Martensite percentage of 6150 steel.

S

S obsessed

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Does 6150 steel produce 100% martensite? I know 1060 is where the line is but then we add in some alloys and it can change things. I do notice a difference between 5160 and 6150 in edge stability but haven't yet tried it against 1060 or even 1055 steels. And while we are at it, how about 4150 and 8650 of which both are somewhat readily available. This question is more about metallurgy and not really at all about edge holding as these are not steels that I would use for knives but rather they are great for bladesmith tooling as well as axes and tomahawks. I know 1055 is used by some scissor manufacturers as well as 1060 and I have some 6150 in perfect sizes to make some shears out of. Is there a formula for how much of a certain type of alloy like chromium that when added will offset the martensite percentage when carbon is restricted?
 
S obsessed said:
Does 6150 steel produce 100% martensite? I know 1060 is where the line is but then we add in some alloys and it can change things. I do notice a difference between 5160 and 6150 in edge stability but haven't yet tried it against 1060 or even 1055 steels. And while we are at it, how about 4150 and 8650 of which both are somewhat readily available. This question is more about metallurgy and not really at all about edge holding as these are not steels that I would use for knives but rather they are great for bladesmith tooling as well as axes and tomahawks. I know 1055 is used by some scissor manufacturers as well as 1060 and I have some 6150 in perfect sizes to make some shears out of. Is there a formula for how much of a certain type of alloy like chromium that when added will offset the martensite percentage when carbon is restricted?
Click to expand...
Are you concerned with carbides or retained austenite? Something else? I’ve never had this question before.

Hoss
 
S obsessed said:
Does 6150 steel produce 100% martensite? I know 1060 is where the line is but then we add in some alloys and it can change things. I do notice a difference between 5160 and 6150 in edge stability but haven't yet tried it against 1060 or even 1055 steels. And while we are at it, how about 4150 and 8650 of which both are somewhat readily available. This question is more about metallurgy and not really at all about edge holding as these are not steels that I would use for knives but rather they are great for bladesmith tooling as well as axes and tomahawks. I know 1055 is used by some scissor manufacturers as well as 1060 and I have some 6150 in perfect sizes to make some shears out of. Is there a formula for how much of a certain type of alloy like chromium that when added will offset the martensite percentage when carbon is restricted?
Click to expand...
Everything will have a small percentage of retained austenite, getting closer to single digits RA will require a tuned austenitizing temperature, proper quenching and cold treatment.

Geometry and how they were sharpened will play a bigger role than pulling hairs about chromium content.

Unless the geometry and sharpening is ruled out by properly quantifying it, we can't say it's the alloy content causing the differences you experienced let alone the fact that simply one steel was heat treated by chance with more optimum austenitizing temperatures for the given alloy rather than being an inherit quality of chromium addition in the material.

In my opinion, seeking a formula for how much of a certain type of alloy like chromium that when added will offset the martensite percentage when carbon is restricted is a "red herring."


I hope my answer doesn't discourage your curiosity.

Best wishes.
 
I think you might be confused about carbon content and martensite. You can still transform the steel to full martensite with less than 0.6% carbon. Even pure iron can be transformed to martensite. It is just lower carbon and therefore lower hardness martensite.
 
Confused yes. For many years now I have had it in my mind that when you get under .6% carbon after a proper heat treat that you will start to have traces of ferrite also. So the microstructure would be martensite, retained austenite, and ferrite. The amount of ferrite increasing as you get lower in carbon percentage. 1045 would always bring this to mind and after a little searching I see there are some heat treats to get 1045 to have some ferrite also for increased toughness but it seems with what I am finding out now that it would be somewhat unreliable to do things this way. I believe these ideas came from back in the day when I was first introduced to heat treating by machinists who always heat to cherry red and dip in used motor oil. Even after reading Larrin's book and others this idea stuck with me and has always been a red flag hence the question here about these other alloys. I think I stuck with the idea because things like 4140 and 4150 had such a large toughness differential that there was extra ferrite in the 4140 after heat treat and the 4150 with the alloys was likely to not have any. I see this is all bogus now. I know below the eutectoid point that after normalizing you get ferrite but that is different.

So just to clarify, even something like 1030 steel after a proper normal heat treat for martensite will produce only martensite and a small amount of austenite. And even after tempering it will be the same correct? In these lower carbon steels, what does the tempered martensite look like or what is it composed of compared to the higher carbon steels? These things are not clear yet to me as most talk is of high carbon steels. Yes I know these lower carbon steels are not for knives but the metallurgy is important to understand to me.
 
