The Effects of Carbon Contents and Ms Temperatures on the Hardness of Martensitic Fe-Ni-C Alloys

The effects oj carbon on the strength oj martensite have been studied by using Fe-i-C alloys with three levels oj AI, temperature oj approximately 350 , 220°, and -25 C. The carbon content mnged from 0 .0 1 2 to 0 .34wtO 0 , while the nickel content was varied to adjust the M " temperature.Vickers hardlless measurements were made to evaluate the strength oj martensite.For a range oj carbon content (X c) below af1/Jroximate0' O.O() wt"", the hardness (H ) is inde/JCI)(/ent oj All, temperatu re, which is re/neseli led by I-I = 164 + 757 • X c II" .However, bC)'ond this content the hardness becomes greater the higher the .lIstemperature, which is represented by H = 170 + 449 .X ,, 1 3Jor the martensite with Ails oj 25 C, H = 302+ 794 .X "Jor the martensite with i1ifs oj 220 C and I-I = 292+ 95() • X,.Jor the martensite with l s oj 350 c C, respectivefy.Precipitation hardening co1I1l ibutes to the overall hardness '1/ martensite with M s oj 350 and 220 C. The two major strengthening mechanisms, such as /Jrecipitation hardening alld solid solu tion hardening Jor the martensite with Aifs oj 350 and 220 C, have been analysed by measuring the eLect.ricalresistivity changes oj the martensite lifter temj)ering.