Raman mapping of corrosion products formed onto spring steelsduring salt spray experiments. A correlation between the scalecomposition and the corrosion resistance

摘要

There is a growing trend in the automotive industry to reduce vehicles weight so as tornincrease fuel efficiency and therefore reduce CO2 emissions. For many automotiverncomponents such as springs, weight reduction is sought through an increase inrnmechanical properties (allowing smaller components size).rnFor ultra high strength springs, a good corrosion resistance becomes essential tornavoid surface damage that will be detrimental to the corrosion-fatigue resistance.rnCorrosion fatigue failures indeed often initiates on surface defects caused byrncorrosion in service (corrosion pits). Therefore, whilst of moderate importance inrnconventional spring steels, the corrosion resistance of ultra high strength springrnsteels is of primary importance.rnFine changes in steel chemical composition can have an important effect onrncorrosion resistance. To understand the individual action of each element on therncorrosion resistance of spring steels, corrosion products formed on samples exposedrnto NaCl environments were characterized using Raman spectroscopy, in a purposelyrndesigned experimental tool that allows mapping of corrosion products on the steelrnsurface (by nature and mass fraction).rnDifferent steel grades were thus characterized after accelerated corrosion tests, andrna clear correlation was established between weight loss and the nature of therncorrosion products.