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    2. ASTM A193 Grade B8 Class 2B

    ASTM A193 Grade B8 Class 2B Bolts

    Carbide Solution Treated and Strain Hardened (Large Diameters)

    ASTM A193 Grade B8 Class 2B refers to austenitic stainless steel bolting materials produced for large-diameter requirements. These fasteners, manufactured from 304 stainless steel (UNS S30400), are subjected to carbide solution treatment and subsequent strain hardening. Class 2B bolts specifically apply to diameters from over 2 inches up to 3 inches inclusive (over M48 to M72 in the metric series), where progressively reduced yield strength targets are specified because uniform strain hardening through the bolt cross-section cannot be guaranteed at larger diameters. For smaller diameters — 1/4 inch up to 2 inches — the higher-strength B8 Class 2 is the matched condition; for non-strain-hardened applications, B8 Class 1 (solution annealed) is specified. Class 2B is the heavy-duty cold-worked B8 grade for large chemical-plant and marine flanged-joint stud bolting where Class 2 tensile values cannot be maintained at larger sizes.

    Class 2B is the intermediate-strength strain-hardened condition between the solution-annealed Class 1 baseline and the high-strength Class 2 designation; the procurement choice typically hinges on the diameter envelope the joint requires. For diameters up to 3/4 inch where full Class 2 strength is attainable with uniform properties, the B8 Class 2 strain-hardened stud bolt page covers the mechanical specifics. For applications where corrosion resistance is paramount but strain-hardening is not, the B8 Class 1 solution-annealed page documents the baseline 75 ksi tensile minimum. For larger threaded-rod assemblies in metric series, the ASME B18.31.1M metric threaded rod dimensions page is the dimensional reference.

    ASTM A193 Grade B8 Bolts Properties

    ASTM A193 Grade B8 Bolts 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 B8 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

    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 A193M Grade B8 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
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