Evaluating surface hardened steels by laser-acoustics
Evaluating surface hardened steels by laser-acoustics
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DOI：
10.1016/j.surfcoat.2011.09.017
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发表时间：
2012-01
影响因子：
5.4
通讯作者：
D. Schneider;Rainer Hofmann;T. Schwarz;T. Grosser;E. Hensel
中科院分区：
文献类型：
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作者：
D. Schneider;Rainer Hofmann;T. Schwarz;T. Grosser;E. Hensel
研究了表面声波作为评价表面硬化钢的一种手段。对42CrMo4、C45、X153CrMoV12.1和90MnCrV8四种不同牌号的钢进行了激光硬化，深度达1.5 mm。激光声波手持式探头的构造使测量表面声波在大型部件上的传播速度成为可能。测量得到表面声波的速度取决于频率在1到10 MHz的范围内。变化的频率使表面声波能够穿透材料的不同深度。研究了该方法能否推算出硬化层深度和表面硬度。这种方法基于这样的假设，即如果钢的显微组织通过马氏体相变而硬化，那么声波的速度就会改变。测试样品还进行了高达620℃的退火热处理，以改变激光硬化区的硬度。这是为了研究声波速度是否与硬度相关。声学方法可用于确定淬火深度和硬度，其灵敏度取决于两个方面：1.马氏体硬化对钢的波速的影响程度；2.可测量速度的准确性。利用声表面波理论计算了一条广义频散曲线，由速度推算出材料的硬化深度。建立这一曲线需要两个测量：测量淬火和非淬火钢中的波速。结果表明，用该方法可以确定淬火深度，误差不大于15%。
The use of surface acoustic waves was studied as a means of evaluating surface-hardened steels. Four different grades of steel, 42CrMo4, C45, X153CrMoV12.1 and 90MnCrV8, were laser hardened up to a depth of 1.5mm. The construction of a laser acoustic handheld probe enabled the measurement of the propagation velocity of the surface acoustic waves on large components. The measurement yields the velocity of the surface acoustic wave depending on frequency in a range from 1 to 10MHz. The varying frequency enables the surface acoustic waves to penetrate varying depth of the material. It was investigated, if the hardening depth and the surface hardness can be deduced from this measurement. This methodology rests on the assumption that the velocity of the acoustic wave varies, if the microstructure of the steel is hardened by a martensitic transformation. Test samples were also annealed up to 620°C to vary the hardness of the laser hardened zone. This was performed to investigate if the acoustic wave velocity correlates with the hardness. The sensitivity of the acoustic method, which can be used to determine the hardening depth and the hardness, depends on two aspects: 1. the amount of the effect of the martensitic hardening on the wave velocity of the steel and 2. the accuracy of the velocity that can be measured. A generalized dispersion curve was calculated using the theory of the surface acoustic wave to deduce the hardening depth from the velocity. Establishing this curve requires two measurements; the measurement of the wave velocities in the hardened and non-hardened steel. Using this methodology, it was found that the hardening depth could be determined with an error not higher than 15%.