ASTM A194 – Mechanical, Material & Chemical Properties

The mechanical integrity of nuts manufactured under ASTM A194/A194M is verified through rigorous hardness and proof load testing to ensure performance in high-pressure and high-temperature environments. These properties are strictly dependent on the material grade, heat treatment process, and the dimensional series (Hex vs. Heavy Hex).

• Hardness Requirements: All nuts must conform to the specific Brinell or Rockwell hardness ranges defined for their grade. For grades such as 2H, 3, and 7, sample nuts undergo additional testing after specific heat treatments to ensure stability.
• Proof Load Verification: Nuts must withstand specified proof loads without failure or thread stripping when tested with a threaded mandrel. Heavy Hex nuts generally feature higher proof stress ratings compared to standard Hex nuts.
• Testing Precedence: In cases where a conflict arises regarding minimum strength, the results of the proof load test prevail over hardness testing.
• Specialized Grades: For critical service grades like 2HM and 7M, 100% hardness testing of each individual nut is required to ensure product consistency.

The following tables detail the specific hardness and proof load requirements for standard inch and metric series.

The chemical composition requirements for ASTM A194/A194M nuts are divided into three primary metallurgical categories: Carbon Steel, Alloy Steel, and Stainless Steel (Martensitic and Austenitic). These compositions are engineered to ensure reliable performance under high-pressure or high-temperature service conditions.

• Carbon & Low Alloy Steels: Grades such as 1, 2, 2H, and 7 utilize controlled carbon and manganese levels, with Grade 7 adding Chromium and Molybdenum for enhanced high-temperature resistance.
• Martensitic Stainless Steels: Grade 6 and 6F (Type 410) are characterized by 11.5–14.0% Chromium, providing a balance of strength and corrosion resistance.
• Austenitic Stainless Steels (Series 8 & 9): These grades feature high Nickel and Chromium content (e.g., Grade 8/304 and Grade 8M/316) for superior corrosion resistance and are often solution annealed to prevent carbide precipitation.
• Manufacturing Control: Bars used for nut production must be hot-wrought and may be further processed by cold drawing or centerless grinding. Steel producers must exercise strict control to eliminate unhomogeneity and porosity.
• Prohibited Elements: The intentional addition of elements like Bismuth (Bi), Selenium (Se), Tellurium (Te), and Lead (Pb) is strictly forbidden except where specifically required for machinability in grades like 6F or 8F.

The table below provides the detailed chemical analysis for each grade, specifying the elemental weight percentages required for compliance.