High-strength wear-resistant steel with excellent low-temperature toughness and method for manufacturing the same

Abstract

This invention relates to a high-strength wear-resistant steel with excellent low-temperature toughness and its preparation method, belonging to the field of iron and steel metallurgical technology. It solves the technical problem of uneven low-temperature toughness and strength in existing low-alloy wear-resistant steels used under low-temperature conditions. The high-strength wear-resistant steel with excellent low-temperature toughness, by mass percentage, comprises: C: 0.1~0.2%, Si: 1.25~1.85%, Mn: 1.2~1.6%, Cr: 1.2~1.8%, Ti: 0.02~0.05%, Nb: 0.02~0.04%, Al: 0.02~0.08%, B: 0.0004~0.003%, Y: 0.001~0.034%, P≤0.018%, S≤0.008%, N≤0.006%, O≤0.003%, with the balance being Fe and unavoidable impurities. The wear-resistant steel of the present invention absorbs Charpy V-notch impact energy above 13J at -20°C, which is 9.0-24.8% higher than the yttrium-free wear-resistant steel with the same basic composition as the present invention; the wear-resistant steel of the present invention has a minimum tensile strength of 1350MPa at -20°C, which is 5.8-10.6% higher than the yttrium-free wear-resistant steel with the same basic composition as the present invention.

Description

Technical Field

[0001] This invention belongs to the field of iron and steel metallurgy technology, and specifically relates to a high-strength wear-resistant steel with excellent low-temperature toughness and its preparation method. Background Technology

[0002] Low-alloy wear-resistant steels are widely used in mining machinery and engineering equipment due to their excellent strength-toughness balance and wear resistance. For steels used in low-temperature conditions (such as -20℃), excellent low-temperature toughness is required in addition to wear resistance. For low-alloy wear-resistant steels requiring low-temperature toughness, the composition is usually slightly adjusted based on conventional low-alloy wear-resistant steels. For example, the NM400D / E composition is obtained by lowering the upper limit of C and increasing the upper limits of Mo and Als based on the NM400 composition, while also imposing corresponding restrictions on the upper limit of carbon equivalent. Although lowering the carbon equivalent is beneficial for improving low-temperature toughness, it also affects the strength and hardness of the steel to varying degrees.

[0003] Therefore, some existing technologies have broken through the carbon equivalent limitation and improved low-temperature toughness by increasing alloy content and strengthening heat treatment process, resulting in wear-resistant steel with excellent low-temperature toughness. However, the strength data of the steel is rarely disclosed, and it is unclear how to achieve the balance between low-alloy wear-resistant steel and low-temperature toughness and strength. Summary of the Invention

[0004] In view of the above-mentioned technical status, the present invention provides a high-strength wear-resistant steel with excellent low-temperature toughness and its preparation method, so as to solve the technical problem of balancing the low-temperature toughness and strength of low-alloy wear-resistant steel used in low-temperature working conditions.

[0005] The objective of this invention is mainly achieved through the following technical solutions:

[0006] On the one hand, the present invention provides a high-strength wear-resistant steel with excellent low-temperature toughness. The composition of the wear-resistant steel, by mass percentage, is as follows: C: 0.1~0.2%, Si: 1.25~1.85%, Mn: 1.2~1.6%, Cr: 1.2~1.8%, Ti: 0.02~0.05%, Nb: 0.02~0.04%, Al: 0.02~0.08%, B: 0.0004~0.003%, Y: 0.001~0.034%, P≤0.018%, S≤0.008%, N≤0.006%, O≤0.003%, with the balance being Fe and unavoidable impurities.

[0007] Furthermore, based on mass percentage, the composition of wear-resistant steel is as follows: C: 0.15~0.17%, Si: 1.55~1.65%, Mn: 1.3~1.5%, Cr: 1.35~1.55%, Ti: 0.02~0.04%, Nb: 0.02~0.04%, Al: 0.05~0.07%, B: 0.001~0.003%, Y: 0.01~0.02%, P≤0.005%, S≤0.005%, N≤0.004%, O≤0.002%, with the balance being Fe and unavoidable impurities.

[0008] Furthermore, the microstructure of wear-resistant steel consists of lath martensite, bainite, and proeutectoid ferrite distributed in a chain-like discontinuous pattern.

[0009] On the other hand, the present invention also provides a method for preparing the above-mentioned wear-resistant steel, comprising the following steps: Step 1: First, put pure iron and ferrochrome into a crucible for induction melting, perform electromagnetic stirring and purify with argon gas, then add other alloy raw materials in sequence, refine at high temperature and cast into a billet. Step 2: After heating and holding the billet at the desired temperature, forge it into a square billet; Step 3: Heat and keep the billet at a constant temperature, then roll it into a sheet through multiple passes; Step 4: Immediately after rolling, water cooling is performed, followed by slow cooling.

[0010] Furthermore, in step 1, the order in which the other alloy raw materials are added is as follows: C, Si, Mn, Nb, Ti, B, Al, Y. The next raw material is added after the previous alloy raw material has been added and melted.

[0011] Furthermore, Y is added as follows: after adding Al, Y is added at an interval of 1 to 4 minutes.

[0012] Furthermore, in step 1, the high-temperature refining temperature is controlled at 1580~1650℃, and the time is 3~8 minutes.

[0013] Furthermore, in step 2, the heating is carried out in the furnace to a temperature of 1230~1270℃, the heating rate is 7~9℃ / min, and the holding time is 50~70min.

[0014] Furthermore, in step 3, the rolling process consists of 4 passes, with the final rolling temperature controlled at 850~890℃.

[0015] Furthermore, in step 4, the water cooling termination temperature is controlled at 500±25℃; the slow cooling method is to place it in an insulated box to slowly cool to room temperature.

