New strategies for refilling single-layer stainless steel on nodular cast iron

In order to improve the wear and corrosion resistance of cast parts without increasing their price, laser cladding is a suitable alternative method. However, applying laser cladding technologies on castings is a difficult and complex process since it can generate: heterogeneous thermal and stress fields due to the properties of the graphite and the matrix, the formation of pores due to the carbon dioxide produced during the irradiation of the laser beam, and formation of hard and brittle phases (martensite and ledeburite) due to the high cooling rate, which can lead to the formation of cracks. In some cases, some of these issues can be solved by preheating the substrate, double or multilayer laser coating. The disadvantage is that these methods are accompanied by a considerable energy consumption, poor production efficiency, increased price, etc.

Therefore, the combination of surface modification and laser cladding makes it possible to obtain castings with high wear resistance and good corrosion behavior. The modified layer on the cast iron before applying the coating is able to prevent the formation of brittle phases in the cast iron, the formation of carbides and the migration of chemical elements to the coating layer.

In this way, the properties of the iron castings, such as corrosion resistance and/or wear resistance, can be optimized more effectively thanks to this combination of surface modification during casting process by means of LMD (laser metal deposition).

This study was carried out with a GJS-500-14 spheroidal cast iron with surface modification with a NiTi powder and a subsequent coating (figure 1). The coating has been done with a 316L powder.

The experimental work has confirmed the viability of the new monolayer stainless refill strategies on spheroidal cast iron, with a structure free of cracks and pores that can be seen in Figure 2. In addition, it has showed improved wear resistance and corrosion behavior compared to spheroidal cast iron.