| 摘要 |
PURPOSE:To produce a high tensile steel plate of high quality having no lead sticking in production of the high tensile steel plate by austemper treatment by maintaining the oxygen component in the heating furnace atmosphere on the lead bath inlet side within a specific amt. range. CONSTITUTION:A steel strip 1 is supplied in an arrow A direction, and is introduced into a heating furnace 4, where electric current is flowed between electroconducting rolls 2, 7 by the voltage to be applied from an AC power source 10 and the strip is heated to 750-1,000 deg.C. At this time, the atmosphere in the furnace is sucked in an arrow C direction through a conduit 6, and the concn. of oxygen is measured intermittently or continuously with a trace oxygen analytical device. When the concn. of oxygen goes out of a 50-10,000ppm range, the gaseous atmosphere to be fed through a gas inlet 5 into the furnace 4 is controlled. The strip 1 out from the furnace 4 is hardened in a lead bath 11 maintained in a constant temp. range at the MS point or above, whereby the isothermal transformation is completed. |
