Observation and Measurement of Heat-treated Metal Using Digital Microscopes

• Quenching
  This heat treatment method hardens steels. Typical steels turn red when heated to approximately 700°C (1292°F) and their crystal structures and properties start to change. This property change is called transformation and the temperature at which the change starts is called the transformation temperature.Quenching is a heat treatment method that changes iron crystals to austenite, where a large amount of carbon is dissolved (solid solution) at temperatures exceeding the transformation temperature, and then cools them rapidly using water or oil to change them to very hard crystals called martensite.
• Annealing
  This heat treatment adjusts the grain size of steel and softens it. Metal is heated to a temperature approximately 50°C (122°F) above its transformation temperature. After the metal is held at this temperature for approximately one hour, it is cooled slowly in the furnace.
  This treatment is performed to make cutting easier during product metalworking.
• Normalizing
  This heat treatment modifies uneven steel structures to make them suitable for cutting and pressing. Crystal grains become smaller and stronger when heated to a temperature approximately 50°C (122°F) above the transformation temperature and then cooled in air.
• Tempering
  This heat treatment reduces the hardness of quenched or normalized steels and increases their tenacity. Steels are heated to approximately 500°C (932°F) and then cooled. This process makes steels harder and more resilient. Tempering is a heat treatment that restores tenacity (toughness) by returning the structure from martensite to one in which fine ferrite and cementite have precipitated.

Room temperature iron takes the form of a body-centered cubic lattice where atoms are located at each vertex and at the center of the cube.
After quenching, the iron takes the form of a face-centered cubic lattice where atoms are located at each vertex and the centers of the faces of the cube, and the carbon melts into this form.
With rapid cooling, iron attempts to return to a body-centered cubic lattice structure. However, because carbon is already taken in, the structure becomes misshapen and hardens.

These are the latest examples of observation and measurement of heat-treated metal using KEYENCE’s VHX Series 4K Digital Microscope.
Vickers hardness—a hardness scale—can be calculated by pushing a rhombic diamond indenter onto the target material and measuring the length of the diagonal line of the Vickers dent created.