Roughing guide rollers for roughing mill

Abstract

The invention belongs to the field of steel section rolling, and particularly relates to a rough rolling guide roller for a rough rolling mill. The alloy used for the guide roller comprises the following components and contents according to mass percentage: C 1.80-2.00%, Si 0.30-0.60%, Mn 0.40-0.70%, Cr 19.00-22.00%, Ni0.16-0.36%, Mo 0.10-0.20%, V 0.55-0.75%, W 1.30-1.50%, rare earth metal 1.0-1.2%, P≤0.030%, S≤0.030%, and the balance is iron. In the above scheme, Cr, W and Mo are added to the guide roller material, which increases the melting point of the alloy material, increases the self-diffusion activation energy of the alloy material and reduces the staggered energy, slows down the self-diffusion, and hinders the generation of dislocation, slip and climb of the material; at the same time, rare earth metal elements are added to the alloy, which not only hinders the sliding of grain boundaries, but also increases the surface energy of grain boundary cracks, avoids the generation of cracks at the grain boundaries during use, greatly improves the hardness and fracture strength of the guide roller alloy material, reduces high temperature sensitivity, and greatly improves the service life of the guide roller.

Description

Technical Field

[0001] The invention belongs to the field of steel section rolling, and in particular relates to a guide roller for a rough rolling unit. Background Art

[0002] The guide is a device installed before and after the rollers of the rolling mill during the rolling process of steel sections to help the rolled pieces enter and exit accurately and stably in a predetermined direction and state. Therefore, the guide is required to have extremely strong wear resistance and high temperature resistance. The unit composed of the first six rolling mills in the steel rolling production line is usually called the rough rolling unit. The rolled pieces in the rough rolling unit have a large cross-sectional area and fast heat dissipation, and the temperature of the rolled pieces drops significantly (generally from about 1020℃ to about 900℃), resulting in a high surface hardness of the rolled pieces, and the impact and wear on the guide also increase accordingly; in addition, the rough rolling guide of the rough rolling unit is heavy, the production cost is high, and the replacement is time-consuming and laborious. Therefore, in order to ensure the rolling operation rate, improve the wear resistance and high temperature resistance of the rough rolling guide, thereby extending the service life of the rough rolling guide, which is a long-term research topic for technicians.

[0003] The Chinese patent entitled "High-temperature wear-resistant alloy material for rolling mill guide and heat treatment method for rolling mill guide" (application publication number CN103757545 A, hereinafter referred to as document 1) adjusts the mass percentage of alloying elements such as carbon, chromium, and manganese, and its components are: C content 1.45~1.6wt%, Cr content 11~12.5wt%, Mn content 0.4~0.8wt%, etc., to obtain a uniform, discontinuous high wear-resistant structure (Cr,Fe)7C3 (HV1200~1800); at the same time, alloying elements Ni, Mo, and Cu are added to improve hardenability, produce secondary hardening, and make carbides small and evenly distributed. The heat treatment process is: first, stress relief annealing is performed at a low temperature of 200-300°C; then, preheating is performed at 500-600°C, and solution treatment is performed at 960-1050°C; finally, high-temperature tempering is performed at 440-480°C and low-temperature tempering is performed at 270-290°C. This solution improves the high-temperature wear resistance of the guide material to a certain extent and increases the service life of the guide.

[0004] The Chinese patent titled "An alloy material for a guide roller and its preparation method" (application publication number CN108642378A) states that the guide material of this solution is Fe with Si, Al, Mn, Mg, Zn, Ti, Cu, Zr, Na / Ca / Sr and rare earth added to it, and the rare earth is one of yttrium, lanthanum and cerium. This solution adds metal zirconium, titanium and rare earth metal elements to improve the wear resistance and oxidation resistance of the guide roller and increase the service life of the guide roller.

