Numerical Simulation Of The Heat Treatment And The Prediction Of Hardening Layer Of Low Carbon Steel Used In Big Gear Shafts

Gear shaft is one of the important parts in machinery.The traditional heattreatment of big gear shraft, for example, surface carburizing and quenching, wascomplex and expensive. In this paper, two steels (40Cr steel and AISI4350steel,which were widely used in big gear shrafts), were taken into consideration. Basedon ABAQUS software, the heat treatment was simulated and the temperature fieldin the quenching process and the hardening layer were investigated. According tothe research, the reasonable heat treatment process of big gear shraft was putforward.To begin with, the property of AISI4350steel was investigated. The phasetransformation kinetics and continuous cooling transformation graph of AISI4350steel were studied. Stress-strain curves of the AISI4350steel was acquired throughthermal compressive experiments. In all the curves, the peak flow stress is almostequal to the flow stress under the steady state. Based on the true stress-true straincurves, the constitutive relationship of AISI4350steel was established. By using theconstitutive equation,0.2pct yield stress was obtained, which was match with theexperimental data. The maximum relative error is less than7%. Therefore, theconstitutive equation can be used for making the reasonable procedures forAISI4350steel. Using artificial neural network (ANN), the thermal deformationtrue stress-strain curve of AISI4350steel was forecast. By this way we can avoidcomplex mathematical formula processing and obtain the curve, which can fit thetrue stress-strain very well.In addition, based on ABAQUS, an axisymmetric finite element model ofsample for the quenching process was established. The distribution of temperaturefie ld, microstructure field and hardness of40Cr and AISI4350in the end quenchingprocess was simulated. Through the end quenching test (Jominy test), thehardenability curves of40Cr steel and AISI4350steel were measured. The thicknessof hardening layer of40Cr steel was about12mm. Since the hardenability ofAISI4350steel was very high, the thickness cannot be measured. Compared withthe hardness distribution curve of test, the calculated result was very good. Beisides,in the hardening layer, the calculated hardness was match with the test hardness of40Cr steel and AISI4350steel, respectively.Finally, according to the former research of the quenching of the workpiece,the model of end quenching was applied on the big gear shaft. The temperature field,stress field and the characteristics of the distribution of the hardening layer were investigated under different heat treatment quenching medium.25℃waterquenching, the thickness of hardening layer in gear side of40Cr gear shaft wasabout35mm, the thickness of hardened layer on gear surface was about10mm. Thethicknes of hardening layer in gear side of was AISI4350steel was more than35mm and hardened layer on gear surface was about20mm. Temperature had greateffect on the heat transfer coefficient of water. After80℃water quenching, Thethickness of the hardening layer of gear shaft teeth reduced to5mm. Differentquenching medium directly affected the thickness of hardening layer of the gearshaft. In25℃oil quenching, the thickness of hardened layer was less than25℃PVA quenching hardened layer. The quenching cooling properties of PVA and25℃water were close.Therefore, the thickness of hardening layer was similar.Besides, the temperature filed, microstructure and hardness of the big gearshraft neck was investigated during the quenching process. The thickness ofhardening layer in20mm and50mm near the end part, was20mm and10mm,respectively.Baed on results, we can put forward reasonable heat treatment processto control the hardening layer of big gear shraft.