Steel SCM445 QT40-45HRC
Hardness band
JIS SCM445 · AISI/SAE 4145
High-strength condition for dies, punches and heavily loaded pins where wear resistance outranks toughness.
Values for the QT40-45HRC condition
Other SCM445 tempers and conditions
SCM445 is listed in 10 conditions; see the grade overview at SCM445.
- SA
- A
- HR
- N
- CD
- QT28-32HRC
- QT
- IH
- QT40-45HRC
- QT48-52HRC
Compare all 10 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Spheroidize annealed | Pick for maximum machinability and best cold-heading/thread-rolling behaviour before hardening. | 430 | 690 | 23 | 14 HRC | 8.2 % IACS |
Solution annealed | Softest supply condition for heavy machining, deep drilling or cold sizing before final hardening. | 470 | 740 | 20 | 212 HB | 44 W/m·K |
Hot rolled | Mill supply condition for stock to be re-heat-treated; scale and decarburised skin must be machined off. | 560 | 900 | 16 | 26 HRC | 7.8 % IACS |
Normalized | Uniform fine-pearlitic structure for forgings prior to machining or as an economical medium-strength condition. | 670 | 1,030 | 14 | 31 HRC | — |
Cold drawn | Close-tolerance bright bar for shafts machined to size without further heat treatment. | 720 | 860 | 12 | 24 HRC | 7.8 % IACS |
Q&T 28–32 HRC (≈285–311 HB) | Tough general-purpose condition for drill collars, tool joints and shafts where impact matters more than peak strength. | 860 | 1,000 | 17 | 30 HRC | — |
QTDefault Quenched and tempered | Standard commercial supply: oil quenched ~840 °C and tempered ~540–600 °C to the JIS strength class; default for shafts, gears and dies. | 950 | 1,130 | 14 | 35 HRC | — |
Induction hardened | Use when bearing journals or gear teeth need a 55+ HRC wear surface with compressive residual stress on a tough Q&T core. | 950 | 1,130 | 12 | 57 HRC | 7.5 % IACS |
QT40-45HRCThis page Q&T 40–45 HRC (low-temperature temper) | High-strength condition for dies, punches and heavily loaded pins where wear resistance outranks toughness. | 1,300 | 1,450 | 10 | 43 HRC | — |
Q&T 48–52 HRC (tool condition) | Near-maximum through hardness for wear parts and small tooling; brittle, only for compression-dominated loads. | 1,550 | 1,750 | 7 | 50 HRC | — |
What is SCM445 QT40-45HRC?
SCM445 QT40-45HRC is SCM445 heat treated to QT40-45HRC — high-strength condition for dies, punches and heavily loaded pins where wear resistance outranks toughness. SCM445 QT40-45HRC has a yield strength of 1,300 MPa (189 ksi) and a tensile strength of 1,450 MPa (210 ksi) — stronger than 95% of steel grades. Elongation at break is 10% and the elastic modulus is 207 GPa (30 Msi). SCM445 QT40-45HRC 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). QT is the default condition FabDigit quotes; QT40-45HRC is available on request or by drawing note.
Advantages
- High strength — 1,300 MPa (189 ksi), better than 95% of steel grades
- Polishes to a fine finish — 65/100, better than 78% of steel grades
Limitations
- Limited ductility — 10%, worse than 91% of steel grades
- Difficult to machine — 28/100, worse than 91% of steel grades
- Difficult to weld — 15/100, worse than 91% of steel grades
- Low fracture toughness — 55 MPa·√m (50.1 ksi·√in), worse than 82% of steel grades
- Limited formability — 20/100, worse than 80% of steel grades
SCM445 QT40-45HRC properties
Typical room-temperature values for SCM445 QT40-45HRC; 14 are specific to this condition. Other listed values are SCM445 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
SCM445 QT40-45HRC 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).
Mechanical16
SCM445 QT40-45HRC has a yield strength of 1,300 MPa (189 ksi) and a tensile strength of 1,450 MPa (210 ksi) — stronger than 95% of steel grades. Elongation at break is 10% and the elastic modulus is 207 GPa (30 Msi).
Thermal6
SCM445 QT40-45HRC is rated for continuous service to 400°C (752 °F). It conducts heat at 42 W/m·K (24.3 BTU/hr·ft·°F), worse than 56% of steel grades. Thermal expansion is 12.3 µm/m·K (6.83 µin/in·°F).
Electrical3
SCM445 QT40-45HRC conducts electricity at 7.8 % IACS, worse than 57% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (12/100), worse than 53% of steel grades.
