2006 Volume 92 Issue 6 Pages 385-392
Over aged samples with Mo added steel after quenching show high tensile strength than that of without Mo steel and show peculiar BH curve plotted against over aging time. To analyze these phenomena, kinetic model for carbide precipitation was derived, which deal with both cementite and cluster. The following results are obtained.
(1) Low carbon steel with Mo, clusters are formed at room temperature after quenching. The site number used for cluster is 1015/mm3, which indicates Mo-C dipole is considerd to be the site of cluster nucleation. Clusters are dissolved with the aging temperature at 200°C in short time.
(2) Clusters are dissolved during BH treatment (170°C ×20 min), which reduce the BH value for the sample without over aging. On the othe hand, the drop of BH with 200°C × 10 min over aging is lower, because clusters are dissolved during over aging. This causes that BH plotted against aging time shows the curve with peak.
(3) The strength by calculation in the case of lower carbon show less value than that of higher carbon case, because cluster nucleation rate deeply depends on carbon content.