Alloy Steel AISI 8642

General Characteristics Alloy Steel AISI  8642

Alloy steel 8642 is a low-alloy steel  containing nickel, chromium and molybdenum as alloying elements. The alloy has good hardenability, and good strength and toughness properties.

 C% Mn% P% S% Si% Ni% Cr% Mo%
0.40/0.45 0.75/1.00 0.040 max 0.040 max 0.20/0.35 0.40/0.70 0.40/0.60 0.15/0.25

Applications
This alloy finds its uses in forging applications where good strength, toughness and wear resistance are of prime importance. It might be used as a substitute for 8640 grade in the production of forged fasteners.

Forging
This alloy is forged at a start temperature of around 2200ºF (1205ºC) and could be forged down to approximately 1700ºF(925ºC.) The alloy is best slow cooled after forging, but may also be transferred to a furnace held at a temperature approximating the forging finishing temperature, soaked then air cooled.

Heat Treatment
Annealing: For optimum machinabilty of this alloy, a microstructure consisting of coarse lamellar pearlite to coarse spheroidite is considered to be optimum. Such a structure can be obtained by austenitizing at 1525ºF (830ºC), furnace cooling to 1310ºF (710ºC) then to 1200ºF (640º) at 20ºF/hr. An alternative is an iso-anneal at 1225ºF (650ºC)

Normalizing: 1600ºF (870ºC) and air cool.

Hardening: The alloy will be austenitized at around 1500 – 1575ºF (815 – 855ºC) and oil or water quenched depending upon section size and intricacy.
Tempering: to desired hardness, using temperatures based on past experience, following water or oil quench.
Machinability: This grade of alloy is readily machined following suitable heat treatment.
Weldability: This steel may be welded by normal fusion methods, but prior to hardening and tempering. Pre heat and post heat are recommended.