Roller material and preparation method

Abstract

The invention belongs to the field of metal materials, and relates to a roller material and a preparation method thereof. The preparation method provided by the invention comprises the following steps: a) sequentially smelting, casting and forging raw materials of the roller to obtain a roller blank; the roller raw material comprises the following components: 0.6 to 1 percent of C, 1.5 to 3.5 percent of Mn, 0.8 to 3 percent of Cr, 0.1 to 0.4 percent of Cu and 93 to 96 percent of Fe; b) carrying out quenching treatment on the roller blank; c) tempering the quenched roller blank, then clamping the two ends of the roller blank to twist, keeping for a period of time, and cooling to obtain the roller blank subjected to deformation heat treatment; d) turning the roller blank subjected to deformation heat treatment to obtain a roller semi-finished product; and e) carrying out surface nanocrystallization treatment on the roller semi-finished product to obtain the roller material. The method provided by the invention can reduce the consumption of alloy for preparing the roller material and improve the comprehensive performance of the roller material.

Description

Technical Field

[0001] The invention belongs to the field of metal materials and relates to a rolling roller material and a preparation method thereof. Background Art

[0002] Roller is the core component of metal rolling process. Its wear resistance, spalling resistance and fatigue life directly determine the stability of rolling process, product quality and production efficiency. Traditional cold rolling roll material design mainly follows the high chromium (Cr) alloying route. Its design concept is gradually increased from the initial 2% Cr to 3%, 5%, 8%, and even to 12% Cr. A large amount of carbides are formed in the matrix through high chromium content to improve wear resistance and hot hardness, and meet the manufacturing needs of large-size and high-load rolls. For example, the Cr12MoV material commonly used in the twenty-roll mill is a material that precipitates a large amount of carbides in the alloy through the synergistic effect of high carbon (1.4% to 1.7%) and high chromium (11% to 13%). These include both primary carbides that are unfavorable to the overall performance and fine and evenly distributed carbides generated by adding micro-alloying elements such as Mo and V. These carbides not only improve wear resistance, but also inhibit the growth of austenite grains. High-speed steel rolls are also based on the basic idea of ​​large-scale alloying to generate carbides. Super-hard carbides precipitated in large quantities from elements such as tungsten (W), molybdenum (Mo), and vanadium (V) are used to strengthen the roll surface, significantly improving wear resistance and hot hardness at high temperatures.

[0003] However, as the rolling process continues to develop towards high load and high precision, the traditional high chromium or high alloy design exposes the following major problems: ① Decreased toughness and increased risk of fracture: Although excessive carbides can significantly improve wear resistance, they will also reduce the toughness of the material and form brittle areas, thereby increasing the risk of crack extension or even fracture of the roll under high load and impact load. ② The heat treatment process is complex and difficult to control: In high Cr or high alloy materials, alloying elements such as Cr will reduce the austenite zone, increase the quenching temperature, and the heat treatment process has strict requirements on parameters such as temperature, holding time and cooling rate. Once the process control is not precise, it is very easy to cause uneven organization, excessive residual austenite, excessive residual stress and even thermal cracks, thereby affecting the final mechanical properties and service life. ③ It is difficult to take into account comprehensive performance: While pursuing high wear resistance and hot hardness, traditional high alloy rolls often sacrifice impact toughness and fatigue performance, and it is difficult to meet the multiple requirements of modern rolling processes for high pressure, high wear resistance and high fatigue resistance. ④ Huge pressure on cost and environmental protection: Alloy elements such as high chromium and high tungsten are scarce and expensive. Their high energy consumption smelting process not only leads to soaring costs, but also the environmental protection treatment of Cr-containing, W-containing wastewater and other harmful substances generated also faces strict supervision and high governance costs, further limiting its large-scale application.

[0004] In order to reduce the manufacturing and usage costs of rolls, and at the same time meet the stringent requirements of high-load and high-precision rolling processes for wear resistance, spalling resistance, and fatigue life, it is urgent to develop a new type of roll material and preparation method. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a roll material and its preparation method, which can reduce the alloy usage in preparing the roll material and improve the comprehensive performance of the roll material.

