| 摘要 |
PURPOSE:To improve the chemical treatment property of high-tension cold rolled steel sheet, by, in continuous annealing of the cold rolled steel sheet, heating previously the steel sheet in an oxidizing atmosphere to form oxide film on the surface of the steel sheet, then by heating and cooling the steel sheet in a reducing atmosphere. CONSTITUTION:In continuous annealing of high-tension cold rolled steel sheet, it is heated initially at a temp. 350-650 deg.C for 5sec-10min in an oxidizing atmosphere, hence Fe and various other alloy elements contained in the steel sheet are equally oxidized to form oxide film on the surface of the steel sheet. Then the steel sheet is heated to 800 deg.C, the recrystallization temp., in a reducing atmosphere composed of 40% hydrogen, the balance being nitrogen, soaked at the temp. for 2min, and is allowed to cool. This heat treatment prevents the selective surface-concentration of Mn, S etc. in the surface of the steel sheet, and improves the surface properties, thereby permitting manufacture of high-tension cold rolled steel sheet excellent in chemical treatment property. |
