Steel 55Cr3 · heat-treated state
Steel 55Cr3-AC
Properties of the AC condition, compared with the other 55Cr3 tempers.
1.7176 annealed to globular carbides — the softest delivery state, used for cold heading, cold extrusion and heavy machining before hardening.
What is 55Cr3-AC?
55Cr3-AC is 55Cr3 heat treated to AC — 1.7176 annealed to globular carbides — the softest delivery state, used for cold heading, cold extrusion and heavy machining before hardening. 55Cr3-AC has a yield strength of 380 MPa (55.1 ksi) and a tensile strength of 640 MPa (92.8 ksi) — weaker than 67% of steel grades. Elongation at break is 22% and the elastic modulus is 206 GPa (29.9 Msi). 55Cr3-AC has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,420°C (2,588 °F). Annealed is the default condition FabDigit quotes; AC is available on request or by drawing note.
Advantages
- Low embodied carbon — 1.9 kg CO₂/kg, better than 99% of steel grades
- Easy to machine — 65/100, better than 93% of steel grades
Limitations
- Limited service temperature — 250°C (482 °F), worse than 85% of steel grades
55Cr3-AC properties
Typical room-temperature values for 55Cr3-AC — 32 properties are specific to this condition; the rest are grade-level values shared by every 55Cr3 temper. Each bar shows where the value sits among the steel grades in FabDigit's library — further right is higher.
Physical3
55Cr3-AC has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,420°C (2,588 °F).
Mechanical13
55Cr3-AC has a yield strength of 380 MPa (55.1 ksi) and a tensile strength of 640 MPa (92.8 ksi) — weaker than 67% of steel grades. Elongation at break is 22% and the elastic modulus is 206 GPa (29.9 Msi).
Thermal6
55Cr3-AC is rated for continuous service to 250°C (482 °F). It conducts heat at 45 W/m·K (26 BTU/hr·ft·°F), better than 66% of steel grades. Thermal expansion is 12.3 µm/m·K (6.83 µin/in·°F).
Electrical2
55Cr3-AC has an electrical resistivity of 2.2×10⁻⁷ Ω·m.
Chemical & Environmental2
Corrosion resistance is not recommended (11/100), worse than 73% of steel grades.
Sustainability4
Producing a kilogram of 55Cr3-AC takes about 23 MJ of energy and emits 1.9 kg of CO₂ — less than 98% of steel grades. Typical recycled content is 30%.
Manufacturability7
55Cr3-AC's machinability is good (65/100, better than 93% of steel grades); weldability poor (32/100); formability good (60/100).
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Other 55Cr3 tempers and conditions
55Cr3 is also supplied in 8 other conditions. The full side-by-side table is on the 55Cr3 overview.
- AnnealedDefaultStock condition for machining, cold forming and pre-heat-treat blanks; hardness capped at 248 HB by EN 10089.480 MPa yield · 225 HB
- Hardened & TemperedPick when maximum load capacity / sag resistance is needed in coil springs and small torsion elements; toughness and hydrogen sensitivity worsen.1,600 MPa yield · 50 HRC
- Q&TStandard service condition for leaf springs, stabiliser bars and torsion bars: austenitise ~850 °C, oil quench, temper 400–480 °C.1,450 MPa yield · 46 HRC
- CH1.7176 bar supplied heat treated to a specified core hardness band, giving uniform medium-high strength for further machining or induction/case work.550 MPa yield · 25 HRC
- S1.7176 annealed to a capped hardness so that bar and coil can be cold sheared/cropped cleanly before forming and hardening.430 MPa yield · 215 HB
- AC1.7176 annealed to globular carbides — the softest delivery state, used for cold heading, cold extrusion and heavy machining before hardening.380 MPa yield · 190 HB
Working with 55Cr3-AC
Is 55Cr3 easy to machine?
Machine in the annealed (+A) state with rigid setups and carbide tooling; at 45–50 HRC only grinding, hard turning with CBN or EDM is practical.
