Abstract
Low temperature screen plasma technology, a high plasma density, through using a low energy supply, shows excellent effects on a low alloy chromium-molybdenum steel for plastic molds because it does not show a compound layer and a high surface hardness without a deterioration in matrix hardness. For interest about hardening depth, both the screen plasma nitriding and plasma nitro-carburizing processes were tested including nitrogen, hydrogen and a methane mixed gas environmental at 653 K, 713 K. The optical emission spectroscopy (OES) has been analyzed during screen plasma nitriding (SPN) and a nitro-carburizing process (SPNC) was proceeded at 713 K and the same pressure. I find it difficult to dissociate nitrogen molecules perfectly with neutral nitrogen atoms via the DC-plasma nitriding process. Therefore, the SPN and SPNC process have shown a high density of plasma species even though low temperature plasma conditions have a high peak intensity of Hβ and Hγ in the results of the analysis by OES. The hardness value was measured with the micro-Vickers hardness tester after the SPN, SPNC process and the chemical composition of nitriding layers were traced by GDOES. The screen nitriding layer via the screen plasma technology has shown excellent properties with a thickness depth of about 850 ~ 900 HV without the deterioration of matrix hardness value.
Highlights
In recognition of its eco-friendliness, the demand for the plasma nitriding process has exploded in the area of surface hardening technology for energy efficiency, low distortion and high performance in the past few decades
The analysis of plasma species generated under the Screen Plasma Nitriding (SPN) and Screen Plasma Nitro-Carburizing (SPNC)
1) Low temperature tempered chromium-molybdenum steel was treated in screen plasma nitriding (SPN) and nitro-carburizing (SPNC) process at temperatures of 653 K and 713 K for 4 hr, 10 hr and 20 hr
Summary
In recognition of its eco-friendliness, the demand for the plasma nitriding process has exploded in the area of surface hardening technology for energy efficiency, low distortion and high performance in the past few decades. Advances in the screen plasma technology like active screen plasma nitriding or ATONA process have made it possible for low temperature hardening to low-alloying steel with a simple design and low energy assumption [5]. From the surface analysis by OM and SEM, and Glow-Discharge Optical Emission Spectroscopy (GDOES), we could find out how to dissociate to a neutral and an ionic nitrogen and to contribute to diffuse in matrix material. It has shown a high concentration of nitrogen with the same hardness profiles without a compound layer and the low hardness deterioration of Quenching-and-Tempering treated AISI4140
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