No abstract

The metallographic analysis method is used to study the original austenite grain change law of Nb-containing high-strength ship steel. Adding Nb to the experimental steel will refine the grains to a certain extent. Different Nb content, the corresponding grain size change trend is different. Under the experimental heating environment of 850°C~1150°C, the grains of the two experimental steels have different degrees of coarsening at different heating temperatures. Compared with the low-C and high-Nb steel (EH36) with the high-C and low-Nb steel (AH36), the former can not only control the austenite grain growth well at lower temperature, but also has a strong inhibitory effect in a higher temperature environment. Based on the experimental data, the austenite grain growth kinetic model of the two experimental steels at the heating temperature of 850°C~1150°C is obtained.

Two kinds of ULCB steel were designed with different Nb content. The yield strength of the steel which was made by adding 0.09%Nb, TMCP (Thermo Mechanical Controlling Processing) and tempering can achieve more than 900MPa. As compared with 0.05%Nb steel, adding 0.09%Nb can refine the austenite grain significantly. Through the analysis by TEM and EDX, a large amount of Nb precipitation particles can be observed in the steel with 0.09% Nb tempered at 650°C for 1h and these particles are generally small than 20nm.

Combined with the Guanzhong basin tectonic evolution, the data of Sr content,87Sr/86Sr ratio and hot water hydrochemistry has been used to study the supply origin and flow path of deep geothermal water in the Guanzhong central region. The Sr isotope study result shows that when accepting recharge, the geothermal water in the northwest and southeast of Xianli terrace both mainly come from northwest direction. A small amount supply source of geothermal water in the Xi 'an city is from Qinling mountain and the principal supply source comes from the west and north direction, however, geothermal water of Chang’an accepts supply from the north of Qinling mountain. Keywords: geothermal water; strontium isotope; basin type; indicating significance

This paper focuses on a new method of aerodynamic drag reduction. In this paper numerical simulation method is adopted to investigate the relationship between the aerodynamic drag characteristics of a blunt body and the distribution of total pressure around the body. The study shows that when the shape of a blunt body is modified to be close to its isobaric surface, the pressure drag of the body can be reduced largely while the viscous drag increases slightly, and the summary of the drag gets lower as a result. This conclusion will have profound guiding significance in the aerodynamic shape designing and the aerodynamic drag reduction of an automobile.