To minimize the wear of components by slide by surface-hardening at least one component of the components, and constituting it from a sintered material for improving slide characteristic which mainly contains ferrite.

The gear of a pump is hardened, particularly, so that the teeth do not wear. Particularly, the wear in a sealed part between high-pressure area and low-pressure area (or a seal segment 31, a segment support 32, and a thrust seal disc 45) is minimized. These parts are formed of a sintered material, and its initial mixture contains 15% to 25% copper, 2.5% to 3% molybdenum disulfide, about 0.4% graphite, and the remainder of iron in the form of ferrite. The hardening of iron is performed according to a known method as gas nitriding. Compared with a pure ferrite mixture, the other components of the sintering initial mixture are used in order to improve the slide characteristic of a completed part. According to this, the parts are resistant to insufficient lubrication that is generated at the time of high pressure, high rotating speed, or high temperature of hydraulic fluid.