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    2. ASTM A193/A193M Grade B8P Class 2

    ASTM A193/A193M Grade B8P Class 2 Stud Bolts – UNS S30500

    Strain hardened high-nickel UNS S30500 stainless steel stud bolts meeting Class 2 diameter-graded strength requirements while maintaining low magnetic permeability.

    ASTM A193/A193M Grade B8P Class 2 Stud Bolts are manufactured from UNS S30500 Type 305 high-nickel austenitic stainless steel and strain hardened to achieve the diameter-dependent elevated mechanical property requirements of the Class 2 designation under ASTM A193. The defining characteristic of UNS S30500 — its exceptionally stable austenitic microstructure due to elevated nickel content of 10.5–13% — means that even after the significant cold work applied to achieve Class 2 strength levels, the material retains very low magnetic permeability, unlike standard 304 grades that can develop measurable magnetic response under heavy cold working. This combination of strain hardened strength and maintained non-magnetic character makes Grade B8P Class 2 stud bolts uniquely valuable in high-pressure bolting applications within magnetically sensitive environments such as scientific instruments, MRI-related industrial equipment, nuclear facilities, and defense systems where both structural performance and electromagnetic neutrality are simultaneously required design constraints.

    ASTM A193/A193M Grade B8P Class 2 Chemical Composition - Austenitic Steels

    Grade Description and UNS Designatio Classes C Mn P S Si Cr Ni
    ASTM A193 Grade B8P S30500 1, 1A, 1D, 2 0.12 2.00 0.045 0.030 1.00 17.0-19.0 11.0-13.0
    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 B8P 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 B8P 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 B8P 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 B8P 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 B8P Class 2 Bolting Components Marking - Austenitic Steels

    Grade Class Grade Symbol
    ASTM A193 Grade B8P Class 2 TB B8PSH

    Related ASTM A193 Grades & ASME Companion Dimensions

    Frequently Asked Questions

    What is ASTM A193 Grade B8P Class 2?
    ASTM A193 Grade B8P Class 2 is a bolting material covering 305 SS for cold-formed deep-draw (UNS S30500). 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 B8P Class 2?
    The UNS designation for ASTM A193 Grade B8P Class 2 is UNS S30500. This corresponds to 305 SS for cold-formed deep-draw. 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 use case for Grade B8P (305 SS) (Class 2)?
    Grade B8P is 305 SS — a higher-Ni variant of 304 (10.5–13% Ni vs 8–10.5% for 304) with very low work-hardening rate. Used where bolts must be cold-formed (e.g. deep-headed or rolled-thread) without sensitivity to strain-induced martensite. Specific to ASTM A193 Grade B8P Class 2: Class 2 — solution treated and strain hardened.
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