Hot-rolled steel sheet for low yield ratio type refractories and steel pipe, as well as methods for their preparation

摘要

PROBLEM TO BE SOLVED: To produce a low yield ratio type fire resisting hot rolled steel sheet and steel pipe having cold low yield ratio at ordinary temp. and excellent in high temp. strength and to provide methods for producing them. ;SOLUTION: This low yield ratio type fire resisting steel sheet is the one having a compsn. contg., by weight, ≤0.02% C, ≤1.0% Si, 0.05 to 2.0% Mn, ≤0.02% S, 0.01 to 0.1% Al, 0.08 to 0.3% Nb, ≤0.2% Ti, 0.0001 to 0.0020% B, and the balance Fe with inevitable impurities, in which the content of Nb also satisfies Nb≥0.05+7.75C-1.98Ti+6.64N+0.000035/(B+0.0004) and yield ratio at ordinary temp. is regulated to ≤70%.;COPYRIGHT: (C)1999,JPO