PRODUCTION OF TEMPERED HIGH-TENSILE STEEL PLATE BY DIRECT HARDENING

摘要

PURPOSE:To produce the steel plate which has no fluctuations in the material quality in the longitudinal direction of the rolled steel plate by heating steel products contg. specific slight ratios of Al, B, N, etc., to a specific temp., and subjecting said products to hot rolling and holding at an equal temp. or air cooling, then to hardening and tempering at specific temps. CONSTITUTION:The ingot of the compsn. which contains, by weight %, 0.01-0.30% C, 0.01-1.00% Si, 0.10-2.00% Mn, 0.005-0.20% Al, 0.0004-0.0020% B, 0.0010-0.0100% N, and a specific ratio of one or =2 kinds of Ni, Cu, Cr, Mo, V, and Nb, or further contg. a slight ratio of Ti or Ca, one or =2 kinds of REM alone or in combination and has the quantitative relation expressed by the formula I between N, Al, B, Ti and temps. T1, T2 is heated to T1 deg.C (1,000-1,300 deg.C) and is hot rolled to a sheet material; thereafter, the steel sheet is subjected to the holding at the equal temp. or air cooling, then to the tempering after hardening at =300 deg.C from the temp. T2 deg.C above the Ar3 transformation point. The high-strength steel plate of =60kgf/mm2 having no fluctuations in the material quality in the longitudinal direction of the steel plate is thus produced.