Method of magnetically processing an iron-carbon alloy

Abstract

A magnetic field assisted processing method entails heating an iron-carbon alloy at an austenitizing temperature for a time duration sufficient for the alloy to achieve an austenitic microstructure; cooling the iron-carbon alloy to an intermediate temperature defined by a continuous cooling transformation (CCT) diagram for the iron-carbon alloy at a rate sufficient to avoid phase transformation of the austenitic microstructure, the intermediate temperature being below a bainitic knee of the CCT diagram and above a martensite start temperature; and applying a high field strength magnetic field of at least about 0.2 Tesla to the iron-carbon alloy after reaching the intermediate temperature. The field is applied for a time duration sufficient to transform the austenitic microstructure into a fine dispersion of one or more iron carbide phases in a ferrite matrix in order to produce a magnetically-processed alloy having improved ductility and strength.

Description

FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT[0001]The invention described in this disclosure was made with government support under Prime Contract Number DE-AC05-000R22725 awarded by the Department of Energy. The government has certain rights in this invention.TECHNICAL FIELD[0002]The present disclosure relates generally to the processing of iron-carbon alloys and more specifically to a magnetic field-assisted processing method.BACKGROUND[0003]The thermal processing of ferrous alloys to achieve good mechanical properties has been widely studied. Most iron-carbon alloys require a rapid quench to reach a metastable martensite phase that can be transformed by heat treatment (tempered) into a desirable microstructure that exhibits good strength and toughness. During the quench, which may occur at a rate of hundreds of degrees per second, the high temperature austenitic phase rapidly cools and is transformed to martensite. Due to the volume expansion (over 4%) that occurs during the phase...

AI Technical Summary

Benefits of technology

[0005]Described herein is a magnetic field assisted processing method that may be used to achieve more homogeneous microstructures and improved mechanical properties in ferrous alloys. Using the method, it is possible to produce iron-carbon alloys that include a fine dispersion of iron carbide particles and exhibit a desirable combination of strength and ductility.

[0006]The method entails heating an iron-carbon alloy at an austenitizing temperature for a time duration sufficient for the alloy to achieve an austenitic microstructure; cooling the iron-carbon alloy to an intermediate temperature defined by a continuous cooling transformation (CCT) diagram for the iron-carbon alloy at a rate sufficient to avoid phase transformation of the austenitic microstructure, the intermediate temperature being below a bainitic knee of the CCT diagram and above a martensite start temperature; and applying a high field strength magnetic field of at least about 0.2 Tesla to the iron-carbon alloy after reaching the intermediate temperature. The field is applied for a time duration sufficient to transform the austenitic microstructure into a fine dispersion of one or more iron carbide phases in a ferrite matrix in order to produce a magnetically-processed alloy having improved ductility and strength.

Problems solved by technology

A downside of austempering, however, is that the transformation from austenite to bainite may take an excessively long time to occur.

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