The superiority of the quality of materials is essential for a good time piece spring. Accordingly the quality of raw materials, composition, heat-treatment, micro-structure, surface finish etc. must be fully examined for making good springs.
The author has investigated influence of impurities, relationship between non-metallic inclusions and cleanliness, change of hardness and micro-structure with a rate of cold working and intermediate annealing, heat-treatment and mechanical properties on the spring steel sheet which had been made of good Masago iron sand.
The author has also investigated for purposes of reference, foreign and Japanese time piece springs which were obtained on the open markets.