General Properties of Martensitic Stainless Steels

Allegheny Ludlum Types 410, 420, 425 Modified, and440A (see composition on Page 2) are hardenable,straight-chromium stainless steels which combine superior wear resistance of high carbon alloys with theexcellent corrosion resistance of chromium stainlesssteels. Oil quenching these alloys from temperaturesbetween 1800°F to 1950°F (982-1066°C) producesthe highest strength and/or wear resistance as well ascorrosion resistance. A range of as-quenched hardnessis achieved in these alloys by varying the carbon levelfrom 0.15% maximum in Type 410 to 0.60-0.75% inType 440A.

A major use for these grades of heat treatable stain-less steels is in cutlery. Depending on the customer’send-use requirements, cutlery alloys are usuallyselected with respect to heat treating response, mechanical properties and fabricating characteristics.When sufficient amounts of carbon are added to straight- chromium stainless steels, the alloy then hasthe capability to transform its microstructure through proper heat treatment (hardening) into one that willpossess optimum strength, hardness, edge retention,and wear resistance. The presence of sufficientchromium will impart the necessary corrosion resis-tance and form chromium carbide particles thatenhance the wear resistance of the given alloy. The higher the carbon content, the greater the amount of chromium carbide particles, and the greater thestrength and hardness for heat treatable straight-chromium stainless steels.

When blanking cutlery parts from annealed raw mate-rial stock, Types 410, 420, and their higher carbonversions (Types 410HC and 420HC) will usually exhibithardness, yield strength, and tensile strength that arelow enough for fine blanking purposes. However, Type440A is not readily amenable to fine blanking due to itshigher strength and hardness in the annealed condition;and therefore, could require more powerful presses toblank parts. In addition, the presence of large primarycarbides in Type 440A would tend to reduce die life.

When buffing blanked parts, the higher hardness of Type 440A in the heat treated condition (hardened)would mean less residual buffing lines on the surfacesof parts but the large primary carbides could be dis-lodged during buffing which would produce scratchescalled “comet-tails”. Stainless steels lower in carboncontent are essentially free of “comet-tails”. Other applications for these grades include dental andsurgical instruments, nozzles, valve parts, hardenedsteel balls and seats for oil well pumps, separatingscreens and strainers, springs, shears, and wearsurfaces.

These alloys are used where strength, hardness, and/or wear resistance must be combined with corrosionresistance.

These alloys are available as plate, sheet, strip and flat bars.