Microalloyed high-strength steels

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Microalloyed high-strength steels

Olsson, Kennet / Gladh, Magnus / Hedi, Jan-Erik / Larsson, Joachim

Extra-high-strength and ultra-high-strength microalloyed and dual-phase steels have been developed for automotive applications to reduce weight, improve formability, and increase strength. These steels include Domex, Docol, and Dogal grades. Domex MC is a range of hot-rolled highstrength cold-forming steels. All grades are microalloyed with niobium (columbium). Grades available in the North American market have minimum yield strengths ranging from 550 to 700 MPa(80 to 100ksi). YP (yield point) Docol and Dogal HDG grades are typical high-strength microalloyed cold-rolled and hot-dip-galvanized steels. Docol and Dogal DP are cold-rolled dualphase steels. These steels are subjected to heat treatment in the continuous annealing line or hotdip galvanizing line, producing a two-phase structure of ferrite that imparts unique forming properties, and martensite that adds strength. Dogal DPX dual-phase steels have improved formability, especially in bending, and are superior to conventional steels in reverse bending operations. Docol M grades are cold-reduced fully martensitic steels. The ultrahigh strength is produced by water quenching from an elevated austenitic temperature range.