• View PDF
    Standard
  •   +91-22-66157017
  •   info@torqbolt.com
    • Home
    2. ASTM A193/A193M Grade B8MLCuNA Class 1A

    ASTM A193/A193M Grade B8MLCuNA Class 1A Stud Bolts – UNS S31254

    Strain hardened super austenitic 254 SMO stainless steel stud bolts with exceptional pitting corrosion resistance for the most demanding service environments.

    ASTM A193/A193M Grade B8MLCuNA Class 1A Stud Bolts are produced from UNS S31254, widely known by the trade designation 254 SMO, a super austenitic stainless steel with a nominal composition of approximately 20% chromium, 18% nickel, 6% molybdenum, 0.7% nitrogen, and 0.75% copper. The high molybdenum and nitrogen content together produce an exceptionally high Pitting Resistance Equivalent Number (PREN), typically above 42, placing this grade among the most corrosion-resistant commercially available austenitic alloys and making it highly resistant to pitting, crevice corrosion, and stress corrosion cracking in seawater and other aggressive chloride environments. Strain hardened to meet the Class 1A requirements of ASTM A193 with testing on the finished fastener, these stud bolts deliver both the mechanical performance demanded by high-pressure systems and the extraordinary corrosion resistance required in seawater handling equipment, desalination plants, pulp and paper bleaching systems, flue gas desulfurization, and offshore subsea applications.

    ASTM A193/A193M Grade B8MLCuNA Class 1A Chemical Composition - Austenitic Steels

    Grade Description and UNS Designatio Classes C Mn P S Si Cr Ni Mo Cu N
    ASTM A193 Grade B8MLCUNA S31254 1A, 1B, 1D, 2 0.020 1.00 0.030 0.010 0.80 19.5-20.5 17.5-18.5 6.0-6.5 0.50-1.00 0.18-0.25
    Product Analysis VariationB 0.005 0.03 0.005 0.002 0.05 0.20 0.15 0.10 . . . 0.02
    • (A) Values are maximums unless a range or a minimum is indicated. Where ellipses appear in this table, there is no requirement and the element need not be determined or reported. The intentional addition of Bi, Se, Te, and Pb is not permitted.
    • (B) Product Analysis-Individual determinations sometimes vary from the specified limits as shown in the tables. The several determinations of any individual element in a heat may not vary both above and below the specified range. Product variation limits are over for maximums, over or under for ranges, and under for minimums, unless otherwise indicated.
    • (C) Typical steel compositions used for this grade include 4140, 4142, 4145, 4140H, 4142H, and 4145H.
    • (D) For bar sizes over 31/2 in. [90 mm], inclusive, the carbon content may be 0.50% max. For the B7M grade, a minimum carbon of 0.28% is permitted, provided that the required tensile properties are met in the section sizes involved, the use of AISI 4130 or 4130H is allowed.
    • (E) Total of soluble and insoluble.
    • (F) Columbium and Niobium are alternate names for element 41 in the Periodic Table of the Elements.

    ASTM A193/A193M Grade B8MLCuNA Class 1A Mechanical Requirements - Austenitic Steels (Inch)

    Grade Diameter,
    in.     		Heat TreatmentB Tensile Strength,
    min, ksi     		Yield Strength, min,
    0.2 % offset, ks     		Elongation in 4 D,min Reduction of Area, min Hardness,
    max
    ASTM A193 Grade B8MLCUNA Class 1A All diameters carbide solution treated in the finished condition 75 30 30 50 192 HBW or 90 HRB
    • (A) To meet the tensile requirements, the Brinell hardness shall be over 200 HBW (93 HRB).
    • (B) Class 1 is solution treated. Class 1A is solution treated in the finished condition for corrosion resistance; heat treatment is critical due to physical property requirement. Class 2 is solution treated and strain hardened. Austenitic steels in the strain-hardened condition may not show uniform properties throughout the section particularly in sizes over 3/4 in. in diameter.
    • (C) For sizes3/4 in. in diameter and smaller, a maximum hardness of 241 HBW (100 HRB) is permitted.
    • (D) For diameters 11/2 and over, center (core) properties may be lower than indicated by test reports which are based on values determined at1/2 radius.

    ASTM A193/A193M Grade B8MLCuNA Class 1A Mechanical Requirements - Austenitic Steels (Metric)

    Grade Class ,
    mm     		Diameter Heat TreatmentB Tensile Strength,
    min,MPa     		Yield Strength, min,
    0.2 % offset, MPa     		Elongation in 4 D,min % Reduction of Area, min % Hardness,
    max
    ASTM A193 Grade B8MLCUNA Class 1A All diameters carbide solution treated in the finished condition 515 205 30 50 192 HBW or 90 HRB
    • (A) To meet the tensile requirements, the Brinell hardness shall be over 200 HBW (93 HRB).
    • (B) Class 1 is solution treated. Class 1A is solution treated in the finished condition for corrosion resistance; heat treatment is critical due to physical property requirement. Class 2 is solution treated and strain hardened. Austenitic steels in the strain-hardened condition may not show uniform properties throughout the section particularly in sizes over M20 mm in diameter.
    • (C) For sizes M20 mm in diameter and smaller, a maximum hardness of 241 HBW (100 HRB) is permitted.
    • (D) For diameters M38 and over, center (core) properties may be lower than indicated by test reports which are based on values determined at1/2 radius.

    ASTM A193/A193M Grade B8MLCuNA Class 1A Bolting Components Marking - Austenitic Steels

    Grade Class Grade Symbol
    ASTM A193 Grade B8MLCUNA Class 1A TB B9K or TB B8MLCuNA  
    TB B8ZZ or TB B8MLCuNA  

    Related ASTM A193 Grades & ASME Companion Dimensions

    Frequently Asked Questions

    What is ASTM A193 Grade B8MLCUNA Class 1A?
    ASTM A193 Grade B8MLCUNA Class 1A is a bolting material covering 6-Mo 254 SMO super-austenitic (UNS S31254). Class 1A — solution treated in finished condition for corrosion resistance. Used in high-temperature, high-pressure flange, pressure-vessel and heat-exchanger bolting service per ASTM A193/A193M.
    What is the UNS designation for ASTM A193 Grade B8MLCUNA Class 1A?
    The UNS designation for ASTM A193 Grade B8MLCUNA Class 1A is UNS S31254. This corresponds to 6-Mo 254 SMO super-austenitic. The UNS code is universal across ASTM, ASME (SA-193), PED 2014/68/EU and NORSOK material specifications. The 'Class 1A' designator denotes the heat treatment condition under ASTM A193 Table 3.
    What is the chloride-pitting envelope for Grade B8MLCuN (Class 1A)?
    B8MLCuN is 254 SMO (UNS S31254) — a 6-Mo super-austenitic with PREN ≈ 43, rated for service in seawater, ferric-chloride, and severe sour-service environments up to 320 °C. Far exceeds 316 (PREN 24) in chloride pitting resistance. Specific to ASTM A193 Grade B8MLCUNA Class 1A: Class 1A — solution treated in finished condition for corrosion resistance.
    Specifications
    Surface Treatments
    Certifications
    About Us
    Questions? Contact us.
    Showcase of our Microsites.
    Satisfaction Survey

    survey

    TUVRheinland CRETIFIED

    © TorqBolt P(Ltd) · Built with in INDIA.