[0016] Compared with the prior art, the present invention can achieve at least one of the following technical effects: (1) By adding rare earth element Y, the present invention utilizes the strong affinity of Y with O and S to transform the long strip MnS and sharp Al2O3 inclusions in steel into fine and round rare earth oxysulfides or rare earth composite inclusions; and the addition of Y homogenizes the lath martensite and bainite matrix structure, thereby reducing the crack initiation sensitivity of the steel. The wear-resistant steel maintains high strength and high hardness while significantly improving low-temperature impact toughness.

[0017] (2) This invention significantly improves hardenability and regulates precipitation through the synergistic alloying of high silicon, high chromium, manganese and boron, enabling the steel plate to quickly pass the dangerous zone of pearlite transformation during the water cooling stage after rolling, and enter slow cooling at around 500℃ after water cooling ends, which can form a multiphase structure mainly composed of bainite and martensite. Bainite provides toughness and martensite provides hardness, thereby significantly improving low-temperature impact toughness while ensuring high hardness. In addition, the small number of chain-like discontinuous proeutectoid ferrites in this invention can passivate crack tips and change crack paths, thereby regulating the phase transformation strain of the surrounding matrix structure and having a toughness buffering effect.

[0018] (3) In the wear-resistant steel of the present invention, the proportion of inclusions with a size of less than 2µm is more than 50%; the proportion of inclusions with a size of ≥8µm is less than 2%. Among them, the proportion of Y inclusions is more than 80%, and the proportion of MnS and aluminum inclusions is less than 20%, which significantly reduces the amount of MnS and aluminum inclusions. The wear-resistant steel of this invention has a Charpy V-notch impact absorption energy of over 13 J at -20°C, which is 9.0-24.8% higher than that of yttrium-free wear-resistant steel with the same basic composition as this invention. The wear-resistant steel of this invention has a room temperature tensile strength of over 1280 MPa and a minimum elongation after fracture of 15%, which is 0.2-6.1% higher than that of yttrium-free wear-resistant steel with the same basic composition as this invention. The wear-resistant steel of this invention has a minimum tensile strength of 1350 MPa at -20°C and a minimum elongation after fracture of 16.5%, which is 5.8-10.6% higher than that of yttrium-free wear-resistant steel with the same basic composition as this invention.

[0019] (4) The wear-resistant steel of the present invention absorbs more than 13J of Charpy V-notch impact energy at -20℃, which is 9.0~24.8% higher than the wear-resistant steel without yttrium with the same basic composition of the present invention; the wear-resistant steel of the present invention has a minimum tensile strength of 1350MPa at -20℃, which is 5.8~10.6% higher than the wear-resistant steel without yttrium with the same basic composition of the present invention. Attached Figure Description

[0020] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0021] Figure 1 The graph shows the Gibbs free energy ΔG generated by typical inclusions Y2O3, Y2O2S, YS, Y2S3 and Al2O3 in the steel of this invention as a function of temperature.

[0022] Figure 2 This is a microstructure diagram of the wear-resistant steel in Example 1.

[0023] Figure 3 The image shows the SEM-EDS image of inclusions in the wear-resistant steel of Example 1.

[0024] Figure 4 The bar chart shows the statistical results of the composition and quantity of inclusions in the wear-resistant steel of Example 1 and Comparative Example 1.

[0025] Figure 5 The bar chart shows the statistical results of the size and quantity of inclusions in the wear-resistant steel of Example 1 and Comparative Example 1.

[0026] Figure 6 The image shows the SEM-EDS image of inclusions in the wear-resistant steel of Comparative Example 1. Detailed Implementation

[0027] The following detailed description, in conjunction with specific embodiments, provides a high-strength wear-resistant steel with excellent low-temperature toughness and its preparation method. These embodiments are for comparative and illustrative purposes only, and the present invention is not limited to these embodiments.

[0028] The inventors discovered that existing low-alloy wear-resistant steels, such as NM400 and NM400D / E, mainly rely on traditional Al deoxidation and Ca treatment as the main inclusion control technologies. However, these methods are not effective in eliminating long strip-shaped MnS and sharp-angled Al2O3 composite inclusions. These highly hard and brittle inclusions with high mismatch degree are prone to stress concentration, becoming crack initiation sources and seriously damaging the strength and low-temperature impact toughness of the steel.

[0029] Accordingly, based on the traditional NM400 series steel, this invention proposes a high-strength wear-resistant steel with excellent low-temperature toughness. Its composition, by mass percentage, is: C: 0.1~0.2%, Si: 1.25~1.85%, Mn: 1.2~1.6%, Cr: 1.2~1.8%, Ti: 0.02~0.05%, Nb: 0.02~0.04%, Al: 0.02~0.08%, B: 0.0004~0.003%, Y: 0.001~0.034%, P≤0.018%, S≤0.008%, N≤0.006%, O≤0.003%, with the balance being Fe and unavoidable impurities.

[0030] The basis for the design of the components of this invention is as follows: Carbon (C) is a fundamental element ensuring the hardness of materials. It ensures wear resistance through solid solution strengthening and the formation of martensitic structures; however, excessive addition significantly degrades weldability and heat-affected zone (HAZ) toughness. This design controls the carbon content at a low to medium level of 0.1%–0.2%, aiming to balance strength and toughness. A lower carbon content effectively reduces the adverse effects of brittle carbides, significantly improving the material's low-temperature impact toughness and weldability, and is a key prerequisite for achieving high toughness. Examples of C contents include 0.1%, 0.11%, 0.12%, 0.13%, 0.14%, 0.15%, 0.16%, 0.17%, 0.18%, 0.19%, and 0.2%.

