Steel 42CrMoS4 · heat-treated state
Steel 42CrMoS4 +AC
Properties of the +AC condition, compared with the other 42CrMoS4 tempers.
Sub-critical/spheroidizing anneal that converts the pearlitic carbides to globular form, giving the softest, most machinable and most cold-formable state of 1.7227 (typically ≤ 241 HB).
What is 42CrMoS4 +AC?
42CrMoS4 +AC is 42CrMoS4 heat treated to +AC — sub-critical/spheroidizing anneal that converts the pearlitic carbides to globular form, giving the softest, most machinable and most cold-formable state of 1.7227 (typically ≤ 241 HB). 42CrMoS4 +AC has a yield strength of 440 MPa (63.8 ksi) and a tensile strength of 680 MPa (98.6 ksi) — stronger than 51% of steel grades. Elongation at break is 22% and the elastic modulus is 210 GPa (30.5 Msi). 42CrMoS4 +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). Q&T is the default condition FabDigit quotes; +AC is available on request or by drawing note.
Advantages
- Easy to machine — 65/100, better than 93% of steel grades
42CrMoS4 +AC properties
Typical room-temperature values for 42CrMoS4 +AC — 37 properties are specific to this condition; the rest are grade-level values shared by every 42CrMoS4 temper. Each bar shows where the value sits among the steel grades in FabDigit's library — further right is higher.
Physical3
42CrMoS4 +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).
Mechanical16
42CrMoS4 +AC has a yield strength of 440 MPa (63.8 ksi) and a tensile strength of 680 MPa (98.6 ksi) — stronger than 51% of steel grades. Elongation at break is 22% and the elastic modulus is 210 GPa (30.5 Msi).
Thermal6
42CrMoS4 +AC is rated for continuous service to 400°C (752 °F). It conducts heat at 44 W/m·K (25.4 BTU/hr·ft·°F), better than 57% of steel grades. Thermal expansion is 12.3 µm/m·K (6.83 µin/in·°F).
Electrical3
42CrMoS4 +AC conducts electricity at 8 % IACS, better than 55% of steel grades.
Chemical & Environmental3
Corrosion resistance is poor (15/100), better than 75% of steel grades.
Sustainability4
Producing a kilogram of 42CrMoS4 +AC takes about 30 MJ of energy and emits 2.1 kg of CO₂ — more than 55% of steel grades. Typical recycled content is 30%.
Manufacturability6
42CrMoS4 +AC's machinability is good (65/100, better than 93% of steel grades); weldability fair (35/100); formability good (55/100).
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Other 42CrMoS4 tempers and conditions
42CrMoS4 is also supplied in 15 other conditions. The full side-by-side table is on the 42CrMoS4 overview.
- Q&TDefaultDefault stocked condition: oil-quenched and high-tempered for 900–1100 MPa strength with good toughness in medium sections.720 MPa yield · 31 HRC
- +QT1100Highest-strength Q&T class, small bars and fasteners where full through-hardening is achieved.980 MPa yield · 37 HRC
- Q&T 32-36 HRCHigher-strength purchased band for highly loaded shafts, tooling holders and fasteners.930 MPa yield · 34 HRC
- +QT1000Standard class for shafts and spindles 16–40 mm needing ≥750 MPa yield.830 MPa yield · 34 HRC
- +CHThrough-hardened (oil quench + temper) 1.7227 bar supplied to a guaranteed core hardness band, giving a uniform ~300 HB tempered-martensite core in medium sections.800 MPa yield · 31 HRC
- Q&T 28-32 HRCCommon purchased hardness band for machinable shafting, gear blanks and hydraulic parts.800 MPa yield · 30 HRC
- NitridedPick when wear resistance and fatigue strength of a Q&T core must be boosted without distortion.720 MPa yield · 58 HRC
- +QT800Heavy-section Q&T class; accepts the lower core strength from limited hardenability.610 MPa yield · 27 HRC
- +QT750Largest standard Q&T class for big forged rolls, rams and heavy shafts.560 MPa yield · 24 HRC
- +NUse for a uniform as-delivered structure in large forgings/bars before machining and final heat treatment.530 MPa yield · 24 HRC
- AnnealedPick for heavy machining/deep-hole work or cold forming before final quench and temper.460 MPa yield · 205 HB
- +ACSub-critical/spheroidizing anneal that converts the pearlitic carbides to globular form, giving the softest, most machinable and most cold-formable state of 1.7227 (typically ≤ 241 HB).440 MPa yield · 195 HB
Working with 42CrMoS4 +AC
Is 42CrMoS4 easy to machine?
