Steel 9Cr18 QT55-58
Hardness band
EN 9Cr18 · UNS S44004 · AISI/SAE 440B
QT55-58 = q&T 55–58 HRC
Standard working condition for corrosion-resistant bearing rings, balls, rollers and valve seats.
Values for the QT55-58 condition
Other 9Cr18 tempers and conditions
9Cr18 is listed in 7 conditions; see the grade overview at 9Cr18.
Compare all 7 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
ADefault Solution annealed | Standard as-supplied bar/ring blank condition: soft enough to turn, drill and cold-form before hardening. | 450 | 760 | 18 | 225 HB | — |
hot rolled and annealed bar/ring blank | Cheapest mill condition for large-diameter bar and forged/rolled bearing ring blanks that will be machined and hardened. | 460 | 780 | 16 | 22 HRC | 2.9 % IACS |
Cold drawn | Choose for close-tolerance small-diameter bar and ball/roller wire feedstock with a bright drawn surface. | 700 | 900 | 10 | 28 HRC | 2.9 % IACS |
Q&T 48–52 HRC | Used for shafts, pump/valve parts and cutlery-type items needing better toughness and stability to ~300 °C, at the cost of hardness and some corrosion resistance. | 1,450 | 1,650 | 5 | 50 HRC | — |
Q&T stabilized | Pick when the bearing or valve part runs continuously at 150–200 °C and must not grow dimensionally. | 1,680 | 1,860 | 4 | 56 HRC | 2.8 % IACS |
QT55-58This page Q&T 55–58 HRC | Standard working condition for corrosion-resistant bearing rings, balls, rollers and valve seats. | 1,740 | 1,930 | 3 | 57 HRC | — |
Q&T + sub-zero 58–60 HRC | Maximum hardness and dimensional stability for precision balls and instrument bearings; toughness is lowest. | 1,830 | 2,000 | 2 | 59 HRC | — |
What is 9Cr18 QT55-58?
9Cr18 QT55-58 is 9Cr18 heat treated to QT55-58 — standard working condition for corrosion-resistant bearing rings, balls, rollers and valve seats. 9Cr18 QT55-58 has a yield strength of 1,740 MPa (252 ksi) and a tensile strength of 1,930 MPa (280 ksi) — stronger than 99% of steel grades. Elongation at break is 3% and the elastic modulus is 200 GPa (29 Msi). 9Cr18 QT55-58 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). A is the default condition FabDigit quotes; QT55-58 is available on request or by drawing note.
Advantages
- High strength — 1,740 MPa (252 ksi), better than 99% of steel grades
- Polishes to a fine finish — 85/100, better than 99% of steel grades
- Good corrosion resistance — 48/100, better than 98% of steel grades
Limitations
- Limited ductility — 3%, worse than 99% of steel grades
- Difficult to machine — 10/100, worse than 99% of steel grades
- Difficult to weld — 8/100, worse than 99% of steel grades
- Limited formability — 3/100, worse than 99% of steel grades
- Limited service temperature — 180°C (356 °F), worse than 98% of steel grades
9Cr18 QT55-58 properties
Typical room-temperature values for 9Cr18 QT55-58; 18 are specific to this condition. Other listed values are 9Cr18 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
9Cr18 QT55-58 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
9Cr18 QT55-58 has a yield strength of 1,740 MPa (252 ksi) and a tensile strength of 1,930 MPa (280 ksi) — stronger than 99% of steel grades. Elongation at break is 3% and the elastic modulus is 200 GPa (29 Msi).
Thermal6
9Cr18 QT55-58 is rated for continuous service to 180°C (356 °F). It conducts heat at 24 W/m·K (13.9 BTU/hr·ft·°F), worse than 90% of steel grades. Thermal expansion is 10.4 µm/m·K (5.78 µin/in·°F).
Electrical3
9Cr18 QT55-58 conducts electricity at 2.9 % IACS, worse than 93% of steel grades.
Chemical & Environmental3
Corrosion resistance is fair (48/100), better than 98% of steel grades.
Sustainability4
Producing a kilogram of 9Cr18 QT55-58 takes about 50 MJ of energy and emits 3.4 kg of CO₂ — more than 93% of steel grades. Typical recycled content is 40%.
Manufacturability8
9Cr18 QT55-58's machinability is not recommended (10/100, worse than 99% of steel grades); weldability not recommended (8/100); formability not recommended (3/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with 9Cr18 QT55-58
Is 9Cr18 easy to machine?