[0006] The present invention provides a preparation method for a roll material, including the following steps:

[0007] a) Smelting, casting, and forging the roll raw materials in sequence to obtain a roll blank;

[0008] In step a), the composition of the roll raw materials includes: C 0.6 - 1 wt%, Mn 1.5 - 3.5 wt%, Cr 0.8 - 3 wt%, Cu 0.1 - 0.4 wt%, Fe 93 - 96 wt%;

[0009] b) Quenching the roll blank to obtain a quenched roll blank;

[0010] c) Tempering the quenched roll blank. After tempering and holding for a period of time, hold both ends of the roll blank for torsion and maintain for a period of time, then cool to obtain a roll blank after deformation heat treatment;

[0011] d) Turning the roll blank after deformation heat treatment to obtain a roll semi-finished product;

[0012] e) Performing surface nanocrystallization treatment on the roll semi-finished product to obtain the roll material.

[0013] Preferably, in step a), the composition of the roll raw materials further includes one or more of Si, Mo, V, Ni, and Nb.

[0014] Preferably, the Si content of the roll raw materials is 0.5 - 1 wt%;

[0015] And / or, the V content of the roll material is 0.1 - 0.2 wt%;

[0016] And / or, the Ni content of the roll material is 0.3 - 0.8 wt%;

[0017] And / or, the Nb content of the roll material is 0.01 - 0.1 wt%.

[0018] Preferably, in step b), the temperature of the quenching treatment is 850 - 1000 °C.

[0019] Preferably, in step c), the tempering temperature is 450 - 550 °C; the tempering holding time is more than 30 min.

[0020] Preferably, in step c), the torsion angle at each end of the roll blank is 3° - 5°; the torsion holding time is 10 - 15 s.

[0021] Preferably, in step d), the roughness of the roll semi-finished product is ≤ 0.8 μm, and the radial runout is ≤ 0.05 mm.

[0022] Preferably, in step e), the surface nanocrystallization treatment method includes at least one or more of shot peening, surface mechanical attrition, surface mechanical rolling, surface mechanical ball burnishing, dynamic plastic deformation, mechanical ball milling, equal-channel angular pressing, and high-energy beam heat treatment.

[0023] Preferably, in step e), the surface grain size of the roll material is < 200 nm.

[0024] The present invention provides a roll material prepared by the preparation method described in the above technical solution.

[0025] Compared with the prior art, the present invention provides a roll material and a preparation method thereof. The preparation method provided by the present invention includes the following steps: a) sequentially melting, casting, and forging the roll raw material to obtain a roll blank; in step a), the composition of the roll raw material includes: C 0.6 - 1 wt%, Mn 1.5 - 3.5 wt%, Cr 0.8 - 3 wt%, Cu 0.1 - 0.4 wt%, Fe 93 - 96 wt%; b) quenching the roll blank to obtain a quenched roll blank; c) performing a tempering treatment on the quenched roll blank, after tempering and holding for a period of time, clamping both ends of the roll blank for torsion and holding for a period of time, and then cooling to obtain a roll blank after thermomechanical treatment; d) performing turning on the roll blank after thermomechanical treatment to obtain a roll semi-finished product; e) performing surface nanocrystallization treatment on the roll semi-finished product to obtain a roll material. The preparation method provided by the present invention breaks through the limitations of traditional high alloying. By optimizing the alloy composition, thermomechanical treatment, and introducing a surface nanocrystallization process, while maintaining sufficient rigidity of the roll core, the hardness and wear resistance of the roll surface are improved, thereby providing better performance guarantee and lower cost input for the rolling process. More specifically, the preparation method provided by the present invention has at least the following beneficial effects:

[0026] ① The present invention changes the development idea of traditional rolls, that is, adding high alloys to increase the wear resistance of rolls. By adopting a low-alloy composition design and combining thermomechanical treatment and surface nanocrystallization, the comprehensive performance of the rolls is improved.

[0027] ②Reduce the production cost of existing high-alloy rolls. Decrease the Cr content (5 - 12%) of traditional Cr5 - Cr8 rolls to 0.8 - 3%, and through the synergistic effect of combining Cu (0.1 - 0.4%), Mn (1.5 - 3.5%) and trace amounts of other alloying elements, achieve a 18 - 25% reduction in raw material costs.

