Heat treatment is an essential part of the knifemaking process that builds up the hardness of your blade and gives your knife a higher sharpness retention. As it goes through this process, you, the knifesmith, will mold the blade to create a knife that is sturdy and useful.
There are two important steps in the heat treatment process, knife forging and tempering. The forging process involved molding the knife at a critically high heat level (typically 900 - 2,000 degrees Fahrenheit) to improve its hardness. Once you are done forging the knife you can move on to the tempering process in which you increase the knife's flexibility and sharpness at a lower temperature, typically between 390 - 800 degrees Fahrenheit.
In order to determine which stage the blade is in, you must pay attention to the color of the blade, which indicates the temperature of the blade. The following chart serves as a guide for you to determine the temperature of your blade according to its color as it goes through heat treatment.
| Forge Welding | Farenheit | Steel Color |
|---|---|---|
| Forging | 2,000° | Bright Yellow |
| 1,900° | Dark Yellow | |
| 1,800° | Orange Yellow | |
| 1,700° | Orange | |
| 1,600° | Orange Red | |
| 1,500° | Bright Red | |
| 1,400° | Red | |
| 1,300° | Medium Red | |
| 1,200° | Dull Red | |
| 1,000° | Slight Red | |
| 900° | Very Slight Red, Mostly Grey | |
| Tempering | 800° | Dark Grey |
| 575° | Blue | |
| 540° | Dark Purple | |
| 520° | Purple | |
| 500° | Brown/Purple | |
| 480° | Brown | |
| 465° | Dark Straw | |
| 445° | Light Straw | |
| 390° | Faint Straw |
