Calculation of the Hardness Space Distribution in the As Quenched Condition of a Medium Hardening Tool Steel

The calculation of the hardness profile is a powerful tool for the selection of the right steel for a given purpose. Computer programs INC-PHATRAN and INDUCTER-B were formerly developed by the authors for the calculation of hardness profiles after heat treatment processes of low alloy and carbon steels. The first one simulates quenching as well as through hardening operations, and the second one models electromagnetic induction heat treatments processes. These codes make use of the SAE Standard 3406 in order to obtain the hardness profile, with enhanced regression coefficients recently obtained by the authors. The present work broadens the field of application of this method, allowing to apply it for low hardenability tool steels such as the ASTM O1 Tool Steel. The method used for the calculation of the hardness profile is here summarized, and an example of application is described, which shows good correspondence between the calculated and measured values.

Prediction and Experimental Validation of Forming Limit Curve of a Quenched and Partitioned Steel

Forming limit curve（FLC）is an effective tool to evaluate the formability of sheet metals.An accurate FLC prediction for a sheet metal is beneficial to its engineering application.A quenched and partitioned steel,known as QP980,is one of the 3rd generation advanced high strength steels and is composed of martensite,ferrite and a considerable amount of retained austenite（RA）.Martensite transformation from RA induced by deformation,namely,transformation induced plasticity（TRIP）,promotes the capability of work hardening and consequently formability.Nakazima tests were carried out to obtain the experimental forming limit strains with the aid of digital image correlation techniques.Scanning electron microscopy（SEM）was employed to examine the fracture morphologies of Nakazima specimens of the QP980 steel.The observed dimple pattern indicated that tensile stress was the predominant factor which led to failure of QP980 specimens.Therefore,maximum tensile stress criterion（MTSC）was adopted as the forming limit criterion.To predict the FLC of QP980 steel,Von-Mises yield criterion and power hardening law were adopted according to the tested mechanical properties of QP980 steel.Results were compared with those derived from other three representative instability theories,e.g.Hill criterion,Storen-Rice vertex theory and Bressan-Williams model,which shows that the MTSC based FLC is in better agreement with the experimental results.