GMW16844

Description / Abstract: Introduction

Note: Nothing in this standard supercedes applicable laws and regulations.

Note: In the event of conflict between the English and domestic language, the English language shall take precedence.

Purpose. This procedure is for determining and rating the level of retained austenite present in the hardened case of nodular (ductile) cast iron camshafts. The camshaft material grade is specified from GMW10.

Retained austenite is a microstructural phase resulting from an incomplete transformation to martensite after a quenching operation. It has a lower hardness, is unstable and is often undesirable in high-precision machine components such as camshafts.

A series of 4 photomicrographs of nodular cast iron with progressive levels of retained austenite are used for evaluation. This visual reference method is preferred over quantitative measurement methods such as x-ray diffraction and image analysis due to the high investment costs and sample size requirements.

Applicability. This document describes the specific procedures for sectioning hardened nodular iron camshaft lobes for analysis of retained austenite. However, the basic principle and analysis can be applied to any case hardened cast iron material with similar microstructures.

Remarks. The intent of this document is to provide a standardized method of preparing and evaluating metallographic samples for determining the amount of retained austenite in the microstructure, and to rate it on a scale of 0 to 4.