Patent ID: 8715427

Claim:
A hot-rolled ultra high strength steel composition, said composition comprising: Ti and N, wherein the concentration of N is between 0 and 100 parts per million (ppm mass); Tifactor =(ppm Ti)−3.42(ppm N)+10 ppm, wherein the Tifactor is between 50 ppm and 400 ppm mass; and further comprising: C: between 1000 ppm and 2500 ppm mass Mn: between 12000 ppm and 20000 ppm mass Si: between 1500 ppm and 3000 ppm mass P: between 280 ppm and 600 ppm mass S: maximum 50 ppm mass Al: maximum 1000 ppm mass B: between 10 ppm and 35 ppm mass Nb: between 200 ppm and 800 ppm mass Cr: between 2500 ppm and 7500 ppm mass Mo: between 1000 ppm and 2500 ppm mass Ca: between 0 and 50 ppm mass the remainder being substantially iron and incidental impurities; wherein the hot-rolled ultra high strength steel composition is in sheet form and comprises a thickness between 0.3 mm and 2.0 mm, said steel composition comprising at least a bainitic and a martensitic phase wherein the phase distribution is such that the sum of the bainitic and martensitic phases is higher than 35%, and tensile strength between 1000 MPa and 1600 MPa.