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Hardening Mild Steel


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Dian. Thanks.  This got me to doing some research into how various  alloys effect steel....So as to the idea that if you increased the Silicon in low carbon steel you could do away tool steel. NOPE.   As Mr. Sells pointed out it takes carbon to form martensite.  After some research I found that  silicon does aid in the transformation of existing carbon into martensite and austenite in carbon steels. BUT , it doesn't make martensite or austenite. Its rather interesting to read how silicon effects the strength and hardening of carbon steels regardless of the carbon  content. Also interesting to see how Silicon effects the formation of martensite and austenite through the temperature  spectrum. 

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perhaps i have caused the confusion to a certain extend by being too lazy to use capital letters (old habit): "si 0.46%".

the composition of the steel in question was: C 0.23%, Mn 0.54%, Si 0.46%, P 0.004%, S 0.0005%.

intercritically annealed at:

800°c/2 hours resulted in 41 hrc, 1280 mpa, 72 joule, 64% martensite

825°c/3 hours resulted in 24 hrc, 935 mpa, 135 joule, 83% martensite.

 

as to "claims", on the contrary, i was hoping maybe somebody on here would be able to confirm it or had further insights in to matter or would even go and reproduce it, as i dont have access to an electric oven at the moment.

 

btw, martensite doesnt need much bulk carbon content to form. as soon as there is austenite, it can be transformed into martensite. depending on its carbon content martensite can be hard of softer. its possible to get large fractions of martensite in very low carbon steels (e.g. 0.05%).  if that were not the case, a lot of modern steels (e.g. such as used for sheet metal for cars) woud not exist. 

if interested, look up "dual phase steels".

 

so whats the end of the story? well, the controversy over hardening mild steel might just be based on different procedures used. if you austenize it at 950°c and quench it it wont work.  intercritical annealing seems to yield results.

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edit: here is a short article that explains dual phase steel quite well. its older, but at least they seem to be using "plane-jane" 1018/1020 steel. they get considerably higher wear resistance compared to another 37 hrc steel.

 

 

0043-1648(95)06796-5.pdf

 

does the link work? (it does on my computer.)

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So. Is there a purpose behind this.  It appears that you want someone to conduct specific specific research on some low carbon steels but whats its end use.  I mean I'm not going to waste my time trying to make a cold chisel out of 1020.  I personally only know of a very few people in this realm have the tools and equipment to ascertain the martensite conversion levels and they are too busy conducting analysis for themselves. It would probably be easier for you to contact a metallurgy company with the proper equipment in your home country for your experiment.

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I for one am thoroughly enjoying the information and discussion. 

 

Any good tool making smith should not only be able to pick out the best material for a given item, but also have the information for proper hardening and tempering.

 

With this they should also possess the ability to figure out how an unknown material can best be used via figuring out what it is. 

 

Being a world class blacksmith is more than just forging metal unless it's not...

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I don't have the patience to type out a full summary of the paper on my phone, but it is only 5 pages and well within the understanding of anyone that wants to read it (perhaps with limited searching for jargon definitions). 

The paper does not say that the material with higher volume % Martensite is softer than the material with lower volume % Martensite, but rather that the material with lower volume % Martensite has higher wear resistance. More on that in a moment, as the conclusion should be qualified. 

On what may be causing the confusion on Martensite and material hardness -- The authors used microhardness testing to determine the hardness of individual phases (Martensite and ferrite) for each processing condition, and the Martensite in the material with lower volume % Martensite was harder than the Martensite in the material with higher volume % Martensite. No bulk material hardness measurements were presented. 

Each of the specimens were tested in a device which caused a cylinder of steel with HRC 50 to rotate against the specimen with a constant force and speed for a specific distance (i.e., length of surface contact). At 5% distance intervals, specimen weight loss was measured, and these measurements were plotted for all specimens. The specimens were replaced into the test equipment with a new surface touching the cylinder each interval to reduce the potential impact of changing surface area. 

The conclusion that increasing volume % Martensite correlates to lower wear resistance was surprising to the authors as well as it is to us. The authors proposed that some energy was absorbed in deforming the ductile ferrite. The increase in wear resistance correlated both to the ductility of the ferrite as well as the hardness of the Martensite. I have quoted the "take home" paragraph below. 

