ASTM A268 TP420( UNS S42000) Seamless Tube , Boiler And Heat Exchanger Application

ASTM A268 TP420( UNS S42000) Seamless Tube ， Boiler and Heat Exchanger Application

GENERAL PROPERTIES:
410， 420， 425 Modified， and 440A alloys are hardenable， straight-chromium stainless steels which
combine superior wear resistance of high carbon alloys with the excellent corrosion resistance of chromium stainless steels. Oil
quenching these alloys from temperatures between 1800°F to 1950°F (982-1066°C) produces the highest strength and/or wear
resistance as well as corrosion resistance. A range of as-quenched hardness is achieved in these alloys by varying the carbon
level from 0.15% maximum in Type 410 alloy to 0.60-0.75% in 440A alloy.

APPLICATIONS:
A major use for these grades of heat treatable stainless steels is in cutlery. Depending on the customer's end-use requirements，
cutlery alloys are usually selected 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 has the capability to transform
its microstructure through proper heat treatment (hardening) into one that will possess optimum strength， hardness， edge
retention， and wear resistance. The presence of sufficient chromium will impart the necessary corrosion resistance and form
chromium carbide particles that enhance the wear resistance of the given alloy. The higher the carbon content， the greater the
amount of chromium carbide particles， and the greater the strength and hardness for heat treatable straight-chromium stainless
steels. When blanking cutlery parts from annealed raw material stock， 410， 420 alloys and their higher carbon versions (410HC and
420HC) will usually exhibit hardness， yield strength， and tensile strength that are low enough for fine blanking purposes. However，
440A alloy is not readily amenable to fine blanking due to its higher strength and hardness in the annealed condition; and
therefore， could require more powerful presses to blank parts. In addition， the presence of large primary carbides in 440A alloy
would tend to reduce die life.When buffing blanked parts， the higher hardness of 440A alloy in the heat treated condition (hardened) would mean less residual buffing lines on the surfaces of parts but the large primary carbides could be dislodged during buffing which would produce scratches called “comet-tails”. Stainless steels lower in carbon content are essentially free of "comet-tails". Other applications for these grades include dental and surgical instruments， nozzles， valve parts， hardened steel balls and seats
for oil well pumps， separating screens and strainers， springs， shears， and wear surfaces.
410， 420， 425 Mod， and 440A alloys exhibit good corrosion resistance to atmospheric corrosion， potable water， and to mildly
corrosive chemical environments because of their ability to form a tightly adherent oxide film which protects their surfaces from
further attack.