Influence of cold rolling reduction on mechanical and magnetic properties and on ultrasound features in low carbon steel

Martinez-de-Guerenu, Ane; CEIT, University of Navarra; Spain

Martinez-De-Guerenu, A.; CEIT; Spain
Jorge-Badiola, D.; CEIT; Spain
Gutiérrez, I.; CEIT; Spain
Stolzenberg, M.; Salzgitter Mannesmann Forschung GmbH; Germany
van den Berg, F.D.; Tata Steel; Netherlands

ID: ECNDT-0244-2018
Download: PDF
Session: Materials Characterization - Magnetic Techniques 1
Room: J2
Date: 2018-06-14
Time: 13:30 - 13:50

Non-destructive evaluation systems based on magnetic and ultrasound techniques are receiving increasing interest for on-line assessment of microstructure and mechanical properties during processing and production of steel strips. On-line measurements give the opportunity to adapt process parameters to the actual state of the material. It is important to separate the effects from different microstructural variables on the parameters derived from these measurement instruments in order to understand the combined effect of various microstructural features in more complex characterisation cases.

With the purpose of analyzing the effect of deformation by cold rolling in steel strips, samples from two industrial hot rolled extra-low carbon steels were cold rolled at laboratory and at a pilot plant between 12% and 81% in 8 deformation steps. Influence of the microstructural changes induced by the cold rolling deformation on electric, magnetic, ultrasonic and mechanical properties are studied. Microstructural changes were observed by optical and EBSD microscopy. Mechanical properties were analysed by tensile testing and Vickers hardness measurements. Dislocation density was calculated by Taylor’s equation from the yield strengths measured by tensile testing. The electrical resistances of the samples were characterised in a 4-point measurement setup using a commercial microOhm meter. Magnetic hysteresis loops were measured by a single sheet tester at laboratory and by a commercial 3MA system. Additionally, ultrasonic attenuation measurements were made adjusting the frequency by standing waves up to a frequency of 10 MHz.

Changes in magnetic and ultrasonic parameters with the cold rolling reduction ratio are discussed in terms of microstructural changes. The coercive field measured by the single sheet tester and by the 3MA system can be directly related to the increase in the dislocation density due to cold rolling reduction. The possible application of these techniques as non-destructive evaluation methods will also be discussed.