Nb-ti-containing cold-rolled roll steel and method for manufacturing the same

Abstract

This invention relates to a cold-rolled steel containing Nb-Ti and its preparation method, belonging to the field of steel preparation technology. The method includes: weighing raw materials according to the composition of the Nb-Ti cold-rolled steel, smelting and casting to obtain a billet; then subjecting the billet to stress-relief heat treatment, forging, normalizing heat treatment, annealing heat treatment, quenching, and double tempering heat treatment sequentially to obtain the Nb-Ti cold-rolled steel. This invention, through composition and heat treatment process design, solves the problems of insufficient wear resistance, poor thermal stability, weak corrosion resistance, and low hardness in the resulting cold-rolled steel caused by uneven stress due to large-sized Cr carbides. It effectively suppresses abrasive wear, fatigue spalling, and corrosion failure of the rolls during rolling, improves the surface cleanliness of the rolled sheet, and precisely controls the thickness fluctuation of the sheet, providing favorable conditions for achieving ultra-high strength and ultra-cleanliness in cold-rolled sheets.

Description

Technical Field

[0001] This invention relates to a cold-rolled steel containing Nb-Ti and its preparation method, belonging to the field of steel preparation technology. Background Technology

[0002] As a core component of cold rolling mills, cold rolling rolls directly affect the rolling precision, surface quality, and production efficiency of sheet metal. With the development of industries such as aerospace, electronics, and new energy vehicles towards high-end, intelligent, and green technologies, higher requirements are being placed on the performance of cold-rolled sheets, demanding ultra-thinness, ultra-high strength, and ultra-cleanliness. This, in turn, is driving the development of cold rolling rolls towards higher precision, higher speed, and longer service life. Currently, the steel widely used in industrial cold rolling rolls is primarily ordinary Cr5 series alloy steel, with a typical chemical composition (mass percentage, %) as follows: C: 0.50%~0.58%, Si: 0.30%~0.70%, Mn: 0.30%~0.70%, Cr: 5.00%~5.60%, Mo: 0.50%~0.60%, V: 0.05%~0.15%, Ni: ≤0.50%, P: ≤0.015%, S: ≤0.010%, with the remainder being Fe and unavoidable impurities. However, this material has obvious limitations in actual service, mainly manifested in failure phenomena such as roller surface wear and peeling, requiring frequent roller replacement, increasing production costs, and seriously affecting production efficiency.

[0003] Traditional cold-rolled roll steel typically employs a high-carbon, high-chromium alloy system. The presence of large-sized chromium carbides within the steel leads to uneven internal stress and poor hardness, making it prone to cracking or poor surface quality during service. Under extreme conditions such as high loads and intense friction, these materials generally exhibit insufficient wear resistance, poor thermal stability, weak corrosion resistance, low hardness, and insufficient strength. This is particularly problematic when rolling high-strength steel and ultra-thin non-oriented silicon steel, making it difficult to meet core requirements such as high precision, long service life, and the absence of surface defects. Therefore, there is an urgent need to develop a new type of cold-rolled roll steel that combines high hardness with excellent wear resistance. Summary of the Invention

[0004] To address the problems of uneven stress caused by large Cr-containing carbides in existing cold-rolled steel, leading to insufficient wear resistance, poor thermal stability, weak corrosion resistance, and low hardness, this invention provides a Nb-Ti-containing cold-rolled steel and its preparation method. This invention, through the design of composition and heat treatment processes, achieves uniform and fine precipitation of Nb-Ti carbides. Simultaneously, the dispersed distribution of carbides ensures uniform microstructure and stress distribution in the cold-rolled steel, steadily improving wear resistance and hardness, thereby guaranteeing an ultra-long service life. It also effectively improves the surface cleanliness of the rolled sheet and precisely controls sheet thickness fluctuations, providing favorable conditions for achieving ultra-high strength and ultra-cleanliness in cold-rolled sheets.

[0005] In a first aspect, the present invention provides a method for preparing Nb-Ti cold-rolled steel rolls, comprising the following steps:

[0006] Step 1: Weigh the raw materials according to the composition of Nb-Ti cold-rolled steel, smelt them in a vacuum induction furnace until fully melted, cast them, and cool them to room temperature in the furnace to obtain a billet; Step 2: Hold the billet obtained in Step 1 at 625℃ for 3 hours, then raise the temperature to 1150~1200℃ and hold for 10~16 hours for stress relief heat treatment. Step 3: The stress-relief heat-treated billet is forged through two upsetting processes and three drawing processes to obtain a forged billet, wherein the initial forging temperature is 1200~1220℃; Step 4: Heat the forging billet obtained in Step 3 from room temperature to 600℃ and hold for 3 hours, then heat it to 960~1010℃ and hold for 10~15 hours, air cool to room temperature, and perform normalizing heat treatment to obtain steel ingot. Step 5: Heat the steel ingot obtained in Step 4 to 650℃ and hold for 3 hours, then heat it to 800℃ and hold for 2 hours, then cool it down to 700℃ and hold for 2 hours, and finally cool it down to 300℃ and cool it to room temperature in the furnace for annealing heat treatment. Step 6: Heat the annealed steel ingot to 980℃ and hold for 1.5 h, then oil cool to room temperature; then heat to 600℃ and hold for 2 h, then cool in the furnace to 300℃ and air cool to room temperature; then heat to 600℃ again and hold for 2 h, then cool in the furnace to 300℃ and air cool to room temperature, and perform quenching and double tempering heat treatment to obtain Nb-Ti cold rolled steel.

