High fatigue resistance roughing work roll for sendzimir mill and method of manufacturing the same

Abstract

The application discloses a high fatigue resistance property Sendzimir roughing mill work roll and a manufacturing method thereof, and chemical components and weight percentages are as follows: carbon 0.80-1.20%; silicon 0.60-1.00%; manganese 0.20-0.60%; phosphorus ≤0.020%; sulfur ≤0.015%; chromium 7.00-10.00%; niobium 0.10-0.30%; molybdenum 1.50-2.50%; vanadium 0.30-0.80%; the rest is iron and inevitable impurities; and the manufacturing method comprises smelting electroslag ingot, high-temperature homogenization treatment, forging roll blank, post-forging heat treatment and final heat treatment. Through the synergistic effect of 'optimizing alloy elements, high-temperature homogenization treatment and multi-directional forging process', the application remarkably refines carbide size, eliminates coarse net-shaped carbides, reduces stress concentration sources, and fundamentally improves the weakening problem of carbide boundaries, thereby greatly improving the fatigue resistance property.

Description

Technical Field

[0001] This invention belongs to the technical field of Sendzimir mill work rolls, specifically relating to a high fatigue-resistant Sendzimir mill roughing work roll and its manufacturing method. Background Technology

[0002] Sendzimir 20-roll mills are primarily used for rolling thin strip materials that are difficult to deform, such as silicon steel and stainless steel. Their roll system has numerous contact pairs, with the work rolls, being the smallest diameter components and directly in contact with the workpiece, bearing immense rolling loads and complex stress states. Approximately 70% of roll failures are caused by fatigue damage, especially in roughing passes. When high-roughness work rolls are used, short cracks and fatigue spalling (shedding) are highly likely to occur on the roll surface, severely impacting roll life and strip surface quality.

[0003] In existing technologies, Sendzimir mill work rolls mostly use Cr12 series high-carbon, high-chromium steel (such as Cr12Mo1V1, Cr12MoVCo, etc.). Cr12 series high-carbon, high-chromium steel has large, network-like carbides that disrupt the matrix. Under cyclic alternating stress, the boundaries of these large carbides easily become crack initiation sites, leading to surface metal spalling after crack propagation.

[0004] Chinese patent document CN115058652A discloses a Sendzimir mill work roll with anti-roll mark properties and its manufacturing method. This document describes a Sendzimir mill work roll with a hardness of over 64 HRC and a grain size of over 9 grades achieved through a special post-forging heat treatment (secondary normalizing + secondary annealing), thus meeting the requirements for anti-roll mark properties. However, its carbide size is still relatively large (bulk carbide size > 20 μm) and exhibits a banded distribution, with a eutectic carbide grade test showing only 3-4 grades.

[0005] Therefore, obtaining smaller, more uniformly distributed, and more wear-resistant carbides to improve the fatigue resistance of rolls is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] The purpose of this invention is to solve the above-mentioned problems and provide a high-fatigue-resistant Sendzimir mill roughing roll with smaller carbide size, more uniform distribution, and eutectic carbide grade test up to 1-2, and a method for its preparation.

[0007] The technical solution to achieve the purpose of this invention is: a high fatigue-resistant Sendzimir mill roughing roll, the chemical composition and weight percentage of which are as follows: carbon 0.80-1.20%; silicon 0.60-1.00%; manganese 0.20-0.60%; phosphorus ≤0.020%; sulfur ≤0.015%; chromium 7.00-10.00%; niobium 0.10-0.30%; molybdenum 1.50-2.50%; vanadium 0.30-0.80%; the remainder being iron and unavoidable impurities.

[0008] Compared to CN115058652A, the working roll material of this invention uses niobium instead of nickel, which results in smaller and more uniformly distributed carbides, thus achieving higher fatigue resistance.

[0009] The manufacturing method of the above-mentioned high fatigue resistance Sendzimir mill roughing work rolls includes smelting electroslag ingots according to chemical composition and weight percentage → high temperature homogenization treatment → forging roll blanks → post-forging heat treatment → final heat treatment.

[0010] The smelting of electroslag ingots includes electric furnace smelting → ladle refining (LF) → vacuum degassing (VD) → protective atmosphere electroslag remelting (ESR) to obtain electroslag ingots with high purity and good density, thereby reducing the original segregation.

