Alloying in high-speed steels (HSS) — effect of manganese In traditional tungsten/molybdenum high-speed steels, manganese is added primarily to toughen the steel and to increase its which property?

Introduction / Context:
Manganese is a common addition to plain-carbon and alloy steels, including high-speed steels (HSS). In HSS, small additions of manganese help achieve a better balance of toughness and hardness after heat treatment. This question checks your understanding of what property manganese is most commonly credited with increasing in this family of tool steels.

Given Data / Assumptions:

• Material class: high-speed steels used for cutting tools.
• Manganese content is typically modest (about 0.2–0.9% depending on grade).
• Standard hardening and tempering cycles for HSS are assumed.

Concept / Approach:
Manganese in steel acts as a deoxidizer and combines with sulphur to form MnS, mitigating hot shortness. It also promotes a deeper hardening response by lowering the critical cooling rate and stabilizing austenite slightly. The net result after proper heat treatment is an increase in hardness and strength, while maintaining or improving toughness compared with manganese-free compositions.

Step-by-Step Solution:
Identify the dominant effect in HSS: manganese enhances hardening response and final hardness after quench/temper.Evaluate options: yield point and melting point are not primary targets in HSS design; critical temperature is actually slightly reduced, not increased, by Mn.Therefore, among the listed choices, “hardness” is the correct property increased in practice.

Verification / Alternative check:
Handbooks list manganese as improving hardenability and contributing to higher as-quenched and tempered hardness, especially when combined with strong carbide formers (W, Mo, V, Cr) that give HSS its red hardness.

Why Other Options Are Wrong:

• Yield point: may rise somewhat with overall strengthening, but it is not the principal HSS design aim for Mn.
• Critical temperature: Mn tends to lower transformation temperatures rather than increase them.
• Melting point: alloying changes melting range slightly, but this is not the targeted effect.
• Hardenability (extra distractor): although true in general, the question asks which property is increased; in tool-steel context and options given, hardness is the accepted answer.

Common Pitfalls:
Confusing “hardness” with “hardenability.” Hardenability is the ability to form martensite through section thickness; hardness is the achieved resistance to indentation after heat treatment.

Final Answer:
hardness