Morphological changes of elongated MnS inclusions during heat treatment process

ABSTRACT The element sulphur is usually added to form MnS inclusions and improve the machinability of micro-alloyed steel. However, the MnS inclusions tend to elongate in rolling direction during hot working process and deteriorate the mechanical properties of steels. In this work, the effect of heat treatment on the morphological changes of elongated MnS inclusions was investigated. The research results show that the as-cast type II MnS inclusions tend to flattened and elongated morphology after rolled. The shape changes of the MnS inclusions during the heat treatment process is flat →cylinderization→ovulation→spheroidization. The morphological changes leading to cylinderization, ovulation and spheroidization of the MnS inclusions are controlled by the potential gradient induced by the inherent curvature difference. The transformation modes of ovulation and spheroidization depend on the initial aspect ratio (Length to width, L/W). The transport mechanisms for cylinderization, ovulation and spheroidization of the MnS inclusions are all controlled by surface diffusion.

[1]  Xinhua Wang,et al.  Morphology, size and distribution of MnS inclusions in non-quenched and tempered steel during heat treatment , 2015, International Journal of Minerals, Metallurgy, and Materials.

[2]  X. Mao,et al.  Effect of ageing on mechanical and impact properties of non-quenched and tempered steel wire strengthened by cold forming , 2014 .

[3]  Sunghak Lee,et al.  Formation Mechanisms of Cracks Formed During Hot Rolling of Free-Machining Steel Billets , 2012, Metallurgical and Materials Transactions A.

[4]  Min Jiang,et al.  Effect of Heat Treatment Conditions on Shape Control of Large-sized Elongated MnS Inclusions in Resulfurized Free-cutting Steels , 2011 .

[5]  Yun-jin Xia,et al.  Simulation of the continuous casting process in a mold of free-cutting steel 38MnVS based on a MiLE method , 2011 .

[6]  Jiang Min,et al.  IN SITU OBSERVATION OF MnS INCLUSION BEHAVIOR IN RESULFURIZED FREE-CUTTING STEEL DURING HEATING , 2011 .

[7]  B. Song,et al.  Intragranular Ferrite Formation Mechanism and Mechanical Properties of Non‐quenched‐and‐tempered Medium Carbon Steels , 2008 .

[8]  H. Hänninen,et al.  Effects of the composition, shape factor and area fraction of sulfide inclusions on the machinability of re-sulfurized free-machining steel , 1996 .

[9]  W. Mcfarland,et al.  Spheroidization of type II manganese sulfides by heat treatment , 1981 .

[10]  Y. Murty,et al.  Behavior of sulfide inclusions during thermomechanical processing of AISI 4340 steel , 1977 .

[11]  R. Mehrabian,et al.  Initial coarsening of manganese sulfide inclusions in rolled steel during homogenization , 1975 .

[12]  Merton C. Flemings,et al.  Effect of homogenization on sulfide inclusions in ferrous alloys , 1974, Metallurgical and Materials Transactions B.

[13]  S. Karas,et al.  Coalescence of Sulfides during Secondary Growth in 3% Silicon—Iron , 1967 .

[14]  F. A. Nichols,et al.  Morphological Changes of a Surface of Revolution due to Capillarity‐Induced Surface Diffusion , 1965 .

[15]  F. Nichols.  On the spheroidization of rod-shaped particles of finite length , 1976 .

[16]  Y. Murty,et al.  Effect of homogenization on sulphide morphology and mechanical properties of rolled AISI 4340 steel , 1975 .

[17]  R. C. Koo,et al.  Mechanism and kinetics of bubble formation in doped tungsten , 1971 .