440C vs 12C27 Steel

440C stainless steel is produced by most steel companies like Niagara Specialty Metals while Sandvik 12C27 is produced by Alleima, formerly known as Sandvik Steel

The key difference in properties between these two stainless steel alloys lies in their microstructure and toughness. 

Sandvik 12C27 is a fine-carbide martensitic stainless steel renowned for its well-rounded characteristics, exceptional toughness, and high purity levels.

Its fine, uniformly distributed carbide structure, achieved through Alleima’s careful manufacturing process, enables easy sharpening, razor-sharp edges, and superior edge stability.

In contrast, 440C is a coarse-carbide chromium steel with larger primary carbides that contribute to its high hardness and wear resistance but may compromise toughness.

440C vs 12C27 Steel At A Glance

Hardness

Hardness is a crucial factor in knife steels as it generally affects all other factors like toughness, edge retention, corrosion, and ease of sharpening.

12C27 steel has a higher attainable hardness range compared to 440C steel at optimal heat treatment.

Alleima datasheets indicate that 12C27 can achieve a hardness range of 54-61 HRC (Rockwell Hardness C scale) when properly hardened and tempered.

On the other hand, 440C steel typically reaches a maximum hardness of around 59 HRC in the as-quenched condition, with tempering reducing the hardness further.

Higher hardness is desirable for knife blades as it enhances edge stability, wear resistance, and the ability to maintain a sharp cutting edge for a longer period.

The fine carbide structure of 12C27, with uniformly distributed and smaller carbides, allows for better edge stability and sharpenability compared to the coarse primary carbides present in 440C steel.

Toughness

12C27 steel exhibits significantly higher toughness than 440C stainless steel, improving knife performance. 

Toughness refers to the ability of a material to absorb energy and resist fracture or chipping, especially under impact loads. 

High toughness is essential for knives to prevent the blade from chipping or breaking during use, ensuring a longer-lasting cutting edge and safer operation.

The fine, uniformly distributed carbide structure of 12C27 steel contributes significantly to its excellent toughness.

The absence of large carbides, present in 440C steel, eliminates potential crack initiation sites and improves the overall toughness.

This fine-grained microstructure allows 12C27 to withstand impact and bending forces better than 440C, making it more suitable for applications where toughness is crucial, such as in hunting, camping, and tactical knives.

Moreover, the higher purity level of 12C27, with fewer non-metallic inclusions, further enhances its toughness by reducing the number of potential defects that can act as crack initiation points. 

While 440C steel may offer higher hardness, its coarse carbide structure and potential for impurities can compromise its toughness.

Thus, 440C is more prone to chipping and fracturing under impact loads, which is undesirable for knife applications that demand a balance of hardness and toughness.

Edge Retention and Wear resistance

440C steel offers superior edge retention and wear resistance compared to 12C27 steel, making it a more suitable choice for knife applications that demand long-lasting cutting performance.

440C steel has a higher overall volume fraction of carbides, including large primary carbides that contribute significantly to its wear resistance.

These coarse carbides can provide excellent abrasion resistance and edge retention for applications where maintaining a sharp edge is crucial, such as in industrial cutting tools or heavy-duty knives.

CATRA edge retention testing by Bohler Udderholm showed that at Rockwell hardness of 59HRC, Aisi 440C Stainless steel achieved a Total Cards Cut (TCC) of 536. 

The CATRA edge retention of 12C27 is expected to be less than that of 440C steel due to the lower carbides essential for such tests.

Edge Stability

Edge stability refers to the ability of a knife’s cutting edge to resist edge rolling, edge chipping, or deformation during use. 

Edge Stability is a crucial factor in determining a blade’s overall cutting performance and longevity. Sandvik 12C27 steel offers a distinct advantage over 440C steel in edge stability.

The fine, uniformly distributed carbide structure of 12C27 steel, combined with its exceptional toughness, contributes significantly to its superior edge stability.

The absence of large, primary carbides eliminates potential sites for carbide dislodgement or breakouts, which can lead to premature edge degradation.

