The application of cast high-speed steel roll in steel rolling production began in 1988, when it was used on a hot strip mill in Japan. Subsequently, the United States and Europe began to introduce the technology of casting high-speed steel rolls. The cast high-speed steel roll was initially used in the front section of the finishing mill of the hot strip mill to replace the high chromium cast iron roll. Later, the cast high-speed steel roll was also used in the finishing and roughing sections, wire rod, bar and cold-rolled strip mills, and satisfactory results were obtained.
The cast high-speed steel composite roll produced by Nippon Steel Corporation with CPC method has high wear resistance. After using the cast high-speed steel rolling rod, the steel passing per millimeter is significantly increased, the number of roll changes is significantly reduced, and the roll grinding amount is reduced. The main reason is that high-speed steel rolls contain high hardness carbides such as MC and M6C. In addition, the matrix structure of high-speed steel rolling rod is composed of stable and high hardness martensite and good hardenability and hardenability, which makes the hardness drop of high-speed steel roll significantly smaller than that of other rolls. These characteristics can ensure that the roll has good wear resistance during the whole working period.
In order to improve the production efficiency of the steel tube mill and reduce the roll consumption, the use of high-speed steel rolls in the steel tube mill is also quite successful. High-speed steel rolls have excellent wear resistance and resistance to surface orange peel defects. Their service life is 6-10 times longer than that of traditional rolls, and there is no steel sticking. Since the trial use of cast high-speed steel rolls in 1993, the Canadian Dofasco company has continuously increased the proportion of use. At present, cast high-speed steel rolls have been used on F2, F3, and F4 racks. After using the high-speed steel roll, the roll consumption is significantly reduced, and the rolling mill operation rate is significantly improved. The average steel passing capacity of F4 stand is increased from 360 t /h in june1992 to 490 t/h in november1994, and the strip surface quality is improved by 20%.
The semi-high speed steel composite roll produced by Hitachi has also achieved good results in rolling mills. Compared with the conventional forged steel roll containing 5.0%cr and 10.0%cr, the semi-high speed steel roll has less wear and a shallow fatigue layer, so the roll consumption is significantly reduced. For the production of the same amount of cold-rolled strip, the roll consumption is only 21% of that of 5.0%cr steel. Recently, the 2050 hot rolling mill of the Vanderbijlpark plant in South Africa used the new hss7 high-speed steel roll developed by Marichal ketin company in Belgium. The steel rolling volume per mm was increased to 12000t, while the ordinary high chromium cast iron roll was only 5000 t. After using high-speed steel rolls, the surface quality of the hot-rolled strip is greatly improved, and the problem of strip quality degradation caused by the iron oxide scale is reduced by 2/3. Using high-speed steel rolls has good economic benefits.
Baosteel 2050 hot strip roughing mill adopts semi high-speed steel roll, which has excellent hot crack resistance and wears resistance, and its service life is more than twice that of the original high chromium cast iron roll; When used in the front stand of finish rolling, its wear resistance is three times that of high chromium cast iron roll, and effectively overcomes the defect of spot strip. It can roll high surface quality strips, prolong the roll change cycle, and improve the production rate of the mill. The high-speed steel roll has been used in the front section of rough rolling and finish rolling of 158opc mill, and it also has good results. Hansteel uses high-speed steel rolls for F2, F3 stands and sometimes F1 stands of CSP production line. It mainly rolls SS400, SPHC, spa2h and other steel grades. The corresponding thickness ranges are 1.8-6 mm and 1 5-3 mm,3-6 mm。 According to the statistics, the millimeter rolling volume is 10500 T, 7800 T and 8200 t respectively, and the average millimeter rolling volume reaches 8900 T, which is 2-3 times that of ordinary high chromium iron rolls. The surface quality of the products is significantly improved; The roll can be used continuously for 2-3 times in each cycle. The roll grinding can be reduced by 1.6 times and the grinding loss can be reduced by 0.4 mm. Under normal conditions, the consumption of each roll can be reduced by about 25 RNM.
The general iron and Steel Research Institute selects high-carbon high-speed steel as the working layer, alloy nodular cast iron as the roll center, and the centrifugal casting method is used to manufacture high-speed steel composite rolling rod, which has the characteristics of high working layer hardness and uniform roll body hardness. The comprehensive life of the rolling mill for the hot-rolled narrow strip is 10.5 times longer than that of the high-alloy cast iron roll. Although the hardness (HRC 65) and wear resistance of the high-speed steel roll ring are not as good as that of the cemented carbide roll ring, the heat cracking resistance is much better than that of the cemented carbide roll ring. Its single groove rolling capacity can reach about 6500 T, which is nearly 1 time higher than that of the cemented carbide roll ring. The total rolling capacity of a pair of high-speed steel roll rings and a pair of cemented carbide roll rings is roughly the same. The benefit of replacing the cemented carbide roll ring with a high-speed steel roll ring is very obvious. In addition, due to the high rolling volume of the single groove of a high-speed steel roll ring, the time of roll change and groove change can be reduced and the operation rate can be improved; The weight of a single piece is much lower than that of cemented carbide roller ring, which can reduce the labor intensity of workers; The refitting of the roll ring only needs to be processed on an ordinary lathe, which reduces the processing cost.
However, when using the high-speed steel roll, it should be noted that the high-speed steel roll is easy to form a temperature difference on the roll due to its poor heat dissipation, so as to reduce the service life of the roll. It is necessary to strengthen the cooling capacity of the roll and keep the roll surface temperature below 50 ℃. In addition, high-speed steel has low toughness and accident resistance. It is suitable for hot rolling mills with stable equipment conditions. In case of any abnormality during the rolling mill operation, it is necessary to stop the mill for inspection at any time to avoid serious roll breakage accidents. When using a high-speed steel roll, because the working roll has high hardness, the relative support roll also needs to be changed from the original cast steel to forged steel.
The grinding properties of high-speed steel are quite different from those of traditional rolls. The equipment, grinding materials and management of the roll grinding workshop should be improved in order to give full play to the special properties of high-speed steel rolls. In addition, it is also important to work to find the cracks in the use of high-speed steel rolls as early as possible and prevent crack propagation. As the compressive residual stress of high-speed steel roll is larger than that of ordinary roll, cracks are not easy to be found. It is necessary to carry out online eddy current flaw detection, ultrasonic flaw detection or magnetic particle flaw detection on the roll that has been removed from the rack on-site, and timely repair and clean the cracks found.
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