining, and then forming multiple right-angle holes at each bevel by machining, with the multiple right-angle holes interconnected to form a vacuum channel; S32, stacking the first high-carbon steel billet, the low-carbon steel billet, and the second high-carbon steel billet in step S31 in a top-to-bottom order, and then forming a composite structure by sealing welding. S33, Vacuum treatment is performed on the composite billet from step S32; S34, Vacuum channels on the composite billet from step S33 are sealed; S35, the composite billet from step S34 is placed in a heating furnace and heated to 1000-1250℃, and held for 1-3 hours; S36, the composite billet from step S35 is vacuum hot rolled, wherein the initial rolling temperature is 1000-1250℃, the final rolling temperature is 850-950℃, and the reduction rate is ≥50%.

[0091] In other words, firstly, the composite billet is rolled using a vacuum hot rolling method. This method facilitates complete metallurgical bonding of the first high-carbon steel billet, the low-carbon steel billet, and the second high-carbon steel billet, resulting in strong bonding and good comprehensive mechanical properties. Furthermore, controlling the process parameters of vacuum hot rolling further enhances the comprehensive mechanical properties of the composite steel plate. Specifically, controlling the heating temperature between 1000 and 1250°C allows carbon and alloying elements to fully diffuse at the composite interface, achieving metallurgical bonding and promoting the homogenization of carbon and alloying elements. A staged controlled rolling method with an initial rolling temperature of 1000–1250°C and a final rolling temperature of 850–950°C fully utilizes the recrystallization and non-recrystallization effects, achieving grain refinement and improving the strength and toughness of the steel. High-reduction rolling with a reduction rate ≥50% further enhances the controlled rolling effect, achieving a grain refinement and strengthening effect.

[0092] This invention, based on a rational chemical composition design and through optimization of the manufacturing method and process parameters of the composite steel plate, can obtain a composite steel plate that combines low cost and good performance. The overall composite steel plate has a surface hardness of 56 HRC or higher, and a room temperature Charpy longitudinal impact energy (KV2) of 100 J or higher, exhibiting advantages such as high strength, high hardness, high wear resistance, good plasticity, toughness, and impact resistance. More specifically, the Rockwell hardness of the first high-carbon steel layer / second high-carbon steel layer of the composite steel plate is 55 HRC or higher, and the room temperature Charpy longitudinal impact energy (KV2) is 10 J to 20 J; the Brinell hardness of the low-carbon steel layer is 150 HB or higher, and the room temperature Charpy longitudinal impact energy (KV2) is 200 J or higher.

[0093] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below.

[0094] Examples 1-3 and Comparative Examples 1-2

[0095] The composite steel plates of Examples 1-3 of the present invention are obtained by the following steps:

[0096] (1) Calculate the margin of the iron billet according to the components and component content shown in Table 1. The content of unavoidable impurities in the iron billet should be considered during the calculation. Then, smelting and casting are carried out to obtain low carbon steel billet, first high carbon steel billet and second high carbon steel billet respectively.

[0097] (2) Remove the rust and oxide layers from the surfaces of the low-carbon steel billet, the first high-carbon steel billet, and the second high-carbon steel billet by machining, with a machining depth of 8 mm.

[0098] (3) The first high-carbon steel billet, the low-carbon steel billet, and the second high-carbon steel billet in step S2 are stacked in order from top to bottom, and then a composite billet is formed by sealing welding.

[0099] Precast steel plates were obtained by rolling composite billets using vacuum hot rolling according to the parameters shown in Table 2 below;

[0100] (4) Perform offline quenching on the rolled precast steel plate according to the parameters shown in Table 2 below.

[0101] The steel plates of Comparative Examples 1-2 were cast according to the composition and composition content shown in Table 1, and rolled and heat-treated using the manufacturing process parameters in Table 2. The difference is that Comparative Examples 1-2 are single-layer slabs.