[0005] However, for the roughing guides of the roughing mill unit, although the service life of the above two solutions has been improved to a certain extent, there is still much room for improvement. Summary of the invention

[0006] The purpose of the present invention is to provide a rough rolling guide roller for a rough rolling mill. By optimizing the composition of the guide roller material and the smelting process, the high temperature wear resistance of the guide roller is greatly improved, avoiding frequent replacement of the guide roller to affect the rolling operation rate.

[0007] To achieve the above-mentioned purpose, the technical solution adopted by the present invention is: a roughing guide roller for a roughing mill, characterized in that the alloy used for the guide roller includes the following components and contents in mass percentage: C 1.80-2.00%, Si 0.30-0.60%, Mn 0.40-0.70%, Cr 19.00-22.00%, Ni 0.16-0.36%, Mo 0.10-0.20%, V0.55-0.75%, W 1.30-1.50%, rare earth metal 1.0-1.2%, P≤0.030%, S≤0.030%, and the balance is iron.

[0008] In the above scheme, Cr, W and Mo are added to the guide roller material, which increases the melting point of the alloy material, increases the self-diffusion activation energy of the alloy material and reduces the staggered energy, slows down the self-diffusion, and hinders the generation of dislocation, slip and climb of the material; at the same time, rare earth metal elements are added to the alloy, which not only hinders the sliding of grain boundaries, but also increases the surface energy of grain boundary cracks, avoids the generation of cracks at the grain boundaries during use, greatly improves the hardness and fracture strength of the guide roller alloy material, reduces high temperature sensitivity, and greatly improves the service life of the guide roller. DETAILED DESCRIPTION

[0009] The technical solution of the present invention is further described in detail below in conjunction with embodiments.

[0010] A rough rolling guide roller for a rough rolling mill unit. The alloy used for the guide roller comprises the following components and contents according to mass percentage: C 1.80-2.00%, Si 0.30-0.60%, Mn 0.40-0.70%, Cr19.00-22.00%, Ni 0.16-0.36%, Mo 0.10-0.20%, V 0.55-0.75%, W1.30-1.50%, rare earth metal 1.0-1.2%, P≤0.030%, S≤0.030%, and the balance is iron.

[0011] The rare earth metal is at least one of Pr and Nd, preferably two. Specifically, the rare earth metal is a mixture of Pr and Nd, wherein the mass ratio of Pr to Nd is (3-4):1. There are a few reports in the prior art that adding rare earth metal elements to alloys can effectively increase the surface energy of grain boundary cracks inside the alloy. However, there are only records of using a single type of rare earth metal in the prior art. The inventors found that the use of two rare earth metal elements, praseodymium (Pr) and neodymium (Nd), when used in combination, has a much better effect on improving the surface energy of grain boundary cracks than a single type of rare earth metal. When applied to guide rollers, the service life is also greatly improved.

[0012] The guide roller is cast using a directional solidification process, with an alloy melting temperature of 1500-1600°C, a temperature gradient of 135-145°C / cm, and a pulling speed of 0.5-0.8 mm / min. The so-called directional solidification, also known as directional crystallization, refers to a process for directional growth of crystals of metals or alloys in a melt. Directional solidification technology is a process for establishing a temperature gradient in a specific direction in a casting mold so that the molten alloy is solidified and cast in the opposite direction of the heat flow according to the required crystal orientation. The directional solidification process used in the present invention can reduce transverse grain boundaries, reduce the tendency to crack, and further increase the service life of the guide roller.

[0013] The heat treatment process used in the casting of the guide roller is: the workpiece is heated to 800-900°C, the workpiece is hot forged or hot rolled under heat preservation, then rapidly cooled in water or oil, tempered at 380-400°C, and then naturally cooled. In the prior art, the casting of the guide roller mostly adopts a heat treatment process of first gradient heating and then gradient cooling. For example, the document 1 cited in the background technology part has a heat treatment process of 200-300°C low-temperature annealing, 500-600°C preheating, 960-1050°C solid solution, 440-480°C high-temperature tempering, and 270-290°C low-temperature tempering. The heat treatment method of high-temperature quenching and low-temperature tempering in this application can improve the strength of the alloy, improve the plasticity and toughness of the alloy, reduce the sensitivity of temper brittleness, improve the brittle fracture resistance at low ambient temperatures, and further improve the service life of the guide roller.

