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    2. ASTM A193/A193M Grade B8N Class 2

    ASTM A193/A193M Grade B8N Class 2 Stud Bolts – UNS S30451

    Strain hardened nitrogen-enhanced 304N stainless steel stud bolts meeting Class 2 diameter-graded mechanical requirements for demanding high-pressure bolting service.

    ASTM A193/A193M Grade B8N Class 2 Stud Bolts are manufactured from UNS S30451 nitrogen-bearing Type 304N austenitic stainless steel and strain hardened to meet the diameter-dependent elevated mechanical property requirements of the Class 2 designation under ASTM A193. Nitrogen addition to the base 304 chemistry provides solid solution strengthening that raises yield and tensile strength in the annealed state, and the subsequent cold working process further amplifies these mechanical properties to the significantly higher levels mandated by Class 2 for each respective diameter range. This double strengthening effect — from both the inherent nitrogen content of UNS S30451 and the applied strain hardening — means that Grade B8N Class 2 stud bolts can achieve particularly favorable mechanical properties relative to the degree of cold work required, compared to standard non-nitrogen-bearing grades. These stud bolts are specified for high-pressure flanged pressure vessels, compressor bodies, and critical piping system bolting where ASME and pressure equipment design codes call for elevated fastener allowable stresses to optimize joint design efficiency.

    ASTM A193/A193M Grade B8N Class 2 Chemical Composition - Austenitic Steels

    Grade Description and UNS Designatio Classes C Mn P S Si Cr Ni N
    ASTM A193 Grade B8N 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 B8N 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 B8N 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 B8N 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 B8N 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 B8N Class 2 Bolting Components Marking - Austenitic Steels

    Grade Class Grade Symbol
    ASTM A193 Grade B8N Class 2 TB B8NSH

    Related ASTM A193 Grades & ASME Companion Dimensions

    Frequently Asked Questions

    What is ASTM A193 Grade B8N Class 2?
    ASTM A193 Grade B8N Class 2 is a bolting material covering 304N nitrogen-enhanced 304 (UNS S30451). 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 B8N Class 2?
    The UNS designation for ASTM A193 Grade B8N Class 2 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 2' designator denotes the heat treatment condition under ASTM A193 Table 3.
    What does the 'N' suffix denote in Grade B8N (Class 2)?
    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 B8N Class 2: Class 2 — solution treated and strain hardened.
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