低碳钢与304不锈钢的超声空蚀机理对比研究

目的研究低碳钢及304不锈钢在蒸馏水中的超声空蚀行为及损伤机理,并评价低碳钢及304不锈钢的抗空蚀能力,为抗空蚀材料的选择提供依据。方法采用符合ASTM国际标准的超声空蚀实验装置,开展低碳钢及304不锈钢在蒸馏水中不同时间的超声空蚀实验,从累积质量损失(失重)、累积质量损失率(失重率)、试样表面形貌和残余应力等方面对两种材料的超声空蚀行为进行描述和对比分析。结果低碳钢试样空蚀开始15 min后进入空蚀加速期,在90 min左右存在较短的空蚀稳定期,而后迅速进入空蚀衰减期;304不锈钢试样在空蚀30min内累积失重率变化缓慢,之后随着空蚀时间的延长而急剧增加,在120min后进入空蚀衰减期。低碳钢与304不锈钢的空蚀变形机制以滑移为主。随着空蚀的发展,低碳钢晶粒经历了晶粒取向→晶粒细化→晶界开裂→晶粒碎化→剥落的变化过程。而在同等实验条件下,304不锈钢试样的变化相对滞后,且残余应力值较大。结论由于空蚀裂纹在304不锈钢中的深层扩展受到奥氏体相的阻碍,从而对空蚀的发展产生关键的抑制作用,使得304不锈钢的抗空蚀能力较强。

Comparative Investigation of Ultrasonic Cavitation Erosion Mechanism for Low-carbon and 304 Stainless Steels

The work aims to study ultrasonic cavitation erosion behavior and mechanism of low-carbon and 304 stainless steels in distilled water, and evaluate cavitation resistance for low-carbon and 304 stainless steels to provide a basis for selecting cavitation resistant materials. An ultrasonic cavitation erosion test rig meeting ASTM international standards was used to conduct ultrasonic cavitation experiments of low-carbon and 304 stainless steels in distilled water for different time. The ultrasonic cavitation behaviors of the two materials were described and analyzed contrastively through cumulative mass loss (weight loss), cumulative mass loss rate (weight loss rate), surface morphology and residual stress. Low carbon steel sample entered acceleration stage after 15 minutes of cavitation, had shorter stabilization stage around 90 minutes of cavitation, and then quickly reached attenuation stage as cavitation time increased. The cumulative weight loss rate of the 304 stainless steel sample changed slowly within 30 minutes of cavitation, and then increased sharply with the increase of cavitation time. After 120 minutes of cavitation, the 304 stainless steel sample entered the attenuation stage. Slip effect dominated the deformation of the two steels during the cavitation erosion process. As the cavitation erosion developed, grains of the low-carbon steel underwent consecutively steps of grain orientation, grain refinement, grain boundary cracking, grain fragmentation and grain flaking. Under the same experimental conditions, corresponding variations of 304 stainless steel were lagging relative to those of the low-carbon steel. The residual stress of 304 stainless steel was relatively high. The extension of cavitation erosion cracks into 304 stainless steel is hindered by the austenite phase, thus significantly inhibiting the growth of cavitation erosion and improving the resistance to cavitation erosion of 304 stainless steel.