Stainless Steel Type 418
| Chemical Analysis | |
|---|---|
| C | Carbon 0.15 – 0.20 |
| Mn | Manganese 0.50 max |
| P | Phosphorus 0.030 max |
| S | Sulfur 0.030 max |
| Si | Silicon 0.50 max |
| Cr | Chromium 12.00 – 14.00 |
| Ni | Nickel 1.80 – 2.20 |
| Mo | Molybdenum 0.50 max |
| W | Tungsten 2.50 – 3.50 |
General Characteristics of Stainless Steel 418
This grade is also known as Greek Ascoloy. It is a chromium-nickel-tungsten martensitic alloy for service up to 1200ºF (650ºC) in highly-stressed parts. It has very good hardenability.
Applications of Stainless Steel 418
This alloy is used in the manufacture of steam turbine buckets and blades, forged compressor parts in gas turbines and forged high temperature bolts.
Forging Stainless Steel 418
The alloy may be readily worked between 2150/1750ºF (1175/955ºC.) Large sections should be preheated to 1200/1400ºF (650/760ºC) prior to heating to forging or rolling temperature. Parts should be cooled slowly following forging.
Heat Treatment
Annealing
The alloy may be process annealed at 1300ºF (705ºC) for 4 hours followed by air cooling, but to obtain maximum softness and complete stress relief a much longer cycle is required. This cycle involves heating to 1450ºF (790ºC) for 2-4 hours, furnace cooling to 800ºF (425ºC) and then air cooling to at least 200ºF (90ºC). Next is a reheat to 1250/1300ºF (675/705ºC) for 12 hours, followed by air cooling.
Hardening
Austenitize at 1700/1800ºF (925/980ºC) followed by air or oil quench depending upon section size or complexity of part. Heavy or complex parts should be preheated to 1200/1400ºF (650/760ºC) prior to hardening.
Tempering
Tempering should be carried out as soon as possible following the hardening treatment. Check with the heat treat operation for temperature and time requirements.
Machinability
Greek Ascoloy machines like types 403 and 410 when in the annealed condition.
Weldability
Preheating to 400/600ºF (205/315ºC) is recommended due to the air hardening qualities of this alloy. Anneal as soon as possible after welding and use a type 310 stainless filler rod for maximum ductility.
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