According to the phenomenon of occurring bainite and martensite in structure of Ф6.5~12mm coil of steel SCM435 rolling in winter season led to higher cracking rate of wire and rod

the analysis on continuous cooling transformation curves of austenite measured by Gleeble-1500 hot simulator and morphology of structure according with cooling rale 0.5~30°C/s has been carried out to get the cooling rate for forming structure of ferrite + pearlite being ≤0.5°C/s；by measuring the cooling rate of Ф6.5~12mm coil of steel SCM435 and observing the corresponding structure

it is found that the temperature of coil leaving insulation cover is ≥600°C with cooling rate 0.8〜4℃/s led to the structure of steel being ferrite + pearlite and partial bainite and martensite. With adjusting loop laying temperature and Stelmor Z1〜Z3 cooling roller speed in wind cooling line for Ф6.5~12mm coil of steel SCM435

the temperature of coil leaving insulation cover is ≤550℃ and the austenite structure of steel is transformed completely into ferrite + pearlite

as a result the cold-heading cracking rate of coil decreases from original 20% to less than 3%.