Introduction
This guide unpacks the metallurgical, mechanical, and application differences between AMS 5655 and AMS 5612 in clear engineering language. Whether you are sourcing open-die forgings, seamless rolled rings, or turbine shaft blanks, this comparison will help you arrive at the right grade selection with confidence. Jiangsu Liangyi manufactures AMS 5655 forging parts from our ISO 9001:2015 certified facility in Jiangyin, China.
What Are AMS 5655 and AMS 5612?
Both specifications are issued by SAE International under the Aerospace Material Specification (AMS) series, covering bars, billets, forgings, and rings of corrosion- and heat-resistant steel alloys. However, the two grades were designed with fundamentally different service envelopes in mind.
AMS 5655 — Type 422 Martensitic Stainless Steel (UNS S42200)
AMS 5655 covers Type 422, a premium martensitic stainless steel engineered specifically for elevated-temperature service. It contains 11–13% chromium with critical additions of molybdenum (Mo), tungsten (W), and vanadium (V) — a triple-carbide-forming alloy package that pins grain boundaries, delays creep, and maintains strength at continuous operating temperatures up to 649°C (1,200°F). The specification mandates double-refining by AOD + ESR to achieve exceptional cleanliness and internal soundness critical for rotating machinery and aerospace structural components.
AMS 5612 — Type 410 Martensitic Stainless Steel (UNS S41000)
AMS 5612 covers Type 410, the foundational martensitic stainless steel grade. It is a simpler alloy: 11.5–13.5% chromium with no deliberate additions of Mo, W, or V. Type 410 was designed as a general-purpose, corrosion-resistant, hardenable stainless steel for mild-to-moderate service conditions. It is widely available, cost-effective, and well-understood. However, its utility diminishes rapidly above 480°C (900°F), where its tempered martensite microstructure begins to soften and lose mechanical integrity.
| Property | AMS 5655 (Type 422) | AMS 5612 (Type 410) |
|---|---|---|
| UNS designation | S42200 | S41000 |
| Cr content | 11.0–13.0% | 11.5–13.5% |
| Mo + W + V additions | Yes (all three) | No (none) |
| Melting route | AOD + ESR (double-refined) | EAF or AOD (single-refined) |
| Max service temp | 649°C / 1,200°F | 480°C / 900°F |
| UTS (Q+T) | ≥ 860 MPa (125 ksi) | ≥ 620 MPa (90 ksi) |
| 0.2% YS (Q+T) | ≥ 725 MPa (105 ksi) | ≥ 450 MPa (65 ksi) |
| Hardness (Q+T) | 28–35 HRC | 18–25 HRC |
| Charpy CVN (RT) | ≥ 27 J | ≥ 40 J |
| Heat treatment | Double temper — mandatory | Single temper — standard |
| Material cost vs baseline | +25–45% premium | Baseline |
| Primary use | Turbines, aerospace, power, nuclear | General industrial, O&G, structural |
Chemical Composition: Where the Difference Begins
The distinction between AMS 5655 and AMS 5612 starts at the ladle. The table below presents nominal composition ranges per SAE International specifications. Pay particular attention to the alloy additions in AMS 5655 that are entirely absent from AMS 5612.
| Element | AMS 5655 — Type 422 | AMS 5612 — Type 410 | Engineering Significance |
|---|---|---|---|
| Carbon (C) | 0.20–0.25% | 0.08–0.15% | Higher C in AMS 5655 enables greater hardenability and higher strength after Q+T. |
| Chromium (Cr) | 11.0–13.0% | 11.5–13.5% | Both provide Cr₂O₃ passive film. Mild-environment corrosion resistance broadly similar. |
| Molybdenum (Mo) | 0.75–1.25% | — (none) | Critical for solid-solution strengthening and resistance to temper softening above 500°C. |
| Tungsten (W) | 0.75–1.25% | — (none) | Forms M₆C carbides that pin grain boundaries, resisting creep and elevated-temperature fatigue. |
| Vanadium (V) | 0.15–0.30% | — (none) | Forms fine VC / V₄C₃ carbides; slows grain coarsening during forging and heat treatment. |
| Nickel (Ni) | 0.50–1.00% | ≤ 0.75% | Modest Ni addition in AMS 5655 improves toughness at lower operating temperatures. |
| Silicon (Si) | ≤ 0.50% | ≤ 1.00% | Controlled in AMS 5655 to avoid silicate inclusions that degrade fatigue properties. |
| Melting route | AOD + ESR double-refined | EAF or AOD single-refined | ESR remelting typically achieves significantly lower sulfide and oxide inclusion levels compared to single-melt Type 410 — commonly reported in the range of 60–80% reduction in published metallurgical literature. |
Temperature Resistance: The Defining Difference
The most commercially consequential distinction between AMS 5655 and AMS 5612 is their behavior at elevated operating temperatures. This single axis determines whether each grade is appropriate for a given application.
