Revision and Interpretation of Determination Method for Bake-Hardening-Index of Steel in GB/T 24174—2009

The main technical content changes of Bake-Hardening-Index determination methods in revision of GB/T 24174—2009 were introduced, relevant verification tests were carried out, and the influence of different sample types, tensile test rate, baking conditions (placing method, heating equipment), baking temperature, holding time and pre-tensile strain setting deviation on the Bake-Hardening-Index determination results were analyzed. The results show that the requirements of sample size, tensile test rate, pre-tensile strain and different yield types used in the calculation of Bake-Hardening-Index were added in the revision of the standard. Different sample types and heating media have little influence on the Bake-Hardening-Index. The factors that easily affect the Bake-Hardening-Index are the way of sample placement, the tensile test rate, the pre-tensile strain, the baking temperature and the holding time for determining Bake-Hardening-Index B_H2H involving upper yield strength. The relatively consistent test results can be obtained by using the standard recommended conditions.