D2 vs 440C Steel

D2 tool steel and 440C stainless steel are both high-carbon steels capable of being heat-treated to hardness levels suitable for most knives. 

440C steel is considered stainless steel due to its high chromium content, and D2 is classified as a non-stainless tool steel. 

This difference in chromium composition and carbide formation leads to a substantial advantage in corrosion resistance for 440C over D2.

Even though D2 contains nominally similar levels of chromium as 440C, about half of that chromium content gets tied up in carbides, unable to contribute to oxidation resistance.

As a result, knives made from 440C demonstrate far better stain and rust resistance compared to D2 blades.

Outside of corrosion performance, however, D2 and 440C have broadly comparable properties like attainable hardness, edge retention, and ease of sharpening.

D2 steel vs 440C Steel At A Glance 

Corrosion Resistance

440C is a stainless steel while D2 steel is a non-stainless steel, 440C steel exhibits far superior corrosion resistance to D2 steel. 

440C stainless steel has higher chromium content in its alloy composition ~16%-18% compared to D2 steel 11.5%.

While the Cr Content is high, half of the chromium in D2 is bound in the carbides, making it unavailable to help protect against rust and discoloration. 

In contrast, the chromium in 440C remains dissolved in the steel matrix resulting in a greater ability to resist oxidation. 

Being a stainless steel, 440C forms a protective chromium-oxide layer on its surface when exposed to moisture. D2 lacks that self-healing quality. 

The result is that 440C has excellent stain and rust resistance suitable for knives, while D2’s corrosion resistance is comparatively quite limited due to its tool steel heritage. 

For knives that will see wet conditions or require a stain-free appearance over time, 440C knife steel superior corrosion properties give it a substantial advantage over D2 from a performance standpoint. 

D2 steel knives can be coated to improve their corrosion resistance and ease of maintenance.

Toughness

Toughness in knife steel is its ability to resist chipping, cracking, or breaking under high impact or abuse during use.

When it comes to toughness, 440C steel has a slight advantage over D2 steel in similar or lower hardness levels.

The lower toughness of D2 steel is likely due to its larger vanadium carbides which act as fracture initiation sites. 

Toughness Data from Crucible and Bohler indicated that 440C was slightly less tough compared to D2 steel.

However, in my real-life testing, 440C steel toughness was slightly better.

The higher toughness of 440C makes it more resistant to chipping and cracking during use as a knife, especially in high-stress tasks like prying. 

While D2 lacks the toughness of 440C, it is comparable to other popular knife steels like 10V and S90V, so D2 is “tough enough” for most cutting applications.

But when fracture resistance is critical, 440C steel’s vastly better toughness compared to D2 makes it the preferred choice for knives that need to withstand high impacts without breaking.

A powder metallurgy version of CPM-D2 was released around 2007 to reduce the carbide size in D2, which improved the toughness, and corrosion resistance.

Hardness

D2 steel can achieve marginally higher Rockwell hardness than 440C stainless steel.

According to testing conducted by Crucible, D2 steel can achieve a hardness up to HRC 62 when heat treated properly.

In comparison, 440C steel typically reaches a hardness of HRC 58-60.

The slightly higher attainable hardness of D2 gives it an edge in wear resistance over 440C.

This makes D2 steel generally preferable for knife applications where hardness and edge retention are critical, such as in slicing knives. 

However, the difference in hardness and wear resistance between the two steels is relatively minor.

Additionally, while D2 can be heat-treated to higher hardness, it becomes more brittle and prone to chipping at those peak hardness levels.

So in practice, many knife makers heat treat D2 to around HRC 60 to optimize the balance of hardness, edge stability, and toughness. 

Edge Retention

D2 steel has a slight advantage over 440C steel in edge retention and wear resistance.

According to CATRA testing by Bohler Uddeholm, D2 was found to have better abrasion resistance compared to 440C.

D2 steel was able to achieve 24% better edge retention compared to 440C steel in the CATRA tests.

The enhanced wear resistance of D2 over 440C can be attributed to its higher achievable hardness after heat treatment, allowing it to better resist loss of material during cutting.

This gives knives made from D2 blade steel a slight durability boost over those made from 440C in terms of maintaining sharpness over prolonged use. 

However, with proper heat treatment, the difference in wear resistance between D2 and 440C is relatively small in practical terms.

Slightly better edge holding may be noticed in D2 knives used for demanding cuts on hard materials.

But for general use, the two steels have similar edge retention.

So while D2 does surpass 440C, the gap in wear resistance between the two knife steels is not substantial enough to be a significant differentiating factor.

Their closeness in hardness and abrasion resistance makes both D2 and 440C suitable for knives meant to hold an edge through moderate wear.

Ease of Sharpening

440C steel likely has a slight advantage over D2 steel when it comes to ease of sharpening and grinding.

As discussed previously, the two steels have broadly similar hardness in common heat treatments, with D2 being perhaps one or two points higher on the Rockwell scale.

However, testing indicates that D2 has moderately better wear resistance compared to 440C stainless steel. 

That suggests the carbides in D2 may be slightly more wear-resistant as well.

Since carbides are the most difficult part of steel to abrade during sharpening, D2 steel therefore takes a bit more effort to grind and hone an edge compared to 440C.

However, for all practical purposes any difference in sharpenability between the two steels is likely to be modest given their overall similarity in hardness.

Many knife makers also elect to heat treat both steels in the optimal balance of edge stability and ease of sharpening. 

Final Thoughts D2 vs 440C Steel

What stands out to me is how 440C stainless surpasses D2 tool steel in corrosion resistance, while D2 bests 440C in terms of maximum hardness and wear resistance.

The high chromium content of 440C combined with its refined carbide formation enables impressive protection against discoloration and oxidation.

D2 steel vanadium-alloyed tool steel composition allows it to reach marginally higher hardness and better edge retention. 

I tend to prefer D2 hardness and edge qualities for most utility cutlery, as I’m willing to trade some staining potential for better cutting ability.

However, for tasks like processing food in wet environments, or applications demanding long-term presentable appearance, I recommend 440C due to its superior corrosion resistance.