ASTM A743 CA6NM is a martensitic hindi kinakalawang na asero casting grade specifically engineered to deliver high strength, paglaban sa kaagnasan, and toughness in severe service environments.
With its 12–14% chromium and 3–4% nickel composition, CA6NM achieves a balanced microstructure that offers superior resistance to cavitation, erosion, and pitting while maintaining excellent weldability compared to other martensitic stainless steels.
This alloy has become a material of choice for hydroturbine runners, Mga Impeller ng Bomba, offshore platform components, and valve bodies, where a combination of structural reliability and environmental resilience is mandatory.
1. What is ASTM A743 CA6NM?
ASTM A743 CA6NM is a martensitic stainless steel paghahagis ng mga grade na ba designed for service in environments requiring high mechanical strength, mahusay na katigasan, and moderate-to-high corrosion resistance.
The “CA” denotes a corrosion-resistant alloy in ASTM casting standards, “6” refers to the alloy series, and “NM” indicates the presence of nickel and molybdenum for enhanced corrosion resistance.
It is widely recognized for its balance of machinability, weldability, and resistance to environmental degradation, making it unique among martensitic grades.
2. Chemical Composition of CA6NM
CA6NM is a 12% kromo, 4% nikel, 0.5% molybdenum martensitic stainless steel developed to combine lakas ng loob, tigas na tigas, at paglaban sa kaagnasan in a single casting alloy.
Its composition is tightly controlled under ASTM A743/A743M to ensure consistent metallurgical performance.
Typical chemical composition limits (% sa pamamagitan ng timbang):
| Elemento | Specification Range (%) | Tungkulin sa Pag-andar |
| Carbon (C) | ≤ 0.06 | Low carbon minimizes carbide precipitation, enhancing toughness and weldability. |
| Mga mangganeso (Mn) | ≤ 1.00 | Improves hot working characteristics and deoxidation during melting. |
| Silicon (Si Si) | ≤ 1.00 | Gumaganap bilang isang deoxidizer; excessive amounts may reduce toughness. |
| Chromium (Cr) | 11.5 – 14.0 | Primary element for passivation and corrosion resistance. |
| Nikel (Ni) | 3.50 – 4.50 | Stabilizes martensite, improves toughness, and enhances resistance to stress corrosion cracking. |
| Molibdenum (Mo) | 0.40 – 1.00 | Boosts pitting resistance, particularly in chloride-containing environments. |
| Posporus (P) | ≤ 0.04 | Kept low to prevent embrittlement. |
| Sulfur (S) | ≤ 0.03 | Low levels maintain toughness and corrosion resistance. |
| Bakal na Bakal (Fe) | Balanse | Matrix element providing structural strength. |
3. Mekanikal & Physical Properties of CA6NM
CA6NM is engineered to deliver a balanced combination of strength, ductility, and fracture toughness, even in large section castings.
Its properties are the result of its 12Cr–4Ni–Mo martensitic composition pinagsama sa controlled heat treatment.
Typical Mechanical Properties
(Values per ASTM A743/A743M requirements; actual results depend on section size, paggamot ng init, and test orientation)
| Pag-aari | Tipikal na Halaga | Test Condition |
| Lakas ng Paghatak (Rm) | 655–795 MPa (95–115 ksi) | Room temperature, tempered martensite |
| Yield Lakas (Rp0.2) | ≥ 450 MPa (65 ksi) | Same as above |
| Pagpapahaba | ≥ 15% | Gauge length = 50 mm |
| Reduction of Area | ≥ 35% | Room temperature |
| Charpy V-Notch Impact Energy | 40–80 J at –46°C (–50°F) | Longitudinal direction |
| Ang katigasan ng ulo | 207–255 HB (Humigit-kumulang. 22–26 HRC) | After tempering |
| Fracture Toughness (K_IC) | ~110–130 MPa·√m | Room temperature, fine-grained condition |
Typical Physical Properties
| Pag-aari | Tipikal na Halaga | Mga Tala |
| Densidad ng katawan | 7.74 g/cm³ (0.280 lb/in³) | Slightly lower than carbon steels due to alloying |
| Modulus ng Pagkalastiko | 200 GPa (29 × 10⁶ psi) | Comparable to other stainless steels |
| Thermal kondaktibiti | ~24 W/m·K at 100°C | Mas mababa kaysa sa carbon steels; nakakaapekto sa pagwawaldas ng init |
| Tiyak na Kapasidad ng Init | 460 J/kg· K | At 20°C |
| Electrical Resistivity | 0.60 μΩ·m | Mas mataas kaysa sa carbon steels, beneficial for some erosion resistance |
| Koepisyent ng Thermal Expansion | 10.8 × 10⁻⁶ /°C (20-100 ° C) | Must be considered in multi-metal assemblies |
4. Paggamot ng Heat & Kontrol ng Microstructure
CA6NM derives its performance not only from its 12% kromo, 4% nikel, and molybdenum chemistry, but also from precise heat treatment sequences that transform its as-cast structure into a matigas ang ulo, tempered martensitic microstructure.
