不锈钢SUS630疲劳断口分析

Research on the Fatigue Fracture Surface of SUS630 Stainless Steel

高速船舶推进轴系为减轻重量,采用高强度合金材料,目前常使用之材料为不锈钢SUS630。对此材料进行了孔蚀试验及疲劳试验,利用电子扫描显微镜就其疲劳断口进行照相,并针对电子扫描照相所获取的图像进行分析。依据图像显示,当无孔蚀发生时,其疲劳断裂原则上遵循疲劳裂纹初始期、疲劳裂纹成长期及疲劳瞬间断裂期三个阶段;但当有孔蚀发生时,其疲劳断裂阶段即无疲劳裂纹初始期,而直接进入疲劳裂纹成长期及疲劳瞬间断裂期两个阶段。因此,当以断口观察来判断断裂原因时,应特别注意。另由电子扫描照相所获取的图像进行分析推算,得知金属材料常数n、C、与疲劳裂纹扩展常数(da/dN)并非固定的常数,随着试验应力大小而变动,针对不锈钢SUS630材质,当ΔK值介于26至46之间时,对于应力幅值不确定时,建议金属材料常数n值取为3及金属材料常数C值取为4.40×10-15。

Usually, high tensile strength alloy is used for propulsion shafting system of high-speed craft for reducing shaft weight and the diameter. In general, the stainless SUS630 is selected. In this paper, pitting corrosion test and fatigue test have been carried out for the sampling piece of such SUS630 shaft. Meanwhile, metallurgical photographing over the fatigue fracture surface by a scanning electron microscope has performed. By the survey of these graphs, it shows that in the case of samples without pitting corrosion holes the fatigue fracture occurred in three stages, i.e. fatigue initialization, fatigue propagation and rapidly abrupt fracture. While, in the case of samples with pitting corrosion holes, the fatigue initialization stage disappear. Thus, owing to this phenomenon, the identification of fatigue fracture should be careful using the metallurgical graphic of the fracture surface. In view of stainless steel SUS630 material, the material constant n value takes is 3 and the metal material constant Cvalue takes is 4.40× 10^-15 when the △K value is situated between 26 to 46.