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    2. ASTM A193/A193M Grade B8C Class 1

    ASTM A193/A193M Grade B8C Class 1 Stud Bolts – UNS S34700

    Niobium-stabilized 347 stainless steel stud bolts designed for high-temperature bolting where intergranular corrosion resistance is critical.

    ASTM A193/A193M Grade B8C Class 1 Stud Bolts are produced from UNS S34700 austenitic stainless steel, which is a niobium (columbium) stabilized grade specifically engineered to resist sensitization and intergranular corrosion that can occur when stainless steel is exposed to elevated temperatures during service or welding. The niobium addition ties up carbon in stable carbides, preventing chromium depletion at grain boundaries and ensuring the material retains its corrosion resistance even after thermal cycling. These stud bolts are supplied in the solution annealed (Class 1) condition and meet all mechanical and chemical requirements set forth in the ASTM A193 specification. Grade B8C is particularly well suited for use in heat exchangers, high-temperature flanges, furnace components, and other assemblies where sustained exposure to temperatures between 800°F and 1500°F is expected, making it a preferred choice in petrochemical, power generation, and aerospace bolting applications.

    ASTM A193/A193M Grade B8C Class 1 Chemical Composition - Austenitic Steels

    Grade Description and UNS Designatio Classes C Mn P S Si Cr Ni CbF
    ASTM A193 Grade B8C 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 B8C Class 1 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 B8C Class 1 All diameters carbide solution treated 75 30 30 50 223 HBW or 96HRBC
    over 3/4 to 1, incl carbide solution treated and strain hardened 115 80 15 35 321 HBW or 35 HRC
    over 1 to 11/4 ,incl 105 65 20 35 321 HBW or 35 HRC
    over 11/4 to 11/2 ,incl 100 50 28 45 321 HBW or 35 HRC
    • (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 B8C Class 1 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 B8C Class 1 All diameters carbide solution treated 515 205 30 50 223 HBW or 96HRBC
    • (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 B8C Class 1 Bolting Components Marking - Austenitic Steels

    Grade Class Grade Symbol
    ASTM A193 Grade B8C Class 1 TB B8C

    Related ASTM A193 Grades & ASME Companion Dimensions

    Frequently Asked Questions

    What is ASTM A193 Grade B8C Class 1?
    ASTM A193 Grade B8C Class 1 is a bolting material covering 347 SS Nb-stabilized for high-temp (UNS S34700). Class 1 — solution treated. 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 B8C Class 1?
    The UNS designation for ASTM A193 Grade B8C Class 1 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 1' designator denotes the heat treatment condition under ASTM A193 Table 3.
    What is the high-temperature advantage of Grade B8C (347 SS) (Class 1)?
    Grade B8C 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 B8C Class 1: Class 1 — solution treated.
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