[0102] Table 1 lists the composition and total amount of corresponding alloying elements of the low-carbon steel layer, the first high-carbon steel layer, the second high-carbon steel layer in the composite steel plates of Examples 1-3, and the steel plates of Comparative Examples 1-2.

[0103] Table 1. Composition and total amount (wt.%) of the low-carbon steel layer, the first high-carbon steel layer, the second high-carbon steel layer, and the steel plates of Comparative Examples 1-3.

[0104]

[0105]

[0106] Table 2 lists the main process parameters of the vacuum hot rolling method and offline quenching treatment of the composite steel plates in Examples 1-3, as well as the main process parameters of the manufacturing method of Comparative Examples 1-2. It is worth noting that the thickness of the steel plate in Comparative Examples 1-2 is 18 mm.

[0107] Table 2 shows the main process parameters for the vacuum hot rolling and offline quenching processes of composite steel plates in Examples 1-3, and the main process parameters for the manufacturing method in Comparative Example 1.

[0108]

[0109] Samples were taken from the low-carbon steel layer, the first high-carbon steel layer, and the second high-carbon steel layer of the composite steel plates obtained in Examples 1-3, as well as the steel plates of Comparative Examples 1-2. Then, hardness tests and room temperature Charpy longitudinal KV2 impact tests were performed on the composite steel plates of Examples 1-3, hardness tests were performed on the steel plate of Comparative Example 1, and room temperature Charpy longitudinal KV2 impact tests were performed on the steel plate of Comparative Example 2. The test results for Examples 1-3 and Comparative Examples 1-2 are shown in Table 3.

[0110] Table 3 lists the hardness test results of the composite steel plate as a whole, the first high-carbon steel layer, the second high-carbon steel layer and the low-carbon steel layer of Examples 1-3, as well as Comparative Example 1.

[0111] Table 3 shows the hardness test results of the composite steel plate as a whole, the first high-carbon steel layer, the second high-carbon steel layer, and the low-carbon steel layer in Examples 1-3, as well as in Comparative Example 1.

[0112]

[0113] In comparison, as shown in Tables 1-3, the total alloy element content of the first high-carbon steel layer, the second high-carbon steel layer, and the low-carbon steel layer in Example 2 of the present invention is 1.869, 2.159, and 2.964, respectively. That is, the total alloy element content of the composite steel plate in Example 2 is <2.964; while the alloy element content of Comparative Example 1 is 2.964. In other words, the alloy element content of Comparative Example 1 is greater than that of Example 2. In the hardness test, the surface hardness of the composite steel plate in Example 2 of the present invention is significantly better than that of Comparative Example 1. That is, compared to Comparative Example 1, the present invention reduces the addition of alloy elements and improves the strength, hardness, and wear resistance of the composite steel plate.

[0114] Table 4 lists the test results of the room temperature Charpy longitudinal impact energy KV2 of the composite steel plate integral, the first high carbon steel layer, the second high carbon steel layer and the low carbon steel layer of Examples 1-3, and Comparative Example 2.

[0115] Table 4 shows the test results of the room temperature Charpy longitudinal impact energy (KV2) of the composite steel plate integral, the first high-carbon steel layer, the second high-carbon steel layer, and the low-carbon steel layer in Examples 1-3, and Comparative Example 2.

[0116]

[0117] In comparison, as shown in Tables 1, 2, and 4, the total alloy element content of the first high-carbon steel layer, the second high-carbon steel layer, and the low-carbon steel layer in Example 3 of the present invention is 2.371, 1.994, and 2.634, respectively. That is, the total alloy element content of the composite steel plate in Example 3 is <2.634; while the alloy element content of Comparative Example 2 is 2.371. In other words, the alloy element content of Example 3 is comparable to that of Example 2. In the impact test, the impact resistance of the composite steel plate of Example 3 of the present invention is better than that of Comparative Example 2. That is, compared with Comparative Example 2, the present invention improves the impact resistance of the composite steel plate.

