Virtually all types of tool steel can be welded by the shielded metal arc, gas tungsten arc, plasma arc, or electron beam processes.  Die units used for blanking, forming, forging, drawing, embossing, coining, or hot and cold trimming can be salvaged or reclaimed using on of these processes.

Tool & die welding applications can be separated into four categories:

Tool and Die Welding Electrodes can be divided into two categories: basic tool steel welding electrodes, and alloy welding electrodes.  A combination of these two types is used for some applications.

Basic Tool Steel Welding Electrodes.   This group of coated electrodes includes water-hardening, air hardening, hot-working and high-speed steel.  These electrodes are in an annealed state, and the weld metal is hardened by air quenching from the high heat to the arc.  The weld deposits are "hard-as-welded," whether they are applied to hardened or annealed tool steel, mild, medium, or high-carbon steel, or to other alloy steels.  The weld deposits can be annealed to facilitate machining, then heat treated and tempered.  As a general rule, weld deposits will respond to the heat treatment recommended for the average tool steel in its classification.

Alloy Welding Electrodes.  Included in this group are low-alloy electrodes for plastic or zinc casting molds and flame-hardening dies.  Also in this group are the more highly alloyed electrodes used to weld dies for forging, drawing and forming.  These electrodes produce machinable weld deposits which are not affected by heat treatment.  They are available in several types, providing a range of hardness in the weld deposits. Additional hardness is obtained by work hardening.

Combination.  Other alloy electrodes are sometimes used in conjunction with tool and die welding electrodes, especially for applications on cast dies for drawing or forming.  Nickel-iron electrodes, nickel electrodes, and copper-nickel electrodes can be used as foundation on cast units, then other tool and die electrodes are used to finish the castings.

Current, Coatings, and Deposits.   Generally, tool and die welding electrodes should be used on direct current electrode positive (DCEP).  The percentage of alloying elements lost in the weld deposits during welding can be regained by selecting an electrode which incorporates the required alloys in the coating.  Mineral-alloyed coatings are preferred.

The introduction of a mineral-alloyed coating on the electrodes also helps produce a desirable spray action of the arc and forms a protective slag, which is easily removed.

Tool and die welding electrodes will produce sound homogeneous weld deposits free from porosity.  In many cases, laboratory tests have revealed weld deposit structures that are superior to parent steel of the same class.

Gas metal arc and flux-cored arc welding can be used to weld tools and dies, generally using small diameter (less than 1.5 mm [0.060 in.]) wires.   The plasma arc, electron beam and laser bean processes, with or without filler metal, can also be used for tool and die welding.

Welding Technique affects the hardness of the weld deposit.  Direct current electrode positive (DCEP) is recommended because it minimizes arc penetration, resulting in less admixture with the base metal.

The smallest electrode adequate for the job should be selected because it requires less heat, and this influences the ultimate hardness of the deposit.

Work position, travel speed, welding current, and manipulation of the arc all exert an influence on weld hardness.

Ultimate hardness and characteristics of the weld deposits can be enhanced by thorough peening while at forging temperatures.  Extended deposits should not be made before peening because the metal will cool; hot metal is more ductile.