Influence Of Cleanliness On Mechanical Properties Of 38CrMoAlA Nitriding Steel

38CrMoAl steel can be made of some parts with special properties such as high impact toughness, resistance to hydrogen embrittlement, fatigue resistance and lower cold-brittle transition temperature. The properties were usually related to the cleanliness of the steel.Therefore, high cleanliness level 38CrMoAl steel was made by the method of vacuum induction and vacuum consumable refusion to investigate austenite grain growth and the related mechanical properties by means of metallographic observation,EDS,V-notch series of shocks,slow strain rate tension,and rotating bending fatigue. The results were compared with that of the common commercial steel smelt by electric furnace.The specimens with the highest cleanliness showed a more evidence of grain growth due to the weak pinning effect of AlN which would precipitateon during austenite growth. V-notch impact tests indentified that the ductile-brittle transition temperature was -60℃, and high-purity double-vacuum steel has better toughness. The high-purity double-vacuum steel had high resistance to hydrogen embrittlement. Whether the hardened and tempered or the nitrogen treatment samples, fatigue test demonstrated that the properties were improved by cleanliness of steel, the fatigue strength of the steel was 20Mpa larger than that of the common commercial steel. Most of the fatigue cracks were found to origin from the machine processing defects and showed little relationship with the cleanliness of steel. However, after surface-nitriding, the cracks were arouseded from the internal defects (internal inclusions, internal matrix) of steel and the fatigue strength of high-purity steel was 120Mpa higher than the low-purity steel..