4640

Alloy Steel

4640 / alloy steel

4640 supplied by Shanxi Youte Steel (jlhsteel.net).

Chemical Composition (%)

C	0.38
NI	1.65
MO	0.2
MN	0.6

Equivalent Grades

SAE J404

Available Forms

Bar, Plate, Tube, Forging, Wire

Uses

Low-alloy engineering steel with enhanced hardenability and strength from alloying elements. Molybdenum (≈0.25%) raises high-temperature strength and prevents temper embrittlement. Nickel (≈1.825%) increases toughness and impact strength at low temperature. Applied to gears, shafts, bolts, connecting rods, pressure parts and heavy forgings in automotive, energy and machinery sectors.

Heat Treatment

Austenitize at 820–870 °C (oil or water quench depending on section) and temper at 400–650 °C to the required strength/toughness balance.

Precautions

Preheat and control interpass temperature when welding; post-weld heat treatment or stress relief is recommended to avoid hard-zone cracking. Use low-hydrogen electrodes. Protect from decarburization during heating (controlled atmosphere or protective coating).

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