Nickel-chromium-molybdenum (Ni-Cr-Mo) steels are a family of alloy steels used where a component needs to combine high tensile strength with good toughness — often in sections too large or too highly stressed for plain carbon steel to harden reliably all the way through.
The family splits into two broad groups. Through-hardening grades — EN19, EN24, and EN25 — are hardened and tempered as a whole section. EN19 (equivalent to SAE/AISI 4140) is used for axles, drive shafts, crankshaft connecting rods, and high-tensile bolts and studs. EN24 (equivalent to SAE/AISI 4340) carries higher nickel content for greater toughness and is used for gears, axles, high-strength studs, and heavy-duty shafting. EN25 carries the highest nickel and molybdenum content in this comparison, intended for the largest or most heavily loaded sections.
Case-hardening and nitriding grades — EN36, EN40B, EN-353, and EN-354 — are treated to give a hard wearing surface over a tough core. EN36 is used for high-duty gears and shafts; EN40B is a nitriding steel used for drills, guides, shafts, gear wheels, and fixings.
EN16 and EN111 are lower-alloy members of the same family, used in less severely stressed applications than EN19/EN24.
The table below cross-references each BS 970 grade against its SAE/AISI and IS equivalents, alongside chemical composition, so you can match a specification from any of the three standards to the same underlying steel.
| NICKEL-CHROMIUM-MOLYBDENUM STEELS | ||||||||
| BS : 970 | SAE/AISI | IS:3930 IS:4432 IS:5517 | C% | Mn% | Si% | Cr% | Ni% | Mo% |
| EN16 | 35Mn6Mo3 | 0.32/0.40 | 1.30/1.80 | 0.10/0.35 | 0.20/0.35 | |||
| EN19 | 4140 | 40Cr4 Mo3 | 0.38/0.45 | 0.50/0.80 | 0.10/0.35 | 0.90/1.20 | 0.20/0.35 | |
| EN24 | 4340 | 40Ni6Cr4Mo3 | 0.35/0.45 | 0.40/0.70 | 0.10/0.35 | 0.90/1.30 | 1.25/1.75 | 0.20/0.35 |
| EN25 | 31Ni10Cr3Mo6 | 0.27/0.35 | 0.50/0.70 | 0.10/0.35 | 0.50/0.80 | 2.30/2.80 | 0.40/0.70 | |
| EN36 | 13Ni3Cr 80 | 0.15/0.18 | 0.30/0.60 | 0.10/0.35 | 0.60/1.10 | 3.00/3.75 | ||
| EN40B | 25Cr13Mo6 | 0.20/0.30 | 0.40/0.65 | 0.10/0.35 | 2.90/3.50 | 0.25/0.40 | 0.40/0.70 | |
| EN111 | 3140 | 35Ni5Cr2 | 0.30/0.40 | 0.60/0.90 | 0.10/0.35 | 0.45/0.75 | 1.00/1.50 | |
| EN-353 | 15 Ni Cr 1 Mo12 | 0.12/0.18 | 0.60/1.00 | 0.10/0.35 | 0.75/1.25 | 1.00/1.50 | 0.80/0.15 | |
| EN-354 | 4320 | 15 Ni 1Cr 1Mo 15 | 0.12/0.18 | 0.60/1.00 | 0.10/0.35 | 0.75/1.25 | 1.50/2.00 | 0.10/0.20 |
For a closer look at the two most commonly specified grades in this family, see our dedicated guides to EN19 Steel and EN24 Steel.
