Steel Suppliers and stockholders - KV Steel Services, Darlaston, West Midlands

817M40 and 817M40T Steel

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

817M40: a popular grade of through-hardening alloy steel; it is readily machinable in the "T" condition. (See our machinability guide).
817M40T is suitable for the manufacture of parts such as shafts, gears and heavy-duty axles as well as studs and bolts.  817M40T can be further surface-hardened - typically to 58-60 HRC - by induction or nitride processes to produce components with enhanced wear resistance.

817M40 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.

In addition, 817M40T retains good impact values at low temperatures, and is frequently specified for harsh offshore applications such as hydraulic bolt tensioners and shipborne mechanical handling equipment.

817M40 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.

817M40 - Chemical composition
Carbon 0.36-0.44%
Silicon 0.10-0.35%
Manganese 0.45-0.70%
Sulphur 0.040 Max
Phosphorus 0.035 Max
Chromium 1.00-1.40%
Molybdenum 0.20-0.35%
Nickel 1.30-1.70%


817M40 - mechanical properties in "T" condition
Max Stress 850-1000 n/mm2  
Yield Stress 680 n/mm2 Min (up to 150mm LRS)
Yield Stress 650 n/mm2 Min (over 150 to 250mm LRS)
0.2% Proof Stress 665 n/mm2 Min (up to 150mm LRS)
0.2% Proof Stress 635 n/mm2 Min (over 150 to 250mm LRS)
Elongation 13% Min (9% if cold drawn)
Impact KCV 50 Joules Min (up to 150mm LRS
Impact KCV 35 Joules Min (over 150 to 250mm LRS)
Hardness 248-302 Brinell  


KV Steel Services is a supplier of 817M40 to local and national businesses


817M40T Steel Bar