MATERIALS TRANSACTIONS
Online ISSN : 1347-5320
Print ISSN : 1345-9678
Effect of Alloying Elements on Variation of Micro-Hardness during Heat Treatment of Hypoeutectic High Chromium Cast Iron
Sudsakorn InthidechYasuhiro Matsubara
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2008 Volume 49 Issue 10 Pages 2322-2330

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Abstract

Hypoeutectic cast irons containing 16 mass% and 26 mass% Cr with single additions of Ni, Cu, Mo and V as well as without alloy addition were prepared to investigate variations of micro-hardness of matrix during heat treatment. In the as-hardened state, Ni and Cu decreased the micro-hardness but Mo increased it slightly. By contrast, V increased the micro-hardness in 16 mass% Cr but reduced it in 26 mass% Cr cast irons. The volume fraction of retained austenite (Vγ) was positively correlated with alloy content except for V addition and it was high at elevated austenitizing temperatures. Tempered micro-hardness curves showed secondary hardening and the degree of secondary hardening (ΔHD) was greater in alloyed specimens comparing with alloy-free specimen. The ΔHD was closely related to Vγ in as-hardened state, and the more the Vγ, the greater the ΔHD. The maximum tempered micro-hardness (HMTmax) was obtained in the specimen tempered at 698 to 873 K depending on the kind and the amount of alloying element where the Vγ was less than 20%. The HMTmax values of Mo and V containing specimens increased with the Vγ in the as-hardened state. The highest value of HMTmax was obtained in those samples containing 3 mass% Mo in both series of the cast irons. The mechanism of secondary hardening in Mo and V containing cast irons was mainly by both the precipitation of special secondary carbide and the transformation of destabilized as-hardened retained austenite into martensite providing the high micro-hardness.

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© 2008 The Japan Institute of Metals and Materials
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