[0028] ③The introduction of Mn in the alloy raw materials will expand the austenite phase region, lower the martensite transformation temperature, and form a considerable amount of retained austenite. These retained austenites can reduce the difficulty of surface nanocrystallization of the roll. After surface nanocrystallization, the retained austenite on the surface will transform into martensite or nano-twins at the nanoscale, significantly improving the surface hardness and wear resistance of the roll.

[0029] ④The introduction of Cu in the alloy raw materials will reduce the stacking fault energy of the alloy, decrease the difficulty of dislocation slip, reduce the difficulty of surface nanocrystallization, and improve the surface nanocrystallization effect.

[0030] ⑤Deformation heat treatment can increase the dislocation density of the roll, strengthen the roll body, improve the basic hardness and stiffness of the roll, and promote subsequent surface nanocrystallization.

[0031] ⑥Surface nanocrystallization can introduce a very high surface compressive stress (up to 1000 MPa), which can inhibit the adverse effects of the residual stress brought by deformation heat treatment, control the roll profile, and at the same time, the surface compressive stress will effectively improve the fatigue resistance of the roll surface. Detailed implementation manners

[0032] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0033] The present invention provides a preparation method for roll materials, including the following steps:

[0034] a) Smelt, cast, and forge the roll raw materials in sequence to obtain a roll blank;

[0035] In step a), the composition of the roll raw materials includes: C 0.6 - 1 wt%, Mn 1.5 - 3.5 wt%, Cr 0.8 - 3 wt%, Cu 0.1 - 0.4 wt%, Fe 93 - 96 wt%;

[0036] b) Quench the roll blank to obtain a quenched roll blank;

[0037] c) Temper the quenched roll blank. After tempering and holding for a period of time, hold both ends of the roll blank and twist for a period of time, then cool to obtain the roll blank after thermomechanical treatment;

[0038] d) Machine the roll blank after thermomechanical treatment to obtain a semi-finished roll;

[0039] e) Perform surface nanocrystallization treatment on the semi-finished roll to obtain the roll material.

[0040] In the preparation method provided by the present invention, in step a), C in the roll raw material is the basis for forming carbides. The roll needs to maintain basic hardness and stiffness, and the carbon content cannot be too low, but too high will reduce toughness. A C content of 0.6 - 1 wt% can ensure that the roll has sufficient hardness and stiffness, while maintaining appropriate toughness to prevent brittle fracture; if the C content < 0.6 wt%, the wear resistance is insufficient; > 1 wt%, the roll may be too brittle and the impact resistance decreases. In the present invention, the C content in the roll raw material can specifically be 0.6 wt%, 0.65 wt%, 0.7 wt%, 0.75 wt%, 0.8 wt%, 0.85 wt%, 0.9 wt%, 0.95 wt% or 1 wt%.

[0041] In the preparation method provided by the present invention, in step a), the main function of Mn in the roll raw material is to improve toughness, expand the austenite phase region, and improve hardenability. During quenching, Mn reduces the martensite transformation temperature and increases the retained austenite (RA), which helps to reduce the difficulty of surface nanocrystallization. In the traditional roll production process, the retained austenite is very sensitive and the less the better, but in the present invention, a certain amount of retained austenite content is required, which helps to improve the toughness of the roll, reduce the difficulty of surface nanocrystallization, and at the same time, the surface hardness and wear resistance can be guaranteed by cooperating with the subsequent production process. In the present invention, the Mn content in the roll raw material can specifically be 1.5 wt%, 1.8 wt%, 2 wt%, 2.3 wt%, 2.5 wt%, 2.7 wt%, 3 wt%, 3.2 wt% or 3.5 wt%.

[0042] In the preparation method provided by the present invention, in step a), the main function of Cr in the roll raw material is to form Cr7C3 carbide, improve wear resistance and hardness, improve hardenability, and improve the tissue uniformity of steel. Excessive Cr (> 3%) will lead to an excessive number of carbides, making the matrix brittle and reducing the impact resistance. In the present invention, the Cr content in the roll raw material can specifically be 0.8 wt%, 1 wt%, 1.2 wt%, 1.5 wt%, 1.7 wt%, 2 wt%, 2.2 wt%, 2.5 wt%, 2.7 wt% or 3 wt%.

