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    2. ASTM A193/A193M Grade B8T Class 2

    ASTM A193/A193M Grade B8T Class 2 Stud Bolts – UNS S32100

    Strain hardened titanium-stabilized 321 stainless steel stud bolts in Class 2 with diameter-graded strength requirements for high-temperature sensitization-resistant service.

    ASTM A193/A193M Grade B8T Class 2 Stud Bolts are produced from UNS S32100 Type 321 titanium-stabilized austenitic stainless steel and strain hardened to achieve the diameter-graded elevated mechanical property requirements of the Class 2 designation within ASTM A193. Titanium stabilization prevents sensitization — the formation of chromium carbides at grain boundaries in the 800–1500°F temperature range — by forming preferential titanium carbides, ensuring that corrosion resistance is preserved in thermally cycled, welded, or high-temperature service conditions. The cold working process significantly raises tensile and yield strength above the solution annealed Class 1 condition, with Class 2 requirements scaled by diameter to reflect practical limitations of strain hardening in larger cross sections. Grade B8T Class 2 stud bolts combine the sensitization immunity of titanium-stabilized 321 stainless with the high mechanical performance achievable through strain hardening, making them suitable for aerospace exhaust system hardware, high-temperature pressure vessels, industrial furnace flanges, and boiler components where both elevated-temperature stability and high fastener strength are required.

    ASTM A193/A193M Grade B8T Class 2 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 2 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 2 3/4 and under carbide solution treated and strain hardened 125 100 12 35 321 HBW or 35 HRC
    over 3/4 to 1, incl 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 2 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 2 M20 and under carbide solution treated and strain hardened 860 690 12 35 321 HBW or 35 HRC
    over M20 to M24, incl 795 550 15 35 321 HBW or 35 HRC
    over M24 to M30, incl 725 450 20 35 321 HBW or 35 HRC
    over M30 to M36, incl 690 345 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 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 2 Bolting Components Marking - Austenitic Steels

    Grade Class Grade Symbol
    ASTM A193 Grade B8T Class 2 TB B8TSH

    Related ASTM A193 Grades & ASME Companion Dimensions

    Frequently Asked Questions

    What is ASTM A193 Grade B8T Class 2?
    ASTM A193 Grade B8T Class 2 is a bolting material covering 321 SS Ti-stabilized for high-temp (UNS S32100). Class 2 — solution treated and strain hardened. 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 2?
    The UNS designation for ASTM A193 Grade B8T Class 2 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 2' designator denotes the heat treatment condition under ASTM A193 Table 3.
    What is the difference between B8T (321 SS) and B8 (304 SS) (Class 2)?
    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 2: Class 2 — solution treated and strain hardened.
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