55Si7

Alloy Steel

55Si7

(EN 10089). Nominal values—confirm mill certificate.

Chemical Composition (%)

C0.52
SI6
P0.035
S0.035

Mechanical Properties

Tensile:≥980 MPa;Yield:≥785 MPa;Elong:≥9%;RA:≥45%

Chinese Standard

EN 10089 55Si7

Available Forms

Bar,Plate

Uses

Spring steel with high elastic limit and fatigue strength for coils, leaf springs, clips and suspension parts. Silicon (≈7%) raises elastic limit and tempering resistance. Supplied as strip, wire and bar; shot-peened after forming for longer service life.

Heat Treatment

Austenitize 830–880 °C (oil quench) and temper at 400–520 °C; stress-relieve formed springs at 230–320 °C after coiling.

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). Shot-peen after coiling to improve fatigue life; avoid sharp bends and surface defects.

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