High temperature fatigue and oxidation characteristics of forged steel piston materials

Abstract In order to study the fatigue characteristics and oxidation characteristics of 38MnVS6 and 42CrMo4, two kinds of forging steel piston materials, under high temperature and high load conditions, the temperature field, fatigue safety coefficient and distribution of surface oxygen layer were compared and analyzed by means of material characteristics detection, calculation of finite element numerical simulation and bench test and so on. Results showed that forging fiber lines of both two kinds of forged steel pistons could meet the process requirements. However, as for the basic characteristic values, the 42CrMo4 piston was better than the 38MnVS6 piston, increasing by 10% approximately on performance values. Besides, the maximum of temperature of the two pistons both appeared around the corner on the top of combustion chamber, and the temperature of the 38MnVS6 piston was even higher. After combining the basic characteristic, the average fatigue safety coefficient of the 42CrMo4 piston in the combustion chamber and the cooling gallery was more important than that of the 38MnVS6 piston, increasing by 3.6–7%. In addition, under the action of high temperature and pressure, obvious surface oxidation was produced on the top of the pistons. Meanwhile, a certain carbon deposit was also formed on the top of cooling galleries. In general, due to the difference of temperature distribution and thermal conductivity, the oxidation and carbon deposition phenomenon of the 42CrMo4 piston was significantly weaker than that of the 38MnVS6 piston the maximum optimization value of which even reached 90%.