Can differences in heat treat result in different rust resistance among the same steels?

D

DangerZone98

Joined
Dec 7, 2019
Messages
3,497
Context: I have these two Cold Steel socket handle Bushmen. Steel used is 1055 if I’m not mistaken. Both are kept in the same location (drawer) and are stored in their factory sheaths. The Bowie version basically has no issues with rust, but the straight spine Bushman seems to be more prone to surface rust. I don’t really use either knife often other than occasional carry around the house.

I scrubbed away with some baking soda and a Q-tip, wiping the blade dry after. Some stains remain, but the knife looks considerably better now.
 
DangerZone98 said:
Context: I have these two Cold Steel socket handle Bushmen. Steel used is 1055 if I’m not mistaken. Both are kept in the same location (drawer) and are stored in their factory sheaths. The Bowie version basically has no issues with rust, but the straight spine Bushman seems to be more prone to surface rust. I don’t really use either knife often other than occasional carry around the house.

I scrubbed away with some baking soda and a Q-tip, wiping the blade dry after. Some stains remain, but the knife looks considerably better now.
Click to expand...
Short answer is yes, the heat treatment can affect how corrosion resistant a steel is, but really only if it is somewhat stainless in the first place. In other words the heat treatment can have an effect on corrosion resistance if there is chromium in the alloy.

Steels that have no chromium such as simple carbon steels(including 1055) shouldn't have better or worse corrosion resistance because of the heat treatment. Things like surface finish and outside influences will be the main factors. A rougher surface finish will tend to be more prone to rust as will the circumstances and way the knife was ground and finished, as will contaminants if the knife wasn't cleaned thoroughly or from the sheath etc.
 
1055 is a carbon steel with 0.5 to 0.6% of carbon. There is also max 0.4% of Chrome and max 0.4% of Nickel so there is nothing in this steel to prevent it from rusting. For carbon steels it also goes that Carbon content increase corrosion rate – more carbon=more prone to rust.
When heat threatening carbon steel carbon atoms bond with iron and form martensite. If the knife was hardened to lower HRc this means less martensite was formed and more carbon was left unbonded in the solution and this carbon will make the steel more rust prone.
This is just a simple explanations but I think it will work in this case.
I would say non heat threatened carbon steel will be a little more prone to rust then heat threatened same carbon steel. I don't know if this would make much difference in real life.
 
Last edited:
chalby said:
Short answer is yes, the heat treatment can affect how corrosion resistant a steel is, but really only if it is somewhat stainless in the first place. In other words the heat treatment can have an effect on corrosion resistance if there is chromium in the alloy.
Click to expand...

Yes; this goes for inox steels. If Chromium stays in the solution and it's not bond with carbon atoms to form Chromium carbides this 'free' Chromium forms Chromium oxides which make the steel rust resistant.

If I may add at this occasion and give D2 steel as an example. D2 is not stainless steel but you can find claims on the internet D2 steel is almost stainless because it has about 12% of Chromium.
Well; wrong.
When heat threatening D2 steel by the book most of this Chromium goes to form Chromium carbides so there is only 4-6% of Chromium left unbonded in the solution.
Only unbonded Chromium in the solution forms Chromium oxides which prevent the steel from rusting.
 
Last edited:
TheOne45 said:
... For carbon steels it also goes that Carbon content increase corrosion rate – more carbon=more prone to rust....
Click to expand...
No, I don't think so. 1095 is no more or less prone to corrosion than 1055. Carbon content doesn't effect corrosion resistance in this case.
 
An increase in carbon content increases average corosion rate.

If you go Googling there is a chance you will find a study, how percentage of carbon affects corrosion rate.
 
TheOne45 said:
An increase in carbon content increases average corosion rate.

If you go Googling there is a chance you will find a study, how percentage of carbon affects corrosion rate.
Click to expand...
I did a quick google search but didn't find anything. Have you got a link?

