不同时机肠梗阻导管置入术在小肠梗阻治疗中的疗效分析

背景目前的研究显示经鼻型肠梗阻导管(nasointestinal tubes,NITs)减压在小肠梗阻(small-bowelobstruction,SBO)的治疗中取得了较好的疗效,但肠梗阻导管置入的时机目前尚无定论.目的对比胃镜下早期(<48 h)及延期(≥48 h)经NITs置入术在SBO治疗中的疗效差异.方法回顾性收集2015-01/2018-02宁波大学医学院附属李惠利医院确诊的非绞窄性SBO病例,分为治疗组和对照组,治疗组采用早期经NITs置入,对照组采用延期经NITs置入.对比分析两组的效果和术后并发症发生情况.采用SPSS19.0软件进行统计分析.结果本研究共纳入133名SBO患者,其中治疗组65名.两组患者间临床特征无明显统计学差异(P>0.05).早期肠梗阻导管减压能增加单次治疗有效率(P=0.04),同时减少48 h内急诊手术率(P=0.04),但无法减少6 mo内手术率(P=0.43).治疗组与对照组相比住院时间(P=0.91)和手术并发症(P=0.21)无明显统计学差异.结论早期经NITs置入能够增加SBO患者的单次治疗有效率,同时减少48 h内急诊手术率.

Effects of TiC on the microstructure and formation of acicular ferrite in ferritic stainless steel

The formation mechanism of acicular ferrite and its microstructural characteristics in 430 ferrite stainless steel with TiC additions were studied by theory and experiment.Using an"edge?to?edge matching"model,a 5.25 mismatch between TiC(FCC structure)and ferritic stainless steel(BCC structure)was identified,which met the mismatch requirement for the heterogeneous nucleation of 430 ferritic stainless steel.TiC was found to be an effective nucleation site for the formation of acicular ferrite in a smelting experiment,as analyzed by metallographic examination,Image-Pro Plus 6.0 analysis software,and SEM–EDS.Furthermore,small inclusions in the size of 2–4?m increased the probability of acicular ferrite nucleation,and the secondary acicular ferrite would grow sympathetically from the initial acicular ferrite to produce multi-dimensional acicular ferrites.Moreover,the addition of Ti C can increase the average microstrain and dislocation density of 430 ferrite stainless steel,as calculated by Williamson-Hall(WH)method,which could play some role in strengthening the dislocation.

Effect of tin addition on the microstructure and properties of ferritic stainless steel

This article reports the effects of Sn on the inclusions as well as the mechanical properties and hot workability of ferritic stainless steel. Precipitation phases and inclusions in Sn-bearing ferritic stainless steel were observed, and the relationship between the workability and the microstructure of the steel was established. Energy-dispersive X-ray spectroscopic analysis of the steel reveals that an almost pure Sn phase forms and MnS-Sn compound inclusions appear in the steel with a higher Sn content. Little Sn segregation was observed in grain boundaries and in the areas around sulfide inclusions;however, the presence of Sn does not adversely affect the workability of the steel con-taining 0.4wt%Sn. When the Sn content is 0.1wt%-0.4wt%, Sn improves the tensile strength and the plastic strain ratio and also improves the plasticity with increasing temperature. A mechanism of improving the workability of ferritic stainless steel induced by Sn addition was discussed：the presence of Sn lowers the defect concentration in the ultra-pure ferritic lattice and the good distribution of tin in the lattice overcomes the problem of hot brittleness that occurs in low-carbon steel as a result of Sn segregation.

Comprehensive model for a slag bath in electroslag remelting process with a current-conductive mould

A mathematical model was developed to describe the interaction of multiple physical fields in a slag bath during electroslag remelting （ESR） process with a current-conductive mould. The distributions of current density, magnetic induction intensity, electromagnetic force, Joule heating, fluid flow and temperature were simulated. The model was verified by temperature measurements during remelting 12CrMoVG steel with a slag of 50wt%-70wt% CaF2, 20wt%-30wt% CaO, 10wt%-20wt% A1203, and 〈10wt% SiO2 in a 600 mm diameter current-conductive mould. There is a good agreement between the calculated temperature results and the measured data in the slag bath. The calculated results show that the maximum values of current density, electromagnetic force and Joule heating are in the region between the comer electrodes and the conductivity element. The characteristics of current density distribution, magnetic induction intensity, electromagnetic force, Joule heating, velocity patterns and temperature profiles in the slag bath during ESR process with current-conductive mould were analyzed.

