| 摘要 |
PURPOSE: A preparation method of high tension steel by adding a very small amount of Ti and Nb and quenching directly is provided to produce steel restraining a temper softening property at above 550°C. economically. CONSTITUTION: High tension steel having good temper softening resistance and a tensile strength of 110 kgf/mm¬2 is manufactured by adding an infinitesimal carbonitride forming element to conventional steel having a tensile strength of 90 kgf/mm¬2 and quenching directly. Slab comprising C 0.13-0.18 wt.%, Mn 0.2-1.5 wt.%, Si 0.15-0.35 wt.%, P below 0.02%, S below 0.08%, Ni 2.0-4.0%, Cr 0.5-2.0 wt.%, Mo 0.3-1.0 wt.%, Nb 0.02-0.06 wt.%, Ti 0.02-0.06 wt.%, Sol-Al 0.02-0.06 wt.%, and residual Fe and unavoidable impurities is heated at 1,150-1,300°C, started to cool within 30 sec., cooled to room temperature at a cooling speed of 10-50°C/sec, and tempered at 550-700°C.
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