The goal of this study is to empirically investigate the major hot rolling processparameters affecting the yield strength, ultimate tensile strength and strain-hardeningexponent of Nb-microalloyed steel sheets. The parameters considered were the roughing,finishing and coiling temperatures. Three levels for each parameter were used to develop amodel relating the process parameters to mechanical properties. By applying the responsesurface methodology, analysis of variance was done to determine the mathematical modelsrelated to each response. The results indicated that decreasing the coiling and finishingtemperatures significantly influenced the mechanical properties. Also, the modelspredicted that the maximum yield strength, ultimate tensile strength and strain-hardeningexponent are simultaneously obtained under the following conditions: roughing temperature= 1097 °C, finishing temperature = 837 °C and coiling temperature = 580 °C. The predictedvalues were close to the experimental values, indicating the suitability of themodels.

Online detection and monitoring of phase transformation using non-destructiveelectromagnetic system in industrial hot strip mill processing of steels are reported. Thesystem renders wide range of possibilities for advanced control and fine tuning of the hotrolling and run-out table cooling parameters. These in turn allow for processmodifications to better control the microstructure of hot rolled bands. In particular,such modifications can attenuate the adverse effects of uncontrollable cooling of hot bandcoils that leads to severely non-homogeneous hot band microstructure. An example ofapplication is given demonstrating how reducing the non-homogeneity of hot bandmicrostructure with the aid of online hot strip mill electromagnetic system can helpeliminating the off-thickness defects in advanced high strength steel full hard stripsthus contributing to lowering the production costs and increasing the yield.

In the present study, the main objective is to improve the mechanical properties of ahigh steel HSLA grade such as X80 for welded pipes. A study was conducted to optimise thethermomechanical treatment and to attain the mechanical properties of the X80 grade ofHSLA steels. From the same chemical composition of the hot rolled X60 grade Nb-Ti-Vmicroalloyed strip steel, we want to enlarge the production to the superior X80 gradetype. Dilatometry tests, hot torsion and hot rolling using a pilot mill allowed thesimulation of operating process sequences. The results of the rolling schedules performedin a pilot mill allowed us to analyse the effect of the deformation parameters(temperature conditions and reduction) on the evolution of the final structure and themechanical properties of the Nb-Ti-V microalloyed steel.

The cracking behaviour of the oxide layer formed during hot rolling was studied togetherwith different combinations of process parameters in order to find their single influenceon the surface quality and formation of oxide defects. Several trials were performed onthe CRM pilot line to study in detail the impact of strip reduction, strip temperature,entry scale thickness, roll degradation, lubrication, skin cooling, chemical compositionand humidity on the scale behaviour. In general, the degree of deformation, entry scalethickness and rolling temperatures are the most important parameters and the importancedecreases in that order.

A new technology for lubricating the work rolls during hot rolling has been successfullytested in the finishing mill of ArcelorMittal Dunkirk. This new technology allows sprayingvery low quantities of pure oil on the work rolls to reduce the rolling forces by up to20% and with an increased efficiency of 50% compared with emulsions. The lubricant was apure natural oil without any additives.