S7
Alloy SteelS7
(ASTM A681). Nominal values—confirm mill certificate.
Chemical Composition (%)
| C | 0.45 |
|---|---|
| CR | 3 |
| MO | 1.3 |
| MN | 0.2 |
| SI | 0.2 |
| P | 0.03 |
| S | 0.03 |
Mechanical Properties
Hardness(annealed):≤229 HB;Hardness(hardened):54-60 HRC
Chinese Standard
ASTM A681 S7
Available Forms
Bar,Plate
Uses
Spring steel with high elastic limit and fatigue strength for coils, leaf springs, clips and suspension parts. Silicon (≈0.35%) 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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