This transformation is essential to achieving the alloy’s targeted balance of lakas ng loob, ductility, paglaban sa kaagnasan, at dimensional na katatagan.
Standard Heat Treatment Sequence
The typical heat treatment for CA6NM castings follows ASTM A743/A743M guidelines and is tailored to section thickness:
Solusyon sa Pagsusubo (Awteritisismo):
- Temperatura: 1010-1050 ° C (1850–1920 °F)
- Layunin: Dissolves carbides and homogenizes alloying elements. Produces a fully austenitic structure before quenching.
- Oras ng Hold: ~1 hour per 25 mm (1 inch) ng kapal ng seksyon, minimum of 2 mga oras.
Pagpapawi:
- Katamtaman: Forced air or oil, depending on casting section size and desired cooling rate.
- Layunin: Transforms austenite to low-carbon martensite while minimizing distortion and residual stresses.
- Tala: Nickel content in CA6NM lowers the martensite start (M_s) temperatura, promoting uniform transformation.
Paghina ng loob:
- Temperatura: 565–620 °C (1050–1150 °F) for standard balance of strength and toughness.
- Layunin: Relieves stresses, Nagpapabuti ng ductility, and adjusts hardness to 22–26 HRC.
- Epekto ng Temperatura: Lower tempering temperatures yield higher strength but reduce impact toughness; higher temperatures improve toughness but slightly lower yield strength.
Microstructure Characteristics
A properly heat-treated CA6NM casting exhibits:
- Tempered Martensite Matrix: Provides high tensile and yield strength with good fracture toughness.
- Refined Grain Size: Nickel addition suppresses grain growth during austenitizing, aiding in high impact energy retention.
- Dispersed Carbides: Fine M₂₃C₆ carbides along lath boundaries improve wear resistance without severely impairing toughness.
- Minimal Retained Austenite (<5%): Excessive retained austenite can lower hardness and dimensional stability, so cooling rates and tempering cycles are carefully controlled.
5. Paghahagis, Machining & Weldability
CA6NM’s value as a hydroturbine, valve, and pump alloy depends not only on its chemistry and heat treatment, but also on its pagiging castable, machinability, and repair weldability.
Casting Processes
CA6NM can be successfully produced using multiple foundry methods, allowing manufacturers to match process capabilities to part geometry, dimensional requirements, at dami ng produksyon.
buhangin paghahagis:
- Pinakamahusay na angkop para sa malaki ang, thick-walled components such as turbine casings, Mga pabahay ng pump, and valve bodies in the 1–5 ton range.
- Mga tipikal na tolerance: ±1 mm per 100 mm sukat.
- Email Address *: Ra 6.3–12.5 μm after shakeout.
- Mga kalamangan: High flexibility in size and shape; economical for low-to-medium volumes.
Pamumuhunan sa Paghahagis (Nawala ang wax):
- Perpekto para sa masalimuot na geometries like turbine blades, valve trims, and runner segments where smooth surfaces and fine detail are critical.
- Dimensional katumpakan: ±0.1 mm.
- Email Address *: Ra 1.6–3.2 μm, reducing machining allowance and improving as-cast hydraulic efficiency.
Centrifugal Casting:
- Gumagawa ng cylindrical or ring-shaped components such as pump sleeves, wear rings, and bearing shells.
- Tinitiyak ang uniform density and minimal segregation—critical for high-pressure sealing surfaces.
- Often used for parts requiring concentricity tolerances within 0.25 mm.
Casting yield rates for CA6NM generally exceed 85% for simple geometries, while more complex shapes with deep pockets or thick-to-thin transitions may drop to 70–75% due to shrinkage cavity management and riser design limitations.
Machining Behavior
CA6NM is significantly easier to machine than fully hardened martensitic steels, especially in the tempered condition (22–26 HRC).
Key machining notes:
- Mga Bilis ng Pagputol: ~30–50 m/min with carbide tooling; hanggang sa 80 m/min with coated carbides in finishing passes.
