| 15-5PH is a kind of martensitic precipitation hardening stainless steel with high strength and good corrosion resistance.It is widely used in aviation,aerospace,nuclear power,navigation,petroleum,chemical and other fields.With the rapid development of the defense industry and its manufacturing industry,the demand for this steel has gradually increased.Aiming at the problems of high strength and low low-temperature toughness of 15-5PH stainless steel used for the shaft of marine sea water pump,this paper studies the influence of heat treatment process on the structure and mechanical properties of 15-5PH stainless steel to achieve the matching of strength and toughness.This paper uses X-ray diffractometer(XRD),scanning electron microscope(SEM),electron backscatter diffraction technique(EBSD),transmission electron microscope(TEM),scanning transmission electron microscope(STEM),selected electron diffraction(SAED)and other characterization instruments The structure is analyzed,the mechanical properties are analyzed by tensile testing machine,pendulum impact testing machine,etc.The thermodynamic calculation software Thermo-Calc is used to calculate the amount of precipitated phases during aging heat treatment,and the effects of different aging heat treatment processes on the structure and mechanical properties of 15-5PH martensitic stainless steel were studied.The research content and results of this article are as follows:(1)The influence of CCT curve and cooling rate of 15-5PH stainless steel on mechanical properties.The phase transition points of 15-5PH stainless steel are Ac1:593℃,Ac3:752℃,Ms:202℃,and Mf:81℃.The CCT curve of 15-5PH stainless steel shows that the cooling rate has no obvious effect on the phase transformation,only the martensitic transformation process,Based on this,the water cooling method has better comprehensive mechanical properties.(2)The effect of aging heat treatment process on the microstructure of 15-5PH stainless steel.During the medium and high temperature aging treatment,the 15-5PH stainless steel lath martensite boundary appeared film-like reversed austenite,there is an orientation relationship between the martensite matrix and the reversed austenite:(?),in line with the known K-S relationship between martensite and austenite.In the single aging heat treatment,the amount of reversed austenite increases with the increase of temperature,and the Cu precipitates also grow and coarsen.During the double aging heat treatment,with the extension of the final aging time,there is no significant change in the reversed austenite content and the coarsening and growth of Cu precipitates.(3)The effect of aging heat treatment process on the mechanical properties of 15-5PH stainless steel.During single-aging heat treatment,as the temperature increases,the lowtemperature impact energy increases and the strength decreases.After optimizing the aging heat treatment process,through the double aging heat treatment process 1040℃+550℃×4h+580℃×1h,the mechanical properties of 15-5PH stainless steel are the yield strength and tensile strength of 1037MPa and 1080MPa,respectively,and low temperature(-40℃)impact energy is 180J.The strength-toughness match is achieved,it improves the low-temperature impact toughness while ensuring high strength,which meets the requirements of the shaft material of the sea water pump for ships and is used in production. |
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