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    2. ASTM A193/A193M Grade B8CLN Class 1D

    ASTM A193/A193M Grade B8CLN Class 1D Stud Bolts – UNS S34751

    Niobium-stabilized, low carbon, nitrogen-enhanced 347LN stainless stud bolts in Class 1D condition for optimized high-temperature creep performance and sensitization resistance.

    ASTM A193/A193M Grade B8CLN Class 1D Stud Bolts are produced from UNS S34751, the niobium-stabilized, low-carbon, nitrogen-bearing variant of 347 stainless steel, and are supplied in the solution annealed Class 1D condition under ASTM A193, which requires grain size control to optimize creep and stress rupture performance in elevated-temperature pressure bolting service. The niobium stabilization prevents sensitization and intergranular corrosion by forming stable niobium carbides and nitrides, the low carbon minimizes carbide precipitation risk during thermal cycling, and the nitrogen provides solid solution strengthening, all while the Class 1D coarse grain structure improves resistance to time-dependent deformation at high temperatures. This multi-faceted combination of stabilization, low-carbon protection, nitrogen strengthening, and grain size optimization makes Grade B8CLN Class 1D stud bolts an excellent specification for high-temperature power generation components, refinery reactor flanges, and critical pressure vessels where long-term service at elevated temperatures demands the highest level of metallurgical assurance.

    ASTM A193/A193M Grade B8CLN Class 1D Chemical Composition - Austenitic Steels

    Grade Description and UNS Designatio Classes C Mn P S Si Cr Ni CbF N
    ASTM A193 Grade B8CLN 347LN, S34751 1, 1A, 1D 0.005-0.020 2.00 0.045 0.030 1.00 17.0-19.0 9.0-13.0 0.20-0.50; 15 × carboncontent, min 0.06-0.10
    Product Analysis VariationB 0.002 under, 0.005 over 0.04 0.01 0.005 0.05 0.20 0.15 0.05 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 B8CLN 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 B8CLN 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 B8CLN 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 B8CLN 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 B8CLN Class 1D Bolting Components Marking - Austenitic Steels

    Grade Class Grade Symbol
    ASTM A193 Grade B8CLN Class 1D TB B103

    Related ASTM A193 Grades & ASME Companion Dimensions

    Frequently Asked Questions

    What is ASTM A193 Grade B8CLN Class 1D?
    ASTM A193 Grade B8CLN Class 1D is a bolting material covering 347LN low-carbon nitrogen-enhanced Nb-stabilized (UNS S34751). 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 B8CLN Class 1D?
    The UNS designation for ASTM A193 Grade B8CLN Class 1D is UNS S34751. This corresponds to 347LN low-carbon nitrogen-enhanced Nb-stabilized. 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.
    What is the difference between Grade B8CLN and Grade B8C (Class 1D)?
    B8CLN is 347LN — Low-carbon (C ≤ 0.030%) Nitrogen-enhanced 347 (Nb-stabilized austenitic). The low carbon reduces sensitization risk; the N restores strength to 75 ksi UTS minimum. Used for high-temperature welded service requiring inter-granular corrosion resistance. Specific to ASTM A193 Grade B8CLN Class 1D: Class 1D — Class 1 base properties for lower-temperature service.
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