Fatigue properties of a nickel-based superalloy at 25 ? and 750 ? were studied under stress ratio R = -1 & 0.1 to identify crack nucleation and growth mechanisms. Results show that interior grain-related cracking is induced by microstructure in Goss or Copper grain. Moreover, owing to competition between temperature and vacuum effects, threshold values for small and long cracks, and the transition crack size, are all lower at elevated temperature. Finally, based on modeling of crack nucleation and growth, a fatigue life model with good prediction results is proposed. The crack nucleation consumes more than 90% of fatigue life.

Fatigue crack propagation behavior of Al7075-T6 and Al2024-T3 under four typical variable amplitude loading (VAL) patterns are investigated by using in-situ testing. The near-tip strain fields and crack opening level are measured combining in-situ optical microscopy testing and digital image correlation (DIC) technique. The crack tip deformation process is directly observed by in-situ scanning electron microscope (SEM). The results show that both the crack propagation behaviors and the crack-tip strain distributions are greatly influenced by the VAL patterns. The shape effect of the overload-induced plastic zone may prolong the crack growth retardation. The crack-front plasticity plays a dominant role in controlling fatigue crack growth. The crack-front plasticity supplies a link between crack closure and crack growth. The crack tip resharpening caused by the underload applied immediately after the overload may reduce the retardation extent. Finally, a modified retardation model is proposed and gives reasonable prediction results of the crack growth rate under VAL.

The utilization of titanium-bearing blast furnace slag (TBFS) has been widely concerned, which is mainly related to the recovery of titanium resources. In order to realize the efficient and clean recovery of titanium resource, the main titanium-bearing phases (CaTiO3, MgTiO(3)and Mg2TiO4) in TBFS with high content of MgO were investigated in CH4-H-2 system in this work. Thermodynamic calculation indicated that CaTiO3, MgTiO(3 )and MgTi2O4 could be ultimately reduced to TiCxOy at 1300 degrees C, 1200 degrees C and 1200 degrees C respectively. The reduction experiments were carried out in flowing CH4-H-2, which considered the influences of time, temperature and addition, the results of which showed that the optimal reduction temperatures of CaTiO3 and MgTiO3 were 1400 degrees C and 1200 degrees C respectively. DFT calculation results also confirmed that MgTiO3 had stronger CH4 adsorption capacity than CaTiO3 and Mg2TiO4. However, Mg2TiO4 could not be reduced completely even at 1450 degrees C, because excessive MgO in the reduced products prevented further reaction in kinetics. Both increasing temperature and adding iron oxides contributed to the reduction kinetics. The results suggested that the appropriate increase of the proportion of MgO in TBFS was beneficial to titanium extraction. This work provides a way to develop new process to extract titanium from TBFS, especially the slag with high MgO. (C) 2021 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

High and very high cycle fatigue tests for TC11 titanium alloy were performed to clarify the interior cracking behavior under fully reversed and pulsating tension at three service temperatures. According to the estimation of threshold values for small and long crack growth, the fatigue design curves are established. Combined with electron backscatter diffraction and fracture mechanics analysis, the interior cracking is closely related to grain strength and size, and microtexture. The interior failure is attributed to the facet formation caused by larger αp phase fracture. Based on FIP model, a temperature-based method is proposed to predict the crack nucleation life.

The fatigue failure behavior and fatigue strength prediction were performed on a Ni-based su-peralloy for the turbine blade in 750 degrees C elevated temperature environment. The asymmetric load tests with the stress ratios R =-1 and 0.1 were tested, followed by microstructure characterization and fracture mode analysis via two & three-dimensional microscopic observation and electron-backscattering diffraction, etc. Results show that as stress level decreases, fatigue failure is less likely to be induced by pore, while the possibility of grain cracking induced failure increases. The larger roughness of the fracture surface is attributed to the geometric incompatibility of grains and the plastic deformation at the crack tip. For the grain related failure, crack nucleation is mainly in Goss grain along the direction of the maximum Schmid factor. Moreover, the threshold values of small & long cracks, the transition crack size from small to long, are all lower for interior failure due to the effect of vacuum environment. Finally, based on El-Haddad model, a new fa-tigue strength prediction model is proposed, and the predicted results are in good agreement with the experimental ones.