[0118] As shown in Tables 1-4, by designing the composition of the composite steel plate in this embodiment of the invention and optimizing the manufacturing process, a composite steel plate with good comprehensive mechanical properties can be produced. The overall surface hardness of the composite steel plate is above 56HRC, and the Charpy longitudinal impact energy KV2 at room temperature is above 100J. It has the advantages of high strength, high hardness, high wear resistance, good plasticity, toughness and impact resistance.

[0119] The present invention separately observed the microstructure of the first high-carbon steel layer and the low-carbon steel layer of the composite steel plate of Example 1, and the results are as follows: Figure 1 and 2 As shown. Figure 1 As shown, the microstructure of the first high-carbon steel layer of the composite steel plate in Embodiment 1 of the present invention includes martensite and retained austenite, with a volume percentage of 95% for martensite and 5% for retained austenite; Figure 2 As shown, the microstructure of the low-carbon steel layer of the composite steel plate in Embodiment 1 of the present invention includes bainite and retained austenite, with a volume percentage of bainite of 91% and a volume percentage of retained austenite of 9%.

[0120] In summary, by designing the composition of the composite steel plate and optimizing the manufacturing process, this invention can obtain a high-surface-hardness, impact-resistant composite steel plate that combines low cost and good performance.

[0121] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A high surface hardness impact resistant clad steel plate characterized by, The first high-carbon steel layer and the second high-carbon steel layer are independently in composition and thickness; The low-carbon steel layer comprises, in mass percentage, C: 0.02% to 0.08%, Si: 0.10% to 0.60%, Mn: 1.00% to 2.00%, P≤0.030%, S≤0.010%, Al: 0.010% to 0.060%, Cr: 0.010% to 0.80%, Mo: 0.01% to 0.60%, Ni: 0.01% to 1.00%, Nb: 0.001% to 0.060%, Ti: 0.001% to 0.060%, and the balance of Fe and inevitable impurities; The first high-carbon steel layer and the second high-carbon steel layer respectively comprise, in mass percentage, C: 0.70% to 0.90%, Si: 0.10% to 0.50%, Mn: 0.20% to 0.80%, Cr: 0.20% to 1.00%, P≤0.030%, S≤0.010%, Al: 0.010% to 0.050%, Mo: 0.01% to 0.60%, Ni: 0.01% to 1.50%, RE: 0.01% to 0.08%, Nb: 0.01% to 0.060%, V: 0.01% to 0.60%, Ti: 0.001% to 0.060%; The first high-carbon steel layer and the second high-carbon steel layer are independently in composition and thickness; 2. A high surface hardness impact resistant clad steel plate characterized by, The low-carbon steel layer comprises, in mass percentage, C: 0.02% to 0.08%, Si: 0.10% to 0.60%, Mn: 1.00% to 2.00%, P≤0.030%, S≤0.010%, Al: 0.010% to 0.060%, Cr: 0.010% to 0.80%, Mo: 0.01% to 0.60%, Ni: 0.01% to 1.00%, Nb: 0.001% to 0.060%, Ti: 0.001% to 0.060%, and the balance of Fe and inevitable impurities; ​ The first high-carbon steel layer and the second high-carbon steel layer respectively have the following composition in percentage by mass: C: 0.70% to 0.90%, Si: 0.10% to 0.50%, Mn: 0.20% to 0.80%, Cr: 0.20% to 1.00%, P≤0.030%, S≤0.010%, Al: 0.010% to 0.050%, Mo: 0.01% to 0.60%, Ni: 0.01% to 1.50%, RE: 0.01% to 0.08%, Nb: 0.01% to 0.060%, V: 0.01% to 0.60%, Ti: 0.001% to 0.060%, and the balance of Fe and inevitable impurities. The first high-carbon steel layer and the second high-carbon steel layer respectively have a microstructure of martensite and residual austenite, wherein the volume percentage of the residual austenite is 3% to 10%.

