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Effect of Part/Die Boundary Conditions on Microstructural Evolution during Hot Stamping 2000 MPa Class Boron Steel
Author(s) -
Taylor Tom,
McCulloch John
Publication year - 2018
Publication title -
steel research international
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.603
H-Index - 49
eISSN - 1869-344X
pISSN - 1611-3683
DOI - 10.1002/srin.201700495
Subject(s) - materials science , austenite , martensite , microstructure , metallurgy , lath , hot stamping , bainite , geometry , volume fraction , composite material , mathematics
Hot stamping is performed with the 2000 MPa class 38MnB5 boron steel. Temperature evolution at critical regions of the part geometry is recorded by in situ thermocouple data logging at the part/die interface. Scanning Electron Microscopy, Energy Dispersive x‐ray Spectroscopy, X‐Ray Diffraction, and Vickers hardness testing are performed at the critical regions of the part geometry in order to evaluate microstructural evolution and correlate to observed temperature evolution. The microstructure is predominantly martensitic in the flat regions of the part geometry, with the exception of < 1.5% retained austenite. The microstructure exhibits higher volume fractions of retained austenite in the radii of the part geometry. The radii of the part geometry are also suspected to exhibit auto‐tempered martensite. The higher volume fractions of retained austenite and presence of auto‐tempered martensite in the radii of the part geometry are primarily correlated to lower cooling rates. In the radii of the part geometry, nano‐scale titanium carbide precipitates are present and the martensite lath size is finer, giving rise to higher local hardness. The characteristics observed in the radii of the part geometry are correlated to hot austenitic plastic deformation and its effect on the subsequent austenite to martensite transformation.