How to Quench a Knife Made from Automotive Leaf Spring Steel?
2 Answers
Remember that the steel should only be heated to a red color, not white, somewhere between orange and yellow. Dip the cutting edge into water for about 2-3 seconds, making sure the back of the blade does not get wet. Heat the steel until it turns red and immediately immerse it in used motor oil. Wait until the oil stops boiling and bubbling, then bury the knife in sand, allowing the sand and blade to cool together.
I use automotive leaf spring steel to make knives, and I believe quenching is the key to success. First, let's talk about preparing the materials: spring steel usually has a high carbon content. Before quenching, you must thoroughly clean the surface to remove oil or rust, otherwise the heating won't be even. I cut the steel plate into the shape of a knife and then heat it on a gas stove or forging furnace, observing the color change. When it reaches a cherry-red color, around 800 degrees Celsius, it's ready. Be careful not to overheat it, or the steel will become brittle. Then quickly remove it and immerse it directly in oil for quenching. I use waste engine oil because its cooling rate is moderate, reducing the risk of the knife cracking. After quenching, the blade becomes hard but too brittle, so tempering is necessary—place it in an oven at around 200 degrees Celsius for half an hour to restore toughness. The whole process requires precise heat control. Beginners should seek help from experienced friends or watch tutorial videos. If the oil catches fire during quenching, quickly cover it to extinguish the flames—safety first. When testing the finished knife, a light swipe should cut paper cleanly, proving its effectiveness. But remember to regularly maintain the blade.