Corrosion behavior of ferritic stainless steel with 15wt% chromium for the automobile exhaust system

The effect of chloride ion concentration, pH value, and grain size on the pitting corrosion resistance of a new ferritic stainless steel with 15wt% Cr was investigated using the anodic polarization method. The semiconducting properties of passive films with different chloride ion concentrations were performed using capacitance measurement and Mott-Schottky analysis methods. The aging precipitation and intergranular corrosion behavior were evaluated at 400- 900℃. It is found that the pitting potential decreases when the grain size increases. With the increase in chloride ion concentration, the doping density and the flat-bland potential increase but the thickness of the space charge layer decreases. The pitting corrosion resistance increases rapidly with the decrease in pH value. Precipitants is identified as Nb（C,N） and NbC, rather than Cr-carbide. The intergranular corrosion is attributed to the synergistic effects of Nb（C,N） and NbC precipitates and Cr segregation adjacent to the precipitates.

Influence of crucible material on inclusions in 95Cr saw-wire steel deoxidized by Si–Mn

To investigate the interaction mechanism between 95 Cr saw-wire steel and different refractories,we conducted laboratory experiments at 1873 K.Five crucible materials(SiO2,Al2 O3,MgO·Al2 O3,MgO,and MgO-CaO)were used.The results indicate that SiO2,Al2 O3,and MgO·Al2 O3 are not suitable for smelting low-oxygen,low-[Al]s 95 Cr saw-wire steel,mainly because they react with the elements in the molten steel and pollute the steel samples.By contrast,MgO-CaO is an ideal choice to produce 95 Cr saw-wire steel.It offers three advantages:(ⅰ)It does not decompose by itself at the steelmaking temperature of 1873 K because it exhibits good thermal stability;(ⅱ)[C],[Si],and[Mn]in molten steel cannot react with it to increase the[O]content;and(ⅲ)it not only desulfurizes and dephosphorizes but also removes Al2 O3 inclusions from the steel simultaneously.As a result,the contents of the main elements([C],[Si],[Mn],[Cr],N,T.O(total oxygen))in the steel are not affected and the content of impurity elements([Al]s,P,and S)can be perfectly controlled within the target range.Furthermore,the number and size of inclusions in the steel samples decrease sharply when the MgO-CaO crucible is used.

Research on droplet formation and dripping behavior during the electroslag remelting process

A better understanding of droplet formation and dripping behavior would be useful in the efficient removal of impurity elements and nonmetallic inclusions from liquid metals. In the present work, we developed a transparent experimental apparatus to study the mechanisms of droplet formation and the effects of filling ratio on droplet behavior during the electroslag remelting（ESR） process. A high-speed camera was used to clearly observe, at small time scales, the droplet formation and dripping phenomenon at the slag/metal interface during a stable ESR process. The results illustrate that a two-stage process for droplet formation and dripping occurs during the ESR process and that the droplet diameter exhibits a parabolic distribution with increasing filling ratio because of the different shape and thermal state of the electrode tip. This work also confirms that a relatively large filling ratio reduces electricity consumption and improves ingot quality.

Reaction mechanisms between molten CaF2-based slags and molten 9CrMoCoB steel

Investigating the reaction mechanism between slag and 9CrMoCoB steel is important to develop the proper slag and produce qualified ingots in the electroslag remelting(ESR) process. Equilibrium reaction experiments between molten 9CrMoCoB steel and the slags of 55 wt%CaF2–20 wt%CaO–3 wt%MgO–22 wt%Al2O3–xwt%B2O3(x = 0.0, 0.5, 1.0, 1.5, 2.0, 3.0) were conducted. The reaction mechanisms between molten 9 CrMoCoB steel and the slags with different B2O3 contents were deduced based on the composition of the steel and slag samples at different reaction times. Results show that B content in the steel can be controlled within the target range when the B2O3 content is 0.5 wt% and the FeO content ranges from 0.18 wt% to 0.22 wt% in the slag. When the B2O3 content is ≥1 wt%, the reaction between Si and B2O3 leads to the increase of the B content of steel. The additions of SiO2 and B2O3 to the slag should accord to the mass ratio of [B]/[Si] in the electrode, and SiO2 addition inhibits the reaction between Si and Al2O3.

