激光超声无损测量40Cr钢渗氮层深度的实验研究

Experimental Investigation on Non-destructive Measuring of the Nitriding Thickness of 40Cr Steel by Laser Ultrasonic

现有的硬度法和金相法无法满足40Cr钢产品渗氮层深度的全覆盖检测的需求,故提出一种利用激光超声技术进行渗氮层深度无损测量的方法。首先,利用脉冲激光在不同渗层深度的40Cr钢表面激励出表面波,通过激光干涉仪接收表面波,从而实现表面波信号的非接触激励和接收。然后,采用二维傅里叶变换(2D-FFT)方法提取出表面波的频散曲线。实验结果表明:随着渗层深度的增加,表面波的相速度也随之增加;表面波在低频时有较大的频散特性,而在高频范围内表面波的传播速度变化较小;当渗氮层深度达到394μm时,表面波速度的变化趋势不明显;表面波的频散曲线和渗氮层深度有一定的对应关系,通过测量表面波的频散曲线可近似得到渗氮层的深度。激光超声技术是一种潜在的40Cr钢渗氮层深度的无损测量方法,具有一定的工程应用价值。

The metalloscopy and microhardness method could not meet the needs of whole testing of nitriding thickness of 40Cr steels products.A laser ultrasonic measurement was proposed to measure the nitriding thickness non-destructively through the dispersion of surface waves.Firstly,the surface waves were excited on the 40Cr steels with different nitriding thickness,and then the surface waves were received by laser interferometer.So the signals of surface waves were excited and received contactless.Finally,the disperse curves of surface waves were extracted by 2D-FFT.It was found that the phase velocity of surface waves increased as the nitriding thickness increased.The dispersion of surface waves with low frequencies was higher than that with high frequencies.The velocity of surface waves would not change when the nitriding thickness was higher than 394μm.The relationship between the disperse curves of surface waves and the nitriding thickness,could be used to measure the nitriding thickness.Therefore,the laser ultrasonic was a feasible method to measure the nitriding thickness of 40Cr steel non-destructively,and it had value in engineering applications.