| 摘要 |
<p>PURPOSE: To secure secondary working resistance in a steel sheet, at the time of producing a hot rolled steel sheet by using iron scrap of a low grade as an iron source, by limiting the contents of P and Sm contained in the steel sheet to a certain range. CONSTITUTION: A low alloy steel having a steel sheet compsn. contg. <=0.040% P and 0.015 to 0.040% S and also satisfying the relationship of P+Sn; <=0.060% is prepd. Preferably, this compsn. is furthermore added with 0.003 to 0.0050% B. At the time of rolling this steel, after melting, it is formed into a slab by continuous casting, which is subsequently subjected to hot rolling at a finishing temp. of the Ar3 transformation point or above by a reheating rolling method or a direct rolling method, and the obtd. steel strip is coiled. As for the temp. at the time of the coiling, the temp. range of 400 to 550 deg.C is regulated in the case the steel compsn. contains no B, and it is regulated to <=700 deg.C in the case of B-added steel to attain the coarsening of the crystalline grains and the suppression of segregation into the grain boundary of P and Sn.</p> |
