Short answer: EN8, EN19 and EN24 all contain about 0.40% carbon; the difference is the alloying. EN8 is plain carbon steel, EN19 adds chromium and molybdenum, and EN24 adds nickel on top. Each step up hardens deeper, keeps its strength in thicker bars and is tougher. Use EN8 for lightly loaded parts, EN19 for medium-duty shafts and gears, and EN24 for heavily loaded or shock-loaded parts, especially in larger sizes.
In this guide: At a glance · Chemical composition · Strength by bar size · Typical uses · Substituting one for another · FAQ
EN8 vs EN19 vs EN24 at a glance
| EN8 | EN19 | EN24 | |
|---|---|---|---|
| BS 970 code | 080M40 | 709M40 | 817M40 |
| Type | Medium-carbon steel | Cr-Mo alloy steel | Ni-Cr-Mo alloy steel |
| Nearest equivalents | C40 / C45, AISI 1040, IS 40C8 | 42CrMo4, AISI 4140, IS 40Cr4Mo3 | 34CrNiMo6, AISI 4340, IS 40Ni2Cr1Mo28 |
| Depth of hardening | Shallow | Medium | Deep |
| Toughness | Fair | Good | Very good |
| Typical hardened strength | Up to about 850 MPa, small sizes only | Up to about 1,000–1,100 MPa | Up to about 1,000–1,300 MPa, even in larger sizes |
| Relative cost | Lowest | Medium | Highest |
For the full list of international names, see our equivalent grades chart.
Chemical composition
| Element, % | EN8 (080M40) | EN19 (709M40) | EN24 (817M40) |
|---|---|---|---|
| Carbon | 0.36–0.44 | 0.36–0.44 | 0.36–0.44 |
| Manganese | 0.60–1.00 | 0.70–1.00 | 0.45–0.70 |
| Silicon | 0.10–0.40 | 0.10–0.35 | 0.10–0.35 |
| Chromium | — | 0.90–1.20 | 1.00–1.40 |
| Molybdenum | — | 0.25–0.35 | 0.20–0.35 |
| Nickel | — | — | 1.30–1.70 |
The carbon is the same in all three, so the difference in behaviour comes almost entirely from the alloying. Chromium and molybdenum let EN19 harden deeper than EN8 and resist softening during tempering. Nickel is what sets EN24 apart: it improves toughness and lets the steel harden right through much thicker sections.
Strength by bar size: why EN24 costs more
The real difference shows in thick bars. During quenching the centre of a large bar cools slowly, and a less alloyed steel simply cannot harden there. These are typical hardened-and-tempered tensile strengths from the European equivalents of each grade (EN 10083):
| Bar size | EN8 type C45 | EN19 type 42CrMo4 | EN24 type 34CrNiMo6 |
|---|---|---|---|
| Up to Ø16 mm | 700–850 MPa | 1100–1300 MPa | 1200–1400 MPa |
| Ø16–40 mm | 650–800 MPa | 1000–1200 MPa | 1100–1300 MPa |
| Ø40–100 mm | 630–780 MPa | 900–1100 MPa | 1000–1200 MPa |
| Ø100–160 mm | not specified | 800–950 MPa | 900–1100 MPa |
| Ø160–250 mm | not specified | 750–900 MPa | 800–950 MPa |
Two things stand out. EN8 is only specified up to about Ø100 mm in the hardened condition, because beyond that it barely responds to hardening. And EN24 in a Ø100–160 mm bar is about as strong as EN19 one size smaller: that extra depth of hardening is what you pay for. See our hardness guide for the same figures in HRC, and the EN24 vs EN24T guide for the standard hardened conditions.
Typical uses
- EN8: lightly loaded shafts, pins, studs, bolts, spindles and general machined parts, often used as supplied or normalised. It is also flame- or induction-hardened on the surface for wear.
- EN19: medium-duty shafts, axles, gears, connecting rods and high-tensile bolts, where EN8 is not strong enough but sections are moderate.
- EN24: heavily loaded and shock-loaded parts: crankshafts, heavy-duty shafts and axles, gears, high-tensile bolts and studs, and parts for earthmoving, mining and oil and gas equipment. It is the usual choice when a large section must be strong right through.
Substituting one for another
- Going up is usually safe. EN24 can normally replace EN19, and EN19 can normally replace EN8, because the higher grade meets or exceeds the lower one's properties. Heat treatment temperatures differ, so tell your heat treater which grade they are working with.
- Going down is risky. EN8 or EN19 in place of EN24 may look fine in a small test piece but will not reach the same core strength in a large part. Never substitute downward without the designer's approval.
- Check the mill test certificate. Make sure the chemistry matches the grade on the drawing, especially the nickel content for EN24.
- Read the full code. EN24, 817M40 and 817M40T are the same steel in different conditions. Our BS 970 codes guide explains how to read them.
EN24 stock in Mumbai
Sai International stocks EN24 / 817M40 round bar from Ø16 to Ø205 mm at Darukhana, Mumbai: annealed up to Ø100 mm and as-rolled from Ø105 mm. EN24T (hardened and tempered) is supplied against orders of 3–5 tons. We do not stock EN8 or EN19. Minimum order is 100 kg, and every dispatch comes with a mill test certificate. Use our round bar weight calculator to work out weights before you order.
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EN8 vs EN19 vs EN24: frequently asked questions
What is the difference between EN8, EN19 and EN24?
All three have about 0.40% carbon. EN8 is a plain carbon steel with no alloying elements. EN19 adds about 1% chromium and 0.3% molybdenum. EN24 adds about 1.5% nickel as well as chromium and molybdenum. Each step up hardens deeper, reaches higher strength in larger sections and is tougher, but also costs more.
Can EN24 be used instead of EN19?
Usually yes. EN24 meets or exceeds EN19's strength and toughness in every common size, so it is a safe upgrade when EN19 is not available. Confirm with the designer, and adjust the heat treatment, because EN24 responds differently.
Can EN19 be used instead of EN24?
Only in smaller sections and lower strength levels. EN19 does not harden as deeply as EN24, so a large EN19 part will not reach the same core strength or toughness. Do not substitute downward without the designer's approval.
Is EN8 an alloy steel?
No. EN8 (080M40) is a medium-carbon steel with no deliberate alloying elements, which is why it is cheaper than EN19 and EN24 and why it cannot be hardened as deeply.
Which is better for shafts: EN8, EN19 or EN24?
EN8 suits lightly loaded shafts and pins. EN19 suits medium-duty shafts, axles and gears. EN24 is used for heavily loaded or shock-loaded shafts, especially in larger diameters, where its nickel gives the toughness and depth of hardening the others cannot.
Does Sai International stock EN8 and EN19?
No. We stock EN24 (817M40) round bar from Ø16 to Ø205 mm in Mumbai, along with EN47, EN36C, EN353 and SAE 8620. EN24T is supplied against orders of 3–5 tons.