Aug 2025
ASTM A193
First introduced in 1936, ASTM A193 is a widely used specification in petroleum, chemical, and power generation industries. It covers alloy steel and stainless steel bolting materials designed for high-temperature or high-pressure applications.
Typical uses include:
Pressure vessels
Valves
Flanges
Fittings
While ASTM A193 fasteners are often available in national coarse (UNC) threads, for traditional applications the standard specifies 8 threads per inch (TPI) for bolt diameters above 1 inch.
Common Grades in ASTM A193
ASTM A193 includes multiple grades of fasteners, each designed for specific operating conditions. Some popular grades are:
B7 – Chromium-molybdenum alloy steel, heat-treated for strength, ideal for high-pressure applications.
B8 – Stainless steel for corrosion resistance and moderate strength.
B8M – Molybdenum-bearing stainless steel for superior corrosion resistance.
(Note: Other grades like B5, B6, and B16 are also covered under ASTM A193 but are not detailed here.)
| Grade |
Description |
| B7 |
Alloy steel, AISI 4140/4142, quenched and tempered for high strength. |
| B8 Class 1 |
Stainless steel, AISI 304, carbide solution treated for corrosion resistance. |
| B8M Class 1 |
Stainless steel, AISI 316, carbide solution treated for enhanced corrosion resistance. |
| B8 Class 2 |
Stainless steel, AISI 304, carbide solution treated and strain hardened for added strength. |
| B8M Class 2 |
Stainless steel, AISI 316, carbide solution treated and strain hardened for added strength and corrosion resistance. |
A193 Mechanical Properties
| Grade |
Size |
Tensile ksi, min |
Yield, ksi, min |
Elong, %, min |
RA % min |
HBW |
Rockwell |
| B7 |
Up to 2-1/2 |
125 |
105 |
16 |
50 |
321 max |
35 HRC max |
| 2-5/8 - 4 |
115 |
95 |
16 |
50 |
| 4-1/8 - 7 |
100 |
75 |
18 |
50 |
| B8 Class 1 |
All |
75 |
30 |
30 |
50 |
223 max |
96 HRB max |
| B8M Class 1 |
All |
75 |
30 |
30 |
50 |
223 max |
96 HRB max |
| B8 Class 2 |
Up to 3/4 |
125 |
100 |
12 |
35 |
321 max |
35 HRC max |
| 7/8 - 1 |
115 |
80 |
15 |
35 |
| 1-1/8 - 1-1/4 |
105 |
65 |
20 |
35 |
| 1-3/8 - 1-1/2 |
100 |
50 |
28 |
45 |
| B8M Class 2 |
Up to 3/4 |
110 |
95 |
15 |
45 |
321 max |
35 HRC max |
| 7/8 - 1 |
100 |
80 |
20 |
45 |
| 1-1/8 - 1-1/4 |
95 |
65 |
25 |
45 |
| 1-3/8 - 1-1/2 |
90 |
50 |
30 |
45 |
A193 Chemical Properties
| Element |
B7 (AISI 4140) |
B8 (AISI 304) |
B8M (AISI 316) |
| Carbon |
0.38 - 0.48% |
0.08% max |
0.08% max |
| Manganese |
0.75 - 1.00% |
2.00% max |
2.00% max |
| Phosphorus, max |
0.035% |
0.045% |
0.045% |
| Sulfur, max |
0.040% |
0.030% |
0.030% |
| Silicon |
0.15 - 0.35% |
1.00% max |
1.00% max |
| Chromium |
0.80 - 1.10% |
18.0 - 20.0% |
16.0 - 18.0% |
| Nickel |
— |
8.0 - 11.0% |
10.0 - 14.0% |
| Molybdenum |
0.15 - 0.25% |
— |
2.00 - 3.00% |
A193 Recommended Hardware
| Bolt Grade |
Nuts |
Washers |
| B7 |
A194 Grade 2H |
F436 |
| B8 Class 1 |
A194 Grade 8 |
SS304 |
| B8M Class 1 |
A194 Grade 8M |
SS316 |
| B8 Class 2 |
A194 Grade 8 |
SS304 |
| B8M Class 2 |
A194 Grade 8M |
SS316 |