Bushing for hydraulic breaker and method for producing the same

A bushing for a hydraulic breaker, the bushing being of a tubular shape having an inner flange protruding radially toward a center from an inner periphery in a region including an axial end, the bushing being made of a steel containing not less than 0.55% by mass and not more than 0.70% by mass of carbon, not less than 0.15% by mass and not more than 0.35% by mass of silicon, not less than 0.4% by mass and not more than 0.9% by mass of manganese, not less than 0.4% by mass and not more than 1.3% by mass of chromium, and not less than 0.10% by mass and not more than 0.55% by mass of molybdenum, with the balance being iron and unavoidable impurities, the bushing comprising:

• a base region having a hardness of not less than 30 HRC and not more than 45 HRC;
• and
• a quench hardened layer formed on an inner periphery side of the base region so as to include an inner peripheral surface of a region including the inner flange, the quench hardened layer having a hardness of not less than 55 HRC and not more than 63 HRC.

A method for producing a bushing for a hydraulic breaker, comprising the steps of:

• preparing a formed body of a tubular shape having an inner flange protruding radially toward a center from an inner periphery in a region including an axial end, the formed body being made of a steel containing not less than 0.55% by mass and not more than 0.70% by mass of carbon, not less than 0.15% by mass and not more than 0.35% by mass of silicon, not less than 0.4% by mass and not more than 0.9% by mass of manganese, not less than 0.4% by mass and not more than 1.3% by mass of chromium, and not less than 0.10% by mass and not more than 0.55% by mass of molybdenum, with the balance being iron and unavoidable impurities, the formed body having a hardness of not less than 30 HRC and not more than 45 HRC;
• and
• forming a quench hardened layer by performing induction hardening processing on a region including an inner peripheral surface of a region including the inner flange of the formed body, the quench hardened layer having a hardness of not less than 55 HRC and not more than 63 HRC.