Introduction
SUS416 is a martensitic stainless steel — commonly referred to as "stainless iron" — and is recognized as the best free-machining grade among all stainless steels. Its Chinese equivalent is Y1Cr13 (GB/T 1220). The addition of sulfur (S ≥ 0.15%) dramatically improves chip-breaking and cutting performance, making SUS416 the go-to material for high-speed automatic lathe and CNC turning operations where stainless steel is required.
Like SUS410, SUS416 belongs to the chromium martensitic stainless steel family. It is magnetic, heat-treatable, and offers moderate corrosion resistance. After passivation, SUS416 can achieve 48 hours of neutral salt spray (NSS) resistance — adequate for many general-purpose applications.
SUS416's primary trade-off is that its corrosion resistance is slightly lower than austenitic grades such as SUS304, but it compensates with significantly superior machinability and the ability to achieve high hardness through heat treatment — a capability the 300-series austenitic grades do not possess.
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SUS416 Chemical Composition
Reference standard: JIS G4303
| Grade | C (%) | Mn (%) | Si (%) | P (%) | S (%) | Ni (%) | Mo (%) | Cr (%) |
|---|---|---|---|---|---|---|---|---|
| SUS416 | ≤ 0.15 | ≤ 1.25 | ≤ 1.00 | ≤ 0.060 | ≥ 0.15 | ≤ 0.60 | ≤ 0.60 | 12.00–14.00 |
Key feature: The minimum sulfur content (≥ 0.15%) is the defining characteristic of SUS416, distinguishing it from SUS410 (S ≤ 0.03%) and enabling its exceptional machinability. This is the same design principle applied in SUS303 within the austenitic family.
Mechanical Properties
Mechanical Properties (Quenched & Tempered, JIS G4303)
| Property | Value (Q&T) |
|---|---|
| Tensile Strength σb | ≥ 540 MPa |
| Yield Strength σ0.2 | ≥ 343 MPa |
| Elongation δ5 | ≥ 25% |
| Reduction of Area ψ | ≥ 55% |
| Impact Energy Akv | ≥ 98 J |
| Hardness (annealed) | ≤ 200 HB |
| Hardness (Q&T) | ≥ 159 HB |
Heat Treatment
| Process | Temperature | Cooling Method |
|---|---|---|
| Annealing | 800–900 °C | Slow cool; or rapid cool from ~750 °C |
| Hardening (Quenching) | 950–1000 °C | Oil quench |
| Tempering | 700–750 °C | Rapid cool |
Microstructure
SUS416 has a martensitic microstructure. It is magnetic in all conditions.
SUS416 vs SUS410: Key Differences
| Criteria | SUS410 | SUS416 |
|---|---|---|
| Sulfur content | ≤ 0.03% | ≥ 0.15% |
| Machinability | Moderate | Excellent (best in class for stainless) |
| Corrosion resistance | Moderate | Slightly lower than SUS410 |
| Weldability | Limited | Not recommended (sulfur causes hot cracking) |
| Hardness after Q&T | High | High (≥ 159 HB) |
| Typical use | General structural, turbine parts | High-speed CNC turning, precision fasteners |
SUS416 vs SUS303: Choosing the Right Free-Machining Grade
Both SUS416 and SUS303 are free-machining stainless steels with sulfur additions, but they serve different needs:
- SUS303 (austenitic): Better corrosion resistance, non-magnetic, not heat-treatable. Preferred when corrosion resistance is the priority.
- SUS416 (martensitic): Magnetic, heat-treatable to high hardness, slightly lower corrosion resistance. Preferred when high hardness after heat treatment is required alongside good machinability.
Applications of SUS416 Stainless Steel
SUS416 is the preferred stainless steel for high-volume automatic machining operations:
- Precision fasteners — bolts, nuts, screws, and studs produced on automatic lathes and CNC turning centers
- Mechanical components — shafts, bushings, bearings, and gears requiring high hardness
- Cutlery & tools — knife blades, scissors, and cutting instruments (after hardening)
- Pump and valve parts — trim, seats, and shafts in mildly corrosive environments
- Automotive & industrial hardware — structural brackets and fittings where magnetic properties are acceptable
Browse our stainless steel fastener products: Stainless Steel Helical Inserts, Castle Nuts (DIN 935) – A2, and Stainless Steel Wood Screws.
Standards reference: JIS G4303 | ASTM A276/A276M | GB/T 1220
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