Study on Carbides in Iron and Steel by Electrolytic Isolation (6th Report). On the Heterogeneities of Cementite in Low Alloy Steels

Thermo-magnetic studies on cementite isolated from low alloy steels confirmed that the compositions of cementite are frequently heterogeneous. (1) In 0.61%, 1.08%Mn steel, tempered between 500 to 650°, the cementite particles randomly contained various amounts of Mn; 1∼3%Mn at 500°,1∼5.5%Mn at 550°,1.5∼6.2%Mn at 600°,and 4∼6.3%Mn at 650°, by 1 hr tempering. It is conceivable that the heterogeneous enrichment of Mn in cementite particles intemp tempering was caused by ununiform or structure-sensitive movement of Mn atoms in ferrite matrix. Similar appearance was recognized in cementite in tempered 1.13%C, 1.42%Cr steel. (2) Cr concentration in pro-eutectoid cementite was higher than in the pearlitic cementite. But, Mn concentration in pro-eutectoid cementite was lower than in pearlitic cementite. Generalizing these results, it is deduced that A1pt-raising elements (Cr,Mo,W,V,Ti etc) dissolve in pro-eutectoid cementite more than in pearlitic cementite. On the contrary, A1pt-lowering elements (Mn,Ni etc) dissolve in pearlitic cementite more than in pro-eutectoid cementite.