Understanding the Corrosion Mechanism of Spring Steel Induced by MnS Inclusions with Different Sizes

This work investigated the effects of differently sized MnS inclusions on the spring steel corrosion mechanism. Accelerated immersion tests, electrochemical measurements and Raman spectroscopy were performed in the vicinity of the MnS inclusions. The number of inclusions associated with existing original micro-crevices was smaller than the quantity of inclusions without crevices. The elemental S concentration decreased monotonically with decreases in the MnS inclusion size regardless of the original micro-crevices. Severe corrosion occurred at MnS inclusions with original micro-crevices, so pitting corrosion was greater. Localized corrosion around the MnS inclusions was found to increase and then decrease with increases in the inclusion size up to 12 mu m. The greatest degree of corrosion occurred with 5 mu m elongated inclusions. Corrosion products were assessed using Raman spectroscopy. A mechanism for corrosion promoted by differently sized MnS inclusions was proposed.