Why can the resulting material properties vary widely within

Why can the resulting material properties vary widely within welding heat-affected zones

Solution

large fabricated structures contain variations in metal properties: welded structures have the weld metal, the heat affected zone, and the base metal, and the heat treatments also change material properties. these variation in metal properties can cause problems when the X-ray diffraction technique and the ultrasonic technique are used. it has been recognized that diffraction lines are broadened, resulting in lower accuracy in strain mesurements when the x-ray diffraction technique is used on heat treated materials