Effect of TiN Precipitates on Austenite Grain Size in Fe–1.5%Mn–0.12%Ti–Si(<1.1%)–C(0.05 and 0.15%) Alloy

Abstract

In order to clarify the effect of non-uniformly dispersed TiN particles on the inhibition of austenite grain growth at non-steady state, an Fe–1.5%Mn–0.12%Ti–Si(<1.1%)–N(20~130 ppm)–C(0.05 and 0.15%) alloy with and without Mg deoxidation has been cooled from 1873 to 1473 K at 50 or 5 K·min⁻¹, followed by quenching. The austenite grain size distributions have been measured as functions of C, N and Si contents, Mg deoxidation and cooling rate. It was found that the γ grain growth is inhibited by the uniformly dispersed TiN particles which are found at 0.05% C. The effect of Si (0~1.1%) content on the γ grain size at given C, N and Ti contents has not been observed. In Mg deoxidation the number of TiN+MgO and TiN particles is about two times larger than that without Mg deoxidation, thus leading to smaller γ grain size. The mean γ grain size, D_A, decreases with increasing the Zener pinning force at 0.05% C, but is independent of it at 0.15% C. The D_A value at 50 K·min⁻¹ is lower than that at 5 K·min⁻¹ at 0.05% C, but the D_A value is independent of the cooing rate at 0.15% C. This is explained by the fact that with decreasing cooling rate the number of uniformly dispersed TiN particles decrease considerably at 0.05% C, but only TiN particles at interdendritic region decrease at 0.15% C.