The hot rolling process of JIS SPA-H steel

The billets are sent and loaded to the hot continuous rolling machines for rolling. The Cu content of JIS SPA-H steel is relatively high, and "copper embrittlement" is easy to occur in the heating process. That is to say, the surface of the slab is easy to crack during the heating process, resulting in the edge crack of the finished JIS SPA-H steel plate. Therefore, the heating should adhere to the principle of "high temperature and fast burning" to ensure that the slab is heated in a reducing or neutral atmosphere. When heating, the heating speed is accelerated, the temperature of the heating section is increased, excessive oxidation is prevented, the enrichment of Cu at the grain boundary and the surface of the slab is reduced, the edge crack of the JIS SPA-H steel is avoided during rolling, and the soaking temperature is properly reduced. The discharging temperature of slab is 1 160 ~ 1 210 ℃, and the heating time is not less than 80 min.

JIS SPA-H steel material is hard, and usually its rolling thickness is thin. In the rolling process, the rolling force and current of finishing machine are large, which is easy to cause accidents. Therefore, the thickness of the intermediate blank should be reduced properly. According to the different specifications of the finished products, the thickness of the intermediate blank is generally 26-29 mm. After leaving the finishing mill, JIS SPA-H steel strip is immediately cooled in a dense way, and the front section is accelerated for cooling. The rear section controls the coiling temperature, which is (620 ± 15) ℃.