| 摘要 |
PURPOSE:To suppress the progression of decarburization of steel ingots by simple means and to prevent the generation of ferrite decarburization in a hot working stage for steel for machine structural purposes by controlling the rate of heating in the reheating stage of the ingots to a specific range. CONSTITUTION:In the process for heating of ingots of steel for hot working, steel for machine structural purposes such as bearing steel, the ingots are heated at 30-120 deg.C/min rates in a 600-800 deg.C range. If the heating temp. is 600 deg.C or below in the heating stage of the object steel kind, the steel is stable as ferrite and pearlite and decarburization progresses hardly. At 800 deg.C or above, it is mainly in an austenite region where the rate of decarburization is relatively low and ferrite decarburization does not progress. Therefore, said temp. range is a target and if the steel is heated at the rate below the lower limit in this range, ferrite decarburization layers wherein decarburization progresses considerably are formed. On the other hand, the heating rate above the upper limit requires special measures for the heating furnace and is undesirable in terms of material quality because coarse grains of crystals are formed locally. |
