Steel C55E QT 40-45 HRC
Hardness band
EN C55E · AISI/SAE 1055 · GB 55
QT 40-45 HRC = q&T to 40–45 HRC
High-hardness condition for blades, wear strips, hand-tool bodies and springs in sections under ~25 mm; toughness drops sharply.
Values for the QT 40-45 HRC condition
Other C55E tempers and conditions
C55E is listed in 10 conditions; see the grade overview at C55E.
Compare all 10 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Annealed | Softest supply condition; choose for heavy machining, cold forming or as a pre-condition before hardening. | 340 | 620 | 20 | 190 HB | — |
Normalized | Uniform fine pearlitic structure for good machinability and predictable strength without quenching distortion. | 390 | 760 | 14 | 225 HB | — |
Hot rolled | Cheapest bar/plate condition for parts that will be re-heat-treated after machining or for low-duty use. | 400 | 720 | 15 | 210 HB | — |
Normalized and tempered | Pick when normalized strength is sufficient but residual stress and hardness scatter must be reduced before precision machining. | 400 | 740 | 15 | 215 HB | — |
+QTDefault Quenched and tempered | Standard engineering condition: best strength/toughness balance for shafts, keyed drive parts and wear plates up to ~40 mm section. | 550 | 850 | 14 | 24 HRC | — |
+QT + induction surface hardened | Tough Q&T core with a hard wear-resistant skin — the classic choice for journal areas of shafts, pins and rollers. | 560 | 870 | 12 | 58 HRC | — |
Stress relieved | Cold-drawn bar with residual stress removed to minimize bending/distortion during asymmetric machining. | 600 | 780 | 10 | 20 HRC | 9.5 % IACS |
Cold drawn | Close-tolerance bright bar with raised strength and good surface finish; use for shafts machined without further heat treatment. | 660 | 820 | 8 | 22 HRC | — |
Q&T to 28–32 HRC | Ordered when a specified through-hardness is required for gear blanks, spline shafts and moderately loaded wear parts. | 740 | 950 | 12 | 30 HRC | — |
QT 40-45 HRCThis page Q&T to 40–45 HRC | High-hardness condition for blades, wear strips, hand-tool bodies and springs in sections under ~25 mm; toughness drops sharply. | 1,130 | 1,350 | 9 | 42 HRC | 44 W/m·K |
What is C55E QT 40-45 HRC?
C55E QT 40-45 HRC is C55E heat treated to QT 40-45 HRC — high-hardness condition for blades, wear strips, hand-tool bodies and springs in sections under ~25 mm; toughness drops sharply. C55E QT 40-45 HRC has a yield strength of 1,130 MPa (164 ksi) and a tensile strength of 1,350 MPa (196 ksi) — stronger than 93% of steel grades. Elongation at break is 9% and the elastic modulus is 210 GPa (30.5 Msi). C55E QT 40-45 HRC has a density of 7.84 g/cm³ (0.283 lb/in³), lighter than 78% of steel grades. It melts at 1,420°C (2,588 °F). +QT is the default condition FabDigit quotes; QT 40-45 HRC is available on request or by drawing note.
Advantages
- High strength — 1,130 MPa (164 ksi), better than 93% of steel grades
Limitations
- Limited formability — 8/100, worse than 97% of steel grades
- Difficult to weld — 12/100, worse than 96% of steel grades
- Limited ductility — 9%, worse than 93% of steel grades
- Difficult to machine — 25/100, worse than 93% of steel grades
- Low fracture toughness — 40 MPa·√m (36.4 ksi·√in), worse than 92% of steel grades
C55E QT 40-45 HRC properties
Typical room-temperature values for C55E QT 40-45 HRC; 17 are specific to this condition. Other listed values are C55E reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
C55E QT 40-45 HRC has a density of 7.84 g/cm³ (0.283 lb/in³), lighter than 78% of steel grades. It melts at 1,420°C (2,588 °F).
Mechanical16
C55E QT 40-45 HRC has a yield strength of 1,130 MPa (164 ksi) and a tensile strength of 1,350 MPa (196 ksi) — stronger than 93% of steel grades. Elongation at break is 9% and the elastic modulus is 210 GPa (30.5 Msi).
