| Shanghai KSB Pump company introduced the production of the German CHTC and HG series high pressure water pump of the 1.6772 grades of steel is completely dependent on importing, not only the high cost, but often can not guarantee the delivery schedule. For this case Li Peiyao with other researchers based on the relationship between alloy elements and properties, as well as the bolting materials’properties for high-pressure pump, It has been finally designed the alloy component and metallurgical process.And in accordance with the naming convention of metal materials this kind of bolt steel named 20CrNi4Mo. Studies have shown that the mechanical properties of this material are met or exceeded in Germany 1.6772 grade steel, can meet the high-pressure feed water pump mechanical properties of conventional bolt material requirements.Due to the high temperature of working condition of the high pressure pump, which is 230℃, which requires bolt steel also must has good high temperature mechanical properties which are creep rupture strength, creep deformation and anti stress relaxation. The tests and analysis results show that the mechanical properties of high-temperature steels above 20CrNi4Mo good to meet the high-pressure feed pump high temperature mechanical properties of the steel bolt these requirements.The main work and research results are as follows:(1) High-temperature tensile test results of 20CrNi4Mo are as follows: The test results under various experimental conditions are met or exceeded the 20CrNi4Mo steel design requirements.(2) The creep properties of the bolt steel were tested at the conditions of 400℃ and three kinds of stress respectively are 320MPa,380MPa and 440MPa. Three conditions of steady-state creep rate are calculated, they are 2.564×l0-11s-1,3.564×l0-11s-1 and 6.781×10-11s-1. Creep limit at 400 degree was calculated by the steady creep rate which is σ1/10000400= 707.9MPa,which is higher than the design specifications σ1/10000400= 440MPa. This material has excellent creep resistance, can meet the actual use requirements.(3) The stress relaxation property of the bolt steel is studied by the stress relaxation test at 400℃ under two stress conditions which are 340MPa and 320MPa. According to the test data, launching the residual stress after 105 hours, the results are 144.7MPa and 134.7MPa. At the same time, the stress relaxation rate of stress relaxation in different test conditions was calculated and the stress relaxation rate are 4.671 ×10-11s-1 and 4.158×10-11s-1. From the above results, we can know that the residual stress of the sample is larger, and the stress relaxation rate is small, which shows that the stress relaxation property of 20CrNi4Mo steel at 400℃ is good.(4) The endurance strength of 20CrNi4Mo is tested under 350℃,400℃,450℃ and various stress conditions.The endurance test results of 20CrNi4Mo steel at 350 ℃Cand 400 ℃ respectively were σ18194350=1000MPa and σ13910400= 770MPa,both larger than the design index of the persistent strength of the material which are σ104350= 775MPa and σ104400= 550MPa.20CrNi4Mo can meet the actual use requirements. Comparing the isothermal line method and time temperature parameter method includ L-M parameter method, K-D parameter method and M-S parameter method according to test results, analysis results show that the L-M parameter method is the most suitable method for the research.Using the L-M parameter method to extrapolating the persistent strength after 105h. The result is σ105230= 186.21MPa, which means 20CrNi4Mo has excellent long-lasting performance and long-term reliable service. |
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