Alloy Steel > Rod & Bar > 8620

8620 is a hardenable chromium, molybdenum, nickel low alloy steel often used for carburizing to develop a case-hardened part. This case-hardening will result in good wear characteristics.

Applications: In the carburized condition this alloy is used for gears, ring gears, shafts and crankshafts.

Machinability: Machining is done prior to carburizing to within as close a tolerance as possible. Finish machining, after heat treatment and/or carburizing, should be at a minimum so as not to impair the hardened case of the part. Machining may be done by conventional means prior to heat treatment – after carburizing machining is usually limited to grinding.

Forming: Forming characteristics of 8620 alloy are good in the annealed condition.

Welding: The alloy may be welded by conventional methods, usually gas or arc welding. Preheating at 400 F is beneficial and subsequent heating after welding is recommended – consult the approved weld procedure for the method used.

Heat Treatment: This alloy may be hardened by heating to 1500 F followed by a water quench. Carburize at 1650 to 1700 F in an appropriate carburizing medium and oil quench to harden. Improved carburized case and core properties can be obtained by furnace cooling from carburizing at 1650 – 1700 F and then reheating to 1575 F.

Forging: The alloy may be forged at 2200 F down to 1800 F prior to the hardening heat treatment or carburizing.

Hot Working: Hot working may be accomplished prior to hardening or carburizing. Consult the alloy supplier for information as to temperatures.

Cold Working: The alloy may be cold worked in the annealed condition by conventional methods. Cold working, as with machining, should be done to as close a tolerance as possible before heat treatment or carburizing.

Annealing: AISI 8620 may be given a full anneal at 1550 F and slow cooling at not more than 50 F per hour down to 850 F. From there it may be air cooled.

Aging: Not applicable to this alloy.

Tempering: Tempering of carburized parts is done at 250 to 300 F and this will result in the alloy having a core strength of approximately 135 ksi minimum with Rockwell C case hardness of 90. Tempering of heat treated and water quenched parts (not carburized) is done at 400 F to 1300 F with greater hardness the lower the tempering temperature.

Hardening: Hardening is done by oil quench from 1675 F. See “Heat Treatment”. Carburizing is accomplished at the same 1650 to 1700 F range in a carburizing “pack” or environment, followed by oil quench for thin sections or a furnace cool for heavier (over 3/4″) sections. Following carburizing of heavy sections a reheat at 1575 F will enhance both case and core properties of the alloy.

Other Comments: This alloy is typically used for carburized parts where a hardened case is desired for wear resistance.