| AH36 steel has great impact toughness,welding performance and corrosion resistance,and is widely used in the construction of ships and offshore platforms.However,in the process of controlled rolling and controlled cooling,defects such as composition segregation and banded structure often occur in the structure,which affect the service performance of the material.It is necessary to eliminate such processing defects through appropriate heat treatment process.In this study,the relationship between the microstructure and the mechanical properties of AH36 steel was investigated by means of optical microscope,SEM,TEM and XRD.The subcritical quenching heat treatment process of AH36 steel was designed by orthogonal regression method.The effects of different quenching and tempering temperatures on the microstructure and properties of AH36 steel were studied by optical microscope,Vickers hardness tester and impact testing machine.The microstructure of AH36 steel was analyzed by optical microscope and SEM,the grain size and morphology of the test steel were obtained,the proportion of pearlite and grain size were analyzed and calculated by Image Pro software.The contribution of fine grain strengthening to yield strength is calculated by using the calculation formula of fine grain strengthening;TEM and JMat Pro thermodynamic software were used to analyze the type,morphology,content and size of nano-precipitates in AH36 steel,the main types of nano-precipitates in AH36 steel are obtained,According to the TEM test results and the size data of precipitates,the contribution of precipitation strengthening to yield strength was calculated;The dislocation density in AH36 steel and the composition of alloying elements in ferrite were calculated by X-ray diffraction and JMat Pro software.Through the calculation results,the contribution values of dislocation strengthening and solid solution strengthening were obtained;Finally,the actual yield strength of AH36 steel is obtained by tensile performance test,and the theoretical yield strength contribution value is obtained by substituting the above theoretical yield strength contribution value into the modified theoretical yield strength calculation formula.Compared with the actual yield strength,there are still a few errors.The subcritical quenching heat treatment test of AH36 steel was carried out according to different quenching temperature and tempering temperature.The microstructure and mechanical properties of AH36 steel with different heat treatment parameters were compared.It was found that the microstructure was significantly changed compared with the original structure.The ferrite and pearlite structure was transformed into ferrite and tempered troostite structure,and the grain size was refined.The hardness and toughness of the experimental steel were greatly improved.It was concluded that the quenching temperature was 810 ℃ and the tempering temperature was 550 ℃,which was the best heat treatment process.According to the mechanical properties data of AH36 steel after subcritical quenching heat treatment,the regression equation of hardness and toughness of AH36 steel after subcritical quenching was deduced,and the significance analysis was carried out.At the same time,the variance analysis and range analysis of the experimental data were carried out to verify the validity of the experimental data.It was concluded that the main factors affecting the hardness and toughness of AH36 steel were tempering temperature and quenching temperature. |
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