The use of HSLA dual phase steel is an effective method of reducing bumper weight while meeting ever increasing government performance requirements. A paper analysis, followed by a hardware evaluation, successfully substituted “dual phase” for conventional HSLA steel at a reduced thickness. Bumpers for the all-new 1979 Cadillac Eldorado were designed and released using dual phase steel with yield strengths of 70-80 ksi for the face bars. Production problems were overcome by modifications of mechanical properties and increased development experience with this steel. To achieve the full work-hardening potential of dual phase steel, bumper sections and draw dies must be designed for a uniform strain greater than three percent.
Future dual phase steel for bumpers in the 80-120 ksi range is desirable, but further improvements in steel-making technology and part and die design techniques are required to achieve this goal.