An overview of the common materials for heavy steel nuts for stud bolts, as per the ASTM A194 (grade 2, 2H, 2HM, 7, 7M, 8, 8M etc) specification.
The ASTM A194 specification covers a variety of carbon, alloy, and martensitic and austenitic stainless steel nuts. Hex heavy nuts are components of boltings sets for flanges.
These nuts are intended for high-pressure or high-temperature service or both. Bars from which the nuts are made shall be hot-wrought.
According to the ASTM A194 norm, the material may be further processed by centerless grinding or by cold drawing.
Austenitic stainless steel may be solution annealed or annealed and strain-hardened. Each alloy shall conform to the chemical composition requirements prescribed.
Hardness tests, proof of load tests, and cone proof load tests shall be made to all nuts to meet the requirements specified.
ASTM A194 stated in either inch-pound units or SI units are to be regarded separately as standard.
The values stated in each system are not exact equivalents; therefore, each system must be used independently by the other. Combining values from the two systems may result in a non-conformity with the specification of the ASTM A194 norm.
Within the text, the SI units are shown in brackets. ASTM A194 covers the size from 1/4 inch. through 4 inches. and the metric sizes between M6 and M100 nominal diameter. It also covers austenitic stainless steel nuts in the size range 1/4 inch. and M6 nominal and upper.
Unless otherwise specified, the American National Standard Heavy Hex Series (ANSI B 18.2.2) shall be used for the threading of the nuts. Heavy hex nuts > = 1 inch. nominal size shall be UNC Series Class 2B fit. Nuts over 1 inch. nominal size shall be either UNC Series Class 2B fit or 8 UN Series Class 2B fit. High strength ASTM A194 grade 2H nuts are the most common type of steel nuts used in combination with A193 B7 stud bolts.
ASTM A194 STEEL NUTS MATERIALS
- ASTM A194 2H: Quenched & tempered carbon steel heavy hex nuts
- ASTM A194 2HM: Quenched & tempered carbon steel heavy hex nuts
- ASTM A194 4: Quenched & tempered carbon-molybdenum heavy hex nuts
- ASTM A194 3
- ASTM A194 6
- ASTM A194 7: Quenched & tempered alloy steel heavy hex nuts
- ASTM A194 7M: Quenched & tempered alloy steel heavy hex nuts
- ASTM A194 8: Stainless AISI 304 heavy hex nuts
- ASTM A194 8A
- ASTM A194 8M: Stainless AISI 316 heavy hex nuts
- ASTM A194 8MA
- ASTM A194 8C
- ASTM A194 8T
ASTM A194 CHEMICAL COMPOSITION
|ASTM A194||Carbon||Manganese||Phosphorous, max||Sulfur, max||Silicon||Chromium||Nickel||Molybdenum||Other Elements|
|ASTM A194 grade 2, 2H and 2 HM||0.40% min.||1.00% max.||0.04%||0.05%||0.40% max|
|ASTM A194 grade 3||0.10% min.||1.00% max.||0.04%||0.03%||1.00%||4.0-6.0%||0.20-0.30%|
|ASTM A194 grade 4||0.40 -0.50%||0.70-0.90%||0.035%||0.04%||0.15-0.35%||0.20-0.30%|
|ASTM A194 grade 6||0.15%||1.00%||0.04%||0.03%||1.00%||11.5-13.5%|
|ASTM A194 grade 6F||0.15%||1.25%||0.06%||0.06%||1.00%||12.0-14.0%||Selenium-0.15% min|
|ASTM A194 grade 7 and 7M (AISI 4140)||0.37-0.49%||0.65-1.10%||0.04%||0.04%||0.15-0.035%||0.75-1.20%||0.15-0.25%|
|ASTM A194 grade 8 (AISI 304)||0.08%||2.00% max||0.05%||0.03%||1.00% max||18.0-20.0%||8.0-11.0%|
|ASTM A194 grade 8M (AISI 316)||0.08%||2.00% max||0.05%||0.30%||1.00% max||16.0-18.0%||10.0-14.0%||2.00-3.00%|
|ASTM A194 grade 8C||0.08%||2.00%||0.045%||0.03%||1.00%||17.0-19.0%||9.0-12.0%||Columbium and Tantalum – 10x carbon content, min|
|ASTM A194 grade 8T||0.80%||2.00%||0.045%||0.30%||1.00%||17.0-19.0%||9.0-12.0%||Titanium-0.70%max, Nitrogen-0.10%|
|ASTM A194 grade 8F||0.15%||2.00%||0.20%||0.15%min||1.00%||17.0-19.0%||8.0-10.0%|
|ASTM A194 grade 8R||0.06%||4.0-6.0%||0.045%||0.03%||1.00%||20.5-23.5%||11.5-13.5%||1.50-3.00%||Columbium and Tantalum-0.10-0.30%, Nirogen-0.20-0.40%, Vanadium-0.10-0.30%|
|ASTM A194 grade 8S||0.10%||7.0-9.0%||0.060%||0.03%||3.5-4.5%||16.0-18.0%||8.0-9.0%||Nitrogen-0.08-0.18%|
|ASTM A194 grade 16||0.36-0.47%||0.45-0.70%||0.035%||0.40%||0.15-0.35%||0.80-1.15%||0.50-0.65%|
ASTM A194 MECHANICAL PROPERTIES
|Grade Identification Marking5||Specification||Material||Nominal Size, In.||Tempering Temp. °F||Proof Load Stress, ksi||Hardness Rockwell||See Note|
|ASTM A194 Grade 2||Medium Carbon Steel||1/4 – 4||0||150||159||352||1,2,3|
|ASTM A194 Grade 2H||Medium Carbon Steel, Quenched and Tempered||1/4 – 4||850||175||C24||C38||1,2|
|ASTM A194 Grade 2HM||Medium Carbon Steel, Quenched and Tempered||1/4 – 4||1150||150||159||237||1,2,3|
|ASTM A194 Grade 4||Medium Carbon Alloy Steel, Quenched and Tempered||1/4 – 4||1100||175||C24||C38||1,2|
|ASTM A194 Grade 7||Medium Carbon Alloy Steel, Quenched and Tempered||1/4 – 4||1100||175||C24||C38||1,2|
|ASTM A194 Grade 7M||Medium Carbon Alloy Steel, Quenched and Tempered||1/4 – 4||1150||150||159||237||1,2,3|
|ASTM A194 Grade 8||Stainless AISI 304||1/4 – 4||–||80||126||300||4|
|ASTM A194 Grade 8M||Stainless AISI 316||1/4 – 4||–||80||126||300||4|
METRIC STEEL NUTS MATERIALS
- Stainless steel 18-8 (A-2): Also known as A-2 stainless, 18-8 is the most common grade of stainless steel for general use.
- Stainless steel 316 (A-4): Also known as A-4 stainless, 316 is a highly corrosion resistant grade of stainless steel. Ideal for saltwater and chlorine environments. More expensive than 18-8.
- Zinc plated steel: A low carbon steel for general use. Zinc plated for moderate corrosion resistance.
- Zinc plated class 8.8 steel: A tempered medium carbon steel. Class 8.8 is hardened, but it is not as strong as class 10.9. It is commonly found in automotive applications. Class 8.8 is similar to grade 5. Zinc plated for moderate corrosion resistance.
- Zinc plated class 10.9 steel: A tempered medium carbon steel. Class 10.9 is stronger than class 8.8 and is commonly found in high strength automotive applications. Class 10.9 is similar to grade 8. Zinc plated for moderate corrosion resistance.
- Chrome plated steel: A low carbon steel for general use. Chrome plated and polished for a mirror-like finish.