[0031] Silicon (Si), as a strong solid solution strengthening element and deoxidizer, is typically set at a relatively high level of 1.25% to 1.85%. This range effectively improves strength, inhibits the precipitation of brittle cementite, and promotes the formation of a more resilient lath bainite / martensite multiphase structure, thus contributing positively to overall mechanical properties. Examples of Si contents include 1.25%, 1.30%, 1.40%, 1.50%, 1.60%, 1.70%, 1.80%, and 1.85%.

[0032] It should be noted that silicon, as a strong solid solution element, also has a significant regulatory effect on phase transformation and precipitation. The conventional Si content does not exceed 1%, while this invention increases the Si content to 1.25~1.85%. Its key purpose is not only to strengthen the structure, but also to inhibit the nucleation and growth of cementite during slow cooling, so that the carbides are smaller and more dispersed, which helps to obtain a more uniform bainite and martensite structure. When the Si content exceeds 1.85%, it is easy to bring about the risk of embrittlement of the hot working surface and structure, which is detrimental to the welding performance.

[0033] Manganese (Mn) is a key element for improving hardenability, ensuring a uniform martensitic / bainitic microstructure in the steel cross-section after rolling or heat treatment. A medium-to-high content range of 1.2% to 1.6%, working synergistically with silicon and chromium, is sufficient to guarantee uniform hardening of the microstructure while also controlling overheating sensitivity. Examples of Mn contents include 1.20%, 1.30%, 1.35%, 1.40%, 1.45%, 1.50%, 1.55%, and 1.60%.

[0034] Chromium (Cr) is mainly used to further improve the hardenability and tempering stability of steel, and to form carbides with carbon to enhance wear resistance. A Cr content of 1.2% to 1.8% forms a good combination with manganese and silicon, jointly constructing an alloy framework that ensures high strength and high hardness of the matrix. Examples of Cr contents include 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, and 1.8%.

[0035] It should be noted that the conventional Cr content does not exceed 1.2%. This invention increases the chromium content while maintaining high silicon content. The synergy between high chromium and high silicon can improve the stability of the microstructure. Silicon strengthens the matrix, while chromium forms a hard phase and refines the microstructure. At the same time, both improve the hardenability of the steel. Combined with the heat treatment process of this invention, a multiphase microstructure with a balance of strength and toughness can be obtained. At the same time, the residual stress and cracking risk caused by full quenching can be reduced. Excessive Cr will lead to coarsening of carbides and a decrease in toughness, as well as an increase in cost. Therefore, the upper limit is set at 1.8%.

[0036] Titanium (Ti) is a strong carbonitride forming element. Its addition within this range primarily aims to form high-temperature stable TiN or Ti(C,N) particles, effectively pinning austenite grain boundaries and preventing their high-temperature growth, thereby refining the final microstructure and laying the microstructural foundation for simultaneously improving strength and toughness. This invention limits the Ti content to 0.02~0.05%, such as 0.02%, 0.022%, 0.029%, 0.031%, 0.039%, 0.041%, 0.049%, 0.05%, etc.

[0037] Niobium (Nb), along with titanium, is an important microalloying element. Its precipitation in austenite can suppress recrystallization, refine grains, and produce a significant precipitation strengthening effect during phase transformation. A content of 0.02–0.04% aims to synergize with titanium to achieve optimal grain refinement and avoid excessive amounts that could lead to carbide coarsening; examples include Nb contents of 0.02%, 0.025%, 0.031%, 0.035%, and 0.04%.

[0038] Aluminum (Al) is primarily used as a deoxidizer here. A content of 0.02% to 0.08% is sufficient to complete the smelting deoxidation, forming Al₂O₃. In yttrium-containing steel, this nascent Al₂O₃ can be modified by subsequently added yttrium, and its content is controlled at a level that completes the basic deoxidation function without generating excessive harmful inclusions. For example, Al contents of 0.02%, 0.03%, 0.04%, 0.05%, 0.054%, 0.06%, 0.07%, 0.079%, and 0.08% are used.

[0039] Boron (B) is an extremely efficient hardenability-enhancing element; even trace amounts can significantly delay ferrite nucleation at austenite grain boundaries. Its content range is critical; the lower limit must ensure hardenability, while the upper limit must strictly prevent the formation of brittle borides that severely impair toughness, reflecting the principles of precision alloying. This invention limits the B content to 0.0004~0.003%, such as 0.0004%, 0.0005%, 0.0007%, 0.0009%, 0.0011%, 0.0019%, 0.0021%, 0.0029%, and 0.003%.

[0040] Yttrium (Y) is the core innovative element of this design. Its mechanism of action is as follows: utilizing its extremely strong affinity for oxygen and sulfur, it transforms harmful elongated MnS and sharp-angled Al2O3 inclusions into fine, rounded, and thermodynamically stable rare earth compounds, fundamentally eliminating crack initiation sites; simultaneously, the solid-solidified yttrium also refines the grain size. The rare earth Y content ranges from 0.001% to 0.034%, with the lower limit ensuring sufficient oxygen and sulfur levels typical of modified steel, and the upper limit preventing the formation of coarse rare earth inclusions. This is crucial for achieving breakthroughs in low-temperature toughness under high hardness. Examples of Y content include 0.001%, 0.0021%, 0.0031%, 0.0041%, 0.0051%, 0.0061%, 0.0071%, 0.0079%, 0.0081%, 0.010%, 0.019%, 0.021%, and 0.034%.

[0041] Phosphorus (P) is a harmful element in steel. Excessive P in steel will lead to a decrease in low-temperature toughness, but excessive control will increase smelting costs. Therefore, this invention limits the P content to below 0.018%, such as below 0.015% or below 0.010%.

[0042] Sulfur (S) is a harmful element in steel. S in steel precipitates in the form of MnS. In high-strength steel, MnS becomes the starting point for damage, leading to deterioration of toughness. However, excessive control increases smelting costs. Therefore, this invention limits the S content to below 0.008%, such as below 0.005%.

