Clean Level Control Study Of Sulfur-bearing Pinion Steel Used On Automobile

Along with the fast development of automotive industry the output of auto gear and the requirement of free-machining performance of steel products are higher and higher. So exploitation of free-machining pinion steel and study of clean degree control is very important.This paper sums up the present state of automobile pinion steel and the smelting processes of main pinion steel grades inside and outside of country. In terms of quaternity short flow process product line characteristic of Fushun special steel and metallurgic quality requirement of automobile sulfur bearing pinion steel system study on improving steel clean level has been done. Study results as follows:(1) In order to lower oxygen content in liquid steel and content of FeO in slag carbon powder is blew onto interface of liquid steel and slag before tapping, through which liquid steel peroxidation when tapping of UHP is solved.(2) That liquid steel is pre-deoxized with aluminium can ensure that there are some remnant aluminium in steel to refine grain. At the same time, right white slag holding time and basicity of refining slag is the precondition of deoxization effect. That final sulfur content on LF is not more than0.008%is a important control point to ensure that sulfide level of product is not more than2.0.(3) Right treating occasion and addition of calcium can lower inclusion level and improve pourability of liquid steel.(4) Yield of sulfur reaches89percent by means of feeding sulfur wire to adjust sulfur content in steel. Moreover sulfur content in steel is easily controlled and sulfide inclusion level is stable.(5) Quantity and size of inclusion in steel all rise after feed sulfur wire into liquid steel on VD. So20minutes of soft blowing operation before casting is very favorable to remove bulky grain inclusion.(6) Expected goals that oxygen content is not more than15×10-6, conformity rate of A type and thin series inclusion is more than95percent and conformity rate of B type and thin series inclusion reaches100percent have been achieved.