"The difference between input and output energies of a tribological system during friction is predominantly frictional energy. Some energy is consumed by deformation and fracture. The consumption of some deformation energy in ductile phase decreases the energy for pure deformation. The consumption proportion of the deformation energy input to the system in the ductile phase depends on the proportion and ductility of the ductile phase. When this proportion and ductility increase, the consumed energy also increases. It can be stated that the proportion of the consumed deformation energy is increased by increasing the ductile ferrite phase proportion in the structure consisting of Martensite and ferrite phases. But the structure should be supported by hard Martensite phase to increase the wear resistance. For this purpose, it is understood that dual phases obtained with lower Austenitizing temperatures provide higher wear resistance."

So about the qualification that I mentioned earlier... The specimens used were of one composition and five processing conditions. The highest wear resistance was also the specimen with the least volume % Martensite. It is unlikely that the trend continues unchanged down to 0% Martensite, but the breakpoint was not determined by further experiments.  Furthermore, changes in the cylinder hardness, rotation speed, or force would also likely change the optimal distribution of ductile ferrite and hard Martensite. 

Also, for those curious -- the hardening media was water, salt, and ice. 

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JLP. it forced me to dig deeper into metallurgy, alloys, and some of the terms commonly thrown around.  You mentioned your reference Book earlier. Which one are you referring to. I need a good desk top steel reference book. 

As an aside. I had the privilege of watching a master Smith demonstrate forge welding a Tulip. I guess that's where the... unless  its not aspect comes in. Truly astonishing. 

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Velegski, I have 5 or 6 books on Metallurgy.   

Not books on alloys persay (exact alloy heat treatment) but more on the science of heat treatment. 

Some of the new books are excellent but I actually grew up reading books from the turn of the 20th century up till about the 50's..   

Over the last few years I have updated the library and maybe the best book out there is one for the knife maker. 

Steel Metallurgy for the Non-metallurgist  by John D. Verhoeven


This one is a good basic book but not as in depth.

Metallurgy Fundamentals  by Daniel A. Brandt

The first book posted is one of my favorites.. 

Steels progress and the science behind it gets more indepth every few years.. 

I like the early books because of what I did as I came up..  But, much of the information has limited use today as the science of steel is much better today.. 

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JLP..Thanks for the info. I'll keep my eyes peeled for them. I've got Verhoevens book on metallurgy of knife steels.  I never intended to get this deep into metallurgy but as I play at making knives and tools I find I need to understand some basics in metallurgy.  This thread is an example. I had an idea of the reasons for alloys in metal, however I didn't know how they played in the heat treat process. I'll  probably never need the real science behind it but its nice to know. Besides it impresses the heck out of the nephews that the old codger knows this stuff. 

You never know when dual phase steel might be the Double jeopardy  answer. 

Thanks 

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Velegski,  even if never truly understood it brain food even rolling around in the back of the mind.

I personally because of what I do having that greater understanding really opens doors as to why the choices for this steel or that steel and why a real reason why that's the choice.

 

Diagnostically it's even more important when figuring out within a given reasoning why something fails or what steels are deep hardening vs shallow.

When it was primarily 10series steels it was pretty simple.

 

Early steel suppliers would send out flyers to smiths and state why their steel was better and the roll it had.

I was lucky enough to run into some of these early flyers and learned about miners steels and drill steels.

Red devil and blue devil were the names.  It gave full heat treat and expected out comes with a disclaimer to always check the steels for suitability. 

These steels were .90c and were water quench only with no temper for use as drills and picks.

Today we would not dream of using that kind of of carbon content without major temper for a rock drill or rock pick. 

They can not be used for hot work and turn to butter at 800f. So no good for hot punches nor hot chisels.

 

In my scrounging I picked up a bunch of rock drills to forge into punches and chisels and the first time I used 1 of the punches on hot work it became soft.

While it might not be red or blue devil brand it has the same characteristics.

So now know what it's suitable for.

Works amazing for any stone tools. Gets 60Hrc with no temper and is extremely durable.

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velegski, there's a 29-part lecture series on YouTube of MIT professor Thomas Eagar's "Welding Metallurgy" course (filmed in 2014) that gives a LOT of really interesting information about how steel metallurgy works (with lots of illustrative anecdotes and real-world examples). If you feel like sitting in on an MIT metallurgy course for free, the playlist is HERE.

Verhoevan's book "Metallurgy of Steel for Bladesmiths & Others Who Heat Treat and Forge Steel" is available online in PDF HERE.

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JHCC. thanks for the input. I mistitled the Verhoevans book I've got. Its the one you mentioned. I'll be watching the MIT videos. The titles to his lesson looked interesting. 

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