Effect of Spheroidization Annealing on Pearlite Banding

Sergey Guk,Ulrich Prahl,Eva Augenstein,Rudolf Kawalla,Maksim Zapara

doi:10.4028/www.scientific.net/msf.949.40

Abstract

The present paper deals with the influence of the duration of isothermal spheroidization annealing on the evolution of pearlite bands in various initial states. In this study, two initial conditions of the steel 16MnCrS5 are considered: a) industrially hot-rolled pearlite structures in their ferritic matrix and b) a specifically adjusted microstructure in the lab condition. Based on the experimental investigations and quantitative microstructural analyses, an empirical model for the prediction of pearlite banding within a broad range of annealing durations could be derived. Both, experiment and model, agree that pronounced pearlite bands in the initial state almost disappear after 25 h of spheroidization annealing. On the other hand, a marginal degree of pearlite banding in the initial state increases slightly during annealing. This fact could be explained by inhomogeneous cementite formation inside and outside the primary segregation regions of manganese.

Highlights

As-rolled steels often exhibit an inhomogeneous microstructure in terms of pearlite banding owing to primary segregations
The present study aims to quantify the effect of spheroidization annealing on the various degrees of pearlite banding in as-rolled steel
It can be seen that the decreasing of pearlite banding degree increase the time of cooling

Summary

Introduction

As-rolled steels often exhibit an inhomogeneous microstructure in terms of pearlite banding owing to primary segregations. Segregations arrange during crystallization and severely deform by subsequent hot forging to a semi-finished part. They affect the formation of the microstructure through both, the local changes of transformation temperatures and the shift of the excess carbon by cooling from the transformation front into the untransformed austenitic regions. Various disadvantages of pronounced pearlite banding for the further processing of semi-finished parts are reported in literature: In general, it is believed that the deformation of the anisotropic microstructure can lead to premature material failure due to localized stress peaks [2, 3]. A reduced fatigue strength and toughness of the finished product are further negative consequences of pronounced pearlite banding [5]

Methods

Results

Discussion

Conclusion