Carburized steel, which is widely used for transmission gears, has an abnormal layer in its surface portion. Therefore, mechanical properties of the steel are improved by removing its surface layer. Since this type of products require dimensional accuracy, it is important to develop a chemical polishing process which uniformly polishes such products regardless of their shape.

An HF-H₂O₂ system was selected as basic bath composition. Although this system has been found to be a good agent by a preliminary experiment, spontaneous decomposition of H₂O₂ is a major problem. To overcome this problem, additives for stabilizing the bath composition have been explored and a superior stabilizer which extends the service life of the bath was found.

A polishing rate sensor was also developed to control the bath composition, and a high dimensional accuracy of the workpiece is obtained with this sensor. A recovery of HF is important for reducing the sludge amount from the bath waste, and the decomposition of H₂O₂ is required in advance because it hampers the HF recovery process. A new catalyst which effectively decomposes H₂O₂ was found.

This polishing method is expected to be applied to the manufacturing of hardened steel parts of complicated shapes in the future.