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    2. ASTM A193/A193M Grade B8M2 Class 2B

    ASTM A193/A193M Grade B8M2 Class 2B Stud Bolts – UNS S31600

    Strain hardened UNS S31600 stainless steel stud bolts meeting the elevated Class 2B yield strength requirements for specialized high-pressure bolting applications.

    ASTM A193/A193M Grade B8M2 Class 2B Stud Bolts are manufactured from UNS S31600 Type 316 molybdenum-bearing austenitic stainless steel and strain hardened to achieve the specific elevated mechanical property requirements of the Class 2B designation, which under ASTM A193 mandates higher minimum yield strength levels compared to the standard Class 2 requirements for the same diameter range, reflecting the use of a more intensive cold working process or more stringent selection criteria within the Class 2 strain hardened family. The 2–3% molybdenum in UNS S31600 provides superior pitting and crevice corrosion resistance in chloride environments, and the Class 2B level of strain hardening delivers yield strength that enables these stud bolts to be used in higher-pressure and higher-load applications than standard Class 2 material allows. Grade B8M2 Class 2B is specified in specialty high-pressure equipment, critical safety-classified bolted joints, and advanced chemical process systems where design codes require both the corrosion resistance of 316-type stainless steel and the elevated yield strength available only from the most intensively worked Class 2B material.

    ASTM A193/A193M Grade B8M2 Class 2B 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 B8M2 Class 2B 2 and under carbide solution treated and strain hardened 95 75 25 40 321 HBW or 35 HRC
    over 2 to 21/2 incl 90 65 30 40 321 HBW or 35 HRC
    over 21/2 to 3 incl 80 55 30 40 321 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 B8M2 Class 2B 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 B8M2 Class 2B M48 and under carbide solution treated and strain hardened 655 515 25 40 321 HBW or 35 HRC
    over M48 to M64, incl 620 450 30 40 321 HBW or 35 HRC
    over M64 to M72, incl 550 380 30 40 321 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 B8M2 Class 2B Bolting Components Marking - Austenitic Steels

    Grade Class Grade Symbol
    ASTM A193 Grade B8M2 Class 2B TB B9G or TB B8M2 TB B9

    Related ASTM A193 Grades & ASME Companion Dimensions

    Frequently Asked Questions

    What is ASTM A193 Grade B8M2 Class 2B?
    ASTM A193 Grade B8M2 Class 2B is a bolting material covering 316 SS strain-hardened Class 2B (UNS S31600). Class 2B — strain hardened higher strength. 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 B8M2 Class 2B?
    The UNS designation for ASTM A193 Grade B8M2 Class 2B is UNS S31600. This corresponds to 316 SS strain-hardened Class 2B. The UNS code is universal across ASTM, ASME (SA-193), PED 2014/68/EU and NORSOK material specifications. The 'Class 2B' designator denotes the heat treatment condition under ASTM A193 Table 3.
    What is the strength class difference between B8M Class 1 and Class 2B (Class 2B)?
    B8M Class 1 is solution treated (75 ksi UTS min). Class 2B is strain-hardened to a higher strength level (110 ksi UTS min), achieved by cold work after solution annealing. Use Class 2B where 316 chemistry is needed with higher mechanical properties. Specific to ASTM A193 Grade B8M2 Class 2B: Class 2B — strain hardened higher strength.
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