Steel 9Cr18Mo
GB 9Cr18Mo · AISI/SAE 440C · JIS SUS440C
9Cr18Mo is a high-carbon martensitic stainless bearing steel, the GB grade corresponding to AISI 440C and JIS SUS440C, hardened by carbon-rich chromium carbides in a martensitic matrix.
Reference datasheet — 9Cr18Mo is not in the instant-quote catalog. Upload your part and an engineer will quote it in this grade or suggest the closest stocked equivalent.
Values for the QT58-60 condition
9Cr18Mo tempers and conditions
9Cr18Mo is supplied in 6 conditions, soft to hard. QT58-60 is the default FabDigit quotes; the values on this page are for it.
Compare all 6 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Solution annealed | Supply state for bar, wire and forging stock that will be machined then hardened. | 450 | 760 | 14 | 25 HRC | — |
Cold drawn | Pick for precision-ground/drawn bar and ball-blank wire needing tight tolerance before hardening. | 660 | 880 | 9 | 29 HRC | 2.9 % IACS |
Q&T 48–52 HRC | Use when parts see 300–450 °C service or need more toughness than a low-temper bearing hardness; corrosion resistance is reduced by the high temper. | 1,550 | 1,700 | 3 | 50 HRC | — |
Q&T 55–57 HRC | Compromise hardness for knives, valve seats and shafts where a little more toughness than 60 HRC is wanted. | 1,750 | 1,860 | 3 | 56 HRC | — |
QT58-60Default Q&T 58–60 HRC | Standard bearing/knife condition: maximum wear resistance and best corrosion resistance of the hardened states. | 1,900 | 1,970 | 2 | 59 HRC | — |
Q&T + sub-zero 60–62 HRC | Choose for maximum hardness and dimensional stability (precision bearings, gauges) at the cost of toughness. | 1,950 | 2,050 | 1.5 | 61 HRC | — |
What is 9Cr18Mo?
9Cr18Mo is a high-carbon martensitic stainless bearing steel, the GB grade corresponding to AISI 440C and JIS SUS440C, hardened by carbon-rich chromium carbides in a martensitic matrix. Engineers select it when a bearing or wear part needs both high hardness and corrosion resistance; hardened bar and rings reach 59 HRC with about 1970 MPa tensile, 1900 MPa yield and 2 % elongation, at a maximum service temperature of 425 °C. Ductility, machinability (rating 10) and toughness are all low, and corrosion resistance (score 55) is below that of austenitic stainless. Use 52100 where corrosion is not a factor. 9Cr18Mo has a density of 7.7 g/cm³ (0.278 lb/in³), lighter than 95% of steel grades. It melts at 1,370°C (2,498 °F). 9Cr18Mo has a yield strength of 1,900 MPa (276 ksi) and a tensile strength of 1,970 MPa (286 ksi) — stronger than 100% of steel grades. Elongation at break is 2% and the elastic modulus is 200 GPa (29 Msi).
What is 9Cr18Mo used for?
- Stainless bearings
- Precision instrument bearings
- Corrosion-resistant rollers
Advantages
- High strength — 1,900 MPa (276 ksi), better than 100% of steel grades
- Good corrosion resistance — 55/100, better than 99% of steel grades
- Polishes to a fine finish — 78/100, better than 95% of steel grades
Limitations
- Limited ductility — 2%, worse than 99% of steel grades
- Difficult to machine — 10/100, worse than 99% of steel grades
- Limited formability — 5/100, worse than 99% of steel grades
- Low fracture toughness — 22 MPa·√m (20 ksi·√in), worse than 98% of steel grades
- Difficult to weld — 12/100, worse than 96% of steel grades
9Cr18Mo properties
Typical room-temperature values for 9Cr18Mo-QT58-60; bars are the position among steel grades.
Physical3
9Cr18Mo has a density of 7.7 g/cm³ (0.278 lb/in³), lighter than 95% of steel grades. It melts at 1,370°C (2,498 °F).
Mechanical15
9Cr18Mo has a yield strength of 1,900 MPa (276 ksi) and a tensile strength of 1,970 MPa (286 ksi) — stronger than 100% of steel grades. Elongation at break is 2% and the elastic modulus is 200 GPa (29 Msi).
Thermal6
9Cr18Mo is rated for continuous service to 425°C (797 °F). It conducts heat at 24.2 W/m·K (14 BTU/hr·ft·°F), worse than 89% of steel grades. Thermal expansion is 10.2 µm/m·K (5.67 µin/in·°F).
Electrical3
9Cr18Mo conducts electricity at 2.9 % IACS, worse than 93% of steel grades.
Chemical & Environmental3
Corrosion resistance is good (55/100), better than 99% of steel grades.
Sustainability4
Producing a kilogram of 9Cr18Mo takes about 55 MJ of energy and emits 4.5 kg of CO₂ — more than 94% of steel grades. Typical recycled content is 30%.
Manufacturability8
9Cr18Mo's machinability is not recommended (10/100, worse than 99% of steel grades); weldability not recommended (12/100); formability not recommended (5/100).
