Welding 4340 Steel. Pre hardened and tempered 4340 can be further. This article provides a detailed introduction to the AISI 4140 materials their properties welding and PWHT requirements.
Guidance details for welding include the use of low-hydrogen electrodes and a preheat from 400 570 º F 200 300 º C if possible to be maintained during welding. 4340 is a 18 nickel - chromium - molybdenum high hardenability high tensile steel - generally supplied hardened and tempered in the tensile range of 930 - 1080 Mpa condition U - Rc 28 - 36. It can be easily gas or arc welded but electrodes of the same composition should be used.
Qualify the base metal composition if possible.
This alloy 4340 may be heat treated to high strength levels while. You also need to understand that welding to hardened H13 and 4140 and 4340 steels will require PWHT below the original tempering temperature used for hardening. 4340 MODIFIED TOOL STEEL. TYPICAL WELDING PROCEDURE The procedure that follows are those that should be used when repairing most The following procedures should be utilized for the repair of AISISAE 4340 TOOL STEEL.