AISI 420 martensitic stainless steel low-temperature plasma assisted carburizing kinetics

The present paper reports the experimental results on martensitic stainless steel low-temperature plasma assisted carburizing kinetics. The treatments were carried out using a gas mixture of 99.5% (80% H2 + 20% Ar) + 0.5% CH4 at temperatures of 623, 673, 723 and 773 K and for times of 4, 8, 12 and 16 h. The peak voltage and the pulse period of the pulsed DC power supply were kept constant at 700 V and 240 μs, respectively. Temperature was controlled by adjusting the duty cycle. The treated samples were characterized by confocal laser scanning microscopy, X-ray diffractometry and microhardness measurements. Results indicate that low-temperature plasma carburizing is a diffusion controlled process. The calculated activation energy for outer and diffusion layer growth was 29 and 85 kJ mol− 1, respectively. An apparently precipitation-free layer can be produced only when the processing temperature is sufficiently low (≤ 723 K) and time sufficiently short (≤ 12 h).