Can 55Cr3 be welded?
Effectively unweldable for structural use (Ceq ≈ 0.85); if unavoidable, preheat 300–350 °C, low-hydrogen consumables and immediate post-weld temper, then re-heat-treat.
Can 55Cr3 be formed, bent or molded?
Coil and bend hot (850–1050 °C) or in the annealed condition; harden from ~840–860 °C in oil and temper 400–480 °C, then stress-relieve set springs at ~250–300 °C.
What surface finishes work on 55Cr3?
Always shot-peen loaded surfaces for fatigue life; protect by phosphate + epoxy/powder paint or zinc-rich coating — avoid acid pickling and standard electroplating without a 190–210 °C hydrogen bake-out.
55Cr3 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 |
|---|---|---|
| CEN 10089 | 0.52 – 0.59 | 0.55 |
| Si | 0.15 – 0.4 | 0.25 |
| Mn | 0.7 – 1 | 0.85 |
| Cr | 0.7 – 1 | 0.85 |
| P | ≤ 0.03 | — |
| S | ≤ 0.03 | — |
| Fe | balance | — |
55Cr3-AC — frequently asked
What is 55Cr3-AC used for?
55Cr3-AC is typically used for leaf springs, heavy coil springs, torsion bars, stabiliser (anti-roll) bars, spring clips and retainers and agricultural tine springs. In short: spring chromium bar.
What is the yield strength of 55Cr3-AC?
55Cr3-AC has a typical yield strength of 380 MPa (55.1 ksi) and a tensile strength of 640 MPa (92.8 ksi) — weaker than 67% of steel grades. Strength varies by condition: see the 9 listed tempers.
Is 55Cr3-AC easy to machine?
Reasonably — machinability is rated good (65/100, better than 93% of steel grades). Machine in the annealed (+A) state with rigid setups and carbide tooling; at 45–50 HRC only grinding, hard turning with CBN or EDM is practical.
Can 55Cr3-AC be welded?
Not readily — weldability is rated poor (32/100). Effectively unweldable for structural use (Ceq ≈ 0.85); if unavoidable, preheat 300–350 °C, low-hydrogen consumables and immediate post-weld temper, then re-heat-treat.
What surface finishes work on 55Cr3-AC?
Always shot-peen loaded surfaces for fatigue life; protect by phosphate + epoxy/powder paint or zinc-rich coating — avoid acid pickling and standard electroplating without a 190–210 °C hydrogen bake-out.
Can 55Cr3-AC be formed, bent or molded?
Coil and bend hot (850–1050 °C) or in the annealed condition; harden from ~840–860 °C in oil and temper 400–480 °C, then stress-relieve set springs at ~250–300 °C.
What is the maximum service temperature of 55Cr3-AC?
55Cr3-AC 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 55Cr3 Annealed and 55Cr3-AC?
Annealed is the default condition — stock condition for machining, cold forming and pre-heat-treat blanks; hardness capped at 248 HB by EN 10089. AC: 1.7176 annealed to globular carbides — the softest delivery state, used for cold heading, cold extrusion and heavy machining before hardening. Yield strength is 480 MPa in Annealed versus 380 MPa in AC.
Can FabDigit make parts in 55Cr3-AC?
Yes — 55Cr3-AC is available for CNC machining and sheet metal with instant online pricing. Upload a STEP file to get a price and a DFM check.
Sources
- EN 10089 — Hot rolled steels for quenched and tempered springs — CEN (2002)
- SAE J404 / J1397 — Chemical compositions and mechanical properties of SAE alloy steels (5155) — SAE International (2009)
- GB/T 1222 (2016)
- ASM Handbook Vol.1: Properties and Selection — Irons, Steels, and High-Performance Alloys — ASM International (1990)
- Spring Design Manual (HS-795) — SAE International (1996)
- Spring steel bar and flat bar grade data (55Cr3 / 1.7176) — European long-products mills (2023)
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.