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.