DOI: 10.3724/SP.J.1037.2012.00451

Acta Metallurgica Sinica (金属学报) 2013/49:2 PP.137-145


Currently, the senior-level hot stamping steels, such as 30MnB5, could not be used widely in automotive body like 22MnB5 hot stamping steel due to its low plasticity and high hydrogen induced cracking sensitivity after hot stamping. However, its good mechanical properties after tempering processes made it suitable for automotive structural parts. In this paper, the 30MnB5 hot stamping steel was quenched and tempered at 200-600°C for 2 min. The orientation relationship (OR) with parent phase and misorientation evolution of martensite variants were characterized by EBSD. The OR between martensite variants and parent phase was determined by using {100} pole figure of martensite variants inside a single prior austenite grain and the method of pole figure contouring. The results showed that, the OR between martensite variants and parent phase in 30MnB5 hot stamping steel after quenching was closer to N-W OR than K-S OR, and the actual pole points were distributed around the theoretical pole points. The OR between martensite and parent phase variants did not change in the samples tempered at different temperatures for 2 min, but the number of martensite variants inside a single prior austenite grain tended to decrease. The misorientation of martensite variants after quenched and tempered at different temperatures were both mainly distributed in the angle range of less than 5°and more than 50°. As tempering temperature increased, the low angle grain boundaries below 5°were decreased slightly while the high angle grain boundaries above 50°reflected an upward trend, but the former still accounted for a large percentage. These low angle grain boundaries below 5°, mainly existing inside martensite variants and derived from the misorientation between martensite laths, were the main reason that led to discrete distribution of angles between different martensite variants around theoretical values.

Key words:30MnB5 hot stamping steel,tempering,EBSD,orientation relationship

ReleaseDate:2015-04-07 15:32:09

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