Effect of residual aluminum on impact toughness of steel at low temperatures

Summary

• 1. The transitional embrittlement of low carbon steel depends on the contents of aluminum and the ferritic grain size.

• 2. The higher the rate of cooling of steel from the austenite range, the finer the grain and the lower the tough-to-brittle transition temperature. The heat treatment temperature (up to 960°C=1760°F) has less effect on the grain size and the transition temperature than the cooling rate.

• 3. Steel with traces of aluminum, after annealing, has an extremely low impact value at −40, −20 and 0°C (−40, −4 and 32°F),of about 1 kg.m/sq.cm.

• 4. As the aluminum content rises, the transition threshold falls. With about 0. 02% aluminum,the impact value is satisfactory at −20 and 0°C (−4 and 32°F) and independent of the cooling rate and heat treatment temperature (up to 960°C= 1760°F).

• 5. To reduce the transition temperature of heavy-section low-carbon steel parts, the aluminum content should be 0.02–0.03%.