[0007] Further, in step 1, the cold-rolled steel is composed of the following chemical composition by mass percentage: C: 0.70%~0.80%, Si: 0.80%~1.00%, Mn: 0.35%~0.50%, Cr: 5.5%~6.5%, Mo: 0.90%~1.10%, V: 0.50%~0.60%, Ni: 0.30%~0.40%, Cu: 0.30%~0.40%, Nb: 0.01%~0.15%, Ti: 0.01%~0.15%, with the remainder being Fe and unavoidable impurities.

[0008] The Nb and Ti elements introduced in this invention can achieve multi-element synergistic precipitation strengthening and grain refinement with Cr and V elements in steel. Specifically, Nb refines austenite grains, forming Nb-containing carbide precipitates that hinder dislocation movement and improve strength and toughness. Ti deoxidizes, forming fine Ti-containing carbide precipitates, which synergistically refine the microstructure with Nb, enhancing the precipitation strengthening effect and solving the problems of coarse microstructure, poor performance uniformity, uneven hardened layer, low hardness, and insufficient strength in traditional cold-rolled roll steel. Furthermore, the Cu element added to the steel further enhances strength, refines grains, and improves corrosion resistance through the precipitation of copper-containing phases.

[0009] This invention precisely designs the elements Cr, C, V, Ni, and Cu to ensure the successful precipitation of sufficient Nb-Ti carbides, and the synergistic precipitation of Cr-V-Ni-Cu to jointly improve wear resistance.

[0010] Compared with conventional Cr5 series cold-rolled roll steel, the Nb-Ti elements introduced in this invention, along with optimized Cr, C, V, Ni, and Cu elements, significantly improve element segregation and stress uniformity caused by uneven carbide distribution, enhance element diffusion rate, and thus improve the overall performance uniformity of the roll. This results in a dispersed and fine distribution of carbides in the steel, improving hot working performance while significantly enhancing wear resistance, extending roll service life, and reducing costs.

[0011] In the method for preparing Nb-Ti cold-rolled steel according to the present invention, in step 1, the melting temperature of the vacuum induction furnace is 1400~1530℃, and the protective atmosphere is argon atmosphere.

[0012] In the preparation method of Nb-Ti cold-rolled steel according to the present invention, in step 2, the billet is heated to 1150-1200℃ at a rate of 5-10℃ / min for 3 hours and then held for 10-16 hours to perform stress-relieving heat treatment.

[0013] The stress-relieving heat treatment described in this invention enables the full diffusion of easily segregating elements Cr, Mo, V, Si, and Mn in steel, thereby reducing lattice distortion, eliminating internal stress in the steel, and dissolving coarse carbides, reducing forging cracks caused by internal stress during the forging process, and providing favorable conditions for the forging process.

[0014] The stress-relief heat treatment process conditions in this invention enable elements in steel to diffuse rapidly, reduce segregation, improve material properties and microstructure uniformity, effectively remove internal stress, and reduce the incidence of cracks during forging.

[0015] In the method for preparing Nb-Ti cold-rolled steel according to the present invention, in step 3, the deformation amount of each upsetting or drawing pass is 35% ± 0.5%, and the final forging temperature of each pass is not lower than 900℃. If it is lower than 900℃, it is returned to the furnace.

[0016] Furthermore, the two upsetting and three drawing processes are performed sequentially as follows: first upsetting, first drawing, second upsetting, second drawing, and third drawing.

[0017] In the method for preparing Nb-Ti cold-rolled steel according to the present invention, in step 4, the forging billet is heated from room temperature to 600℃ at a rate of 4~7℃ / min and held for 3 h, then heated to 960~1010℃ at a rate of 1.2~1.5℃ / min and held for 10~15 h, then air-cooled to room temperature and subjected to normalizing heat treatment.

[0018] The normalizing heat treatment process conditions described in this invention are formulated based on the temperature range of austenite and ferrite. These conditions can ensure the dispersed precipitation of Nb-Ti carbides and make the austenite grains fine, thereby further improving wear resistance, strength and hardness.

[0019] In the method for preparing Nb-Ti cold-rolled steel according to the present invention, in step 5, the steel ingot is heated to 650°C at a rate of 6~8°C / min and held for 3 h, then heated to 800°C at a rate of 9~11°C / min and held for 2 h, then cooled to 700°C at a rate of 1~3°C / min and held for 2 h, and finally cooled to 300°C at a rate of 1~2°C / min and cooled to room temperature in the furnace for annealing heat treatment.

