Steel SMn420-A vs SMn420-QT
Steel · SMn420 temper comparison
SMn420-A and SMn420-QT are two conditions of the same steel grade, SMn420: A (solution annealed) versus QT (quenched and tempered). The chemistry is identical, so every difference below comes from the condition. SMn420-QT is the stronger of the two: yield strength 600 MPa (87 ksi) against 300 MPa (43.5 ksi) for SMn420-A, about 100% more; tensile strength follows at 780 MPa (113 ksi) vs 490 MPa (71.1 ksi). In exchange, SMn420-A is the more ductile: elongation 30% versus 19% for SMn420-QT, and SMn420-QT is harder (240 HB vs 143 HB). On the shop floor, SMn420-A machines more easily (good vs fair) and SMn420-A welds better (good vs fair).
SMn420-AChoose it when the part is bent, formed or impact-loaded, or when the part is machined in volume.
SMn420-QTChoose it when strength drives the design.
SMn420-A vs SMn420-QT: 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.
Tensile Strength (Ultimate)
Yield Strength (0.2% offset)
Elongation at Break
Reduction in Area
Fatigue Strength (Endurance Limit)
Charpy V-Notch Impact (RT)
Hardness, Brinell
Hardness, Rockwell B
Same in both: Elastic (Young's) Modulus 205 GPa29.7 Msi · Shear Modulus 80 GPa11.6 Msi · Bulk Modulus 160 GPa23.2 Msi · Poisson's Ratio 0.29 · Shear Strength 380 MPa55.1 ksi
Physical
Density and transition temperatures.
Same in both: Density 7.85 g/cm³0.28 lb/in³ · Melting Point (Solidus) 1,425°C2,597 °F · Liquidus Temperature 1,500°C2,732 °F
Thermal
How each material carries heat and how hot it can run.
Same in both: Thermal Conductivity 44 W/m·K25.4 BTU/hr·ft·°F · Specific Heat Capacity 470 J/kg·K0.11 BTU/lb·°F · Thermal Expansion (CTE, 20–100 °C) 12.2 µm/m·K6.8 µin/in·°F · Latent Heat of Fusion 270 J/g116 BTU/lb · Max Service Temperature (continuous) 400°C752 °F · Min Service Temperature -40°C-40 °F
Electrical
Conductivity and insulation.
Same in both: Electrical Conductivity 8.6 % IACS · Electrical Resistivity 2×10⁻⁷ Ω·m7.87 µΩ·in
Chemical & Environmental
Corrosion and environmental resistance (0–100 scores).
Same in both: Galvanic Potential (seawater, vs SCE) -0.6 V · Corrosion Resistance 11 / 100
Manufacturability
FabDigit workshop ratings (0–100 scores) — how each material behaves on the machine.
Machinability
Machinability Rating (AISI 1212 = 100 %)
Weldability
Formability (cold)
Same in both: Brazeability / Solderability 70 / 100 · Polishability 55 / 100
Sustainability
Primary-production footprint per kilogram.
Same in both: Embodied Energy (primary production) 26 MJ/kg11,178 BTU/lb · Embodied Carbon (primary production) 2.1 kg CO₂/kg · Embodied Water 45 L/kg5.4 gal/lb · Typical Recycled Content 25%
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.
SMn420-A vs SMn420-QT — frequently asked
Is SMn420-QT stronger than SMn420-A?
Yes. SMn420-QT has a typical yield strength of 600 MPa (87 ksi) against 300 MPa (43.5 ksi) for SMn420-A — about 100% more. Tensile strength is 780 MPa (113 ksi) vs 490 MPa (71.1 ksi).
Which condition does FabDigit quote by default, A or QT?
HR is the default SMn420 condition in the FabDigit quote flow (neither A nor QT). The other condition is available on request or by drawing note — specify it in the material field or the part notes and the quote is priced for it.
Which is easier to machine, SMn420-A or SMn420-QT?
SMn420-A. Its machinability rates good (63/100) against fair (48/100) for SMn420-QT; for welding the order is SMn420-A first (good, 62/100) then SMn420-QT (fair, 45/100).
Ready to make it?
Upload a CAD file and FabDigit prices the part in SMn420-A and SMn420-QT 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.