UNS S42200 / AISI 422 Open-Die Forgings: Bars, Rings, Discs and Turbine Components

1. Designations and equivalent grades

This steel travels under a lot of names, and buyers often quote two or three of them on the same enquiry. The table below lists the ones we see most often on drawings and purchase orders.

One point worth checking before you place an order. The EN and ASTM chemistry windows overlap but do not match. EN 1.4935 allows tungsten 0.4 to 0.6 per cent and vanadium 0.25 to 0.35 per cent, while the ASTM window for S42200 is tungsten 0.75 to 1.25 and vanadium 0.15 to 0.30. On a rotating part that difference can matter to the end user, so name one standard on the order and we certify to that one rather than treating them as the same material.

2. Chemical composition

ASTM limits for Grade 616 / UNS S42200 are given below, with iron making up the balance at around 82 per cent.

Published ASTM ranges vary slightly between sources, with some datasheets quoting Mo and W from 0.75 and Si up to 0.75. For rotating turbine parts we normally melt AOD and then remelt by ESR. The remelt tightens the inclusion rating and lifts transverse toughness, which shows up where it counts, on blade roots and disc rims. Say so in the enquiry if ESR is mandatory for you.

3. Physical properties

4. Mechanical properties

Strength in this grade is set almost entirely by the tempering temperature, so the figures below are kept separate by the standard they come from instead of being merged into one set.

4.1 AMS 5655, hardened and tempered

Some circulated copies of this table print the tensile and yield figures the other way round, which cannot be right since yield always sits below ultimate. The order above is the physically correct one. Other suppliers publish a lower minimum set for general bar, around 897 MPa tensile with 15 per cent elongation and 290 HB maximum, so always work to the acceptance values written into your own order.

4.2 EN 1.4935 delivery classes

4.3 Yield strength at temperature

This is the data that actually sizes a turbine part, and it shows what the molybdenum, tungsten and vanadium are buying.

Creep rupture strength for 1.4935 is quoted above 275 MPa for 100,000 hours at 500 C. Note the gap between the two temperature limits you will see in print. The 1200 F (649 C) figure applies to short term and oxidation limited duty, while EN sets 580 C as the ceiling for continuous creep loaded operation. Both are correct in their own context, and the lower one is the number to design long life rotating parts against.

5. Forging and heat treatment

Section size drives quench response, so we set the heat treatment route against the actual forging envelope instead of running one recipe for everything. On heavy discs and rings we take test prolongations from the forging itself, which means the certified properties come from the part rather than from a separate coupon.

Machining

Machinability is close to 18-8 austenitic stainless and a little easier. Sharply ground tools and a steady speed and feed keep galling down. Published starting points for cobalt high speed tooling are 90 to 120 sfpm turning, 40 to 75 sfpm drilling, 70 to 120 sfpm milling and 20 to 60 sfpm reaming, with 8 to 14 degrees side rake on turning tools, a 140 degree drill point, and 10 to 15 degrees back rake for threading.

Welding

Hard. EN assigns 1.4935 to welding group 7.2 under ISO/TR 20172. Any weld calls for preheat, interpass temperature control and post weld heat treatment, and most turbine specifications rule out weld repair on finished parts. Where the geometry allows it, a one piece forging is the cheaper and safer route than a fabrication.

6. Forged product forms in UNS S42200

7. Where the grade is used

UNS S42200 gets specified where a part has to hold load and resist scaling in hot, mildly corrosive service without paying for an austenitic or nickel alloy. Published application lists cover steam and gas turbine components, turbine blades, compressors, rotors, aircraft parts, valves and high temperature bolting. Corrosion resistance extends to atmosphere, fresh water, steam and the milder acids and alkalies, so it is the wrong pick for aggressive chloride service or strong acids.

8. Testing and documents

Every UNS S42200 forging ships with an EN 10204 3.1 certificate covering melt analysis, heat treatment records and mechanical results, with product analysis added on request. Depending on the specification we also run ultrasonic testing to ASTM A388 or SEP 1921, magnetic particle inspection to ASTM E709, grain size and inclusion rating, hardness survey, Charpy V notch impacts at the stated temperature, and intergranular corrosion testing. Witness inspection by TUV, SGS, BV, Lloyd's or your own engineer is routine here and welcome.

9. Common questions

10. Request a quotation

Quoting takes very little from you. We need the grade and standard, for instance UNS S42200 to ASTM A565 Grade 616, the forged shape with finished dimensions or a drawing, the quantity, the delivery condition you want (+QT700, +QT800 or a hardness band), and any NDT or third party inspection that applies. Drawings in PDF, DWG or STEP all work.

Data sources

Figures on this page come from ASTM A565 / A565M, AMS 5655, EN 10088-3:2014 and EN 10302, together with published datasheets for the grade. Where sources disagree, both are shown rather than averaged, which is the case for density at 7.7 to 7.8 g/cm3 and for modulus at 190 to 216 GPa. Everything here is indicative. The governing numbers for any order are the ones on the mill certificate that ships with the goods.