- Tool Wear: Moderate—nickel improves toughness but can cause work hardening if feeds are too light.
- Coolant Use: Recommended for surface finish consistency and thermal stability.
- Katatagan ng Dimensyon: Low retained austenite content means minimal distortion after rough machining.
- Machining Allowances: 3–6 mm is typical to remove surface scale and casting skin after heat treatment.
Weldability
CA6NM is more weldable than conventional 410 hindi kinakalawang dahil sa:
- Mababang carbon na nilalaman (≤0.06%)
- Nickel addition (~4%) stabilizing austenite during cooling
- Lower risk of hydrogen cracking when preheat and post-weld heat treatment are applied
Best practices for welding:
- Preheating: 150-250 ° C (300–480 °F) to reduce thermal gradients and hydrogen cracking risk.
- Filler Metal Selection: Matching composition filler (hal., AWS ER410NiMo for GTAW/GMAW or E410NiMo for SMAW) to maintain strength and corrosion resistance.
- Interpass Temperature: < 250 °C (480 °F) to avoid over-tempering adjacent heat-affected zones.
- Post-Weld Heat Treatment (PWHT): Local or full tempering at 565–620 °C (1050–1150 °F) to restore toughness and hardness uniformity.
Repair welding:
- Common in large hydroturbine runners or valve bodies to correct porosity or surface defects.
- Success depends on strict control of welding parameters, joint cleanliness, and PWHT application.
6. Paglaban sa kaagnasan: Tailored to Aqueous Environments
CA6NM’s corrosion resistance is engineered for freshwater, tubig dagat, and mild chemical environments, making it far more resistant than carbon steel or low-alloy castings, and competitive with some austenitic grades in specific scenarios:
- Freshwater and Steam: The chromium oxide layer resists oxidation and pitting in freshwater (hal., river water, coolant systems) with corrosion rates <0.02 mm / taon.
It also withstands wet steam at 200–300°C, a key trait for power plant components. - Tubig dagat: Molybdenum additions enhance resistance to chloride-induced pitting.
In seawater immersion tests, CA6NM exhibits a corrosion rate of 0.05–0.1 mm/year—superior to 410 hindi kinakalawang na asero (0.2–0.3 mm/year) but slightly less than 316 (0.01–0.03 mm/year). - Mild Chemicals: Resists dilute acids (hal., 5% Sulpuriko acid), alkalis (hal., 10% Sodium hydroxide), and petroleum products, making it suitable for oilfield valves and chemical processing pumps.
Limitations exist: CA6NM is not recommended for strong acids (hal., 37% hydrochloric acid) or high-chloride environments (hal., brines with >10% NaCl), where austenitic grades like CF8M (316 equivalent) perform better.
7. Typical Applications of CA6NM
ASTM A743 CA6NM’s mataas na lakas, excellent toughness at low temperatures, at paglaban sa kaagnasan, cavitation, and erosion make it the go-to material for critical hydraulic, marine, and energy sector components.
| Application Sector | Typical Components | Key Performance Requirements Met by CA6NM |
| Hydropower | Turbine runners (Kaplan, Francis, bulb), wicket gates, guide vanes, stay rings | High cavitation resistance, erosion resistance, toughness at low temperature |
| Marine & Malayo sa pampang | Mga blades ng propeller, Mga Hub, rudder stocks, pump shafts, seawater valve bodies | Seawater corrosion resistance, good fatigue strength, low magnetic permeability |
| Langis & Gas | Subsea pump impellers, Mga manggas, gate/globe/check valve trim, choke valves | Chloride stress corrosion resistance, erosion resistance, mataas na lakas |
| Industrial Pumping | Centrifugal pump impellers, wear rings, mga casings, diffuser plates | Email Address *, corrosion resistance in brackish water and chemicals |
| Mga Halaman ng Desalination | High-pressure pump shafts, mga impeller, sealing rings | Resistance to chloride-induced pitting, dimensional na katatagan |
| Tidal & Renewable Energy | Tidal turbine blades, Mga Hub, mga shaft | Combined erosion and chloride corrosion resistance, pangmatagalang tibay |
| pagtatanggol / Naval | Submarine propellers, shaft liners, steering gear components | Low magnetic signature, cavitation resistance, mekanikal na pagiging maaasahan |
