Studying the Influence of Tempering Conditions on Tempered Martensite Embrittlement of Low Alloy Steel

Abstract

This work focused on studying the effects of quenching mediums and tempering conditions on the tempered martensite embrittlement of SA335P11 low alloy steel that is mainly used for high pressure steel pipes in thermal power plants. The specimens are quenched in AH metal working fluid that is generally used to quench metal samples and tempered 150 - 500 oC to assure that embrittlement occurred at the temperature range of 200- 350 oC. Heat treated samples are subjected to hardness test and fracture toughness test to determine the degree of tempered martensite embrittlement. Effects of tempering temperature and time, and quenching medium on tempered martensite embrittlement are discussed based on the fracture toughness and hardness of the heat treated samples. The results showed that under the tempering temperatures of 200oC to 350 oC, fracture toughness and hardness of samples are rapidly decreased. Furthermore, fracture toughness increases and hardness decreases with increasing the tempering time. Moreover, higher the cooling rate of quenching medium, fracture toughness of the specimen is decreased and hardness is increased.