A flatness control in a cold rolling has a significant importance for product quality and productivity. An automatic feedback flatness control based on influence coefficient is therefore commonly used in 4Hi or 6Hi rolling mills. In this kind of conventional feedback control, to determine the influence coefficients, flatness actuators are independently operated in the actual mills. It is known that effects of flatness actuators on the strip flatness changes based on the thermal crown, wear of work rolls and so on. Building and managing a model which considers such effects of all parameters are unrealistic. On the other hand, due to the difficulty of determining the influence coefficients, such flatness control is not common in 12Hi or 20Hi multi-high rolling mills. In this study, a new flatness control based on deep learning, which doesn’t need influence coefficients was proposed. In the actual mill trials, same strip flatness was obtained with fewer manually operated flatness actuators. In the considerations, it was found that the correct influence coefficients can be learned in the training phase.

The present study was undertaken to investigate changes in the solidification microstructure consisting of Zn(hcp), α-Al(fcc), and Zn₂Mg phases in the hot-dip Zn–6Al–3Mg (mass%) alloy coating during isothermal holding at an elevated temperature of 200°C (below the solidus temperature), in terms of the transformation from Zn₂Mg metastable phase to Zn₁₁Mg₂ stable phase. The macroscopic Vickers hardness increased approximately from 150 HV to 180 HV after holding at 200°C for 36 ks. The hardness change corresponded well with the occurrence of the Zn₂Mg→Zn₁₁Mg₂ phase transformation identified by X-ray diffraction analyses. The Zn₁₁Mg₂ stable phase nucleated at the interface between Zn₂Mg and Zn(hcp) phases, and grew by consuming both phases formed in the initial solidification microstructure. Nanoindentation measurements revealed that the Zn₁₁Mg₂ phase had a lower hardness than the Zn₂Mg phase. Therefore, the significant growth of the Zn₁₁Mg₂ phase, which consumes a large part of the soft Zn(hcp) phase, could contribute to the observed hardening of the hot-dip Zn–Al–Mg alloy coating during isothermal holding.

Strain-induced lattice defects that form during the incubation stage of hydrogen embrittlement fracture in the plastic region were quantified and their relationship with mechanical properties and fracture morphologies was investigated. Pure iron was subjected to plastic strain by tensile testing at various strain rates and hydrogen charging conditions. After charging tracer hydrogen as a probe for detecting lattice defects under conditions that reached equilibrium, specimens were quickly cooled with liquid nitrogen to prevent hydrogen desorption, and total tracer hydrogen was detected using low-temperature thermal desorption spectroscopy (L-TDS), which is capable of continuously elevating the temperature and subsequently performing measurement from that temperature. Dislocation density was not affected by the strain rate or hydrogen content. However, the vacancy concentration increased in the presence of hydrogen and displayed strain rate dependence even at the same strain level. A comparison of the mechanical properties with/without hydrogen showed that the flow stress with hydrogen increased with a decreasing strain rate compared with that without hydrogen, i.e., dislocation mobility decreased. It was established that strain-induced vacancies, which were excessively generated in the presence of hydrogen and formed complexes with it, were responsible for reducing dislocation mobility. Furthermore, fractures, albeit predominantly quasi-cleavage ones, along the {001} plane, which is the cleavage plane in body centered cubic iron, were present on the fracture surfaces, and their proportion increased with decreasing dislocation mobility. This suggests that vacancy-hydrogen complexes contribute to cleavage fracture by inhibiting dislocation motion.