Machine only in the annealed condition with sharp carbide tools, rigid setups, low-to-moderate speed and heavy coolant; hardened parts (55–60 HRC) must be ground, EDM'd or hard-turned with CBN.
Can 9Cr18 be welded?
Not recommended for structural joints — high carbon gives hard, crack-prone martensite; if unavoidable, preheat 200–300 °C, use matching or 309/310 filler and immediately anneal or temper.
Can 9Cr18 be formed, bent or molded?
Only light cold forming/bending in the annealed state (large radii, no sharp bends); hot work 1100→900 °C with slow cooling and mandatory post-forging anneal to avoid quench cracking.
What surface finishes work on 9Cr18?
Passivate per ASTM A967 (nitric or citric) after grinding to restore the chromium oxide film; takes a mirror polish at 57 HRC and accepts hard chrome, black oxide or PVD coatings (keep bake/coating temperature below the tempering temperature).
9Cr18 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 |
|---|---|---|
| CGB/T 1220 / GB/T 3086 | 0.9 – 1 | 0.95 |
| Si | ≤ 0.8 | 0.4 |
| Mn | ≤ 0.8 | 0.45 |
| Cr | 17 – 19 | 18 |
| Niresidual | ≤ 0.6 | 0.25 |
| Moresidual only; the Mo-alloyed version is 9Cr18Mo (0.40–0.70 Mo) | ≤ 0.3 | 0.1 |
| Curesidual | ≤ 0.3 | — |
| P | ≤ 0.04 | — |
| Sbearing quality often ≤0.020 | ≤ 0.03 | — |
| Fe | balance | — |
9Cr18 QT55-58 — frequently asked
What is 9Cr18 QT55-58 used for?
9Cr18 QT55-58 is typically used for stainless bearing components, pump shafts and valve parts. In short: stainless bearing grade; hardens to 55–60 HRC; 440B-class corrosion resistance.
What is the yield strength of 9Cr18 QT55-58?
9Cr18 QT55-58 has a typical yield strength of 1,740 MPa (252 ksi) and a tensile strength of 1,930 MPa (280 ksi) — stronger than 99% of steel grades. Strength varies by condition: see the 7 listed tempers.
Is 9Cr18 QT55-58 easy to machine?
Not especially — machinability is rated not recommended (10/100, worse than 99% of steel grades). Machine only in the annealed condition with sharp carbide tools, rigid setups, low-to-moderate speed and heavy coolant; hardened parts (55–60 HRC) must be ground, EDM'd or hard-turned with CBN.
Can 9Cr18 QT55-58 be welded?
Not readily — weldability is rated not recommended (8/100). Not recommended for structural joints — high carbon gives hard, crack-prone martensite; if unavoidable, preheat 200–300 °C, use matching or 309/310 filler and immediately anneal or temper.
What surface finishes work on 9Cr18 QT55-58?
Passivate per ASTM A967 (nitric or citric) after grinding to restore the chromium oxide film; takes a mirror polish at 57 HRC and accepts hard chrome, black oxide or PVD coatings (keep bake/coating temperature below the tempering temperature).
Can 9Cr18 QT55-58 be formed, bent or molded?
Only light cold forming/bending in the annealed state (large radii, no sharp bends); hot work 1100→900 °C with slow cooling and mandatory post-forging anneal to avoid quench cracking.
What is the maximum service temperature of 9Cr18 QT55-58?
9Cr18 QT55-58 is rated for continuous use to about 180°C (356 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between 9Cr18-A and 9Cr18 QT58-60?
A is the default condition — standard as-supplied bar/ring blank condition: soft enough to turn, drill and cold-form before hardening. QT58-60: maximum hardness and dimensional stability for precision balls and instrument bearings; toughness is lowest. Yield strength is 450 MPa in A versus 1,830 MPa in QT58-60.
Sources
- GB/T 1220 Stainless steel bars — SAC (China) (2007)
- GB/T 3086 High carbon chromium stainless bearing steel — SAC (China) (2019)
- ASTM A276 / UNS S44003–S44004 stainless bars and shapes — ASTM (2017)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels and High-Performance Alloys (440A/B/C) — ASM International (1990)
- ASM Handbook Vol.13B — Corrosion: Materials (martensitic stainless steels) — ASM International (2005)
- ASM Handbook Vol.16 — Machining (machinability ratings of stainless steels) — ASM International (1989)
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.