HOT ROLLED HIGH STRENGTH STEEL SHEET EXCELLENT IN FORMABILITY AND FATIGUE CHARACTERISTIC AND HAVING THERMAL SOFTENING RESISTANCE

• Main Authors: WAKITA JUNICHI, KONO OSAMU
• Format: Patent
• Language: English
• Published: 03.06.1997
• Edition: 6
• Subjects: ALLOYS; CHEMISTRY; FERROUS OR NON-FERROUS ALLOYS; METALLURGY; TREATMENT OF ALLOYS OR NON-FERROUS METALS

PROBLEM TO BE SOLVED: To produce a hot rolled high strength steel sheet satisfying formability, fatigue characteristics and thermal softening resistance by specifying its componental compsn., composing its microstructure of ferrite as primary phases and secondary phases and specifying the ferrite occupancy ratio, the ratio in micro Vickers hardness between the ferrite and secondary phases and the ferrite grain size. SOLUTION: This steel sheet has a compsn. contg., by weight, 0.001 to 0.20% C, 0.5 to 5.0% Si, 0.1 to 3.5% Mn, 0.003 to 0.06% Al, <=0.05% P, <=0.01% S, and the balance Fe, in which the Si wt.% and Mn wt.% satisfy the inequality, the microstructure is composed of ferrite as primary phases and secondary phases, and the ferrite occupancy ratio >=50%, the hardness in the secondary phases/ the hardness in the ferrite <=1.5 and the ferrite grain size (d: mm) satisfy the formula. The steel sheet has the characteristics of the balance between strength and total elongation (tensile strength MPa × total elongation %, and so forth) >=18000, the balance between strength and uniform elongation >=12000, the balance between strength and bore expanding ratio >=900, fatigue limit ratio %i0.50, fatigue limit >=250(MPa) and thermal softening quantity <=55(MPa).