[0043] While nitrogen (N) can form fine precipitates with Nb, Ti, Al, etc., pinning heated austenite grains and thus inhibiting grain coarsening and improving low-temperature toughness, this effect requires precise control of alloying elements and nitrogen content to be significant. Furthermore, increasing the amount of dissolved N can impair the toughness of the base material and the weld heat-affected zone. Therefore, this invention limits the N content to below 0.006%, such as below 0.0049%.

[0044] Oxygen (O) forms oxides with Al and other elements, affecting the strength and toughness of materials. When the O content exceeds 0.003%, inclusions increase, impairing strength and toughness. Therefore, this invention limits the O content to below 0.003%, such as below 0.0019%.

[0045] Furthermore, the composition of the high-strength wear-resistant steel with excellent low-temperature toughness of the present invention is optimized. According to the mass percentage, its composition is: C: 0.15~0.17%, Si: 1.55~1.65%, Mn: 1.3~1.5%, Cr: 1.35~1.55%, Ti: 0.02~0.04%, Nb: 0.02~0.04%, Al: 0.05~0.07%, B: 0.001~0.003%, Y: 0.01~0.02%, P≤0.005%, S≤0.005%, N≤0.004%, O≤0.002%, with the balance being Fe and unavoidable impurities.

[0046] Secondly, this invention proposes a method for preparing the above-mentioned wear-resistant steel, comprising the following steps: Step 1: First, put pure iron and ferrochrome into a crucible for induction melting, perform electromagnetic stirring and purify with argon gas, then add other alloy raw materials in sequence, refine at high temperature and cast into a billet. Step 2: After heating and holding the billet at the desired temperature, forge it into a square billet; Step 3: Heat and keep the billet at a constant temperature, then roll it into a sheet through multiple passes; Step 4: Immediately after rolling, water cooling is performed, followed by slow cooling.

[0047] Specifically, in step 1, after the pure iron and ferrochrome in the crucible have completely melted into liquid, electromagnetic stirring is performed for 3 to 5 minutes, and then protective argon gas is introduced into the furnace. The order of adding other alloying materials is as follows: C→Si→Mn→Nb→Ti→B→Al→Y. Each alloying material is added and melted before the next is added. After adding Al, a 1-4 minute interval is observed before finally adding rare earth Y. C, Si, and Mn are the basic elements of steel; adding them first allows for rapid alloying and initial deoxidation. Nb and Ti are then added, preferentially forming carbonitrides with N. B is added after Nb and Ti to avoid the formation of BN, thus maintaining the added trace amounts of B and improving hardenability. Al, as the final deoxidizer, needs to be added after alloying. After Al deoxidation, Y is added a few minutes later to modify sulfide inclusions and deoxidation inclusions. The presence of inclusions is a prerequisite for its addition, especially deoxidation inclusions; adding Y before deoxidation would cause it to react with oxygen and be largely consumed, contradicting the purpose of adding Y.

[0048] The high-temperature refining process employs electromagnetic stirring, with the refining temperature controlled at 1580~1650℃ and the time at 3~8 minutes. The casting temperature is controlled at 1530~1580℃, and the material is poured into a cylindrical mold cavity.

[0049] Specifically, in step 2, after the ingot is demolded, the riser is cut off, the outer diameter is machined, and the furnace is heated to 1230~1270℃, such as 1241℃, 1251℃, 1261℃, etc., with a heating rate of 7~9℃ / min. Then, it is held at the temperature for 50~70min, and then forged into a square billet with a cross section of 150mm×40mm.

[0050] Specifically, in step 3, the billet is heated in the furnace to 1230~1270℃, such as 1241℃, 1251℃, 1261℃, etc., and then held at that temperature for 50~70 minutes; the rolling process consists of 4 passes, with a reduction rate of 30~36% per pass, to roll into an 8mm thick steel plate; the final rolling temperature is controlled at 850~890℃.

[0051] Specifically, in step 4, the water cooling termination temperature is controlled at 500±25℃; the slow cooling method is to place it in an insulated box to slowly cool to room temperature, with a cooling rate of 0.2~0.4℃ / min.

[0052] It should be noted that conventional wear-resistant steels often employ a full quenching process, water-cooling to below the Ms point, to obtain a large amount of martensite. However, this method easily introduces significant stress, increasing the risk of deformation and cracking, and may degrade low-temperature toughness due to an excessively high martensite ratio. This invention significantly improves hardenability and controls precipitation through a synergistic alloying process of high silicon, high chromium, manganese, and boron. This allows the steel plate to quickly pass through the dangerous zone of pearlite transformation during the post-rolling water-cooling stage, and then undergoes slow cooling at around 500°C after water cooling terminates. This results in the formation of a multiphase structure dominated by bainite and martensite. Bainite provides toughness, while martensite provides hardness, thus significantly improving low-temperature impact toughness while maintaining high hardness. Therefore, the quenching temperature of this invention is controlled above the Ms point.

[0053] The microstructure of the high-strength wear-resistant steel with excellent low-temperature toughness of the present invention consists of lath martensite, bainite, and chain-like discontinuous proeutectoid ferrite. Its microstructure is characterized by a fine internal texture within dark lath bundles, with the lath bundles interwoven. It should be noted that the proeutectoid ferrite in this invention, distributed in a chain-like discontinuous manner and in small quantities, can blunt crack tips and alter crack paths, thereby regulating the phase transformation strain of the surrounding matrix and providing a toughness buffer.

