Cryogenic transition detection

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 near cryogenic temperatures according to an initial temperature time cycle;
• wherein the near Cryogenic temperature is less than −70° F.;
• during the cooling, monitoring the manufactured item for emissions resultant from a material phase transition;
• recording the emissions, as a function of temperature or time;
• adjusting the initial temperature time cycle as a function of the emissions to form an adjusted temperature time cycle;
• controlling the temperature of the manufacture item as a function of the adjusted temperature time cycle;
• wherein the adjusted temperature time cycle includes a heating cycle, wherein said heating cycle incrementally increases the temperature to greater than +220° F.
• determining a second metric representing the at least one characteristic of the manufacture item at a second temperature subsequent to the near-cryogenic cooling;
• comparing the first metric with the second metric;
• and,
• detecting the defect based upon the comparison.

A method of detecting a material transformation comprising:

• incrementally reducing temperature of the product to near cryogenic temperatures according to a predetermined temperature curve and measuring a characteristic of the product during each increment;
• recording the characteristic measurements as a function of temperature;
• filtering successive characteristic measurements;
• and,
• determining the material transformation based upon the filtered successive characteristic measurements;
• wherein the characteristic is an ultrasonic acoustic emission;
• wherein the temperature curve includes a heating cycle, wherein said heating cycle incrementally increases the temperature of the product to greater than +220° F. and a cooling cycle to the near cryogenic temperature of less than −70° F.;
• and
• the material transformation is an austenite to martensite phase transition.