What is the difference between B8 Class 1 and Class 1A?

The distinction is when the carbide solution heat treatment is performed in the manufacturing sequence. Class 1 receives the solution treatment as bar stock or during initial forming and then is machined into bolts; Class 1A receives the solution treatment in the finished condition after all machining and thread-rolling. Class 1A is specified when corrosion resistance at the thread root is critical and any cold-work introduced by machining must be relieved. Mechanical minima are 75 ksi tensile and 30 ksi yield, identical to Class 1, but Class 1A's hardness ceiling is tighter at 192 HBW (90 HRB) vs Class 1's 223 HBW per ASTM A193 Table 2.

Why does Class 1A use a lower hardness ceiling than Class 1?

Because Class 1A is solution-treated as the final manufacturing step (after machining), the ASTM A193 specification verifies that the bar enters service with the fully annealed microstructure required for maximum corrosion resistance. A tighter hardness cap of 192 HBW vs 223 HBW for Class 1 is the procurement control that flags any residual cold-work or incomplete carbide dissolution. For service in chloride or sour environments where pitting resistance is critical, the lower hardness gives an additional safety margin over standard Class 1 supply.

Can B8 Class 1A be used for NACE MR0175 sour-service bolting?

Yes. Class 1A in the solution-annealed-in-finished-condition state satisfies the NACE MR0175 / ISO 15156-3 Table A.2 requirement of 22 HRC maximum hardness for austenitic stainless steels in H2S-containing environments. Class 1A's 192 HBW (90 HRB) ceiling sits well below the 22 HRC threshold. Pair with ASTM A194 Grade 8A nuts (the solution-annealed-in-finished-condition counterpart) and confirm the mill certificate documents the heat-treat sequence per A193 Section 6.2.

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ASTM A193 Grade B8 Class 1A Bolts

Name: ASTM A193 Grade B8 Class 1A
Brand: TorqBolt
SKU: B8-Class-1A
Availability: InStock

Carbide Solution Treated after Finishing Operations

ASTM A193 Grade B8 Class 1A is a specialized austenitic stainless steel bolting material. Unlike Class 1, Class 1A fasteners are subjected to a carbide solution treatment (annealing) *after* all finishing operations, including thread rolling and head forming, are completed. This process ensures that any residual stresses from manufacturing are relieved and the material achieves the most uniform microstructure and maximum corrosion resistance throughout the entire fastener. It is typically used in critical applications requiring high integrity and resistance to intergranular corrosion.

Class 1A is functionally Class 1 with the solution treatment moved to the end of the manufacturing sequence. The headline mechanical numbers match the standard solution-annealed grade discussed on the B8 Class 1 page, while the hardness ceiling is tighter; review that page for the chemistry context shared by both classes. When the procurement spec calls for higher tensile strength than solution-annealing alone delivers, fabricators specify the strain-hardened sibling covered on the B8 Class 2 page. For dimensional reference on metric socket-head cap screws compatible with Class 1A bar stock, the ASME B18.3.1M metric socket head dimensions page governs head geometry and thread length tolerances.

ASTM A193 Grade B8 Bolts Properties

ASTM A193 Grade B8 Bolts Chemical Requirements

Austenitic Steels

Grade	Description and UNS Designation	Classes	C	Mn	P	S	Si	Cr	Ni
ASTM A193 Grade B8	304, S30400	1A	0.08	2.00	0.045	0.030	1.00	18.0-20.0	8.0-11.0
ASTM A193 Grade B8	Product Analysis Variation^B	1A	0.01	0.04	0.010	0.005	0.05	0.20	0.15

ASTM A193 Grade B8 Class 1A Mechanical Requirements

Austenitic Steels (Inch)

Grade	Diameter, in.	Heat Treatment^B	Tensile Strength, min, ksi	Yield Strength, min, 0.2 % offset, ksi	Elongation in 4 D, min	Reduction of Area, min	Hardness, max
ASTM A193 Grade B8 Class 1A	All diameters	carbide solution treated in finished condition	75	30	30	50	223 HBW or 96 HRB^C

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 A193M Grade B8 Class 1A	All diameters	carbide solution treated in finished condition	515	205	30	50	223 HBW or 96 HRB^C

ASTM A193 Grade B8 Class 1A (the B8A designation) shares identical mechanical property requirements with B8 Class 1 — both are 304 stainless bolts in the carbide-solution-treated condition. The distinction is the sequence: Class 1A receives the solution treatment after all finishing operations (thread rolling, head forming, machining), restoring corrosion resistance that may have been reduced by cold work. Class 1 is treated before finishing. For procurement teams specifying intergranular-corrosion-critical service — pharmaceutical, food-grade, or sour-gas applications where cold-worked surfaces would compromise NACE MR0175 compliance — Class 1A is the qualified condition.

Related 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

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