Axial loading tests with stress ratios of -1 and 0.1 at 25 ?C and 650 ?C were performed to investigate the effect of elevated temperature on high-cycle and very-high-cycle fatigue properties of a Ni-based superalloy manufactured by selective laser melting. Interior fatigue failure with longer life is greatly promoted at elevated temperature, which is induced from the crystallographic facets associated with grain structure. By means of electronbackscattered diffraction and stress intensity factor evaluation, the interior failure mechanisms are elucidated. Based on the proposed microstructure-based crack nucleation life model, a good agreement between the predicted and experimental results is obtained.

Titanium carbides, oxides, nitrides, and carbonitrides possess many special and excellent properties. But the high production cost caused by the traditional carbothermic reduction process severely limits the wide applications. In this study, a novel synthesis process has been proposed by reducing and carbonitriding TiO2 with a CH4-H2-N2 gas mixture at low temperatures. The synthesis of Ti(C, N, O), reaction mechanism, and the composition of the product have been investigated. Thermodynamic analysis indicated that TiO2 could be ultimately reduced and carbonitrided to Ti(C, N, O) by CH4-H2-N2 gas mixture. Based on the predictions of thermodynamics, the effects of reduction time, temperature, and gas composition have been studied experimentally. The obtained results indicated that increasing reduction temperature and introduction of N2 are beneficial to the synthesis of Ti(C, N, O). Finally, the optimum reaction conditions have been obtained. The density functional theory (DFT) results further demonstrated the reaction mechanism. This work provides a new approach to prepare metallic carbonitrides from their oxides.

Titanium carbides, oxides, nitrides and carbonitrides possess many special and excellent properties. But the high production cost caused by the traditional carbothermic reduction process severely limits the wide applications. In this study, a novel synthesis process has been proposed by reducing and carbonitriding TiO 2 with CH 4 -H 2 -N 2 gas mixture at low temperatures. The synthesis of Ti(C, N, O), reaction mechanism and the products composition have been investigated. Thermodynamic analysis indicated that TiO 2 could be ultimately reduced and carbonitrided to Ti(C, N, O) by CH 4 -H 2 -N 2 gas mixture. Based on the predictions of thermodynamics, the effects of reduction time, temperature, and gas composition have been studied experimentally. The obtained results indicated that increasing reduction temperature and introduction of N 2 are beneficial to the synthesis of Ti(C, N, O). Finally, the optimum reaction conditions have been obtained. The density functional theory (DFT) results further demonstrated the reaction mechanism. This work provides a new approach to prepare metallic carbonitrides from their oxides.

The utilization of titanium-containing blast furnace slag has been an unsolved problem for a long time. Failure to make effective use of the slag, which is caused by a high TiO2 content within it, not only results in a waste of resources, especially titanium, but also increases environmental risk. The key to address the problem is the enrichment and extraction of TiO2 from the slag first. Therefore, in order to study the enrichment of titanium, the crystallization behavior of TiO2-CaO-SiO2-Al2O3-MgO pentabasic slag, the main compositions of titanium-containing blast furnace slag, within the basicity range of 1.1–1.4 was investigated theoretically and experimentally. Thermodynamic calculation shows that perovskite is the main titanium-containing phase and titanium can be enriched in perovskite. By decreasing the temperature, perovskite precipitates at first. Additionally, with the increase of basicity, perovskite precipitation temperature increases continuously, and its amount of precipitation almost does not change, while the amounts of other phases change obviously. The experimental results demonstrate similar results except for the amount of perovskite (with the increase of basicity, perovskite precipitation amount increases slightly), caused by kinetic reason. In addition, the morphology of the slag at different scales was observed. The surface of the cooled slag is granular, vein-like, and irregular, multilaterally shaped from outside to inside. The crystal is dendritic with a spine-like trunk, and the edge is blade-like. In terms of the structure of the crystal, the inner part of it is perovskite, and the outer part is covered with a layer of other phases with spinel inlaying it. Finally, the precipitated mechanism is proposed as well.