3. The high surface hardness impact-resistant composite steel plate according to claim 1 or 2, characterized by, The low-carbon steel layer has a microstructure of bainite and residual austenite, wherein the volume percentage of the residual austenite is 4% to 11%.

4. The high surface hardness impact-resistant composite steel plate according to claim 1 or 2, characterized by, The low-carbon steel layer has a Brinell hardness of 150 HB or higher and a room-temperature Charpy longitudinal impact energy KV2 of 200 J or higher.

5. The high surface hardness impact-resistant composite steel plate according to claim 1 or 2, characterized by, The low-carbon steel layer has a thickness of 2 mm to 12 mm.

6. The high surface hardness impact-resistant composite steel plate according to claim 1 or 2, characterized by, The first high-carbon steel layer and the second high-carbon steel layer respectively have a Rockwell hardness of 55 HRC or higher and a room-temperature Charpy longitudinal impact energy KV2 of 10 J to 20 J.

7. The high surface hardness impact-resistant composite steel plate according to claim 1 or 2, characterized by, The first high-carbon steel layer and the second high-carbon steel layer respectively have a thickness of 2 mm to 12 mm.

8. The high surface hardness impact-resistant composite steel plate according to claim 1 or 2, characterized by, The first high-carbon steel layer and the second high-carbon steel layer are continuous casting blanks of the same chemical composition and the same thickness specification.

9. The method of producing a high surface hardness impact-resistant clad steel plate according to any one of claims 1 to 8, characterized in that, The method comprises the following steps: S1, proportioning and smelting and casting according to the components of the low-carbon steel layer, the first high-carbon steel layer and the second high-carbon steel layer respectively to obtain low-carbon steel blanks, first high-carbon steel blanks and second high-carbon steel blanks; S2, respectively performing surface treatment on the surfaces to be contacted of the low-carbon steel blanks, the first high-carbon steel blanks and the second high-carbon steel blanks in step S1; S3, sequentially performing grouping and rolling on the low-carbon steel blanks, the first high-carbon steel blanks and the second high-carbon steel blanks in step S2 to obtain a preformed steel plate; S4, performing offline quenching on the preformed steel plate in step S3 to obtain the composite steel plate; In step S4, the quenching temperature is 850 to 950 ℃, and the composite steel plate is quenched in water to 100 to 300 ℃ and then tempered at a temperature of 150 to 350 ℃; The holding time t of the tempering temperature is in minutes, and the thickness d of the composite steel plate is in millimeters, and the holding time and the thickness of the composite steel plate satisfy the following relationship: t = nd, wherein n is 2 to 4.

10. The method of claim 9, wherein, In step S2, the rust layer and the oxide layer of each surface to be contacted are respectively removed by mechanical processing, and the processing depth is 5 mm to 10 mm.

11. The method of claim 10, wherein, The step S3 comprises: S31, forming a plurality of bevels on each surface to be contacted of the low-carbon steel blanks, the first high-carbon steel blanks and the second high-carbon steel blanks in step S2 by mechanical processing, and then forming a plurality of right-angle holes at each bevel by mechanical processing, and the plurality of right-angle holes are connected to form a vacuum channel. S32, the first high carbon steel billet, low carbon steel billet, second high carbon steel billet in step S31 is stacked in order from top to bottom, and a composite billet is formed by sealing welding treatment; S33, the composite billet in step S32 is subjected to vacuumizing treatment; S34, the vacuum channel on the composite billet in step S33 is blocked; S35, the composite billet in step S34 is heated to 1000-1250℃ in a heating furnace, and the temperature is kept for 1-3h; S36, the composite billet in step S35 is subjected to vacuum hot rolling, and in the vacuum hot rolling step, the rolling temperature is 1000-1250℃, the final rolling temperature is 850-950℃, and the reduction is ≥50%.

Images