They are also used for their wear resistance in, cutlery, medical tools (scalpels, razors and internal clamps),[12] ball bearings, razor blades, injection molds for polymers, and brake disks for bicycles and motorbikes.

I have the single and double cut versions of this brand and they have worked pretty good for me.  Double cut for steel, single cut for aluminum.

Martensitic stainless steels, depending upon their carbon content and are often used for their corrosion resistance and high strength in pumps, valves, and boat shafts.[4]

Martensite definitionengineering

How ismartensiteformed

In looking at McMaster seems like a set of 8 is $133.  So maybe that set of 4 at the Hammer Store for $70 wasn't as expensive as I thought.  Although I'd imagine the quality at McMaster is much higher than the Hammer Store...

I buy from mscdirect, Grainger, or summit. Probably more expensive but at the same time the first two cater to the business customers.

Martensitic stainless steel can be nondestructively tested using the magnetic particle inspection method, unlike austenitic stainless steel.

Martensite definitionchemistry

The characteristic body-centered tetragonal martensite microstructure was first observed by German microscopist Adolf Martens around 1890. In 1912, Elwood Haynes applied for a U.S. patent on a martensitic stainless steel alloy. This patent was not granted until 1919.[8]

Martensitestructure

So I need a set of carbide bits and they're surprisingly hard to find in stock.  None of the Lowes/Home Depot/Ace carry them.  The Hammer Store had one set of 4 for $70, which seems uncharacteristically expensive for the Hammer Store.

Martensiteformula

Additions of B, Co, Nb, Ti improve the high temperature properties, particularly creep resistance. This is used for heat exchangers in steam turbines.

When formability, softness, etc. are required in fabrication, steel having 0.12% maximum carbon is often used in soft condition. With increasing carbon, it is possible by hardening and tempering to obtain tensile strength in the range of 600 to 900 MPa (87 to 131 ksi), combined with reasonable toughness and ductility. In this condition, these steels find many useful general applications where mild corrosion resistance is required. Also, with the higher carbon range in the hardened and lightly tempered condition, tensile strength of about 1,600 MPa (230 ksi) may be developed with lowered ductility.

They can make tool steel that's absolute garbage but any carbide tooling has been fine. I guess there's only one formula and it's hard to make it poorly.

If you just need to do a small amount of grinding you could risk a cheap Amazon set but i would imagine they wouldn't last long.

Martensitecomposition

Martensite definitionsteel

I've been reasonably impressed with that set for the price. Enough so that I bought 2 of them (1 for the home shop, 1 for the warehouse).

Grainger can't find their ass with both hands, at least the ones I've dealt with can't. I call for something, give them the number from their catalog and I get "not a good number". Really? it's from your website. I've also given them the page number from the current paper catalog and they can't find it.

Martensitic stainless steel is a type of stainless steel alloy that has a martensite crystal structure. It can be hardened and tempered through aging and heat treatment.[1][2][3][4] The other main types of stainless steel are austenitic, ferritic, duplex, and precipitation hardened.[5]

Martensitemicrostructure

In 1912, Harry Brearley of the Brown-Firth research laboratory in Sheffield, England, while seeking a corrosion-resistant alloy for gun barrels, discovered and subsequently industrialized a martensitic stainless steel alloy. The discovery was announced two years later in a January 1915 newspaper article in The New York Times.[6] Brearly applied for a U.S. patent during 1915. This was later marketed under the "Staybrite" brand by Firth Vickers in England and was used for the new entrance canopy for the Savoy Hotel in 1929 in London.[7]

They may contain some Ni (Type 431) which allows a higher Cr and/or Mo content, thereby improving corrosion resistance and as the carbon content is also lower, the toughness is improved. Grade EN 1.4313 (CA6NM) with a low C, 13%Cr and 4%Ni offers good mechanical properties, good castability, and good weldability. It is used for nearly all the hydroelectric turbines in the world, including those of the huge "Three Gorges" dam in China.

Martensitic stainless steels can be high- or low-carbon steels built around the composition of iron, 12% up to 17% chromium, carbon from 0.10% (Type 410) up to 1.2% (Type 440C):[9]

Martensitic stainless alloys are hardenable by heat treatment, specifically by quenching and stress relieving, or by quenching and tempering (referred to as QT).[10][11] The alloy composition, and the high cooling rate of quenching enable the formation of martensite. Untempered martensite is low in toughness and therefore brittle.Tempered martensite gives steel good hardness and high toughness as can be seen below, and is largely used for medical surgical instruments, such as scalpels, razors, and internal clamps.[12]

I bought a set from HF about 30 years ago and have used them extensively (still do) and they've held up great......but I seem to remember them costing about $10 - no idea where they get $70 for them.