The effects of both the microstructure and the original grain size on three-roll screw rolling process of Ti6Al4V titanium alloy bar were studied in the present work. The microstructure of Ti6Al4V titanium bar had a great influence on the mechanical properties of the rolling bar. When the original size was large, the grains were apparently refined but the microstructure was uneven. But for semi-finished titanium bar composed of fine equiaxed grains, the grains after rolling were fine and uniform. During the rolling process, the Ti6Al4V titanium alloy microstructure changed from equiaxed structure to the basket-weave one. After annealing at 800℃ for 1.5 hours and then cooling in air, the average tensile strength decreased from 984 MPa to 964 MPa; while after annealing at 950℃ for 1.5 hours and then cooling by water, and aging at 540℃ for 6 hours then cooling by air, the average tensile strength increased from 979 MPa to 1107 MPa.

As a special hardenable α titanium alloy, Ti-2.5 Cu alloy was a candidate material for high temperature components requiring high strength and plasticity. The effect of prestrain on the precipitation behaviors was investigated in the present study. Tensile tests show that elongation up to 22 % can be obtained after solid solution (SS) treatment. Thereafter, prestrain in tension with 5 %, 10 %, 15 % and 20 % was carried out for the SS samples and then duplex aging was applied. Transmitting electron microscopy (TEM) investigations show that larger Ti2Cu particles were observed in the prestrained condition than free aging one, as prestrain significantly speeds up the precipitation kinetics. The strength firstly increases and then decreases for the prestrained samples after duplex aging, where the competition between precipitation hardening and recovery softening should be responsible. With the consideration of SS, precipitation and recovery, a strength model for duplex aging combined with prestrain was established, which is in well agreement with experiments. Present study may provide a promising way to obtain the strength of deformed hcp materials in industry application.

The present paper mainly studies how the LF slag deoxidizer,LF dynamics condition and the Ca-treatment affect the desulphurization after RH.The results show that the w(FeO+MnO) can be controlled in below 0.5 % after adding more than 300 kg aluminum particles in the refining slag and w(S) in the steel is reduced from original 30×10-6 to 630×10-6;and when the bottom gas flow rate is 500 L/min w(S) in the steel can be reduced to 6×10-6 after 10 min and too high or too low blow argon flow rate will affect the desulfurization efficiency.In this research later Ca-treatment in RH has no desulfurization ability,but addition of the calcium cladded wire can inhibit the sulfur pick-up and keep the sulfur content in a low level.

The non-metallic inclusions have a critical influence on the quality of the sheet billet.In the current study,the distribution,size and morphology of the non-metallic inclusion in SPHC sheet billet were analyzed using SEM,EDS and sample-electrolysing.The results showed that the total oxygen content distributed uniformly in the billet.The sulfur content was highest at the center of thickness direction and it was higher at the side of inner arc than at the side of outer arc.The amounts of large inclusions were most at the center and it was least at the side on the width direction.

Ca treatment effected on 55SiMnMo steel inclusion behaviors has been studied,the 55SiMnMo production process was Consteel EAF-LF-VD-Continuous casting.The micro-inclusions,inclusion composition change and macro-inclusions had been analyzed.The results show that Ca treatment reaction was not complete in 2 min after Ca addition,at the end of VD the inclusion degeneration was obvious and calcium mainly reacted with the surface of the inclusion.After Ca addition,the Ca content in the inclusion increased significantly,(Al2O3)decreased from 80%～ 90% at the start of VD to 40%～ 60% in the tundish.(Mg)eventually decreased to less than 10%.Ca treatment has little effect on macro-inclusions.

