Online ND-characterization and mechanical property determination of cold rolled steel strips

The object was the development of a measuring method allowing the non-destructive determination of the yield strength Rp0.2 and the deep drawing parameters rm (vertical anisotropy) and Δr (planar anisotropy) on hot-dip galvanised steel strips during the production process. To determine the mentioned quantities two different non-destructive methods have been developed and tested in a hot-dip galvanising line. An electromagnetic method which allows the measurement of the incremental permeability and further derived quantities has been used to determine the yield strength. Using a multiple-parameter analysis, correlation relations between the micro-magnetic measuring quantities and the destructively determined yield strength values of the investigated steel strips have been evaluated. Beside the multiple regression method also a neural network has been tested. An ultrasonic methods also working on an electromagnetic basis has been used to determine the deep drawing properties represented by the parameters of the plastic anisotropy. The method is based on the direction dependence of the velocity of a SH wave (Shear horizontal) which is strongly correlated to the texture of the material. Both measuring methods were tested online on strips of different steel grades of which the properties were between 130MPa to 300Mpa (yield strength), 1.0 to l.9 (rm) and 0.3 to 0.7 (Δr). (author)