Steel SACM645
EN 41CrAlMo7-10 · JIS G 4202 SACM645 · GB 38CrMoAlA, 38CrMoAl · also Nitralloy 135
SACM645 is a JIS G4053 aluminum–chromium–molybdenum nitriding steel (38CrMoAlA, 41CrAlMo7-10, Nitralloy 135) formulated to form a very hard diffused case over a quenched-and-tempered core.
Values for the Q&T condition
SACM645 tempers and conditions
SACM645 is supplied in 4 conditions, soft to hard. Q&T is the default FabDigit quotes; the values on this page are for it.
Compare all 4 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Solution annealed | Pick for deep machining, cold sawing or re-forging before the final Q&T + nitride cycle. | 430 | 700 | 20 | 205 HB | — |
Normalized | Use as an intermediate grain-refining / stress-relieving condition on forged blanks; not the final delivery state. | 690 | 900 | 15 | 26 HRC | 7.7 % IACS |
Q&TDefault Quenched and tempered | The standard stocked and pre-nitride condition: tough 850–1000 MPa core that stays dimensionally stable through the 500–540 °C nitriding cycle. | 780 | 950 | 17 | 28 HRC | — |
Q&T + Nitrided | Final service condition for screws, barrels, spindles and gauges needing extreme surface hardness and wear/scuff resistance with no quench distortion. | 790 | 960 | 15 | 67 HRC | — |
What is SACM645?
SACM645 is a JIS G4053 aluminum–chromium–molybdenum nitriding steel (38CrMoAlA, 41CrAlMo7-10, Nitralloy 135) formulated to form a very hard diffused case over a quenched-and-tempered core. In the default Q&T condition it gives 780 MPa yield, 950 MPa tensile, 17 % elongation and about 270 HB (28 HRC), and gas or plasma nitriding raises the surface to 900–1100 HV with little distortion; service to roughly 450 °C. Limits are poor weldability caused by the high Al and Cr, no corrosion resistance, and moderate machinability. Where welded joints are required, 42CrMo4/4140 is the usual alternative. SACM645 has a density of 7.8 g/cm³ (0.282 lb/in³), lighter than 87% of steel grades. It melts at 1,425°C (2,597 °F). SACM645 has a yield strength of 780 MPa (113 ksi) and a tensile strength of 950 MPa (138 ksi) — stronger than 86% of steel grades. Elongation at break is 17% and the elastic modulus is 207 GPa (30 Msi).
What is SACM645 used for?
- Nitrided drive and transmission shafts
- Extruder screws and barrels
- Gear and pinion working surfaces
- Precision machine spindles
- Cam shafts and cam followers
- Valve stems and spindles
- Gauges, mandrels and guide bushings
Advantages
- High strength — 780 MPa (113 ksi), better than 86% of steel grades
- High service temperature — 450°C (842 °F), better than 86% of steel grades
Limitations
- Difficult to weld — 18/100, worse than 87% of steel grades
- High embodied carbon — 2.5 kg CO₂/kg, worse than 82% of steel grades
SACM645 properties
Typical room-temperature values for SACM645-Q&T; bars are the position among steel grades.
Physical3
SACM645 has a density of 7.8 g/cm³ (0.282 lb/in³), lighter than 87% of steel grades. It melts at 1,425°C (2,597 °F).
Mechanical16
SACM645 has a yield strength of 780 MPa (113 ksi) and a tensile strength of 950 MPa (138 ksi) — stronger than 86% of steel grades. Elongation at break is 17% and the elastic modulus is 207 GPa (30 Msi).
Thermal6
SACM645 is rated for continuous service to 450°C (842 °F). It conducts heat at 36 W/m·K (20.8 BTU/hr·ft·°F), worse than 73% of steel grades. Thermal expansion is 12.2 µm/m·K (6.78 µin/in·°F).
Electrical3
SACM645 conducts electricity at 7.5 % IACS, worse than 67% of steel grades.
Chemical & Environmental3
Corrosion resistance is poor (15/100), better than 75% of steel grades.
Sustainability4
Producing a kilogram of SACM645 takes about 34 MJ of energy and emits 2.5 kg of CO₂ — more than 82% of steel grades. Typical recycled content is 28%.
Manufacturability6
SACM645's machinability is fair (42/100, worse than 73% of steel grades); weldability poor (18/100); formability poor (25/100).
Common Calculations5
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Strength versus weight in the steel family
Yield strength against density for every steel grade FabDigit runs. SACM645 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with SACM645
Is SACM645 easy to machine?
Machine fully in the Q&T condition (≈270 HB, ~45 % of 1212) with rigid setups and coated carbide; leave 0.05–0.10 mm grinding stock because nitriding must be the last operation.
Can SACM645 be welded?
Practically unweldable for structural joints — high Al and Cr give air-hardening and crack-prone HAZ; if unavoidable, preheat 300–350 °C, use low-hydrogen/matching filler and re-temper immediately, and never weld a nitrided surface.
Can SACM645 be formed, bent or molded?
Hot forge 1150–850 °C followed by slow cooling and annealing; cold forming is limited to minor straightening, and a stress relief at ~600 °C before nitriding prevents distortion.
