Tool Steel EN 24

BS970: 1955 EN24, BS970/PD970: 1970 onwards 817M40. Related European grades: 34CrNiMo6, Werkstoff No. 1.6582 US Grade: SAE (AISI) 4340.

EN24 is usually supplied in the finally heat treated condition (quenched and tempered to “T” properties) up to a limiting ruling section of 250mm, which is superior to grades 605M36, 708M40 or 709M40 -see properties below. Please refer to our selection guide for comparisons.

EN24 is a very popular grade of through-hardening alloy steel, which is readily machinable in the “T” condition. (Refer to our machinability guide). EN24T is most suitable for the manufacture of parts such as heavy-duty axles and shafts, gears, bolts and studs. EN24T can be further surface-hardened typically to 58-60 HRC by induction or nitride processes, producing components with enhanced wear resistance.

In addition to the above, EN24T is capable of retaining good impact values at low temperatures, hence it is frequently specified for harsh offshore applications such as hydraulic bolt tensioners and shipborne mechanical handling equipment.

EN24 sections larger than 250mm may still be available in the quenched and tempered condition, but it should be noted that a fall-off in mechanical properties may be apparent approaching the centre of the bar.

It is therefore recommended that larger sizes are supplied in the annealed (softened) condition, and that quenching and tempering is carried out after initial stock removal. This should achieve better mechanical properties towards the core.

We stock EN24 in bright bar and blocks and black bar, square, flats and blocks.

Chemical Composition

Properties Metric Imperial
Density 7.85 g/cc 0.284 lb/in3

Mechanical Properties

Tensile strength Rm Mpa Yield stress Re MPa Rp 0.2 Mpa A min on 5.65 Impact Hardness HB Limiting Ruling Section
Heat Treatment Izod KCV J mm
T 850/1000 650 635 13 30 35 248/302 250
U 925/1075 755 740 12 35 42 269/331 100
V 1000/1150 850 835 12 35 42 293/352 63
W 1075/1225 940 925 11 30 35 311/375 29
X 1150/1300 1020 1005 10 25 28 341/401 29
Y 1225/1375 1095 1080 10 18 21 363/429 209
Z 1550 1235 1125 5 8 19 444 29
20-100℃ 10.8*10-6 20-300℃ 11.7*10-6
20-200℃ 11.1*10-6 20-400℃ 12.0*10-6
20-220℃ 11.3*10-6 100-200℃ 11.4*10-6
20-240℃ 11.3*10-6 200-300℃ 12.7*10-6

EN24 Equivalents

BS970: 1955 EN24
BS970/PD970: 1970 onwards 817M40
European 34CrNiMo6
Werkstoff No. 1.6582
US SAE (AISI) 4340
Carbon(C) Directly influences the hardness and strength of the steel, decreases toughness.
Chromium(Cr) Improves Hardenability, high temperature strength, wear resistance and even corrosion resistance(Cr>14%).
Cobalt(Co) Improves retention of hardness at high temperatures.
Molybdenum(Mo) Increases yield point and strength. Improves Hardenability and wear resistance. Manganese Lowers effects of Iron sulphides, increases hardenability, wear resistance.
Nickel(Ni) Increases toughness at lower temperatures, slows the corrosion process. Improves toughness, grain structure, high temperature strength, wear resistance, etc.
Vanadium(V) Increases wear resistance, high temperature strength, retention of hardness etc.
Silicon(Si) It is a deoxidizing agent. Increases strength and wear resistance. It is of importance that certain elements are as low as possible. Elements like Hydrogen, Oxygen, Nitrogen, Phosphorous, Sulphur create defects inside & also reduce the mechanical properties of steels.

Heat uniformly and thoroughly at the selected tempering temperature, up to 660°C and hold at heat for two hours per inch of total thickness.
Tempering between 250-375°C in not recommended as this can seriously reduce the steels impact value.


Heat uniformly to 823/850°C until heated through. Quench in oil.

Stress Relieving

Heat slowly to 650-670°C, soak well. Cool the EN24 tool in a furnace or in air.