Which tool steel is most corrosion resistant? D2?

kuraki said:
How would you heat treat D2 for ultimate wear resistance? High end of the austenitizing temperature and low temper temp? There's no secondary hardening bump in high temp tempers with D2? So what would yield the largest carbide size?

Asking due to making radius platens from D2.
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The largest carbides in D2 are controlled by "primary carbides" which are formed during casting. I'm not sure I know what you mean though when you ask what would yield the largest carbide size.

The "ultimate wear resistance" would be achieved at its max hardness. For a given hardness, using a lower austenitizing temperature can actually lead to better wear resistance because you have higher carbide volume. However, to achieve max hardness you will need a higher austenitizing temperature. You need to use cryo of course.
 
I was under the impression carbide size had some dependence on austenitizing temperature but I could just be confusing that with grain size.
 
kuraki said:
I was under the impression carbide size had some dependence on austenitizing temperature but I could just be confusing that with grain size.
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You can get grain growth if overaustenitizing. If toughness is not a requirement it may not matter though.
 
Carbide size is a matter of chemical composition, type and speed of solidification, ingot size, amount and type of reduction, and annealing procedure.

Carbide size is not affected by heat treatment, smaller carbides do dissolve
during austenitizing

Hoss
 
Larrin said:
...
Here is the chromium in solution I calculated, along with two stainless steels for comparison at the top:
Cn21YaH.png


As you can see, D2 does not have the highest chromium in solution! While A8 mod (chipper knife steel) is less commonly used, 3V is certainly pretty common, and it is predicted to have significantly more chromium in solution than D2. Another interesting note is that most of the chromium in 52100 is in solution rather than being tied by carbides, which is perhaps expected by its relatively low bulk chromium content. One potential caveat: if any of these steels are heat treated with an upper temper, a significant amount of chromium will be precipitated out as carbides reducing the corrosion resistance, which is why datasheets for stainless steels always say use the lower temper for best stain resistance. Therefore, 3V might only be superior to D2 if using a lower temper.
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You can add Böhler-Uddeholm Sleipner tool steel to Your list. It have 7,8%Cr and 2,5% Mo. I made one blade from this steel and it's very impressive.
 
Jesenius said:
You can add Böhler-Uddeholm Sleipner tool steel to Your list. It have 7,8%Cr and 2,5% Mo. I made one blade from this steel and it's very impressive.
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Sleipner is good stuff, but needs high temper, wish reduces free Cr. Only if you use cryo to eliminate RA and then low temper you will have lots of free Cr to make it stainless (almost), I think. I’m sure Larrin will correct me if I’m wrong.
 
Jesenius said:
I don't do subzero treatment (yet). You can hold RA very low by tempering it at about 530-540°C. As You can see in this material specification no subzero treatment is needed (see page 7, bottom right where it is compared).
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You’re right, it’s the industry standard, but that way you’ll have a secondary Hardening response, wish diminishes free Cr in steel. According to some metallurgists and others, cryo (or just subzero treatment-70C/-80C) is the way to go to reduce RA (except for PM HSS, RA in those steels needs high tempers, no matter what.) and then 400F tempering. Ideally, austenite, quench, cryo, temper, cryo, temper and a third temper won’t harm.
 
Well, surely they have right. Please, ask them what amount of Cr (say in %, i am simple man) will be reduced with compare to subzero treatment. Thank You!
 
Larrin said:
I got 6.1% Cr and 2.2% Mo with 1900°F austenitize. Using an upper temper would reduce Cr and Mo in solution.
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Well, You can harden it from 950°C (1742°F) and at about 1000°C (1832°F) still get over 64 Hrc. It is significant difference, isn't it? Anyway, at 1900F it's surely better than D2.
 
Jesenius said:
Well, You can harden it from 950°C (1742°F) and at about 1000°C (1832°F) still get over 64 Hrc. It is significant difference, isn't it? Anyway, at 1900F it's surely better than D2.
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The austenitizing temperature affects the chromium content in solution, so in all cases I chose a mid-point austenitize based on the published datasheets.
 
Do I right understood that You have spectral chromatograph or so? If not where can I read that? Thank You.
 
This thread is an explanation of what makes some alloys more corrosion resistant than others, it’s not about a specific alloy.

Hoss
 
Your questions are fine. Bulk chemistry measurements are most commonly made with Optical Emission Spectroscopy. Howeve, these types of instruments measure bulk composition which is different than the matrix composition that I said was calculated with thermodynamic software.
 
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