English 
| Quantity: | |
|---|---|
Eternal
AISI 440C forged stainless steel is a high-carbon, high-chromium martensitic stainless steel. It contains 0.95%–1.20% carbon and 16.00%–18.00% chromium. It is one of the stainless steels with the highest hardness after heat treatment. After quenching and tempering, its hardness can reach over 58 HRC. Jiangyin Eternal Heavy Industry Co., Ltd. uses electroslag remelting (ESR) or vacuum arc remelting (VAR) to refine steel ingots. It produces them by free forging and isothermal spheroidizing annealing. The carbides are fine, uniform, and evenly spread. It is suitable for valves, shafts, and other mechanical parts that have strict requirements for hardness, wear resistance, and corrosion resistance.
Performance | 440C | Customer value |
Hardness | QT ≥58HRC，cryogenic 59~61HRC | Satisfy high-load and high-maintenance requirements |
Wear resistance | The high-carbon and high-chromium composition forms a large amount of hard carbides, resulting in excellent wear resistance. | Extend the service life of the parts and reduce the frequency of replacements |
Corrosion resistance | With a chromium content of 16 to 18%, it exhibits excellent corrosion resistance in the atmosphere, water, seawater and some acidic and alkaline salt solutions. | Suitable for corrosive environments, eliminating the need for additional coatings |
Dimensional stability | Cooperation with deep cooling treatment can significantly reduce the content of residual austenite. | Precision parts remain undamaged after long-term use. |
High Temperature Performance | Having excellent dimensional stability at high temperatures | Suitable for applications such as corrosion-resistant high-temperature bearings |
Compared with 304/316 austenitic stainless steel: 440C can reach very high hardness through heat treatment (above 58 HRC), while 304/316 cannot be strengthened by heat treatment. Their hardness is only about HRB 80, and they cannot resist wear or carry loads.
Compared with 420/430 martensitic stainless steel: 420 contains about 0.15–0.40% carbon, and its hardness after quenching is only 50–55 HRC. 440C contains close to 1% carbon, has much more carbides, and its wear resistance and maximum hardness are far higher than 420.
Compared with high-speed steel (such as M2): 440C has much better corrosion resistance than high-speed steel. It can work in air, water, and some corrosive environments. It is suitable for applications that need both wear resistance and corrosion resistance.
Element | wt（%） | Function |
C | 0.95~1.20 | Forming a large amount of hard carbides, providing core elements with high hardness and wear resistance |
Cr | 16.00~18.00 | Provide corrosion resistance, forming a passivation film; and also participate in the formation of carbides. |
Mo | 0.40~0.65 | Improve the hardening property and the tempering resistance, enhance the stability of carbides, and improve the corrosion resistance |
Si | ≤1.00 | Dopant element, solid solution strengthening |
Mn | ≤1.00 | Improve hardenability |
P/S | ≤0.040 / ≤0.030 | Impurity elements are strictly controlled to ensure the purity of the material. |
440C is a high-carbon, high-chromium martensitic stainless steel. Its plasticity and thermal conductivity are poor, so its forging difficulty is much higher than that of ordinary stainless steel. The high carbon content makes the material brittle. The forging temperature window is only about 150–200°C, which places very high demands on the operation rhythm. Jiangyin Eternal Heavy Industry Co., Ltd. has built a mature process system through long-term production practice:
Use ESR/VAR refined steel ingots to improve carbide distribution, reduce segregation, and control material purity from the source.
Perform optical emission spectrometry (OES) at incoming inspection to verify composition, and use ultrasonic testing to check for internal defects.
Preheat the billet to 550–650°C, and soak it fully according to the cross-section size to make the core temperature uniform.
Strictly control the initial forging temperature at 1050–1100°C. It is strictly forbidden to exceed 1150°C, so as to avoid coarse grains and excessive δ-ferrite formation.
Use a protective atmosphere furnace throughout heating, and control the decarburized layer (furnace gas dew point -40°C).
The final forging temperature must be higher than 900°C. The ideal range is 950–1000°C. It is absolutely forbidden to forge below 850°C. Otherwise, the material resistance will rise sharply and plasticity will drop greatly, which can easily cause forging cracks.
Adopt the “light-heavy-light” forging principle: use small deformation and a fast pace for light forging at the beginning and end, and use large deformation forging in the middle stage when plasticity is good.
Use a multi-directional repeated upsetting-drawing process. The forging ratio should be ≥4. This fully breaks the eutectic carbide network and breaks coarse continuous network carbides into a fine, dispersed distribution, greatly improving the transverse toughness of the final product.
It is strictly forbidden to cool rapidly in air or on cold ground. Otherwise, the structural stress and thermal stress caused by high-carbon martensite transformation will cause forging cracks.