Machines best at 200–260 HB; the 0.02–0.04 % S gives short chips and ~10–15 % better tool life than 42CrMo4 — use coated carbide, rigid setups and reduce speeds sharply above 320 HB.
Can 42CrMoS4 be welded?
Weldable only with care: preheat 250–350 °C, low-hydrogen consumables, interpass control and post-weld temper/stress relief below the last tempering temperature; the sulphur raises hot-cracking risk, so 42CrMo4 (non-resulphurised) is preferred for welded assemblies.
Can 42CrMoS4 be formed, bent or molded?
Hot forge 1100–850 °C then slow-cool or normalize; cold forming only in the annealed/+FP state with generous radii — Q&T material is essentially non-formable.
What surface finishes work on 42CrMoS4?
Takes hard chrome, zinc/zinc-nickel, phosphate, black oxide, nitriding and paint; bake at 190–220 °C after acid pickling/plating to avoid hydrogen embrittlement, and expect fine sulphide streaks on high-polish surfaces.
42CrMoS4 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 | 0.02 |
| Sdeliberate S addition for machinability (the 'S' in 42CrMoS4) | 0.02 – 0.04 | 0.03 |
| Cr | 0.9 – 1.2 | 1.05 |
| Mo | 0.15 – 0.3 | 0.22 |
| Fe | balance | — |
42CrMoS4 +AC — frequently asked
What is 42CrMoS4 +AC used for?
42CrMoS4 +AC is typically used for shafts, bolts and studs. In short: free-cutting Cr-Mo bar.
What is the yield strength of 42CrMoS4 +AC?
42CrMoS4 +AC has a typical yield strength of 440 MPa (63.8 ksi) and a tensile strength of 680 MPa (98.6 ksi) — stronger than 51% of steel grades. Strength varies by condition: see the 16 listed tempers.
Is 42CrMoS4 +AC easy to machine?
Reasonably — machinability is rated good (65/100, better than 93% of steel grades). Machines best at 200–260 HB; the 0.02–0.04 % S gives short chips and ~10–15 % better tool life than 42CrMo4 — use coated carbide, rigid setups and reduce speeds sharply above 320 HB.
Can 42CrMoS4 +AC be welded?
With care — weldability is rated fair (35/100). Weldable only with care: preheat 250–350 °C, low-hydrogen consumables, interpass control and post-weld temper/stress relief below the last tempering temperature; the sulphur raises hot-cracking risk, so 42CrMo4 (non-resulphurised) is preferred for welded assemblies.
What surface finishes work on 42CrMoS4 +AC?
Takes hard chrome, zinc/zinc-nickel, phosphate, black oxide, nitriding and paint; bake at 190–220 °C after acid pickling/plating to avoid hydrogen embrittlement, and expect fine sulphide streaks on high-polish surfaces.
Can 42CrMoS4 +AC be formed, bent or molded?
Hot forge 1100–850 °C then slow-cool or normalize; cold forming only in the annealed/+FP state with generous radii — Q&T material is essentially non-formable.
What is the maximum service temperature of 42CrMoS4 +AC?
42CrMoS4 +AC 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.
Can FabDigit make parts in 42CrMoS4 +AC?
Yes — 42CrMoS4 +AC is available for CNC machining 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 — Part 3: Alloy steels — CEN (2006)
- EN 10277 / EN 10278 bright steel product standards — CEN (2018)
- GB/T 3077 (42CrMo) — SAC (2015)
- ASM Handbook Vol. 1 — Properties and Selection: Irons, Steels — ASM International (1990)
- ASM Handbook Vol. 19 — Fatigue and Fracture — ASM International (1996)
- 1.7225 / 1.7227 (42CrMo4, 42CrMoS4) engineering steel datasheets — Ovako / Böhler / Deutsche Edelstahlwerke (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.