[0054] It should be noted that thermodynamic calculations show that Y has a stronger affinity for O and S than Al and Mn, preferentially forming the highly stable Y₂O₃ and Y₂O₂S. Specifically, Figure 1 The variation of Gibbs free energy ΔG with temperature in the formation of typical inclusions Y2O3, Y2O2S, YS, Y2S3, and Al2O3 in steels of this steel grade and composition within the temperature range of 500~2000℃ is presented. Figure 1As shown, the ΔG values ​​for Y₂O₃, Y₂O₂S, YS, Y₂S₃, and Al₂O₃ are all negative and increase approximately linearly with increasing temperature, indicating that these inclusions can spontaneously form within the smelting temperature range. At 1600℃, the absolute values ​​of ΔG are in the order of Y₂O₃ > Y₂O₂S > Al₂O₃ > Y₂S₃ > YS, with Y₂O₃ being the most stable, followed by the oxysulfide Y₂O₂S and the oxide Al₂O₃. The sulfide YS has the worst thermodynamic stability. Considering the industrial smelting temperature (approximately 1600℃), it can be seen that Y₂O₃ and Y₂O₂S still have relatively large negative ΔG values, indicating that rare earth Y preferentially reacts with O and S to form stable inclusions and has a significant modifying and substitution effect on the original Al₂O₃ inclusions.

[0055] The addition of Yttrium transforms the original elongated MnS and angular Al2O3 inclusions in the steel into fine, spherical composite inclusions or rare earth inclusions such as Y2O3, Y2O2S, YS, and Y2S3. This morphological change significantly reduces matrix stress concentration and crack initiation. Specifically, the Yttrium-containing composite inclusions in the steel have a double-core-shell structure, with Y-Al-O oxides as the core and rare earth sulfides or rare earth oxysulfides wrapped around the outer layer. The morphology of the composite inclusions is spherical or ellipsoidal.

[0056] Automatic analysis of the size distribution characteristics of inclusions within a 4×4mm area in steel using Aspex software shows that the proportion of inclusions smaller than 2µm in the wear-resistant steel of this invention is over 50%, while the proportion of inclusions larger than or equal to 8µm is less than 2%. Among these inclusions, Y-containing inclusions account for over 80%, while MnS and aluminum inclusions account for less than 20%.

[0057] The wear-resistant steel with the composition of this invention, as well as the yttrium-free wear-resistant steel with the same basic composition as this invention, were subjected to Charpy pendulum impact tests at -20°C, tensile tests at room temperature and -20°C, and surface Brinell hardness tests. The Charpy pendulum impact tests were performed according to GB / T 229-2020, with specimens parallel to the rolling direction, measuring 55×10×5mm, and featuring a V-notch. The room temperature tensile tests were performed according to GB / T 228.1-2021; the tensile tests at -20°C were performed according to GB / T228.3-2019; and the surface Brinell hardness tests were performed according to GB / T231-2018.

[0058] The wear-resistant steel of this invention has a Charpy V-notch impact absorption energy of over 13 J at -20°C, which is 9.0-24.8% higher than that of yttrium-free wear-resistant steel with the same basic composition as this invention. The wear-resistant steel of this invention has a room temperature tensile strength of over 1280 MPa and a minimum elongation after fracture of 15%, which is 0.2-6.1% higher than that of yttrium-free wear-resistant steel with the same basic composition as this invention. The wear-resistant steel of this invention has a minimum tensile strength of 1350 MPa at -20°C and a minimum elongation after fracture of 16.5%, which is 5.8-10.6% higher than that of yttrium-free wear-resistant steel with the same basic composition as this invention.

[0059] It should be noted that yttrium-free wear-resistant steel with the same basic composition as the present invention refers to steel whose other components, except for the absence of yttrium, are all within the scope of wear-resistant steel of the present invention.

[0060] Example 1 A high-strength wear-resistant steel with excellent low-temperature toughness has the following composition by mass percentage: C: 0.17%, Si: 1.51%, Mn: 1.49%, Cr: 1.49%, Ti: 0.028%, Nb: 0.022%, Al: 0.042%, B: 0.0011%, Y: 0.001%, P: 0.004%, S: 0.0025%, N: 0.004%, O: 0.002%, with the balance being Fe and unavoidable impurities.

[0061] A method for preparing the above-mentioned wear-resistant steel includes the following steps: Step 1: First, put pure iron and ferrochrome into a crucible for induction melting, perform electromagnetic stirring and purify with argon gas, then add other alloy raw materials in sequence, refine at high temperature and cast into a billet. After the pure iron and ferrochrome in the crucible have completely melted into a liquid, they are electromagnetically stirred for 5 minutes, and then argon gas is introduced into the furnace as a protective gas. The alloy raw materials are added in the following order: C→Si→Mn→Nb→Ti→B→Al→Y. Rare earth Y is added 2 minutes after Al is added. High-temperature refining is carried out by electromagnetic stirring. The high-temperature refining temperature is controlled at 1580℃ for 5 minutes. The casting temperature is 1550℃, and the casting is poured into a cylindrical mold cavity to obtain a 20kg billet.

[0062] Step 2: After heating and holding the billet at the desired temperature, forge it into a square billet; After demolding the ingot, the riser is cut off, the outer diameter is machined, and the furnace is heated to 1250℃ at a heating rate of 7℃ / min. Then, it is held at this temperature for 60 minutes and forged into a square billet with a cross section of 150mm×40mm.

[0063] Step 3: Heat and keep the billet at a constant temperature, then roll it into a sheet through multiple passes; The billet is heated to 1250℃ in the furnace and then held for 50 minutes; the rolling process consists of 4 passes, with a reduction rate of 30-36% per pass, to produce an 8mm thick steel plate; the final rolling temperature is controlled at 870℃.

[0064] Step 4: Immediately after rolling, water cooling is performed, followed by slow cooling.

[0065] The water cooling termination temperature is controlled at 500℃; place it in an insulated box to cool slowly to room temperature at a cooling rate of 0.2℃ / min.

