The Manufacture of Si-Mn As-hot-rolled Dual Phase Steel Sheets

Abstract

The Si-Mn steels have been hot-rolled and coiled at the very low temperature after rapid cooling in runout table of hot strip mills to produce as-hot-rolled dual phase (AHR DP) steel sheets which prove to be both economical and excellent in quality. The results obtained are as follows:
(1) The strengthening effect of carbon is very large but ductility does not decrease so much by increasing carbon content as to deteriorate the good strength-ductility combination.
(2) The Si addition of a higher content raises the critical coiling temperature under which DP steel can be obtained and it improves much the strength-ductility combination.
(3) The coiling temperature is the most important factor affecting strength and elongation of AHR DP steel and its appropriate range depends on the controlling capacity of cooling and the quality level of materials.
(4) Variations of mechanicl properties within a coil as well as throughout coils can be minimized by the control of chemical composition and rolling condition, and especially by the use of continuously-casted steel.
(5) When compared to conventional high strength low alloy steels, the hot-rolled DP steel shows a smaller planar anisotropy of properties and larger work- and bake-hardenability; the Si-Mn AHR DP steel, on the other hand, has a better combination of strength and ductility than the heat treated DP steel.
(6) Performances of Si-Mn AHR DP steel sheets are good especially in hole expansion property and stretchabilty.