RESEARCH OF THE MECHANICAL PROPERTIES OF U10A STEEL FOR THE PRODUCTION OF HIGH-STRENGTH COLD-ROLLED STRIPS AFTER CYCLIC ANNEALING AND PLASTIC DEFORMATION

10.25712/ASTU.1811-1416.2024.02.013

Abstract

The article examines the effect of cyclic annealing of high-carbon steel U10A on changes in its mechanical properties, microstructure and shape of graphite inclusions for further assessment of the steel’s suitability for plastic deformation. The initial hot-rolled structure of U10A steel consisting of lamellar pearlite and graphite inclusions of various shapes which has insufficient ductility through the measured elongation parameter d = 3.4 % has been researched. To increase ductility, a mode of spheroidizing cyclic annealing on granular pearlite with an average size of 2-5 μm has been developed to reduce steel strength characteristics and increase the plastic ones. It has been established that the above annealing also has a positive effect on the change in the shape of graphite inclusions – a change in their shape to spherical is shown, as well as a reduction in their size to 4-8 μm and a uniform distribution in the structure, which contributes to subsequent plastic deformation without destruction. Evaluation of the results of mechanical tests after plastic deformation by pressing with a degree of 65 % of annealed U10A steel allows us to conclude that it is possible to obtain the required tensile strength and hardness according to GOST 21996–76 for high-strength cold-rolled strips without the risk of damaging the rolls.