CPM S30V vs S35VN

CPM S30V and S35VN are two highly regarded stainless steels in the knife industry, both developed by Crucible Industries. CPM S30V, introduced in the late 1990s, was designed to offer an optimal blend of toughness, wear resistance, and corrosion resistance.

It quickly became popular for its balance of performance attributes, making it suitable for both everyday carry (EDC) and specialized tasks. S35VN, developed as an evolution of S30V, was released in 2009 to address some of the shortcomings of S30V, particularly in terms of toughness and ease of sharpening.

Key Characteristics:

S30V: Known for its excellent edge retention, good toughness, and corrosion resistance, S30V has become a benchmark for premium stainless steels in knife making. Its development involved input from knife companies, knifemakers, and heat treaters to achieve a balanced steel that could be heat treated in various furnaces.
S35VN: Building on S30V, S35VN introduced enhancements in toughness while maintaining high edge retention and corrosion resistance. It features a slight reduction in carbon content and vanadium, with the addition of niobium to improve toughness and machinability. This steel was designed to be more user-friendly for sharpening and to offer better performance in real-world conditions where toughness is crucial.

By comparing these two steels, we can better understand which might be the best choice for specific applications, from EDC knives to specialized tools, based on their scientific properties and real-world performance.

Composition Analysis

Here is a detailed comparison of the chemical composition of S30V and S35VN:

Element	S30V	S35VN
Carbon (C)	1.45%	1.40%
Chromium (Cr)	14.00%	14.00%
Vanadium (V)	4.00%	3.00%
Molybdenum (Mo)	2.00%	2.00%
Niobium (Nb)	–	0.50%
Nitrogen (N)	0.20%	–

Explanation of Key Alloying Elements:

Carbon (C): Provides hardness and wear resistance. S30V has slightly higher carbon content, contributing to its superior edge retention.
Chromium (Cr): The primary element for corrosion resistance. Both steels use 14% chromium, ensuring excellent corrosion resistance.
Vanadium (V): Forms vanadium carbides, which are harder than chromium carbides, enhancing wear resistance. S30V’s higher vanadium content gives it an edge in wear resistance over S35VN.
Molybdenum (Mo): Enhances toughness and corrosion resistance. Its presence in both steels aids in maintaining these properties without compromising hardness.
Niobium (Nb): Added to S35VN to improve toughness by refining the grain structure and reducing the amount of chromium carbides. This results in better toughness without sacrificing edge retention significantly.
Nitrogen (N): Only present in S30V, it improves the steel’s hardenability and corrosion resistance.

The slight reduction in carbon and vanadium in S35VN, combined with the addition of niobium, makes it more durable in terms of resistance to chipping and breaking, while maintaining a high level of performance in edge retention and corrosion resistance. This slight shift in composition aims to provide a steel that is easier to sharpen and work with while still offering high performance.

Performance Metrics

Edge Retention

Edge retention is a critical performance metric for knife steel, often measured using the CATRA (Cutlery and Allied Trades Research Association) test, which involves cutting a standard material and measuring the number of cuts before the edge dulls.

S30V: Known for its exceptional edge retention, S30V typically scores high in CATRA tests. On average, S30V achieves around 450-550 cuts in CATRA tests .
S35VN: While also very good, S35VN slightly lags behind S30V in edge retention due to its composition changes aimed at improving toughness. It generally scores between 400-500 cuts in CATRA tests .

Toughness

Toughness refers to a steel’s ability to resist chipping, breaking, or deforming under impact or stress. The Charpy V-notch impact test is commonly used to measure toughness.

S30V: S30V exhibits good toughness, with typical Charpy impact values around 15-20 ft-lbs . While this is not the toughest steel, it provides a reasonable balance with its other properties.
S35VN: With the addition of niobium, S35VN has improved toughness over S30V, often achieving values around 22-25 ft-lbs . This is a significant enhancement, making it more suitable for applications where toughness is critical.

