Effects of laser microtexturing on the surface properties and tribological behaviour of hot forging tool steels

Laser microtexturing is a promising technique to enhance the limited durability of forging tools by generating reservoirs capable of trapping lubricant particles, thus reducing friction even under hot working conditions. This work aims to evaluate the effects of laser microtexturing variables on the surface properties and wear resistance of AISI H13 hot forging tool steel. For the first time, the application of laser microtexturing treatments was performed on H13 steel in three heat treatment conditions: annealing without subsequent heat treatment, quenching and tempering, and nitriding after quenching and tempering. The effects of laser intensity, scanning speed, pitch, and number of passes on roughness, hardness, and wettability were analysed for each heat treatment condition. Roughness increased when using higher laser intensity and number of passes, or lower scanning speed, whereas the surface hardness was barely altered by laser treatments. Moreover, the treatments that produced higher roughness improved surface wettability for forging lubricants, and the grooves generated through laser treatments effectively retained graphite particles from hot forging lubricants, which is expected to be beneficial for the tribological behaviour of hot forging tools. Wear tests in a lubricant medium at room temperature revealed that treatments with lower heat inputs and larger pitches led to reduced mass losses. Finally, the major novelty of this work is the development, for the first time, of ring compression tests on laser-microtextured tools to evaluate friction under hot forging conditions. These tests revealed a clear decrease in the coefficient of friction in textured samples compared to non-textured ones, especially when using higher scanning speeds or larger pitches. Overall, this work provides new insights into improving the tribological performance of hot forging tools through laser microtexturing treatments.