50 HRC..... 465 custom vs 440c 10

[fapper]

There are two kinds of heat hardenable steels,those that have carbon so carbides are created,like 440c and then the PH martensite steels like 17-4 or custom 465.

The carbide steels like 440c can have higher peak hardness than hardest PH steels like custom 465,but what if I heat threated and aged both steels to be 50 HRC?

They way I see it is this,at 50 HRC the 465 us significantly more corrosion resistant and tougher than 440c,the yield strenght is about the same,why would I then choose 440c or other similiar carbide steel at 50 HRC over custom 465?

Is the HRC rating missleading? Will the carbide steel at same HRC rating have improved scratch,abrasion or wear resistance?


Another comparison would be 10-2-3 Beta titanium hardened to 48 HRC vs some Stellite alloy with similiar HRC rating.The titanium is worst when it comes to galling,and Stellite is best,but for abrassion and scratch,would there be difference if they have same HRC becose Stellite got carbides and beta titanium doesnt?

 

[EdStainless]

I have a file folder on abrasive wear, some papers back to the coal slurry work in the 60's.
The only thing that is clear is that if you have two alloys that share a general composition and hardening mechanism, then the harder one will probably have better wear resistance.
But across a range of media and environments there is no way to look at a group of alloys and predict abrasive wear resistance.
In some cases carbides help, in others intermetallic precipitates are plenty good.
The only generalities are that Al and Ti alloy have poor wear resistance at any hardness, and that Co based alloys always overachieve.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[fapper]

why do CO alloys have usually good wear resistance? Is it becose its hexagonal close packed shape?

 

[priyam07]

To reply to fapper: "You say the carbides are like hard cobbles and the steel matrix is like the mortat.I wonder,why even bother with carbides/cobbles,why not just use super hard mortar/steel matrix?"

Because the carbides can go up to really high hardness such as 2200HV for WC used in a metal (Ni) matrix with 40 HRC that outperforms quenched and tempered steel with 52 HRC (for example).

 

[EdStainless]

priyam, because the carbides have such low toughness that any impact or flexing will cause fracture.
The binder allows for parts of useful size to be built. For small diameter wire you can make draw dies from diamond or single carbide pieces, but they have to held tightly in compression.

fapper, it has to do with slip planes and strain hardening, which go back to the HCP structure.
For example even Co alloys without carbides are very resistant to cavitation damage, even better than some very hard materials that will fail in fatigue or fracture.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[Maui]

Fapper,

You asked,

You say the carbides are like hard cobbles and the steel matrix is like the mortat.I wonder,why even bother with carbides/cobbles,why not just use super hard mortar/steel matrix?

Because the hardness of the steel matrix is generally limited to about 60 HRC for most of the higher carbon steel alloys. But the carbides themselves are much harder than this with values that can range from about 64 HRC for cememtite to 84 HRC for vanadium carbide. Carbides are very hard and wear resistant particles, but they are brittle. The steel matrix in which they are embedded is softer than the carbide particles, but is much more ductile. This is the reason why this combination is so effective in providing good wear resistance. The carbides are held in place by the steel matrix and they provide a hard and wear resistant surface to resist abrasion. The Rockwell C hardness that you would obtain by making a direct hardness measurement on a sample piece of one of these steel alloys represents an average hardness value of the carbides and the steel matrix. When you are referring to hardness readings in your previous posts it does not appear as though you understood this. Does this explanation make it clear?

Maui

 

[priyam07]

Thanks Maui, I think you made it clear what I intended in my reply.