Influence by Nitrogen on Hot Workability of C-Mn Steel at Temperature Ranging from 740 to 900℃

Investigated is the influence by Element N on the hot workability of the C-Mn steel within the temperature range as 740~900℃.Also discussed are the mechanism of the influence, and the effects by N and Al.To simulate the thermo-mechanical conditions, tensile tests are carried out to the specimens as directly heated to a temperatures ranging from 740 to 900℃ with an initial strain rate of 1×10^-3s^-1.After each test, the reduction of cross section area of the specimen is used to measure the hot ductility.The test results indicate that when nitrogen content is rising, the hot ductility of the C-Mn steel is going down within the temperature range as 740~900℃, whereas the stress peak going up.It is also identified that nitrogen causes fine AlN precipitated along the austenite grain boundaries, promoting low ductility intergranular failure, and that nitrogen also retards dynamic re-crystallization, which probably is why nitrogen widens the hot ductility trough area.Moreover the AlN precipitation is determined by the product of N content and Al content, and therefore the hot ductility of the said steel can be improved by means of decreasing Al content within the foresaid temperature range.