Sigma Phase Embrittlement (σ-Phase)
Engineering definition, metallurgical mechanisms, standard testing specifications, and manufacturing guidelines for closed-die forgings up to 50 kg.
Quick AnswerFeatured
An extremely hard, brittle intermetallic Fe-Cr-Mo phase that precipitates in duplex and high-chromium stainless steels between 600°C and 900°C, destroying impact toughness.
Technical Explanation & Metallurgical Principles
Sigma (σ) phase is the greatest metallurgical danger in duplex stainless steel manufacturing. Even 1% to 2% sigma phase precipitation at grain boundaries drastically reduces Charpy impact toughness from >100 Joules down to single digits and causes catastrophic loss of pitting resistance.
Key Engineering Specifications & Parameters
| Technical Parameter / Metric | Engineering Benchmark / Value |
|---|---|
| Precipitation Window | 600°C to 900°C (peak formation around 800°C–850°C) |
| Detection Test | ASTM A923 Method A (etch structure) & Method C (ferric chloride test) |
| Countermeasure | Immediate water quench from solution annealing temp >1040°C |
Application at Jayesh Forge (Rajkot Plant)
100% verified free of detrimental intermetallic phases via ASTM A923 Method C Charpy and corrosion testing on every duplex batch.
Related Materials, Standards & Products
Related Metallurgical & Testing Terms
Duplex Stainless Steel (2205 / F51 / S31803)
A dual-phase stainless steel possessing an approximate 50% austenitic and 50% ferritic microstructure, combining twice the yield strength of 316L with supreme chloride pitting resistance.
Solution Annealing (Solution Treatment)
Heating austenitic or duplex stainless steel above 1040°C to dissolve all chromium carbides, followed by rapid water quenching to trap elements in solid solution.
Charpy V-Notch Impact Test (CVN)
A standardized dynamic test that measures the kinetic energy absorbed by a notched 10x10mm specimen when fractured by a swinging pendulum hammer at specified temperatures.
Questions Regarding Sigma Phase Embrittlement (σ-Phase)
Yes, re-solution annealing the component above 1040°C followed by forced water quenching completely redissolves sigma phase back into austenite and ferrite.
Request a Forging Quote with Sigma Phase Embrittlement (σ-Phase) Compliance
Our Rajkot metallurgy desk is ready to review your technical drawings, testing protocols, and delivery schedules for custom closed-die forgings strictly up to 50 kg.