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    2. ASTM A193/A193M Grade B8S Class 1D

    ASTM A193/A193M Grade B8S Class 1D Stud Bolts – UNS S21800

    Nitronic 60 galling-resistant stainless steel stud bolts in the Class 1D condition with grain size control for high-temperature anti-galling pressure bolting applications.

    ASTM A193/A193M Grade B8S Class 1D Stud Bolts are manufactured from UNS S21800 Nitronic 60 austenitic stainless steel and are supplied in the solution annealed Class 1D condition per ASTM A193, incorporating grain size control to enhance elevated-temperature creep resistance alongside the defining characteristic of this alloy — outstanding resistance to galling and adhesive wear at threaded and bearing contact surfaces. The elevated silicon content (3.5–4.5%) and nitrogen of Nitronic 60 effectively prevent metal-to-metal adhesion and seizing under high contact pressure, and the Class 1D grain size requirement adds long-term thermal stability to this already impressive property profile. Grade B8S Class 1D stud bolts are particularly valuable in high-temperature flanged assemblies, boiler and steam system valve bonnet bolting, and process equipment that operates at elevated temperatures and must be regularly opened for maintenance, where the dual risk of galling during assembly and creep relaxation during service would otherwise compromise the integrity of the bolted joint.

    ASTM A193/A193M Grade B8S Class 1D Chemical Composition - Austenitic Steels

    Grade Description and UNS Designatio Classes C Mn P S Si Cr Ni N
    ASTM A193 Grade B8S S21800 1C, 1D 0.10 7.0-9.0 0.060 0.030 3.5-4.5 16.0-18.0 8.0-9.0 0.08-0.18
    Product Analysis VariationB 0.01 0.06 0.005 0.005 0.15 0.20 0.10 0.01
    • (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 B8S 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 B8S Class 1D All diameters carbide solution treated 95 50 35 55 271 HBW or 28 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 B8S 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 B8S Class 1D All diameters carbide solution treated 655 345 35 55 271 HBW or 28 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 B8S Class 1D Bolting Components Marking - Austenitic Steels

    Grade Class Grade Symbol
    ASTM A193 Grade B8S Class 1D TB B102

    Related ASTM A193 Grades & ASME Companion Dimensions

    Frequently Asked Questions

    What is ASTM A193 Grade B8S Class 1D?
    ASTM A193 Grade B8S Class 1D is a bolting material covering Nitronic 60 (S21800) galling-resistant austenitic (UNS S21800). 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 B8S Class 1D?
    The UNS designation for ASTM A193 Grade B8S Class 1D is UNS S21800. This corresponds to Nitronic 60 (S21800) galling-resistant austenitic. 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 specify Grade B8S (Nitronic 60) (Class 1D)?
    Grade B8S is Nitronic 60 (S21800) — a high-silicon (3.5–4.5%), high-manganese (7–9%) austenitic with exceptional galling and seizing resistance, making it the default choice for valve stems, bushings and high-vibration bolted joints where thread galling is a risk. Specific to ASTM A193 Grade B8S Class 1D: Class 1D — Class 1 base properties for lower-temperature service.
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