Heat Treating Hints^sm
© 1995-2005
The Herring Group, Inc.

Heat Treating Hints^sm is one of our ways of sharing knowledge with the Industry we love. This is a changing series of technical articles which will be updated every month, and is designed to inform and educate. We cover a wide range of subjects extracted from our vast library of technical knowledge.

“The Heat Treat Doctor” presents…

What is Retained Austenite?

This article provides the heat treater and metallurgist with a better understanding of what retained austenite is and how it affects the properties of components. Austenite that does not transform to martensite upon quenching is called retained austenite (RA).  Thus retained austenite occurs when steel is not quenched to the Mf or martensite finish temperature, that is, low enough to form 100% martensite. Since the Mf drops below room temperature in alloys containing more than 0.30% carbon significant amounts of untransformed, or “retained” austenite may be present, intermingled with martensite at room temperature. The amount of retained austenite is a function of the carbon content, alloy content (especially nickel and manganese), quenchant temperature and subsequent thermal and/or mechanical treatments.

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Field Failure Analysis

In the real world, components fail. There are many reasons why. If a premature failure occurs, it is important to evaluate all possible causes and then isolate a root cause that can be corrected to assure that the problem will not reoccur. Failures that occur during testing on the factory floor, in controlled laboratory conditions or during product manufacture can be classified as “regular” failures – ones in which a significant amount of resources (people and test equipment) can be brought to bear on the problem. By contrast, field failures are those in which an assembly has failed in its normal working environment, often remote to the manufacturer, and where resources for analysis can be limited and must be transported to the jobsite. This article offers some simple suggestions to help better evaluate field failures.

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Understanding Carburized Case Depth

Carburizing followed by quenching is a case hardening process used to produce a hard, wear resistant surface layer, or case, on top of a ductile shock resistant under layer, or core. Parts made from wrought steel, and powder metal are commonly heat treated using this process. In some instances, stainless steels and other materials are also carburized.

The carburizing process has a great deal of variability induced by changes in process parameters over time. This variability is compounded by the fact that no two furnaces carburize exactly alike. The process is dependent on material choice, equipment, and process technique. For each component there is an optimum material and process combination that must be empirically determined. This article explains the important of proper interpretation and measurement case depth to evaluate carburized parts.

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Temper Embrittlement

In general, embrittlement is a reduction in the normal ductility of a metal due to a physical or chemical change. Temper embrittlement is a phenomenon inherent in many steels, characterized by reduced impact toughness and occurs in certain quenched and tempered steels and even in ductile irons with susceptible compositions. This form of embrittlement does not affect room temperature tensile properties but causes significant reductions in impact toughness and fatigue performance. Although normally associated with tempered martensite, temper embrittlement can also occur if the matrix is tempered to the fully ferritic condition. This article investigates this phenomena and its effect on heat treating.

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Generic and practical information is presented on this Website and in these downloadable files.  It is not intended to replace or supplement federal, state, and local codes, government standards, insurance requirements, company policies and procedures, or common sense. In addition, all equipment manufacturers’ instructions and operating and maintenance manuals should always be thoroughly read and followed. Further, personnel training should be provided unequivocally to everyone who will be associated with operating such equipment. It is the responsibility of the individual downloading this information to pass along these and other warnings as appropriate prior to the use of the material. The Limit of Liability Statement found elsewhere on this Website applies to this information.

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