[0020] In the method for preparing Nb-Ti cold-rolled steel according to the present invention, in step 6, the steel ingot is heated to 980°C at a rate of 5~7°C / min and held for 1.5 h, then oil-cooled to room temperature; subsequently, it is heated to 600°C at a rate of 10~12°C / min and held for 2 h, then cooled to 300°C in the furnace and air-cooled to room temperature.

[0021] Secondly, the present invention provides Nb-Ti cold-rolled steel obtained by the above method.

[0022] Furthermore, the Nb-Ti cold-rolled steel has a hardness of 55~58 HRC, a yield strength of 1850~2050 MPa, and a tensile strength of 2320~2420 MPa.

[0023] The beneficial effects of this invention are: This invention, through its synergistic design of composition and heat treatment processes, fundamentally solves the key problems of existing traditional cold-rolled roll steel, such as the aggregation and distribution of large-sized carbides, slow element diffusion rates, and insufficient wear resistance. Compared with traditional cold-rolled roll steel, this invention can significantly improve the uniformity of microstructure and properties by increasing the element diffusion rate, reducing lattice distortion, decreasing the number of large-sized carbides in the steel, and increasing the number of fine, dispersed Nb-Ti carbides, thereby improving the steel's wear resistance, hardness, strength, and corrosion resistance.

[0024] The heat treatment process in this invention requires no special equipment modification, exhibits high compositional stability and repeatability, and is suitable for industrial production. The novel cold-rolled roll steel prepared using this invention can be applied to key components such as support rolls in modern high-precision production lines, effectively improving service life, extending the service life of cold-rolled rolls, and reducing time and economic costs. This provides favorable conditions for the development of ultra-thin, ultra-high-strength, and ultra-clean cold-rolled sheets, and provides technical support for the future goals of higher precision, higher speed, and longer service life of new cold-rolled rolls. Attached Figure Description

[0025] Figure 1 This is a microstructure diagram of the billet obtained by vacuum induction furnace smelting in Example 1.

[0026] Figure 2 This is a microstructure diagram of the stress-relief annealed structure in Example 1.

[0027] Figure 3 This is a microstructure image of the forged sample in Example 1.

[0028] Figure 4 This is a microstructure image of the sample after normalizing heat treatment in Example 1.

[0029] Figure 5 The image shows the SEM microstructure after the friction test under the 40 N load condition in Example 1. Detailed Implementation

[0030] The following non-limiting embodiments are intended to enable those skilled in the art to more fully understand the invention, but do not limit the invention in any way.

[0031] Unless otherwise specified, the experimental methods described in the following examples are conventional methods; the reagents and materials described are commercially available unless otherwise specified.

[0032] The hardness of the Nb-Ti cold-rolled steel obtained in the following examples was measured by the following method: the test sample after full heat treatment was cut into a size of 12 mm × 12 mm × 10 mm by wire cutting. After the surface was polished, the hardness of the sample was measured using an HRS-150D multi-functional digital display Rockwell hardness tester. Five points were randomly measured and the average value was taken.

[0033] The yield strength and tensile strength of the Nb-Ti cold-rolled steel obtained in the following examples were measured according to the following methods: For the tensile test, standard tensile specimens were prepared according to GB / T228.1—2010 "Metallic Materials - Tensile Testing at Room Temperature". The steel ingots, after complete heat treatment, were processed according to the above national standard requirements. The original gauge length was 15 mm, the parallel section was 25 mm, the total specimen length was 70 mm, and the diameter of the parallel section of the circular specimen was 5 mm. The tensile test was conducted on a Shimadzu AGS-X electronic tensile testing machine, using displacement loading control, with a tensile speed of 1 mm·min. -1 .

[0034] The wear resistance of the Nb-Ti cold-rolled roll steel obtained in the following examples and the cold-rolled roll steel obtained in Comparative Example 1 were measured according to the following method: The test was conducted according to GB / T 12444—2006 "Metallic Materials Wear Test Methods Part 1: Test Ring-Block Sliding Wear Test", using a CFT-II multifunctional material surface friction performance comprehensive tester. The sample size was 10mm × 22mm × 10mm. The test environment was room temperature (25 ± 2℃), dry friction without lubrication, using Si3N4 balls with a diameter of 5mm for the friction pair, a stroke of 10mm, and a test time of 30min. Three parallel samples were tested under each load condition, and the average value was taken as the final test result. The specific test conditions were as follows: When the load was 40 N: the sliding rate was 200 mm / min, and the total sliding distance L was 6m. When the load was 200 N: the sliding rate was 300 mm / min, and the total sliding distance L was 9m.

[0035] The calculation formulas for volumetric wear rate and the percentage reduction in wear rate are as follows: (1) Formula for calculating weight loss:

[0036] In the formula, Δm is the weight loss (g), m1 is the mass of the sample before grinding (g), and m2 is the mass of the sample after grinding (g).

[0037] (2) Formula for calculating wear volume:

[0038] In the formula, V is the wear volume (mm). 3 Δm is the weight loss (g), and ρ is the material density (g / mm³).3 ).

