Steels for precision measuring instruments Which steel is commonly used for precision measuring instruments due to its dimensional stability and controlled thermal expansion?

Introduction / Context:
Precision measuring instruments (e.g., gauges, comparators, precision rules) demand dimensional stability over temperature fluctuations. Alloys with controlled thermal expansion and good stability are preferred to minimize measurement error.

Given Data / Assumptions:

• “Nickel steel” here refers to Fe–Ni alloys with elevated nickel, including low-expansion grades such as Invar-type compositions.
• Applications require low coefficient of thermal expansion and good machinability/finishing.
• Not focused on cutting action or impact toughness; accuracy and stability dominate.

Concept / Approach:
Fe–Ni alloys around 36% Ni (Invar family) exhibit exceptionally low thermal expansion near room temperature. Broader “nickel steels” with substantial Ni also enhance stability compared with plain carbon steels. While nickel–chromium steels are strong, their thermal expansion is not as uniquely low. High speed steel is for cutting tools (hot hardness), and chrome–vanadium steels are for springs or tools, not typically for precision standards.

Step-by-Step Solution:
Identify the key requirement: minimal dimensional change with temperature.Match alloy system: Fe–Ni (nickel steel) provides low expansion (Invar) and stability.Eliminate tool steels and spring steels used for entirely different properties.Therefore, choose nickel steel.

Verification / Alternative check:
Metrology standards and gauge blocks often use low-expansion alloys (Invar, Super-Invar) or stabilized tool steels for specific use cases; the canonical low-expansion choice remains Ni-rich iron alloys.

Why Other Options Are Wrong:
Nickel–chrome, HSS, and Cr–V steels prioritize strength/hardness rather than low expansion; manganese steel (Hadfield) is impact- and wear-resistant with high expansion, unsuitable for precision dimension control.

Common Pitfalls:
Assuming “strongest steel” yields best measuring accuracy; dimensional stability, not ultimate strength, is the controlling criterion.

Final Answer:
nickel steel