Research On Controlled Cooling Process Of High-speed Wire SWRH82B Steel

With the development of our national economy in recent years, the consumption of high-strength reinforcement wire and standard wire increases sharply. Because of the harsh application conditions, the demand is increasing on the property of raw material high-speed wire rod. Therefore, it is very practical to improve the combination property of high-speed wire rod with the help of controlled cooling process technology.The cooling rate of hot rolled high-speed wire rod is usually limited to 10?/s so as to avoid abnormal microstructure, especially for martensite. Just because of this, the pearlite interlamellar spacing was also limited, which depresses the property of high-speed wire rod. In order to further refine the pearlite interlamellar spacing, and improve the tensile strength of SWRH82B wire, a water mist cooling device was installed in the traditional Stelmor cooling line. In this way, the cooling rate can be increased, and the pearlite interlamellar spacing will be more fine. The main contents and results are as followed:1. The static CCT curve and dynamic CCT curves of test steel were plotted by transformation temperature determined on the dilatometric curves with the help of metallographic observation micro-hardness analysis. Process simulation showed that the pearlitic transformation temperature in practical production was 700-550?,and the optimal cooling rate was 10?/s.2. In the Stelmor cooling system added ultra-fast cooling process, the higher was the cooling rate, the more fine was the pearlite interlamellar spacing. But the final cooling temperature, which usually has a fluctuation in practical production, has little effect on the pearlite interlamellar spacing.3. After the experimental steel was corroded by oversaturated solution of picric acid in 40-60?, the boundaries of pearlite colony can be clearly observed, The mean size of pearlite colony, about 4,00?m, can be calculated through this method. which is more precise than EBSD.(the mean size of pearlite colony is about 8.00?m) The pearlite interlamellar spacing, about 0.100-0.120?m,can be calculated precisely by means of EPMA and line scanning of carbon content.4. The research shows that, although the pearlite interlamellar spacing was refined from 0.120?m to 0.100?m after the ultra-fast cooling process, on the contrary, the size of pearlite colony was bigger from 3.90?m to 4.10?m and the tensile strength was lower. The results can be explained as followed:After the ultra-fast cooling process, a high density of dislocation existed in the hot rolled high-speed wire rod. There was not enough time for the dislocations to recover and rearrange, so the dislocation wall can not be formed and the grain became coarser.5. The dislocations in the hot rolled high-speed wire rod after ultra-fast cooling can recover and rearrange through relaxation, which can refine not only decreases the pearlite interlamellar spacing, but also the pearlite colony, resulting in the improving the tensile strength of tested steel effectively. When the relaxation time was different, the refinement effect was different, so there was a optimal relaxation time, about 40s.The results suggested that the property of high-speed wire can be improved effectively by means of ultra-fast cooling in traditional Stelmor cooling line and a certain relaxation time.