[0039] (3) Formula for calculating volumetric wear rate:

[0040] In the formula, Wv is the volumetric wear rate (mm). 3 / (N·m)), V is the wear volume (mm). 3 F is the test load (N), and L is the total sliding distance (m).

[0041] (4) Formula for calculating the percentage reduction in wear rate:

[0042] In the formula, η is the percentage reduction in volumetric wear rate (%), and Wv is the volumetric wear rate of the cold-rolled roll steel obtained in Comparative Example 1 (mm). 3 / (N·m)), Wv is the volumetric wear rate (mm) of the Nb-Ti cold-rolled roll steel obtained in this invention. 3 / (N·m)).

[0043] Example 1 The chemical composition of a cold-rolled steel containing Nb-Ti is as follows: C: 0.79%, Si: 0.85%, Mn: 0.50%, Cr: 5.88%, Mo: 0.91%, V: 0.55%, Ni: 0.36%, Cu: 0.33%, Nb: 0.08%, Ti: 0.11%, with the remainder being Fe and unavoidable impurities.

[0044] The above-mentioned method for preparing cold-rolled steel includes the following steps: Step 1: Weigh the raw materials according to the above chemical composition ratio, and smelt them in a vacuum induction furnace under an argon atmosphere and at 1480°C until fully melted. Cast the mixture and cool it to room temperature in the furnace to obtain a cast billet. Figure 1 The microstructure of the cast billet shows that there is obvious dendritic structure, indicating elemental segregation between dendrites, which requires further stress-relieving annealing.

[0045] Step 2: Hold the billet obtained in Step 1 at 625℃ for 3 hours, then raise the temperature to 1200℃ at 7℃ / min and hold for 15 hours for stress relief heat treatment. Figure 2 The image shows the microstructure after stress-relief annealing. It can be seen that the dendritic structure in the microstructure has been significantly eliminated, indicating that the element distribution is uniform at this time, effectively eliminating internal stress and improving forging performance.

[0046] Step 3: The stress-relief heat-treated billet is forged to obtain a forged billet. The process involves two upsetting operations and three drawing operations. The initial forging temperature is 1220℃, and the forging process is upsetting-drawing-upsetting-drawing-drawing, with deformation amounts of 34.8%, 34.9%, 35.2%, 35.1%, and 35.0% for each pass, respectively. Figure 3 The image shows the microstructure of the forged billet. It can be seen that the grains in the forged structure are coarse, the size distribution is uneven, and large-sized carbides are present.

[0047] Step 4: Heat the forging billet from room temperature to 600℃ at 6℃ / min and hold for 3 h, then heat it to 980℃ at 1.5℃ / min and hold for 15 h, air cool to room temperature, and perform normalizing heat treatment to obtain steel ingot; Figure 4 The image shows the microstructure of the steel ingot. It can be seen that large-sized carbides are decomposed, while small-sized carbides are dispersed, providing favorable conditions for the spheroidization and precipitation of carbides in the next annealing heat treatment.

[0048] Step 5: Heat the steel ingot from room temperature to 650℃ at 8℃ / min and hold for 3 hours, then heat it to 800℃ at 11℃ / min and hold for 2 hours, then cool it down to 700℃ at 3℃ / min and hold for 2 hours, and finally cool it down to 300℃ at 1.5℃ / min and cool it to room temperature in the furnace for annealing heat treatment.

[0049] Step 6: Heat the annealed steel ingot to 980℃ at 7℃ / min and hold for 1.5 h, then oil cool to room temperature; then heat to 600℃ at 12℃ / min and hold for 2 h, then cool in the furnace to 300℃ and air cool to room temperature; then heat to 600℃ again at 12℃ / min and hold for 2 h, then cool in the furnace to 300℃ and air cool to room temperature, and perform quenching and double tempering heat treatment to obtain Nb-Ti cold rolled steel.

[0050] The mechanical properties of the Nb-Ti cold-rolled steel prepared in this embodiment were analyzed. The measured hardness was 57.3 HRC, yield strength was 2000.37 MPa, tensile strength was 2324.93 MPa, and material density was 7.86 × 10⁻⁶ MPa. -3 g / mm 3 Under a load of 40 N, the pre-grind mass was 21.5391 g, the post-grind mass was 21.5389 g, the weight loss Δm = 0.0002 g, and the volumetric wear rate was 1.06 × 10⁻⁶ g. -4 mm 3 The average friction coefficient is 0.318 / (N·m). Under a load of 200 N, the mass before grinding is 21.7059 g, the mass after grinding is 21.6985 g, the weight loss Δm = 0.0074 g, and the volumetric wear rate is 5.23 × 10⁻⁶. -4 mm3 / (N·m), with an average friction coefficient of 0.446. Figure 5 The tissue morphology of the sample after the 40 N load friction and wear test under a SEM microscope shows that the morphology mainly consists of a large number of furrows and a small number of spalling pits. No black oxidation wear traces were found, indicating that the wear mechanism is mainly abrasive wear, while there is also a certain degree of adhesive wear.

