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"Carbon steel" can mean a lot of different things, but a low carbon steel like A36 or AISI 1020 might have something like 60 HRB. A medium carbon steel would be closer to 90 (similar in hardness to the knife we were testing in the video). Quench hardened steel is much harder, hard enough that it really shouldn't be tested on the Rockwell B scale. We instead use the Rockwell C scale (more load with a sharper indenter), which would give a value of 60-65 HRC for quench hardened steel. That's off the charts for Rockwell B, but would be well over 120 HRB, much harder than the stainless steel knife we tested.

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That diagram is not accurate for 3XX series steels because they have large nickel additions which increase the size of the austenite phase.

It is difficult to regain the hardness in ferritic stainless steels. A typical steel could be normalized (heated to austenite, then cooled in air), but that doesn't work for stainless steel since it doesn't have a phase change when heated. Plastic deformation via cold working or hot working the steel could regain its strength, but not without altering its shape.

You are correct. The gained ductility is relatively minor, but larger grains are slightly more ductile than small grains.

Time is a factor for producing Chromium Carbide (CrC) precipitation. Water quenching a think blade is fast heat loss process and does not produce much CrC. However, for thicker blades, CrC precipitation is a possibility.

quenching in water provides a greater hardness than quenching in oil. Our goal was showing quenching will not increase the hardness of stainless steel.

To measure microstructure hardness and depending on the size of grain, Vickers microhardness or for smaller grains Atomic Force Microscopy (AFM) can be used.

Perhaps look into carburizing process for SS or other surface hardening methods listed in here: www.worldstainless.org/Files/issf/non-image-files/PDF/Euro_Inox/Surface_Hardening_EN.pdf

@@everydaymaterials9830 thank you very much ❤️

@@everydaymaterials9830 thank you very much ❤️

Perhaps it is martensitic which has close to 1% carbon id can be quenched hardened, For this video we had ferritic stainless steel which has low carbon (less than 0.2%) which doesn't produce sufficient martensite after quenching and therefore can't be hardened.

@@everydaymaterials9830 jus for some clarification you don’t need 1% C to make a stainless martensitic. 403/410 type stainless steels are commonly used martensitic grades in the power industry and often have C contents below .15%. My company buys annealed 403 forgings that as received measure around 80 HRB and will quench harden to about 44 HRC with only .12% C.

work hardening should introduce dislocations and make granular movement more difficult -> harder

Some grades of stainless steel can get harder by adding alloying elements such as copper followed by a special heat treatment known as precipitation hardening (PH) which allows formation of hard intermetallic compounds within the steel. Example 17-4 PH steel which has added copper. Plain ferritic stainless steel has low carbon content but by adding upto 1% carbon which can transform it to martensitic stainless steel series which are hard.

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