Maximum Continuous Service Temperature
Maximum recommended continuous service temperature per SAE AMS specification guidelines. AMS 5655 outperforms AMS 5612 by 169°C (305°F).
Above 480°C, the iron-carbide precipitates in Type 410 begin to coarsen and dissolve (over-tempering), causing the martensitic matrix to progressively lose strength. The Mo₂C, W₂C, and VC carbides in AMS 5655 are thermodynamically stable at these temperatures and continue providing precipitation hardening through the 649°C ceiling.
Temper Resistance
AMS 5655 retains roughly 32–34 HRC after tempering at 593°C. At the same temperature, AMS 5612 (Type 410) is reduced to approximately 22–24 HRC. For turbine blade root forgings, compressor discs, or boiler valve stems where hardness below 28 HRC is unacceptable for fatigue life, this difference eliminates AMS 5612 entirely from the shortlist.
Mechanical Properties Comparison
The following values reflect typical properties for each grade in the most commonly specified heat-treated condition. Actual values depend on forging reduction ratio, section size, and heat treatment parameters.
- UTS
- ≥ 860 MPa (125 ksi)
- 0.2% YS
- ≥ 725 MPa (105 ksi)
- Elongation
- ≥ 16%
- Reduction of area
- ≥ 50%
- Hardness
- 28–35 HRC
- Charpy (CVN)
- ≥ 27 J @ RT
- Max service temp
- 649°C (1,200°F)
- UTS
- ≥ 620 MPa (90 ksi)
- 0.2% YS
- ≥ 450 MPa (65 ksi)
- Elongation
- ≥ 20%
- Reduction of area
- ≥ 60%
- Hardness
- 18–25 HRC
- Charpy (CVN)
- ≥ 40 J @ RT
- Max service temp
- 480°C (900°F)
AMS 5612 (Type 410) achieves higher elongation and toughness than AMS 5655 at equivalent temperatures — making it the better choice when ambient-temperature ductility is the primary design constraint. AMS 5655's strength advantage only fully materializes when both grades are evaluated at service temperature, not room temperature.
Heat Treatment Requirements
AMS 5655 — Type 422 Heat Treatment Sequence
- Normalize: 980–1,040°C (1,800–1,905°F), air cool — refines as-forged grain structure.
- Austenitize: 1,010–1,065°C (1,850–1,950°F), hold 1 hr per 25 mm of section, oil or air quench.
- Double temper (mandatory): 565–650°C (1,050–1,200°F), minimum 2 hours per cycle — ensures complete transformation of retained austenite and full precipitation of M₂₃C₆ and MC carbides.
- Stress relieve (optional): 50°C below final temper temperature for 2 hours.
AMS 5612 — Type 410 Heat Treatment Sequence
- Anneal: 815–900°C (1,500–1,650°F), furnace cool — soft, machinable microstructure.
- Austenitize: 925–1,010°C (1,700–1,850°F), oil or air quench.
- Temper (single cycle): 150–370°C for high hardness; 580–700°C for improved toughness.
Machinability and Weldability
Machinability
AMS 5612 (Type 410) in the annealed condition rates at approximately 55–65% of the machinability of AISI 1212 free-machining carbon steel — easier to machine than AMS 5655 due to its lower carbon content and absence of refractory carbide-forming elements.
AMS 5655 (Type 422) in the annealed condition machines at approximately 40–50% of AISI 1212, due to hard Mo₂C and VC carbide particles that accelerate tool wear. Carbide-tipped or coated tooling (TiAlN, TiN) is strongly recommended. Near-net-shape forging from Jiangsu Liangyi can significantly reduce machining allowances on large AMS 5655 components, depending on part geometry and final drawing tolerances.
Weldability
- AMS 5612 (Type 410): Preheat to 200–300°C; PWHT at 700–760°C recommended to restore HAZ toughness.
- AMS 5655 (Type 422): Preheat to 250–350°C; PWHT mandatory at 650–700°C for at least 2 hours. Failure to PWHT results in HAZ embrittlement and risk of brittle fracture under cyclic loading.
