Innovative methodology for through process inclusion level forecasting of engineering steel (INCLUSION) : final report

The project objective is to develop a method able to forecast the occurrence and geometry of large and harmful defects on rolled samples from a relatively rapid analysis of a limited number of inclusions in samples taken on cast products. The expected benefit of this information is to readdress the production scheduling in order to avoid, or reduce, downgrading of products. This new method is based on two tools: statistical inclusion analysis method called 'Extreme Values Analysis (EVA) Statistics'; inclusion deformation models. EVA is used to determine the expected maximum size of inclusions from a limited number of analysis of steel samples at the end of casting. This statistic approach is necessary to provide the right input to the elongation models. In fact the improved steel production of modern steelmaking plants led to a drastic reduction of the amount of inclusions dispersed in metals. Therefore conventional approaches of detecting average dimensions and number of particles are not useful for particle rating. From the information on inclusions present on as cast products, deformation models, purposely developed, calculate occurrence and geometrical characteristics of defects as a function of rolling programme. The method has been applied on two selected steel grades produced from the two industrial partners of the project. In one case the evaluation of the quality of the product is based on the microscopic analysis of the defect size. Inspection of the defect size in the final products confirmed the prediction based on statistical analysis of samples from as products and deformation models. In the second case the product quality is evaluated from fatigue tests. For this reason a known model, which correlates defect size with fatigue limit has been applied using as input the predicted defect size. The obtained values resulted in agreement with the measured values. The developed method can be used to: support the management of steel rolling operations; evaluate the advantages arising from a reduction of inclusion size in the billet on the quality of the final product.