Sulfur Free Cutting Steel Smelting Technology Laboratory Studies

The steel products are used as primary material of automobile manufacturing and account for about 70% for the total weight of each one which the proportions of free-cutting steel, carbon steel and alloy steel reach 2.1%, 5.8% and 3.7%, respectively. In resent years, the annual quantity demanded for free-cutting steel in domestic is about form 400,000 to 500,000 tons, but the actual output is only 20,000 tons. Therefore, there are tremendous development potential of free-cutting steel production. This paper concentrates on the steel-making (?)process of re-sulfurized free-cutting steel in Panzhihua iron & steel for the purpose of accelerating the adjustment of steel products structure, enlarging the special steel kinds and improving the benefits for the company.The correlation between slag properties and sulfur yield was investigated. The results showed that these factors, such as basicity, temperature and FeO content of slag, would affecte sulfur yield and the basicity of slag was the dominator. The relation between the basicity of slag and sulfur yield was as follows:y=82.078-30.169ln(x-0.135).The sulfur yield decreased along with increase of slag temperature and increased when the FeO content is enhanced from 0.928% to 6.429%. Base on it, free-cutting non-quenched and tempered steel YF45MnVS was made. The sulfur yield was between 82.55% and 74.4%, and the average yield was 78.48%. At the same time, VT wire was adopted for vanadium alloying, and the vanadium yield was up to 91.9%.Considering the shape, distribution, quantity and composition of the inclusion would influence the machinability of steels, the technology of inclusion controlling was investigated. As a result, the proportion of fusiform inclusion in free-cutting steel Y45S20 was in the range from 63.3% to 85.58% by calcium treatment, and the average ration reached 74%. With the ratio of Ca vs. S increasing, the quantity of inclusion decreased and the proportion of fusiform inclusion increased evidently. The inclusion could help to improve the machinability of steels by deoxidizing of early weaker and terminal deeper. Moreover, the main type of the inclusions was complex one which core was oxide surrounded by sulfide after calcium treated.How to avid the cracks occurred during continuous casting is an important problem. The straightening temperature could be gained by thermal simulation tests. The thermal simulation tests of YF45MnVS and Y45S20 indicated that the shrinkage of section was the lowest at 850℃ and exceeded 60% when above 950℃. So the straightening temperature above 950℃ was recommended.The mechanical properties of Y45S20 and YF45MnVS made in laboratory were come to the requirement of the relative standard respectively. The contrastive experiments on the machinability of Y45S20 and 45 steel showed that the chips of the former was longer and tighter than that of the latter. The surface roughness of Y45S20 was better than that of 45 steel.