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    2. ASTM A193/A193M Grade B8T Class 1

    ASTM A193/A193M Grade B8T Class 1 Stud Bolts – UNS S32100

    Titanium-stabilized 321 stainless steel stud bolts engineered to resist sensitization and intergranular corrosion in sustained high-temperature service.

    ASTM A193/A193M Grade B8T Class 1 Stud Bolts are manufactured from UNS S32100 austenitic stainless steel, commonly referred to as Type 321, which incorporates titanium as a stabilizing element to prevent sensitization — the chromium carbide precipitation at grain boundaries that occurs when standard austenitic stainless steels are held in the temperature range of approximately 800°F to 1500°F. By preferentially forming titanium carbides, this grade preserves the chromium content in solid solution, ensuring continued corrosion resistance in both as-welded and thermally cycled conditions. Supplied in the solution annealed Class 1 condition per ASTM A193 requirements, Grade B8T stud bolts are used in aircraft exhaust systems, boiler components, pressure vessels, and high-temperature flanges where long-term thermal stability and resistance to oxidation are paramount. The combination of stabilization and the fundamental 18-8 chromium-nickel composition makes these stud bolts a reliable solution for demanding service environments across aerospace, petrochemical, and power generation sectors.

    ASTM A193/A193M Grade B8T Class 1 Chemical Composition - Austenitic Steels

    Grade Description and UNS Designatio Classes C Mn P S Si Cr Ni Ti N
    ASTM A193 Grade B8T 321, S32100 1, 1A, 2 0.08 2.00 0.045 0.030 1.00 17.0-19.0 9.0-12.0 5 × (C + N) to 0.70 0.10
    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 B8T 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 B8T 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 B8T 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 B8T 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 B8T Class 1 Bolting Components Marking - Austenitic Steels

    Grade Class Grade Symbol
    ASTM A193 Grade B8T Class 1 TB B8T

    Related ASTM A193 Grades & ASME Companion Dimensions

    Frequently Asked Questions

    What is ASTM A193 Grade B8T Class 1?
    ASTM A193 Grade B8T Class 1 is a bolting material covering 321 SS Ti-stabilized for high-temp (UNS S32100). 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 B8T Class 1?
    The UNS designation for ASTM A193 Grade B8T Class 1 is UNS S32100. This corresponds to 321 SS Ti-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 difference between B8T (321 SS) and B8 (304 SS) (Class 1)?
    B8T is 321 stainless — Ti-stabilized 304. The titanium addition (Ti ≥ 5×C, max 0.70%) prevents chromium-carbide precipitation in the 425–815 °C sensitization range, providing better high-temperature inter-granular corrosion resistance than plain B8. Specific to ASTM A193 Grade B8T Class 1: Class 1 — solution treated.
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