[0066] Figure 2 This is a microstructure diagram of the wear-resistant steel in this embodiment. Figure 2 As can be seen, the microstructure consists of lath martensite and bainite, as well as chain-like discontinuous proeutectoid ferrite. Its microstructure characteristics are: fine texture inside dark lath bundles, interwoven lath bundles, and some chain-like discontinuous distribution of spot-like proeutectoid ferrite. Figure 3 This is a SEM-EDS image of inclusions in the wear-resistant steel of this embodiment. Figure 3 As can be seen, the inclusions in the steel are spherical yttrium oxide sulfides with a diameter of 1~2µm and uniform composition.

[0067] The size, composition, and quantity of inclusions in the wear-resistant steel of this embodiment were statistically analyzed using Aspex software. Figure 4 This includes a bar chart showing the statistical results of the composition and quantity of inclusions in the wear-resistant steel of this embodiment. Figure 5 The table includes a bar chart showing the statistical results of the size and quantity of inclusions in the wear-resistant steel of this embodiment.

[0068] The wear-resistant steel of this embodiment was subjected to Charpy pendulum impact tests at -20℃, tensile tests at room temperature and -20℃, and surface Brinell hardness tests. The Charpy pendulum impact tests were performed according to GB / T 229-2020, with specimens parallel to the rolling direction, measuring 55×10×5mm, and featuring a V-notch. The room temperature tensile tests were performed according to GB / T 228.1-2021; the tensile tests at -20℃ were performed according to GB / T 228.3-2019; and the surface Brinell hardness tests were performed according to GB / T231-2018. The test results are shown in Table 1.

[0069] Example 2 A high-strength wear-resistant steel with excellent low-temperature toughness has the following composition by mass percentage: C: 0.17%, Si: 1.50%, Mn: 1.47%, Cr: 1.50%, Ti: 0.025%, Nb: 0.022%, Al: 0.035%, B: 0.0005%, Y: 0.0047%, P: 0.004%, S: 0.003%, N: 0.002%, O: 0.0015%, with the balance being Fe and unavoidable impurities.

[0070] A method for preparing the above-mentioned wear-resistant steel includes the following steps: Step 1: First, put pure iron and ferrochrome into a crucible for induction melting, perform electromagnetic stirring and purify with argon gas, then add other alloy raw materials in sequence, refine at high temperature and cast into a billet. After the pure iron and ferrochrome in the crucible have completely melted into a liquid, electromagnetic stirring is performed for 3 minutes, followed by the introduction of argon as a protective gas into the furnace. The alloy raw materials are added in the following order: C→Si→Mn→Nb→Ti→B→Al→Y, with rare earth Y added 4 minutes after the addition of Al. High-temperature refining is carried out using electromagnetic stirring, with the temperature controlled at 1650℃ for 8 minutes. The casting temperature is 1540℃, and the casting is poured into a cylindrical mold cavity to obtain a 20kg billet.

[0071] Step 2: After heating and holding the billet at the desired temperature, forge it into a square billet; After demolding the ingot, the riser is cut off, the outer diameter is machined, and the furnace is heated to 1270℃ at a heating rate of 9℃ / min. Then, it is held at that temperature for 70 minutes and forged into a square billet with a cross section of 150mm×40mm.

[0072] Step 3: Heat and keep the billet at a constant temperature, then roll it into a sheet through multiple passes; The billet is heated to 1270℃ in the furnace and then held for 70 minutes; the rolling process consists of 4 passes, with a reduction rate of 30-36% per pass, to produce an 8mm thick steel plate; the final rolling temperature is controlled at 860℃.

[0073] Step 4: Immediately after rolling, water cooling is performed, followed by slow cooling.

[0074] The water cooling termination temperature is controlled at 490℃; it is placed in an insulated box to cool slowly to room temperature at a cooling rate of 0.3℃ / min.

[0075] The wear-resistant steel of this embodiment was subjected to Charpy pendulum impact test at -20°C, tensile test at room temperature and -20°C, and surface Brinell hardness test. The test methods were the same as in Example 1, and the test results are shown in Table 1.

[0076] Example 3 A high-strength wear-resistant steel with excellent low-temperature toughness has the following composition by mass percentage: C: 0.17%, Si: 1.50%, Mn: 1.55%, Cr: 1.53%, Ti: 0.025%, Nb: 0.021%, Al: 0.040%, B: 0.0008%, Y: 0.034%, P: 0.004%, S: 0.008%, N: 0.005%, O: 0.0022%, with the balance being Fe and unavoidable impurities.

[0077] A method for preparing the above-mentioned wear-resistant steel includes the following steps: Step 1: First, put pure iron and ferrochrome into a crucible for induction melting, perform electromagnetic stirring and purify with argon gas, then add other alloy raw materials in sequence, refine at high temperature and cast into a billet. After the pure iron and ferrochrome in the crucible have completely melted into a liquid, they are electromagnetically stirred for 4 minutes, and then argon gas is introduced into the furnace as a protective gas. The alloy raw materials are added in the following order: C→Si→Mn→Nb→Ti→B→Al→Y. Rare earth Y is added 3 minutes after Al is added. High-temperature refining is carried out by electromagnetic stirring. The high-temperature refining temperature is controlled at 1620℃ for 3 minutes. The casting temperature is 1570℃, and the casting is poured into a cylindrical mold cavity to obtain a 20kg billet.

[0078] Step 2: After heating and holding the billet at the desired temperature, forge it into a square billet; After demolding the ingot, the riser is cut off, the outer diameter is machined, and the furnace is heated to 1255℃ at a heating rate of 8℃ / min. Then, it is held at that temperature for 50 minutes and forged into a square billet with a cross section of 150mm×40mm.