Up-pulling force analysis for ESC hollow cylindrical casting

Electroslag casting(ESC)is an important method to produce high quality castings.In this study,the ESC up-pulling inner mold method(EUPIM)was used to produce hollow cylindrical castings with the multiple consumable electrodes.The radial deformation,the axial and radial internal stress of the inner mold,and the axial internal stress of the slag shell were analyzed using the finite element method(FEM)with the aid of ANSYS software.The ProCAST software was used to calculate the specific heat,heat conductivity and density curve of Cu.Simulation results show that the radial deformation,the axial and radial internal stress of the inner mold,and the axial internal stress of the slag shell near the slag-metal interface of hollow cylndrical casting gradually increase from 0 s to 360 s after the ESC starting(slagging)process but before applying the up-pulling force.The suitable initial up-pulling moment of the inner mold is at around 180-198 s after the starting process.

Industrial test of a 6-m long bearing steel ingot by electroslag remelting withdrawing process

In this study, the key technologies of a 6-m long bearing steel ingot produced by electroslag remelting withdrawing(ESRW) process, including bifilar mode supply, slag system development, and design of mold, were studied based on the laboratory research achievements. The 6-m long ingot of bearing steel GGr15 with a cross-section of 300 mm × 340 mm was produced using the ESRW process with a bifilar mode and a multi-taper T-mold in a plant. The testing results show that the melting rate using the ESRW bifilar mode technology is three times faster than traditional electroslag remelting(ESR), and the power consumption is only 1,320 k Wh per ton steel. Through testing for the chemical composition, macrostructure and inclusions of remelted ingot, it can be concluded that the ESRW bifilar mode technology not only retains the characteristics of traditional ESR, but also improves the production efficiency and reduces the cost compared to traditional ESR.

Effects of B segregation on Mo-rich phase precipitation in S31254 super-austenitic stainless steels:Experimental and first-principles study

Precipitation in super-austenitic stainless steels will significantly affect their corrosion resistance and hot workability.The effects of Cr and Mo on precipitation behaviors were mainly achieved by affecting the driving force for precipitation,especially Mo has a more substantial promotion effect on the formation of theσphase than Cr.In the present study,B addition to the S31254 super-austenitic stainless steels shows an excellent ability to inhibit precipitation.The effect of B on the precipitation behaviors was investigated by microstructure characterization and theoretical calculations.The experimental observation shows that the small addition of B inhibits the formation of theσphase along grain boundaries and changes from continuous to intermittent distribution.Moreover,the inhibitory effect increased obviously with the increase of B content.The influence of B addition was theoretically analyzed from the atomic level,and the calculation results demonstrate that B can inhibit the formation ofσphase precipitates by suppressing Mo migration to grain boundaries.It is found that B and Mo are inclined to segregate atΣ5 andΣ9 grain boundaries,with B showing the most severe grain boundary segregation tendency.While B distribution at the grain boundary before precipitation begins,the segregation of Mo and Cr will be restrained.Additionally,B’s occupation will induce a high potential barrier,making it difficult for Mo to diffuse towards grain boundaries.

Mechanism of local solidification time variations with melt rate during vacuum arc remelting process of 8Cr4Mo4V high-strength steel

A 2D axisymmetric numerical model was established to investigate the variations of molten pool with different melt rates during the vacuum arc remelting of 8Cr4Mo4V high-strength steel,and the ingot growth was simulated by dynamic mesh techniques.The results show that as the ingot grows,the molten pool profile changes from shallow and flat to V-shaped,and both the molten pool depth and the mushy width increase.Meanwhile,the variation of both the molten pool shape and the mushy width melt rate is clarified by the thermal equilibrium analysis.As melt rate increases,both the molten pool depth and the mushy width increase.It is caused by the increment in sensible heat stored in the ingot due to the limitation of the cooling capacity of the mold.The nonlinear increment in sensible heat leads to a nonlinear increase in the mushy width.In addition,as melt rate increases,the local solidification time(LST)of ingot decreases obviously at first and then increases.When melt rate is controlled in a suitable range,LST is the lowest and the secondary dendrite arm spacing of the ingot is the smallest,which can effectively improve the compactness degree of 8Cr4Mo4V high-strength steel.

