Study on the Heat-treatment of ZG0Cr16Ni5Mo Used on Hydraulic Turbine Blades
|Course||Materials Science and Engineering|
|Keywords||Cr-Ni-Mo low-carbon martensitic stainless steel induced austenite δ-ferrite strain induced martensite|
This paper mainly has five parts. First of all, it introduced the requirement for the performance of the hydraulic turbine blades materials and the actuality development of the hydraulic turbine blades materials in China. On the second, it presented the technical research on the widely used material of ZG0Crl6Ni5Mo, included heat-treatment test, mechanic properties test and microstructure analysis. On the third, with the test it educed the heat-treatment process of the ZG0Crl6Ni5Mo and applied in the actual manufacture. In the forth part, it mainly introduced the factors effect on the mechanical properties, included the heat-treatment and the microstructure. The emphases was placed on the induced Austenite, setted forth whose formation, characters, quantity and influence to the ZG0Crl6Ni5Mo. At last, it made a brief summarize on this useful material.Have read a lot of literature and datum, based on them, the author design this test, the microstructure of the low-carbon martensitic stainless steel of ZG0Crl6Ni5Mo was analyzed by using X-ray diffractometer, metallographic microscope, scanning electron microscope (SEM) and transmission electron microscope (TEM).The works proved that using the electrical oven refining can accurately control the chemical content and reduce the cast defects, which is the premise insurance for the blades’ quality, and justified heat-treatment process is the key to insure the quality of the blades, that is high temperature normalize with two times temper and the treatment time decided by the size of the blade. Both results of the mechanical properties test and the microstructure observation concluded that the induced austenite in ZG0Crl 6Ni5Mo has great effect on its property, which comes into being during the temper process and can be got at 10~ 15% in amount.Because the induced austenite dispersal among the plates of the tempered martensite with high disperity, it makes the steel has great thermal stability and mechanical unstability. The hydrogen atom is difficult to diffuse and concentrate in -ferrite, so the scattered induced austenite can prevent the hydrogen brittleness. The great thermal stability means that the steel can be kept unchanged when the temperature has great change, this is no doubt a quite advantage to weld. The mechanical unstability means that the strain can promote the formation of the martensite, this kind of formation behavior shall decrease the bad affect of the strain, that is to say, it is very good forbroken-hardness and resistance to cavitation erosion.To sum up, the low-carbon martensitic stainless steel has good comprehensive mechanical property , weldability, good ability to control the cracking, hydrogen brittleness and cavitation. Now the low-carbon martensitic stainless steel is widely used on large welded structure of hydro power plant, pump etc.