Cryogenic non destructive testing (NDT) and material treatment

摘要

A non-destructive test using cryogenic temperatures is capable of detecting defects in materials that result from residual stress from manufacturing and from retained austenite. The subject materials or parts that are subjected to cryogenic temperatures approaching and below˜−300° F., −184° C., 89° K, thereby causing permanent deformations or characteristic changes in the material if excessive residual stress, retained austenite or discontinuities exist. To determine the extent of changes, a first metric of the subject material is determined, the material is then subjected to cryogenic cooling thereby triggering any deformation or characteristic changes. Subsequent to the cryogenic cooling, the subject material may be returned to a second temperature whereby a second metric representing based on the same characteristic of the subject material is determined The comparison of the first and second metrics reveals the deformation or change resultant from the defect. In addition characteristic changes in the subject material during cryogenic cooling may be use to detect the phase transition of the retained austenite to martensite.

主权项

1. A method for detecting a defect in a manufactured item, comprising:
determining a first metric representing at least one characteristic of the manufactured item at first temperature; cooling the manufactured item to a cryogenic temperature; heating the manufactured item to a second temperature subsequent to the cryogenic cooling; determining a second metric representing the at least one characteristic of the manufacture item at a second temperature subsequent to the cryogenic cooling; comparing the first metric with the second metric; and, detecting the defect based upon the comparison; wherein the first temperature is greater or equal to 32 degrees F.; wherein the step of heating the manufactured item to the second temperature includes heating the manufactured item to a predetermined high temperature above second temperature and allowing the manufacture item to cool to second temperature; wherein the predetermined high temperature is greater or equal to 150 degrees Fahrenheit and the cryogenic temperature is −70 F or colder.