8. Comparisons: CA6NM vs CA15 (410), 17-4PH, Duplex 2205
| Pag-aari / Tampok | CA6NM (ASTM A743) | CA15 (410 SS) (ASTM A743) | 17-4PH (ASTM A747 CB7Cu-1) | Duplex 2205 (ASTM A890 Grade 4A) |
| Uri ng / Microstructure | Martensitiko (mababang C, 12Cr + Ni) | Martensitiko (high C, 12Cr) | Precipitation-hardening martensitic | Ferritic-austenitic (Duplex) |
| Tipikal na komposisyon (wt%) | C ≤ 0.06, Cr 11.5–14, Ni 3.5–4.5, Mo 0.4–1.0 | Cr 11.5–14, Ni ≤ 1.0, C 0.15 | C ≤ 0.07, Cr 15–17, Ni 3–5, Cu 3–5 | C ≤ 0.03, Cr 21–23, Ni 4.5–6.5, Mo 2.5–3.5 |
| Lakas ng Paghatak (MPa) | 655–760 | 550–690 | 930–1,100 | 620–880 |
| Yield Lakas (MPa) | 450–550 | 350–450 | 725–1,035 | 450–620 |
| Pagpapahaba (%) | 15–20 | 10–15 | 8–12 | 20–25 |
| Ang katigasan ng ulo (HB) | 200–240 | 180–230 | 300–360 | 220–270 |
| Toughness at 0°C (J) | Napakahusay (≥ 40) | Makatarungan (10–20) | Katamtaman (20–30) | Napakahusay (≥ 60) |
| Paglaban sa kaagnasan | Good in fresh/seawater, resists cavitation | Makatarungan, prone to pitting in chlorides | Mabuti na lang, but not for severe chloride environments | Excellent chloride and pitting resistance |
| Cavitation Resistance | Mataas na | Mababa ang | Katamtaman | Mataas na |
| Paggamot ng Heat | Solution anneal + pag-uugali | Tempering only | Solusyon + pagtanda | Solution anneal only |
| Katatagan | Mabuti na lang, suitable for sand & pamumuhunan paghahagis | Good for sand casting | Katamtaman, more complex due to precipitation hardening | Katamtaman, requires precise control |
| Weldability | Mabuti na lang, but requires pre/post heat treatment | Katamtaman, prone to cracking | Mabuti na lang, but post weld aging required | Mabuti na lang, sensitive to intermetallics |
| Machinability | Katamtaman | Mabuti na lang | Makatarungan | Katamtaman |
| Antas ng Gastos | Katamtaman | Mababa ang | Mataas na | Mataas na |
| Mga Karaniwang Aplikasyon | Hydraulic turbines, Mga Impeller ng Bomba, mga propeller ng dagat | General pump parts, low-duty valves | Aerospace, high-strength shafts | Offshore structures, desalination equipment |
9. Common Equivalents
CA6NM’s unique balance of strength, tigas na tigas, and corrosion resistance positions it among several related martensitic stainless steels. Its common equivalents in other standards or grades include:
- UNS J91660: Unified Numbering System designation for CA6NM.
- ASTM A297 Type CA6NM: An alternative ASTM designation for similar castings.
- EN 1.4528 / X12CrNiSi17-7: European equivalent martensitic stainless steel grade, used in casting or forging.
- JIS SUS630: Japanese equivalent precipitation hardening stainless steel, shares some similar applications though differing in microstructure.
- CA15 (ASTM A743 CA15): A higher carbon martensitic grade with similar chemistry but different mechanical and toughness profiles.
10. Pangwakas na Salita
ASTM A743 CA6NM offers a proven balance of strength, paglaban sa kaagnasan, at tigas na tigas that makes it indispensable in demanding rotating machinery and marine/offshore applications.
Its enhanced weldability and cavitation resistance allow for longer service life and reduced maintenance downtime—making it a cost-effective choice for severe environments.
Mga FAQ
Is CA6NM magnetic?
Oo nga, it is martensitic and exhibits magnetic properties.
Is CA6NM suitable for seawater immersion?
No—its pitting corrosion rate (0.1–0.2 mm/year) makes it unsuitable for long-term seawater exposure. Use duplex 2205 sa halip.
What is the maximum temperature for CA6NM?
It retains useful strength up to 400°C. Above 500°C, oxidation and softening occur; use nickel-based alloys for higher temps.
Can CA6NM be used in food processing?
No—its moderate corrosion resistance and potential for pitting in acidic foods make austenitic grades (hal., CF8) better.
How does CA6NM compare to 17-4PH in strength?
17-4PH offers higher tensile strength (860–1100 MPa) but is less castable; CA6NM is preferred for complex castings.
What is the typical lead time for CA6NM castings?
4–8 weeks for sand castings; 6–12 weeks for investment castings (due to mold making).
