Steel 9Cr18Mo QT55-57
Hardness band
GB 9Cr18Mo · AISI/SAE 440C · JIS SUS440C
QT55-57 = q&T 55–57 HRC
Compromise hardness for knives, valve seats and shafts where a little more toughness than 60 HRC is wanted.
Values for the QT55-57 condition
Other 9Cr18Mo tempers and conditions
9Cr18Mo is listed in 6 conditions; see the grade overview at 9Cr18Mo.
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 | — |
QT55-57This page 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 QT55-57?
9Cr18Mo QT55-57 is 9Cr18Mo heat treated to QT55-57 — compromise hardness for knives, valve seats and shafts where a little more toughness than 60 HRC is wanted. 9Cr18Mo QT55-57 has a yield strength of 1,750 MPa (254 ksi) and a tensile strength of 1,860 MPa (270 ksi) — stronger than 99% of steel grades. Elongation at break is 3% and the elastic modulus is 200 GPa (29 Msi). 9Cr18Mo QT55-57 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). QT58-60 is the default condition FabDigit quotes; QT55-57 is available on request or by drawing note.
Advantages
- High strength — 1,750 MPa (254 ksi), better than 99% of steel grades
- Good corrosion resistance — 50/100, better than 99% of steel grades
- Polishes to a fine finish — 78/100, better than 95% of steel grades
Limitations
- Limited ductility — 3%, 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 — 24 MPa·√m (21.8 ksi·√in), worse than 98% of steel grades
- Difficult to weld — 12/100, worse than 96% of steel grades
9Cr18Mo QT55-57 properties
Typical room-temperature values for 9Cr18Mo QT55-57; 11 are specific to this condition. Other listed values are 9Cr18Mo reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
9Cr18Mo QT55-57 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 QT55-57 has a yield strength of 1,750 MPa (254 ksi) and a tensile strength of 1,860 MPa (270 ksi) — stronger than 99% of steel grades. Elongation at break is 3% and the elastic modulus is 200 GPa (29 Msi).
Thermal6
9Cr18Mo QT55-57 is rated for continuous service to 250°C (482 °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 QT55-57 conducts electricity at 2.9 % IACS, worse than 93% of steel grades.
Chemical & Environmental3
Corrosion resistance is fair (50/100), better than 99% of steel grades.
Sustainability4
Producing a kilogram of 9Cr18Mo QT55-57 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 QT55-57's machinability is not recommended (10/100, worse than 99% of steel grades); weldability not recommended (12/100); formability not recommended (5/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with 9Cr18Mo QT55-57
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.
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.
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 | — |
9Cr18Mo QT55-57 — frequently asked
What is 9Cr18Mo QT55-57 used for?
9Cr18Mo QT55-57 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 QT55-57?
9Cr18Mo QT55-57 has a typical yield strength of 1,750 MPa (254 ksi) and a tensile strength of 1,860 MPa (270 ksi) — stronger than 99% of steel grades. Strength varies by condition: see the 6 listed tempers.
Is 9Cr18Mo QT55-57 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 QT55-57 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 QT55-57?
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 QT55-57 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 QT55-57?
9Cr18Mo QT55-57 is rated for continuous use to about 250°C (482 °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.
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. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.