440C Stainless Steel (UNS S44004)
Martensitic (high-carbon) · ASTM A276 · Density 7.75 g/cm³
440C (UNS S44004) is a high-carbon martensitic stainless steel that hardens to 58–60 HRC — the hardest of the standard stainless grades. With about 1% carbon and 17% chromium it combines tool-steel wear resistance with useful corrosion resistance, making it the default stainless for bearings, valve seats, pump parts and premium knife blades.
Chemical Composition (wt%)
| C | Mn | Si | Cr | Mo | P | S |
|---|---|---|---|---|---|---|
| 0.95–1.20 | ≤1.00 | ≤1.00 | 16.0–18.0 | ≤0.75 | ≤0.040 | ≤0.030 |
Single values are maximums unless a range is shown. Balance: Fe. Per ASTM A276.
Mechanical Properties
| Hardness (annealed) | ≤269 HBW |
|---|---|
| Hardness (hardened & tempered) | 58–60 HRC |
| Tensile strength (hardened, typical) | ≈1970 MPa |
| Tensile strength (annealed, typical) | ≈760 MPa |
Room-temperature values are summarized for the product form and condition represented by ASTM A276; confirm section size, delivery condition and current governing edition before ordering.
Physical Properties & Structure
| Density | 7.75 g/cm³ |
|---|---|
| Magnetic response | Magnetic in annealed and hardened conditions. |
| Microstructure | Martensitic (high-carbon) |
Corrosion Resistance & Limits
- Corrosion resistance depends on chromium, carbon, heat-treatment condition and surface finish and is generally below common 304-type austenitic stainless steel.
- Avoid assuming hardness implies corrosion resistance. Chlorides, tempering condition, retained scale and grinding contamination must be evaluated for the part.
Fabrication & Heat Treatment
| Welding | Welding requires grade- and section-specific preheat, filler and post-weld heat treatment to control hard cracking and restore properties. |
|---|---|
| Forming | Carry out substantial forming in the annealed condition and allow for reduced ductility as carbon and target hardness increase. |
| Machining | Machine in the annealed or softened condition where possible; hardened material needs appropriate tooling, speeds and allowance for final grinding. |
| Heat treatment | Final properties depend on a specified austenitize, quench and temper route. Temperature, hold time, section size and required hardness belong on the order. |
Equivalent Grades
The closest international equivalents of 440C Stainless Steel are 1.4125 (X105CrMo17) in the EN system, SUS440C in the JIS system, 102Cr17Mo in the GB system.
These are common corresponding designations, not unconditional substitutes. Verify chemistry, mechanical properties, product standard, delivery condition, dimensions and project approval before changing designation.
| System | Designation |
|---|---|
| UNS | S44004 |
| EN | 1.4125 (X105CrMo17) |
| JIS | SUS440C |
| GB | 102Cr17Mo |
Reference Product Forms & Dimensional Ranges
Common reference product forms for 440c stainless steel: Bar.
| Bar diameter | 3–200 mm |
|---|---|
| Condition | Annealed; hardening & tempering on request |
| Precision | h9 / h11 ground bar available |
Common surface and delivery options: Hot rolled, peeled, bright drawn, ground or polished bar condition according to tolerance.
These published ranges are engineering references, not a live-stock or production-capability promise. Confirm the required product form, dimensions, condition, finish and supply route in the quotation.
Typical Applications
- Rolling-element bearings and races
- Valve seats, balls and needles
- Pump shafts and wear sleeves
- Knife blades and cutting tools
- Surgical and dental instruments
Frequently Asked Questions
What hardness can 440C reach after heat treatment?
Austenitizing at 1010–1065 °C, oil or air quenching, and low-temperature tempering around 160–200 °C gives 58 HRC minimum, typically 58–60 HRC. Higher tempering temperatures trade hardness for toughness but drop corrosion resistance and should stay below 425 °C.
Will 440C rust?
It is the least corrosion resistant of the popular stainless grades because most of its chromium is tied up in carbides. It performs well dry, oiled or in mild atmospheres, but pits in salt spray and prolonged wet exposure — passivation after grinding noticeably improves it.
How does 440C compare with D2 tool steel?
They machine and harden similarly, but 440C is a true stainless with ~17% chromium, while D2 at ~12% Cr is only semi-stainless. D2 holds a working edge slightly longer; 440C stays cleaner in wet or hygienic service. For food-contact cutting tools 440C is the safer specification.
440C Compared With Other Grades
Organizational author: Tsingshan (Shandong) Iron & Steel Co., Ltd..Review method, status and limitations.
Other stainless steel grades:
304304L316316L201321310S4104302205202301309S316Ti347904L409L4204394414442507303317L254 SMO17-4 PH2304
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