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飞机前起落架旋转叉上的小轴系采用30CrMnSi-2A钢制造。其热处理规范为600～650℃预热再加热至900℃保温38分钟,然后在285～320℃硝盐槽中等温60分钟,于高于60℃的水中冷却。磨后于200～250℃回火3小时,空冷。设计要求强度为(?)kg·f/mm~2。 1974年初使用单位用磁力探伤检查,发现前起落架旋转叉上的小轴的R处有裂纹。检查经飞行479～1191个起落的小轴,发现18个小轴在R外均有裂纹。图1 小轴的全貌,箭头指处为裂纹缩小1/4倍(8.5折) 一裂纹产生原因分析 1 机械性能试验对有裂纹的小轴作机械性能试验,测试结果:σ_b=169kg·f/mm~2。ψ=59%。δ=15%,HRC=48。强度符合设计要求。 2 断口分析小轴的全貌见图1。18个小轴除1个仅一侧有裂
The small shaft on the fork of the front landing gear of the aircraft is made of 30CrMnSi-2A steel. The heat treatment specifications for the 600 ~ 650 ℃ preheated and then heated to 900 ℃ for 38 minutes, then 285 ~ 320 ℃ in a salt bath isothermal 60 minutes, more than 60 ℃ water cooling. After grinding at 200 ~ 250 ℃ tempering 3 hours, air-cooled. Design requirements for the intensity (?) Kg · f / mm ~ 2. Early 1974, the use of magnetic flaw detection unit and found that the front landing gear rotating fork on the small axis of R cracks. Check the 479 ~ 1191 flights by the small axis of the rise and fall, found that 18 small axes in the R have cracks outside. Figure 1 small axis of the whole picture, the arrow refers to the crack at the reduction of 1/4 (8.5 fold) a crack Analysis 1 mechanical properties of small cracks on the shaft for mechanical properties test, the test results: σ_b = 169kg · f / mm ~ 2. ψ = 59%. δ = 15%, HRC = 48. The strength meets the design requirements. 2 fracture analysis of the whole picture of the small shaft shown in Figure 1.18 small axis in addition to only one side of a cracked