of creating a new steel alloy, or repositioning an existing one, with the knife
making industry in mind requires precise consideration of the demands of blade
users and the ways in which alloy chemistry can help meet them. Metallurgists
will tell you that however hard they try, they can’t formulate a “perfect”
steel for any application, including knife making. Every alloy represents some
form of compromise among attributes. That’s because adding or boosting the
amount of one element to heighten one aspect of a blade steel’s performance can
have an adverse effect on another critical element of the metal’s ability to
withstand the stresses applied to a cutting edge in the real world.
considerations in mind, Carpenter created its CTS family of alloys for use in
cutting blade applications, including implements for use in surgery, food
processing and recycling equipment, ice skates, scissors, and hand tools, as
well as bladed implements for sporting, hunting, self-defense, and military applications.
This family of specialty alloys offers outstanding edge retention in steels
that machine to a fine edge and display consistent response to heat treatment.
Of course, virtually all of these steels originated for use in other
applications before they gained the CTS designation. For example, CTS XHP
started out as a formulation targeted toward the aerospace industry’s need for
alloys fall into three categories, including low alloy martensitic stainless
steels, bearing steels, and powder metals. Low alloy martensitic stainless
steels incorporate only about 0.6 percent carbon, along with between 12 percent
and 18 percent chromium. Their simple basic chemistry lends itself to
modifications through the additions of small amounts of other elements,
including molybdenum, vanadium, tungsten, and niobium, to enhance specific
performance characteristics such as edge retention or corrosion resistance.
Bearing steels bump up both the carbon content and the amounts of additional elements,
forming more-complex chemistry than low alloy martensitic stainless steels.
Finally, powder metal alloys use new-era steel making techniques to produce
high levels of wear resistance. CTS XHP fits into the powder metal alloy
Among the members
of the CTS alloy family, CTS XHP offers a high degree of corrosion resistance
as well as excellent edge retention. With an ability to resist humidity and
other elements of a domestic environment, as well as the elements present in a
very mildly challenging industrial environment, CTS XHP’s corrosion resistance
equals that of 440C, a high-carbon stainless steel with good wear resistance
and hardness. CTS XHP also demonstrates hardness that nearly matches what
metallurgists expect from the tool steel D2. Depending on its heat treatment
and other factors, CTS XHP can reach hardness levels of 60 to 64 HRC as
measured on the Rockwell C scale. The combination of corrosion resistance and
hardness means that CTS XHP compares either as a high-hardness version of 440C
or as a D2 replacement with greater corrosion resistance.
2009, Carpenter launched the CTS family as a product line of 14 alloys
specifically targeting various needs of the knife making industry. Some of the
CTS alloys, including CTS XHP, are fabricated through Carpenter’s proprietary
Micro-Melt powder metallurgy. This technological breakthrough overcomes a major
limitation of traditionally produced steel alloys.
One of the
biggest challenges facing blade steel producers lies in formulating the right
combination of elements in the right proportions to produce alloys that offer
the desired mix of hardness, toughness, corrosion resistance, edge retention,
and wear resistance necessary for use in knives that can hold up to the demands
of daily use. Beyond the alloy chemistry itself, however, the production
process through which the steel takes shape also plays a definitive role in
determining how the alloy performs.
traditional steel making, the elemental components of an alloy mix and melt
together in an electric arc furnace. When the mixture reaches the readiness
point, it pours into molds that produce individual ingots. As the metal cools,
however, the individual elements that make up the alloy separate from one
another, producing a result that offers limited consistency throughout each
ingot because pockets of specific elements can form as inclusions that disrupt
the uniformity of the metal. This process of separation, called segregation,
curtails the performance capabilities of the steel as well as its
batch-to-batch reliability. Segregation’s effects become more pronounced as
alloy formula complexity increases, making the problem an even greater concern
when it comes to the steels best suited to blade production, most of which
feature complex chemistries. Corrosion resistance and wear resistance
especially suffer when elemental segregation occurs during steel production.