[0051] Example 2 The chemical composition of a cold-rolled roll steel containing Nb-Ti is as follows: C: 0.76%, Si: 0.92%, Mn: 0.43%, Cr: 6.33%, Mo: 0.98%, V: 0.59%, Ni: 0.37%, Cu: 0.33%, Nb: 0.09%, Ti: 0.08%, with the remainder being Fe and unavoidable impurities.

[0052] The above-mentioned method for preparing cold-rolled steel includes the following steps: Step 1: Weigh the raw materials according to the above chemical composition ratio, and smelt them in a vacuum induction furnace under an argon atmosphere and at 1480°C until fully melted. Cast the mixture and cool it to room temperature in the furnace to obtain a cast billet. Step 2: Hold the billet obtained in Step 1 at 625℃ for 3 hours, then raise the temperature to 1190℃ at 6℃ / min and hold for 11 hours for stress relief heat treatment. Step 3: The stress-relief heat-treated billet is forged to obtain a forged billet. The process involves two upsetting operations and three drawing operations. The initial forging temperature is 1210℃, and the forging process is upsetting-drawing-upsetting-drawing-drawing, with deformation amounts of 34.7%, 35.3%, 35.2%, 34.9%, and 35.3% for each pass, respectively. Step 4: Heat the forging billet from room temperature to 600℃ at 5℃ / min and hold for 3 h, then heat it to 990℃ at 1.3℃ / min and hold for 11 h, air cool to room temperature, and perform normalizing heat treatment to obtain steel ingot; Step 5: Heat the steel ingot from room temperature to 650℃ at 7℃ / min and hold for 3 hours, then heat it to 800℃ at 10℃ / min and hold for 2 hours, then cool it down to 700℃ at 2℃ / min and hold for 2 hours, and finally cool it down to 300℃ at 1.4℃ / min and cool it to room temperature in the furnace for annealing heat treatment. Step 6: Heat the annealed steel ingot to 980℃ at 7℃ / min and hold for 1.5 h, then oil cool to room temperature; then heat to 600℃ at 10℃ / min and hold for 2 h, then cool in the furnace to 300℃ and air cool to room temperature; then heat to 600℃ again at 11℃ / min and hold for 2 h, then cool in the furnace to 300℃ and air cool to room temperature, and perform quenching and double tempering heat treatment to obtain Nb-Ti cold rolled steel.

[0053] The mechanical properties of the Nb-Ti cold-rolled steel prepared in this embodiment were analyzed. The measured hardness was 57.6 HRC, yield strength was 1987.36 MPa, tensile strength was 2295.71 MPa, and material density was 7.86 × 10⁻⁶ MPa. -3 g / mm 3 Under a load of 40 N, the pre-grind mass was 21.1756 g, the post-grind mass was 21.1753 g, the weight loss Δm = 0.0003 g, and the volumetric wear rate was 1.59 × 10⁻⁶ g. -4 mm 3 The average friction coefficient is 0.325, with a friction value of / (N·m). Under a load of 200 N, the mass before grinding is 21.3522 g, the mass after grinding is 21.3447 g, the weight loss Δm = 0.0075 g, and the volumetric wear rate is 5.30 × 10⁻⁶. -4 mm 3 / (N·m), with an average friction coefficient of 0.450.

[0054] Example 3 The chemical composition of a cold-rolled steel containing Nb-Ti is as follows: C: 0.73%, Si: 0.81%, Mn: 0.45%, Cr: 5.86%, Mo: 1.00%, V: 0.50%, Ni: 0.40%, Cu: 0.31%, Nb: 0.12%, Ti: 0.05%, with the remainder being Fe and unavoidable impurities.

[0055] The above-mentioned method for preparing cold-rolled steel includes the following steps: Step 1: Weigh the raw materials according to the above chemical composition ratio, and smelt them in a vacuum induction furnace under an argon atmosphere and at 1480°C until fully melted. Cast the mixture and cool it to room temperature in the furnace to obtain a cast billet. Step 2: Hold the billet obtained in Step 1 at 625℃ for 3 hours, then raise the temperature to 1185℃ at 7℃ / min and hold for 13 hours for stress relief heat treatment. Step 3: The stress-relief heat-treated billet is forged to obtain a forged billet. The process involves two upsetting operations and three drawing operations. The initial forging temperature is 1200℃, and the forging process is upsetting-drawing-upsetting-drawing-drawing, with deformation amounts of 35.2%, 35.1%, 35.0%, 34.7%, and 35.0% for each pass, respectively. Step 4: Heat the forging billet from room temperature to 600℃ at 6℃ / min and hold for 3 h, then heat it to 1000℃ at 1.2℃ / min and hold for 12 h, air cool to room temperature, and perform normalizing heat treatment to obtain steel ingot; Step 5: Heat the steel ingot from room temperature to 650℃ at 7℃ / min and hold for 3 hours, then heat it to 800℃ at 9℃ / min and hold for 2 hours, then cool it down to 700℃ at 3℃ / min and hold for 2 hours, and finally cool it down to 300℃ at 1.6℃ / min and cool it to room temperature in the furnace for annealing heat treatment. Step 6: Heat the annealed steel ingot to 980℃ at 6℃ / min and hold for 1.5 h, then oil cool to room temperature; then heat to 600℃ at 11℃ / min and hold for 2 h, then cool in the furnace to 300℃ and air cool to room temperature; then heat to 600℃ again at 10℃ / min and hold for 2 h, then cool in the furnace to 300℃ and air cool to room temperature, and perform quenching and double tempering heat treatment to obtain Nb-Ti cold rolled steel.

