Steel 42CrMo4-QT800
Heat-treated state
EN 42CrMo4 · AISI/SAE 4140 · JIS SCM440 · GB 42CrMo
Medium-section Q&T class for large shafts and forged rings.
Values for the QT800 condition
Other 42CrMo4 tempers and conditions
42CrMo4 is listed in 17 conditions; see the grade overview at 42CrMo4.
Compare all 17 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Spheroidize annealed | Annealed to globular (spheroidized) carbides for the softest, most ductile structure — the preferred feedstock for cold extrusion, cold heading and deep machining. | 380 | 630 | 24 | 185 HB | 44 W/m·K |
soft annealed (+A), max 241 HB | Softest condition — pick it for deep machining, cold forming or as a pre-heat-treat blank. | 415 | 655 | 20 | 13 HRC | — |
Treated for High Shearability | EN 10083 delivery condition treated to a controlled soft structure (≤248 HB) so that bar can be cold-sheared into billets without cracking. | 450 | 750 | 18 | 220 HB | 43 W/m·K |
Cold rolled | Thin strip/sheet form for stamped or formed blanks that are hardened afterwards. | 480 | 700 | 12 | 17 HRC | 7.8 % IACS |
HRDefault Hot rolled | Cheapest stock form for parts that will be heat treated after rough machining. | 550 | 850 | 14 | 23 HRC | — |
Q&T strength class Rm 750–900 MPa (bar 160–250 mm) | Lowest EN 10083-3 Q&T class, used for heavy sections where full hardening depth is impossible. | 560 | 820 | 16 | 23 HRC | 7.8 % IACS |
QT800This page Q&T strength class Rm 800–950 MPa (bar 100–160 mm) | Medium-section Q&T class for large shafts and forged rings. | 610 | 880 | 15 | 26 HRC | 7.8 % IACS |
Cold drawn | Bright, close-tolerance bar for turned parts and shafting where no further heat treatment is planned. | 650 | 850 | 10 | 25 HRC | — |
air cooled from ~870 °C | Uniform fine-grain structure for forgings and weld fabrications before final quench and temper. | 650 | 1,000 | 18 | 30 HRC | — |
Q&T strength class Rm 900–1100 MPa (bar 40–100 mm) | Most common ordered Q&T class for medium-diameter shafts and gear blanks. | 720 | 1,000 | 14 | 31 HRC | 7.8 % IACS |
Carburized and hardened | Bar hardened and tempered to a specified core hardness band (typically ~280–320 HB), the usual pre-condition before nitriding or induction case hardening. | 800 | 1,000 | 13 | 31 HRC | 43 W/m·K |
Q&T strength class Rm 1000–1200 MPa (bar 16–40 mm) | Higher-strength class for small shafts, pins, high-tensile bolting and connecting rods. | 820 | 1,100 | 12 | 34 HRC | 7.8 % IACS |
Induction hardened | For journals, splines and gear teeth needing 50–58 HRC wear surface with a ductile core. | 830 | 1,000 | 12 | 54 HRC | 7.8 % IACS |
Quenched and tempered | Standard delivered condition for loaded shafts, gears and couplings; best strength/toughness balance. | 850 | 1,000 | 14 | 31 HRC | — |
Pre-hardened ("4140 HT") stock | Distributor pre-hardened bar/plate machined to final size with no further heat treatment; also the NACE-friendly upper bound is 22 HRC, so check sour-service specs. | 850 | 1,000 | 15 | 30 HRC | 7.8 % IACS |
Q&T core + gas/plasma nitrided case | Choose for wear surfaces and better fatigue/corrosion on shafts and dies; case is 0.2–0.5 mm deep with a tough Q&T core. | 850 | 1,000 | 13 | 31 HRC | 7.8 % IACS |
Q&T strength class Rm 1100–1300 MPa (bar ≤16 mm) | Maximum standard Q&T class; highest strength but lowest toughness and highest cracking sensitivity. | 980 | 1,200 | 10 | 38 HRC | 7.8 % IACS |
What is 42CrMo4-QT800?
42CrMo4-QT800 is 42CrMo4 heat treated to QT800 — medium-section Q&T class for large shafts and forged rings. 42CrMo4-QT800 has a yield strength of 610 MPa (88.5 ksi) and a tensile strength of 880 MPa (128 ksi) — stronger than 77% of steel grades. Elongation at break is 15% and the elastic modulus is 210 GPa (30.5 Msi). 42CrMo4-QT800 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). HR is the default condition FabDigit quotes; QT800 is available on request or by drawing note.
Advantages
- Polishes to a fine finish — 70/100, better than 87% of steel grades
- High strength — 610 MPa (88.5 ksi), better than 77% of steel grades
42CrMo4-QT800 properties
Typical room-temperature values for 42CrMo4-QT800; 22 are specific to this condition. Other listed values are 42CrMo4 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
42CrMo4-QT800 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
42CrMo4-QT800 has a yield strength of 610 MPa (88.5 ksi) and a tensile strength of 880 MPa (128 ksi) — stronger than 77% of steel grades. Elongation at break is 15% and the elastic modulus is 210 GPa (30.5 Msi).
