12C27 VS D2 Steel

Sandvik 12C27, now produced by Alleima (formerly Sandvik), and D2 are two common steel types that have found widespread use in cutlery industry.

Sandvik 12C27 is a fine-carbide, martensitic stainless steel known for its excellent balance of hardness, toughness, and corrosion resistance, making it a popular choice for kitchen knives. 

D2 is a high-carbon, high-chromium tool steel characterized by its coarse-carbide structure, which contributes to its exceptional wear resistance and edge retention.

12C27 excels in toughness and corrosion resistance, owing to its lower carbon content and more uniform carbide distribution, while D2 stands out for its superior hardness and wear resistance, attributed to its higher carbon content and large, hard carbides. 

12C27 steel is more suitable for applications requiring a balance of properties and ease of maintenance, whereas D2 is preferred for its edge retention and wear resistance, albeit at the cost of reduced toughness and corrosion resistance compared to its stainless counterpart.

12C27 VS D2 Steel At A Glance

Hardness

12C27 can typically achieve a maximum hardness of around 61 HRC (Rockwell C scale) after heat treatment, while D2 can reach much higher hardness levels, potentially up to 63 HRC.

The higher attainable hardness of D2 is due to its higher carbon content (around 1.5% compared to 12C27’s 0.6%) and the presence of large carbide-forming elements like chromium, molybdenum, and vanadium.

These alloying elements in D2 form hard carbides during heat treatment, contributing to its increased hardness.

For knives, higher hardness generally translates to better edge retention and wear resistance, which means D2 knives may stay sharp longer under heavy use. 

Toughness

12C27 steel exhibits superior toughness compared to D2 steel.

12C27 is characterized as having very high toughness, rated 9 out of 10 on a toughness scale, while maintaining good hardness levels.

In contrast, D2 steel, despite its higher hardness, exhibits lower toughness. This difference in toughness significantly impacts knife performance.

Higher toughness in 12C27 translates to better resistance against chipping and breaking under stress, making it more suitable for tasks involving lateral stress or impact.

The superior toughness of 12C27 is attributed to its lower carbon content (0.6% compared to D2’s 1.5%) and simpler alloy composition, resulting in a finer, more uniform microstructure.

D2, on the other hand, contains large, unevenly distributed carbides that, while contributing to wear resistance, reduce overall toughness.

The production process also plays a role; 12C27’s toughness is enhanced through careful heat treatment and quenching, optimizing its martensitic structure without excessive carbide formation.

In contrast, D2’s toughness is limited by its large carbides, which can act as stress concentration points.

For knives, 12C27’s higher toughness makes it more forgiving and less prone to chipping during heavy use, especially in scenarios where the blade might encounter unexpected resistance or twisting forces.

Edge Retention

D2 steel demonstrates superior edge retention and wear resistance compared to 12C27 steel.

D2 blade steel exceptional performance in these areas is primarily due to its high carbon content (around 1.5%) which form hard carbides during heat treatment.

These carbides, particularly the chromium carbides, contribute significantly to D2’s wear resistance and edge retention.

In contrast, 12C27 has a lower carbon content (0.6%) and fewer alloying elements, resulting in fewer and smaller carbides.

D2’s edge retention was found to be superior to several other steels in CATRA testing, including 440C, while 12C27 is described as having “good” edge retention but not exceptional.

D2 knives will typically maintain their sharp edge for much longer periods of heavy use compared to 12C27 knives.

This makes D2 particularly suitable for applications requiring extended cutting performance without frequent resharpening.

D2 wear resistance is enhanced by its large, unevenly distributed carbides, which form during the heat treatment process.

While these large carbides can negatively impact toughness, they significantly boost wear resistance.

The conventional production of D2 results in these characteristic large carbides, although newer methods like powder metallurgy (CPM-D2) can produce a more refined carbide structure, improving toughness without significantly sacrificing wear resistance.

Corrosion Resistance

12C27 steel is a stainless steel while D2 steel is a non stainless steel. 12C27 steel has a significant advantage in corrosion resistance compared to D2 steel. 

D2 steel, despite having a high total chromium content of around 12%, suffers from reduced effective corrosion resistance due to its carbide structure.

The large, primary carbides in D2 steel, formed by its high carbon content (about 1.5%) and other alloying elements, trap a significant amount of chromium.

These large carbides do not dissolve easily during the hardening process, which means much of the chromium remains locked within them and unavailable for forming the protective passive film.

12C27’s superior corrosion resistance makes it a better choice for environments where moisture exposure is a concern, such as in kitchen knives or outdoor tools used in humid conditions.

D2, while offering excellent wear resistance and edge retention, would require more careful maintenance and protection against corrosion in similar environments.

Ease of Sharpening

12C27 steel is notably easier to sharpen and grind compared to D2 steel, which has a significant impact on knife production and maintenance.

12C27 is described as having excellent sharpenability and high grindability, making it a preferred choice for low-cost manufacturing of knives.

This ease of sharpening and grinding is largely due to its relatively simple composition and uniform microstructure with fewer and smaller carbides.

Final Thoughts on 12C27 VS D2 Steel

D2, with a good heat treat, truly impresses with its edge retention and slicing ability. Its high wear resistance allows it to maintain its edge for extended periods, which can be a significant advantage in heavy-use scenarios.

However, I generally find myself gravitating towards 12C27, especially for kitchen knives or tools that require frequent sharpening.

The ease of sharpening 12C27 is a major selling point for me – it’s much less time-consuming to maintain, which is crucial in a busy kitchen environment.

Moreover, 12C27’s ability to take thinner edge grinds allows for achieving wickedly sharp edges, even if they don’t last as long as D2 due to its lower wear resistance.

That said, the corrosion resistance of 12C27 is a significant factor in my preference, particularly where exposure to moisture and acidic foods is constant.

While D2 offers exceptional performance in many areas, it does require more keen maintenance in daily use to prevent corrosion.