| U | Chemical symbol for Uranium. |
| Ultimate Analysis | In chemistry, this is a quantitative analysis in which percentages of all elements in the substance are determined. |
| Ultimate Tensile Strength | The highest load applied in breaking a tensile test piece divided by the original cross- sectional area of the test piece. |
| Ultrasonic Inspection | A means of locating defects in steel. When acoustic energy in the ultrasonic range is passed through steel, the sound waves tend to travel in straight lines, rather than diffusing in all directions as they do in the audible range. If there is a defect in the path of the beam it will cause a reflection of some of the energy, depleting the energy transmitted. This casts an acoustic shadow which can be monitored by a detector placed opposite the transducer or energy source. If the acoustic energy is introduced as a very short burst, then the reflected energy coming back to the originating transducer can also be used to show the size and depth of the defect. Ultrasonic techniques can be used to detect deeply located defects or those contained in the surface layer. Skill and experience are required in interpreting the results portrayed on the cathode ray tube. |
| Unkilled Steel | Steel which has been insufficiently deoxidized and evolves gas during solidification with the formation of blow-holes. |
| Upsetting | Working a piece of steel so that its length is shortened and its cross-sectional area is increased. Its effect is to increase ductility in the radial and tangential directions. |
| Uranium | A white malleable metal which is softer than steel. Its specific gravity is 18.7, it melts at a temperature of 2400ºC. |
