What Material Can Achieve 8.8 Grade After Heat Treatment for Elongated Screws?

Release time：2020-01-16 18:44 Browse：

1. Carbon Steel

• 35# Steel (AISI 1035)

• Suitable for screws ≤16mm diameter; achieves Grade 8.8 after quenching & tempering.

• 45# Steel (AISI 1045)

• Suitable for screws >16mm; meets Grade 8.8 after heat treatment.

• ML35 (Cold Heading Steel)

• Used for cold-formed bolts; reaches Grade 8.8 after tempering.

2. Low-Alloy Steel

• 40Cr (AISI 5140)

• Better hardenability than carbon steel; reaches Grade 8.8+.

• SCM435 (AISI 4135)

• Common for high-strength fasteners (Grade 8.8–10.9).

3. Other Suitable Materials

• 10B21 (Low-Carbon Boron Steel)

• Suitable for cold forming; Grade 8.8 after heat treatment.

• 45K

• Some manufacturers use it directly for Grade 8.8 screws without extra heat treatment.

Heat Treatment Process

• Quenching + Tempering

• Quenching medium: Water or oil (depending on material).

• Tempering temperature: 400–600°C for strength-toughness balance.

• Prevent deformation:

• Control quenching temperature and cooling rate for long screws.

Key Notes

1. Stainless steel (304/316) cannot reach Grade 8.8 (typically Grade 4.8–6.8).

2. Extra-long screws (>150mm): Use SCM435 or 35CrMo for better toughness.

3. Surface treatment: Electroplating (e.g., zinc) or black oxide for corrosion resistance.