右美托咪定和咪达唑仑对ICU老年患者机械通气的镇静效果研究

目的探讨脑电双频谱指数(BIS)监测下持续静脉泵注右美托咪定和咪达唑仑对老年心脏手术患者术后机械通气的镇静效果。方法选取择期行瓣膜置换手术,并于术后带气管导管进入重症加强护理病房(ICU)的老年患者68例,平均随机分为右美托咪定组和咪达唑仑组。右美托咪定组患者首先静脉泵注0.5μg/kg右美托咪定10 min,然后以0.2μg/(kg·h)的速度持续静脉泵注。咪达唑仑组患者首先静脉泵入咪达唑仑负荷剂量0.06 mg/kg,然后以0.4 mg/(kg·h)的速度持续静脉泵注。记录泵注镇静药物前,以及泵注药物后1、2和3 h两组患者各时间点的平均动脉压(MAP)、呼吸频率(RR)、脉搏氧饱和度(Sp O_2)、心率(HR)、改良警觉/镇静评分(MOAA/S)、BIS、脱机时间及不良反应。药物泵注3 h后,将BIS值控制在61~75,并根据BIS值调整药物泵注的速度。结果两组患者在实施不同镇静方案后各时间点的MAP、RR、Sp O_2、HR、MOAA/S评分比较,差异无统计学意义(P>0.05)。与镇静前相比,两组患者RR、HR降低,MOAA/S升高,右美托咪定组患者实施镇静后各时间点的BIS、MOAA/S高于咪达唑仑组,低血压、心动过缓等不良反应的发生率低于咪达唑仑组,右美托咪定组患者自转入ICU至开始脱机的时间、脱机时间短于咪达唑仑组(P<0.05)。结论右美托咪定和咪达唑仑持续静脉泵注对ICU老年心脏手术患者术后持续机械通气具有良好的镇静效果,但在等效镇静水平下,右美托咪定脱机时间更短,不良反应发生率更低。

Nucleation Behavior Analysis of Intragranular Acicular Ferrite in a Ti-killed C-Mn Steel

By using a Gleeble 350013 thermo-mechanical simulator, the nucleation behavior of intragranular acicular ferrites （IAF） was studied in a Ti-killed C-Mn steel. During continuous cooling transformation, the allotriomorphic ferrite （AF） and ferrite side plate （FSP） microstructures grew more rapidly with the temperature decreasing from 800 to 650 ℃, and the IAF microstructure was dominant within austenite grain with further cooling to 600 ℃. The diffusion bonding experiment and the effect of C, Mn and Si concentrations on the Ao3 temperature by thermodynam- ic calculation confirm that Ti2O3 itself absorbs neighboring Mn atoms to form Mn-depleted zone （MDZ）, which pro- motes the nucleation of IAF microstructure effectively. High temperature holding tests indicate that the nucleation potential of IAF microstructure was lowered in the Ti-killed C-Mn steel when it was treated at high temperature （1250 ℃ ） for a longer time, which is attributed to the saturated absorption degree of Mn atoms by titanium oxide.

Interlayer engineering for titanium clad steel by hot roll bonding

Hot roll bonding was carried out between commercially pure titanium TA2 and high-strength low-alloy steel Q390 using pure Nb or Mo interlayer at 950 ~C with a total reduction ratio of 86.7%. Interfacial microstructure and bonding properties of titanium clad steel plates were investigated by electron microscopy and mechanical tests. The results showed β-Ti, TiC and Fe2Ti reaction phases were generated at Ti/steel interface for the clad plates with no interlayer. Inserting Nb or Mo interlayer can effectively suppress the formation of brittle phases, while the weak bonding joint transferred to Nb/steel or Mo/steel interface. And some micro-voids were found at the interface of Nb/steel and Mo/steel. The improved shear strength of clad plates with Nb interlayer might be attributed to the elimination of brittle phases at bonding interface. The small size and little quantities of the micro-voids at Nb/steel interface had a relatively weak effect on shear strength. However, the large number and big size of micro-voids were responsible for the degradation of shear strength for the clad plates with Mo interlayer.

