Papers by Keyword: Nitrogen Solubility

Abstract: In this paper, a new vanadium nitrogen (V-N) microalloyed high strength weathering steel with the yield strength and tensile strength higher than 550 MPa and 650 MPa was designed and developed by using thermodynamic model of nitrogen solubility and phase diagram database of CALPHAD. Based on the established thermodynamic model, the effect of C content on nitrogen solubility in molten steel was investigated. The nitrogen solubility increases with the decrease of C content and the increase of temperature. In order to obtain higher N content in steel, C content must be controlled at a low range of 0.03~0.04%. Furthermore, an allowable concentration range of C and N was selected based on the phases quantity prediction of VN/V(C,N), (Cr, Fe)₇C₃, AlN and γ through the CALPHAD approach. Consequently, five new weathering steels were designed with variations of (C+N) content or N/C ratio. And then the four selected steels were cast, hot rolled and air cooled. The tensile tests at the room temperature show that the yield strength and tensile strength of steel with 0.032% C and 0.038%N satisfy the requirements of new generational weathering steel.

Abstract: The kinetics of nitrogen absorption in Fe-Cr-Mn (Mo) alloys under 0.1 MPa nitrogen pressure and 1873K was investigated by top blowing nitrogen gas into the steel melts. A thermodynamic model of nitrogen solubility was established. Also the effect of surface active elements oxygen and sulfur on nitrogen absorption was studied. The results show that Fe-Cr-Mn (Mo) melts achieve nitrogen saturation value within 50 minutes, the nitrogen solubility increases with the content of chromium and manganese, but the experiment values of nitrogen solubility are general lower than theoretical values because of the open nitrogen gas atmosphere and high surface active elements content in the steel melts. The nitrogen absorption can be described well by a second order reaction and the interfacial reaction is restrictive step. The rate of nitrogen absorption decreases by lowering the surface reaction constant due to oxygen and sulfur in the steel melts. The effect of the surface active elements oxygen and sulfur on nitrogen absorption can be described well as .

Abstract: The experiments of smelting high nitrogen nickel-free stainless steel were carried out in the high temperature and high pressure reaction kettle. The nitrogen content was more than 1.36% by using the method of high pressure and bottom blowing nitrogen. With controlling high pressure nitrogen atmosphere and bottom blowing nitrogen, internal react were investigated by single factor experiment. Experimental results shown that there is saturated solubility, while smelting 18Mn18CrN steel with high pressure and bottom blowing nitrogen. Thermodynamic calculation model nitrogen solubility under the condition of high pressure was established, and the influence of nitrogen partial pressure on saturated solubility was researched.

Abstract: High nitrogen stainless steels with excellent mechanical and corrosion resistance properties is focused on to develop a new class of engineering material. The manufacture process of high nitrogen stainless steels under high nitrogen pressure is complicated. There are some theoretical problems to be solved for large scale melting and cast high nitrogen stainless steels. The thermodynamic calculation models of nitrogen solubility in the liquid phase, δ ferrite phase and γ austenitic phase built can well predict the nitrogen solubility and analyze the effect of temperature, alloy components and nitrogen pressure on the nitrogen solubility. The minimum nitrogen pressure for preventing the nitrogen porosity formation has been calculated by the micro-segregation. By the analysis nitrogen behavior of melting and cast high nitrogen stainless steels, it is possible to produce high nitrogen stainless steels in a large scale in China.

Abstract: Diffusivities of nitrogen and argon in a borosilicate glass were determined with two different methods: (1) from gas exchange experiments between molten glass and bubbles containing nitrogen and argon, and (2) from solution rates of nitrogen and argon in glass during saturation experiments. Between 1200°C and 1580°C the diffusion coefficients of nitrogen and argon yielded the following equations:      − = − RT s m DN 134900 exp 10 22 . 1 ] / [ 6 . 2 2 and      − = − RT s m DAr 125300 exp 10 08 . 1 ] / [ 6 . 2 , with R=8.314 J/(mol.K). The solubilities and residual gas concentration in the glass which are necessary for the calculation of the diffusivities were determined with the high temperature vacuum extraction method.