Instead, the small, well-dispersed carbides in 12C27 provide a more stable cutting edge that can withstand impact loads and abrasive wear without compromising its keenness or integrity.

In contrast, the coarse, primary carbides present in 440C steel can act as weak points along the cutting edge, increasing the risk of chipping, rolling, or the formation of micro-serrations.

These imperfections not only diminish the sharpness of the edge but also contribute to accelerated dulling, requiring more frequent resharpening or replacement of the blade.

The higher toughness of 12C27 steel allows thinner edges in fine-slicing knives and better resistance to fracture in heavy-use knives due to its fine carbide structure.

12C27 knives can maintain their cutting performance and edge keenness for longer periods, whether used for delicate slicing tasks or heavy-duty cutting applications, thanks to their superior edge stability.

This attribute not only enhances the user experience but also contributes to the overall longevity and reliability of the knife, making 12C27 steel a preferred choice.

Corrosion Resistance

12C27 steel and 440C steel are stainless steels with good corrosion resistance due to their high chromium content, essential for forming a protective passive oxide layer on the surface. 

However, 440C stainless steel has a slight advantage in overall corrosion resistance compared to 12C27 stainless steel.

The higher chromium content of 440C steel, ranging from 16% to 18%, contributes to its enhanced corrosion resistance. 

While 12C27 steel has a lower chromium content of around 13.5%, it still falls within the range considered suitable for stainless steels and provides good corrosion resistance for most applications.

The coarse, primary carbides present in 440C steel are less likely to fully dissolve during the hardening process.

This means a larger portion of the chromium remains tied up in these carbides and is unavailable for forming the protective passive film.

In contrast, the fine, uniformly distributed carbides in 12C27 steel are more likely to dissolve during hardening, releasing the chromium into the matrix.

This allows for a higher proportion of chromium to contribute to the formation of the protective oxide layer, enhancing the overall corrosion resistance of 12C27 steel.

While 440C steel may have a slightly higher chromium content, the presence of large, undissolved carbides can potentially limit the effectiveness of this chromium in providing corrosion protection.

On the other hand, the fine carbide structure of 12C27 steel ensures that a greater portion of the available chromium is utilized for passivation.

This results in 12C27 steel having comparable, if not better, corrosion resistance than 440C steel in many applications.

Ease of Sharpening

12C27 steel offers a significant advantage over 440C steel in ease of sharpening and grinding, which is crucial for daily knife applications.

The presence of fine, well-dispersed carbides in 12C27 steel makes it easier to grind and maintain a sharp cutting edge compared to 440C steel, which contains larger, primary carbides.

The fine carbide structure of 12C27 steel, with a maximum carbide size of 2 microns, facilitates the grinding process and enables the achievement of razor-sharp edges.

On the other hand, the coarse, primary carbides present in 440C steel, which can be up to 10 times larger than those in 12C27, can cause micro-serrations or breakouts along the cutting edge during sharpening.

Ease of sharpening makes 12C27 steel more suitable for fine slicing knives and knives that require a delicate cutting edge, such as chef knives or carving knives.

Final Thoughts on 12C27 Steel vs 440C Steel

In conclusion, I have had the privilege of using both 12C27 and 440C steels over the years for various knife applications, including kitchen knives. 

My observation is that 440C when properly heat-treated, undoubtedly possesses impressive edge retention and slicing ability. 

However, I generally prefer 12C27, especially for knives that require frequent sharpening, such as kitchen knives.

The fine-carbide microstructure of 12C27 allows for ease of sharpening and the ability to achieve wickedly sharp edges through thinner grinds, which is particularly advantageous for precision cutting tasks. 

I have not noticed any significant variation in corrosion resistance between these two steels in daily use, likely due to 12C27 purity standards.

440C excels in specific applications that demand exceptional wear resistance and where a slightly more robust edge is preferred.

The well-rounded nature of 12C27, with its superior toughness, edge stability, and ease of sharpening, makes it my go-to choice for knives.