I think you are more likely to get pearlite mixed with martensite from improper quench medium.

Hoss
 
If you use a magnet to huddle temperature for these steels you will have left over ferrite in the mix after quenching.

Remember that hypereutectoid steels (more than 0.8% C) have two phases at their hardening temperature. One is austenite. The other is undisolved carbide. Eutectoid steel will have only one phase in this temperature range which is austenite.

The trick is a hypoeutectoid steel (less than 0.8% C) will have two phases also. One is austenite, the other is ferrite. If you quench from here, the ferrite stays. You have to heat hypoeutectoid steels hot enough to remove the ferrite. Backyard bladesmiths often don’t have the temperature control to do this.

If you can get all the ferrite dissolved, then you can get a near 100% martensite structure, though it’s maximum potential hardness is limited according to its carbon content. A very fast quench is needed for 10xx steels in this range too. Iced salt water is sometimes too slow. Steels like 41xx, 86xx, and 43xx will harden fully with oils if you can get the temperature right.
 
Last edited by a moderator:
S obsessed said:
Confused yes. For many years now I have had it in my mind that when you get under .6% carbon after a proper heat treat that you will start to have traces of ferrite also. So the microstructure would be martensite, retained austenite, and ferrite. The amount of ferrite increasing as you get lower in carbon percentage. 1045 would always bring this to mind and after a little searching I see there are some heat treats to get 1045 to have some ferrite also for increased toughness but it seems with what I am finding out now that it would be somewhat unreliable to do things this way. I believe these ideas came from back in the day when I was first introduced to heat treating by machinists who always heat to cherry red and dip in used motor oil. Even after reading Larrin's book and others this idea stuck with me and has always been a red flag hence the question here about these other alloys. I think I stuck with the idea because things like 4140 and 4150 had such a large toughness differential that there was extra ferrite in the 4140 after heat treat and the 4150 with the alloys was likely to not have any. I see this is all bogus now. I know below the eutectoid point that after normalizing you get ferrite but that is different.

So just to clarify, even something like 1030 steel after a proper normal heat treat for martensite will produce only martensite and a small amount of austenite. And even after tempering it will be the same correct? In these lower carbon steels, what does the tempered martensite look like or what is it composed of compared to the higher carbon steels? These things are not clear yet to me as most talk is of high carbon steels. Yes I know these lower carbon steels are not for knives but the metallurgy is important to understand to me.
Click to expand...


Looks like I didn't fully understand the original question.

Like M me2 said, you have to austenitize PAST the two phase region area with hypoeutectoid steels.



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Like Larrin Larrin said you can still get full Martensite with hypoeutectoid steels under 0.6% carbon you specified.

Which means leftover ferrite would be due to improper heat treatment.

Like you said, it is important to understand metallurgy but it's also important to have good temperature control, not just relying on magnets and a forge.


Here is an example from Samuels 1999

He did some metallography showing the transformation in low carbon steels among other things.

0.39% carbon steel.
We can still get a full tempered martensite matrix depending on heat treatment.

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0.1% carbon steel.

Looks like there isn't sufficient carbon to avoid ferrite in this material.

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Thanks guys! No one misunderstood anything. The question should have never been a question to begin with really.
I certainly understand temperature control is very important. So with a eutectoid steel that was normalized to make a pearlite structure and then bringing it up to non magnetic would be enough to make the pearlite snap into austenite and from there we can quench to martensite correct? But with a hypoeutectoid steel that would be normalized and would be of pearlite and ferrite, the non magnetic temp would transform the pearlite but the ferrite would require yet a higher temperature correct? Instead of higher temperature could a longer soak time also transform the ferrite? I am guessing if we were to work up a heat treat for say 1045 we would still use the lowest austenitizing temperature that would give the highest hardness just like everything else along with proper quench medium. I am bringing this all up so I understand completely.
 
S obsessed said:
Thanks guys! No one misunderstood anything. The question should have never been a question to begin with really.
I certainly understand temperature control is very important. So with a eutectoid steel that was normalized to make a pearlite structure and then bringing it up to non magnetic would be enough to make the pearlite snap into austenite and from there we can quench to martensite correct? But with a hypoeutectoid steel that would be normalized and would be of pearlite and ferrite, the non magnetic temp would transform the pearlite but the ferrite would require yet a higher temperature correct? Instead of higher temperature could a longer soak time also transform the ferrite? I am guessing if we were to work up a heat treat for say 1045 we would still use the lowest austenitizing temperature that would give the highest hardness just like everything else along with proper quench medium. I am bringing this all up so I understand completely.
Click to expand...

