What's the chemical composition(%) of SA387 Gr.91 steel? Carbon: 0.08-0.12, Manganese: 0.30-0.60, Phosphorus: 0.020 max., Sulfur: 0.010 max.,Silicon: 0.20-0.50, Chromium: 8.00-9.50, Molybdenum: 0.85-1.05, Nickel: 0.40 max., Vanadium: 0.18-0.25, Columbium