Impact of zinc halide addition on the growth of zinc-rich layers generated by sherardizing

• Zinc rich layers are grown on steel substrates by vapor galvanizing (sherardizing process).
• Annealing is performed under rotation and pack cementation.
• Small additions of zinc halides to the process enhance the Fe–Zn layer growth.
• The movement of the Fe–Zn interphase boundaries is investigated.
• Finite difference methods are used to simulate the phase growth during sherardizing.

The growth kinetics of Fe–Zn phases formed by vapor–solid diffusion reactions between evaporated zinc and a low carbon steel substrate are examined. Experiments with various zinc powder mixtures were performed in sealed quartz glass ampoules at 663 K and for annealing times up to 16 h. The formed intermetallic phases are investigated by optical microscopy, scanning electron microscopy and energy dispersive X-ray spectroscopy. Emphasis is put on the addition of various zinc halides (ZnCl2, ZnBr2, ZnI2) to the process that causes an increase in total layer thickness. The results presented show that this increase is due to a modification of the zinc powder properties that improves the sherardizing process. Finite difference methods are used to simulate the Fe–Zn phase growth during sherardizing. The understanding gained from experiments and simulations of Fe–Zn multiphase growth will help to improve the sherardizing of steel in industrial facilities.