The role of heat-plastic treatment in shaping the structure and mechanical properties of steel types meant for rolling wire rods

摘要

The paper presents the tests results of influence of the rolling process parameters on the liability to plastic deformation, mechanical properties and structure of steel types 23MnB4, 30MnB4, C45 and C70 meant for rolling wire rods in a modern continuous mill. The plasticity assessment was conducted with the use of hot torsion test using torsial plasto- meter in rolling temperature range for the wire rod from 850 to 1150°C with deformation speed of 0.1, 1 and 10 s'1. The dependencies of yield stress to deformation were determined together with values characterising the liability such as: maximum yield stress, value of deformation equivalent to maximum stress and deformation to failure. Those values were dependent on temperature and speed of deformation as well as activation energy and Zener-Hollomon parameter. It was stated, on the basis of conducted plastometric tests of steel types 23MnB4, 30MnB4, C45 and C70 that they are characterised with big deformability reaching the value of boundary deformation eg above the value of 20 in the lowest deformation temperature and constant increase of deformability with the increase of temperature. However, the values of maximum yield stress vary depending on tested steel type and they are more dependent on temperature and speed of deformation. Tests concerning the influence of rolling parameters and cooling on the quantitative features ofpearlite microstructure and mechanical properties of wire rods were conducted on model rolling mills in VSB Ostrava. Microstructure tests of steel types 23MnB4, 30MnB4, C45 and C70 after plastometric tests and rolling tests were conducted with the use of light and scanning microscopy. Additionally, quantitative analysis of microstructure ofpearlitic steel was conducted with the use of new computer program "PILS" - Pearlite Inter-Lamellar Spacing.