Abstract
The surface hardening and softening behavior of two types of medium carbon martensitic steel (AISI P20-improved and AISI P21) after laser-assisted heat treatment was quantitatively compared. The laser-assisted heat treatment was performed using a high-power diode laser with in situ temperature and laser power control (two-color pyrometer system). For AISI P20-improved steel, the peak hardness value within the hardening zone was approximately 640 HV after laser-assisted heat treatment at a temperature of 1473 K. In other words, the hardness increased by 120% from the base metal level (290 HV). However, for AISI P21 steel, the hardness within the heat-treated zone did not change from that of the base metal (410 HV), despite being accompanied by martensite transformation. Moreover, it was clearly observed that the hardness dropped below the level of the base metal at the boundary between the heat-treated zone and the base metal region, forming a softening zone. This softening behavior was strongly related to coarsening and a looser distribution of Cu precipitates compared with that of the base metal region, despite the same matrix phase (i.e., tempered martensite) existing in the softening zone and in the base metal region.
Highlights
In recent years, plastics or fiber-reinforced plastics have played an important role in engineering materials
Bouquet et al [33] and Kwok et al [34] reported the surface heat treatment results of plastic mold steels, relevant fundamental studies on local softening behavior based on microstructural characterization have not been reported for Cu-bearing plastic mold steels, such as this study aims to characterize the local surface softening behavior of AISI P21 steel according to its microstructural evolution during laser-assisted heat treatment
It has been well known that these two kinds of materials accompany quenching with the age-hardening process [30,31], the main constituent phase was surmised as tempered martensite
Summary
Plastics or fiber-reinforced plastics have played an important role in engineering materials. They have been extensively applied to automobiles, shipbuilding, airplanes, and home appliance housings owing to their specific characteristics, such as corrosion resistance, resistance to chemicals, low density, and ease of manufacture [1]. In this regard, plastic materials have increasingly replaced metallic components in these industrial fields. In the automotive industry, many components have been manufactured by the plastic injection of glass-fiber-reinforced plastics.
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