Benchmark · 4 materials
Steel 8640 vs Steel 4140 vs Steel 4150 vs Steel 4340
All steel grades — bands show the family's 10th–90th percentile. The best value in each row is in bold; metric first, imperial in gray.
Properties
| Property | 8640 | 4140 | 4150 | 4340 |
|---|---|---|---|---|
| Yield strengthMPa | 540 MPa78 ksi | 655 MPa95 ksi | 760 MPa110 ksi | 860 MPa125 ksi |
| Tensile strengthMPa | 1,080 MPa157 ksi | 725 MPa105 ksi | 825 MPa120 ksi | 1,035 MPa150 ksi |
| Specific strengthMPa·cm³/g | 69 | 83 | 97 | 110 |
| Densityg/cm³ | 7.85 g/cm³0.284 lb/in³ | 7.85 g/cm³0.284 lb/in³ | 7.85 g/cm³0.284 lb/in³ | 7.85 g/cm³0.284 lb/in³ |
| Hardness (HB equiv.)HB | 200 HB | 200 HB | 210 HB | 217 HB |
| Max service temp°C | 480 °C896 °F | 425 °C797 °F | 425 °C797 °F | 425 °C797 °F |
| Min service temp°C | -50 °C-58 °F | -40 °C-40 °F | -40 °C-40 °F | -40 °C-40 °F |
| Electrical conductivity% IACS | 9.7 % IACS5.6 MS/m | 7.8 % IACS4.5 MS/m | 7.8 % IACS4.5 MS/m | 7.8 % IACS4.5 MS/m |
| Machinability/100 | Very good75 / 100 | Good60 / 100 | Good55 / 100 | Fair50 / 100 |
| Weldability/100 | Very good75 / 100 | Good60 / 100 | Fair45 / 100 | Fair50 / 100 |
| Formability/100 | Fair40 / 100 | Fair45 / 100 | Fair35 / 100 | Fair35 / 100 |
| Relative cost | $$ Standard | $$ Standard | $$$ Premium | $$$ Premium |
| Processes | CNC, Sheet | CNC, Sheet, Cast/Forge | CNC, Sheet | CNC, Sheet |
Where each grade sits
One track per property; coloured markers are the compared grades, the shaded band is the steel family 10th–90th percentile and the tick its median.
Yield strength540 MPa
250 MPafamily median 540 MPa1,270 MPa
Tensile strength1,080 MPa
420 MPafamily median 800 MPa1,750 MPa
Density7.85 g/cm³
7.8 g/cm³family median 7.85 g/cm³7.85 g/cm³
Hardness (HB equiv.)200 HB
134 HBfamily median 210 HB558 HB
Max service temp480 °C
200 °Cfamily median 400 °C540 °C
Electrical conductivity9.7 % IACS
5.7 % IACSfamily median 9.7 % IACS12 % IACS
Machinability75 / 100
29 / 100family median 75 / 10075 / 100
Relative cost31
14family median 2553
8640414041504340
Strength versus weight
Manufacturing and finishing
| Capability | 8640 | 4140 | 4150 | 4340 |
|---|---|---|---|---|
| CNC machining | Yes | Yes | Yes | Yes |
| Sheet metal | Yes | Yes | Yes | Yes |
| Casting & forging | — | Yes | — | — |
| Default condition | HR | HR | HR | HR |
| Min. machined wall | 0.8 mm | 0.8 mm | 0.8 mm | 0.8 mm |
| Best machined surface | Ra 1.6 µm | Ra 1.6 µm | Ra 1.6 µm | Ra 1.6 µm |
| Heat treatments | Quench & Temper, Full Anneal, Stress Relief | Quench & Temper, Full Anneal, Stress Relief | Quench & Temper, Full Anneal, Stress Relief | Quench & Temper, Full Anneal, Stress Relief |
| AlCrN | Yes | Yes | Yes | Yes |
| AlTiN | Yes | Yes | Yes | Yes |
| Black Oxide | Yes | Yes | Yes | Yes |
| CVD Al2O3 | Yes | Yes | Yes | Yes |
| CVD TiCN | Yes | Yes | Yes | Yes |
| CVD TiN | Yes | Yes | Yes | Yes |
| Cerakote | Yes | Yes | Yes | Yes |
| Chemical Etching | Yes | Yes | Yes | Yes |
| Chrome Plating | Yes | Yes | Yes | Yes |
| Copper Plating | Yes | Yes | Yes | Yes |
| CrN | Yes | Yes | Yes | Yes |
| DLC | Yes | Yes | Yes | Yes |
| Dot Peen Marking | Yes | Yes | Yes | Yes |
| E-Coating | Yes | Yes | Yes | Yes |
| Electro-chemical Etching | Yes | Yes | Yes | Yes |
| Electroless Nickel (EN) | Yes | Yes | Yes | Yes |
| Embossing / Debossing | Yes | Yes | Yes | Yes |
| Epoxy Coating | Yes | Yes | Yes | Yes |
Showing 18 of 47 finishes — the full list is on each grade's datasheet.
Typical handbook values for the default condition, normalised for comparison. Hardness on non-Brinell scales is converted approximately for charting only. Request certified data with your order for design-critical properties.