Stainless steel shaped by hammering or pressing hot metal — open-die forgings such as shafts, discs and blocks, closed-die forgings such as valve bodies and fittings, and seamless rolled rings for flanges and bearing races. Forging closes porosity and aligns the grain, giving sounder metal than a casting for pressure parts, shafts and heavy flanges.
A forging starts as an ingot, a continuously cast bloom or a rolled billet, heated to roughly 1,100–1,200 °C for austenitic grades and worked under a press or hammer. Open-die forging shapes the metal between flat or simple dies and is used for shafts, discs, blocks and large hollows; closed-die forging presses it into a shaped cavity for repeat parts such as fittings and valve bodies; ring rolling pierces a disc and rolls it out into a seamless ring.
The working breaks up the cast structure, closes internal porosity and lines the grain up with the shape of the part. That is why pressure codes prefer forgings for weld-neck flanges, tube sheets, nozzles and high-pressure valve bodies, and why shafts for pumps and propellers are forged rather than cast.
Austenitic forgings are solution annealed — heated above about 1,040 °C and water quenched — to dissolve carbides and give full corrosion resistance; duplex forgings need a carefully controlled anneal and a fast quench to avoid sigma phase, and precipitation-hardening grades such as 17-4PH (type 630) are aged to the condition ordered (H900 to H1150). Large austenitic forgings are coarse-grained and harder to inspect ultrasonically than carbon steel, so the inspection method and acceptance level have to be agreed before forging.
In the GCC, stainless forgings are bought mainly for desalination plant (super duplex and 6Mo flanges and tube sheets), oil and gas (wellhead and valve parts to API and operator specifications, with sour-service compliance to ISO 15156) and petrochemical heat exchangers. Most are imported from forge shops in Europe, India, China and Korea, often as rough-machined blanks finished by local machine shops.
Forgings are ordered to a drawing or to a 'forged and rough machined' envelope. The order states the grade and specification, delivery condition, the machining allowance, the test location (where test pieces are taken) and the ultrasonic acceptance level.
| Region | Standard | What it covers |
|---|---|---|
| USA | ASTM A182/A182M ASTM |
Forged or rolled alloy and stainless steel pipe flanges, forged fittings, valves and parts for high-temperature service |
| USA | ASTM A473 ASTM |
Stainless steel forgings for general use |
| USA | ASTM A705/A705M ASTM |
Age-hardening stainless steel forgings — 17-4PH (630), 15-5PH and others |
| USA | ASTM A965/A965M ASTM |
Steel forgings, austenitic, for pressure and high temperature parts |
| USA | ASTM A484/A484M ASTM |
General requirements for stainless steel bars, billets and forgings |
| USA | ASTM A745/A745M ASTM |
Ultrasonic examination of austenitic steel forgings |
| Europe | EN 10250-4 CEN-CENELEC |
Open die steel forgings for general engineering purposes — stainless steels |
| Europe | EN 10222-5 CEN-CENELEC |
Steel forgings for pressure purposes — martensitic, austenitic and austenitic-ferritic stainless steels |
| Europe | EN 10228-4 CEN-CENELEC |
Non-destructive testing of steel forgings — ultrasonic testing of austenitic and austenitic-ferritic stainless steel forgings |
| Japan | JIS G3214 JSA |
Stainless steel forgings for pressure vessels |
Grade equivalents and the standards bodies: Steel grades & standards
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