Contribution Oral Presentation
THE PROTECTION OF GA COATED HOT STAMPED STEEL THROUGH THE APPLICATION OF MoS2
The automotive industry have come under increased pressure to reduce vehicle emissions whilst simultaneously improving safety. Light weighting through downgauging is a common strategy employed by steel makers to address these issues. This has led to increased volumes of Advanced High Strength Steels (AHSS), Ultra High Strength Steels (UHSS) and Press Hardenable Steels (PHS) being used in Automotive Body in White. Press hardenable steels (PHS) are formed at high temperature (~950°C) whilst in the austenitic region before being quenched to room temperature within a press to form the harder martensitic phase. The heat treatment is conducted in atmospheric conditions to allow the rapid transfer in and out of the furnace. Oxygen within the atmosphere causes decarburisation of the substrate’s outer layer leading to the undesirable formation of ferrite phase upon quenching. A further problem with the use of PHS is in service corrosion protection. Traditional hot dip galvanised (HDG) coatings evaporate at 907°C meaning they do not survive the heat treatment process for PHS. Therefore a novel strategy is required to provide some level of processing and in-service protection of PHS. This paper investigates the use of a 10 μm Galvanneal (GA) coated PHS, overcoated with 15 - 40 μm Molybdenum Disulphide (MoS2) with a view to providing protection of the GA during heat treatment. MoS2 is a thermally stable 2D material commonly used to provide lubrication to sliding components. Scanning electron microscopy and Scanning Vibrating Electrode Technique (SVET) was used to elucidate the effectiveness of the MoS2 layer in preventing the loss of zinc rich phases from the surface of the steel. Visual inspection of samples post heat treatment showed the MoS2 coated sample provided greater protection than uncoated GA. The MoS2 coated samples showed no evidence of decarburisation of the PHS. SVET experiments on the cut edges of the coated material were performed on post heat treated samples in 3.5% NaCl solution at 21°C. The SVET is able to resolve anodic and cathodic events occurring on the surface in solution. Results showed the MoS2 overcoated GA coating is still able to provide galvanic protection post heat treatment at 950°C. SEM images reveal the presence of zinc on the substrate of the coated MoS2 samples. The results demonstrate that the overcoating of GA coated PHS is a promising strategy for providing process and in-service protection.
yes it is a PhD work and a PhD student will hold the presentation
Press-hardening, Galvanneal, MoS2, AHSS, UHSS, SVET, Automotive, Corrosion