How to weld cast iron

Even though cast iron belongs to the group of materials difficult to weld, correct conduct of this activity allows to obtain very satisfactory results.

How to carry out cast iron welding?

We will give you some tips in the below article.

Weldability of cast iron

Cast iron is an iron and coal alloy and frequently also of additional components such as sulphur, phosphorus, manganese, silicon and other elements.

A large portion of coal makes the material brittle which results in difficulties while welding.

A significant role is played by the contents of other elements.

High level of silicon, sulphur, phosphorus in cast iron impacts unbeneficially the properties and parameters of the weld, hindering the possibility of realizing an order.

Welding is possible in case of grey cast iron where coal occurs as graphite, while white cast iron (with coal bound in concrete) is a non-weldable version.

How to weld cast iron?

Despite difficulties caused by fragility or presence of oxides characterized by low fusibility, cast iron may be subjected to the process of welding.

Such treatments are normally applied in a situation of supplementing defects, regenerating or repairing cast iron elements.

We distinguish three methods of welding cast iron: hot, cold and semi-hot.

In the first case it is necessary to evenly (with maximum speed of 100 degrees of Celsius per minute), slow heating up of the whole casting up to the temperature of approx. 700 degrees, followed by maintaining this temperature until the end of the process.

Importantly, the temperature cannot fall below 600 degrees.

Once the activity is finished, the casting must be slowly cooled down in order to avoid material fractures.

This treatment must be carried out electrically or via gas by means of oxygen-acetylene flame.

Cold welding, that is without pre-heating consists, on the other hand, on entering as little heat to the connector as possible.

One may perform them via arc welding methods:

TIG, MIG/MAG or with the application of overed electrode.

This procedure limits welding tensioning and, as a result, prevents the occurrence of fractures.

In order to further decrease tensioning it is recommended to hammer the subsequent layers in the weld.

It is worth to remember about making narrow, short welding beads, using low current intensity and applying electrodes for the cast iron with small diameter.

Moreover, it is advisable to make frequent breaks while welding.

The third method is applied rather seldom, normally in case of casting without cross ribs, with uncomplicated shapes, where large differences in wall thickness occur.

In the semi-hot technique, heating up to the temperature within the range of 250-500 degrees of Celsius is performed only in the welding spot and not in the whole casting.

Small part may be welded even without pre-heating.

What to weld cast iron with?

Applying the hot technique, cast iron sticks and a special flux must be used as binders, whilst applying cold technique – steel electrodes and nickel alloys. In case of semi-hot technique – grey cast iron binder should be applied.

Furthermore, one may bind one cast iron element with another as well as use the so called melting welding, the goal of which is to weld cast iron with steel.

MAG arc melting welding uses grown binders, whilst  welding of cast iron with brass requires gas melting welding.