| 摘要 |
PROBLEM TO BE SOLVED: To secure high strength and high environmental brittleness resistance by covering at least a part of the surface of a spring steel base material with a corrosion protective film functioning as a sacrifice anode and adding carbonitride forming elements in the spring steel base material. SOLUTION: Spring steel provided with a tensile strength of 1800MPa or more is used as a base material, and at least a part of the surface of the spring steel base material is covered with a corrosion protective film functioning as a sacrifice anode. In this way, a high stress spring can be electrochemically protected from corrosion effectively. However, hydrogen is generated when the spring steel base material is electrochemically protected from corrosion by means of the sacrifice anode, and a detrimental action such as generation of delayed fracture and promotion of growth of a crack based on corrosion fatigue is exerted. Then, carbonitride forming elements such as Ti, Nb, Ta are added to the spring steel base material so that a great amount of fine carbonitride is deposited in the base material. As a result, impurities such as hydrogen and phosphorus penetrating into the base material can be trapped by means of the carbonitride, so that environmental brittleness can be suppressed. |
