PhD opportunities

Tribological modeling of stainless steel cold strip rolling

Thesis proposal

Area of expertiseComputational mechanics and Materials
Doctoral SchoolDoctoral School for Fundamental and Applied Sciences
SupervisorM. Pierre MONTMITONNET
Co-supervisorMme Imene LAHOUIJ
Research unitCentre for material forming
Starting dateOctober 1st 2022
KeywordsCold rolling, tribology, numerical modeling, Thermal transfer, adhesion, lubricants and additives
AbstractCold rolling must reduce strip thickness, but also improve its mechanical properties and control its surface aspect. For stainless steels, the process starts from a very rough, shot-blasted and etched surface, whereas a mirror-like aspect must be reached in the end. This implies closing the deep shot-blast craters (Fig. 1a [1]). The latter are reservoirs for the lubricant, the pressurization of which opposes smoothening. Expelling oil from craters and closing them belongs to the lubrication mechanism called “micro-plasto-hydrodynamic” (Fig. 1b [2]).
If the contact temperature increases too much, an adhesive transfer layer forms on the rolls. It then ploughs the strip surface (Fig. 2) and increases friction considerably [3]. The resulting damage may cause gloss-degrading microcracks in the end.
The proposed work is at the crossroad of strip-roll system thermal transfer, metal-metal adhesion in lubricated contacts, superficial material damage and modeling in tribology. The practical goal for Aperam is to equip its pass scheduling mechanical model of rolling with a capacity to predict these phenomena in order to determine schedules of both high productivity and low strip surface damage. The work program includes:

1) a thermal model of the strip – roll coupled system using the Finite Difference Method (FDM), knowing that strip plastic deformation is the main heat source friction, the contact surface friction a secondary but important one and that thermal transfer occurs under a high Péclet number, i.e. dominant advection.

2) implementation of a lubricant film thickness model based on Reynolds equation. The Lo & Wilson model [2] will be exploited for the first passes until crater are closed, a more standard form for the final passes [4].

3) on the basis of the lubricant film thickness, of surface temperature and of a simple superficial material damage model, adhesive transfer will be analyzed as in [5], in terms of its occurrence as well as the resulting roll roughness. The latter will be used in relevant tribological models of friction between rough surfaces [6], to determine boundary friction whenever critical conditions are met for the formation of the adhesive transfer layer.

4) This set of models and their conclusions will be checked by laboratory tribometry, by pilot rolling mill experiments under carefully monitored thermal conditions, as well as by plant production data analysis.
ProfileMechanics, Numerical modeling, Python language.
A first experience, theoretical or practical, in tribology and/or thermal transfer will be appreciated.
A motivation for experiments is necessary.
Rigor, dedication to a subject, aptitude to teamworking are important
Mastering of the English language is necessary (level B2 minimum)
FundingConvention CIFRE