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.
What A194 8R is.
ASTM A194 Grade 8R is the XM-19 (Nitronic 50) nut that completes an A193 B8R stud bolt set. It shares the stud's nitrogen-strengthened chemistry, so it is stronger and more pitting resistant than 316 nuts and stays non-magnetic after machining.
Grade 8RA is the same nut solution treated after finishing. We machine both from certified S20910 bar; Nitronic 60 (Grade 8S) nuts are the usual anti-galling alternative on Nitronic 50 studs.
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 A194/A194M-24, Tables 1, 2 and 3 (verified against the specification). Confirm the edition called out on your purchase order with our estimating team.
Mechanical properties.
| Nut style and size (in.) | Proof load stress (ksi) | Hardness, min | Hardness, max |
|---|---|---|---|
| Heavy hex, all sizes | 80 | 183 HBW / 88 HRB | 271 HBW / 25 HRC |
| Hex (finished pattern), all sizes | 75 | 183 HBW / 88 HRB | 271 HBW / 25 HRC |
| Grade 8RA (solution treated in the finished condition), all sizes | 80 heavy hex · 75 hex | 183 HBW / 88 HRB | 271 HBW / 25 HRC |
Values per ASTM A194/A194M-24, Tables 1, 2 and 3 (verified against the specification). Confirm the edition called out on your purchase order with our estimating team. Jam nuts: 46 % of the tabulated proof load.
Specifications that apply.
How A194 8R ships from Houston.
- Heavy hex nuts (the default for pressure bolting)
- Finished hex nuts
- Jam nuts
- Custom and special nuts to drawing
A194 8R fasteners we make.
Every item is manufactured to your drawing or standard in A194 8R, imperial or metric, with an EN 10204 3.1 certificate.
What is ASTM A194 Grade 8R?
Grade 8R is the XM-19 nut in A194. Like the B8R stud it is a nitrogen-strengthened austenitic stainless with roughly 22 percent chromium, 12.5 percent nickel and 2 percent molybdenum, machined from solution-annealed bar, non-magnetic. Its corrosion resistance exceeds 316 in seawater and its hardness window, 183 to 271 HBW, sits above the plain Grade 8 family.
Galling on Nitronic 50 joints
A Nitronic 50 nut on a Nitronic 50 stud can gall like any same-alloy austenitic pairing. The proven fix is a Nitronic 60 nut, Grade 8S, on the B8R stud; otherwise use an anti-seize or a PTFE coating.
Testing, certification and marking
- Hardness tested per lot; proof-load tested on request or where the specification requires it
- Grade symbol 8R, or 8RB on nuts machined from bar (ASTM A194 Table 7), and manufacturer's identification on one face of every nut
- EN 10204 3.1 material test report with heat number and chemistry; 3.2 witness available
- Oversize tapping for coated studs and PTFE / zinc / hot-dip galvanized finishes available
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.
ASTM A194 / ASME SA-194ASTM 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 A194 / ASME SA-194ASTM A194 Grade 8M (316 Stainless)
316 stainless heavy hex nut for B8M studs — molybdenum-bearing for chloride and marine service, 80 ksi proof load.