Materials Transactions Online

Materials Transactions, Vol.58 No.04 (2017) pp.655-662
© 2017 The Japan Institute of Metals and Materials

Effect of Molybdenum Content on Heat Treatment Behavior of Multi-Alloyed White Cast Iron

Thanit Meebupha1, Sudsakorn Inthidec2, Prasonk Sricharoenchai1 and Yasuhiro Matsubara3

1Department of Metallurgical Engineering, Faculty of Engineering, Chulalongkorn University, Bangkok, 10330, Thailand
2Department of Manufacturing Engineering, Faculty of Engineering, Mahasarakham University, Mahasarakham, 44150, Thailand
3National Institute of Technology-Kurume College, Fukuoka 830-8555, Japan

The effect of the Molybdenum (Mo) content on the heat treatment behavior of multi-alloyed white cast iron was investigated. The cast iron with varying Mo contents from 0.12 to 7.66% under the basic alloy composition of 5% Cr, W and V each was prepared. After annealing at 1223 K for 18 ks, the test specimens were austenitized at 1373 K for 3.6 ks in a vacuum furnace and subsequently hardened by a jet-spray of liquid nitrogen. The tempering was carried out at temperatures from 673 to 873 K at 50 K intervals for 12 ks. It was found that the hardness in the as-hardened state was increased progressively with an increase in the Mo content. The volume fraction of the retained austenite (Vγ) decreased markedly when the Mo content was increased over 1.17%. In the tempered state, the hardness curve showed clear secondary hardening due to the precipitation of fine secondary carbides and a reduction of the Vγ. The Vγ value in each specimen decreased gradually as the tempering temperature was elevated, but reduced greatly when tempered at 748 to 823 K. The maximum tempered hardness (HTmax) was obtained in the specimen tempered at 798 K where the Vγ was less than 10%. The HTmax increased first, and then subsequently decreased with an increase in the Mo content. The highest HTmax value, 946 HV30, was obtained in the specimen with 4.98%Mo. It was found that the 15-37%Vγ in the as-hardened state was necessary to get the hardness over 900 HV30 by tempering. The degree of secondary hardening (ΔHs) increased as the Mo content rose from 0.12 to 4.98% where the difference between the Vγ in the as-hardened state and that at HTmax (ΔVγ) was 22-23%.

[doi:10.2320/matertrans.M2016396]

(Received 2016/11/07; Accepted 2017/01/27; Published 2017/03/25)

Keywords: multi-alloyed white cast iron, heat treatment, hardness, volume fraction of retained austenite, molybdenum effect

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