Quench Induced Work Hardening Distributions in Cylindrical Components

Abstract Modern design codes require austenitic components to be subjected to a Quality Heat Treatment (QHT) that involves a rapid cooling by means of a water bath quench, for example, to produce optimal mechanical properties and to increase corrosion resistance. However, quenching of thick austenitic components from near solutionising temperatures creates large thermal gradients in the component which can be the very steep due to the significant heat flux that develops during the quench, particularly within the transition and nucleate boiling regimes, and due to the diffusivity of the component. When the component thickness is large enough, the thermal gradients can introduce thermal stresses that are in excess of the yield stress of the material. This causes plasticity which causes the material to work harden. Therefore, the strain hardened distribution following the quench is determined by the material diffusivity and quench heat flux which causes a plastic strain field. This paper presents the results of Finite Element Analyses (FEA) used to study the impact of a water bath quench on the tensile properties of thick, cylindrical and complex shaped, austenitic Type 316 stainless steel components. The FEA indicates that these plastic strain fields display local minima aligned with the T/4 and 3T/4 though thickness locations of cylindrical components. The FEA predicted plastic strain fields are used to estimate strain hardened distributions which correlate with the tensile property variations observed in acceptance tests of similar industrial sized components. The output of the study can be used as an aid by the designer, manufacturer and / or forgemaster to ensure that the baseline properties of these components are high enough in advance of the quench so that the component remains design code compliant after the quench when accounting for local minima introduced during the quench. This will minimise scrappage rates during the manufacture of safety-critical austenitic components if the design code acceptance criteria aren’t met.