[0043] In the preparation method provided by the present invention, in step a), the main function of Cu in the roll raw material is to reduce the stacking fault energy, improve the dislocation slip ability, and facilitate surface nanocrystallization. During the tempering process, Cu forms nano-precipitates, improving the tempering strength and wear resistance. Excessive Cu may cause hot working cracks, and it is more appropriate to control it within the range of 0.1 - 0.4 wt%. In the present invention, the Cu content in the roll raw material may specifically be 0.1 wt%, 0.15 wt%, 0.2 wt%, 0.25 wt%, 0.3 wt%, 0.35 wt% or 0.4 wt%.

[0044] In the preparation method provided by the present invention, in step a), the composition of the roll raw material preferably further includes one or more of Si, Mo, V, Ni, and Nb. Si can increase hardenability, and Mo, V, Ni, and Nb can form finer carbides, improving the hardness of the roll and simultaneously refining the austenite grains. In the present invention, the Si content in the roll raw material is preferably 0.5 - 1 wt%, and may specifically be 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt% or 1 wt%; the V content in the roll material is preferably 0.1 - 0.2 wt%, and may specifically be 0.1 wt%, 0.12 wt%, 0.15 wt%, 0.17 wt% or 0.2 wt%; the Ni content in the roll material is preferably 0.3 - 0.8 wt%, and may specifically be 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt% or 0.8 wt%; the Nb content in the roll material is preferably 0.01 - 0.1 wt%, and may specifically be 0.01 wt%, 0.03 wt%, 0.05 wt%, 0.08 wt% or 0.1 wt%.

[0045] In the preparation method provided by the present invention, in step a), the Fe content in the roll raw material is preferably the balance.

[0046] In the preparation method provided by the present invention, in step a), the melting can be carried out by conventional processes, including but not limited to converter steelmaking, secondary refining, etc.

[0047] In the preparation method provided by the present invention, in step a), the casting can be carried out by conventional processes, including but not limited to continuous casting, die casting, precision casting, etc.

[0048] In the preparation method provided by the present invention, in step a), the forging can be carried out by conventional processes, including but not limited to multi-directional forging, multi-stage forging, multi-directional die forging, etc.

[0049] In the preparation method provided by the present invention, in step b), the temperature of the quenching treatment is preferably 850 - 1000 °C, specifically it can be 850 °C, 860 °C, 870 °C, 880 °C, 890 °C, 900 °C, 910 °C, 920 °C, 930 °C, 940 °C, 950 °C, 960 °C, 970 °C, 980 °C, 990 °C or 1000 °C; the cooling method of the quenching treatment is preferably oil cooling, water cooling or air cooling.

[0050] In the preparation method provided by the present invention, in step c), the temperature of the tempering treatment is preferably 450 - 550 °C, specifically it can be 450 °C, 460 °C, 470 °C, 480 °C, 490 °C, 500 °C, 510 °C, 520 °C, 530 °C, 540 °C or 550 °C; the tempering holding time is preferably more than 30 min, more preferably 30 - 60 min, specifically it can be 30 min, 35 min, 40 min, 45 min, 50 min, 55 min or 60 min.

[0051] In the preparation method provided by the present invention, in step c), the torsional loading rate at each end of the roll blank is preferably 0.1 - 1 ° / s, specifically it can be 0.1 ° / s, 0.2 ° / s, 0.3 ° / s, 0.4 ° / s, 0.5 ° / s, 0.6 ° / s, 0.7 ° / s, 0.8 ° / s, 0.9 ° / s or 1 ° / s; the torsional angle at each end of the roll blank is preferably 3 - 5 °, specifically it can be 3 °, 3.5 °, 4 °, 4.5 ° or 5 °; the holding time of the torsion is preferably 10 - 15 s, specifically it can be 10 s, 11 s, 12 s, 13 s, 14 s or 15 s.

[0052] In the preparation method provided by the present invention, in step c), the cooling method is preferably water cooling.

