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抄録

Structural characteristics of lath martensite were investigated in detail using Fe-C alloys and plain carbon steels with carbon contents of up to 0.8%, 18%Ni maraging steel and Fe-0.2%C alloys with an addition of about 1% of Mn, Si, Ni, Cr, or Mo. The construction of lath martensite structure changes with carbon content. The packet regions are clearly formed within a prior austenite grain at lower carbon content (up to about 0.4%C), but they are not observed in the range of 0.5-0.8%C. The block regions within a packet are observed only in the steels bclow about 0.3%C. Structure of lath martensite in the 18Ni maraging steel is characterized by the block regions which are well-developed and completcly partition a packet region, whereas the blocks in the low carbon steels are not well-developed regions. A packet size gradually decreases with increase in carbon content up to 0.4%C and rapidly decreases in the 0.6 and 0.8%C. A linear relation exists between the austenite grain size and packet size in Fe-0.2%C alloy and 18Ni maraging steel. The increase in block width of maraging steel with increasing austenite grain size is very small. Alloying elements within about 1% have little effect on the construction of lath martensite and the packet size.