Cold-Rolled High-Strength Steels for Automotive Applications 730527
The metallurgical possibilities for increasing the strength of cold-rolled sheet are briefly reviewed. Solid solution hardening, precipitation hardening, grain refinement, and dislocation substructure can be used to varying extents to strengthen partially or fully recrystallized sheets. Yield strengths ranging 45-100 ksi (310-690 MPa) and higher appear to be technically feasible, and steels with yield strengths up to 65 ksi (450 MPa) are close to commercial production.
The average plastic strain ratios of the high-strength cold-rolled steels are somewhat higher (1.0-1.35) than for similar hot-rolled steels but still relatively poor when compared to low-strength aluminum killed deep drawing sheet. The forming limit curves and forming performance of cold-rolled sheet are similar to hot-rolled high-strength steels indicating that less severe part design, improved die design, improved lubrication and shop practice, and control of steel cleanliness and sulfide shape will be essential if the new steels are to be properly exploited in automobile parts.