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    ASTM A194 Grades — Carbon, Alloy, Stainless Nut Selector Guide

    ASTM A194/A194M covers heavy hex nuts in carbon, alloy, and stainless steel grades for high-pressure and high-temperature bolting service. This overview groups all major A194 grades by material family with selection guidance.

    Carbon Steel Grades

    GradeMaterialUNSTypical Service
    Grade 1Low-carbon steelK01503General bolting up to 800°F
    Grade 2Q&T medium-carbonK04100Higher-strength general bolting
    Grade 2HQ&T carbon steelK04100Refinery/petrochem (most common A194 grade)
    Grade 2HMQ&T carbon (sour)K04100NACE sour-service H2S environments

    Alloy Steel Grades

    GradeMaterialUNSTypical Service
    Grade 35Cr-0.5Mo alloyS50100High-temperature 5Cr alloy service
    Grade 4Q&T Cr-Mo alloyG41400Higher-strength alloy bolting
    Grade 7AISI 4140 Cr-Mo Q&TG41400Refinery (paired with A193 B7)
    Grade 7MAISI 4140 (sour)G41400Sour-service (paired with A193 B7M)
    Grade 16Cr-Mo-V alloy—High-temperature up to 1100°F

    Stainless Steel Grades (Type 304 Family)

    GradeMaterialUNSTypical Service
    Grade 8Type 304 austeniticS30400General stainless service
    Grade 8A304 (Class 1A)S30400Solution-treated in finished condition
    Grade 8FType 303 free-machiningS30300Improved machinability variant
    Grade 8LNType 304LN low-C N-strengthenedS30453Higher strength low-carbon 304
    Grade 8NType 304N N-strengthenedS30451Nitrogen-strengthened 304
    Grade 8PType 305 low work-hardeningS30500Cold-formed nut service

    Stainless Steel Grades (Type 316 / Mo-bearing)

    GradeMaterialUNSTypical Service
    Grade 8MType 316 Mo-bearingS31600Chloride-pitting resistance (marine, brine)
    Grade 8MA316 (Class 1A)S31600Solution-treated finished condition
    Grade 8MLNType 316LN low-C N-strengthenedS31653Higher strength low-C 316
    Grade 8MNType 316N N-strengthenedS31651Nitrogen-strengthened 316
    Grade 8MLCUNType 254 SMO super-austeniticS312546Mo Cu-N super-austenitic

    Stabilised Stainless Grades

    GradeMaterialUNSTypical Service
    Grade 8CType 347 Nb-stabilisedS34700Intergranular-corrosion-resistant high-temp
    Grade 8TType 321 Ti-stabilisedS32100High-temperature stabilised austenitic

    High-Strength / Specialty Stainless

    GradeMaterialUNSTypical Service
    Grade 6Type 410 martensiticS4100012Cr martensitic stainless
    Grade 6FType 416 free-machiningS41600Free-machining martensitic
    Grade 8RNitronic 50 (XM-19)S20910High-strength nitrogen-strengthened
    Grade 8SNitronic 60S21800Galling-resistant austenitic
    Grade 9CAL-6XN super-austeniticN083676Mo-N super-austenitic alloy

    Selection Guide

    • General refinery/petrochem bolting: Grade 2H (carbon) or Grade 7 (Cr-Mo, paired with B7)
    • Sour-service (H2S): Grade 2HM (carbon) or Grade 7M (Cr-Mo, paired with B7M)
    • Standard stainless service: Grade 8 (304)
    • Chloride / marine service: Grade 8M (316) or Grade 8MLCUN (254 SMO)
    • High-temperature stabilised: Grade 8C (347) or Grade 8T (321)
    • High-temperature alloy: Grade 16 (Cr-Mo-V)

    For the full ASTM A194/A194M specification: PDF download. Dimensional reference: ASME B18.2.2 heavy hex. A194 hub.

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