Cleanliness of steels is one of the major factors influencing the final product quality. This paper introduced industrial practice of producing clean steel by EAF-LF-VD-Billet casting process. The cleanliness of 55SiMnMo steel during the whole producing process was analyzed by methods of sampling systematically and comprehensive analysis including total oxygen and nitrogen content analysis, optical microscope observation and SEM+EDS. The factors affecting the steel cleanliness were discussed. Some measures to improve steel cleanliness were proposed.

For a more profound understanding of the relationship between the iron ore grade and coke ratio,molten iron output,based on the Rahm method,the coke ratio reduction can be calculated when iron ore grade 1% changes,the statistical data and theoretical calculation are carried on a domestic 2500 m3blast furnace.The results show that as the ore grade increased,the effect on coke ratio reduction becomes more and more small,molten iron output grows with the iron ore grade linearly.When the iron ore grade is 56.4% in practice,ore grade increase: coke ratio reduction:hot metal output increase is 1∶1.6∶1.77,which is similar to the actual statistics 1∶1.74∶2.39,but is different from the empirical value1∶2∶3,so the calculation results is effective.And this research provides a commonly calculation method of understanding the relations between iron ore grade and coke ratio、molten iron output in the production of blast furnace.

In the current study, in order to investigate the formation and evolution of Al-Ti-Mg-O inclusions in the steels, the amount, size, morphology and composition of inclusions formed in Al-Ti-Mg deoxidized steel were investigated. At low Al and low Mg content, with Ti content increasing in steel, inclusions transferred from MgO-Al2O3, MgO-TiOx and Al2O3-TiOx to Al2O3-rich Al2O3-TiOx inclusions and eventually TiOx-rich Al2O3-TiOx inclusions, and the number and area fraction of inclusions decreased continuously. The maximum average size of inclusions was 4.41μm. When the content of Al was low and Ti content was about 0.0040 mass% in metal, with the increase of Mg content in the steel, inclusions was Ti-rich Al2O3- TiOx first and eventually Al2O3-rich MgO-Al2O3-TiOx generated, the number and area fraction of inclusions had a tendency of increasing, and the biggest average diameter inclusions was 3.59μm.

According to the similar principles,water model with geometric ratio of 1∶ 3 was set up for 150t ladle of Xingcheng special Steel.On the basis of the prototype evaluation,the position of argon blowing was improved and the optimal project was that bottom nozzle positions were at the radius of 1/3 and 0.64 with the angle of 180°and when the actual flow rate was 600L/min,the shortest mixing time was 48.8s.

The scouring action on 150 tons devanadium Oxygen Converter's inner-lining has been studied by water model experiment with similarity ratio 6 : 1.In experiment,conductivity meter was linked to pressure probes for texting the change of pressure on converter's innerlining directly,which was under the conditions of top blowing,combined blowing and top-bottom-side blowing.It was shown from the investigation that the pressure on the inner-lining between nozzles of top lance was higher than the other part.The pressure on some part,which was influenced by the flow rate of top gas,could be reduced by the concentration of bottom tuyeres; but the flow rate of bottom gas should not be too high.Under the condition of this experiment,the case A and B were unreasonable,because side gas not always weaken the scouring action and increase the shortest mixing time.

According to the similitude principle,1:3 water mechanical model has been established for 150 t ladle in Xingcheng Steel.The best bottom nozzle position and the gas flow rate are defined by measuring the mixing time under different bottom blowing conditions.The results show that the original program with two nozzles blowing is not good enough because of washing erosion to the ladle lining from too much blowing gas.The optimum program after optimizing is that the 53 s shortest mixing time can be obtained when best argon blowing position is at 0.5 R with the angle of 135° and the critical flow rate is 550~600 L/min.