Effect Of Heat Treatment On The Structure And Mechanical Properties Of Fe-Cr-Co-Ni-Al-Mo-Ti Alloys

The precipitation-strengthened iron-based alloy,has low cost and good performance,which is a high-temperature structural material with great application potential.However,the Ni Al phase-strengthened iron-based alloy is limited by its shortcomings of poor strain in room tempreture,and it is difficult to meet the further requirements of our country’s current economic development and national defense construction.Recent years,researchers have improved the performance of iron-based alloys by adding Ti element to iron-based alloys to form（Ni Al+Ni₂Ti Al）composite precipitation phases.In this paper,Fe-10Cr-12.5Ni-12.5Co-4.5Al-2Mo-x Ti（x=0.5wt.%,1wt.%,1.5wt.%,2wt.%）was prepared by vacuum melting with Fe-based alloys as the research object.The effect of Ti content and heat treatment process on the microstructure and mechanical properties of the alloys in this paper were systematically studied by means of X-ray diffraction analyzer（XRD）,scanning electron microscope（SEM）,transmission electron microscope（TEM）,field emission electron microscope（FESEM）,micro-hardness test and room temperature tensile performance test.The main conclusions are as follows:For experimental alloys with different Ti element content,under the same heat treatment process conditions,as the aging time increases,the alloy hardness first rises,and then slowly decreases after reaching the peak;with the increase of the Ti element content,the strength and hardness of the peak-aged alloy gradually increases,while the strain of the alloy gradually decreases.Under the different heat treatment conditions,the experimental alloy matrix is mainly composed of ferrite and austenite,and with the increasing of Ti element content,the ferrite content in the alloy matrix gradually increases.When the Ti content of the experimental alloy is 0.5wt.%,the main precipitated phase in the matrix is B2;and when the Ti content of the experimental alloy increase to 1.0wt.%,the main precipitates in the matrix are B2 and L2₁phase.Under the same aging process conditions,with the increasing of the solid solution temperature,the precipitation phase in the Fe-10Cr-12.5Ni-12.5Co-4.5Al-2Mo-1Ti alloy will coarsen,the density will decrease,and the content of austenite in the matrix will increase too,which causes the hardness and strength of the alloy to decrease and the strain to increase.In addition,under the condition of lower solid solution temperature（850℃）,the increasing of the aging temperature will lead to the decreasing of the precipitation phase density and the coarsening of the size,thereby reducing the comprehensive mechanical properties of the alloy;while at the higher solid solution temperature condition（950℃,1000℃）,the increase of aging temperature can refine the precipitated phase and increase the density of the precipitated phase,thereby improving the mechanical properties.