ASTM A193 Grade B8 SS 304 Studs & Bolts
A detailed technical reference covering material identity, international designations, chemistry, mechanical properties, heat treatment, Class 1 and Class 2, A320 B8, dimensions, threads and industrial applications.
At a Glance
Material: Type 304 stainless steel
UNS: S30400
Bolting specification: ASTM A193 / A193M Grade B8
Classes: Class 1 and Class 2
Typical forms: Studs, stud bolts, bolts and screws
What Is Stainless Steel 304?
Stainless Steel 304 is an austenitic chromium-nickel stainless steel. It is widely used because a useful combination of corrosion resistance, ductility, formability and general engineering performance is provided. However, the designation “304” identifies the alloy; it does not by itself define the fastener product standard.
Different Names & Designations
| AISI / SAE | Type 304 |
| UNS | S30400 |
| EN | 1.4301 |
| EN steel name | X5CrNi18-10 |
| JIS | SUS 304 |
| Common trade description | 18/8 stainless steel |
| ISO material designation | ISO 15510 family designation should be checked against the exact chemical limits required. |
304 Alloy ≠ Fastener Specification
AISI 304, ASTM A240 Type 304, EN 1.4301 and SUS 304 describe the material family. In contrast, ASTM A193 Grade B8 specifies stainless-steel bolting for particular service conditions.
Therefore, a customer should specify both the material/grade and the product specification. For example: ASTM A193 Grade B8 Class 1, SS 304, M20 × 150, metric coarse thread.
SS 304 – Chemical Composition Reference
| Element | Typical / maximum requirement for Type 304 reference | Function / significance |
|---|---|---|
| Carbon (C) | ≤ 0.08% | Controlled to maintain corrosion and fabrication characteristics. |
| Manganese (Mn) | ≤ 2.00% | Deoxidation and austenitic alloy balance. |
| Silicon (Si) | ≤ 1.00% | Deoxidation element. |
| Phosphorus (P) | ≤ 0.045% | Controlled impurity. |
| Sulfur (S) | ≤ 0.030% | Controlled for corrosion and processing performance. |
| Chromium (Cr) | 18.00–20.00% | Provides the stainless passive film and corrosion resistance. |
| Nickel (Ni) | 8.00–10.50% for common Type 304 limits | Stabilizes the austenitic structure and supports ductility. |
| Iron (Fe) | Balance | Base metal. |
Exact limits vary slightly by product standard and edition. ASTM A193 B8 has its own chemistry requirements; therefore, the applicable A193 certificate should govern when B8 is specified.
Mechanical Properties of SS 304 and A193 B8
The alloy chemistry may be similar, but mechanical requirements depend on the product specification, heat treatment, diameter and class. This distinction is important when comparing ordinary SS 304 material with ASTM A193 B8 fasteners.
Type 304 – General Product Reference
| Property | Common reference value |
|---|---|
| Tensile strength | 515 MPa minimum |
| Yield strength, 0.2% | 205 MPa minimum |
| Elongation | 40% minimum is commonly specified for annealed Type 304 flat products |
| Hardness | Typically ≤ 201 HB / ≤ 92 HRB for annealed Type 304 product references |
ASTM A193 Grade B8 Class 1
| Property | Minimum / maximum |
|---|---|
| Tensile strength | 515 MPa minimum |
| Yield strength, 0.2% | 205 MPa minimum |
| Elongation in 4D | 30% minimum |
| Reduction of area | 50% minimum |
| Hardness | 223 HBW or 96 HRB maximum |
What Exactly Is ASTM A193 Grade B8?
ASTM A193/A193M covers alloy-steel and stainless-steel bolting intended for high-temperature or high-pressure service and other special-purpose applications. Grade B8 is the Type 304 stainless-steel bolting grade within this specification.
Material
Type 304 / UNS S30400 austenitic stainless steel.
Specification
ASTM A193/A193M Grade B8, with the applicable class and supplementary requirements.
Service
Pressure vessels, valves, flanges, fittings, piping and other specified industrial service.
ASTM A193 B8 Class 1 vs Class 2
Both classes use Type 304 stainless steel. The major difference is the metallurgical condition and resulting strength requirements.
