To find the cause of deformation of high Cr grinding balls and its remedial measure to obtain lesser wear/ metric tonnes of cement production

Objectives

  • The main objective of this investigation was to improve the wear resistance property of the high Cr (~12% Cr) Cast Iron Grinding balls.
  • Find the cause of deformation/ de-shaping/ breakage of high Cr grinding balls.
  • Provide remedial measure to prevent de-shaping/deformation and thus achieve lesser wear /metric tonnes of cement production.

Technical Details

  • Non-uniform microstructure and hardness properties were found be the main cause for low wear resistance of grinding media.
  • Pearlite phase was identified in various grinding balls which are due to flaws in controlling heat-treatment and quenching procedures precisely.
  • Porosity was found to be present in various grinding media which were responsible for fragmentation of the grinding media.
  • Abrasion mechanisms such micro-cutting and micro-fatigue are found to be prominent mechanisms involved in deshaping of grinding media.
  • Process has been developed to achieve cast iron grinding media with microstructure as martensite, retained austenite M7C3 and M3C to achieve hardness of 65-67HRC. The process is developed to achieve fine martensite with less residual stress.
  • Alloys are also developed to achieve cast iron grinding media with microstructure as martensite, retained austenite M7C3 and M3C to achieve hardness of 66-68 HRC. The alloys are developed to achieve fine martensite lath with less residual stress.

Achievement (Output/outcome)

The variations in microstructure by process optimization and alloy design lead to significant improvement in wear resistance of grinding balls. Process has been developed which shows 20 % improved wear resistance of virgin material. Alloy has also been developed which shows 25% improved wear resistance of virgin material.

  • Joint Patent 0019NF2018has been filed on “A Process for the Preparation of High Chrome Cast Iron for Grinding Media Application”.
  • Joint Patent 0020NF2018A has been filed on “A Process for preparation of austempered high chromium bainitic cast iron for grinding media applications”.

Impact

The variations in microstructure by process optimization and alloy design lead to significant improvement in wear resistance of grinding balls. Process has been developed which shows 20 % improved wear resistance of virgin material. Alloy has also been developed which shows 25% improved wear resistance of virgin material.

Fig.1: Scanning Electron Microscopy image of high chrome cast iron having fine martensite, M7C3 and M3C phases.

Fig.2: Transmission Electron Microscopy image of cast iron having fine martensite (~3 nm), M7C3 and M3C phases.

Fig.3: Plant Trial data on Specific Wear rate (SWR) for process and Alloy modified samples wrt to original alloy.