Nickel-chromium low alloy steels are designed to increase what?

• A. decrease hardenability
• B. increase hardenability and response to heat treatment
• C. be weldable without heat input
• D. have no alloying effects

Answer: (B)

Nickel and chromium in low alloy steels are added to boost hardenability, allowing thicker sections to form martensite during quenching, and they also improve how the steel responds to heat treatment. The hardenability increase comes from the alloying elements delaying transformation and broadening the range of temperatures and cooling rates that produce a hard, martensitic structure, so more of the cross-section can harden instead of just the surface. This same combination also enhances the effectiveness of heat treatment, giving greater strength and toughness after processes like quenching and tempering because the alloyed microstructure responds more vigorously to heat treatment. The other options don’t fit because these steels do not decrease hardenability, aren’t designed to be welded without any heat input, and do have alloying effects that change properties.