How to Weld EN24/ AISI 4340 and EN 24/4340 with A36 or carbon steel


What is EN24 material?

EN24 is a very high-strength steel alloy that is supplied hardened and tempered. The grade is a nickel-chromium-molybdenum combination – this offers high tensile steel strength, with good ductility and wear resistance characteristics. With relatively good impact properties at low temperatures, EN24 is also suitable for a variety of elevated temperature applications.

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EN 24 also fall under 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 condition.

EN24- 4340 welding

The strength of both materials can change greatly depending on the thermal treatment that has been performed: annealing, normalizing or quenching and tempering. Flame hardening can be used to additionally harden the outside of these materials while keeping the interior relatively soft.

Material Specifications

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

Chemical Properties

How to Weld EN24

Mechanical Properties

How to Weld EN24

Welding procedure for EN 24 or AISI 4340

This grade is readily welded in the annealed condition, but welding in the hardened and tempered condition should be avoided where possible because of the effect on mechanical properties. Welding in the nitrided or flame or induction hardened conditions is not recommended.

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.

  • Qualify the base metal composition, if possible.
  • Visually inspect the tool or die to determine the reason for failure and establish the exact area of repair. Record any dimensions that will be altered during the course of repair for reference when remachining to original dimensions.
  • Machine, grind, or Arc Air Gouge defective areas, etc. If arc air gouging is the preparation method to be used, then preheating before preparation must be exercised. Preparation for welding by remachining or grinding does not require preheating.
  • Preheat 600° – 700°F. for one hour per inch of thickness.
  • Select the appropriate welding process for the repair condition encountered. Choose one or more of the following welding processes. The G.T.A.W. or tig process can be welded using ER4340 type filler wire, using direct current straight polarity (D.C.S.P.) with 100% argon shielding gas; or S.M.A.W. or stick electrode process; or G.M.A.W. or wire welding process using direct current reverse polarity (D.C.R.P.) for both processes use 75% argon, 25% Co2 shielding gas with flow rate of 40 – 60 C.F.H. when using the wire process.
  • Alloy Selection: Select an alloy that meets the service requirements of the tool or die while in operation.
  • Peen each weld deposit immediately after breaking arc.
  • Eliminate all undercuts, square-up rounded corners, etc.
  • Immediately after welding, the dies should be post heated back to preheat temperature 700° to equalize weld deposit and tool or die temperature prior to slow cooling. If the preheat temperature has been maintained during welding, this step may be skipped; thereby ,commencing immediately to the following step.
  • Slow cool welded tool or die to room temperature for a minimum of 150°
  • Temper the welded tool or die by immediately placing the section into the furnace at 800° for one hour per inch of tool or die thickness.
  • Slow cool to room temperature.
  • Commence with machining.

Welding electrode/ TIG -MIG Filler for EN24/ AISI 4340 Welding

Use E8018-B2 or ER80S-B2 when carry out weld builtup 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 requires strength in E24/ AISI 4340 materials, welding can be carried out using E10018-D2 or ER10018-D2 filler wire. These consumables matching strength but have high risk of hydrogen cracking thus proper preheating, fully baked low hydrogen electrodes and slow cooling is mandatory.

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