ASTM A193 B8CLNCUBA Class 1A Stud Bolts

ASTM A193/A193M Grade B8CLNCuBA Class 1A Stud Bolts – UNS S34752

Strain hardened, advanced niobium-stabilized stainless stud bolts with copper and boron for outstanding creep resistance and high-temperature bolting strength.

ASTM A193/A193M Grade B8CLNCuBA Class 1A Stud Bolts are produced from UNS S34752, the most comprehensively alloyed grade in the B8C family, incorporating niobium stabilization, low carbon content, controlled nitrogen, copper, and boron, and are additionally strain hardened to achieve the peak mechanical performance demanded by the Class 1A classification within ASTM A193, with testing on the finished fastener ensuring verified compliance. The copper enhances resistance to reducing acid corrosion and contributes to precipitation strengthening, while boron is recognized for its powerful effect in improving grain boundary cohesion and resisting creep and stress relaxation at high temperatures — properties that directly translate to sustained clamping force retention in long-term elevated-temperature bolted joint service. Strain hardening further elevates the already superior mechanical properties of this advanced alloy, making Grade B8CLNCuBA Class 1A stud bolts the premier choice for supercritical and ultra-supercritical boilers, steam turbine casings, and high-temperature pressure-retaining assemblies where exceptional long-term performance at extreme conditions is non-negotiable.

ASTM A193/A193M Grade B8CLNCuBA Class 1A Chemical Composition - Austenitic Steels

Grade	Description and UNS Designatio	Classes	C	Mn	P	S	Si	Cr	Ni	Mo	Cu	Cb^F	N
ASTM A193 Grade B8CLNCUBA	S34752^G	1, 1A, 1D	0.005-0.02	2.00	0.035	0.010	0.60	17.0-19.0	10.0-13.0	0.20-1.20	2.50-3.50	0.20-0.50; 15 × carboncontent, min	0.06-0.12
Product Analysis Variation^B	0.002 under, 0.005 over	0.04	0.01	0.005	0.05	0.20	0.15	. . .	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 B8CLNCUBA

S34752^G

1, 1A, 1D

0.005-0.02

2.00

0.035

0.010

0.60

17.0-19.0

10.0-13.0

0.20-1.20

2.50-3.50

0.20-0.50; 15 × carboncontent, min

0.06-0.12

Product Analysis Variation^B

0.002 under, 0.005 over

0.04

0.01

0.005

0.05

0.20

0.15

. . .

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 B8CLNCuBA Class 1A Bolting Components Marking - Austenitic Steels

Grade	Class	Grade Symbol
ASTM A193 Grade B8CLNCUBA	Class 1A	TB B8ZA or TB B8CLNCuBA

Grade

Class

Grade Symbol

ASTM A193 Grade B8CLNCUBA

Class 1A

TB B8ZA or TB B8CLNCuBA

Frequently Asked Questions

What is ASTM A193 Grade B8CLNCUBA Class 1A?

ASTM A193 Grade B8CLNCUBA Class 1A is a bolting material covering Cu-Mo-N modified 347 austenitic (UNS S34752). 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 B8CLNCUBA Class 1A?

The UNS designation for ASTM A193 Grade B8CLNCUBA Class 1A is UNS S34752. This corresponds to Cu-Mo-N modified 347 austenitic. 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.

Why specify Grade B8CLNCuB instead of standard B8CLN (Class 1A)?

B8CLNCuB is a Cu-Mo-N modified 347LN austenitic — the copper, molybdenum and nitrogen additions improve resistance to severe acid-chloride environments while maintaining Nb stabilization against sensitization. Specific to ASTM A193 Grade B8CLNCUBA Class 1A: Class 1A — solution treated in finished condition for corrosion resistance.

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