A higher carbon content definitely negatively affects corrosion resistance in steels that contain chromium.
 
I found this link:


I have no idea, if you can see the difference in corrosion rate in real life if you have two samples (or knives) made of the same steel with small difference in carbon content.

It's more likely there was something else going on like one knife was used to cut something and not cleaned all the way.
Could be there are some remains of something inside the sheath of the knife with more corrosion.

Who would know. Carbon steel rusts and that's it.
I would polish the knife with buffing wheel and green compound and call it a day.

How about a test,
polish both knives the same way, put them both on a shelf then put a drop of water on each blade and see which blade rusts more. 😉
 
Last edited:
Interesting read. Thank you.

It's doubtful to me whether there would be any meaningful difference in knives in normal use though, even with big differences in carbon content. The study also mentioned that there was a greater difference in tests using acid over the "wet" test (which would be arguably more relevant for people using carbon steel knives and the corrosion rates of those samples was pretty similar even if there was a slight upward trajectory). Either way, the almost complete lack of corrosion resistance in carbon steels as we know it makes it a bit of a moot point in a practical sense.

Also, the samples used in the study were normalized pearlite not hardened steel, so how well that study translates to knife steels is unclear.
 
It's doubtful to me whether there would be any meaningful difference in knives in normal use though, even with big differences in carbon content.
Click to expand...

I agree.
From a practical standpoint I would say oxidation is common for carbon steel because there is nothing in there to prevent it from rusting. I think there is no point doing scientific expertises (perhaps expertizes in US english? ;) ) about that fact.
So what other owners of carbon steel knives do to prevent oxidation?
-Cleaning and oiling the blade
-Forced patina
-Some sort of a coating over the blade
-Polishing the blade – polished surface is less prone to oxidate then rough surface
So much can I contribute from a real life to help the owner of those two knives.
 
Last edited:
Alberta Ed said:
A light coat of Vaseline or one of several specific rust protectants like BreakFree CLP will prevent rust from developing.
Click to expand...
I’ve seen ancient threads here though that advise against Vaseline. Something about water getting into the Vaseline that can rust the knife?
 
I'm not sure where some of the comments get their information but heat treat can definitely change corrosion resistance in carbon steel as well as stainless probably to a much lesser degree at first. It can be seen in examples of severely neglected axe heads of homogeneous steel that are zone hardened, the harder bit(nearest the edge) will have clearly different levels of corrosion than the much softer eye area. Even taking into account the probability of the edge having had a much smoother surface finish there will be a visible line where you can see where the hardness is different with different levels of corrosion damage on either side of the temper line. Reguarding the difference in corrosion on the Cold steel bushman models, it could be surface decarburization from the heat treating process was never removed before the blades were coated, or perhaps some type of carbon migration from the manufacturering process, due to the heating the blade to facilitate the forming of the socket handle.
 
thebrain said:
I'm not sure where some of the comments get their information but heat treat can definitely change corrosion resistance in carbon steel as well as stainless probably to a much lesser degree at first. It can be seen in examples of severely neglected axe heads of homogeneous steel that are zone hardened, the harder bit(nearest the edge) will have clearly different levels of corrosion than the much softer eye area. Even taking into account the probability of the edge having had a much smoother surface finish there will be a visible line where you can see where the hardness is different with different levels of corrosion damage on either side of the temper line. Reguarding the difference in corrosion on the Cold steel bushman models, it could be surface decarburization from the heat treating process was never removed before the blades were coated, or perhaps some type of carbon migration from the manufacturering process, due to the heating the blade to facilitate the forming of the socket handle.
Click to expand...
The more I've read up on it, it's possible as has been discussed above. Especially severely neglected steel as was simulated in the study linked.
 
I am not familiar with the 2 knives you have however a high polish will have more resistance to corrosion than a sanded or brushed finish on metals, even carbon steels.
304 high polish can have more resistance than 316 #4 finish in a pool environment for example .
 
You must log in or register to reply here.
Back
Top