ASTM A194 Grades: Chemistry, Heat Treatment and Hardness

ASTM A194/A194M-20a covers carbon steel, alloy steel and stainless steel nuts for bolts for high-pressure or high-temperature service, or both. The tables below group every grade in Table 1 by material, with its manufacturing route (clause 6) and hardness (Table 2). Proof stress groups follow the tables. Grades 4 and 43 are not in the 2020a edition; see the note at the end.

Carbon Steel Grades

Alloy Steel Grades

Martensitic Stainless Grades

Austenitic Stainless Grades (Grade 8 Family)

Plain types are hot or cold forged or machined from bar (6.5). The A types are carbide-solution treated after forming (6.6) and are softer. Stainless steel for all types of Grade 6 and 8 is melted by electric furnace or vacuum induction, optionally remelted (6.1).

Carbide-Solution-Treated A Types

UNS N08367 Grades

Proof Stress by Grade Group

• Grade 1: 130 000 psi [895 MPa] heavy hex, 120 000 psi [825 MPa] hex.
• Grades 2, 2HM, 6, 6F and 7M: 150 000 psi [1035 MPa] heavy hex, 135 000 psi [930 MPa] hex.
• Grades 2H, 3, 7 and 16: 175 000 psi [1205 MPa] heavy hex, 150 000 psi [1035 MPa] hex.
• All types of Grade 8, and Grades 9C and 9CA: 80 000 psi [550 MPa] heavy hex, 75 000 psi [515 MPa] hex.

Sources: Tables 3 to 6. At 1 in. (8 threads per inch) the heavy hex proof loads are 78 780, 90 900, 106 000 and 48 480 lbf for these four groups (Table 3). Jam nuts are proof loaded at 46 % of the tabulated load, and proof loads are not design loads.

Where to Look Next

• Sour service: ISO 15156-2:2020 Table A.4 lists Grades Grade 2HM and Grade 7M as acceptable nuts for A193 B7M and A320 L7M bolts.
• Low temperature: ASTM A320/A320M-21 (10.1, 10.2) names A194 Grade 7 and 7M nuts for its ferritic bolting and Grades 8, 8C, 8T, 8F, 8M, 8LN and 8MLN for its austenitic bolting; A194 Supplementary Requirement S3 adds Charpy testing for Grades 7 and 7M.
• Grades 4 and 43: neither is in A194/A194M-20a. A320 still refers to A194 Grade 4, and Grade L43 nuts are an A320 material; see Grade 43.
• Comparisons: Grade 7 vs 7M · Grade 2H substitutes · A194 vs A563.

Dimensions: ASME B18.2.2 heavy hex · hex. Full specification: ASTM A194 PDF · A194 hub.

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