[0079] Step 3: Heat and keep the billet at a constant temperature, then roll it into a sheet through multiple passes; The billet is heated to 1255℃ in the furnace and then held for 50 minutes; the rolling process consists of 4 passes, with a reduction rate of 30-36% per pass, to produce an 8mm thick steel plate; the final rolling temperature is controlled at 880℃.

[0080] Step 4: Immediately after rolling, water cooling is performed, followed by slow cooling.

[0081] The water cooling termination temperature is controlled at 510℃; it is placed in an insulated box to cool slowly to room temperature at a cooling rate of 0.4℃ / min.

[0082] The wear-resistant steel of this embodiment was subjected to Charpy pendulum impact test at -20°C, tensile test at room temperature and -20°C, and surface Brinell hardness test. The test methods were the same as in Example 1, and the test results are shown in Table 1.

[0083] Example 4 A high-strength wear-resistant steel with excellent low-temperature toughness has the following composition by mass percentage: C: 0.16%, Si: 1.58%, Mn: 1.4%, Cr: 1.45%, Ti: 0.03%, Nb: 0.03%, Al: 0.06%, B: 0.002%, Y: 0.017%, P: 0.004%, S: 0.0035%, N: 0.0035%, O: 0.0011%, with the balance being Fe and unavoidable impurities.

[0084] A method for preparing the above-mentioned wear-resistant steel includes the following steps: Step 1: First, put pure iron and ferrochrome into a crucible for induction melting, perform electromagnetic stirring and purify with argon gas, then add other alloy raw materials in sequence, refine at high temperature and cast into a billet. After the pure iron and ferrochrome in the crucible have completely melted into liquid, they are electromagnetically stirred for 4 minutes, and then argon gas is introduced into the furnace as a protective gas. The alloy raw materials are added in the following order: C→Si→Mn→Nb→Ti→B→Al→Y. Rare earth Y is added 2 minutes after Al is added. High-temperature refining is carried out by electromagnetic stirring. The high-temperature refining temperature is controlled at 1600℃ for 6 minutes. The casting temperature is 1560℃, and the casting is poured into a cylindrical mold cavity to obtain a 20kg billet.

[0085] Step 2: After heating and holding the billet at the desired temperature, forge it into a square billet; After demolding the ingot, the riser is cut off, the outer diameter is machined, and the furnace is heated to 1240℃ at a heating rate of 8℃ / min. Then, it is held at that temperature for 55 minutes and forged into a square billet with a cross section of 150mm×40mm.

[0086] Step 3: Heat and keep the billet at a constant temperature, then roll it into a sheet through multiple passes; The billet is heated to 1240℃ in the furnace and then held for 55 minutes; the rolling process consists of 4 passes, with a reduction rate of 30-36% per pass, to produce an 8mm thick steel plate; the final rolling temperature is controlled at 880℃.

[0087] Step 4: Immediately after rolling, water cooling is performed, followed by slow cooling.

[0088] The water cooling termination temperature is controlled at 510℃; it is placed in an insulated box to cool slowly to room temperature at a cooling rate of 0.2℃ / min.

[0089] The wear-resistant steel of this embodiment was subjected to Charpy pendulum impact test at -20°C, tensile test at room temperature and -20°C, and surface Brinell hardness test. The test methods were the same as in Example 1, and the test results are shown in Table 1.

[0090] Comparative Example 1 This comparative example is identical to Example 1 in all components except for the absence of Y, and the preparation method is exactly the same as that in Example 1.

[0091] Statistical analysis was performed on the size, composition, and quantity of inclusions in the wear-resistant steel of this comparative example. Figure 4 This includes a bar chart showing the statistical results of the composition and quantity of inclusions in the wear-resistant steel in this comparative example. Figure 5 The table includes a bar chart showing the statistical results of the size and quantity of inclusions in the wear-resistant steel in this comparative example.

[0092] Figure 6 This is a SEM-EDS image of inclusions in the wear-resistant steel of this comparative example. Figure 6 As can be seen, the inclusions are irregularly pointed shapes with a diameter of 2~4µm, and the composition is mainly Al2O3 as the core, surrounded by MnS and TiN.

[0093] The wear-resistant steel of this comparative example was subjected to Charpy pendulum impact test at -20℃, tensile test at room temperature and -20℃, and surface Brinell hardness test. The test methods were the same as in Example 1, and the test results are shown in Table 1.

[0094] Comparative Example 2 This comparative example is identical to Example 2 in all components except for the absence of Y, and the preparation method is exactly the same as that in Example 2.

[0095] The wear-resistant steel of this comparative example was subjected to Charpy pendulum impact test at -20℃, tensile test at room temperature and -20℃, and surface Brinell hardness test. The test methods were the same as in Example 1, and the test results are shown in Table 1.

[0096] Comparative Example 3 This comparative example is identical to Example 3 except that Y is not added, and the preparation method is exactly the same as that of Example 3.

[0097] The wear-resistant steel of this comparative example was subjected to Charpy pendulum impact test at -20℃, tensile test at room temperature and -20℃, and surface Brinell hardness test. The test methods were the same as in Example 1, and the test results are shown in Table 1.

[0098] Comparative Example 4 The composition of this comparative example is exactly the same as that of Example 4. In the preparation method, the water cooling termination temperature in step 4 is controlled at 45°C, followed by low-temperature tempering, and then holding at 230°C for 150 minutes. After the holding is completed, it is air-cooled to room temperature. The rest is exactly the same as that of Example 4.

[0099] The wear-resistant steel of this comparative example was subjected to Charpy pendulum impact test at -20℃, tensile test at room temperature and -20℃, and surface Brinell hardness test. The test methods were the same as in Example 1, and the test results are shown in Table 1.

