The production flowsheet of Ф6.5~20mm coil of cold-heading steel SWRCH35K is 120t LD-LF-180mmx180mm billet casting-rolling. The effect of composition
structure
surface quality of casting billet
inclusions in steel and rolling process on cold-heading properties of steel SWRCH35K (/%: 0.35~0.37C
0.11~0.14Si
0.71~0.72Mn
0. 016~0.023P
0.005~0.007S
0.023 ~0.030Alt) has been analyzed to get the main reasons to cause coldheading cracks are cold-heading steel coil surface crack defects and near surface large scale inclusions. By using the measures including increasing amount of pre-deoxidizing aluminium pig in LD tapping from 120~150kg to 160~180kg
increasing LF end slag basicity from 3.0 to 3.5 and decreasing ( FeO+MnO) from ≤1.5% to ≤1.2%
decreasing supperheating extent of liquid from 20~40℃ to 20~35°C and increasing finish rolling temperature and finishing temperature respectively from 940°C and 860℃ to 950℃ and 880℃,the cold-heading cracking rate of steel decreases from 18.60% to 5.80%.