Dissolution kinetics and reaction mechanism of Al_(2)O_(3) in molten CaF_(2)-CaO-Al_(2)O_(3) slag

The dissolution behavior of Al_(2)O_(3) in molten CaF_(2)-CaO-Al_(2)O_(3) slag,a basic slag system of electroslag remelting process,was investigated by rotating cylinder method using corundum rods to simulate Al_(2)O_(3) inclusions in steel.The experimental results show that the dissolution rate of Al_(2)O_(3);rods in CaF_(2)-CaO-Al_(2)O_(3) slag increases with the increase in rotating speed and temperature,and the rate-controlling step is the mass transfer in the slag.The dissolution rate of Al_(2)O,in CaF_(2)-CaO-Al_(2)O_(3) slag increases with the increase in the ratio of CaO to Al_(2)O_(3),which is due to the increase in dissolution driving force and the decrease in slag viscosity.The apparent activation energy of the mass transfer of AlOs in slag C is calculated to be 222.86 kJ mol^(-1).During the dissolution of Al_(2)0,inclusions in the slag,it reacts with F in liquid slag at first,then reacts with CaO to form the intermediate compounds of xCaO-yAl_(2)O_(3) system,and finally dissolves in molten slag.The dissolution rate of Al_(2)O_(3) inclusions in CaF_(2)-CaO-Al_(2)O_(3) slag for electroslag remelting is positively correlated with the ratio of the dissolution driving force and slag viscosity,and the correlation coeficient is 2.487×10^(-11).

Numerical investigation on melting characteristics of scrap with heat and mass transfers in molten steel

Herein,a numerical simulation with simultaneous heat and mass transfers is carried out to investigate the scrap melting characteristics in molten steel after model verification by published experimental data.The numerical results show that the scrap melting stages consist of the frozen shell formation stage,the frozen shell remelting stage and the parent scrap melting stage.The heat transfer coefficient and the carbon mass transfer coefficient between the scrap and the molten steel are,respectively,in the range of 4209-6249 W m^(-2) K^(-1) and 6.4×10^(-5) m s^(-1).Meanwhile,the effects of process parameters on scrap melting time were studied.An increase in the scrap preheating temperature(T_(scrap)),the molten steel temperature(T_(steel))and the carbon content of molten steel(C_(steel)),and a decrease in the scrap thickness dscrap,can reduce the frozen shell existence time,as well as the scrap melting time.On this basis,a quantitative relationship between the aforementioned process parameters and the scrap melting time is obtained to predict the formation of frozen shell(W),which provides process guidance for shortening the scrap melting time.The quantitative relationship is expressed as:lnΨ=311.32-2.34ln(T_(scrap))-39.99ln(T_(steel))-0.08ln(d_(scrap))-0.57ln(C_(steel)).

Effect of magnesium on microstructure and properties of 440C stainless bearing steel melted under pressurized conditions

The effects of magnesium(Mg)on the microstructure and properties of 440C stainless bearing steel melted under pressurized conditions were studied.Adding Mg improved the cleanliness of molten steel,modified the inclusions in steel,enhanced the distribution of carbides,and improved the mechanical properties and corrosion resistance of experimental steel.In detail,the contents of TO,S,and N in steel decreased from 0.0013 to 0.0003 wt.%,from 0.0032 to 0.0018 wt.%and from 0.0088 to 0.0049 wt.%,respectively.In addition,the transformation order of oxide inclusions in steel is Al_(2)O_(3)→MgO∙Al_(2)O_(3)→MgO,where the content of Mg in steel sharply increased from 0.00 to 29×10^(-4),81×10^(-4),and 160×10^(-4)wt.%,and the transformation order of S-containing inclusions in steel is MnS→Mg–S–Mn(–MgO)→Mg–O–S.Moreover,the number and size of inclusions and the proportion of large-size inclusions in steel decreased rapidly.Furthermore,the network structure of carbides in steel collapsed,the size of carbides was reduced,and the distribution was more uniform.Finally,the tensile strength,impact toughness,and pitting corrosion resistance of the experimental steel were significantly improved.

