Welding of cast iron

All types of cast iron have a high carbon content: 3-4%. Welding of such material is possible only with proper welding materials.

Sometimes, with manufacturing new products a method called: hot cast iron welding is applied. The welded element is heated up before and after welding.

For cast iron repairs should be used materials containing nickel or nickel and iron. They can be used for all types of cast iron and they do not require heating up before or after welding. This method is called cold cast iron welding.

Grey and spheroidal cast iron can be also successfully welded, but the white cast iron characterizes  too high hardness and cannot be welded.

PRACTICAL ADVICES

Pre-heating

In general, the cast iron should not be heaten up. When the elements are very heavy, sometimes a heating max. up to 300°C is carried out. In such case the whole element should be heated up and continuous welding should be performed. During the welding the material has to be maintained in the temperature of the heating. After finishing the welding the material has to be slowly cooled in the furnace or under the insulation (cover).

Hammering

If, while welding of the cast iron with the „cold” method, the free shrinkage is impossible, then inevitable is the hammering of every stitch of the weld. It happens most often with repair welding. Thanks to hammering a stress caused by a welding shrink can be reduced and partially transformed into compressive stress. This will lower the total value of the rudimentary stress in welded material. Electrodes RepTec Cast31 or RepTec Cast 1 are recomended there. A weld with a low linear energy is connected with the use of short-diameter electrode. The diameter of the electrode should be at least one size smaller than the electrode using for carbon steel welding.

The length of the weld stitches must be between 5-10cm. The stitch of the weld should be hammered immediately after welding, before its cooling. Energetic hammering all over the weld will cause the deformation of the stitch and then reversal of the stress caused by welding shrink. Each hit of the hammer has to visibly deform the welding stitch. The temperature between the stitches cannot exceed 100°C.

Cast iron saturated with oils

When the cast iron has a contact with oils for a longer period of time, it may become difficult to weld. During welding oils ignites and they create gases that cause porosity of the metal. When welding aluminium-silicon casting alloy a covered electrode RepTec AISI12 with the maximum content of silicon 12% can be used. Covered electrodes RepTec AISI5 were designed for repairs sheet metal and aluminium sections. These are electrodes with direct current which have good weldability, are packed in hermetic cans and have no susceptibility to formation of porosity.

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