Master bladesmith Walter Sorrells shows how to test steel for knife-making in this video. Steel can be “spark tested” to narrow down its specific type and composition, by analyzing the sparks the steel throws when put on a grinder (a belt or bench grinder – anything that can grind steel). Spark testing is often used by knife makers to tell whether or not a piece of salvaged steel can still be used to make a serviceable knife.
Walter says he’s not a big fan of “mystery steel.” This means steel where no one is sure what it’s made of; he says this can be dangerous, because not all kinds of steel are alike. Some can be heat-treated, for example, while others are not as forgiving. This can result is a waste of time and resources. So here are some ways sparks can tell if a piece of steel is good enough.
He starts with the most common kind of steel available – mild steel, which has low carbon and is used for rebar, etc. It throws long sparks, like little meteorites. Mild steel, welding steel, structural steel, A36 all describe the same general category of steels that are too low in carbon to be used for knife-making. These ones can’t harden, and will get dull in a heartbeat.
For those who don’t have professional heat-treating equipment, the best bet is a high-carbon steel like that which is designated in the US as ten series steels. High carbon steels throw very “sparky” sparks, flying off the grinder in little balls of sparks.
For comparison, he runs different steels on the grinder. There’s 1050, medium carbon steel, followed by 1075 and 1084. 1084 has higher manganese content. As the numbers go up, the carbon content goes up. As the carbon goes up, the sparks tend to run shorter, and break apart into dandelion-like shapes quickly. He demonstrates with a piece of high-carbon Tamahagane steel, well over 1% with no manganese. The sparks are very short.
Walter runs 01 steel, which he says has more manganese and is the ideal starter steel for new knife makers. Then there’s 5160, 52100 and moves on to steel with heavier alloys, like L6 , 15N20, 80CRV2, S5, Hitachi Blue Steel. Everything so far can be turned into a knife in a primitive home shop, he says.
Steels that wouldn’t be good include: 316 stainless, 303, 304. Suitable are 440C, S30V, CTS-XHP, and so on. Walter reminds viewers that these steels all heat-treat differently, so it will take some trial and error to get each to optimum hardness. So spark testing is essentially to help knife makers rule out some steels, but it doesn’t give the exact type of steel — more of a general test to check on overall usability.