| Delamination behavior in tensile specimen of cold rolled 0.07C-1.4Mn-0.08Nb steel was studied after aging treatment at 600℃. By increasing aging time the degree of delamination increased at first and then decreased gradually. The susceptibility of delamination was strongly related withe the distribution of carbide at the elongated ferrite grain boundaries. Microstructural characteristics of the samples which had been aged to bring about the maximum degree of delamination, were filmy structure of carbides at the elongated ferrite grain boundaries. These filmy structure of carbide was changed into separate spheroidal structure by increasing the aging time further more, and they were distributed at or near grain boundaries. Additionally, recrystallization by the prolonged aging time had helped also decreasing the delamination. By applying tensile stress, many of the micro-cracks had occurred at the interface of ferrite grains and carbides, along ferrite grain boundaries, and then connecting these micro-cracks, delamination crack had propagated. |
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