[0011] The high-temperature homogenization treatment involves subjecting the electroslag ingot to a long-term (≥20h) high-temperature diffusion annealing at 1150℃~1200℃ to dissolve coarse eutectic carbides and reduce compositional inhomogeneity.

[0012] The forging process differs from the traditional Sendzimir mill roughing roll forging process, which only involves elongation. Instead, it employs a multi-directional forging process of "upsetting-elongation-upsetting-elongation". The forging ratio is controlled at ≥7, and the final forging temperature is controlled at above 900℃ to break up the carbide network and improve its distribution morphology.

[0013] The post-forging heat treatment involves normalizing at 900–1000℃ followed by spheroidizing annealing at 750–850℃ to obtain a uniform spheroidized pearlite structure while reducing forging stress.

[0014] The final heat treatment includes preheating, quenching, cryogenic treatment, and tempering.

[0015] The preheating process employs a two-stage preheating method, with the first preheating temperature at 350–450°C and the second preheating temperature at 800–850°C, in order to reduce thermal stress.

[0016] The quenching process involves heating in a protective atmosphere furnace at 1020–1080°C, followed by oil cooling after holding to ensure the matrix transforms into martensite while controlling deformation.

[0017] The cryogenic treatment temperature is -100℃ to -60℃, and the cryogenic treatment time is 2 to 3 hours, in order to promote the transformation of residual austenite into martensite and improve hardness stability.

[0018] The tempering process involves three high-temperature tempering processes at 500–550°C, with each tempering lasting 4–6 hours to fully relieve stress, allow carbides to disperse and precipitate, and achieve a secondary hardening effect.

[0019] The positive effects of this invention are as follows: Through the synergistic effect of "optimized alloying elements + high-temperature homogenization treatment + multi-directional forging process", this invention significantly refines the carbide size, eliminates coarse network carbides, and reduces stress concentration sources, thereby fundamentally improving the problem of carbide boundary weakening. It effectively inhibits the initiation and propagation of fatigue short cracks, significantly reduces the risk of fatigue chipping under rough rolling conditions, and thus greatly improves fatigue resistance. The improved matrix toughness makes the roll less prone to sudden fracture when facing rolling impact or local overload, while the hardness can still be maintained at about 64HRC, with good hardness uniformity and high wear resistance. Attached Figure Description

[0020] Figure 1 Metallographic image (100×) of the carbide structure of the work roll prepared in Example 1.

[0021] Figure 2 Metallographic image (100×) of the carbide structure of the work roll prepared in Comparative Example 1. Detailed Implementation

[0022] (Example 1) The chemical composition and weight percentage of the high fatigue resistance Sendzimir mill roughing rolls in this embodiment are as follows: carbon 0.85%; silicon 0.72%; manganese 0.34%; phosphorus ≤0.015%; sulfur ≤0.010%; chromium 8.20%; niobium 0.15%; molybdenum 1.70%; vanadium 0.60%; the remainder being iron and unavoidable impurities.

[0023] The method for manufacturing high fatigue-resistant Sendzimir mill roughing rolls in this embodiment includes the following steps: ① Smelt electroslag ingots according to their chemical composition and weight percentage.

[0024] The process of electric furnace smelting → ladle refining (LF) → vacuum degassing (VD) → protective atmosphere electroslag remelting (ESR) is adopted to obtain electroslag ingots with high purity and good density.

[0025] ② Heat the electroslag ingots to 1180℃ in the furnace and hold for 24 hours for high-temperature homogenization treatment.

[0026] ③ After exiting the furnace, the roll blank is immediately subjected to "upsetting-drawing-upsetting-drawing" forging. The initial forging temperature is 1150℃, the final forging temperature is 950℃, and the forging ratio is 7.5 to obtain the roll blank.

[0027] ④ Immediately after forging, normalize at 950℃, and after air cooling, perform isothermal spheroidizing annealing at 800℃.

[0028] ⑤ After rough machining, perform final heat treatment.

[0029] Preheat at 400℃ for 2 hours, then increase the temperature to 850℃ and preheat for another 2 hours.

[0030] Then, the temperature is raised to 1050℃ (holding coefficient 1.0 min / mm) for quenching, and then oil-cooled to room temperature.

[0031] Then it was immediately transferred to a -80℃ cryogenic chamber for cryogenic treatment for 2.5 hours.

[0032] Finally, the product undergoes three high-temperature tempering processes at 520℃, with each tempering lasting 5 hours. It is then air-cooled to room temperature and precision machined to the finished product dimensions.