[0056] The mechanical properties of the Nb-Ti cold-rolled steel prepared in this embodiment were analyzed. The measured hardness was 56.2 HRC, yield strength was 1925.62 MPa, tensile strength was 2319.71 MPa, and material density was 7.86 × 10⁻⁶ MPa. -3 g / mm 3 Under a load of 40 N, the pre-grind mass was 21.5122 g, the post-grind mass was 21.5120 g, the weight loss Δm = 0.0002 g, and the volumetric wear rate was 1.06 × 10⁻⁶ g. -4 mm 3 The average friction coefficient is 0.318 / (N·m). Under a load of 200 N, the mass before grinding is 21.4765 g, the mass after grinding is 21.4689 g, the weight loss Δm = 0.0076 g, and the volumetric wear rate is 5.37 × 10⁻⁶. -4 mm 3 / (N·m), with an average friction coefficient of 0.439.

[0057] Example 4 The chemical composition of a cold-rolled steel containing Nb-Ti is as follows: C: 0.71%, Si: 0.96%, Mn: 0.41%, Cr: 6.24%, Mo: 1.06%, V: 0.53%, Ni: 0.40%, Cu: 0.32%, Nb: 0.11%, Ti: 0.07%, with the remainder being Fe and unavoidable impurities.

[0058] The above-mentioned method for preparing cold-rolled steel includes the following steps: Step 1: Weigh the raw materials according to the above chemical composition ratio, and smelt them in a vacuum induction furnace under an argon atmosphere and at 1480°C until fully melted. Cast the mixture and cool it to room temperature in the furnace to obtain a cast billet. Step 2: Hold the billet obtained in Step 1 at 625℃ for 3 hours, then raise the temperature to 1159℃ at 9℃ / min and hold for 14 hours for stress relief heat treatment. Step 3: The stress-relief heat-treated billet is forged to obtain a forged billet. The process involves two upsetting operations and three drawing operations. The initial forging temperature is 1205℃, and the forging process is upsetting-drawing-upsetting-drawing-drawing, with deformation amounts of 34.9%, 35.2%, 34.7%, 35.0%, and 35.4% for each pass, respectively. Step 4: Heat the forging billet from room temperature to 600℃ at 7℃ / min and hold for 3 hours, then heat it to 960℃ at 1.4℃ / min and hold for 14 hours. Air cool it to room temperature and perform normalizing heat treatment to obtain steel ingot. Step 5: Heat the steel ingot from room temperature to 650℃ at 6℃ / min and hold for 3 hours, then heat it to 800℃ at 10℃ / min and hold for 2 hours, then cool it down to 700℃ at 3℃ / min and hold for 2 hours, and finally cool it down to 300℃ at 1.3℃ / min and cool it to room temperature in the furnace for annealing heat treatment. Step 6: Heat the annealed steel ingot to 980℃ at 5℃ / min and hold for 1.5 h, then oil cool to room temperature; then heat to 600℃ at 12℃ / min and hold for 2 h, then cool in the furnace to 300℃ and air cool to room temperature; then heat to 600℃ again at 12℃ / min and hold for 2 h, then cool in the furnace to 300℃ and air cool to room temperature, and perform quenching and double tempering heat treatment to obtain Nb-Ti cold rolled steel.

[0059] The mechanical properties of the Nb-Ti cold-rolled steel prepared in this embodiment were analyzed. The measured hardness was 57.5 HRC, yield strength was 2010.59 MPa, tensile strength was 2335.37 MPa, and material density was 7.86 × 10⁻⁶ MPa. -3 g / mm 3 Under a load of 40 N, the pre-grind mass was 21.5535 g, the post-grind mass was 21.5532 g, the weight loss Δm = 0.0003 g, and the volumetric wear rate was 1.59 × 10⁻⁶ g. -4 mm 3 The average friction coefficient is 0.325, with a friction value of / (N·m). Under a load of 200 N, the mass before grinding is 21.7381 g, the mass after grinding is 21.7303 g, the weight loss Δm = 0.0078 g, and the volumetric wear rate is 5.51 × 10⁻⁶. -4 mm 3 / (N·m), with an average friction coefficient of 0.443.

[0060] Example 5 The chemical composition of a cold-rolled roll steel containing Nb-Ti is as follows: C: 0.77%, Si: 0.85%, Mn: 0.44%, Cr: 6.10%, Mo: 1.05%, V: 0.54%, Ni: 0.30%, Cu: 0.32%, Nb: 0.13%, Ti: 0.12%, with the remainder being Fe and unavoidable impurities.

