Steel A48 Class 40-FH vs A48 Class 40-SR
Steel · A48 Class 40 temper comparison
A48 Class 40-FH and A48 Class 40-SR are two conditions of the same steel grade, A48 Class 40: FH (full hard) versus SR (stress relieved). The chemistry is identical, so every difference below comes from the condition. Both yield at about 230 MPa — the mechanical properties are the same, and the difference is in how the stock is processed and what it is certified to (full hard versus stress relieved). A48 Class 40-SR is the more ductile: elongation 0.6% versus 0.4% for A48 Class 40-FH, and A48 Class 40-FH is harder (480 HB vs 230 HB). A48 Class 40-SR runs hotter in service (400°C vs 250°C continuous). On the shop floor, A48 Class 40-SR machines more easily (good vs poor) and A48 Class 40-SR welds better (poor vs not recommended).
A48 Class 40-SRChoose it when the part is bent, formed or impact-loaded, or when the part sees heat.
A48 Class 40-FH vs A48 Class 40-SR: 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.
A48 Class 40-FHA48 Class 40-SR
Mechanical
Strength, stiffness, ductility and hardness at room temperature.
Tensile Strength (Ultimate)
Yield Strength (0.2% offset)
Elongation at Break
Compressive Strength
Shear Strength
Fatigue Strength (Endurance Limit)
Fracture Toughness (K_IC)
Charpy V-Notch Impact (RT)
Hardness, Brinell
Hardness, Rockwell B
Same in both: Elastic (Young's) Modulus 125 GPa18.1 Msi · Shear Modulus 50 GPa7.3 Msi · Bulk Modulus 87 GPa12.6 Msi · Poisson's Ratio 0.26
Physical
Density and transition temperatures.
Same in both: Density 7.15 g/cm³0.26 lb/in³ · Melting Point (Solidus) 1,150°C2,102 °F · Liquidus Temperature 1,240°C2,264 °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 460 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 220 J/g94.6 BTU/lb · Min Service Temperature -30°C-22 °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) -0.61 V
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: Castability 95 / 100 · Brazeability / Solderability 45 / 100 · Polishability 35 / 100
Sustainability
Primary-production footprint per kilogram.
Same in both: Embodied Energy (primary production) 18 MJ/kg7,739 BTU/lb · Embodied Carbon (primary production) 1.7 kg CO₂/kg · Embodied Water 50 L/kg6 gal/lb · Typical Recycled Content 90%
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.
A48 Class 40-FH vs A48 Class 40-SR — frequently asked
What is the difference between A48 Class 40-FH and A48 Class 40-SR?
A48 Class 40-FH and A48 Class 40-SR are two conditions of the same steel grade, A48 Class 40: FH (full hard) versus SR (stress relieved). The chemistry is identical, so every difference below comes from the condition. Both yield at about 230 MPa — the mechanical properties are the same, and the difference is in how the stock is processed and what it is certified to (full hard versus stress relieved).
Which condition does FabDigit quote by default, FH or SR?
AC is the default A48 Class 40 condition in the FabDigit quote flow (neither FH nor SR). 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, A48 Class 40-FH or A48 Class 40-SR?
A48 Class 40-SR. Its machinability rates good (68/100) against poor (15/100) for A48 Class 40-FH; for welding the order is A48 Class 40-SR first (poor, 25/100) then A48 Class 40-FH (not recommended, 5/100).
Ready to make it?
Upload a CAD file and FabDigit prices the part in A48 Class 40-FH and A48 Class 40-SR 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.