[0033] The surface hardness of the working roll obtained in this embodiment is 64.2 HRC, and the hardness uniformity is ≤1.0 HRC.

[0034] The eutectic carbides were graded according to the fourth rating chart of the national standard GB / T 14979-1994 "Evaluation Method for Eutectic Carbide Inhomogeneity of Steel". The result was Grade 1, with the maximum carbide size ≤10μm. The metallographic photograph of the carbide microstructure is shown below. Figure 1 .

[0035] (Comparative Example 1) The working roll was prepared according to the material and method described in Example 1 of Chinese Patent Document CN115058652A. The surface hardness of the working roll body is 64.7 HRC and the hardness uniformity is ≤1.0 HRC.

[0036] The eutectic carbides were graded according to the fourth rating chart of the national standard GB / T 14979-1994 "Evaluation Method for Eutectic Carbide Inhomogeneity of Steel". The result was grade 3-4, with bulk carbide size >20μm. The metallographic photograph (100×) of the carbide microstructure is shown below. Figure 2 .

[0037] (Examples 2 to 5) The manufacturing method of the working rollers in each embodiment is the same as that in Embodiment 1, except for the chemical composition and weight percentage, as shown in Table 1.

[0038] Table 1 carbon 0.85% 0.95% 0.82% 0.85% 0.85% silicon 0.72% 0.76% 0.65% 0.72% 0.72% manganese 0.34% 0.43% 0.30% 0.34% 0.34% phosphorus ≤0.015% ≤0.015% ≤0.015% ≤0.015% ≤0.015% sulfur ≤0.010% ≤0.010% ≤0.010% ≤0.010% ≤0.010% chromium 8.20% 8.80% 7.80% 8.20% 8.20% niobium 0.15% 0.15% 0.15% 0.20% 0.10% molybdenum 1.70% 2.10% 1.55% 1.70% 1.70% vanadium 0.60% 0.70% 0.40% 0.60% 0.60% Roller body surface hardness 64.2 HRC 64.4 HRC 64.0 HRC 64.3 HRC 64.1 HRC Eutectic Carbide Rating Level 1 Level 1 Level 1-2 Level 1 Level 1-2 .

Claims

1. A high fatigue-resistant Sendzimir mill roughing work roll, the chemical composition and weight percentage of which are as follows: carbon 0.80-1.20%; silicon 0.60-1.00%; manganese 0.20-0.60%; phosphorus ≤0.020%; sulfur ≤0.015%; chromium 7.00-10.00%; niobium 0.10-0.30%; molybdenum 1.50-2.50%; vanadium 0.30-0.80%; the remainder being iron and unavoidable impurities.

2. A method for manufacturing the high fatigue resistance Sendzimir mill roughing roll as described in claim 1, characterized in that: The process includes: smelting electroslag ingots according to chemical composition and weight percentage → high-temperature homogenization treatment → forging roll blanks → post-forging heat treatment → final heat treatment; the high-temperature homogenization treatment involves high-temperature diffusion annealing of the electroslag ingots at a temperature of 1150℃~1200℃ for 20~30h; the forging adopts a forging process of "upsetting-drawing-upsetting-drawing", with a forging ratio of 7~9 and a final forging temperature of 900~980℃.

3. The method for manufacturing the high fatigue resistance Sendzimir mill roughing roll according to claim 2, characterized in that: The smelting of electroslag ingots includes electric furnace smelting → ladle refining → vacuum degassing → protective atmosphere electroslag remelting.

4. The method for manufacturing the high fatigue resistance Sendzimir mill roughing roll according to claim 2, characterized in that: The post-forging heat treatment consists of normalizing at 900–1000℃ followed by spheroidizing annealing at 750–850℃.

5. The method for manufacturing the high fatigue resistance Sendzimir mill roughing roll according to claim 2, characterized in that: The final heat treatment includes preheating → quenching → cryogenic treatment → tempering; The preheating adopts a two-stage preheating method, with the first preheating temperature being 350-450℃ and the second preheating temperature being 800-850℃; The quenching temperature is 1020–1080℃; The cryogenic treatment temperature is -100℃ to -60℃, and the cryogenic treatment time is 2 to 3 hours; The tempering process involves three high-temperature tempering processes, with a tempering temperature of 500–550°C and a holding time of 4–6 hours for each process.

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