What is EN24 (AISI 4340) material?
EN24 (AISI 4340) is a very high-strength steel alloy that is supplied hardened and tempered. The steel is having high carbon with added Nickel, Chromium and molybdenum to enhance the heat treatment response. The added alloying elements provides high tensile strength, good ductility, abrasion resistance and good toughness at low temperature to the material. The alloy can also be used for high temperature applications.
EN 24 also falls under the AISI classification as AISI 4340 which is a Nickel-Chromium-Molybdenum alloy steel having high toughness, high strength, and very good fatigue resistance in heat-treated conditions. Heat treatment process can enhance the mechanical properties of EN24 or AISI 4340 material to a great extent.
Due to high carbon content and alloying with nickel and chrome, the heat treatment response of EN24 is very good. Annealing, Q & T, and normalizing heat treatments are used for this material to change the mechanical and chemical response to suit various service conditions.
Due to high carbon content, material also respond very good for surface heat treatments such as flame hardening & case hardening.
The UNS Number of EN24 or AISI 4340 is UNS G43400. The material specifications for technical and delivery conditions for EN 24/ AISI 4340 are listed below for reference:
BS 970:1955 EN24T
BS 970:1991 817M40T
German / DIN 34CrNiMo6
French AFNOR 35NCD6
American AISI / SAE 4340
German Werkstoff No. 1.6582
European Standard EN10277-5
EN 24 (AISI 4340) contains carbon from 0.36% to 0.44%, silicon 0.45% to 0.70%, Mo 0.20%- 0.35%, Cr 1.00% to 1.40%, Ni 1.3%- 1.7%.
Welding procedure for EN 24 or AISI 4340 (DIN 34CrNiMo6)
EN 24 or AISI 4340 material if in annealed condition can be welded without much concerns. For steel in quenched & tempered condition is difficult to weld and welding of such type should be avoided. Also material having nitriding or flame hardened condition should be avoided due to weldability issues such as cracking in HAZ and weld.
Welding with low-hydrogen electrodes and a preheat from 400 –570ºF (200 – 300º C,) to be maintained during welding. Parts should be slow cooled after welding in glass wool or asbestos cloth blanket.
Welding electrode/ TIG -MIG Filler for EN24/ AISI 4340 (DIN 34CrNiMo6) Welding
Use E8018-B2 or ER80S-B2 when carrying out weld built up or crack repairs. These consumables will have low strength than the actual EN24/ AISI 4340 Q & T material although offer similar metallurgy and crack-resistant weld.
For weld joints that requires strength in E24/ AISI 4340 materials, welding can be carried out using E10018-D2 or ER10018-D2 filler wire. These consumables match strength but have a high risk of hydrogen cracking thus proper preheating, fully baked low hydrogen electrodes and slow cooling is mandatory.
Welding EN24 (AISI 4340) to mild/carbon steel
Stick welding of EN24 (AISI 4340) to mild steel or carbon steel is carried out using E7018 or E8018-B2 rod. Welding rod shall be baked prior to use. All low hydrogen stick welding rods must be baked to ensure weld is free from hydrogen cracking.
TIG or MIG-MAG welding of EN24 (AISI 4340) to mild steel or carbon steel is carried out using ER70S-2 or ER80S-B2type filler wire.
Preheat & Interpass for AISI 4340 (EN24) welding
Preheat must be applied for welding of AISI 4340 (EN24) material. Apply a minimum preheat temperature of 300°F- 400°F (150°C- 200°C). The interpass temperature shall be a maximum of 400°F ( 200°C). Ensure preheat maintenance until the welding is completed. In case of weld interruption, apply the preheat again before the start of the welding.