[0100] Table 1 Test results of the examples and comparative examples

[0101] As shown in Table 1, compared with Comparative Example 1, Example 2 and Comparative Example 2, and Example 3 and Comparative Example 3, the hardness, room temperature tensile strength, room temperature elongation, and -20°C elongation of Example 1 are comparable. However, the impact absorption energy at -20°C and the tensile strength at -20°C of Example 1 are higher than those of Comparative Example 2. Specifically, the impact absorption energy at -20°C of Example 1 is 9.0~24.8% higher than that of Comparative Example 2, and the tensile strength at -20°C of Example 1 is 5.8~10.6% higher than that of Comparative Example 2. Compared with Comparative Example 4, Example 4 has higher hardness and tensile strength because Comparative Example 4 is quenched and cooled below the Ms point, but its elongation and impact absorption energy at -20°C are lower. The impact absorption energy at -20°C of Example 4 is 37.4% higher than that of Comparative Example 4. In addition, the impact absorption energy at -20°C of Example 4 with the preferred composition is higher than that of Examples 1~3, at 16.9J.

[0102] from Figure 4 As can be seen from the statistical results of inclusion composition in steel from Comparative Example 1 and Example 1, the addition of rare earth elements significantly altered the type and distribution of inclusions. In Comparative Example 1, MnS was the dominant inclusion, accounting for 67% of the total, followed by Al-type inclusions at 31%. After adding rare earth element Y, the inclusions in Example 1 became dominated by Y-type inclusions, reaching 83% of the total. Simultaneously, the contents of Al-type inclusions and MnS decreased significantly, accounting for 10% and 6% respectively, while the TiN content remained at a low level. The addition of rare earth elements promoted the formation of Y-type inclusions and significantly modified the original MnS and Al-type inclusions.

[0103] from Figure 5 It is evident that the addition of rare earth element Y significantly altered the size characteristics of the inclusions. In Comparative Example 1, the inclusion particle size distribution was relatively dispersed, mainly concentrated in the ranges of 2–4 µm, 1–2 µm, and 4–8 µm, accounting for 42%, 30%, and 25% respectively. The proportion of large inclusions ≥8 µm was relatively low, at 3%. In Example 1, the particle size distribution showed a clear trend of refinement: 1–2 µm inclusions became the dominant group, with their proportion increasing significantly to 53%; the proportion of 2–4 µm inclusions decreased to 33%; the proportion of 4–8 µm inclusions decreased to 13%; and the proportion of large inclusions ≥8 µm decreased to 1%.

[0104] In summary, the addition of rare earth element Y alters the morphology, composition, and particle size distribution of inclusions in steel, thereby improving the impact absorption energy and tensile strength at -20℃ while maintaining the hardness and room temperature mechanical properties. Furthermore, the quenching process of this invention results in a microstructure of steel dominated by bainite and martensite, as well as chain-like discontinuous proeutectoid ferrite, thus improving low-temperature toughness.

[0105] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A high-strength wear-resistant steel with excellent low-temperature toughness, characterized in that, The wear-resistant steel, by mass percentage, comprises: C: 0.1~0.2%, Si: 1.25~1.85%, Mn: 1.2~1.6%, Cr: 1.2~1.8%, Ti: 0.02~0.05%, Nb: 0.02~0.04%, Al: 0.02~0.08%, B: 0.0004~0.003%, Y: 0.001~0.034%, P≤0.018%, S≤0.008%, N≤0.006%, O≤0.003%, with the balance being Fe and unavoidable impurities.

2. The wear-resistant steel according to claim 1, characterized in that, The wear-resistant steel, by mass percentage, comprises: C: 0.15~0.17%, Si: 1.55~1.65%, Mn: 1.3~1.5%, Cr: 1.35~1.55%, Ti: 0.02~0.04%, Nb: 0.02~0.04%, Al: 0.05~0.07%, B: 0.001~0.003%, Y: 0.01~0.02%, P≤0.005%, S≤0.005%, N≤0.004%, O≤0.002%, with the balance being Fe and unavoidable impurities.

3. The wear-resistant steel according to claim 1 or 2, characterized in that, The microstructure of the wear-resistant steel consists of lath martensite, bainite, and proeutectoid ferrite distributed in a chain-like discontinuous pattern.

4. A method for preparing the wear-resistant steel according to any one of claims 1 to 3, characterized in that, The method includes the following steps: Step 1: First, put pure iron and ferrochrome into a crucible for induction melting, perform electromagnetic stirring and purify with argon gas, then add other alloy raw materials in sequence, refine at high temperature and cast into a billet. Step 2: After heating and holding the billet at the desired temperature, forge it into a square billet; Step 3: Heat and keep the billet at a constant temperature, then roll it into a sheet through multiple passes; Step 4: Immediately after rolling, water cooling is performed, followed by slow cooling.

5. The method according to claim 4, characterized in that, In step 1, the order in which the other alloy raw materials are added is as follows: C, Si, Mn, Nb, Ti, B, Al, Y. The next raw material is added after the previous alloy raw material has been added and melted.

6. The method according to claim 5, characterized in that, The addition of Y is as follows: Y is added 1 to 4 minutes after the addition of Al.

7. The method according to claim 4, characterized in that, In step 1, the temperature of the high-temperature refining is controlled at 1580~1650℃, and the time is 3~8 minutes.

8. The method according to claim 4, characterized in that, In step 2, the heating is carried out by heating in the furnace to 1230~1270℃, the heating rate is 7~9℃ / min, and the holding time is 50~70min.

9. The method according to claim 4, characterized in that, In step 3, the rolling process consists of 4 passes, and the final rolling temperature is controlled at 850~890℃.

10. The method according to claim 4, characterized in that, In step 4, the water cooling termination temperature is controlled at 500±25℃; the slow cooling method is to place it in an insulated box to slowly cool to room temperature.

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