A plasma electrolytic borocarburizing process (PEB/C) in borax electrolyte with glycerin additive was employed to fabricate a hardening layer on Q235 low-carbon steel. Optical emission spectroscopy(OES) was utilized to investigate the spectroscopy characteristics of plasma discharge around the steel during PEB/C process. Some plasma parameters were calculated in terms of OES. The electron temperature and electron concentration in plasma discharge zone is about 3000-12,000 K and 2 x 10(22)m-(3)-1.4 x 10(23)m-(3). The atomic ionization degrees of iron, carbon and boron are 10(-16)-10(-3), and 10(-23)-10(-6), 10(-19)-10(-4), respectively, which depend on discharge time. The surface morphology and cross-sectional microstructure of PEB/C hardening layer were observed, and the electrolyte decomposition and plasma discharge behaviors were discussed. (C) 2014 Elsevier B.V. All rights reserved.