Microcracking sensitivity in Fe-C plate martensite

Abstract

Metallographic analysis was used to study the effect of carbon content, grain size, quench rate, and retained austenite on microcracking in Fe-C martensites. It was found that microcracking is directly related to an increase in the carbon content of the martensite and that there exists a carbon content which corresponds to both the onset of microcracking and the formation of plate martensite. Retained austenite indirectly affects microcracking in that more complete transformation yields more martensite and consequently more microcracking. Grain size changes from 100 to 1200 μ, introduced by varying the austenitizing temperature from 1800° to 2400°F and varying the time at 2000°F for 15 hr, did not affect microcracking or the amount of retained austenite. Finally, the investigation emphasizes that microcracking is a manifestation of the impingement of martensite plates and is not a function of the stress state introduced by the quenching medium.