Steel Spark Test - Is it Mild Steel or Hardened? | DIY Vlog #32

[@Beyondact]

YAY! run that intro! I've always known there's different steels but not much thoughts gone in to it after they made it the same price at the scrapper back in like early/mid 90's.

[@ratchriat1716]

well explain and a good demo enjoyed the video.

[@samrodian919]

That is a high carbon steel that has been hardened and tempered by the looks of it. In its original form high carbon or tool steel is in the soft state so it can be machined into tools etc. On,y after it has been heat treated and this means hardening and tempering, two separate processes, hardening consists of heating to cherry red which is above the steels critical temperature you can easily test that temp by seeing if a magnet will stick to it. In proper controlled hardening the steel is held above its critical temp for around an hour then rapidly cooled in water, or brine or oil of various types. At the end of this process the metal I'd absolutely dead hard, but it is extremely brittle and if dropped or you try to bend it it is very likely to snap or shatter, so the tempering process is to bring that dead hardness back to a suitable hardness without the brittleness. Generally the steel is pickles or some other process to clean it back to bright metal and then heated until there starts a colour change in the oxides forming on the metal as it heats up generally most tools are taken up to around the pale to dark straw colour but usually not more than light purple, and higher than this is getting into the really hardened stages and of course brittleness generally most edge tools like woodworking chisels go up to dark straw or maybe light purple. Sorry I have not put temperatures in here because I've forgotten them, and I learned them in Fahrenheit anyway!