[0061] The above-mentioned method for preparing cold-rolled steel includes the following steps: Step 1: Weigh the raw materials according to the above chemical composition ratio, and smelt them in a vacuum induction furnace under an argon atmosphere and at 1480°C until fully melted. Cast the mixture and cool it to room temperature in the furnace to obtain a cast billet. Step 2: Hold the billet obtained in Step 1 at 625℃ for 3 hours, then raise the temperature to 1173℃ at 5℃ / min and hold for 16 hours for stress relief heat treatment. Step 3: The stress-relief heat-treated billet is forged to obtain a forged billet. The process involves two upsetting operations and three drawing operations. The initial forging temperature is 1216℃, and the forging process is upsetting-drawing-upsetting-drawing-drawing, with deformation amounts of 35.0%, 34.8%, 34.6%, 35.3%, and 35.1% for each pass, respectively. Step 4: Heat the forging billet from room temperature to 600℃ at 5℃ / min and hold for 3 hours, then heat it to 975℃ at 1.5℃ / min and hold for 11 hours. Air cool it to room temperature and perform normalizing heat treatment to obtain steel ingot. Step 5: Heat the steel ingot from room temperature to 650℃ at 8℃ / min and hold for 3 hours, then heat it to 800℃ at 10℃ / min and hold for 2 hours, then cool it down to 700℃ at 2℃ / min and hold for 2 hours, and finally cool it down to 300℃ at 1.8℃ / min and cool it to room temperature in the furnace for annealing heat treatment. Step 6: Heat the annealed steel ingot to 980℃ at 6℃ / min and hold for 1.5 h, then oil cool to room temperature; then heat to 600℃ at 12℃ / min and hold for 2 h, then cool in the furnace to 300℃ and air cool to room temperature; then heat to 600℃ again at 11℃ / min and hold for 2 h, then cool in the furnace to 300℃ and air cool to room temperature, and perform quenching and double tempering heat treatment to obtain Nb-Ti cold rolled steel.

[0062] The mechanical properties of the Nb-Ti cold-rolled steel prepared in this embodiment were analyzed. The measured hardness was 57.8 HRC, yield strength was 2005.64 MPa, tensile strength was 2330.15 MPa, and material density was 7.86 × 10⁻⁶ MPa. -3 g / mm 3Under a load of 40 N, the pre-grind mass was 21.6854 g, the post-grind mass was 21.6852 g, the weight loss Δm = 0.0002 g, and the volumetric wear rate was 1.06 × 10⁻⁶ g. -4 mm 3 The average friction coefficient is 0.318 / (N·m). Under a load of 200 N, the mass before grinding is 21.1359 g, the mass after grinding is 21.1279 g, the weight loss Δm = 0.0080 g, and the volumetric wear rate is 5.65 × 10⁻⁶. -4 mm 3 / (N·m), with an average friction coefficient of 0.448.

[0063] Comparative Example 1 The difference between this comparative example and Example 1 is that the chemical composition of the obtained cold-rolled steel is different, specifically: C: 0.54%, Si: 0.45%, Mn: 0.52%, Cr: 5.15%, Mo: 0.53%, V: 0.11%, P: ≤0.015%, S: ≤0.010%, with the remainder being Fe and unavoidable impurities. All other operations are the same as in Example 1.

[0064] Mechanical properties of the cold-rolled roll steel prepared in this comparative example were analyzed. The measured hardness was 53.7 HRC, yield strength was 1685.56 MPa, tensile strength was 1978.32 MPa, and material density was 7.85 × 10⁻⁶ MPa. -3 g / mm 3 Under a load of 40 N, a sliding speed of 200 mm / min, a time of 30 min, a stroke of 10 mm, and a total sliding distance of 6 m, the mass before grinding was 21.5375 g, the mass after grinding was 21.5370 g, the weight loss Δm = 0.0005 g, and the volumetric wear rate was 2.65 × 10⁻⁶ g. -4 mm 3 The average friction coefficient is 0.450. Under a load of 200 N, a sliding speed of 300 mm / min, a test time of 30 min, and a total sliding distance of 9 m, the mass before grinding is 21.2952 g, the mass after grinding is 21.2767 g, the weight loss Δm = 0.0185 g, and the volumetric wear rate is 13.1 × 10⁻⁶ m / s. -4 mm 3 / (N·m), with an average friction coefficient of 0.580.

[0065] Compared with the cold-rolled roll steel obtained in Comparative Example 1, the cold-rolled roll steel obtained in Example 1 showed a reduction in volumetric wear rate of 60.0% and 60.1% under loads of 40 N and 200 N, respectively.

[0066] Compared with the cold-rolled roll steel obtained in Comparative Example 1, the cold-rolled roll steel obtained in Example 2 showed a reduction in volumetric wear rate of 40.0% and 59.5% under loads of 40 N and 200 N, respectively.

[0067] Compared with the cold-rolled roll steel obtained in Comparative Example 1, the cold-rolled roll steel obtained in Example 3 showed a reduction in volumetric wear rate of 60.0% and 59.0% under loads of 40 N and 200 N, respectively.

