ASTM A193 B8CLN Class 1 Stud Bolts | 347LN SS

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

Niobium-stabilized, low carbon, nitrogen-enhanced 347LN stainless steel stud bolts for high-temperature and corrosion-critical bolting applications.

ASTM A193/A193M Grade B8CLN Class 1 Stud Bolts are produced from UNS S34751, a refined variant of the niobium-stabilized 347 stainless steel that also incorporates a low carbon content and controlled nitrogen addition. The niobium stabilization prevents sensitization and intergranular corrosion by forming stable carbides and nitrides, the low carbon reduces the risk of chromium depletion during welding, and the nitrogen addition provides solid solution strengthening to compensate for the mechanical property reduction associated with lower carbon levels. Supplied in the solution annealed Class 1 condition per ASTM A193, these stud bolts offer a well-rounded performance profile for high-temperature flanged joints, heat exchangers, and pressure vessels that also require resistance to sensitization without post-weld heat treatment. The B8CLN grade is particularly valued in power generation, petrochemical, and refinery applications where welded assemblies must perform reliably under elevated thermal loads for extended service periods.

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

Grade	Description and UNS Designatio	Classes	C	Mn	P	S	Si	Cr	Ni	Cb^F	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 Variation^B	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.

Grade

Description and UNS Designatio

Classes

Cb^F

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 Variation^B

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 1 Mechanical Requirements - Austenitic Steels (Inch)

Grade	Diameter, in.	Heat Treatment^B	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 1	All diameters	carbide solution treated	75	30	30	50	223 HBW or 96 HRB^C
(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.

Grade

Diameter,
in.

Heat Treatment^B

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 1

All diameters

carbide solution treated

223 HBW or 96 HRB^C

(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 1 Mechanical Requirements - Austenitic Steels (Metric)

Grade Class , mm	Diameter	Heat Treatment^B	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 1	All diameters	carbide solution treated	515	205	30	50	223 HBW or 96 HRB^C
(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.

Grade Class ,
mm

Diameter

Heat Treatment^B

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 1

All diameters

carbide solution treated

515

205

223 HBW or 96 HRB^C

(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 1 Bolting Components Marking - Austenitic Steels

Grade	Class	Grade Symbol
ASTM A193 Grade B8CLN	Class 1	TB B8Y or TB B8CLN

Grade

Class

Grade Symbol

ASTM A193 Grade B8CLN

Class 1

TB B8Y or TB B8CLN

Frequently Asked Questions

What is ASTM A193 Grade B8CLN Class 1?

ASTM A193 Grade B8CLN Class 1 is a bolting material covering 347LN low-carbon nitrogen-enhanced Nb-stabilized (UNS S34751). Class 1 — solution treated. 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 1?

The UNS designation for ASTM A193 Grade B8CLN Class 1 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 1' designator denotes the heat treatment condition under ASTM A193 Table 3.

What is the difference between Grade B8CLN and Grade B8C (Class 1)?

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 1: Class 1 — solution treated.

Specifications

Surface Treatments

Xylan 1070 / 1014 / 1400 / 1424

Xylar 2 / 101

Geomet 321 / 500 / 720

SermaGard 1105 / 1280

Dacromet 320 / 500

TakeCoat 1000 Ceramic

Delta Tone/Seal

Magnigard

MolyKote

Sherardized

Zinc-Cobalt (ASTM B840)

Zinc-Nickel (ASTM B841)

Certifications

ISO 9001 - 2015 Certified
PED 2014/68/EC
NACE MR0175/ISO 15156-2
NORSOK M-650
DFAR
MERKBLATT AD 2000 W2/W7/W10

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

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

ASTM A193/A193M Grade B8CLN Class 1 Mechanical Requirements - Austenitic Steels (Inch)

ASTM A193/A193M Grade B8CLN Class 1 Mechanical Requirements - Austenitic Steels (Metric)

ASTM A193/A193M Grade B8CLN Class 1 Bolting Components Marking - Austenitic Steels

Related ASTM A193 Grades & ASME Companion Dimensions

Frequently Asked Questions

Specifications

Surface Treatments

Certifications

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