Erosion wear in heat treated tool steels used in core boxes at automotive foundries

Sand cores are extensively used on automotives foundries, if a core box is used as core making pattern; erosive wear damage is caused by the silica sand blown. Multiple sand impacts affect the dimensional profile of the core box when the sand is blown causing core rejection. The objective of the present study is to determine the erosion wear rate and the erosive wear mechanism on two tool steel grades, AISI H13 and AISI P20. Both the steels were heat treated, quenched and tempered, to obtain certain hardness values similar to those are used in core boxes. In addition studies on annealed AISI H13 and carburized AISI P20 were proposed to get broader hardness values. The tests were developed in a sand blast type machine specially designed to impact the blown sand in six different angles between 20° and 90°, the blown pressure was same as that utilized in core making machines. The erosion rate is defined as loss of weight caused by the mass of the erosive particles impacted. When the steels are under maximum hardness condition the higher erosion rate is found for angles greater than 60°. The erosive mechanism was characterized using optical and electronic microscopy techniques on the worn layer. When, the hardness is maximum the loss of weight is due to shear adiabatic bands where as in the annealed samples these bands were not observed.