Immediately after forging, put the forgings into a slow cooling pit or furnace for isothermal spheroidizing annealing.
Typical spheroidizing annealing process: heat to 850–870°C and hold → rapidly cool to 720–750°C and hold for 4–8 hours → furnace cool to 500°C, then air cool. Annealed hardness ≤ HB 255.
Normal annealing: Heat to 850–920°C and slow cool. Annealed hardness ≤269 HB, easy for machining.
Stress relief annealing: Hold at 677–732°C, then air cool or furnace cool.
For large workpieces, two-stage preheating is recommended: preheat at 800°C → second preheat at 1000°C → raise to 1052°C and hold → oil quench.
For small workpieces, the preheating process can be simplified.
Hardness after quenching should be ≥58 HRC.
Immediately after quenching, perform liquid nitrogen cryogenic treatment (-196°C).
It can reduce retained austenite by about 11.7%, increase hardness by 2.3 HRC, and after a 72-hour neutral salt spray test, there is no clear pitting on the surface.
After cryogenic treatment, low-temperature tempering can produce fine secondary carbide precipitation in the matrix, further improving hardness and wear resistance.
Low-temperature tempering: 100–180°C, fast cool. Used for cutting tools, bearings, and other cases requiring high hardness.
Medium-temperature tempering: 200–250°C. Used for structural parts that need a balance of toughness.
Customer pain points | Regular supplier issues | Our solution |
Carbide segregation | The carbides are distributed in a network or band-like pattern, resulting in anisotropic properties. | Multi-directional forging + large forging ratio, dispersion of carbides |
Forge cracking | Improper temperature control led to cracking on the surface or inside of the forging. | Strict temperature window management + Slow cooling system |
Excessive carbon removal layer | The surface decarburization layer of the forging is too thick, resulting in cracking during subsequent heat treatment. | Protective atmosphere heating + post-forging peeling treatment |
Internal porosity / pores | The rate of non-conformity in the flaw detection process is relatively high. | ESR/VAR refining + thorough integration |
Uneven hardness | The hardness dispersion of the same batch of forgings exceeded ±1.5HRC. | Precise temperature control ±5℃ + Uniform furnace loading + Process verification |
Hardening break | The absence of decarburization layer removal led to cracking due to the concentration of quenching stress. | Thorough peeling before heat treatment + graded preheating |
Excessive retained austenite | Size is unstable and it deforms during use. | Deep cold treatment + multiple tempering processes |
Insufficient wear resistance | Improper tempering temperature results in poor morphology of carbides. | Optimizing the tempering process to promote secondary hardening |
440C forged bars are widely used in the following demanding applications:
Bearing industry: rolling bearing rings, balls, rollers — using high hardness and wear resistance to withstand high loads.
Valves and pumps: needle valves, ball valve seats, check valves, pump shafts, pump bodies — dual needs of corrosion resistance and wear resistance.
Cutting tools and medical instruments: surgical blades, industrial scissors, mechanical blades, cutting tools for injection molding components.
Aerospace: high-precision bearings, valve cores, valve bushings in fuel accessories.
Precision machinery: cams, gears, shafts, bushings, wear-resistant textile parts.
Molds: injection mold inserts, wear-resistant structural parts.
Supply forms: round bars (ø5–ø600 mm), forged blanks (open die forging/closed die forging), square bars, flat steel. ESR/VAR double-refined material is available.
What is the difference between 440C and 9Cr18 (95Cr18)? Can they be used interchangeably?
440C is an American standard AISI/SAE grade. 9Cr18 (now 95Cr18) is the corresponding Chinese national standard grade. Their chemical composition is basically the same, so they can be used interchangeably. The main difference is that the control ranges for impurity elements and inspection requirements are slightly different under different standard systems. We can supply according to the standard system specified by the customer.
What quality certification documents can you provide for your 440C forged bars?
The following can be provided with the goods: chemical composition analysis report (spectral testing), mechanical property test report (hardness, tensile), ultrasonic testing report (according to ASTM A388 or GB/T 6402), metallographic structure inspection report (carbide distribution rating), and heat treatment curve records. If third-party testing (SGS/BV, etc.) is required, it can be arranged separately.
What are the most common problems with 440C forgings in use? How can they be avoided?
The two most common problems are heat treatment cracking and uneven hardness. Cracking mainly comes from the decarburized layer on the forging surface not being removed. During quenching, the surface and core structure transformation is not synchronized, causing stress concentration. Uneven hardness is related to heating temperature deviation, furnace loading method, and cooling rate. Our suggestions are: before heat treatment, be sure to remove the decarburized layer (recommended single-side removal ≥2 mm); use stage preheating for quenching; for large cross-section parts, oil quenching is recommended instead of air cooling
