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    2. ASTM A193/A193M Grade B8 Class 2

    ASTM A193/A193M Grade B8 Class 2 Stud Bolts – UNS S30400

    Strain hardened UNS S30400 stainless steel stud bolts with diameter-graded mechanical requirements under ASTM A193 Class 2 for high-pressure bolting applications.

    ASTM A193/A193M Grade B8 Class 2 Stud Bolts are manufactured from UNS S30400 Type 304 austenitic stainless steel and supplied in the strain hardened condition, distinguishing them from Class 1 (solution annealed) material by their significantly higher tensile and yield strength achieved through controlled cold working of the bar prior to machining of threads. The Class 2 designation in ASTM A193 specifies diameter-dependent mechanical property requirements, recognizing that the degree of strength increase from strain hardening is progressively less achievable in larger diameter bars due to the reduced degree of cold work penetration toward the center of the stock. As a result, minimum tensile and yield strength requirements decrease in defined incremental steps as bolt diameter increases — from the highest requirements for diameters up to 3/4 inch through progressively reduced values for larger diameters. Grade B8 Class 2 stud bolts provide the corrosion resistance of 304 stainless combined with strength levels substantially above the annealed condition, making them widely used in high-pressure flanged joints, pressure vessels, and pumps and compressors across oil refinery, chemical plant, and power generation applications.

    ASTM A193/A193M Grade B8 Class 2 Chemical Composition - Austenitic Steels

    Grade Description and UNS Designatio Classes C Mn P S Si Cr Ni
    ASTM A193 Grade B8 304, S30400 1, 1A, 1D, 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
    • (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 B8 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 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
    2 and under 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 B8 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 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
    • (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 B8 Class 2 Bolting Components Marking - Austenitic Steels

    Grade Class Grade Symbol
    ASTM A193 Grade B8 Class 2 TB B8SH

    Related ASTM A193 Grades & ASME Companion Dimensions

    Frequently Asked Questions

    What is ASTM A193 Grade B8 Class 2?
    ASTM A193 Grade B8 Class 2 is a bolting material covering 304 SS general-purpose austenitic (UNS S30400). 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 B8 Class 2?
    The UNS designation for ASTM A193 Grade B8 Class 2 is UNS S30400. This corresponds to 304 SS general-purpose austenitic. 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.
    When is ASTM A193 Grade B8 the right choice (Class 2)?
    Grade B8 (304 SS) is specified when general atmospheric corrosion resistance is needed at moderately elevated temperatures up to 538 °C (1000 °F). It is NOT recommended in chloride or sour-service environments — switch to B8M (316 SS with Mo) or B8C (347 Nb-stabilized) instead. Specific to ASTM A193 Grade B8 Class 2: Class 2 — solution treated and strain hardened.
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