Sustainability4
Producing a kilogram of SCM445 QT40-45HRC takes about 30 MJ of energy and emits 2.3 kg of CO₂ — more than 56% of steel grades. Typical recycled content is 30%.
Manufacturability6
SCM445 QT40-45HRC's machinability is poor (28/100, worse than 91% of steel grades); weldability poor (15/100); formability poor (20/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with SCM445 QT40-45HRC
Is SCM445 easy to machine?
Machine in the annealed/normalised state where possible; at 32–39 HRC use rigid setups, coated carbide, 60–110 m/min and positive rake, and finish-grind after hardening.
Can SCM445 be welded?
Poor weldability (CE ≈ 0.85): preheat 300–350 °C, low-hydrogen consumables, control interpass, and temper/PWHT at 600–650 °C immediately — avoid welding on finished hardened parts.
Can SCM445 be formed, bent or molded?
Hot forge 1100–1200 °C with slow cooling or immediate normalising; cold forming limited to light straightening in the annealed condition.
What surface finishes work on SCM445?
No corrosion resistance — protect by black oxide, phosphate + oil, hard chrome or QPQ nitrocarburising; bake after plating to avoid hydrogen embrittlement, and cap hardness at 22 HRC for sour service.
SCM445 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 | 0.43 – 0.48 | 0.45 |
| Si | 0.15 – 0.35 | 0.25 |
| Mn | 0.3 – 0.6 | 0.45 |
| P | ≤ 0.03 | — |
| S | ≤ 0.03 | — |
| Cr | 0.9 – 1.2 | 1.05 |
| Mo | 0.15 – 0.3 | 0.22 |
| Niresidual max | ≤ 0.25 | — |
| Curesidual max | ≤ 0.3 | — |
| Fe | balance | — |
SCM445 QT40-45HRC — frequently asked
What is SCM445 QT40-45HRC used for?
SCM445 QT40-45HRC is typically used for high-strength shafts, drill collars, spline shafts and heavy bolts. In short: highest-strength SCM through-hardener; stronger than SCM440; strength over weldability.
What is the yield strength of SCM445 QT40-45HRC?
SCM445 QT40-45HRC has a typical yield strength of 1,300 MPa (189 ksi) and a tensile strength of 1,450 MPa (210 ksi) — stronger than 95% of steel grades. Strength varies by condition: see the 10 listed tempers.
Is SCM445 QT40-45HRC easy to machine?
Not especially — machinability is rated poor (28/100, worse than 91% of steel grades). Machine in the annealed/normalised state where possible; at 32–39 HRC use rigid setups, coated carbide, 60–110 m/min and positive rake, and finish-grind after hardening.
Can SCM445 QT40-45HRC be welded?
Not readily — weldability is rated poor (15/100). Poor weldability (CE ≈ 0.85): preheat 300–350 °C, low-hydrogen consumables, control interpass, and temper/PWHT at 600–650 °C immediately — avoid welding on finished hardened parts.
What surface finishes work on SCM445 QT40-45HRC?
No corrosion resistance — protect by black oxide, phosphate + oil, hard chrome or QPQ nitrocarburising; bake after plating to avoid hydrogen embrittlement, and cap hardness at 22 HRC for sour service.
Can SCM445 QT40-45HRC be formed, bent or molded?
Hot forge 1100–1200 °C with slow cooling or immediate normalising; cold forming limited to light straightening in the annealed condition.
What is the maximum service temperature of SCM445 QT40-45HRC?
SCM445 QT40-45HRC is rated for continuous use to about 400°C (752 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between SCM445-QT and SCM445-SA?
QT is the default condition — standard commercial supply: oil quenched ~840 °C and tempered ~540–600 °C to the JIS strength class; default for shafts, gears and dies. SA: pick for maximum machinability and best cold-heading/thread-rolling behaviour before hardening. Yield strength is 950 MPa in QT versus 430 MPa in SA.
Sources
- JIS G4053 — Low-alloyed structural steels for machine structural use (SCM445) — JSA (2016)
- GB/T 3077 — Alloy structural steels (45CrMo) — SAC (2015)
- SAE J404 / ASTM A29 — Chemical compositions of SAE alloy steels (4145) — SAE / ASTM (2020)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels, and High-Performance Alloys — ASM International (1990)
- ASM Handbook Vol.4 — Heat Treating — ASM International (1991)
- Alloy steel 4145H / 4145H Mod drill-collar bar datasheets — various bar producers (2022)
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.