Study on effects of alternating current field to pack boriding of medium carbon steel

Abstract

A plain medium carbon steel was borided by alternating current field enhanced pack boriding (ACFEPB). Diffusion kinetics and case characteristics of the borided steel were investigated to understand effects of an alternating current field (ACF) on pack boriding. Conventional pack boriding (CPB) was also employed for comparison. A series of boriding were conducted at temperatures of 873, 973, 1073 and 1173 K for 1, 2, 4 and 6 h, respectively, with a fixed current of 4 A. The morphology and types of borides formed in the steel were investigated by optical microscopy and X-ray diffraction, respectively. Boride growth kinetics was analysed by measuring the average thickness of the boriding case as a function of time and temperature. The growth rate of the ACFEPB case versus time showed the same parabolic character as CPB. The parameters of the boron diffusion kinetics, D = D₀exp(−QR⁻¹T⁻¹), have been determined. The results showed that the ACF enhanced inter-diffusion of boron in the substrate. The value of D, diffusion coefficient, in ACFEPB was more than 4 times of that in the CPB. The activation energy Q (44·45 kJ mol⁻¹) of the borided steel in the ACFEPB was less than 1/4 of that (180·6 kJ mol⁻¹) in the CPB.

Keywords:

• Kinetics
• Pack boriding
• Activation energy
• Alternating current field

Acknowledgement

The authors would like to thank the financial support from the National Science Foundation of China (Grant No. 51171032).