Heat treatment of cast steel parts

Heat treatment is an important phase in the manufacturing cycle of steel castings. Unlike a number of wrought products, steel castings are usually delivered heat-treated, ready for use before final machining, or even machined.

The essential role of heat treatments is to modify the raw casting structure obtained in the mold in order to obtain the desired characteristics.

In fact, the raw casting structure is far from leading to optimal characteristics because it is generally coarse and heterogeneous:

• or because it results from an allotropic transformation from an austenitic structure formed at high temperature: this is the case for unalloyed or alloyed steels up to around 16% chromium;

• either because it is a direct result of solidification, in whole or in part, and/or because undesirable precipitates have formed during cooling in the mold: this is the case for austenitic manganese steels and austenitic and austeno-ferritic stainless steels.

The various conventional quality heat treatments, i.e. those intended to give parts the characteristics required for their use, do not differ in principle from those applied to wrought products of identical grades.

In addition to these conventional treatments, which are applied to virtually all cast steels (with the exception of refractory steels in particular), depending on their composition and processing, the parts may be subjected to additional quality and/or special heat treatments.

The various heat treatments applicable to steels in general are defined in standard NF EN 10052. In addition, the various product standards for cast steels, classified by use, give, by way of indication, the heat treatments applicable to each grade to obtain guaranteed mechanical properties, depending on thickness.

Readers may find it useful to refer to the following articles in the same treatise:

• Transformations in steels ;

• articles in the Heat treatment section.