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    2. ASTM A193/A193M Grade B8A Class 1A

    ASTM A193/A193M Grade B8A Class 1A Stud Bolts – UNS S30400

    Strain hardened UNS S30400 stainless steel stud bolts with elevated tensile strength, meeting Class 1A requirements for high-pressure bolting service.

    ASTM A193/A193M Grade B8A Class 1A Stud Bolts are manufactured from UNS S30400 austenitic stainless steel and are distinguished from Class 1 by the application of strain hardening — a cold working process that significantly increases tensile and yield strength compared to the solution annealed condition. The Class 1A designation under ASTM A193 specifically refers to strain-hardened fasteners where the properties are verified on the individual finished fastener itself, rather than on the raw bar stock, ensuring that the actual bolts meet the elevated mechanical requirements regardless of diameter variations. This approach provides higher assurance of performance for critical pressure-containing joints. Grade B8A Class 1A stud bolts are widely used in high-pressure flanged connections, pressure vessels, and heat exchangers in oil refineries, chemical plants, and power generation facilities where the combination of corrosion resistance offered by 304 stainless steel and improved mechanical strength from strain hardening is required to meet design and safety standards.

    ASTM A193/A193M Grade B8A Class 1A Chemical Composition - Austenitic Steels

    Grade Description and UNS Designatio Classes C Mn P S Si Cr Ni
    ASTM A193 Grade B8A 304, S30400 1, 1A, 1D, 2 0.08 2.00 0.045 0.030 1.00 18.0-20.0 8.0-11.0
    Product Analysis VariationB 0.01 0.04 0.010 0.005 0.05 0.20 0.15
    • (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 B8A 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 B8A 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 B8A 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 B8A 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 B8A Class 1A Bolting Components Marking - Austenitic Steels

    Grade Class Grade Symbol
    ASTM A193 Grade B8A Class 1A TB B8A

    Related ASTM A193 Grades & ASME Companion Dimensions

    Frequently Asked Questions

    What is ASTM A193 Grade B8A Class 1A?
    ASTM A193 Grade B8A Class 1A is a bolting material covering 304 SS general-purpose austenitic (UNS S30400). 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 B8A Class 1A?
    The UNS designation for ASTM A193 Grade B8A Class 1A is UNS S30400. This corresponds to 304 SS general-purpose 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.
    When is ASTM A193 Grade B8AA the right choice (Class 1A)?
    Grade B8AA (304 SS) is specified when general atmospheric corrosion resistance is needed at moderately elevated temperatures up to 538 °C (1000 °F). It is NOT recommended in chloride or sour-service environments — switch to B8M (316 SS with Mo) or B8C (347 Nb-stabilized) instead. Specific to ASTM A193 Grade B8A Class 1A: Class 1A — solution treated in finished condition for corrosion resistance.
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