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    2. ASTM A193/A193M Grade B8M Class 1D

    ASTM A193/A193M Grade B8M Class 1D Stud Bolts – UNS S31600

    Molybdenum-bearing 316 stainless steel stud bolts in the Class 1D condition with grain size control for optimized high-temperature creep resistance and corrosion performance.

    ASTM A193/A193M Grade B8M Class 1D Stud Bolts are produced from UNS S31600 Type 316 molybdenum-bearing austenitic stainless steel and are supplied in the solution annealed Class 1D condition, which under ASTM A193 incorporates specific austenite grain size requirements — generally ASTM grain size number 7 or coarser — designed to enhance creep strength and resist stress relaxation during sustained high-temperature service. The 2–3% molybdenum content of UNS S31600 provides superior resistance to pitting and crevice corrosion in chloride-containing environments compared to standard 304-type grades, and this advantage is preserved in the Class 1D condition alongside the enhanced elevated-temperature mechanical stability achieved through grain size control. Grade B8M Class 1D stud bolts are specified for high-temperature flanges, chemical reactor pressure boundaries, and steam service piping in petrochemical, power generation, and offshore applications where both the corrosion resistance of molybdenum-bearing 316 stainless and the long-term creep performance associated with Class 1D grain size requirements must be simultaneously guaranteed.

    ASTM A193/A193M Grade B8M Class 1D Chemical Composition - Austenitic Steels

    Grade Description and UNS Designatio Classes C Mn P S Si Cr Ni Mo
    ASTM A193 Grade B8M 316, S31600 1, 1A, 1D, 2 0.08 2.00 0.045 0.030 1.00 16.0-18.0 10.0-14.0 2.00-3.00
    Product Analysis VariationB 0.01 0.04 0.010 0.005 0.05 0.20 0.15 0.10
    • (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 B8M Class 1D 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 B8M Class 1D All diameters carbide solution treated 75 30 30 50 223 HBW or 96 HRBC
    • (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 B8M Class 1D 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 B8M Class 1D All diameters carbide solution treated 515 205 30 50 223 HBW or 96 HRBC
    • (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 B8M Class 1D Bolting Components Marking - Austenitic Steels

    Grade Class Grade Symbol
    ASTM A193 Grade B8M Class 1D TB B95

    Related ASTM A193 Grades & ASME Companion Dimensions

    Frequently Asked Questions

    What is ASTM A193 Grade B8M Class 1D?
    ASTM A193 Grade B8M Class 1D is a bolting material covering 316 SS Mo-bearing for chloride/sour (UNS S31600). Class 1D — Class 1 base properties for lower-temperature service. 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 B8M Class 1D?
    The UNS designation for ASTM A193 Grade B8M Class 1D is UNS S31600. This corresponds to 316 SS Mo-bearing for chloride/sour. The UNS code is universal across ASTM, ASME (SA-193), PED 2014/68/EU and NORSOK material specifications. The 'Class 1D' designator denotes the heat treatment condition under ASTM A193 Table 3.
    Why is ASTM A193 Grade B8M preferred over B8 (Class 1D)?
    Grade B8M (316 SS with 2–3% Mo) provides significantly improved pitting and crevice corrosion resistance vs B8 (304 SS) in chloride, sour-service and marine environments. PREN ≈ 24 for 316 vs ≈ 19 for 304. Specific to ASTM A193 Grade B8M Class 1D: Class 1D — Class 1 base properties for lower-temperature service.
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