高炭素鋼ぜんまいの疲労特性に及ぼす未溶解炭化物の影響

概要

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In order to improve the fatigue life of main springs, the optimum heat-treatment condition of high carbon steels in view point of increasing fatigue life and the relationship between fatigue life and microstructure was investigated for high carbon steel (JIS SK-5) main springs, which sreapplied to, mainly, retractors of safety belts of automobiles.The results obtained are as followed;(1) The optimum heat-treatment conditions are;Prior Structure: Fine spheroidite Tempering Temperature: 400°C Quenching Temperature: 800°C Line Speed: 9∼13.5m/sec.(2) Following results are obtained about the relationship between microstructure and fatigue life.a) There is a relation between hardness and fatigne life, but it is more important in industrial stand point, that there are difference of fatigue life among steels with same hardness.b) The differnces of fatigue life at same hardness level are considered to relate to the difference of distribution of undissolved carbide after quenching.c) The most favorable distribution conditions of undissolved carbide to increase fatigue life are;Amount: 4∼6% Mean free path: 2 micron Mean radius: 0.7∼0.8 micron