Corrosion Resistance

Corrosion resistance is important for knives that are exposed to moisture or harsh environments. Here’s how S30V and S35VN compare:

S30V: With its high chromium content and the addition of nitrogen, S30V has excellent corrosion resistance, often rated as very good to excellent in various tests .
S35VN: S35VN maintains similar corrosion resistance to S30V, thanks to the same chromium content, although the lack of nitrogen might slightly reduce its resistance. It is still considered very good in corrosion resistance tests .

Hardness Range

Hardness is measured in Rockwell C (HRC) scale, which indicates the steel’s ability to resist deformation.

S30V: S30V can be heat treated to achieve a hardness range of 58-61 HRC. This range allows for a fine balance between hardness, toughness, and edge retention .
S35VN: S35VN can reach a similar hardness range, typically 58-61 HRC, but its composition changes allow for a slight increase in toughness at the same hardness levels .

Through these performance metrics, we can infer that while S30V has a slight edge in edge retention, S35VN compensates with better toughness, making it a more versatile choice for applications where durability under stress is paramount. Both steels offer excellent corrosion resistance, suitable for most environments where knives are commonly used.

Heat Treatment Considerations

Heat treatment is a critical process in knife making that significantly influences the final properties of the steel. Here, we analyze the heat treatment requirements for S30V and S35VN:

Optimal Heat Treatment Temperatures

S30V:
- Austenitizing: Typically done at 1975°F to 2050°F (1079°C to 1121°C). This temperature range ensures the dissolution of carbides, which is vital for achieving high hardness and edge retention .
- Tempering: After quenching, S30V is tempered at 300°F to 400°F (149°C to 204°C) to reach the desired hardness while maintaining toughness. Multiple temper cycles are often used to stabilize the steel .
S35VN:
- Austenitizing: A slightly lower range of 1950°F to 2025°F (1066°C to 1107°C) is recommended, allowing for better control over grain size and toughness due to the presence of niobium .
- Tempering: Tempering temperatures range from 300°F to 425°F (149°C to 218°C). The addition of niobium allows for a wider optimal tempering range, providing flexibility in achieving the desired balance between hardness and toughness .

Tempering Requirements

S30V: Multiple temper cycles are recommended, usually at least two, to achieve stability. A double temper at 400°F (204°C) for two hours each is common .
S35VN: Similar to S30V, multiple temper cycles are employed, but due to its improved toughness, it can handle slightly higher tempering temperatures without significant loss in edge retention. A double temper at 400°F (204°C) or even 425°F (218°C) can be used .

Common Heat Treatment Challenges

S30V:
- Warpage: Due to its high hardness, S30V can be prone to warping if not properly supported during quenching.
- Grain Growth: Over-austenitizing can lead to grain growth, which might reduce toughness if not managed properly .
S35VN:
- Consistency: The presence of niobium makes S35VN more consistent in its heat treatment response, reducing the risk of grain growth and improving overall toughness.
- Sharpening: While S35VN is designed to be easier to sharpen, achieving the optimal temper can still be challenging to balance toughness and edge retention.

Cryogenic Treatment

Both steels can benefit from cryogenic treatment:

S30V: Cryogenic treatment after austenitizing can enhance wear resistance and edge retention by converting retained austenite into martensite. However, it might slightly reduce toughness .
S35VN: Cryogenic treatment is also beneficial, but the steel’s niobium content helps in reducing retained austenite, potentially requiring less cryogenic treatment to achieve the same benefits .

The heat treatment process for both S30V and S35VN requires careful control to achieve the desired balance of properties. While S30V might need more precise temperature control during austenitizing to avoid grain growth, S35VN offers a bit more leeway due to its composition changes. Understanding these processes helps in selecting the right steel for specific applications, especially when considering the balance between edge retention, toughness, and ease of sharpening.

