SG iron designation per Indian standards — interpret “SG 400/15” According to Indian standard specifications, what does the designation SG 400/15 indicate for spheroidal graphite cast iron?

Introduction / Context:
Ductile iron (spheroidal graphite iron, SG iron) grades are designated to reflect minimum tensile strength and minimum percentage elongation. Correct interpretation ensures proper material selection for strength and ductility requirements in cast components such as housings, hubs, and crankshafts.

Given Data / Assumptions:

• Designation format “SG X/Y”.
• X is a stress value in MPa, Y is a ductility measure in percent.
• Indian standards align with the widespread convention used across many specifications.

Concept / Approach:
“SG 400/15” denotes a ductile iron with minimum ultimate tensile strength of 400 MPa and a minimum elongation at fracture of 15%. Brinell hardness is specified separately and not encoded in this two-number grade string. Compressive strength is not the basis for this designation either.

Step-by-Step Solution:

Verification / Alternative check:
Standards catalogues and supplier datasheets list SG 400/15 with UTS ≥ 400 MPa and elongation ≥ 15%; hardness windows are typical but separate.

Why Other Options Are Wrong:

• BHN and compressive-strength interpretations do not match the designation scheme.
• “None of the above” is invalid because option describing tensile strength and elongation exists.

Common Pitfalls:
Confusing yield and ultimate strengths; assuming hardness is embedded in the grade.

Final Answer: