The Research Of Organization And Mechanical Properties Of New Maraging Stainless Steel

Maraging Stainless steel is developed based on maraging steel, which has all the advantages of maraging steel and a certain degree of corrosion resistance, and whoes strength is generally between 1300~1500MPa. Maraging stainless steel has become the direction of an ultra-high strength steels on a high-strength stainless steel, which has been applied broadly in the aviation, aerospace and other tip-realms, as well as petroleum, chemical industry, and machinery manufacturing and other civilian areas.In this paper, the present alloy melted is a maraging stainless steel whose nominal composition is 00Cr13Ni7Co5Mo4Ti and the purpose is study ultra-high strength and tougness maraging stainless steel. By means of metallographic microscope (OM), Scaning electron microscope (SEM), tranxmission electron microscope (TEM), selected area electtron diffraction (SAED), X-ray diffractometry (XRD), universal material testing machine, Rockwell hardometer and other mechanical property analytical methods, the effects of solution treatment and aging treatment on microstructure and mechanical properties of maraging stainless steel were studied. The thermodymamic software Thermo-Calc was used to analogue the change of precipitated phases among the solution and aging process. Finally, the grain refinement process was studied.The results of mechanical property indicated that the best heat treatment craft of 00Cr13Ni7Co5Mo4Ti maraging stainless steel is solution treatment at 1050℃for 1h and aging treatment at 450℃for 9h, under which maraging stainless steel can be achieved good tenacious performance and strength of extension is 1670 MPa and yield strength is 1510MPa, and elongation and reduction of area are 12.1% and 55.6% separately, and notched bar impact strength can reach 100J/cm2.Microscope structure display that solution temperature has relatively minor impact on the solution organization of maraging stainless steel and the pattern and space length of martensite lath are not vary with the increment of solution temperature. The microscope structure of maraging stainless steel is fine martensite structure and small quanlity residual austenite after aging treatment. Reversed austenite distributed around the lath martensite as the shape of thin slice, which is very beneficial to improve the toughness of the material. TEM observation and selected area electron diffraction analysis of the specimen show that the precipitated phase of maraging stainless steel isη-Ni3Ti of hexagonal structure, and which is the same with the thermodynamic calculations. The precipitated phase Ni3Ti is strip whose length orientation and [111]M of martensite matrix is concordance.Using the new process of variable-temperature cyclic transformation recrystallize refine grain utilized the principle of cyclic transformation refine of grain can refine the grain of maraging stainless steel and finally obtain an average grain size of about 7mm, which increase the strength and plasticity to different extent. Finally, the strength of extension is 1850 MPa and yield strength is 1659MPa, and elongation and reduction of area can reach 12.2% and 61.1% separately.