Steel 4340 vs S690QL
Steel · grade comparison
Steel 4340 and S690QL are both steel grades, both high strength steel. S690QL is the stronger of the two: yield strength 760 MPa (110 ksi) against 620 MPa (89.9 ksi) for 4340, about 23% more. In exchange, 4340 is the more ductile: elongation 18% versus 16% for S690QL, and 4340 is harder (285 HB vs 265 HB). 4340 runs hotter in service (400°C vs 350°C continuous) and 4340 conducts heat better (44.5 W/m·K vs 35 W/m·K). On the shop floor, S690QL welds better (good vs poor) and S690QL sits in a lower cost tier (standard, $$) than 4340 (premium, $$$).
4340Choose it when the part is bent, formed or impact-loaded, or when the part sees heat.
S690QLChoose it when strength drives the design, or when it will be welded.
4340 vs S690QL: propertiesHow to read these bars
- One bar per material. A full bar is the highest value among all steel grades in the FabDigit library; each bar is drawn as a share of that.
- The better value (by the usual engineering direction) is in bold. Rows with no direction — density, thermal conductivity — have no bold.
- Values are typical room-temperature figures for the condition named on each card.
- Confirm against the certified mill or resin datasheet before design release.
How to read these bars
- One bar per material. A full bar is the highest value among all steel grades in the FabDigit library; each bar is drawn as a share of that.
- The better value (by the usual engineering direction) is in bold. Rows with no direction — density, thermal conductivity — have no bold.
- Values are typical room-temperature figures for the condition named on each card.
- Confirm against the certified mill or resin datasheet before design release.
Mechanical
Strength, stiffness, ductility and hardness at room temperature.
Elastic (Young's) Modulus
Shear Modulus
Poisson's Ratio
Tensile Strength (Ultimate)
Yield Strength (0.2% offset)
Elongation at Break
Reduction in Area
Compressive Strength
Shear Strength
Fatigue Strength (Endurance Limit)
Fracture Toughness (K_IC)
Charpy V-Notch Impact (RT)
Hardness, Brinell
Hardness, Rockwell B
Hardness, Rockwell C
Hardness, Vickers
Same in both: Bulk Modulus 160 GPa23.2 Msi
Physical
Density and transition temperatures.
Melting Point (Solidus)
Liquidus Temperature
Same in both: Density 7.85 g/cm³0.28 lb/in³
Thermal
How each material carries heat and how hot it can run.
Thermal Conductivity
Specific Heat Capacity
Thermal Expansion (CTE, 20–100 °C)
Latent Heat of Fusion
Max Service Temperature (continuous)
Same in both: Min Service Temperature -40°C-40 °F
Electrical
Conductivity and insulation.
Electrical Conductivity
Electrical Resistivity
Chemical & Environmental
Corrosion and environmental resistance (0–100 scores).
Corrosion Resistance
Same in both: Galvanic Potential (seawater, vs SCE) -0.62 V
Manufacturability
FabDigit workshop ratings (0–100 scores) — how each material behaves on the machine.
Machinability
Machinability Rating (AISI 1212 = 100 %)
Weldability
Formability (cold)
Castability
Brazeability / Solderability
Polishability
Sustainability
Primary-production footprint per kilogram.
Embodied Carbon (primary production)
Same in both: Embodied Energy (primary production) 32 MJ/kg13,758 BTU/lb · Embodied Water 60 L/kg7.2 gal/lb · Typical Recycled Content 30%
Common Calculations
Ratios derived from the values above.
Specific Strength (UTS / density)
Specific Stiffness (E / density)
Modulus of Resilience
Thermal Diffusivity
Thermal Shock Resistance Index
Strength versus weight
Yield strength against density for every steel grade in the FabDigit library; the compared grades are highlighted. Up and left is stronger for its weight.
Manufacturing and finishing
| Capability | 4340 | S690QL |
|---|---|---|
| Default condition | HR | Q&T |
| Relative cost | $$$ Premium | $$ Standard |
| Min. machined wall | 0.8 mm | 0.8 mm |
| Best machined surface | Ra 1.6 µm | Ra 1.6 µm |
Both are offered for CNC machining and Sheet metal. Both take the same 38 finishes: AlCrN, AlTiN, Black Oxide, CVD Al2O3, CVD TiCN, CVD TiN, Cerakote, Chrome Plating, Copper Plating, CrN, DLC, E-Coating and 26 more.
4340 vs S690QL — frequently asked
Is S690QL stronger than 4340?
Yes. S690QL has a typical yield strength of 760 MPa (110 ksi) against 620 MPa (89.9 ksi) for 4340 — about 23% more. Tensile strength is 830 MPa (120 ksi) vs 950 MPa (138 ksi).
Which is cheaper, 4340 or S690QL?
S690QL is the lower-cost material: it sits in the standard tier ($$) while 4340 is premium ($$$). Part price depends far more on geometry, tolerance and quantity than on raw stock — upload a CAD file for a live quote.
Which is easier to machine, 4340 or S690QL?
4340, by a small margin. Both rate fair for machinability — 48/100 against 40/100 for S690QL; for welding the order is S690QL first (good, 65/100) then 4340 (poor, 33/100).
Ready to make it?
Upload a CAD file and FabDigit prices the part in 4340 and S690QL side by side — material, machining time, tolerance and finish in one quote. Certified material data ships with the order on request.
Typical handbook values for the conditions named above, normalised for comparison. Hardness on non-Brinell scales is converted approximately for charting only. Request certified data with your order for design-critical properties.