[0053] In the preparation method provided by the present invention, in step d), the turning processing method preferably includes rough turning and finish turning; the roughness of the roll semi-finished product obtained after turning is preferably ≤0.8 μm, more preferably ≤0.6 μm, still more preferably ≤0.4 μm, and most preferably ≤0.2 μm; the radial runout of the roll semi-finished product obtained after turning is preferably ≤0.05 mm, more preferably ≤0.03 mm, still more preferably ≤0.02 mm.

[0054] In the preparation method provided by the present invention, in step e), the surface nanocrystallization treatment method includes one or more of shot peening, surface mechanical grinding, surface mechanical rolling, surface mechanical ball burnishing, dynamic plastic deformation, mechanical ball milling, equal channel angular pressing and high energy beam heat treatment.

[0055] In the preparation method provided by the present invention, in step e), the surface grain size of the roll material obtained after the surface nanocrystallization treatment is preferably <200 nm, and specifically may be 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, 160 nm, 170 nm or 180 nm.

[0056] In the preparation method provided by the present invention, in step e), after the surface nanocrystallization treatment is completed, the grain size of the obtained roll material increases gradually from the surface to the interior, that is, nanocrystalline (<200 nm), submicron crystalline (200 nm to <1 μm), micron crystalline (1 to 10 μm), and coarse crystalline (>10 μm). Among them, the depth of the nanocrystalline layer is preferably 0.005 to 0.05 mm, and specifically may be 0.005 mm, 0.01 mm, 0.015 mm, 0.02 mm, 0.025 mm, 0.03 mm, 0.035 mm, 0.04 mm, 0.045 mm or 0.05 mm; the depth of the submicron crystalline layer is preferably 0.1 to 1 mm, and specifically may be 0.1 mm, 0.2 mm, 0.3 mm, 0.4 mm, 0.5 mm, 0.53 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm or 1 mm; the depth of the micron crystalline layer is preferably 0.1 to 1 mm, and specifically may be 0.1 mm, 0.2 mm, 0.3 mm, 0.38 mm, 0.4 mm, 0.5 mm, 0.6 mm, 0.67 mm, 0.7 mm, 0.8 mm, 0.9 mm or 1 mm.

[0057] The present invention also provides a roll material prepared by the preparation method according to the above technical solution.

[0058] The technical solution provided by the present invention breaks through the limitations of traditional high alloying. By optimizing the alloy composition, thermomechanical treatment, and introducing the surface nanocrystallization process, while maintaining sufficient rigidity of the roll core, the hardness and wear resistance of the roll surface are improved, thereby providing better performance guarantee and lower cost input for the rolling process. More specifically, the technical solution provided by the present invention has at least the following beneficial effects:

[0059] ① The present invention changes the development idea of traditional rolls, that is, adding high alloys to increase the wear resistance of rolls. By adopting a low-alloy composition design and combining thermomechanical treatment and surface nanocrystallization, the comprehensive performance of the rolls is improved.

[0060] ② Reduce the production cost of existing high-alloy rolls, reduce the Cr content (5 - 12%) of traditional Cr5 - Cr8 rolls to 0.8 - 3%, and combine the synergistic effects of Cu (0.1 - 0.4%), Mn (1.5 - 3.5%) and trace amounts of other alloying elements to achieve a 18 - 25% reduction in raw material costs.

[0061] ③ The introduction of Mn in the alloy raw materials will expand the austenite phase region, lower the martensite transformation temperature, and form a considerable amount of retained austenite. These retained austenites can reduce the difficulty of surface nanocrystallization of the roll. After surface nanocrystallization, the retained austenite on the surface will transform into martensite or nanotwins at the nanoscale, significantly improving the surface hardness and wear resistance of the roll.

[0062] ④ The introduction of Cu in the alloy raw materials will reduce the stacking fault energy of the alloy, decrease the difficulty of dislocation slip, reduce the difficulty of surface nanocrystallization, and improve the surface nanocrystallization effect.

[0063] ⑤ Deformation heat treatment can increase the dislocation density of the roll, strengthen the roll body, improve the basic hardness and stiffness of the roll, and promote subsequent surface nanocrystallization.

[0064] ⑥ Surface nanocrystallization can introduce a very high surface compressive stress (up to 1000 MPa), which can inhibit the adverse effects of the residual stress caused by deformation heat treatment, control the roll profile, and at the same time, the surface compressive stress will effectively improve the fatigue resistance of the roll surface.

