According to Indian standard specifications, SG 400/15 means

• spheroidal graphite cast iron with B.H.N. 400 and minimum tensile strength 15 MPa
• spheroidal graphite cast iron with minimum tensile strength 400 MPa and 15 percent elongation
• spheroidal graphite cast iron with minimum compressive strength 400 MPa and 15 percent reduction in area
• none of the above