| Feature | B8 Class 1 | B8 Class 2 |
|---|---|---|
| Base material | Type 304 / S30400 | Type 304 / S30400 |
| Solution treatment | Required | Required |
| Strain hardening | No | Yes |
| Nominal strength level | 75 ksi tensile / 30 ksi yield | Strength depends on diameter; substantially higher than Class 1 |
| Typical small-diameter Class 2 requirement | — | Up to 3/4 in: 125 ksi tensile / 100 ksi yield |
| Ductility | Higher | Reduced as strength is increased |
| Ordering | Specify B8 Class 1 | Specify B8 Class 2 and diameter range |
Class 2 Mechanical Requirements – Important Diameter Effect
| Diameter | Tensile, min. | Yield, min. | Elongation, min. | RA, min. | Hardness, max. |
|---|---|---|---|---|---|
| Up to 3/4 in (≤20 mm) | 860 MPa | 690 MPa | 12% | 35% | 321 HBW / 35 HRC |
| Over 3/4 to 1 in (20–25 mm) | 795 MPa | 550 MPa | 15% | 35% | 321 HBW / 35 HRC |
| Over 1 to 1-1/4 in (25–32 mm) | 725 MPa | 450 MPa | 20% | 35% | 321 HBW / 35 HRC |
| Over 1-1/4 to 1-1/2 in (32–40 mm) | 690 MPa | 345 MPa | 28% | 45% | 321 HBW / 35 HRC |
These values are presented as a technical reference. The current ASTM A193/A193M edition, exact diameter, product form and class specified on the purchase order should govern.
Solution Annealing / Carbide Solution Treatment
Austenitic stainless-steel B8 material is solution treated to obtain the required metallurgical condition. The treatment is important because improper thermal processing can affect corrosion resistance and mechanical properties.
1. Heating
The material is heated into the specified solution-treatment temperature range under a controlled procedure.
2. Soaking
A sufficient holding time is used to obtain a uniform metallurgical condition through the relevant section.
3. Rapid Cooling
Rapid cooling is used to retain the desired austenitic condition and minimize harmful carbide precipitation.
AISI 304 vs AISI 304L
| Feature | AISI 304 | AISI 304L |
|---|---|---|
| Carbon limit | ≤ 0.08% | ≤ 0.030% |
| Family | Austenitic stainless steel | Low-carbon austenitic stainless steel |
| Main advantage | General-purpose corrosion resistance and mechanical performance | Lower carbon reduces sensitization risk during welding |
| Welded fabrication | Good | Often preferred for welded assemblies where low-carbon grade is specified |
| A193 relationship | B8 is based on Type 304 / S30400 | 304L should not automatically be substituted for B8 |
ASTM A320 Grade B8 vs ASTM A193 Grade B8
Both specifications include B8 austenitic stainless-steel bolting based on Type 304. However, the service intent is different. ASTM A320 is specifically for low-temperature service and includes impact requirements appropriate to that application.
| Parameter | ASTM A193 B8 | ASTM A320 B8 |
|---|---|---|
| Base material | Type 304 / S30400 | Type 304 / S30400 |
| Main service focus | High-temperature, high-pressure and special-purpose bolting | Low-temperature service bolting |
| Available conditions | Solution treated; strain-hardened classes as specified | Solution annealed or annealed and strain-hardened conditions are covered |
| Mechanical testing | Tension, hardness and applicable requirements | Tension, hardness plus low-temperature impact requirements |
| Selection basis | Pressure / temperature / project specification | Low-temperature design and impact requirements |
Dimensions & Thread Standards – Metric and Inch
ASTM A193 defines the bolting material requirements. The dimensional standard is normally specified separately. Therefore, an order should identify the material specification and the dimensional/thread standard.
Metric Fasteners
| Standard | Product / Function | Typical use |
|---|---|---|
| ISO 4014 | Hexagon head bolts, product grades A and B; partially threaded configurations | Metric hex bolts |
| ISO 4017 | Hexagon head screws, product grades A and B; fully threaded configurations | Metric fully threaded hex fasteners |
| ISO 3506-1:2020 | Mechanical properties of corrosion-resistant stainless-steel bolts, screws and studs | Stainless fastener property classes |
| ISO 261 / ISO 262 | Metric thread system and selected diameter/pitch combinations | Metric thread selection |
| ISO 965-1 | Metric thread tolerance system | Thread fit / tolerance |
| DIN 931 | Common legacy designation for partially threaded hexagon head bolts | DIN-style metric procurement |
| DIN 933 | Common legacy designation for fully threaded hexagon head bolts | DIN-style metric procurement |
| ASME B18.31.1M | Metric continuous and double-end studs | Metric studs |
Inch / Unified Fasteners
| Standard | Product / Function | Typical use |
|---|---|---|
| ASME B18.2.1 | Square, hex, heavy hex and askew head bolts and screws – inch series | Inch hex bolts and screws |
| ASME B18.31.2 | Continuous-thread, double-end and flange bolting studs – inch series | Stud bolts / flange studs |
| ASME B18.2.2 | Square and hex nuts – inch series | Matching inch nuts |
| ASME B1.1 | Unified Inch Screw Threads, UN and UNR series | UNC / UNF / UNEF thread selection |
| ASTM A193 / ASME SA193 | Bolting material specification | Material / service requirement |
Applications of ASTM A193 B8 SS 304 Studs & Bolts
Oil & Gas
Flanges, valves, piping and equipment connections where stainless-steel bolting is specified.
