Abstract: In heating step S101, a steel sheet is heated and made in an austenite state. In heating step S101, the whole region of the steel sheet is evenly heated, and the whole region of the steel sheet is made in the austenite state. In cooling step S102, only a first region set on the steel sheet in the austenite state is forcibly cooled (rapidly cooled) within a temperature range of a range where martensitic transformation does not occur. In cooling step S102, a second region other than the first region is cooled by natural cooling to maintain a state in which a temperature is higher than in the first region.

Abstract: In heating step S101, a steel sheet is heated and made in an austenite state. In heating step S101, the whole region of the steel sheet is evenly heated, and the whole region of the steel sheet is made in the austenite state. In cooling step S102, only a first region set on the steel sheet in the austenite state is forcibly cooled (rapidly cooled) within a temperature range of a range where martensitic transformation does not occur. In cooling step S102, a second region other than the first region is cooled by natural cooling to maintain a state in which a temperature is higher than in the first region.

Abstract: Manganese oxide and tantalum oxide are added to a piezoelectric ceramic composition based on lead zinc-niobate titanate zirconate. The composition is suitable for piezo-electric transformers since its mechanical quality factor (Qm) is improved without reducing its electromechanical coupling coefficient (k31), and good high-power properties and high mechanical strength are obtained. In another embodiment, manganese oxide and at least one of antimony oxide and niobium oxide are added to a piezoelectric ceramic composition based on lead zinc-niobate titanate zirconate.