Manufacturability
The process limits FabDigit applies to SACM645. Every SACM645 part is priced by an engineer; design inside these and the quote comes back without a redesign loop.
CNC machining
| Machinability | Better42 / 100 |
|---|---|
| ISO material group | P.2 |
| Cutting speed (rough / finish) | 180 / 210 m/min |
| Minimum wall | 0.8 mm |
| Minimum internal radius | 1 mm |
| Drill depth limit | 5× diameter |
| Best surface (machined / polished) | Ra 1.6 / — |
| Hardenable after machining | No |
Sheet metal
| Formability | Fair25 / 100 |
|---|---|
| Weldability | Better18 / 100 |
SACM645 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 | 0.4 – 0.5 | 0.45 |
| Si | 0.15 – 0.35 | 0.25 |
| MnJIS G 4202 | 0.6 – 0.9 | 0.75 |
| P | ≤ 0.03 | |
| S | ≤ 0.03 | |
| Cr | 1.3 – 1.7 | 1.5 |
| Mo | 0.15 – 0.3 | 0.22 |
| Alnitride-forming element, key to the grade | 0.7 – 1.2 | 0.95 |
| Niresidual, max | ≤ 0.25 | |
| Curesidual, max | ≤ 0.3 | |
| Fe | balance |
What surface finishes work on SACM645?
Gas or plasma nitride 500–540 °C for 20–90 h to a 0.2–0.6 mm case of 900–1100 HV; remove the brittle white layer by light lapping/polishing; the nitrided surface takes only light oxidation or oiling — plating and anodizing are not applicable.
Surface treatments FabDigit runs on steel parts — pick them in the quote configurator or call them out on the drawing. Each links to its datasheet in the surface-finish library (thickness, specs, call-out, material verdicts).
Plating
CVD Coating
Black / Phosphate
Thermal Spray
Equivalent designations
Standards and trade names that resolve to Steel SACM645 in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- EN / DIN / Werkstoff-Nr.
- 41CrAlMo7-10
- JIS
- G 4202 SACM645
- Trade names
- Nitralloy 135
How much does SACM645 cost?
SACM645 is a standard-cost steel ($$), cheaper than about 71% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
SACM645 — frequently asked
What is SACM645 used for?
SACM645 is typically used for nitrided drive and transmission shafts, extruder screws and barrels, gear and pinion working surfaces, precision machine spindles, cam shafts and cam followers and valve stems and spindles. In short: nitridable aerospace bar.
What is the yield strength of SACM645?
SACM645 has a typical yield strength of 780 MPa (113 ksi) and a tensile strength of 950 MPa (138 ksi) — stronger than 86% of steel grades. Strength varies by condition: see the 4 listed tempers.
Is SACM645 easy to machine?
Not especially — machinability is rated fair (42/100, worse than 73% of steel grades). Machine fully in the Q&T condition (≈270 HB, ~45 % of 1212) with rigid setups and coated carbide; leave 0.05–0.10 mm grinding stock because nitriding must be the last operation.
Can SACM645 be welded?
Not readily — weldability is rated poor (18/100). Practically unweldable for structural joints — high Al and Cr give air-hardening and crack-prone HAZ; if unavoidable, preheat 300–350 °C, use low-hydrogen/matching filler and re-temper immediately, and never weld a nitrided surface.
What surface finishes work on SACM645?
Gas or plasma nitride 500–540 °C for 20–90 h to a 0.2–0.6 mm case of 900–1100 HV; remove the brittle white layer by light lapping/polishing; the nitrided surface takes only light oxidation or oiling — plating and anodizing are not applicable.
Can SACM645 be formed, bent or molded?
Hot forge 1150–850 °C followed by slow cooling and annealing; cold forming is limited to minor straightening, and a stress relief at ~600 °C before nitriding prevents distortion.
What is the maximum service temperature of SACM645?
SACM645 is rated for continuous use to about 450°C (842 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between SACM645 Q&T and SACM645-A?
Q&T is the default condition — the standard stocked and pre-nitride condition: tough 850–1000 MPa core that stays dimensionally stable through the 500–540 °C nitriding cycle. A: pick for deep machining, cold sawing or re-forging before the final Q&T + nitride cycle. Yield strength is 780 MPa in Q&T versus 430 MPa in A.
How much does SACM645 cost?
SACM645 is a standard-cost steel ($$), cheaper than about 71% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
Can FabDigit make parts in SACM645?
Yes — SACM645 is available for CNC machining and sheet metal; every part is priced by an engineer rather than instantly. Upload a STEP file to get a price and a DFM check.
Sources
- JIS G 4202 Aluminium chromium molybdenum steels — Japanese Standards Association (2015)
- GB/T 3077 Alloy structural steels (38CrMoAl) — SAC (2015)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels — ASM International (1990)
- ASM Handbook Vol.4A — Steel Heat Treating (Nitriding) — ASM International (2013)
- Machinery's Handbook (machinability and nitriding steels) — Industrial Press (2020)
- 38CrMoAl — Mysteel / 1688 (2025)
Property data is compiled from published supplier and standards handbooks and normalised for comparison; hardness values on non-Brinell scales are converted approximately for charting only. Manufacturability limits are FabDigit quote-engine defaults and may be relaxed by engineering review. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.