[0068] Compared with the cold-rolled roll steel obtained in Comparative Example 1, the cold-rolled roll steel obtained in Example 4 showed a reduction in volumetric wear rate of 40.0% and 57.9% under loads of 40 N and 200 N, respectively.

[0069] Compared with the cold-rolled roll steel obtained in Comparative Example 1, the cold-rolled roll steel obtained in Example 5 showed a reduction in volumetric wear rate of 60.0% and 56.9% under loads of 40 N and 200 N, respectively.

Claims

1. A method for preparing Nb-Ti cold-rolled steel rolls, characterized in that: Includes the following steps: Step 1: Weigh the raw materials according to the composition of Nb-Ti cold-rolled steel, smelt them in a vacuum induction furnace until fully melted, cast them, and cool them to room temperature in the furnace to obtain a billet; Step 2: Hold the billet obtained in Step 1 at 625℃ for 3 hours, then raise the temperature to 1150~1200℃ and hold for 10~16 hours for stress relief heat treatment. Step 3: The stress-relief heat-treated billet is forged through two upsetting processes and three drawing processes to obtain a forged billet, wherein the initial forging temperature is 1200~1220℃; Step 4: Heat the forging billet obtained in Step 3 from room temperature to 600℃ and hold for 3 hours, then heat it to 960~1010℃ and hold for 10~15 hours, air cool to room temperature, and perform normalizing heat treatment to obtain steel ingot. Step 5: Heat the steel ingot obtained in Step 4 to 650℃ and hold for 3 hours, then heat it to 800℃ and hold for 2 hours, then cool it down to 700℃ and hold for 2 hours, and finally cool it down to 300℃ and cool it to room temperature in the furnace for annealing heat treatment. Step 6: Heat the annealed steel ingot to 980℃ and hold for 1.5 h, then oil cool to room temperature; then heat to 600℃ and hold for 2 h, then cool in the furnace to 300℃ and air cool to room temperature; then heat to 600℃ again and hold for 2 h, then cool in the furnace to 300℃ and air cool to room temperature, and perform quenching and double tempering heat treatment to obtain Nb-Ti cold rolled steel.

2. The method for preparing Nb-Ti cold-rolled steel according to claim 1, characterized in that: In step 1, the cold-rolled steel is composed of the following chemical composition by mass percentage: C: 0.70%~0.80%, Si: 0.80%~1.00%, Mn: 0.35%~0.50%, Cr: 5.5%~6.5%, Mo: 0.90%~1.10%, V: 0.50%~0.60%, Ni: 0.30%~0.40%, Cu: 0.30%~0.40%, Nb: 0.01%~0.15%, Ti: 0.01%~0.15%, with the remainder being Fe and unavoidable impurities.

3. The method for preparing Nb-Ti cold-rolled steel according to claim 1, characterized in that: In step 2, the billet is held at 625℃ for 3 hours and then heated to 1150-1200℃ at a rate of 5-10℃ / min and held for 10-16 hours for stress relief heat treatment.

4. The method for preparing Nb-Ti cold-rolled steel according to claim 1, characterized in that: In step 3, the deformation amount of each upsetting or drawing pass is 35% ± 0.5%, and the final forging temperature of each pass is not lower than 900℃. If it is lower than 900℃, it is returned to the furnace.

5. The method for preparing Nb-Ti cold-rolled steel according to claim 1, characterized in that: In step 4, the forging billet is heated from room temperature to 600℃ at a rate of 4~7℃ / min and held for 3 hours, then heated to 960~1010℃ at a rate of 1.2~1.5℃ / min and held for 10~15 hours, then air-cooled to room temperature for normalizing heat treatment.

6. The method for preparing Nb-Ti cold-rolled steel according to claim 1, characterized in that: In step 5, the steel ingot is heated to 650℃ at a rate of 6~8℃ / min and held for 3 hours, then heated to 800℃ at a rate of 9~11℃ / min and held for 2 hours, then cooled to 700℃ at a rate of 1~3℃ / min and held for 2 hours, and finally cooled to 300℃ at a rate of 1~2℃ / min and cooled to room temperature in the furnace for annealing heat treatment.

7. The method for preparing Nb-Ti cold-rolled steel according to claim 1, characterized in that: In step 6, the steel ingot is heated to 980°C at a rate of 5-7°C / min and held for 1.5 h, then oil-cooled to room temperature; subsequently, it is heated to 600°C at a rate of 10-12°C / min and held for 2 h, then cooled to 300°C in the furnace and air-cooled to room temperature.

8. The method for preparing Nb-Ti cold-rolled steel according to claim 1, characterized in that: In step 1, the melting temperature of the vacuum induction furnace is 1400~1530℃, and the protective atmosphere is argon atmosphere.

9. Nb-Ti cold-rolled steel obtained by the method according to any one of claims 1 to 8.

10. The Nb-Ti cold-rolled roll steel according to claim 9, characterized in that: The Nb-Ti cold-rolled steel has a hardness of 55~58 HRC, a yield strength of 1850~2050 MPa, and a tensile strength of 2320~2420 MPa.

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