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ASTM A194

ASTM A194


Scope

The ASTM A194 specification covers carbon, alloy and stainless steel nuts intended for use in high-pressure and/or high-temperature service. Unless otherwise specified, the American National Standard Heavy Hex Series (ANSI B 18.2.2) shall be used. Nuts up to and including 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 common in the marketplace and are often substituted for ASTM A563 grade DH nuts due to the limited availability of DH nuts in certain diameters and finishes.

Grades

Grade IDDescription
2Carbon steel heavy hex nuts
2HQuenched & tempered carbon steel heavy hex nuts
2HMQuenched & tempered carbon steel heavy hex nuts
4Quenched & tempered carbon-molybdenum heavy hex nuts
7Quenched & tempered alloy steel heavy hex nuts
7MQuenched & tempered alloy steel heavy hex nuts
8Stainless AISI 304 heavy hex nuts
8MStainless AISI 316 heavy hex nuts

Mechanical Properties – Grade Identification Markings

Grade Identification Marking5SpecificationMaterialNominal Size, In.Tempering Temp. ˚FProof Load Stress, ksiHardness RockwellSee Note
MinMax
ASTM A194 Grade 2Medium Carbon Steel1/4 – 410001501593521,2,3
ASTM A194 Grade 2HMedium Carbon Steel, Quenched and Tempered1/4 – 41000175C24C381,2
ASTM A194 Grade 2HMMedium Carbon Steel, Quenched and Tempered1/4 – 410001501592371,2,3
ASTM A194 Grade 4Medium Carbon Alloy Steel, Quenched and Tempered1/4 – 41100175C24C381,2
ASTM A194 Grade 7Medium Carbon Alloy Steel, Quenched and Tempered1/4 – 41100175C24C381,2
ASTM A194 Grade 7MMedium Carbon Alloy Steel, Quenched and Tempered1/4 – 411001501592371,2,3
ASTM A194 Grade 8Stainless AISI 3041/4 – 4-801263004
ASTM A194 Grade 8MStainless AISI 3161/4 – 4-801263004
NOTES:

  1. The markings shown for all grades of A194 nuts are for cold formed and hot forged nuts. When nuts are machined from bar stock, the nut must additionally be marked with the letter ‘B’. The letters H and M indicate heat treated nuts.
  2. Properties shown are those of coarse and 8-pitch thread heavy hex nuts.
  3. Hardness numbers are Brinell Hardness.
  4. Nuts that are carbide-solution treated require additional letter A – 8A or 8MA.
  5. All nuts shall bear the manufacturer’s identification mark. Nuts shall be legibly marked on one face to indicate the grade and process of the manufacturer. Marking of wrench flats or bearing surfaces is not permitted unless agreed upon between manufacturer and purchaser. Nuts coated with zinc have an asterisk (*) marked after the grade symbol. Nuts coated with cadmium shall have a plus sign (+) marked after the grade symbol.
  6. Other less common grades exist, but are not listed here.

Inch Fastener Standards. 7th ed. Cleveland: Industrial Fasteners Institute, 2003. N-80 – N-81.

Chemical Properties

Element2, 2H, and 2HM47 and 7M (AISI 4140)8 (AISI 304)8M (AISI 316)
Carbon0.40% min0.40 – 0.50%0.37 – 0.49%0.08% max0.08% max
Manganese1.00% max0.70 – 0.90%0.65 – 1.10%2.00% max2.00% max
Phosphorus, max0.040%0.035%0.035%0.045%0.045%
Sulfur, max0.050%0.040%0.040%0.030%0.030%
Silicon0.40% max0.15 – 0.35%0.15 – 0.35%1.00% max1.00% max
Chromium0.75 – 1.20%18.0 – 20.0%16.0 – 18.0%
Nickel8.0 – 11.0%10.0 – 14.0%
Molybdenum0.20 – 0.30%0.15 – 0.25%2.00 – 3.00%