The hydrogen embrittlement susceptibility of high strength TRIP/TWIP steels with the tensile strength of 600 Mpa to 900 Mpa grade was investigated using cathodically hydrogen charged specimens. TWIP steels with full austenite structure show a lower hydrogen content than do TRIP steels. The uniform distribution of strong traps throughout the matrix in the form of austenite is considered beneficial to reduce the hydrogen embrittlement susceptibility of TWIP steels. Moreover, an austenite structure with very fine deformation twins formed during straining could also improve the ductility and reduce notch sensitivity. In Ubend and deep drawing cup tests, TWIP steels show a good resistance to hydrogen embrittlement compared with TRIP steels.Key words hydrogen embrittlement, TRIP steel, TWIP steel, mechanical property.
서 론
There have been increasing demands for improving safety, fuel economy and dent resistance in the automotive industry. To meet these demands, a super‐formable high strength steel with excellent formability was investigated. The mechanical properties and precipitation behaviour of Ti‐Nb bearing Interstitial Free (IF) steels with various contents of Ti and P were studied. In addition, the effect of processing conditions such as the cold reduction ratio and the annealing temperature on the formability was analysed. Improved mean r‐value was obtained in Ti‐0.01Nb steels with Ti content ranging from 0.015% to 0.025%. This improvement was due to non‐scanvenging effect and FeTiP precipitates. Furthermore, with an increase in P content, the mean r‐value was increased because of grain refinement in the hot rolled strip.
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