Quantitative Analysis of Hardening Due to Carbon in Solid Solution in Martensitic Steels

Abstract

The relationship between hardness and solute carbon concentration estimated via electrical resistivity measurement was investigated in as-quenched and tempered martensitic steels containing carbon of 0.3-0.6 mass%. As a result of corelating the amount of hardening due to carbon in solid solution with the solute carbon concentration, by the calculation to subtract precipitation strengthening, grain refinement strengthening, dislocation strengthening, and softening due to retained austenite from the total strengthening, we derived an equation of solid solution strengthening, where the hardening increases proportionally to the 1/2 or 2/3 power of the solute carbon concentration. It was confirmed that the effects of the factors other than solid solution strengthening due to carbon on hardness are relatively small in tempered specimens when the tempering temperature is less than 673 K; therefore, the change in hardness in tempered martensitic steels can be mostly explained by solute carbon concentration regardless of carbon content.

Effects of Retained Austenite upon Softening during Low-temperature Tempering in Martensitic Carbon Steels

“…Figure15 compares the relationship between C sol and HV α' obtained in this study against the previously reported 17). It is confirmed that hardness decreases along the curves of Eqs.…”

“…We previously reported upon the hardening produced in 0.3C steel by the precipitation of fine metastable carbides. 17) The similar hardening observed in 20%CR 0.3C-10Ni steel may also have been produced by the same cause. On the other hand, in the 0.3C-10Ni steel with retained austenite, the hardness decreased rapidly and monotonically without producing hardening.…”

“…It was confirmed that, in the 0.3C-10Ni steel with retained austenite, HV α' decreases significantly compared to the 0.3C steel without retained austenite. In a previous study, 17) we researched the relationship between HV α' and C sol in Fe-2Mn-0.5Si-C alloys and found that the hardening attributable to solute C (ΔHV sol.C ) is expressed as obtained in this study against the previously reported. 17) It is confirmed that hardness decreases along the curves of Eqs.…”

“…In a previous study, 17) we researched the relationship between HV α' and C sol in Fe-2Mn-0.5Si-C alloys and found that the hardening attributable to solute C (ΔHV sol.C ) is expressed as obtained in this study against the previously reported. 17) It is confirmed that hardness decreases along the curves of Eqs. ( 17) and (18) for both alloys; this suggests that the softening with tempering at 373 K is primarily caused by decreasing C sol .…”