How to Quench a Knife Made from Automotive Leaf Spring Steel?

[McEmersyn]

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.

[MaryLee]

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.

[Emery]

When making knives from quenched automotive spring steel, safety is paramount, and I strongly advise beginners not to rush. The heating temperature during quenching is critical: heat the steel until it turns red but not orange, as excessive heat can cause melting. Oil quenching is the mainstream method due to its fast cooling rate, which hardens the steel. While I’ve used cooking oil successfully, ensure the oil container is deep enough and act swiftly—transfer the steel from the furnace to the oil within a second or two. Any delay can soften the steel, wasting your effort. After quenching, don’t use the blade immediately; temper it by baking at 150-200°C for half an hour to remove brittleness. Otherwise, the knife may crack and cause injury. Additionally, protective gear is essential—I always wear thick gloves, goggles, and an apron to guard against oil splashes or debris. From an environmental standpoint, repurposing scrap car parts is commendable, but used quenching oil must be recycled to avoid pollution. Overall, patience and proper tool preparation are key; if unsure, practice with small test pieces first.

[MacLeah]

The basic principle of using automotive spring steel plates to make knives through quenching is rapid cooling to harden the steel. Spring steel has high carbon content. When heated to the critical temperature (approximately 760-800°C) during quenching, appearing cherry red in color, it is immersed in a cooling medium—either oil or water works, with oil being more stable. After quenching, temper immediately by heating in an oven at around 200°C to reduce brittleness. The entire process demands precision, and a thermometer can be a great help.