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    2. ASTM A193 Grade B8 Class 2

    ASTM A193 Grade B8 Class 2 Bolts

    Carbide Solution Treated and Strain Hardened 304 Stainless Steel

    ASTM A193 Grade B8 Class 2 fasteners are manufactured from 304 stainless steel and are subjected to a carbide solution treatment followed by strain hardening. This strain hardening process significantly increases the yield and tensile strength of the fasteners compared to Class 1. B8 Class 2 bolts are highly sought after for structural applications and high-pressure piping where superior strength and excellent resistance to corrosion and high temperatures are required.

    On material test reports and bolt-head mill stamps, ASTM A193 Grade B8 Class 2 carries the B8SH mill-mark designation — the "SH" suffix indicates Strain-Hardened condition, distinguishing it from the plain B8 mark used for the solution-annealed Class 1 condition. Both are 304 stainless bolts at the same UNS S30400 chemistry; the difference is the cold- work step applied after solution treatment that raises the tensile minimum from 75 ksi (Class 1) to 125 ksi for diameters 3/4 inch and under in Class 2. Hardness is correspondingly higher in Class 2 (321 HBW max / 35 HRC max) versus 223 HBW max in Class 1, which is why Class 2 is excluded from sour- service applications under NACE MR0175 (the 22 HRC austenitic-stainless hardness ceiling).

    Class 2 strain-hardened B8 stud bolts sit at the upper strength tier of the austenitic family, with tensile minima of 125 ksi in diameters up to 3/4 inch dropping to 100 ksi between 1-1/4 and 1-1/2 inches per ASTM A193 Table 2. Compare the solution-annealed baseline on the B8 Class 1 page to see the strength uplift cold-work provides, and review the B8 Class 2B intermediate-strength page for joints where full Class 2 strain-hardening is unsuitable due to diameter or property-uniformity constraints. For applications on ASME B16.5 raised-face flanges where torque values matter for joint integrity, the ASME B16.5 pipe flange bolting page provides the companion dimensional data for stud-pair selection.

    ASTM A193 Grade B8 Class 2 Bolts Properties

    ASTM A193 Grade B8 Class 2 Bolts Chemical Requirements

    Austenitic Steels

    Grade Description and UNS Designation Classes C Mn P S Si Cr Ni
    ASTM A193 Grade B8 304, S30400 2 0.08 2.00 0.045 0.030 1.00 18.0-20.0 8.0-11.0
    Product Analysis VariationB 0.01 0.04 0.010 0.005 0.05 0.20 0.15

    ASTM A193 Grade B8 Class 2 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 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

    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 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
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