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CPM REX121 is a highly specialized abrasive-wear choice, while MagnaCut is much more balanced for toughness and corrosion resistance. These steels are far apart in purpose. Choosing between them means deciding whether extreme wear resistance is worth the ownership compromises.
Performance Ratings
For the science, we turn to Dr. Larrin Thomas of Knife Steel Nerds, who has kindly allowed us to share his ratings here.
The toughness score of 7 is for original Crucible MagnaCut. In written feedback to KnifeInformer, Dr. Thomas provided a toughness rating of 8.5 for Erasteel MagnaCut; his January 2026 testing explains the differences between the two versions. This table uses the original version.
| Property | CPM MagnaCut | CPM REX 121 |
|---|---|---|
| Abrasive edge retention | ||
| Toughness | ||
| Corrosion resistance |
Heat treatment, hardness and geometry affect actual knives.
REX121 Prioritizes Abrasive Wear
CPM REX121 has a much higher abrasive edge-retention rating than MagnaCut. That is relevant for demanding abrasive slicing, not a measure of initial sharpness or overall knife quality.
The scale is not a cutting-time multiplier. A large numerical lead does not promise a proportional increase in useful cuts on every material.
Our MAGNACUT steel profile explains its properties and care in more detail.
MagnaCut Has More Damage Tolerance
The toughness comparison strongly favors original MagnaCut. We would prefer it for a wider range of cutting tasks where resistance to chipping matters.
A REX121 knife should be selected for its intended slicing role, not treated as tougher because its wear score is exceptional.
Our REX121 steel profile explains its properties and care in more detail.
REX121 Needs More Attention
MagnaCut has much greater corrosion resistance. CPM REX121 is not stainless, so moisture care and storage are part of the choice.
Consider sharpening equipment and the maker’s guidance before buying a specialist wear steel. The material label alone does not make maintenance effortless.
A Specialist or an Everyday Balance?
We would choose MagnaCut for most mixed everyday use. REX121 makes more sense when abrasive wear is clearly the limiting issue and you accept the lower toughness and extra care.
For occasional packages or food preparation, we would not chase REX121’s wear score at the expense of the more useful balance MagnaCut offers.
Composition
Our steel composition guide explains the elements and the differences between reported values, ranges and limits.
CPM MagnaCut: Niagara typical composition, mass %; selected elements, not a batch analysis. Niagara Specialty Metals: CPM MagnaCut.
CPM REX 121: Zapp CPM REX 121 reported composition, mass %; the datasheet describes non-binding average values, not a finished-blade assay. Zapp: CPM REX 121 datasheet.
| Element | CPM MagnaCut | CPM REX 121 |
|---|---|---|
| Carbon (C) | 1.15% | 3.4% |
| Chromium (Cr) | 10.7% | 4% |
| Vanadium (V) | 4% | 9.5% |
| Molybdenum (Mo) | 2% | 5% |
| Niobium (Nb) | 2% | Not listed |
| Nitrogen (N) | 0.2% | Not listed |
| Tungsten (W) | Not listed | 10% |
| Cobalt (Co) | Not listed | 9% |
| Sulfur (S) | Not listed | 0.1% |
Compare Two Knife Steels
Sources and Update Notes
- Dr. Larrin Thomas: knife steel ratings · Property ratings; the scores describe steels rather than individual finished knives.
- Niagara Specialty Metals: CPM MagnaCut
- Zapp: CPM REX 121 datasheet
