Impact Toughness of Mower Blades

The purpose of this work is to improve the safety and durability of agricultural and off highway rotary cutter blades. Field experience has resulted in specifying low blade hardness to prevent catastrophic impact failure and the obvious safety concerns. However, low hardness reduces yield strength and increases failures from bending, fatigue and wear. To develop a relationship between impact toughness and blade performance in the field, we chose to examine the material mechanical property of notched impact toughness as measured by the ASTM E-23 Charpy V-notch Impact Test. The first part of this work was to do a survey of the industry for charpy notched impact toughness on commercially available blades. The results showed a wide range of hardness and charpy toughness. Impact testing also showed that impact toughness can be controlled to higher minimum values than previously available. The variables studied indicate that the microstructure produced in the heat treat process has the largest influence on toughness. Also, recent field experience indicates that material above the industry average appears to be a safe toughness level for most applications. This suggests blades with more resistance to bending, fatigue and wear can be produced at safe toughness levels.