The single hot thermocouple technique(SHTT) and high temperature equilibrium technique were combined to investigate the phase diagram of the CaO-SiO_2-5%MgO-20%Al_2O_3-TiO_2 system.The 1300 ℃ to 1500 ℃ liquidus lines are calculated according to the thermodynamic equations based on the pseudo-melting temperatures measured by the single hot thermocouple technique.The phase equilibria relationships are experimentally determined at 1400 ℃ using the high temperature equilibria technique followed by X-ray fluorescence(XRF),X-ray diffraction(XRD),scanning electron microscopy(SEM) and energy dispersive X-ray spectroscopy(EDX) analysis.The liquid phase(L),melilite solid solution phase((C_2MS_2,C_2AS)_(ss)),diopside phase(CMS_2) and perovskite phase(CaOTiO_2) are found.Coupled with the liquidus lines and equilibria results,the phase diagram is constructed for the specified region of the CaO-SiO_2-5%MgO-20%Al_2O_3-TiO_2 system.
A coupled thermodynamic model of inclusions precipitation both in liquid and solid phase and microsegregation of solute elements during solidification of heat-resistant steel containing cerium was established.Then the model was validated by the SEM analysis of the industrial products.The type and amount of inclusions in solidification structure of 253 MA heat-resistant steel were predicted by the model,and the valuable results for the inclusions controlling in 253 MA steel were obtained.When the cerium addition increases,the types of inclusions transform from SiO2 and MnS to Ce2O3 and Ce2O2S in 253 MA steel and the precipitation temperature of SiO2 and MnS decreases.The inclusions CeS and CeN convert to Ce2O3 and Ce2O2S as the oxygen content increases and Ce2O3 and CeN convert to Ce2O2 S,Ce3S4,and MnS as the sulfur content increases.The formation temperature of SiO2 increases when the oxygen content increases and the MnS precipitation temperature increases when the sulfur content increases.There is only a small quantity of inclusions containing cerium in 253 MA steel with high cleanliness,i.e.,low oxygen and sulfur contents.By contrast,a mass of SiO2,MnS and Ce2O2 S are formed in steel when the oxygen and sulfur contents are high enough.The condition that MnS precipitates in 253 MA steel is 1.2 w[O]+w[S]>0.01%and SiO2 precipitates when 2 w[O]+w[S]>0.017%(w[S]<0.005%)and w[O]>0.006%(w[S]>0.005%).
Weathering steel is widely used in various fields due to its excellent mechanical properties and high corrosion resistance. The effect of chromium content on the S450 EW weathering steel in cyclic immersion test was studied. The results indicated that the corrosion resistance of S450 EW weathering steel is closely related to chromium content. The addition of chromium significantly inhibited the weathering steel corrosion. The corrosion rate of experimental steel after 96 h immersion was 1.101 g·m-2·h-1. The rust of S450 EW weathering steel was mainly constituted of Fe OOH and Fe3O4 phase, and the elevation of chromium content promoted the formation of α-Fe OOH. The fine precipitates of the two phases contributed to the formation of dense dust layer of test steel. Furthermore, the increase of chromium is beneficial for the cure of original defects and cracks of the rust layer via the enrichment of chromium. The corrosion potential and the resistance of corrosion process were thus increased, protecting the experimental steel from further corrosion. A S450 EW steel with corrosion resistance more than 1.5 times of Q450NQR1 steel was prepared.
As the raw materials in the post process of rolling and heat treatment, ingots have great effects on the properties of the final products. Inclusions and solidification structures are the most important aspects of the quality of ingots. Niobium and titanium are usually used to react with carbon and nitrogen to improve the properties of ferritic stainless steels. In this research, combined with thermodynamic calculation, effects of niobium and titanium on the inclusions and solidification structures in three kinds of high pure ferritic stainless steels with different titanium additions were investigated by optical microscope(OM), scanning electron microscope(SEM), transmission electron microscope(TEM), and energy disperse spectrometer(EDS). Results show that Al2O3 and a few(Nb,Ti)N particles form when titanium addition is 0.01 %.Furthermore, inclusions are mainly Ti N and Al2O3–Ti Ox–Ti N duplex inclusions when titanium addition is more than0.10 %. Those two types of inclusions are in well distribution, and can afford nuclei to the solidification process.Therefore, the ratio of equiaxed zone increases with the increase of titanium addition. The ratio increases from42.1 % to 64.0 % with the titanium addition increasing from 0.01 % to 0.10 %, and it increases to 85.7 % when the titanium addition reaches 0.34 %.