Thermal6
C55E QT 40-45 HRC is rated for continuous service to 250°C (482 °F). It conducts heat at 44 W/m·K (25.4 BTU/hr·ft·°F), better than 57% of steel grades. Thermal expansion is 11.5 µm/m·K (6.39 µin/in·°F).
Electrical3
C55E QT 40-45 HRC conducts electricity at 9 % IACS, better than 71% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (10/100), worse than 86% of steel grades.
Sustainability4
Producing a kilogram of C55E QT 40-45 HRC takes about 25 MJ of energy and emits 2 kg of CO₂ — less than 82% of steel grades. Typical recycled content is 30%.
Manufacturability7
C55E QT 40-45 HRC's machinability is poor (25/100, worse than 93% of steel grades); weldability not recommended (12/100); formability not recommended (8/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with C55E QT 40-45 HRC
Is C55E easy to machine?
Machine in +A or +N (≈55–65 % of 1212); above 30 HRC use coated carbide, rigid setups and reduced feeds — grind above 45 HRC.
Can C55E be welded?
Poor weldability (CE ≈ 0.7): preheat 250–350 °C, low-hydrogen consumables, slow cooling and post-weld tempering to avoid HAZ martensite cracking.
Can C55E be formed, bent or molded?
Cold forming limited to gentle bends in the annealed condition (r ≥ 2–3 t); hot forge at 1100–850 °C then normalize.
What surface finishes work on C55E?
No natural corrosion resistance — protect with black oxide, phosphate + oil, zinc/nickel plating or paint; hardened surfaces polish and hard-chrome plate well.
C55E 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 |
|---|---|---|
| C | 0.52 – 0.6 | 0.55 |
| Si | ≤ 0.4 | 0.25 |
| Mn | 0.6 – 0.9 | 0.75 |
| PE-quality: controlled P | ≤ 0.03 | — |
| SE-quality: controlled S | ≤ 0.04 | — |
| Crresidual | ≤ 0.4 | — |
| Niresidual | ≤ 0.4 | — |
| Moresidual | ≤ 0.1 | — |
| Cr+Mo+Nisum of residuals per EN 10083-2 | ≤ 0.63 | — |
| Fe | balance | — |
C55E QT 40-45 HRC — frequently asked
What is C55E QT 40-45 HRC used for?
C55E QT 40-45 HRC is typically used for machine shafts, gears, springs and wear parts. In short: higher strength than C45; spring and wear grade; poor weldability at 0.55 % C.
What is the yield strength of C55E QT 40-45 HRC?
C55E QT 40-45 HRC has a typical yield strength of 1,130 MPa (164 ksi) and a tensile strength of 1,350 MPa (196 ksi) — stronger than 93% of steel grades. Strength varies by condition: see the 10 listed tempers.
Is C55E QT 40-45 HRC easy to machine?
Not especially — machinability is rated poor (25/100, worse than 93% of steel grades). Machine in +A or +N (≈55–65 % of 1212); above 30 HRC use coated carbide, rigid setups and reduced feeds — grind above 45 HRC.
Can C55E QT 40-45 HRC be welded?
Not readily — weldability is rated not recommended (12/100). Poor weldability (CE ≈ 0.7): preheat 250–350 °C, low-hydrogen consumables, slow cooling and post-weld tempering to avoid HAZ martensite cracking.
What surface finishes work on C55E QT 40-45 HRC?
No natural corrosion resistance — protect with black oxide, phosphate + oil, zinc/nickel plating or paint; hardened surfaces polish and hard-chrome plate well.
Can C55E QT 40-45 HRC be formed, bent or molded?
Cold forming limited to gentle bends in the annealed condition (r ≥ 2–3 t); hot forge at 1100–850 °C then normalize.
What is the maximum service temperature of C55E QT 40-45 HRC?
C55E QT 40-45 HRC 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.
Sources
- EN 10083-2: Steels for quenching and tempering — Non-alloy steels — CEN (2006)
- EN 10277 / EN 10025 bright and hot-rolled product conditions — CEN (2018)
- ASM Handbook Vol.1: Properties and Selection — Irons, Steels and High-Performance Alloys (AISI 1055) — ASM International (1990)
- Machinery's Handbook, machinability ratings — Industrial Press (2020)
- ISO 18265 hardness conversion tables — ISO (2013)
- Mysteel / carbon bar price series and 1688 — Mysteel, SMM (2026)
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.