| 摘要 |
PURPOSE:To easily and directly produce a bar steel and wire rod having spheroidizing structure by hot-rolling a carbon steel, finish-rolling through suitable recuperating heat after forcedly cooling the surface part to Ms point or lower and holding to isothermal temp. at the specific temp. immediately thereafter. CONSTITUTION:After heating the carbon steel or alloy steel having 0.03-1.5% C in a heating furnace 20, it is rolled by rough-rolling mill line 21 and an intermediate- rolling mill line 22. The rolled material obtd. by this process having at least Ar1 point or higher temp. at the central part is forcedly cooled in the intermediate cooling zone 24, and the temp. of surface part is lowered to Ms point or lower, to form the quenching structure, such as martensite. Next, by adjusting the recuperating heat time till the rolled material attains the finish-rolling mill line 23, the temp. at the central part is lowered to Ar1 or lower, to a pearlite transformation. Next, the rolled material is finish-rolled in the finish-rolling mill line 23 and just after that, the isothermal holding is executed in a heat-treatment furnace 27 at the temp. range of Ac1 point-600 deg.C for 0.5-5hr to coagulate and grow the carbide. In this way, the bar steel and wire rod having spheroidizing structure are obtd.
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