Knife Steel

Crucible’s High Speed Rex 45 Steel: How Good Is It?

Crucible’s High Speed Rex 45 Steel How Good Is It

CPM Rex 45 is a high-speed powder metallurgy steel produced by Crucible, part of the long Rex steel series that includes Rex 76, 121, and others. As expected from powder metallurgy steels, Rex 45 boasts impressive hardness and toughness, excelling in multiple aspects as a knife steel. With additional vanadium, tungsten, and cobalt elements not commonly found in regular ingot steel.

CPM Rex 45 steel is often the preferred choice for advanced cutting tools and industrial applications where maintaining sharpness is paramount. With a hardness surpassing many other steels, Rex 45 is capable of sustaining a keen edge through extensive use, yet it maintains a level of toughness that resists brittleness under stress. This is due in part to its fine microstructure, achieved through the powder metallurgy process, which uniformly distributes the alloying elements throughout the steel.

Although CPM Rex 45 can be challenging to sharpen and manufacturer due to its hardness, the benefits of its edge retention are well-regarded. This high-speed tool steel may not be as widely known as other types, but its high wear resistance makes it a strong candidate for tools that undergo intense and sustained use. Whether it’s in industrial settings or the rigorous demands of outdoor activities, tools made with Rex 45 steel are designed to last and perform at a high level.

Overview of Rex 45 steel

Rex 45 Steel is a type of high-speed tool steel renowned for its impressive cutting performance abilities. Manufactured using powder metallurgy by Crucible. CPM Rex 45 is engineered for specialized industrial applications where superior red hardness and the capacity to withstand high temperatures during operation are essential.

CPM Rex 45 remains a relatively niche steel for knives, with only a handful of custom knife makers using this steel. Spyderco has utilized Rex 45 for some of their models, but they have since been discontinued. The reasons behind this are two-fold. First, CPM Rex 45 is not the most cost-effective option among all the great premium steels available. While it boasts great all-around performance, it may not be considered the absolute best. Secondly, Rex 45 isn’t easy to work with. From a manufacturer’s perspective, forging Rex 45 steel knives requires a considerable amount of effort and is more time-consuming.

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Rex 45 chemical composition

Rex 45 chemical composition
  • Carbon: 1.30% 
  • Chromium: 4.05% 
  • Vanadium: 3.05% 
  • Tungsten: 6.25% 
  • Molybdenum: 5.00% 
  • Cobalt: 8.00% 
  • Sulfur: 0.22%

Due to being a powder metallurgy steel, Rex 45 contains a high amount of unique alloying elements. Namely vanadium, tungsten, and cobalt. These elements are rarely seen in high carbon or stainless steel. The addition of cobalt to the existing M3 high-speed steel is what sets CPM Rex 45 apart. Cobalt largely contributes to the steel’s hardness, making Rex 45 as hard as 67 HRC.

Tungsten and molybdenum are critical in maintaining the steel’s hardness when faced with high-heat conditions. Meanwhile, chromium serves the dual purpose of enhancing corrosion resistance and contributing to overall toughness by forming chromium carbides.

Lastly, Rex 45 blade owes its exceptional edge retention to vanadium, which forms vanadium carbides—some of the hardest carbides known, ensuring a lasting sharpness for cutting tools.

Rex 45 physical properties

We have already established that Rex 45 is a higher-end steel that offers great performance all around. Well, how good is it exactly? Let’s take a closer look individually.

Hardness and edge retention

Hardness and edge retention typically go hand in hand. Therefore, since Rex 45 steel is renowned for its high hardness, it naturally follows that it boasts exceptional edge retention as well. Most knifemakers heat treat it to around the 63-65 HRC mark. While we haven’t had the opportunity to test the steel for precise edge retention numbers in TCC, its edge retention should be commendable.

Toughness and durability

CPM Rex 45 exhibits a lower toughness score comparable to 15V or Maxamet. The high hardness of the steel inherently limits its potential for achieving a higher toughness score. However, it remains sufficiently tough for moderate use across various applications. Nevertheless, it doesn’t quite match the toughness of certain other tool steels that sacrifice hardness for increased toughness.

Rust resistance

Rex 45 offers decent rust resistance. It’s not the top contender in this regard. But it is nowhere near as afraid of rust as carbon steel like 1095.

Wear resistance

knife being heat treated and sparks flying

REX 45 steel exhibits excellent wear resistance, attributable to the carbon content and vanadium carbides in the steel. This characteristic means that the steel can withstand abrasive and adhesive wear, making it suitable for demanding cutting operations or machining tough materials.


Due to its hardness, sharpening REX 45 steel can be challenging, requiring more effort or harder abrasives. Nonetheless, a properly tempered and annealed blade can be resharpened to its original keen edge, ensuring prolonged high performance.

Rex 45 alternatives

Crucible isn’t the only company exploring high-speed powder metallurgy steel. Competitors offer their own models with similar chemical components and performance. Such as Vanadis 30 by Uddeholm, Erasteel ASP 2030, Bohler S590, Hitachi HAP40, and more. Comparing these steels is somewhat pointless due to their marginal differences. For sellers or designers researching their next knife steel, availability and price are often more important factors in decision-making.

Rex 45 vs. Rex 76

Rex 45 and Rex 76 are two closely related steels from the same Rex series by Crucible. Both are high-speed powder metallurgy steels known for their extreme hardness. Rex 76 was originally designed to achieve a remarkable 70 HRC. With slightly higher levels of carbon, vanadium, tungsten, and cobalt, Rex 76 surpasses Rex 45 in hardness and edge retention. However, this comes at a cost—its increased hardness compromises its toughness compared to Rex 45, making it more challenging to sharpen and work with.

Rex 45 vs. M4

CPM M4 is often compared to Rex 45 as they share nearly identical compositions. The main difference being M4’s lack of cobalt. Generally, M4 exhibits better wear resistance and toughness compared to Rex 45. However, the addition of cobalt in Rex 45 enhances its hardness. Regarding edge retention, KnifeSteelNerds suggests that if both are heat treated to high hardness, Rex 45 outperforms M4. But if treated to around 61 HRC, M4 shows superior edge retention.

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Investing high speed steel

Once more, it’s crucial to emphasize that Rex 45 isn’t the optimal choice for knife-making and selling to customers. Its extreme hardness and higher cost make it less appealing to most knifemakers unless specifically requested. Rex 45’s characteristics make it more suited for cutting tools in other metalworking applications rather than as a knife steel.

If you’re seeking similar steels for knife-making, we recommend exploring Crucible’s powder metallurgy stainless steel. S90V, S30V, S35VN, are all great choices. For those interested in learning more about steel selection for mass production or starting their own knife manufacturing venture, contact LeeKnives today! We’re your premier OEM knife factory, ready to fulfill orders worldwide.


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