Abstract
Laser heat-treatment and laser nitriding were conducted on an AISI P21 mold steel using a high-power diode laser with laser energy densities of 90 and 1125 J/mm2, respectively. No change in surface hardness was observed after laser heat-treatment. In contrast, a relatively larger surface hardness was measured after laser nitriding (i.e., 536 HV) compared with that of the base metal (i.e., 409 HV). The TEM and electron energy loss spectroscopy (EELS) analyses revealed that laser nitriding induced to develop AlN precipitates up to a depth of 15 μm from the surface, resulting in surface hardening. The laser-nitrided P21 exhibited a superior wear resistance compared with that of the base metal and laser heat-treated P21 in the pin-on-disk tribotests. After 100 m of a sliding distance of the pin-on-disk test, the total wear loss of the base metal was measured to be 0.74 mm3, and it decreased to 0.60 mm3 for the laser-nitrided P21. The base metal and laser heat-treated P21 showed similar wear behaviors. The larger wear resistance of the laser-nitrided P21 was attributed to the AlN precipitate-induced surface hardening.
Highlights
AISI P21 steel is used for plastic injection molds due to its good mechanical properties with excellent machinability [1]
A few nanometer-size particles were observed, and these are known as Cu particles [3,29,30]
This study investigated the influence of laser heat-treatment and laser nitriding on the microstructural evolution and tribological characteristics of AISI P21 mold steel
Summary
AISI P21 steel is used for plastic injection molds due to its good mechanical properties with excellent machinability [1]. Plastic injection molds are expected to be used for several million shots for the mass production of plastic products. The molds can be damaged by wear, corrosion, and fatigue during plastic injection molding. The damaged molds should be replaced to maintain a satisfactory quality of plastic products, increasing the production cost. Appropriate surface treatments can prevent damages to the mold, resulting in an extended mold lifespan. Several studies have investigated the application of surface treatments to mold steels and tool steels in the form of surface heat-treatment [2,3,4,5], nitriding [3,6,7,8], surface coating and alloying [9,10,11,12], and peening [5,13,14]
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