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    2. ASTM A193/A193M Grade B8NA Class 1A

    ASTM A193/A193M Grade B8NA Class 1A Stud Bolts – UNS S30451

    Strain hardened nitrogen-enhanced 304N stainless steel stud bolts with improved strength characteristics for elevated-pressure bolting applications.

    ASTM A193/A193M Grade B8NA Class 1A Stud Bolts are produced from UNS S30451, the nitrogen-enhanced variant of Type 304 austenitic stainless steel, commonly designated 304N, and are strain hardened to achieve the elevated mechanical requirements of the Class 1A designation within the ASTM A193 specification, with testing conducted directly on the finished fastener. Unlike the low-carbon 304L base of UNS S30453, the UNS S30451 grade retains standard carbon levels while relying on nitrogen addition (0.10–0.16%) to improve yield and tensile strength in the annealed condition, and the subsequent cold working further increases strength beyond what nitrogen alone can achieve. These stud bolts maintain the corrosion resistance, austenitic microstructure, and weldability characteristic of the 304 family while providing the superior mechanical performance needed in high-pressure flanges, pressure vessel closures, and structural bolted connections where higher design stresses are specified by applicable codes such as ASME Section VIII.

    ASTM A193/A193M Grade B8NA Class 1A Chemical Composition - Austenitic Steels

    Grade Description and UNS Designatio Classes C Mn P S Si Cr Ni N
    ASTM A193 Grade B8NA 304N, S30451 1A, 1B, 1D, 2 0.08 2.00 0.045 0.030 1.00 18.0-20.0 8.0-11.0 0.10-0.16
    Product Analysis VariationB 0.01 0.04 0.010 0.005 0.05 0.20 0.15 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 B8NA Class 1A 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 B8NA Class 1A All diameters carbide solution treated in the finished condition 75 30 30 50 192 HBW or 90 HRB
    • (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 B8NA Class 1A 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 B8NA Class 1A All diameters carbide solution treated in the finished condition 515 205 30 50 192 HBW or 90 HRB
    • (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 B8NA Class 1A Bolting Components Marking - Austenitic Steels

    Grade Class Grade Symbol
    ASTM A193 Grade B8NA Class 1A TB B8V or TB B8MA

    Related ASTM A193 Grades & ASME Companion Dimensions

    Frequently Asked Questions

    What is ASTM A193 Grade B8NA Class 1A?
    ASTM A193 Grade B8NA Class 1A is a bolting material covering 304N nitrogen-enhanced 304 (UNS S30451). Class 1A — solution treated in finished condition for corrosion resistance. 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 B8NA Class 1A?
    The UNS designation for ASTM A193 Grade B8NA Class 1A is UNS S30451. This corresponds to 304N nitrogen-enhanced 304. The UNS code is universal across ASTM, ASME (SA-193), PED 2014/68/EU and NORSOK material specifications. The 'Class 1A' designator denotes the heat treatment condition under ASTM A193 Table 3.
    What does the 'N' suffix denote in Grade B8NAA (Class 1A)?
    The 'N' suffix denotes nitrogen enhancement — 0.10–0.16% N added to 304 austenitic chemistry. This increases yield strength to 50 ksi minimum (vs 30 ksi for standard 304) and modestly improves pitting resistance. UTS minimum is 90 ksi. Specific to ASTM A193 Grade B8NA Class 1A: Class 1A — solution treated in finished condition for corrosion resistance.
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