4140H

Alloy Steel

4140H

(AISI/SAE H). Nominal values—confirm mill certificate.

Chemical Composition (%)

C0.37
MN0.65
SI0.15
CR0.75
MO0.15
P0.035
S0.04

Mechanical Properties

Tensile:≥655 MPa;Yield:≥415 MPa;Elong:≥25%

Equivalent Grades

SAE H 4140H

Available Forms

Bar,Plate

Uses

Low-alloy engineering steel with enhanced hardenability and strength from alloying elements. Chromium (≈0.975%) improves hardenability, wear and corrosion resistance. Molybdenum (≈0.2%) raises high-temperature strength and prevents temper embrittlement. 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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