The effect of heating and thermocycling on the mechanical properties of carbon steel rope wire

Abstract

Heating and thermal cycling of carbon steel rope wire significantly affect the mechanical properties and durability of the entire rope under operating conditions. However, despite a large amount of studies aimed at determination of the reasons for destruction of the ropes of foundry cranes at metallurgical plants and development of measures for their elimination, accidents attributed to sudden rupture unfortunately occur. Therefore, the problem is still urgent and requires further research. Nowadays, new exhaust air suction systems for hot air streams mounted in converter shops of metallurgical enterprises reduce dangerously high temperatures to T = 240 – 300°C thus providing the possibility to avoid overheating of the ropes. However, the rope metal is exposed to a strong impact of blue brittleness – phenomenon, which causes reduction of the metal plasticity in this temperature range. We present the results of studying the impact of the heating temperature and number of cycles in thermocycling on changes in the characteristics of the mechanical properties of steel 70KK wire ropes in tensile tests. Tests of the wire samples are carried out at room temperature and after their exposure to high-intensity heating and thermal cycling at different temperatures and number of cycles. confirmed Presence of zones of blue brittleness is proved experimentally for the wire rope with a diameter of 1.65 mm in a temperature range of 200 – 240°C. It is shown, that the largest reduction in the relative narrowing (21%) and increase in the ultimate tensile stress by 4.8% occurred at a temperature of 240°C. This phenomenon should be taken into account when assessing the structural strength of steel. It is shown that there are reserves to increase the life cycle of ropes, taking into account the data on diagnostics of the mechanical and magnetic characteristics in industrial conditions.