HOT ROLLED STEEL SHEET WITH EXCELLENT CHEMICAL CONVERSION TREATABILITY

• Main Authors: HAYASHIDA TERUKI, OBARA MASAHIRO
• Format: Patent
• Language: English
• Published: 02.06.2005
• Edition: 7
• Subjects: ALLOYS; CHEMICAL SURFACE TREATMENT; CHEMISTRY; CLEANING OR DEGREASING OF METALLIC MATERIAL BY CHEMICALMETHODS OTHER THAN ELECTROLYSIS; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATIONOR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY IONIMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; COATING MATERIAL WITH METALLIC MATERIAL; COATING METALLIC MATERIAL; DIFFUSION TREATMENT OF METALLIC MATERIAL; FERROUS OR NON-FERROUS ALLOYS; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION INGENERAL; METALLURGY; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THESURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; TREATMENT OF ALLOYS OR NON-FERROUS METALS

PROBLEM TO BE SOLVED: To uniformly form a chemical conversion coating on the whole surface of a high-strength hot rolled steel sheet having increased Si content, to obviate the necessity of the addition of a new step to a process for manufacturing the steel sheet and also to facilitate quality control. SOLUTION: The hot rolled steel sheet has a composition which contains, by mass, 0.03 to 0.15% C, 0.8 to 3.0% Si, 0.5 to 3.0% Mn, ≤0.07% P, ≤0.01% S, 0.015 to 0.1% Al and 0.001 to 0.008% N and to which Ti, Nb, etc., are added if necessary. Further, the concentrations of Si and Mn in oxides at the surface of the steel sheet are made to ≤3.5% and ≤3.5%, respectively. It is preferable that the hot rolled steel sheet has ≤3.0μm average roughness Ra and that the number of pittings resultant from pickling is made to ≤5 pieces on average in a 10×10μm square grid. This steel sheet can be manufactured by pickling scale after hot rolling by immersion in a solution of 7 to 15% HCl concentration and 4 to 12% Fe ion concentration at 80 to 98°C solution temperature for ≥40 s. COPYRIGHT: (C)2005,JPO&NCIPI