New coatings for continuous casting rolls

Rolls in the steel industry withstand very high loads, thermal cycling leading to thermal fatigue, and severe environmental attack. The fatigue behavior of coatings is not only dependant on the Hertzian contact pressure alone, but it is highly influenced by the machine characteristics. Rolls in a continuous casting machine (CCM) are mainly exposed to: (a) thermal fatigue due to high temperature thermal cycling, (b) high bending stresses associated with the slab weight, (c) corrosion-oxidation and (d) wear due to abrasive solid mold fluxes and oxide scale on the slab surface. A reciprocating tribological test allowed characterizing failures due to the thermal and mechanical stresses. The test was divided into two main phases that are repeated until the maximum test time was reached. Phase 1 had a duration of 60 min at 400 °C, 10 Hz, 30 N (Hertzian pressure 1300 MPa) and phase 2 had a duration of 15 min at 900 °C, 1 Hz, 30 N (Hertzian pressure 1300 MPa). The cycle was repeated until the end of the coating lifetime or interrupted after 8 h. A second test for a shorter period of time (50% of the total test duration) was carried out. All tests were in ambient air without any lubricant. The coatings were also characterized by abrasive wear tests. This measurement was performed with an abrasive solution (SiC particles in water). The test load and speed were 0.4 N and 10 cm/s, respectively. Abrasive tests lasted 1 min. Several coating produced with different coating techniques (laser cladding, thermal spray+chemical slurry and welding) were characterized to validate them a surface solution for casting rolls.