steel question

[Cliff Stamp]

Cliff, that second link is the only site I believe I have seen that places D2 higher than M2 for wear resistance. I have to question the opinion on that one.

It isn't an opion, Alvin is quoting ASM reference texts, it seemed odd to me to so I checked it out. The D2 series in general is ranked higher in tool steel references, as well as data sheets, Timkens for example. M2 however tends to make a better fine cutting blade and will outperform D2 in many industry applications because of grain structure, hardness, and heat resistance.

http://www.timken.com/products/spec..._Files/air_melt/ColdWorkToolSteels/TLS D2.pdf

I think the data they provide at Crucible is for "optimal" hardness on steels based on what I've read.

There really isn't an "optimal" hardness in general, D2 has two broad tempers, low and high for either wear resistance or toughness, but even in them you can push further towards one than the other. Similar with stainless steels and wear resistance vs corrosion resistance, Verhoeven discusses this in detail by showing how the amount of Cr dissolves is strongly dependent on soak temperature.

-Cliff

 

[STR]

That link doesn't show D2 as higher in wear resistance than M2. It shows them dead even. So again there is a difference in opinion or the so called facts posted. It also shows the comparison at 60Rc for D2 and 62Rc for M2.

It isn't worth getting into. I still think M2 has a higher wear resistance than D2. I haven't seen data to convince me that D2 has a significant advantage over 154CM in either edge holding, wear resistance or toughness.

D2 is a great cutlery steel though. I'd sure take it over 154CM for most jobs, but if you are planning lots of kitchen use or food prep it may be better to go with the stainless as Cliff already mentioned earlier.

Steve

 

[Cliff Stamp]

That link doesn't show D2 as higher in wear resistance than M2.

D2 is about 6.5 and M2 5.5, D2 clearly passes a line that M2 doesn't reach, and the M2 blade is harder than the D2 one . Again, these are not subjective opinons, these are materials tests. The reason that different tests can show different results is because there are many ways to test attributes, even abrasive wear can be tested in various methods, and there are several other types of wear such as adhesive.

It also shows the comparison at 60Rc for D2 and 62Rc for M2.

Steels are rarely compared at the same hardness because they all peak differently. M2 has a toughness peak at that hardness, it is where Benchmade runs it and that hardness for D2 is also one of the common peaks. Both can be made much harder, 64/65, and can be pushed 1-2 points higher with oil quenches and cold treatments. As noted there is of course more to tool lifetime than wear resistance and M2 tends to outlast D2 for several reasons.

-Cliff

 

[DGG]

While 154CM has only a slightly higher amount of Cr, after heat treating there is 11/12% of Cr free in 154CM, only 2-3% of the Cr is actually in carbide form. D2 retains much more of the Cr in carbide due to the much higher carbon content and lower soaking temperature and thus is much lower in corrosion resistance. This can be significantly influenced by how the two steels are heat treated of course.



154CM and D2 have similar max hardness and D2 has a much higher wear resistance, thus they will be similar on some cutting and D2 will have an advantage on others, so unless corrosive materials are cut D2 is likely the better cutting steel assuming both are heat treated for optimal hardness / wear resitance.

-Cliff

Cliff - Please explain (slowly) the difference between "free" and "carbide form" and what the real world significance of each is. You are way over my head with your comments. Tanks!

 

[Ring]

Not to hijack the thread to much, but what about O-1 tool steel in comparison to say s30v or say VG-10 or that of even D-2.

All I know is that O-1 is more likely to rust.

I am led to believe that O-1 retains a good edge and is tough. But how to compare it to the others mentioned?

 

[Cliff Stamp]

Steel consists of two main forms, ferrite and carbide. The ferrite is the main part, and refered to as the "steel matrix" as it is what everything basically sits in. Think of it like concrete which consists of cement (ferrite) and sand+rocks (carbide).

Elements like Chromium can be free in the ferrite, meaning they are not attached to anything, just hanging out, or can bond with carbon to form carbides (which are essentially just little hard bits in the steel) and they are no longer free to bond with anything else as the carbon keeps a tight hold on them.

Now when the surface of the steel is struck by an oxygen atom it will attack any available ferrite and combine with iron to make an oxide (rust) and which is soft and weak and brittle. However if there is chromium in the ferrite it will jump infront of the iron in a noble sacrifice and you will get chromium oxide formed.

The chromium oxide will actually form a layer on the surface of the steel unlike the iron oxide and will actually stop any more oxygen from getting inside and it just bounces off the chromium oxide barrier and then wanders off looking for better grazing areas.

However if the chromium is in carbide form, it is attached to carbon already and when the oxygen comes in hungrily for the ferrite, the chromium can no longer protect the iron because the carbon will not let it move and so the oxygen will readily start consuming the iron and making rust.

Now what is the good side to the carbides? Ferrite is really weak and easily machined, the carbides make it much stronger and give it much better wear resistance. Thus you have to pick one or the other, you can't optimally have maximum corrosion resistance or wear resistance and strength at the same time because the chromium can't be in two places at once.

In regards to steels, the basic point is you can't just say more Cr = more corrosion resistance, you need to have the Cr free in the ferrite so check the carbon content because if it is high the carbon will have locked up the Cr in carbides, this is why 440A is much more corrosion resistant than 440C even though both have the same Cr content.

This is further complicated as there are other elements such as vanadium which will actually knock chromium out of the way and take the carbon from it which will also allow for free chromium even with a lot of carbon because the chromium does not have the strength to push the vanadium out of the way and get any carbon of its own so it just hangs out in the ferrite waiting for oxygen.

-Cliff