Application Guide: What Each Grade Is Designed For
Where AMS 5655 (Type 422) Is the Correct Choice
- Gas and steam turbine blading: High-pressure section blades must sustain centrifugal loads at continuous temperatures above 500°C. AMS 5655 was designed specifically for this application.
- Compressor rotor discs and shafts: Large-diameter open-die forgings where fatigue resistance under rotating bending loads and elevated-temperature strength apply simultaneously.
- Boiler valve stems and bodies: Continuous steam service above 500°C where AMS 5612 would soften and creep under sustained mechanical load.
- Aerospace structural forgings: Where AMS traceability, ESR cleanliness, and high-cycle fatigue resistance are all contractual requirements.
- Combined-cycle power plant components: Rotor shaft blanks, turbine blade forgings, and heat exchanger components in continuous high-temperature service.
- Nuclear coolant pump shafts: Where ESR cleanliness, full traceability, and documented elevated-temperature mechanical properties are non-negotiable.
Where AMS 5612 (Type 410) Is the Correct Choice
- Pump components at ambient temperature: Where corrosion resistance and hardness are required but service temperatures remain below 400°C.
- Oil and gas valve trim and seats: Medium-pressure, NACE MR0175 compliant service where Type 410 is approved and cost-effective.
- Structural brackets and fasteners: Where Type 410's lower cost and ease of machining deliver value without compromising service integrity.
- Hydraulic cylinder rods and general shaft applications: Where surface hardness and mild corrosion resistance are required but the 480°C ceiling is never approached.
- Cost-driven high-volume programs: Where engineering confirms the temperature ceiling is not a constraint and the 25–45% material saving at scale is significant.
Cost Considerations
AMS 5655 (Type 422) carries a material premium of approximately 25–45% over AMS 5612 (Type 410) on a per-kilogram basis, driven by the Mo, W, V alloy content and the mandatory AOD + ESR double-melt production route. For applications genuinely requiring AMS 5655, this premium is typically far outweighed by the cost of component failure or unplanned maintenance.
Decision Matrix: Which Grade Should You Specify?
Specify AMS 5655
- Service temperature exceeds 480°C (900°F)
- Sustained strength at elevated temperature required
- Aerospace AMS traceability in contract
- ESR cleanliness level is mandatory
- UTS ≥ 860 MPa after Q+T required
- High-cycle fatigue under rotating/cyclic loads
- Third-party inspection required (can be arranged on request)
- EN 10204-3.2 MTC with countersignature
- Power generation, nuclear, or aerospace projects
Specify AMS 5612
- Service temperature stays below 480°C (900°F)
- General corrosion resistance in mild environments
- Cost-sensitive structural applications
- High-volume programs with material budget constraints
- Single-temper heat treatment is acceptable
- Room-temperature elongation and toughness are priority
- O&G valve trim, pump shafts, general machinery
- Heavy machining required — lower tool wear
Conclusion
AMS 5655 (Type 422) and AMS 5612 (Type 410) are not competing grades — they are complementary grades designed for different service envelopes. The choice between them is driven by a single dominant question: does the application require sustained mechanical performance above 480°C?
If yes, AMS 5655 is the correct specification. Its Mo + W + V carbide network, ESR cleanliness level, and mandatory double-temper heat treatment exist precisely to satisfy that requirement — and no cost-optimization will bridge that performance gap at elevated temperature.
If no, AMS 5612 (Type 410) is a capable, cost-effective choice for structural, corrosion-resistant, and hardened applications at ambient to moderate temperatures.
Jiangsu Liangyi manufactures both grades as open-die forgings, seamless rolled rings, and shaft billets from our ISO 9001:2015 certified facility in Jiangyin, Jiangsu Province, China. For full technical specifications, size range, and MTC documentation requirements, see our dedicated AMS 5655 open-die forging parts page. All forgings ship with EN 10204-3.1 MTCs as standard; 3.2 countersignature is available on request, and third-party inspection (buyer-nominated agency) can be accommodated. Ships to 50+ countries with 4–6 week standard lead times.
Frequently Asked Questions
Request a Free AMS 5655 or AMS 5612 Forging Quotation
ISO 9001:2015 certified. AOD + ESR double-refined AMS 5655 open-die forgings and seamless rolled rings, 30 kg to 30 tons. EN 10204-3.1/3.2 MTC. Third-party inspection (SGS, BV, TÜV, DNV etc.) can be arranged on request. Ships to 50+ countries in 4–6 weeks.