Modulus of elasticity of steel: why every steel is about as stiff

What does the modulus of elasticity of steel mean for a real part?

For a deflection calculation of a steel part, use 200 GPa unless the datasheet of the steel you will buy states another value. 44 of 48 steel profiles in our data lie within 5% of 200 GPa, and deflection changes by the same percentage as the modulus. To make a part stiffer, make the section deeper or the span shorter, because deflection falls with the cube of the depth and rises with the cube of the span.

Which modulus should be used in a hand calculation?

For a hand calculation of a steel part, 200 GPa is within about 5% of almost every grade we hold (44 of 48), and 48 of 48 are within 10%. Austenitic stainless grades such as 316L and 321 print 193 GPa in at least one source, and the ferritic 409 and 444 print 208 to 220 GPa. If your part is deflection-limited and the margin is small, use the value from the datasheet of the steel you will buy, not a generic one. Deflection is proportional to 1/E, so using 200 GPa where a datasheet says 193 GPa changes the deflection by 3.6%.

What makes a steel part stiffer?

In every formula above, deflection falls with the modulus E and with the second moment of area I, and it rises with the cube of the span. For a rectangle I grows with the cube of the depth. Making a bar 26% deeper halves its deflection; shortening the span by 20% roughly halves it again. A better steel does neither. This is why a thin plate of any steel is floppy, and why ribs, flanges and tubes work: they put material far from the neutral axis.

What does strength change, if not stiffness?

A harder or higher-strength steel lets you load a part further before it takes a permanent set. It does not reduce the elastic bend at a given load. In the calculator, the stress row compares the peak bending stress with the yield strengths in each grade's record. 1018 ranges from 240 to 370 MPa depending on the datasheet's condition, 4140 from 570 to 1,235 MPa, and both print a modulus near 200 GPa. See also yield strength vs tensile strength.

How do aluminium and titanium compare with steel?

The median aluminium alloy in our data is 2.9 times less stiff than the median steel and the median titanium alloy 1.8 times less stiff. They are also lighter, so a deeper section can recover the stiffness at less mass. That is the second preset in the calculator. It only works where the extra depth fits, and it does nothing for bolted joints, thin walls or buckling. Compare the grades on the pages for steel vs aluminium, titanium vs steel and titanium vs aluminium.

Is cast iron as stiff as steel?

The two cast irons in our data print 68.9 to 169 GPa between them. Gray cast iron prints 103 to 118 GPa for EN-GJL-250 and 68.9 to 144.8 GPa across four ASTM A48 classes in another source, which does not say whether its figures are minimum or typical. If a drawing says "iron", do not use 200 GPa. See iron vs steel.

Which data on the modulus of elasticity of steel is missing?

Not found in any source we hold: a modulus of elasticity for 1.2316 stainless plastic mould steel, Fecralloy, Ferroalloys, Silver steel, PH 13-8Mo stainless steel and 300M ultra-high-strength steel, and for 4 aluminium profiles. A shear modulus is held for only 8 steel profiles, and the test temperature, form or heat treatment is not stated for 45 of 83 room-temperature steel records. These gaps stay blank.

• No sourced modulus. 1.2316 stainless plastic mould steel, Fecralloy, Ferroalloys, Silver steel, PH 13-8Mo stainless steel and 300M ultra-high-strength steel have no modulus in any source we hold, so they are not in the calculator or the charts. Among aluminium profiles, alloys 2319 and 4047 and 2 master-alloy and intermetallic records have none either. We do not fill the gap from memory.
• Conditions are often missing. 45 of the 83 room-temperature steel records say the test temperature, form or heat treatment is not stated. Treat them as typical values.
• Typical, not guaranteed. Datasheet moduli are typical values. Design codes and specifications may require different values (general engineering knowledge, not in our data). Several aluminium datasheets note that the quoted value averages tension and compression, with compression about 2% higher.
• Some values are dynamic. The 440C record is marked as a dynamic modulus, as printed, and sits at 209.6 GPa next to 200 GPa from static datasheets. Dynamic and static moduli can differ a little (general engineering knowledge, not in our data).
• Few shear and Poisson records. Shear modulus is printed for 8 steels and Poisson's ratio for 20; many grades have neither. Several of the Poisson records are bands (0.27 to 0.30) printed by databases for a whole grade.
• Family records left out. Two profiles describe groups of alloys rather than one grade (5XXX aluminium and minor titanium alloys). They are left out of the grade count. Their numbers are on their profile pages. A class value for gamma titanium aluminide, quoted from a comparison table, is also left out. 18 modulus records in all are excluded from the room-temperature figures (elevated temperature or class values); the CSV lists each with the reason.
• Solid rectangles only. The calculator does not cover tubes, angles or I-sections, which are stiffer for their weight. It does not include self-weight or shear deformation, and it assumes the section stays straight and flat (general engineering knowledge, not in our data).
• Cast iron. Cast irons are included for contrast. Only two profiles, and one carries four class values with no stated basis.
• No price, availability or processing data on this page. It is about elastic stiffness only.

Related on Space Mushroom

• How stiff are engineering materials? Modulus from plastic to tungsten
• Young's modulus of materials: steels, aluminium, titanium, polymers compared
• Which carbon or alloy steel should you choose?
• Which stainless steel to choose
• Which tool steel: D2, H13, P20, 1.2316 or 1.2738?
• Which aluminium alloy to choose
• Which titanium grade to choose
• Yield strength vs tensile strength: how big is the gap?
• Stainless steel vs carbon steel
• 1018 vs 4140 steel
• Steel vs aluminium
• Titanium vs steel
• Carbon and alloy steels, tool steels, stainless steels, aluminium alloys, titanium alloys, cast irons