| 摘要 |
PURPOSE:To produce a steel plate of superior hydrogen sulfide crack resistance by hot rolling the low carbon steel of extremely less S content and contained with the specific amount of Ca then subjecting the same to hardening and tempering by the specific conditions. CONSTITUTION:A steel slab contg. 0.05-0.20% C, 1.0%>Mn, 0.003%>S and Ca at a value at which the ratio of Ca/S becomes 1-10 is heated to 1,000-1,180 deg.C. As the process for the next hot rolling and subsequent processes, rolling is finished at >=800 deg.C temperatures or working is performed by a twice heating and twice rolling method. In this method, the steel slab is once heated to >=1,100 deg.C, after which the rolling is suspended where intermediate plate thickness is attained, and the slab is again cooled down to <=600 deg.C, thence, it is again heated to 800-1,000 deg.C above the Ac3 transformation point and the rolling is finished at <=75% draft and at >= 800 deg.C. Thence, steel slab is anuealed directly >=750 deg.C, then is tempered <=Ac1 transformation point in above described both process. |
