METHOD FOR DESTRUCTION-FREE DETERMINATION OF THE DEPTH OF HARDENING ON SURFACE-HARDENED COMPONENTS

Abstract

In the method for determining the depth of hardening d.sub.H, a predefinable number of at least 5 pulses of transverse ultrasonic waves are coupled into a component at a surface of the component. An individual pulse has at least one oscillation period. Between the individual pulses, the variance in the amplitude heights of ultrasonic waves backscattered or reflected back from the component is detected, during which the propagation time t.sub.L of the ultrasonic waves is determined. The difference between maxima and minima of the determined variances of the ultrasonic waves following the in-coupling is then formed, this value being multiplied by a factor between >0 and 1 and the product being summed with the minimum of the determined variances. The depth of hardening d.sub.H is determined under consideration of the product from the determined propagation time V.sub.LZ, the cosine of the angle .sub.r at which the ultrasonic waves are coupled into the component surface, and the sound velocity c.sub.T of the ultrasonic waves in the component material.

Claims

1-7. (canceled)

8. A method for destruction-free determination of the depth of hardening d.sub.H at surface-hardened component parts, in which a predefinable number of at least 5 pulses of transverse ultrasonic waves are coupled into a component at a surface of the component in question, wherein an individual pulse has at least one oscillation period, and, between the individual pulses, the variance in the amplitude heights of ultrasonic waves back-scattered or reflected back from the component at the surface is detected, during which the transit time t.sub.L of the back-scattered or reflected ultrasonic waves is determined starting from the particular moment in time of the emission and/or in-coupling of the ultrasonic waves into the component surface until the detection of these back-scattered or reflected ultrasonic waves of the individual pulses, for which a difference between maxima and minima of the determined variances of the back-scattered or reflected ultrasonic waves following the in-coupling is then formed, wherein this value is multiplied by a factor between >0 and 1, said factor being material-dependent and dependent on the particular hardening process, and the product being summed with the minimum of the determined variances, wherein the particular depth of hardening d.sub.H is determined under consideration of the product from the determined transit time t.sub.L, the cosine of the resultant angle .sub.r at which the ultrasonic waves propagate in the component, and the sound velocity c.sub.T of the ultrasonic waves in the component material.

9. The method according to claim 8, wherein the predefinable number of pulses of transverse ultrasonic waves coupled into a component at the surface of the component is at least 100.

10. The method according to claim 8, wherein the position at which ultrasonic waves are coupled into the surface and detected is changed during execution of the method within a surface region which has an area of at most 3000 mm.sup.2.

11. The method according to claim 8, wherein ultrasonic waves are coupled into the component surface at an angle .sub.i in the range of 15 to 50.

12. The method according to claim 8, wherein ultrasonic waves are coupled in with in each case a constant frequency in a frequency range of 5 MHz to 50 MHz.

13. The method according to claim 8, wherein the detection is performed at an individual pulse length in the range of 5 ns to 100 ns and/or at a detection rate in the range of 50 MHz to 1000 MHz.

14. The method according to claim 8, wherein the integer multiple of the fundamental frequency and/or the harmonic frequency are taken into consideration when determining the variance.

15. The method according to claim 8, wherein transverse ultrasonic waves with a solid wedge-shaped element or a liquid medium are coupled in at the surface of the particular component.

Description

[0031] In the drawing:

[0032] FIG. 1 shows two graphs of the variances of the amplitude heights and the transit time t.sub.L determined for two different steels with the maxima and minima taken into consideration in the evaluation.

[0033] To determine the depth of hardening d.sub.H, one example uses an unfocused longitudinal ultrasonic probe that couples ultrasonic waves at a frequency of 20 MHz into a Rexolite 1422 wedge at an angle of inclination of 28 with respect to the lower sound exit face of the wedge. A thin film of oil is applied as a coupling medium between the ultrasonic-wave-emitting surface of the probe and the wedge. Between the wedge and the test component, a water-based gel is coupled to the particular surface of the test component as a further coupling medium. The probe is excited with short and strong single pulses. The particular pulse length is 50 ns for a broadband ultrasonic signal and the electrical voltage applied to the piezo elements of the probe is 350 V for a high sound pressure. Due to the different sound velocities in the wedge material made of Rexolite and in the test body made of steel and due to coupling into the component at an angle .sub.i larger than the first critical angle, mainly transverse waves below 40 are induced in the test component. These transverse waves are back-scattered depending on the grain size. 160 pulses are executed, recorded and saved, one after the other. The number of 160 pulses is a compromise here between test speed and a sufficiently large data set. The recording length here is 20 us and the detection rate is 100 MHz. While emitting the pulses, the test head with wedge-shaped element is manually moved back and forth by approximately 10 mm. Lateral or circular movements are also possible. The variance of the amplitude heights over the transit time of the 160 pulses is calculated from the recorded ultrasonic signals. The resulting curve is evaluated.

[0034] An entrance echo of back-scattered or reflected ultrasonic waves is detected at the surface of the test component with the coupling layer between wedge-shaped element and test component surface. Due to the movement of the probe over the surface, the entrance echo is also visible in the display of the variances with a large deflection. For depths of hardening d.sub.H greater than 1.5 mm, a local minimum follows the entry echo in the representation of the determined variances V.sub.LZ over the transit time. The variance value of the minimum is dependent on the mean grain size of the surface layer and the depth of hardening d.sub.H. Variance values caused by the electronic noise of the test hardware are not undershot by the variance of reflected and detected ultrasonic wave amplitudes. The minimum is followed by the local maximum of the back-scatter with a characteristic increase between these two values. This increase can be attributed to the transition from the hardened surface layer to the core of the component. Since the depth of hardening d.sub.H is always present in this transition, the flank is analyzed in greater detail. The difference between the local minimum and local maximum of the variance values V.sub.LZ is determined. The difference is multiplied by a factor K between 0 and 1. This factor K is dependent on the hardening method and the particular steel grade. The product is summed with the local minimum. The transit time at which the edge exceeds this value for the first time is then determined. This transit time is subtracted with the transit time of the maximum of the variance of the entrance echo. This difference, the transit time t.sub.L, is calculated with the sound velocity of the transverse wave in the test body and with the angle .sub.r with which the ultrasonic waves propagate in the component to determine the depth of hardening d.sub.H. An entry echo is constituted by reflected ultrasonic waves from the component surface.

[0035] In the graph shown in FIG. 1 on the left, 160 pulses were evaluated for a test component made of 16MnCr5 that was case-hardened, and in the graph shown on the right, 160 pulses were also evaluated for a test component made of C45 that was induction-hardened.

[0036] The pitch-catch test setup in a V arrangement can be used to determine small depths of hardening d.sub.H, which are superimposed by the entrance echo in the pulse-echo arrangement. For this purpose, a special wedge geometry is advantageous, in which a part of the individual ultrasonic waves is cut off. Thus, the highest possible sound pressure can be realized in front of the wedge-shaped element. For the first time, the depth of hardening d.sub.H of casehardened components and hardened components with a small hardness gradient can be determined destruction-free via ultrasonic back-scatter. Alternatively, a transceiver probe with specific roof angle can be used.