Some forms of post production processing can overcome segregation at least
partially, but the effects linger at least to some extent regardless of the
steps taken to neutralize or offset them.
problem of segregation required an enormous amount of ingenuity. Crucible
Industries became the first to do so when it pioneered the process known as
Crucible Powder Metallurgy, or CPM. Other steel producers, including Carpenter
Technology, have formulated their own versions of this process. Carpenter’s
Micro-Melt alloys demonstrate the homogeneously refined microstructure typical
of powder metallurgy.
of powder metallurgy miniaturizes the production of ingots down to particle
size. Instead of large molded steel products, the outcome of the Micro-Melt
process is a fine powder. The elemental components of an alloy mix and melt
together at extremely high temperatures in a vacuum inside an electric arc
furnace. The vacuum melting process helps raise the uniformity of the alloy
mixture at the same time that it eliminates inclusions or irregularities. Once
molten and mixed, the alloy pours into an electroslag heated tundish, or
trough. In the tundish, a plasma torch heats the alloy to purify it. The molten
result streams through a nozzle in the form of a mist, where it encounters
high-pressure liquid nitrogen. The interaction of molten alloy and inert gas
produces atomized droplets of steel that quickly form into powdered particles
approximately 150 micrometers in size. Because the molten metal forms and cools
so rapidly into tiny pieces, the forces that introduce segregation have neither
the time nor the space to exert a negative influence on the resulting powder as
it forms. Instead of a large blob of steel cooling in a mold, the outcome of
powder metallurgy turns each tiny particle into a cleanly homogeneous miniature
processes can turn this metal powder into its intermediate or final forms. In
some cases, the steel producer is charged with crafting short-run or
experimental products through on-site prototyping processes. For customers such
as knife makers, who buy their metals in strip or billeted forms, the
particulate outcome of powder metallurgy becomes the input into a process known
as hot isostatic pressing. Once the steel maker cleans the particles and sorts
them by size, the alloy powder loads into an autoclaved chamber or enclave, in
which heat and pressure form the particulate steel into a billet or roll,
condensing it into a solid mass. This heat-and-pressure process, called
sintering, takes place just below the temperature at which the metal would melt.
The combination of heat and pressure alters the fundamental chemistry of the
steel, combining elements together through processes of interaction and
inclusion. For example, carbon interacts with vanadium and also becomes
incorporated into iron molecules. When heat treatment forces carbon to saturate
into iron, the resulting chemical structure takes on the name austenite, or
sintering process alters the alloy’s chemical processes, the steel is quenched
in air or liquid, rapidly lowering its temperature. At this point, the carbon
that had entered iron molecules becomes a permanent part of them. This further
alteration of austenitic steel produces martensitic steel, which exhibits a
lenticular, or lens shaped, grain structure. Further heat treatment at low
temperatures raises the toughness of martensitic steel at the expense of some
hardness and strength, but it also neutralizes the brittle nature of the
combination of powder metallurgy and hot isostatic pressing adds complexity to
the alloy manufacturing process and can raise the price of the steel, but the
homogeneous, unsegregated result can be worth the additional cost. Powdered
processes can produce steels with greater edge retention than those that emerge
from traditional processes. Powdered alloys also polish well. The down side of
their ability to accept and hold a fine, sharp edge appears when they must be
sharpened. Powdered steels typically require more effort and patience to
sharpen than lesser alloys do.
hardness of a powder metallurgical steel alloy results partially from its
chemical composition and partially from the way it’s heat treated in
post-production steps. For knife makers, too much hardness can yield too little
resistance to damage. As with many aspects of steel performance, the outcome of
heat treatment represents a compromise between two competing but desirable
Alloy Formula and
creates CTS XHP with a nominal alloy formulation that includes 1.6 percent
carbon, 16 percent chromium, 0.5 percent manganese, 0.8 percent molybdenum, 0.4
percent silicon, 0.4 percent vanadium, and 0.3 percent nickel.
Carbon increases hardness and wear
resistance at the expense of reduced toughness and potential brittleness. CTS
XHP guards against brittleness in the heat treatment stage that follows
sintering and quenching during the initial production of the alloy.