[0065] For the sake of clarity, the following will be described in detail through the following examples.

[0066] Example 1

[0067] I. Composition design (wt.%)

[0068] C 0.8%, Mn 2.5%, Cr 1.5%, Cu 0.3%, and the balance is Fe.

[0069] II. Preparation process

[0070] (1) Melting and casting

[0071] Electric furnace melting: The raw material ratio is scrap steel (60%), pig iron (30%), and alloy materials (10%). The alloying elements are accurately proportioned according to the target composition; the melting temperature is 1550 - 1600 °C, and the alloying elements are added in stages. Cr and Cu are added in the later stage of melting to reduce burning loss.

[0072] Ladle furnace refining: The refining temperature is 1580 - 1620 °C, the refining time is ≥ 20 minutes, and the vacuum degree is ≤ 67 Pa (degassing treatment).

[0073] Continuous casting: The superheat is controlled at 35 °C ± 5 °C, the casting speed is 1.2 - 1.5 m / min, the diameter of the continuous casting billet is Φ300 mm, and the surface quality requirements are no cracks and shrinkage cavities.

[0074] (2) Forging

[0075] The heating temperature is 1150°C ± 10°C, the heating-up time is 8 hours, and the heat preservation time is 180 minutes; the forging ratio is 4:1, multi-directional forging (three upsetting and three drawing processes) is adopted, the upsetting deformation amount each time is 30%, and the final forging temperature is ≥900°C; after forging, it is air-cooled to room temperature.

[0076] (3) Quenching treatment

[0077] The quenching temperature is 920°C ± 10°C, the heating rate is 3 - 5°C / min, and the heat preservation time is 200 minutes; the cooling medium is fast quenching oil, the oil temperature is 60 - 80°C, the stirring speed is 0.8m / s, and it is cooled to room temperature.

[0078] (4) Thermomechanical treatment

[0079] Tempering treatment: The tempering temperature is 500°C ± 5°C, and the heat preservation time is 40 minutes.

[0080] Torsional loading: At the tempering temperature, a 4° torsional angle is synchronously applied to both ends of the roll, the loading rate is 0.5° / s, and after maintaining for 12 seconds, it is water-cooled (the cooling rate is ≥300°C / s).

[0081] (5) Turning

[0082] Rough turning parameters: The unilateral allowance is 5mm, the feed rate is 0.3mm / r, the cutting speed is 80m / min, and the surface roughness Ra is 3.2μm.

[0083] Fine turning parameters: The feed rate is 0.1mm / r, the cutting speed is 120m / min, the radial runout is ≤0.03mm, and the surface roughness Ra is 0.6μm.

[0084] (6) Surface nanocrystallization (shot peening)

[0085] Shot peening parameters: The diameter of the steel shot is 5mm (hardness 60 - 63HRC), the shot peening pressure is 0.4MPa, and the shot peening time is 30 minutes.

[0086] Gradient structure: The surface grain size is 150nm, the depth of the nanocrystalline layer is 0.01mm, the depth of the sub-micron crystalline layer is 0.3mm, the depth of the micron crystalline layer is 0.5mm, and the total depth of the gradient layer is 0.81mm.

[0087] Performance evaluation:

[0088] The total alloy composition content is 4.3%, which is 64% less than that of the conventional high-chromium roll (calculated according to 12%); the surface grain size of the roll is 150nm, the surface hardness of the roll reaches 95 - 97HSD, and the surface compressive stress is 780MPa.

[0089] Example 2

[0090] I. Composition design (wt.%)

[0091] C 0.6%, Mn 3.2%, Cr 0.8%, Cu 0.1%, V 0.15%, Nb 0.05%, and the balance is Fe.

[0092] II. Preparation Process

[0093] (1) Melting and Casting

[0094] Vacuum induction melting: The raw materials are pure scrap steel (S ≤ 0.010%, P ≤ 0.015%). The melting temperature is 1600 - 1650°C, the vacuum degree is ≤ 10 Pa, and Mn, Cu, V, and Nb alloys are added in the later stage of melting.

