This refers to higher tensile strength grades. Solution-annealed 304SS typically has an ultimate tensile strength of 75 ksi (515 MPa), Brinnell hardness 201, and Rockwell B Hardness 92. Quarter-hard steel has tensile strength of 115 – 135 ksi. It is harder to form than solution-annealed 304SS. Solution-annealed steel has undergone thermal treatment beyond stress relieving to give the higher tensile strength and hardness.