Effect of melt current on multi-physical field and heat flow distribution during ESR process based on model of dynamic formation of slag skin

A numerical model coupled with a multi-physical field based on dynamic formation of slag skin is established.After validation by comparing the experimental and simulation results of depth of metal pool,slag skin thickness and melt rate,it is utilized to investigate the effect of melt current on the coupled multi-physical field,slag skin thickness,metal pool depth and the heat flow distribution during electroslag remelting(ESR)Inconel 625 solidification process.The results showed that with the increase in the melt current,the velocities of ESR system and the temperature of metal pool increased,whereas the highest temperature of slag bath firstly decreased and then increased.With the increase in the melt current,the slag skin thickness,metal pool depth and melt rate increased.Furthermore,the characteristics of the heat flow distribution and the effect of melt current on the heat flow distribution were analysed.

XGBoost-based model for predicting hydrogen content in electroslag remelting

An Xtreme Gradient Boosting(XGBoost)-based endpoint hydrogen content prediction model was proposed for the electroslag remelting process,the data collected in the field were pre-processed,and the characteristic variables of the physical parameters related to the variation of hydrogen content in the electroslag remelting process were selected by machine learning analysis and metallurgical mechanism.The kernel ridge regression model,ridge regression model,XGBoost model,support vector regression model and gradient boosting regression model were developed and validated using the electroslag remelting data collected from the steel mills,and the model structure and parameters were adjusted several times.The prediction accuracy of hydrogen content was compared horizontally.The XGBoost model was validated for the test set with the following hit rates:70.59%,82.35% and 100% for the endpoint hits at the allowable hydrogen content error of ±0.05×10^(-6),±0.10×10^(-6) and ±0.50×10^(-6),respectively.

Effect of partial replacement of carbon by nitrogen on intergranular corrosion behavior of high nitrogen martensitic stainless steels

The microstructure evolution and intergranular corrosion(IGC) behavior of high nitrogen martensitic stainless steels(MSSs) by partial replacing C by N were investigated by using microscopy, X-ray diffraction, nitric acid tests and double-loop electrochemical potentiokinetic reactivation(DL-EPR) tests. The results show that the partial replacement of C by N first reduces and then increases the size and content of precipitates in high nitrogen MSSs, and converts the dominant precipitates from M23C6 to M2N,furthermore first improves and then deteriorates the IGC resistance. The high nitrogen MSS containing medium C and N contents provides good combination of mechanical properties and IGC resistance.

Effects of Temperature and Strain Rate on Flow Behavior and Microstructural Evolution of Super Duplex Stainless Steel under Hot Deformation

Hot compression tests were carried out in the temperature range of 1 223-1 473 Kand strain rate range of0.01-30s^-1 to investigate the flow behavior and microstructural evolution of super duplex stainless steel 2507（SDSS2507）.It is found that most of the flow curves exhibit a characteristic of dynamic recrystallization（DRX）and the flow stress increases with the decrease of temperature and the increase of strain rate.The apparent activation energy Qof SDSS2507 with varying true strain and strain rate is determined.As the strain increases,the value of Qdeclines in different ways with varying strain rate.The microstructural evolution characteristics and the strain partition between the two constituent phases are significantly affected by the Zener-Hollomon parameter（Z）.At a lower lnZ,dynamic recovery（DRV）and continuous dynamic recrystallization（CDRX）of the ferrite dominate the softening mechanism during the compression.At this time,steady state deformation takes place at the last stage of deformation.In contrast,a higher lnZ will facilitate the plastic deformation of the austenite and then activate the discontinuous dynamic recrystallization（DDRX）of the austenite,which leads to a continuous decline of the flow stress even at the last deformation stage together with CDRX of the ferrite.

Aluminum,titanium and oxygen control during electroslag remelting of stainless steel based on thermodynamic analysis

Experimental investigation and thermodynamic calculation were carried out to study the effect of slag on alloying elements during electroslag remelting with developing a thermodynamic model to control titanium and aluminum in in got.The thermodynamic model based on ion and molecule coexistence theory and conservation law of element atoms was established to analyze the change in aluminum and titanium along the height of ingot.The results show that low CaO slag is suitable for electroslag remelting of metal containing high titanium-to-aluminum ratio.As electroslag remelting process consists of slag temperature-rising and temperature-stable periods,TiO2 should be added into water-cooled copper mold during temperature-rising period in order to keep the thermodynamic equilibrium between titanium and aluminum,and the amount of TiO2 is the difference value calculated by the reaction between titanium and alumina at 1477 and 1677℃.