[0014] Example 1

[0015] A rough rolling guide roller for a rough rolling mill unit. The alloy used for the guide roller includes the following components and contents according to mass percentage: C 1.82%, Si 0.45%, Mn 0.60%, Cr 20.00%, Ni 0.25%, Mo 0.15%, V 0.65%, W1.40%, Pr0.75%, Nd 0.25%, P≤0.030%, S≤0.030%, and the balance is iron.

[0016] The guide roller is cast using a directional solidification process, with an alloy melting temperature of 1550° C., a temperature gradient of 140° C. / cm, and a pulling speed of 0.6 mm / min.

[0017] The heat treatment process used in the guide roller casting is: the workpiece is heated to 850°C, hot forged under heat preservation, then rapidly cooled in water, tempered at 400°C, and then cooled naturally.

[0018] Embodiment 2-5

[0019] The same technical scheme as that of Example 1 is adopted, wherein the alloy composition used for the guide roller is shown in Table 1.

[0020] Example 6

[0021] The same technical solution as in Example 1 is adopted, wherein the same heat treatment process as in Document 1 is adopted during casting.

[0022] Table 1 Alloy composition used for guide rollers in Examples 1-6 (by mass percentage)

[0023]

[0024] Among them, P≤0.030% and S≤0.030% in the alloy, and the balance is iron.

[0025] Example 7

[0026] The same technical solution as that of Example 1 is adopted, wherein the rare earth metal element used as the alloy component of the guide roller is replaced with La 1.00%.

[0027] The data obtained from the guide roller test performance obtained in the above Examples 1-7 are shown in Table 2.

[0028] Table 2 Performance test of guide roller obtained in the embodiment

[0029] Hardness HRC <![CDATA[Tensile strength N / mm 2 > Online time (h) Example 1 60 1980 10000 Example 2 54 1760 6000 Example 3 53 1690 5800 Example 4 53 1700 5900 Example 5 48 1250 4500 Example 6 52 1710 5700 Example 7 53 1680 6000

[0030] Among them, the online time is the accumulated online time of replacement after the guide rollers are in similar wear condition and affect the rolling operation.

[0031] It can be seen from the above data that the use of the technical solution of the present invention greatly increases the service life of the guide roller.

Claims

1. A roughing guide roller for a roughing mill, characterized in that: The alloy used for the guide roller includes the following components and contents according to mass percentage: C 1.80-2.00%, Si 0.30-0.60%, Mn0.40-0.70%, Cr 19.00-22.00%, Ni 0.16-0.36%, Mo 0.10-0.20%, V0.55-0.75%, W 1.30-1.50%, rare earth metal 1.0-1.2%, P≤0.030%, S≤0.030%, and the balance is iron.

2. The roughing guide roller for the roughing mill according to claim 1, characterized in that: The rare earth metal is at least one of Pr and Nd.

3. The roughing guide roller for the roughing mill according to claim 1 or 2, characterized in that: The rare earth metal is a mixture of Pr and Nd, wherein the mass ratio of Pr to Nd is (3-4):

1.

4. The roughing guide roller for the roughing mill according to claim 1, characterized in that: The guide roller is cast by a directional solidification process, with an alloy melting temperature of 1500-1600° C., a temperature gradient of 135-145° C. / cm, and a pulling speed of 0.5-0.8 mm / min.

5. The roughing guide roller for the roughing mill according to claim 1, characterized in that: The heat treatment process used in the guide roller casting is: the workpiece is heated to 800-900°C, hot forged or hot rolled under heat preservation, then quickly cooled in water or oil, tempered at 380-400°C, and then cooled naturally.

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