Chemical Plants
Pumps, piping, vessels, process equipment and structural equipment connections.
Petrochemical
Heat exchangers, flanges, valves and process piping applications.
Power & Utilities
Selected equipment and piping applications where Grade B8 is specified by design.
Valves & Pumps
Stud bolts and fasteners for bolted joints, flanges and equipment assemblies.
Water & Infrastructure
Equipment, tanks, piping and general industrial installations where SS 304 is suitable.
How to Specify ASTM A193 B8 Correctly
Include These Details in the RFQ
- ASTM A193 / ASME SA193
- Grade B8
- Class 1 or Class 2
- Nominal diameter
- Length
- Metric or inch thread
- Thread pitch / UNC / UNF as applicable
- Dimensional standard
- Nut grade, when required
- Surface finish / passivation requirement
- Testing, PMI and inspection requirements
- Mill Test Certificate / EN 10204 requirement
Example Specification
Stud Bolt: ASTM A193 Grade B8 Class 2
Material: SS 304 / UNS S30400
Size: M20 × 150 mm
Thread: Metric coarse
Configuration: Full thread / stud bolt as specified
Inspection: Dimensional + hardness + material identification + MTC as required
Why Aanuraj Fasteners?
Aanuraj Fasteners Pvt Ltd is focused on industrial fasteners where material traceability, dimensional accuracy, thread quality and consistent manufacturing are important.
Manufacturing Capability
Hot forging, CNC machining and thread rolling are used for engineered stainless-steel and alloy fasteners.
Quality & Traceability
Material identification, dimensional inspection, thread inspection, hardness verification and documentation can be provided according to order requirements.
Technical Support
Our team can help interpret grade, class, size, thread, dimensional standard and application requirements before supply.
Read Further – Standards & Technical References
The following resources can be used for deeper technical verification and standard interpretation.
A dedicated Wikipedia article specifically titled “ASTM A193 Grade B8” was not located in the search. The ASTM and ASME sources above should be treated as the primary references for specification and dimensional requirements.
Aanuraj Fasteners Pvt Ltd. Type 304 stainless fasteners offers corrosion resistance. Lesser to type 316 stainless due to the added molybdenum.
Grade B8 Class 1 fasteners require carbide solution treatment,
Class 2 fasteners require an additional strain hardening operation which increases the strength and reduces the susceptibility to galling.
Class 2 fasteners are marked “RAJ B8” with the grade symbol underlined.
ASTM A193 GR.B8 STANDARD PDF DOWNLOAD
Standards |
ASTM A 193 Gr.B8 |
CLASS: |
CL.1/CL.2 |
MOC: |
SS 304 |
Dimensions: |
ASME B18.2.1 , ASME B18.3 |
THREADS INCHES: |
ASME B1.1 2A/3A Unified Threads |
THREADS METRICS: |
B1.13M 6h Coarse Threads |
Additional Requirements: |
NACE MR0103/MR0175/ ISO 15156 Compliance |
Mandatory Requirements: |
Free from Mercury & Radioactive Contamination |
Chemical elements % @ AISI 304
ChemicalElements |
Min.% |
Max.% |
Product Variationover or Under |
Carbon C% |
0.08 |
0.01 over |
|
Manganese Mn |
2.00 |
0.04 over |
|
Phosphorus |
0.045 |
0.010 over |
|
Sulfur |
0.030 |
0.005 over |
|
Silicon |
1.00 |
0.05 over |
|
Nickel |
8.0 |
10.50 |
0.15 |
Chromium |
18.0 |
20.00 |
0.20 |
Mechanical Properties: Metric Products:
MechanicalElements |
Tensile Strength Min MPA |
Yield Strength Min MPA |
Elongation Min% |
Reduction Min% |
Hardness Max |
|
ASTM A193 GRADE B8 CL.1 |
||||||
75 [515] |
30 [205] |
30 |
50 |
96 HRB |
||
ASTM A193 GRADE B8 CL.2 |
||||||
M20 and under |
125 [860] |
100[690] |
12 |
35 |
35 HRC |
|
M20 to M25 |
115[795] |
80[550] |
15 |
30 |
35 HRC |
|
M25 to M32 |
105[725] |
65[450] |
20 |
35 |
35 HRC |
|
M32 to M40 |
100[690] |
50[345] |
28 |
45 |
35 HRC |
|
Annealing Process:
ANNEALING TEMPERATURE |
HOURS |
QUENCHING MEDIA |
140 TO 150 |
RUNNING |
|
1050°c |
MINUTES |
WATER |