高Cr-Niオーステナイト鋼の高温疲労強度
高Cr-Niオーステナイト鋼の研究-II
1962 年 48 巻 1 号 p. 38-44
詳細
1962 年 48 巻 1 号 p. 38-44
Effect of alloying elements, mnelting process, heat treatments and grain size on high-temperature fatigue strength were investigated with AISI type 309, 310 and 330 steels to obtain some practical design data. The results obtained were discussed on the basis of precipitation hardening of austenite. In this experiment tests were carried out at 650°C, 800°C and room temperature, using a rotary bending fatigue testing machine.
The results obtained are as follows:
(1) There is a defite fatigue limit at 65°C which is higher than the proof strength at this temperature, and this fact is explained by precipitation hardening of austenite.
But no definite fatigue limit is abserved at 800°C.
(2) The endurance ratio at 650°C is considerably higher than that at room temperature.
This indicates that the strengthening of austenite due to precipitation takes place during the fatigue test at this testing temperature.
(3) At 650°C the fatigue limit is lower than the creep rupture strength obtained from a short-time rupture test (up to 10h). But the creep rupture strength for 1ong-time test (more than 10h) are lower than the fatigue limit. The creep rupture strength, therefore, is more important than the fatigue strength in determining the working stress of a high-temperature machine elements.
(4) Carbon and nitrogen are very effective elements in improving the fatigue strength of these stee1s, while silicon and nickel have a minor effect, but no effect is observed with chramium.
(5) Specimens melted in vacuum shows little influence on the fatigue strength as compared with that melted in air of the corresponding chemical analysis.
(6) As the temperature of the solution treatment of specimen is raised up to 1200°C, the fatigue strength of type 309 and 310 steels is increased even though there is a considerable grain growth.
(7) The fatigue strength at 650°C of austenitic stainless steels is contralled not only by the resistance of plastic deformation of austenite but also by the precipitation hardening which takes place in austenitic matrix during repeated loadings.
