Increased fatigue strength of cast iron components through optimization of residual stresses, part 2

Purpose and goal

The current project (Part II) is the continuation of a VINNOVA/FFI-project (nr 2009-4145, Part I). The ultimate goal of both parts is to increase the fatigue strength of grey cast iron and even compacted graphite iron used in heavy duty vehicles through optimization of residual stresses. All the main goals for Part II, except completion of a PhD thesis, have been met. Due to sick leave, the PhD student was not engaged in Part II.

Expected results and effects

Up to 75% increase in bending fatigue limit for LGI and 34% for CGI were obtained by blast cleaning (uncontrolled shot peening) which induced compressive residual stresses and hardened the casting skin in test specimens. There is potential for optimization of the process currently used by Scania. Strengthening-annealing of blasted specimens did not further increase the fatigue limit. Allowable service temperature was found higher for CGI than LGI, which can also depend on blast intensity. 3 papers were published at international conferences and 3 more papers are under preparation.

Planned approach and implementation

The project work was carried out through close cooperation of project partners. Six work packages with tasks designed to deliver results to meet the project goals were set-up. Blast cleaning, long term annealing and bending fatigue tests were performed by the industrial partners while the academic partner was responsible for microstructural, residual stress and fractographic analyses to correlate the fatigue behavior to the treatment processes. The academic partner also had the main role in writing the publications. The collaboration has been very successful.