Morphology and Crystallography of Ausferrite in Austempered Ductile Iron

Chengduo Wang,Songjie Li,Peixu Yang,Xueshan Du,Yufu Sun

doi:10.3390/met7070238

Abstract

The microstructure of austempered ductile iron was investigated by electron backscatter diffraction technique. The results show that the orientation relationship between acicular bainitic ferrite and austenite is Greninger–Troiano relationship. A single austenite grain is divided into four packets and each packet contains six variants that share a {011}α (i.e., {111}γ) plane. When two γ grains are twinned, the twins share a {111}γ plane and have seven packets. The adjacent acicular bainitic ferrite plates (or laths) sharing a 〈 001 〉 γ axis have small misorientation of about 5.7°. The adjacent acicular bainitic ferrite plates (or laths) not sharing a 〈 001 〉 γ axis have two high misorientation angles of ~54.3° and ~60.0°. Further, the low angle boundary to high angle boundary ratio is far less than the ratio of the variant pairs with small misorientation to the ones with large misorientation. This work is available for structures obtained as a consequence of the heat treatment of austempering.

Highlights

Phase transformations strongly influence the microstructures of materials and, their mechanical properties [1,2,3]
The inverse pole figure (IPF) orientation maps of the acicular bainitic ferrite and retained austenite in Figure 1a are shown in Figure 1b,c, respectively
Refining prior austenite is an effective way of refining acicular bainitic ferrite

Summary

Introduction

Phase transformations strongly influence the microstructures of materials and, their mechanical properties [1,2,3]. The orientation relationship is generally described as K–S or N–W relations [12,13,14,15,16,17,18,19,20]. Sometimes the orientation relationship between γ and martensite is characterized as the G–T relationship [21,22,23,24], which is generally considered to be intermediate [24,25,26] between K–S relation and N–W relation the {111}γ plane is not exactly parallel to the {110}α plane in G–T relation. The Pitsch and N–W are two complementary orientation relations (the parallel planes and directions of martensite and those of γ are interchanged). The G–T and G–T0 are complementary to each other

Objectives

Methods

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Discussion

Conclusion