Common Calculations5
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Strength versus weight in the steel family
Yield strength against density for every steel grade FabDigit runs. 9Cr18Mo is highlighted; hover a dot for its name, or open the interactive family chart.
Working with 9Cr18Mo
Is 9Cr18Mo easy to machine?
Machine only in the annealed state with rigid setups, sharp carbide tooling, low speed and heavy coolant; at 58–60 HRC use grinding, hard turning with CBN or EDM.
Can 9Cr18Mo be welded?
Effectively non-weldable for structural joints — high carbon martensite cracks; if unavoidable, preheat 200–300 °C, use 410NiMo/austenitic filler and re-anneal or re-harden afterwards.
Can 9Cr18Mo be formed, bent or molded?
Hot work 1050–1150 °C with slow cooling and immediate spheroidize anneal (840–880 °C, slow cool); cold forming is limited to light heading/coining of annealed wire.
9Cr18Mo chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| Csome GB/T 1220 revisions allow up to 1.20 % | 0.95 – 1.1 | 1 |
| Cr | 16 – 18 | 17 |
| Mo | 0.4 – 0.7 | 0.55 |
| Si | ≤ 0.8 | 0.4 |
| Mn | ≤ 0.8 | 0.4 |
| Niresidual | ≤ 0.3 | |
| Curesidual | ≤ 0.25 | |
| P | ≤ 0.03 | |
| S | ≤ 0.03 | |
| Fe | balance |
What surface finishes work on 9Cr18Mo?
Harden before finishing, then passivate (citric or nitric per ASTM A967) after grinding/polishing to restore the chromium oxide film; hard chrome, PVD nitride coatings and black oxide are all common.
Surface treatments FabDigit runs on steel parts — pick them in the quote configurator or call them out on the drawing. Each links to its datasheet in the surface-finish library (thickness, specs, call-out, material verdicts).
Organic Coating
Black / Phosphate
Thermal Spray
Equivalent designations
Standards and trade names that resolve to Steel 9Cr18Mo in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- AISI / SAE
- 440C
- JIS
- SUS440C
How much does 9Cr18Mo cost?
9Cr18Mo is a premium-cost steel ($$$), cheaper than about 51% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
9Cr18Mo — frequently asked
What is 9Cr18Mo used for?
9Cr18Mo is typically used for stainless bearings, precision instrument bearings and corrosion-resistant rollers. In short: hardest stainless bearing steel; corrosion-resistant 440C equivalent; very poor machinability.
What is the yield strength of 9Cr18Mo?
9Cr18Mo has a typical yield strength of 1,900 MPa (276 ksi) and a tensile strength of 1,970 MPa (286 ksi) — stronger than 100% of steel grades. Strength varies by condition: see the 6 listed tempers.
Is 9Cr18Mo easy to machine?
Not especially — machinability is rated not recommended (10/100, worse than 99% of steel grades). Machine only in the annealed state with rigid setups, sharp carbide tooling, low speed and heavy coolant; at 58–60 HRC use grinding, hard turning with CBN or EDM.
Can 9Cr18Mo be welded?
Not readily — weldability is rated not recommended (12/100). Effectively non-weldable for structural joints — high carbon martensite cracks; if unavoidable, preheat 200–300 °C, use 410NiMo/austenitic filler and re-anneal or re-harden afterwards.
What surface finishes work on 9Cr18Mo?
Harden before finishing, then passivate (citric or nitric per ASTM A967) after grinding/polishing to restore the chromium oxide film; hard chrome, PVD nitride coatings and black oxide are all common.
Can 9Cr18Mo be formed, bent or molded?
Hot work 1050–1150 °C with slow cooling and immediate spheroidize anneal (840–880 °C, slow cool); cold forming is limited to light heading/coining of annealed wire.
What is the maximum service temperature of 9Cr18Mo?
9Cr18Mo is rated for continuous use to about 425°C (797 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between 9Cr18Mo QT58-60 and 9Cr18Mo-A?
QT58-60 is the default condition — standard bearing/knife condition: maximum wear resistance and best corrosion resistance of the hardened states. A: supply state for bar, wire and forging stock that will be machined then hardened. Yield strength is 1,900 MPa in QT58-60 versus 450 MPa in A.
How much does 9Cr18Mo cost?
9Cr18Mo is a premium-cost steel ($$$), cheaper than about 51% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
Sources
- GB/T 1220 (2007)
- ASTM A276 / ASTM A756 (440C stainless bar and bearing steel) — ASTM International (2017)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels, and High-Performance Alloys (440C) — ASM International (1990)
- ASM Handbook Vol.19 — Fatigue and Fracture — ASM International (1996)
- 440C / X105CrMo17 martensitic stainless datasheets — Böhler / Sandvik / Outokumpu (2021)
Property data is compiled from published supplier and standards handbooks and normalised for comparison; hardness values on non-Brinell scales are converted approximately for charting only. Manufacturability limits are FabDigit quote-engine defaults and may be relaxed by engineering review. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.