Steel 38Si7 +H vs 38Si7 +QT
Steel · 38Si7 temper comparison
38Si7 +H and 38Si7 +QT are two conditions of the same steel grade, 38Si7: +H (supplied to a specified hardenability (Jominy) band) versus +QT (quenched and tempered). The chemistry is identical, so every difference below comes from the condition. 38Si7 +QT is the stronger of the two: yield strength 1,150 MPa (167 ksi) against 400 MPa (58 ksi) for 38Si7 +H, about 188% more; tensile strength follows at 1,300 MPa (189 ksi) vs 660 MPa (95.7 ksi). In exchange, 38Si7 +H is the more ductile: elongation 17% versus 9% for 38Si7 +QT, and 38Si7 +QT is harder (390 HB vs 220 HB). 38Si7 +H runs hotter in service (350°C vs 250°C continuous) and 38Si7 +H conducts electricity better (7.8 % IACS vs 7 % IACS). On the shop floor, 38Si7 +H machines more easily (fair vs poor) and 38Si7 +H welds better (30 vs 15 out of 100).
38Si7 +HChoose it when the part is bent, formed or impact-loaded, or when the part sees heat.
38Si7 +QTChoose it when strength drives the design.
38Si7 +H vs 38Si7 +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
Compressive Strength
Shear Strength
Fatigue Strength (Endurance Limit)
Fracture Toughness (K_IC)
Charpy V-Notch Impact (RT)
Hardness, Brinell
Hardness, Rockwell C
Hardness, Vickers
Same in both: Elastic (Young's) Modulus 206 GPa29.9 Msi · Shear Modulus 79.5 GPa11.5 Msi · Bulk Modulus 160 GPa23.2 Msi · Poisson's Ratio 0.29
Physical
Density and transition temperatures.
Same in both: Density 7.8 g/cm³0.28 lb/in³ · Melting Point (Solidus) 1,420°C2,588 °F · Liquidus Temperature 1,490°C2,714 °F
Thermal
How each material carries heat and how hot it can run.
Thermal Conductivity
Max Service Temperature (continuous)
Same in both: Specific Heat Capacity 470 J/kg·K0.11 BTU/lb·°F · Thermal Expansion (CTE, 20–100 °C) 11.5 µm/m·K6.4 µin/in·°F · Latent Heat of Fusion 250 J/g107 BTU/lb · Min Service Temperature -40°C-40 °F
Electrical
Conductivity and insulation.
Electrical Conductivity
Electrical Resistivity
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 35 / 100 · Polishability 60 / 100
Sustainability
Primary-production footprint per kilogram.
Same in both: Embodied Energy (primary production) 24 MJ/kg10,318 BTU/lb · Embodied Carbon (primary production) 1.9 kg CO₂/kg · Embodied Water 60 L/kg7.2 gal/lb · Typical Recycled Content 30%
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.
38Si7 +H vs 38Si7 +QT — frequently asked
Is 38Si7 +QT stronger than 38Si7 +H?
Yes. 38Si7 +QT has a typical yield strength of 1,150 MPa (167 ksi) against 400 MPa (58 ksi) for 38Si7 +H — about 188% more. Tensile strength is 1,300 MPa (189 ksi) vs 660 MPa (95.7 ksi).
Which condition does FabDigit quote by default, +H or +QT?
+QT is the default 38Si7 condition in the FabDigit quote flow. 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, 38Si7 +H or 38Si7 +QT?
38Si7 +H. Its machinability rates fair (50/100) against poor (30/100) for 38Si7 +QT; for welding the order is 38Si7 +H first (poor, 30/100) then 38Si7 +QT (poor, 15/100).
Ready to make it?
Upload a CAD file and FabDigit prices the part in 38Si7 +H and 38Si7 +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.