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Extrait / Introduction

Extrait / Introduction :

conditions can induce phosphorus intergranular segregation, which also contributes to increase the DBTT. In this study, a correlation between phosphorus intergranular segregation measured by Auger electron spectroscopy and metallographic etching of the steel in a picric acid reagent was established. The segregation takes place in the former austenitic grain boundaries, but also in the martensite lath packet boundaries. The working conditions (times up to 15700 hours at 320°C) of the steel were reproduced in order to highlight the conditions in which intergranular brittleness appears and to quantify its influence on the DBTT. We observe a synergetic effect between the hardness and the phosphorus intergranular segregation rate: intergranular brittleness appears provided that phosphorus segregation is high enough after tempering (tempering treatment at 600°C for example) and that the steel is hard enough after ageing at 320°C. Applying a tensile stress on the steel during ageing at 320°C makes the grain boundaries more brittle. The results are synthesised in the form of an empirical relation that enables to predict the DBTT from Vickers hardness and intergranular segregation measurements. Key-words: segregation, Auger spectroscopy, metallography, intergranular

Plan

Plan :

conditions can induce phosphorus intergranular segregation, which also contributes to increase the DBTT. In this study, a correlation between phosphorus intergranular segregation measured by Auger electron spectroscopy and metallographic etching of the steel in a picric acid reagent was established. The segregation takes place in the former austenitic grain boundaries, but also in the martensite lath packet boundaries. The working conditions (times up to 15700 hours at 320°C) of the steel were reproduced in order to highlight the conditions in which intergranular brittleness appears and to quantify its influence on the DBTT. We observe a synergetic effect between the hardness and the phosphorus intergranular segregation rate: intergranular brittleness appears provided that phosphorus segregation is high enough after tempering (tempering treatment at 600°C for example) and that the steel is hard enough after ageing at 320°C. Applying a tensile stress on the steel during ageing at 320°C makes the grain boundaries more brittle. The results are synthesised in the form of an empirical relation that enables to predict the DBTT from Vickers hardness and intergranular segregation measurements. Key-words: segregation, Auger spectroscopy, metallography, intergranular

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