ASTM 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.
What A193 B8R is.
ASTM A193 Grade B8R is bolting made from XM-19, better known as Nitronic 50. Nitrogen, manganese and extra chromium, nickel and molybdenum give it a 55 ksi minimum yield strength in the solution-treated condition, nearly double that of 304 or 316, together with corrosion resistance that exceeds 316 in seawater and most process environments.
It stays fully austenitic and non-magnetic, keeps its toughness at cryogenic temperature and is the grade of choice for marine, naval, pump and valve applications where a stainless fastener has to carry real load. We machine B8R from certified S20910 bar and pair it with ASTM A194 Grade 8R nuts.
Chemical composition.
| Element | Symbol | Min % | Max % |
|---|---|---|---|
| Carbon | C | — | 0.06 |
| Manganese | Mn | 4.0 | 6.0 |
| Phosphorus | P | — | 0.045 |
| Sulfur | S | — | 0.030 |
| Silicon | Si | — | 1.00 |
| Chromium | Cr | 20.5 | 23.5 |
| Nickel | Ni | 11.5 | 13.5 |
| Molybdenum | Mo | 1.50 | 3.00 |
| Nitrogen | N | 0.20 | 0.40 |
| Niobium (columbium) | Nb | 0.10 | 0.30 |
| Vanadium | V | 0.10 | 0.30 |
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 | 100 | 55 | 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 B8R 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 B8R fasteners we make.
Every item is manufactured to your drawing or standard in A193 B8R, imperial or metric, with an EN 10204 3.1 certificate.
What is ASTM A193 B8R?
B8R covers bolting in UNS S20910, a nitrogen-strengthened austenitic stainless originally developed by Armco as Nitronic 50. Compared with 316 it carries about 22 percent chromium, 12.5 percent nickel, 2 percent molybdenum, 5 percent manganese and 0.3 percent nitrogen. Nitrogen is the key: it strengthens the austenite without cold work, so the solution-treated material meets 100 ksi tensile and 55 ksi yield with 35 percent elongation, and it also improves pitting resistance. Because the alloy is a stable austenite it does not become magnetic when machined or cold worked, and it retains its impact strength down to cryogenic temperatures.
Why specify B8R
- Strength: yield roughly twice that of B8 or B8M Class 1 without strain hardening, so large diameters get the full properties.
- Corrosion: pitting and crevice resistance better than 316 in seawater, brine and many acids.
- Non-magnetic: permeability stays near 1.0 after cold work, unlike 304 and 316.
- Temperature: usable from cryogenic service to about 1200 °F.
Nuts and galling
Pair B8R studs with ASTM A194 Grade 8R nuts. Nitronic 50 galls like other austenitic stainless steels, so use an anti-seize, a PTFE coating or Nitronic 60 (Grade 8S) nuts, which are formulated specifically to resist galling against Nitronic 50 studs.
Testing, certification and marking
- Tensile and hardness tested per heat-treat lot on the finished product
- Grade symbol B8R and manufacturer's identification on every piece
- EN 10204 3.1 material test report with heat number and chemistry; 3.2 witness available
- Magnetic permeability and PMI verification available on request
Recent A193 B8R jobs.
ASTM A194 Grade 8R (Nitronic 50 / XM-19)
Nitronic 50 heavy hex nut for B8R studs — high-strength, non-magnetic and seawater resistant; 80 ksi proof load.
ASTM A193 / ASME SA-193ASTM 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.
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.