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    2. ASTM A193/A193M Grade B8CA Class 1A

    ASTM A193/A193M Grade B8CA Class 1A Stud Bolts – UNS S34700

    Strain hardened, niobium-stabilized 347 stainless steel stud bolts delivering enhanced mechanical strength for high-temperature and high-pressure service.

    ASTM A193/A193M Grade B8CA Class 1A Stud Bolts are produced from UNS S34700 niobium-stabilized austenitic stainless steel and processed through strain hardening to achieve the elevated mechanical properties required by the Class 1A classification under ASTM A193, where testing is performed on the finished fastener to verify compliance. Combining the inherent stabilization benefits of niobium — which prevents sensitization and intergranular corrosion during high-temperature exposure or welding — with the improved tensile and yield strength gained through cold working, Grade B8CA Class 1A stud bolts represent a well-rounded solution for demanding service environments. They are particularly suited for bolting flanges, pressure vessels, and piping systems that operate at elevated temperatures where both mechanical integrity over time and resistance to carbide precipitation must be ensured. Industries such as power generation, refinery operations, and petrochemical processing routinely specify this grade where high-temperature service combined with elevated pressure demands cannot be satisfied by standard solution annealed grades alone.

    ASTM A193/A193M Grade B8CA Class 1A Chemical Composition - Austenitic Steels

    Grade Description and UNS Designatio Classes C Mn P S Si Cr Ni CbF
    ASTM A193 Grade B8CA 347, S34700 1, 1A, 1D, 2 0.08 2.00 0.045 0.030 1.00 17.0-19.0 9.0-12.0 10 × C to 1.10
    Product Analysis VariationB 0.01 0.04 0.010 0.005 0.05 0.20 0.15 0.05 under
    • (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 B8CA 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 B8CA 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 B8CA 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 B8CA 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 B8CA Class 1A Bolting Components Marking - Austenitic Steels

    Grade Class Grade Symbol
    ASTM A193 Grade B8CA Class 1A TB B8TB B or TB B8CA

    Related ASTM A193 Grades & ASME Companion Dimensions

    Frequently Asked Questions

    What is ASTM A193 Grade B8CA Class 1A?
    ASTM A193 Grade B8CA Class 1A is a bolting material covering 347 SS Nb-stabilized for high-temp (UNS S34700). 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 B8CA Class 1A?
    The UNS designation for ASTM A193 Grade B8CA Class 1A is UNS S34700. This corresponds to 347 SS Nb-stabilized for high-temp. 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 high-temperature advantage of Grade B8CAA (347 SS) (Class 1A)?
    Grade B8CAA is 347 SS, niobium-stabilized austenitic. The Nb addition prevents chromium-carbide precipitation at the grain boundaries during prolonged exposure between 425–815 °C (sensitization), maintaining inter-granular corrosion resistance for high-temperature service. Specific to ASTM A193 Grade B8CA Class 1A: Class 1A — solution treated in finished condition for corrosion resistance.
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