Thermal6
42CrMo4-QT800 is rated for continuous service to 400°C (752 °F). It conducts heat at 42.6 W/m·K (24.6 BTU/hr·ft·°F), worse than 51% of steel grades. Thermal expansion is 12.3 µm/m·K (6.83 µin/in·°F).
Electrical3
42CrMo4-QT800 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 42CrMo4-QT800 takes about 30 MJ of energy and emits 2.2 kg of CO₂ — more than 56% of steel grades. Typical recycled content is 30%.
Manufacturability7
42CrMo4-QT800's machinability is fair (47/100, worse than 58% of steel grades); weldability poor (32/100); formability poor (25/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with 42CrMo4-QT800
Is 42CrMo4 easy to machine?
Machine annealed (≤241 HB) or at 28–32 HRC with rigid setups, coated carbide, 80–160 m/min and generous coolant; above 40 HRC switch to CBN/ceramic or grinding.
Can 42CrMo4 be welded?
Weldable with low-hydrogen consumables but requires 200–350 °C preheat, controlled interpass temperature and post-weld temper at 550–650 °C to avoid HAZ cracking.
Can 42CrMo4 be formed, bent or molded?
Hot forge 1100–850 °C then normalize; cold forming only in the annealed condition with generous radii — springback and cracking are high at ≥250 HB.
What surface finishes work on 42CrMo4?
No anodizing; protect with black oxide, phosphate + oil, zinc or hard-chrome plate, or nitride; polishes well to a mirror finish in the Q&T condition but rusts if left bare.
42CrMo4 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 | 0.38 – 0.45 | 0.42 |
| Si | ≤ 0.4 | 0.25 |
| Mn | 0.6 – 0.9 | 0.75 |
| P | ≤ 0.03 | — |
| S42CrMo4; ≤0.005 for 42CrMoS4 grade the range is 0.020–0.040 | ≤ 0.04 | — |
| Cr | 0.9 – 1.2 | 1.05 |
| Mo | 0.15 – 0.3 | 0.22 |
| Fe | balance | — |
42CrMo4-QT800 — frequently asked
What is 42CrMo4-QT800 used for?
42CrMo4-QT800 is typically used for drive shafts and axles, gears and pinions, forged industrial parts, hydraulic cylinder rods, high-strength bolts and studs and crankshafts. In short: european Cr-Mo machining bar.
What is the yield strength of 42CrMo4-QT800?
42CrMo4-QT800 has a typical yield strength of 610 MPa (88.5 ksi) and a tensile strength of 880 MPa (128 ksi) — stronger than 77% of steel grades. Strength varies by condition: see the 17 listed tempers.
Is 42CrMo4-QT800 easy to machine?
Reasonably — machinability is rated fair (47/100, worse than 58% of steel grades). Machine annealed (≤241 HB) or at 28–32 HRC with rigid setups, coated carbide, 80–160 m/min and generous coolant; above 40 HRC switch to CBN/ceramic or grinding.
Can 42CrMo4-QT800 be welded?
Not readily — weldability is rated poor (32/100). Weldable with low-hydrogen consumables but requires 200–350 °C preheat, controlled interpass temperature and post-weld temper at 550–650 °C to avoid HAZ cracking.
What surface finishes work on 42CrMo4-QT800?
No anodizing; protect with black oxide, phosphate + oil, zinc or hard-chrome plate, or nitride; polishes well to a mirror finish in the Q&T condition but rusts if left bare.
Can 42CrMo4-QT800 be formed, bent or molded?
Hot forge 1100–850 °C then normalize; cold forming only in the annealed condition with generous radii — springback and cracking are high at ≥250 HB.
What is the maximum service temperature of 42CrMo4-QT800?
42CrMo4-QT800 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 42CrMo4-HR and 42CrMo4-QT1100?
HR is the default condition — cheapest stock form for parts that will be heat treated after rough machining. QT1100: maximum standard Q&T class; highest strength but lowest toughness and highest cracking sensitivity. Yield strength is 550 MPa in HR versus 980 MPa in QT1100.
Can FabDigit make parts in 42CrMo4-QT800?
Yes — 42CrMo4-QT800 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 10083-3 — Steels for quenching and tempering, alloy steels — CEN (2006)
- GB/T 3077 — Alloy structural steels (42CrMo) — SAC (2015)
- ASTM A29/A29M and SAE J404 (4140) — ASTM / SAE (2020)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels and High-Performance Alloys — ASM International (1990)
- ASM Handbook Vol.19 — Fatigue and Fracture — ASM International (1996)
- 42CrMo4 / 1.7225 alloy steel datasheet — Ovako / Böhler / Dörrenberg (typical mill data) (2023)
- 42CrMo — Mysteel / 1688 (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.