Hy-80 steel is a steel alloy made up of Nickel, Chromium and Molybdenum with high yield strength and toughness. These properties make Hy-80 steel ideal for naval applications where a material is needed that can undergo high pressure and stress. The goal of this research is to examine the effects of heat treatment with various holding times on the microstructure, hardness, and toughness of Hy80 steel. In this project samples will undergo several different holding times ranging from 1 to 42 hours to investigate the extent of temper embrittlement on the samples at a temperature of 525 degrees Celsius. Various measurements will be taken with Charpy impact testing to measure the amount of energy that is absorbed by the sample, Rockwell hardness testing, and a scanning electron microscope (SEM) will be used to observe changes in microstructure. This research will help determine how holding times affect mechanical and structural properties of Hy80 steel.