A Method to Determine Lankford Coefficients (R-Values) for Ultra High Strength Low Alloy (Uhsla) Steels

Abstract

For Ultra High Strength Low Alloy Steels (UHSLAS) it is difficult to determine Lankford parameters, since the measurement of a stable strain ratio is often not possible. This report presents a method for determining Lankford coefficients for UHSLA Steels. The method is based on a combination of a theoretical material model and on experiences from a material data base. The Hill'48 yield condition is used to calculate the Lankford coefficients as a function of the yield stress. An empirical model based on the BILSTEIN material data base is used to predict the anisotropy. The result from earing test is used as an input parameter for the empirical model. The method is first checked using data from tensile tests. The predicted Lankford coefficients are compared with measured Lankford coefficients. In a further step, this method is applied to low alloyed steels with a yield stress of more than 900 MPa. For these materials the Lankford coefficients could not be measured by tensile tests. Predicted Lankford coefficients are used in the numerical simulation of earing test and compared with experimental results. In summary, it can be stated that the method presented here is suitable for predicting Lankford coefficients in case of an impossible direct measurement.