The amount of high strength steel used in body-in-white (BIW) applications is steadily gaining. In recent European passenger car models already more than 60 percent of the total BIW weight is represented by high strength steel. Simultaneously the share of ultra-high strength steel is gaining share as well. Particularly hot stamping steel reaches sometimes up to 15 percent of the structural body weight. However, concerns by several carmakers have been brought forward about delayed cracking of such ultra-high strength steels especially under the simultaneous condition of mechanical stress and hydrogen pick-up due to welding or corrosion processes for instance. Several questions are pending unanswered: How sensitive is a material to delayed cracking? - Which is a representative test? - What can be done to reduce the sensitivity? The present paper develops an approach to these questions by looking at the origins and mechanisms of delayed cracking. Then the issue of hydrogen induced cracking is considered. Based on the substantial experiences available from other fields like pipeline and engineering steels, guidelines are developed for the micro-structural engineering of ultra-high strength automotive sheet with reduced sensitivity for delayed cracking.
Delayed cracking in ultra-high strength automotive steels: Damage mechanisms and remedies by microstructural engineering
MS&T, Materials Science and Technology, 2008 ; 1744-1755
2008
12 Seiten, 38 Quellen
Aufsatz (Konferenz)
Englisch
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