Real-World Performance

Edge Stability

Edge stability refers to how well a blade maintains its sharpness without deforming under stress, particularly relevant for tasks involving significant lateral forces:

CPM S30V: It provides excellent edge stability with its balanced combination of hardness and toughness. However, if subjected to excessive lateral stress or impact, it might experience slight microchipping. This steel is highly regarded for maintaining its edge geometry in various cutting conditions, making it suitable for tasks requiring consistent edge performance like slicing meat or skinning animals[2][3].
CPM S35VN: The addition of niobium in S35VN enhances edge stability by improving toughness, making it less prone to chipping under stress. This steel offers improved resistance to edge deformation, providing a more stable cutting edge over time, especially in scenarios where toughness is critical, like wood carving or batoning[3][7].

Sharpening Behavior

Sharpening behavior is influenced by the steel’s composition and hardness:

CPM S30V: While S30V is known for its edge retention, its high hardness can make sharpening a bit more challenging. It requires diamond stones or advanced sharpening systems to achieve a sharp edge. However, once honed, it maintains its sharpness for an extended period[6][5].
CPM S35VN: S35VN is slightly easier to sharpen than S30V due to its slightly lower vanadium content and improved toughness. This makes it more accessible for users without specialized sharpening equipment, although it still requires some effort to achieve a razor-sharp edge[3][7].

Wear Patterns

Wear patterns develop over time on blades, influenced by their use:

CPM S30V: This steel exhibits slow wear due to its high wear resistance. However, under extreme conditions, it might show micro-chipping, especially if sharpened at very low angles. Over time, S30V knives might need more frequent sharpening to remove these small chips[2][6].
CPM S35VN: With its balanced composition, S35VN tends to wear more evenly without chipping as frequently as S30V. This steel’s toughness helps it resist wear and maintain its edge longer in practical use, making it more forgiving for everyday tasks[3][7].

Practical Applications

Practical applications highlight where each steel excels:

CPM S30V:
EDC Knives: Its superior edge retention makes S30V an excellent choice for EDC knives, where maintaining sharpness over long periods is crucial. It’s widely used in folding knives due to its durability and resistance to wear[1][3].
Tactical Knives: S30V’s balanced properties make it popular for tactical applications, where a reliable edge is essential[1].
CPM S35VN:
Bushcraft and Outdoor Knives: The enhanced toughness of S35VN makes it ideal for bushcraft tasks that involve chopping, batoning, or striking hard surfaces[3][7].
Custom Knives: Its improved machinability and edge stability make it a favorite among custom knife makers who prioritize durability and performance in their designs[1][7].

Both S30V and S35VN are suitable for outdoor activities due to their corrosion resistance and edge retention. However, if you prioritize toughness and ease of sharpening, S35VN might be the better choice, while S30V excels in scenarios where edge retention is paramount.

Direct Comparison Table

Property	S30V	S35VN
Edge Retention	CATRA score ~140	CATRA score ~150
Toughness	Rating: 5/10	Rating: 6/10
Corrosion Resistance	Rating: 7/10	Rating: 7/10
Maximum Hardness	HRC ~61	HRC ~61
Ease of Sharpening	Rating: 5/10	Rating: 6/10
Cost Factor	Lower	Slightly Higher

In conclusion, both steels offer exceptional performance, but their differences in toughness, edge retention, and sharpening behavior make them suited for different applications. Your choice would depend on whether you prioritize edge retention (S30V) or toughness and ease of maintenance (S35VN) in your knife use.

Citations:
[1] https://www.hudsontoolsteel.com/technical-data/steelCPMS30V
[2] https://knifesteelnerds.com/2021/10/19/knife-steels-rated-by-a-metallurgist-toughness-edge-retention-and-corrosion-resistance/
[3] https://www.tuofa-cncmachining.com/tuofa-blog/s35vn-steel.html
[4] https://knifesteelcomparison.com/20cv-vs-s30v/
[5] https://damascussteelbillets.com/s35vn-vs-s30v/
[6] http://www.dougritter.com/pop_up_cpms30v.htm
[7] https://www.crucible.com/pdfs/BladeShowBookletFinal05092016.pdf
[8] https://nobliecustomknives.com/cpm-s30v-steel/
[9] https://knifesteelnerds.com/2020/04/13/s30v-steel-history-and-properties/