ASTM A193 Grade B6 (410 Stainless)
Hardenable 410 stainless bolting — 110 ksi with corrosion resistance B7 lacks, for valve trim, steam and mildly corrosive service.
What A193 B6 is.
ASTM A193 Grade B6 is bolting made from AISI 410, the basic 12 percent chromium martensitic stainless steel. Unlike the austenitic B8 grades it can be hardened by heat treatment, so B6 reaches 110 ksi minimum tensile strength while still resisting atmospheric corrosion, steam and mild chemical exposure.
It is a common choice for valve bonnets and trim, steam turbine hardware and pump bolting where B7 would rust and 304 would be too soft. Grade B6X is the controlled-hardness version, limited to 26 HRC, for sour service. We machine B6 from certified 410 bar and pair it with ASTM A194 Grade 6 nuts.
Chemical composition.
| Element | Symbol | Min % | Max % |
|---|---|---|---|
| Carbon | C | 0.08 | 0.15 |
| Manganese | Mn | — | 1.00 |
| Phosphorus | P | — | 0.040 |
| Sulfur | S | — | 0.030 |
| Silicon | Si | — | 1.00 |
| Chromium | Cr | 11.5 | 13.5 |
Values per ASTM A193/A193M-24, Tables 1 and 2 (verified against the specification). Confirm the edition called out on your purchase order with our estimating team.
Mechanical properties.
| Nominal diameter (in.) | Tensile strength, min (ksi) | Yield strength 0.2% offset, min (ksi) | Elongation in 4D, min (%) | Reduction of area, min (%) | Hardness, max |
|---|---|---|---|---|---|
| B6 — 4 and under | 110 | 85 | 15 | 50 | Not specified |
| B6X — 4 and under | 90 | 70 | 16 | 50 | 26 HRC |
Values per ASTM A193/A193M-24, Tables 1 and 2 (verified against the specification). Confirm the edition called out on your purchase order with our estimating team.
Specifications that apply.
How A193 B6 ships from Houston.
- Full-thread studs and stud bolts
- Double-end and tap-end studs
- Hex and heavy hex bolts
- Socket head cap screws
- Threaded rod (cut and rolled thread)
- Machined components from certified bar
A193 B6 fasteners we make.
Every item is manufactured to your drawing or standard in A193 B6, imperial or metric, with an EN 10204 3.1 certificate.
What is ASTM A193 B6?
B6 is the martensitic stainless grade in A193. Type 410 contains 11.5 to 13.5 percent chromium and enough carbon to transform to martensite on quenching, so it is heat treated like an alloy steel rather than solution annealed like 304 or 316. The result is a magnetic stainless with roughly the strength of B7M and far better resistance to rusting, steam and oxidation up to about 1200 °F. It is not a substitute for the austenitic grades in chloride or strongly acidic environments; 410's corrosion resistance is modest and it can pit in seawater.
B6 versus B6X
B6X is Grade B6 tempered to a maximum hardness of 26 HRC with a 90 ksi minimum tensile strength. The lower hardness qualifies it for hydrogen sulfide service under NACE MR0175, where standard B6 is too hard. Order B6X for sour wellhead and gas plant applications; standard B6 for everything else.
Nuts and washers
Pair B6 with ASTM A194 Grade 6 nuts, or Grade 6F where free-machining 416 is acceptable, so both parts of the joint are the same stainless. Washers are normally 410 or 416 as well.
Testing, certification and marking
- Tensile and hardness tested per heat-treat lot on the finished product
- Grade symbol B6 and manufacturer's identification on every piece
- EN 10204 3.1 material test report with heat number and chemistry; 3.2 witness available
Recent A193 B6 jobs.
ASTM A194 Grade 6 (410 Stainless)
The 410 stainless heavy hex nut for A193 B6 studs — hardened and tempered, 20 to 28 HRC, for valve and steam service.
ASTM A193 / ASME SA-193ASTM A193 Grade B8 Class 1 (304 Stainless)
304 stainless bolting — Class 1 for corrosion resistance and cryogenic-to-1500 °F service, Class 2 strain hardened to 125 ksi for strength.
ASTM A193 / ASME SA-193ASTM A193 Grade B7
The workhorse alloy-steel bolting grade for flanges, valves and pressure equipment — 125 ksi tensile, quenched and tempered 4140.