ASTM A193 B8MLCUN Class 1B Stud Bolts | 254 SMO

ASTM A193/A193M Grade B8MLCuN Class 1B Stud Bolts – UNS S31254

Super austenitic 254 SMO stainless steel stud bolts in the Class 1B condition offering exceptional pitting and crevice corrosion resistance for aggressive service environments.

ASTM A193/A193M Grade B8MLCuN Class 1B Stud Bolts are manufactured from UNS S31254, the super austenitic stainless steel widely known as 254 SMO, featuring a nominal composition of approximately 20% chromium, 18% nickel, 6% molybdenum, 0.7% nitrogen, and 0.75% copper, and are supplied in the Class 1B condition combining solution annealing with light cold drawing for dimensional refinement and modest strength enhancement. With a Pitting Resistance Equivalent Number typically exceeding 42, UNS S31254 is among the most corrosion-resistant austenitic alloys commercially available, providing outstanding resistance to pitting, crevice corrosion, and stress corrosion cracking in seawater, acidic chloride solutions, and oxidizing environments where standard 316-type grades suffer accelerated attack. The copper addition further improves resistance to reducing acids including sulfuric acid at moderate concentrations. These stud bolts are specified for seawater handling systems, desalination plants, flue gas desulfurization equipment, offshore platforms, and pulp bleaching applications where service conditions exceed the capabilities of conventional austenitic stainless steel grades.

ASTM A193/A193M Grade B8MLCuN Class 1B Chemical Composition - Austenitic Steels

Grade	Description and UNS Designatio	Classes	C	Mn	P	S	Si	Cr	Ni	Mo	Cu	N
ASTM A193 Grade B8MLCUN	S31254	1A, 1B, 1D, 2	0.020	1.00	0.030	0.010	0.80	19.5-20.5	17.5-18.5	6.0-6.5	0.50-1.00	0.18-0.25
Product Analysis Variation^B	0.005	0.03	0.005	0.002	0.05	0.20	0.15	0.10	. . .	0.02
(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

ASTM A193 Grade B8MLCUN

S31254

1A, 1B, 1D, 2

0.020

1.00

0.030

0.010

0.80

19.5-20.5

17.5-18.5

6.0-6.5

0.50-1.00

0.18-0.25

Product Analysis Variation^B

0.005

0.03

0.005

0.002

0.05

0.20

0.15

0.10

. . .

0.02

(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 B8MLCuN Class 1B 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 B8MLCUN Class 1B	All diameters	carbide solution treated	80	35	30	40	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 B8MLCUN Class 1B

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 B8MLCuN Class 1B 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 B8MLCUN Class 1B	All diameters	carbide solution treated	550	240	30	40	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 B8MLCUN Class 1B

All diameters

carbide solution treated

550

240

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 B8MLCuN Class 1B Bolting Components Marking - Austenitic Steels

Grade	Class	Grade Symbol
ASTM A193 Grade B8MLCUN	Class 1B	TB B8MLCuN

Grade

Class

Grade Symbol

ASTM A193 Grade B8MLCUN

Class 1B

TB B8MLCuN

Frequently Asked Questions

What is ASTM A193 Grade B8MLCUN Class 1B?

ASTM A193 Grade B8MLCUN Class 1B is a bolting material covering 6-Mo 254 SMO super-austenitic (UNS S31254). Class 1B — solution treated higher-strength. 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 B8MLCUN Class 1B?

The UNS designation for ASTM A193 Grade B8MLCUN Class 1B is UNS S31254. This corresponds to 6-Mo 254 SMO super-austenitic. The UNS code is universal across ASTM, ASME (SA-193), PED 2014/68/EU and NORSOK material specifications. The 'Class 1B' designator denotes the heat treatment condition under ASTM A193 Table 3.

What is the chloride-pitting envelope for Grade B8MLCuN (Class 1B)?

B8MLCuN is 254 SMO (UNS S31254) — a 6-Mo super-austenitic with PREN ≈ 43, rated for service in seawater, ferric-chloride, and severe sour-service environments up to 320 °C. Far exceeds 316 (PREN 24) in chloride pitting resistance. Specific to ASTM A193 Grade B8MLCUN Class 1B: Class 1B — solution treated higher-strength.

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 B8MLCuN Class 1B Stud Bolts – UNS S31254

ASTM A193/A193M Grade B8MLCuN Class 1B Chemical Composition - Austenitic Steels

ASTM A193/A193M Grade B8MLCuN Class 1B Mechanical Requirements - Austenitic Steels (Inch)

ASTM A193/A193M Grade B8MLCuN Class 1B Mechanical Requirements - Austenitic Steels (Metric)

ASTM A193/A193M Grade B8MLCuN Class 1B Bolting Components Marking - Austenitic Steels

Related ASTM A193 Grades & ASME Companion Dimensions

Frequently Asked Questions

Specifications

Surface Treatments

Certifications

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