Chromium gives stainless steel both its
categorization and its corrosion resistance. An alloy requires a minimum of 12
percent chromium to qualify as a stainless steel. The designation “stainless”
represents an oversimplification or overstatement, of course, as any stainless
steel reacts at least to some extent to the enduring presence of substances
that cause oxidation. The term “corrosion resistance” more accurately states
the performance of stainless steel. Chromium also contributes to increased
hardness and greater tensile strength. Like too much carbon, too much chromium
can decrease toughness.
Manganese raises hardness, wear resistance,
and tensile strength, and helps reduce brittleness. Like too much carbon, too
much manganese can lead to brittleness. During steel production, manganese aids
in the process of removing oxygen and therefore staving off the prospect of
Molybdenum fosters edge retention and increases
Silicon increases hardness. Like manganese,
silicon helps deoxidize steel during molten phases of production, reducing the
likelihood of pitting in the finished product.
Vanadium helps yield a finer-grained steel
that demonstrates increased toughness after heat treatment. Vanadium also
increases edge retention and wear resistance.
Nickel boosts toughness and low-temperature
CTS XHP in Knife
When CTS XHP
entered the Carpenter Technology lineup as a blade steel in October 2009, knife
makers explored it as a substitute for familiar alloys such as 440C and D2. In
addition, they looked at it on its own merits as a new option on which they
might come to rely. Because custom knife makers create their products in
smaller quantities than production manufacturers do, they have less economic
ability and incentive to take risks on unfamiliar steels. As a result, new
steels tend to materialize in production knives before they show up in custom
products. In fact, some large companies go to great lengths to feature the “new
steel on the block” as a means of attracting and retaining customers who buy on
the basis of seeking out new materials.
offers features that the knife making industry immediately found attractive.
Its wear resistance, the promise of high performance reliability from batch to
batch of the alloy, its edge retention, its corrosion resistance: These
qualities offer obvious benefits in knife production. At the same time, its
high performance parameters come at a reasonable price.
courted leading knife designers, including Gayle Bradley, Tom Overeynder, and
Warren Osborne, inviting them to experiment with CTS XHP and other steels in
the CTS family. The fine grain structure, machinability, heat treatability,
corrosion resistance, and edge retention of the alloy attracted their
attention, as did CTS XHP’s ability to hold a mirror finish without extensive
also dedicated itself to building Spyderco’s interest in its CTS family.
Beginning with the inception of the CTS suite as a product line, Spyderco has
used as many as nine of the CTS family of blade steel alloys in its products.
Along with CTS XHP, these include CTS 204P, CTS B70P, CTS B75P, CTS BD1, CTS
BD30P, CTS 204P, CTS 20CP, and CTS 40CP.
planned its initial use of CTS XHP in the creation of a 5.3-ounce knife with a
3.13-inch skinner blade. The remainder of the knife’s materials also consisted
of Carpenter steels, including a jewelry-grade alloy called Bio-Blue for one of
the handle scales. The knife went into pre-production in 2012, slated for
distribution to every one of Carpenter’s employees, who numbered nearly 5,000
at the time.
In the 2016
Spyderco product lineup, eight knives feature blades manufactured from
Carpenter’s CTS XHP. These include two flippers, the C172CFTIP Domino and the
C182CFTIP Dice; the Chaparral Series of gentlemen’s folding knives, including
the C152CFP Chaparral Carbon Fiber/G-10 Laminate, the C152TIP Chaparral
Titanium, the C152STIBLP Chaparral Blue Stepped Titanium, and the C152STIP
Chaparral Stepped Titanium; the C160P Foundry gentlemen’s folding knife; the
C158TIP Techno specialty knife; the C185TIP Slysz Bowie specialty knife; and
the Ethnic Series C173GP Hungarian Folder.
Formulation Comparisons: Carpenter CTS XHP vs. 440C and D2
Carpenter CTS XHP
Carpenter Stainless Type 440C
Carpenter No. 610 Tool Steel
(equivalent to D2)