Recent studies have shown that the main factors affecting the fatigue life and reliability of oil-quenched-tempered steel wire for valves are the form and content of inclusions in steel: large particles do not deform Type D inclusions and Type B inclusions lead to a sharp decrease in the fatigue life of the spring, while phosphorus, The high content of sulfur, arsenic, lead, tin, and antimony will also increase the temper brittleness of steel. Ultimately reduce the fatigue life. For this reason, ultra-pure oil quenched-tempered steel wire was developed.
The so-called ultra-pure steel is refined outside the furnace, vacuum degassed, electroslag remelting, composite slag system, inclusion deformation treatment, electromagnetic stirring and other technical means to minimize the gas (oxygen, nitrogen, hydrogen) in the steel. The content of non-metallic elements (phosphorus, sulfur, arsenic) and low melting point metals (lead, tin, antimony) can transform large non-deformable inclusions into plastic or semi-plastic fine inclusions. At present, 55CrSiA ultra-pure steel developed in Japan and Europe The 67CrVA. ultra-pure steel developed has made remarkable achievements.
The cause of elastic yellow fracture under low stress is non-metallic inclusions, and the cause of fracture under high stress is often surface defects. Therefore, it is necessary to strengthen the grinding and cleaning of the billet used for rolling wire rod, and strengthen the research on the control of cooling and rolling of the wire rod. Or stripping or grinding the wire surface. Clear defects such as surface decarburization, cracks, and folding. At present, among the oil-quenched steel wire production enterprises in China, only Shanghai Steel No. 2 Plant has stripping equipment, while other manufacturers have no secondary equipment. This is also an important factor restricting the improvement of the quality of oil quenched steel wire products in my country. The intermediate annealed structure of the wire rod or semi-finished product should be fine flake pearlite to meet the requirements of rapid heating for oil quenching. Some materials suggest that the intermediate heat treatment of 67CrVA. adopts lead quenching treatment to prepare for oil quenching heating.