[0095] Die casting process: The pouring temperature of the molten steel is 1550°C, the preheating temperature of the mold is 600°C, and the diameter of the casting blank is Φ250 mm.

[0096] (2) Forging (two-stage forging)

[0097] The first stage: Rough forging at 1150°C (deformation amount 50%), and the final forging temperature ≥ 1000°C;

[0098] The second stage: Finish forging at 900°C (deformation amount 30%), and the final forging temperature ≥ 800°C, forging ratio 3.5:1.

[0099] (3) Quenching Treatment

[0100] Quenching temperature 950°C ± 10°C, heating rate 5°C / min, holding time 1.5 minutes per millimeter of thickness (holding for 300 minutes at 200 mm thickness); The cooling process is water cooling, the cooling rate ≥ 50°C / s, and the hardness after quenching is HRC 55 ± 1.

[0101] (4) Thermomechanical Treatment

[0102] Tempering treatment: Tempering temperature 450°C ± 5°C, holding for 60 minutes, and nitrogen is introduced into the furnace for protection (oxygen content ≤ 0.3%).

[0103] Torsional loading: Torsional forces are applied synchronously to both ends of the roll at the tempering temperature, and the torsional forces are applied in two times; Among them, the loading rate of the first torsion is 0.3° / s, the torsional angle is 1.5°, and it is held for 5 s; After an interval of 5 s, the second torsion is carried out, the loading rate is 0.3° / s, and the torsional angle is 1.5° (i.e., the total torsional angle is 3°), and it is water cooled after holding for 10 s (cooling rate ≥ 15°C / s).

[0104] (5) Turning

[0105] Rough turning parameters: Unilateral allowance 3 mm, feed rate 0.4 mm / r, cutting speed 60 m / min, surface roughness Ra 6.3 μm.

[0106] Precision turning parameters: feed rate 0.08 mm / r, cutting speed 150 m / min, radial runout ≤0.02 mm, surface roughness Ra 0.4 μm.

[0107] (6) Surface nanocrystallization (mechanical rolling)

[0108] Mechanical rolling parameters: rotational speed 300 r / min, pressure 10 kN, reciprocating rolling 10 times.

[0109] Gradient structure: surface grain size 100 nm, depth of nanocrystalline layer 0.03 mm, depth of submicron crystalline layer 0.53 mm, depth of micron crystalline layer 0.67 mm, total depth of gradient layer 1.23 mm.

[0110] Performance evaluation:

[0111] The total alloy composition content is 4.3%, a 64% reduction compared to conventional high-chromium rolls (calculated at 12%); the surface grain size of the roll is 100 nm, the surface hardness of the roll reaches 100 - 102 HSD, and the surface compressive stress is 980 MPa.

[0112] Example 3

[0113] I. Composition design (wt.%)

[0114] C 1.0%, Mn 1.8%, Cr 2.2%, Cu 0.4%, Ni 0.5%, Si 0.8%, the balance is Fe.

[0115] II. Preparation process

[0116] (1) Melting and casting

[0117] Converter + LF furnace refining: desulfurization rate ≥90% (end sulfur ≤0.008%); temperature during Ni and Cu alloying stage is 1600 °C, wire feeding alloying.

[0118] Precision casting: mold material is graphite mold, preheating temperature is 800 °C, pouring temperature is 1520 °C, near-net-shape machining allowance ≤2 mm.

[0119] (2) Forging (multi-directional die forging)

[0120] Die temperature 400 °C, billet heating temperature 1100 °C, deformation amount 70% (three-way compression ratio 2:1:2); finish forging temperature ≥850 °C, spray cooling after forging (cooling rate 20 °C / s), eliminating casting shrinkage cavity, billet diameter Φ450 mm.

[0121] (3) Quenching treatment (step quenching)

[0122] The heating temperature is 850°C ± 10°C, and the holding time is 450 minutes; in the first stage, water cooling is carried out to 300°C (cooling rate ≥ 30°C / s), and in the second stage, air cooling is carried out to room temperature.

[0123] (4) Deformation heat treatment

[0124] Tempering treatment: The tempering temperature is 550°C ± 5°C, and the holding time is 30 minutes.

