What is XM-19? Stainless Steels
XM-19 is a highly alloyed austenitic stainless steel as listed in ASTM A276/A479 as UNS S20190. It is also commonly referred to as Nitronic 50 and Fermonic 50, which are trademarks of AK Steel Inc and Langley Alloys respectively.
Through the combination of chromium content (20.50-23.50%), increased molybdenum content (1.5 – 3.0%) and raised levels of nitrogen (0.20 – 0.40%) its pitting resistance equivalent number (PREN) exceeds 34. This is comparable with that of a duplex stainless steel such as Sanmac 2205 (1.4462). Therefore, it provides good levels of corrosion resistance, way beyond standard 3xx grades where the PREN = 25.
Applications include Oil & Gas industry downhole equipment, marine pumps, valves, masts, tie downs, fixtures and fittings, food processing equipment and pulp and paper Industry valves and fittings. Of all these applications, valve stems are perhaps the most common end use for this application. As an austenitic stainless steel, it has better impact strength across a wider range of temperatures than alternative grades. This is relevant as the stems can be subjected to more of a shock loading when actuating a large valve. The next most common application would be fixtures and fittings for marine applications, due to the relative ease of fabrication without compromising the good corrosion resistance.
DIN 1.3964 is frequently referenced in relation to XM-19. However, this particular caption has an increased molybdenum content (3.0 – 3.5%), along with an associated increase in nickel content (15.0-17.0%) to retain the desirable austenitic microstructure. These alloy increases will certainly improve the corrosion performance, but also increase the cost markedly too. As a result, DIN 1.3964 lies outside the XM-19 and the two alloys cannot be considered identical.
Langley Alloys offers XM-19 in two specifications; a standard annealed (solution annealed) version [Fermonic 50 – Annealed] and a higher strength version [Fermonic 50 – HS]. The strength is increased through a combination of either cold working or warm working (rolling at lower temperatures) to impart a degree of strain hardening.