ASTM A193 Grade B8S (Nitronic 60)
Nitronic 60 bolting — the anti-galling stainless: 95 ksi, non-magnetic, and threads that will not seize against other stainless steels.
What A193 B8S is.
ASTM A193 Grade B8S is bolting made from Alloy 218, Nitronic 60. Its silicon and manganese additions change the way the surface work-hardens so that stainless-on-stainless threads do not weld together under load, the failure that plagues 304 and 316 fasteners. It does this while matching 316 in general corrosion resistance and offering 95 ksi minimum tensile strength.
B8S is used wherever a stainless joint is assembled and disassembled repeatedly, or where lubricants are not allowed: valve stems, food and pharmaceutical equipment, nuclear plants and marine hardware. We machine it from certified S21800 bar and pair it with ASTM A194 Grade 8S nuts, or use it as the nut on Nitronic 50 studs.
Chemical composition.
| Element | Symbol | Min % | Max % |
|---|---|---|---|
| Carbon | C | — | 0.10 |
| Manganese | Mn | 7.0 | 9.0 |
| Phosphorus | P | — | 0.060 |
| Sulfur | S | — | 0.030 |
| Silicon | Si | 3.5 | 4.5 |
| Chromium | Cr | 16.0 | 18.0 |
| Nickel | Ni | 8.0 | 9.0 |
| Nitrogen | N | 0.08 | 0.18 |
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 |
|---|---|---|---|---|---|
| Class 1C and 1D — all diameters | 95 | 50 | 35 | 55 | 271 HBW / 28 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 B8S 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 B8S fasteners we make.
Every item is manufactured to your drawing or standard in A193 B8S, imperial or metric, with an EN 10204 3.1 certificate.
What is ASTM A193 B8S?
B8S covers bolting in UNS S21800, Nitronic 60. The alloy has about 17 percent chromium, 8.5 percent nickel, 8 percent manganese and 4 percent silicon with a nitrogen addition. The silicon and manganese alter the surface behaviour of the austenite so that when two Nitronic 60 surfaces, or Nitronic 60 and another stainless, slide under pressure they do not cold-weld. Independent galling tests rate it well above 304, 316 and even 17-4 PH. Corrosion resistance is similar to 316 in most environments, and the alloy is non-magnetic and tough to cryogenic temperatures.
Using B8S to solve galling
The most common use is as the nut side of a stainless joint: an A194 Grade 8S nut on a B8, B8M or B8R stud gives a dissimilar pairing that assembles dry. Where the entire fastener must be lubricant-free, both stud and nut are made in Nitronic 60. The material can also be specified for valve stems and wear surfaces that run against stainless seats.
Strength and limits
B8S is rated 95 ksi tensile and 50 ksi yield, a step below B8R but well above solution-treated 304 or 316. It is not a high-temperature creep grade; keep it below about 1000 °F and do not expect the pitting resistance of a super austenitic or duplex in hot chlorides.
Testing, certification and marking
- Tensile and hardness tested per heat-treat lot on the finished product
- Grade symbol B8S 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 B8S jobs.
ASTM A194 Grade 8S (Nitronic 60)
Nitronic 60 heavy hex nut — the anti-galling nut for stainless studs, assembled dry without seizing; 80 ksi proof load.
ASTM A193 / ASME SA-193ASTM A193 Grade B8R (Nitronic 50 / XM-19)
Nitronic 50 bolting — twice the yield strength of 316 with better seawater corrosion resistance and no loss of ductility, non-magnetic even after cold work.
ASTM A193 / ASME SA-193ASTM A193 Grade B8M Class 1 (316 Stainless)
316 stainless bolting with molybdenum for chloride and pitting resistance — offshore, marine, chemical and coastal plant fasteners.