[0125] Torsional loading: At the tempering temperature, a 5° torsional angle is synchronously applied to both ends of the roll, the loading rate is 1° / s, and after holding for 15 seconds, water cooling is carried out (cooling rate ≥ 25°C / s).

[0126] (5) Turning

[0127] Rough turning parameters: Unilateral allowance is 2 mm, feed rate is 0.2 mm / r, cutting speed is 100 m / min, and surface roughness Ra is 3.2 μm.

[0128] Finish turning parameters: Feed rate is 0.05 mm / r, cutting speed is 200 m / min, radial runout ≤ 0.02 mm, and surface roughness ≤ 0.2 μm.

[0129] (6) Surface nanocrystallization (laser shock + mechanical ball milling)

[0130] Laser shock parameters: Wavelength is 1064 nm, energy density is 10 J / cm 2 , pulse width is 20 ns, shock is carried out 3 times, and surface pre-compressive stress ≥ 800 MPa.

[0131] Mechanical ball milling parameters: Zirconia ball milling medium (Φ3 mm), ball-to-material ratio is 10:1, rotation speed is 300 rpm, ball milling time is 4 h, and surface grain size is 80 nm.

[0132] Gradient layer depth: Surface grain size is 120 nm, nanocrystalline layer is 0.02 mm, sub-micron crystalline layer is 0.8 mm, micron crystalline layer is 0.38 mm, and total depth is 1.2 mm.

[0133] Performance evaluation:

[0134] The total alloy composition content is 5.7%, which is 52.5% less than that of the conventional high-chromium roll (calculated according to 12%); the surface grain size of the roll is 120 nm, the surface hardness of the roll reaches 102 - 104 HSD, and the surface compressive stress is 1080 MPa.

[0135] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can still be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A preparation method of a roll material, characterized in that It includes the following steps: a) Smelt, cast and forge the roll raw materials in sequence to obtain a roll blank; In step a), the composition of the roll raw materials includes: C 0.6 - 1 wt%, Mn 1.5 - 3.5 wt%, Cr 0.8 - 3 wt%, Cu 0.1 - 0.4 wt%, Fe 93 - 96 wt%; b) Quench the roll blank to obtain a quenched roll blank; c) Temper the quenched roll blank. After tempering and holding for a period of time, hold both ends of the roll blank and twist for a period of time, then cool to obtain a roll blank after thermomechanical treatment; d) Machine the roll blank after thermomechanical treatment to obtain a roll semi-finished product; e) Perform surface nanocrystallization treatment on the roll semi-finished product to obtain a roll material.

2. The preparation method according to claim 1, characterized in that, In step a), the composition of the roll raw materials further includes one or more of Si, Mo, V, Ni and Nb.

3. The roll material according to claim 2, characterized in that, The Si content of the roll raw materials is 0.5 - 1 wt%; And / or, the V content of the roll material is 0.1 - 0.2 wt%; And / or, the Ni content of the roll material is 0.3 - 0.8 wt%; And / or, the Nb content of the roll material is 0.01 - 0.1 wt%.

4. The preparation method according to claim 1, wherein, In step b), the temperature of the quenching treatment is 850 - 1000 °C.

5. The preparation method according to claim 1, wherein In step c), the temperature of the tempering treatment is 450 - 550 °C; the holding time for tempering is more than 30 min.

6. The preparation method according to claim 1, characterized in that, In step c), the torsion angle of each end of the roll blank is 3° - 5°; the holding time for torsion is 10 - 15 s.

7. The preparation method according to claim 1, characterized in that, In step d), the roughness of the roll semi-finished product is ≤ 0.8 μm, and the radial runout is ≤ 0.05 mm.

8. The preparation method according to claim 1, characterized in that, In step e), the method of surface nanocrystallization treatment includes at least one or more of shot peening, surface mechanical attrition, surface mechanical rolling, surface mechanical ball burnishing, dynamic plastic deformation, mechanical ball milling, equal-channel angular pressing and high-energy beam heat treatment.

9. The preparation method according to claim 1, wherein, In step e), the surface grain size of the roll material is < 200 nm.

10. A roll material, characterized in that, The roll material is obtained by the preparation method according to any one of claims 1 - 9.