I strongly recommend reading this article.

There's a lot of answers to your questions in it.

 
Longer soaks won’t get rid of the ferrite in austenite. Those diagrams are equilibrium diagrams, meaning they assume everything is as stable as it will ever get.

I’ve thought of getting a 4340 chopper but have never made the jump. 1045 would be difficult due to the fast quench requirement.

Be aware the pearlite is just a specific mixture of ferrite and cementite. The ferrite and cementite form alternating layers. In a normalized hypoeutectoid steel, I’d guess no separate ferrite, but the ferrite layers in pearlite would be thicker. You’d still need higher temperature to get rid the ferrite
 
me2 said:
In a normalized hypoeutectoid steel, I’d guess no separate ferrite, but the ferrite layers in pearlite would be thicker.
Click to expand...

No, in a hypoeutectoid steel you'll still get proeutectiod ferrite upon air cooling from A3.


Just like is seen in the iron carbon phase diagram I shared above.



It is similar to how in hypereutectiod steels we get proeutectiod carbide formation when air cooling from Acm


In hypoeutectoid steels, the first product that forms upon slow cooling is ferrite which rejects the carbon into remaining austenite regions.

The more carbon rich austenite will make pearlite upon further cooling leaving us with patches of pearlite and ferrite at room temp rather than the exclusively pearlite structures that we see in eutectoid steels.
 
Maybe or maybe not. I’m sure someone has actually done it and has pictures. The diagram is an equilibrium diagram and doesn’t predict air cooled structures very well.
 
This is a very simplified explanation of what the carbon content does to change hardness.

I like to use bricks/concrete/cement in explaining steel structures. In this case we are talking about martensite.
Let's look at martensite as cement. We will not pay attention to the aggregate (carbides and alloys) and water (heat) in this example.

The portland is the carbon and the sand is the iron in our simplified cement/martensite example.
Mix sand and Portland and you will get cement. All cement looks more of less the same once mixed and poured.
We think of cement as a very hard material, but that isn't always the case. The portland-sand (carbon-iron) amounts controls how hard it is. If the concrete mixed with the right amount of portland and sand, it gets hard and strong. Lower the portland too much and it gets soft and so weak it won't hold up to use (hypoeutectoid like 1018). Raise it too much and it gets so hard it becomes brittle it breaks easily (hypereutectoid like cast iron). There is a perfect zone in the middle of the two extremes that works for concrete as a good building material (eutectoid for steel).

In steel, you can only raise or lower the percentage of carbon a small amount before it makes the material unusable. +/- .25% is about what works (.60% to 1.1% carbon content for knives). We call this range of carbon percentage "knife steels". Lower, and while still martensite it will be too soft ...higher and while still martensite it will be too brittle.
 
me2 said:
Maybe or maybe not. I’m sure someone has actually done it and has pictures. The diagram is an equilibrium diagram and doesn’t predict air cooled structures very well.
Click to expand...

Yes, the diagram is not an actual micrograph and is simplified for learning purposes. While the morphology of the phases can be different when not at equilibrium etc, we should still get a separate ferrite phase rather than pearlite with larger ferrite bands inside.

Teerapong Samran in 2010 did some micrographs.

DWMDutg.png


Normalized at 1650f for 1 hr.

Separate ferrite phase seen rather than just pearlite with larger ferrite bands.

There were other micrographs by other authors on other steels like 1045 that showed grain boundary ferrite after normalizing from 1830°f and air cooling along with widmanstatten ferrite in some areas.

Still had separate ferrite from pearlite.

I don't own any hypoeutectoid steels so unfortunately I can't get any micrographs of my own for you.
 
I dug around a bit and was able to find some continuous cooling transformation diagrams for 1060 and 1045 steel. They indeed predict a small amount of ferrite, somewhere between 5% and 9%. The trick is finding a diagram that starts at the proper temperature. The first few I found started from about 1450 F. Not quite high enough to answer the question at hand. The ones that start above the A3 temperature still had some ferrite.

1055/1060 has become one of my favorite steels for outdoor knives brush knives. I may have to revisit my 4340 knife concept.
 
Here I am Devin. That article Deadbox Hero shared from Larrin answers every question I have ever had with all this. It all makes sense now after understanding ferrite sticking around wasn't a thing. Thanks guys for the help. I am glad I finally asked. I am working on completing my heat treat oven and this problem has haunted me for many years.
 
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