Phase and structural transformations when forming a welded joint from rail steel. Report 1. Thermokinetic diagram of decomposition of supercooled austenite of R350LHT rail steel

A thermokinetic diagram of decomposition supercooled austenite R350LHT steel was constructed based on the results its dilatometric, metallographic and hardness analysis during continuous cooling in isothermal conditions. It found that at a rate 0.1 1 °C/s causes by pearlite mechanism. After lower rate, structure is coarser has (289 HV). This due to higher temperature range transformation, which diffusion processes associated with transformation into occur more actively. In rates from 5 10 °C/s, occurs according martensitic mechanism, leads formation pearlite-martensite structure. When under study cooled 30 100 transforms high formed. With an increase steel, observed 289 (at °C/s) 864 – 0 896 HV respectively). The conducted studies allow boundaries search for optimal parameters welding heat treatment modes investigated rail be narrowed. To obtain required structures physical mechanical properties (austenite undergoes mechanism), should carried out no than °С/s.