four kinds of forged steel supporting rolls final heat treatment

Final heat treatment process of four kinds of forged steel supporting rolls comparative analysis

Forged steel support roll is the core functional part of modern steel rolling equipment, which mainly bears the rolling load of working roll or intermediate roll. The product specification is big, the technical content is high, its use performance directly decides the rolling mill stability, the production line straight line and the product quality.

At present, in the main production process of forged steel supporting roller, the final heat treatment refers to the heat treatment of surface quenching and tempering on the body part of the supporting roller. It is the key process to determine the working layer structure, hardness distribution, stress distribution and performance of the supporting roller, and is also the core of the manufacturing technology of the supporting roller. Therefore, a great deal of attention has been paid to the research on the final heat treatment technology of the forged steel support roller at home and abroad.

The final heat treatment technology of the forged steel supporting roller mainly includes the following four processes: the non-penetration heating and quenching technology of the trolley furnace or well furnace, the continuous induction heating and quenching technology, the heating and quenching technology of the differential furnace and the low-frequency static overall induction heating and quenching technology. These four methods are used for different products and different users. Among them, the heating and quenching technology of differential furnace is the most widely used in China, while the most advanced low-frequency static integral induction heating and quenching technology has not been reported in China at present, and only a few Japanese enterprises are using it in the world. However, the forged steel support roll produced by this technology performs well in baosteel rolling mill.

Continuous development of final heat treatment technology

The technology of heating and quenching by means of impervious heating in trolley furnace or well furnace. Opaque burn whole quenching technology is to use ordinary or pit type furnace, trolley furnace will backup roll after preheating, along with the rapid increase in temperature furnace, the furnace temperature rapid rise to the quenching temperature above 20 ℃ ~ 50 ℃ range, to roll surface temperature display arrived after quenching temperature insulation, control gain austenitizing time of heat preservation layer depth, and then released before burning through quenching, poor temperature quenching effect. Using this process, the supporting roller neck is also heated in the furnace, and is through heating, is equal to a strengthening treatment, so in the subsequent roller body spray quenching roller neck to take protective measures to avoid hardening, and then after the overall tempering, the roller body, roller neck simultaneously meet different hardness requirements.

Continuous induction heating and quenching technology. The technology of continuous induction heating and quenching of the supporting roller refers to the quenching technology in which the supporting roller is preheated in the trolley furnace and then hoisted into the induction ring for heating and cooling at the same time. This technology is similar to the production of the working roller and the intermediate roller. The induction ring used is the induction ring with a lower height. Therefore, the induction ring has a smaller heating area, a shorter heating time and a shallow austenitized layer. Although it has strong water-jet cooling ability and can make the surface obtain high hardness, the depth of hardened layer obtained after quenching is relatively shallow. In addition, the roller neck does not need special protection when using this quenching technology to produce supporting rollers. At present, for some support rolls with small depth requirements (≤40mm), continuous induction heating and quenching technology are adopted in enterprises without differential furnace and overall induction heating equipment.

Heating and quenching technology of differential furnace. Differential temperature furnace heating quenching technology refers to the backup roll of pallet car furnace preheating roll under special open jewels differential temperature inside the furnace, the use of gas or gas combustion as a heat source, by high-speed burner jet flame to rapid heating of the roll surface, roll caused by internal and external temperature difference is big, make the roll surface to obtain certain depth layer of austenite and core remained below the phase transition point, for cooling the surface of the heat treatment method. Differential heat treatment process was first developed in the United States in the 1970s, the special heat treatment furnace is an open and closed gas furnace. Later, this process and equipment were adopted by many roll manufacturers in the world and became the main process form of heat treatment of supporting roller. At present, the production of supporting roller by this method is the mainstream in China. According to the specific conditions of each roller manufacturer, the fuel used is propane gas, natural gas and producer gas, etc., and the effect is better if the heating value is high. The main feature of differential furnace heating is that the high speed burner can make the furnace temperature rise speed ≥200℃/h, and the surface of the supporting roller can also rise quickly, so as to achieve good differential temperature effect. The quenching cooling methods after heating of differential furnace include oil quenching, water quenching oil cooling and spray cooling, etc. Among these cooling methods, spray cooling is the first to be adopted, and the cooling intensity can be flexibly adjusted by adjusting the wind pressure and water pressure. At present, large-scale supporting roller manufacturers in China all adopt this technology to produce, which can obtain the metallographic structure of the roll body dominated by bainite. The hardness of the roll body is controlled at 55HSD~71HSD, the depth of hardened layer ≤90mm, and the surface hardness uniformity of the roll body is controlled at ±2HSD~3HSD.

Low frequency static integral induction heating and quenching technology. Low-frequency static integral induction heating and quenching technology refers to the use of low-frequency induction ring to the surface of the supporting roller body for overall heating, followed by spray cooling quenching. The technology was first developed and applied by HITACHI in Japan in the 1980s, followed by the technical transformation and popularization of this method by JCFC and JSW, which represents the advanced level of the final heat treatment technology of the supporting roller. Using this technology to produce forged steel support roller is an effective method to improve the surface hardness of the support roller body, increase the hardening layer depth of the roll body and increase the surface hardness uniformity of the roll body. Compared with the differential temperature quenching process, it has the advantages of high heating efficiency, good temperature difference effect, high surface hardness of the roll body, deep quenching layer and less energy consumption.