Effects of Cu on Corrosion Resistance of Low Alloyed Steels in Acid Chloride Media

The corrosion resistance of two kinds of low alloyed steels was studied according to the test procedures for qualification of corrosion resistant steel for cargo oil tanks issued by International Maritime Organization. The results indicated that the addition of Cu improved the corrosion resistance of the NS-D36 steel to more than three times that of the conventional D36 steel in the strong acid solution containing chloride （10% NaC1, pHi0.85）. The anodic polarization behavior of the copper-bearing steel was studied by polarization curves and electrochemical impedance spectroscopy （EIS）, and alloying element Cu showed beneficial effects including an active potential range, low current density and high transfer resistance of electric charge. The rust layer was analyzed by scanning electron microscopy （SEM） and Auger electron spectroscopy （AES）, and the results pointed out that the mechanism of copper＇s benefi cial effects was based on the suppression of anodic dissolution by metallic copper re-deposition on the steel surface immersed in the strong acid chloride media.

Strengthening and toughening mechanism of a Cu-bearing high-strength low-alloy steel with refined tempered martensite/bainite(M/B)matrix and minor inter-critical ferrite

The microstructure–mechanical property relationship of a Cu-bearing low-carbon high-strength low-alloy steel,subjected to a novel multistage heat treatment including quenching(Q),lamellarization(L)and tempering(T),is presented.Yield strength of 989.5 MPa and average toughness at-80℃of 41 J were obtained in this steel after quenching and tempering(QT)heat treatments.Specimen QLT gained a little lower yield strength(982.5 MPa),but greatly enhanced average toughness at-80℃(137 J).To further clarify the strengthening and toughening mechanisms in specimen QLT,parameters of microstructural characteristic and crack propagation process were compared and analyzed for specimens Q,QL,QT and QLT.The microstructure of tempered martensite/bainite(M/B)in specimen QT changed to refined tempered M/B matrix mixed with minor IF(inter-critical ferrite)in specimen QLT.Cu-rich precipitates existed in tempered M/B for both specimens QT and QLT,as well as in IF.Compared with QT,adding a lamellarization step before tempering made the effective grains of specimen QLT refined and also led to coarser Cu-rich precipitates in tempered M/B matrix.The weaker strengthening effect of coarser Cu-rich precipitates should be a key reason for the slightly lower yield strength in specimen QLT than in specimen QT.No austenite was found in all specimens Q,QL,QT and QLT.Specimen QLT showed purely ductile fracture mode at-80℃due to the refined effective grains.The greatly improved toughness is mainly attributed to the enhanced energy of crack propagation.The combination of refined microstructure,softened matrix and deformation of minor'soft'IF during crack propagation led to the most superior toughness of specimen QLT among all specimens.

Hot roll bonding between commercially pure titanium and high-strength low-alloy steel using Fe interlayer

Hot roll bonding was carried out between commercially pure titanium TA2 and high-strength low-alloy steel Q390 using no interlayer and Fe interlayer at temperatures of 850,900,950 and 1000℃with a total reduction ratio of 86.7%.Interfacial microstructure and bonding property of clad plates were investigated by electron microscopy and shear test.The results showed that with the increase in heating temperature,the shear strength of titanium clad steel plates decreases obviously.Compared with that of titanium clad steel plates with no interlayer,inserting Fe interlayer between titanium and steel can improve the shear strength at 850 and 900℃but deteriorate the shear strength at 950 and 1000℃.The reason for this consequence was that Fe interlayer prevented the reaction diffusion of C in titanium to form a thinner TiC layer at 850 and 900℃,while Fe interlayer promoted the reaction diffusion of Fe in titanium to generate thicker Fe2Ti and FeTi intermetallic compound layers at 950 and 1000℃.

High Temperature Oxidation Resistance of 9Ni Steel

Oxidation rates and scale/steel interface configuration of 9Ni steels were investigated at 1000--1 250 ℃ in air. The results revealed that Cu addition caused high temperature oxidation resistance to deteriorate. High tempera ture oxidation rates increased and scale/steel interface configuration became complicated due to Cu addition. Scale/ steel interface appeared to be network above certain temperature. Temperature required to form network scale/steel interface dropped more than 100 ℃ for 1.5% Cu-containing steel. （Fe,Ni,Cu）x Oy in inner oxidation layer dissocia ted to Fe-Ni-Cu phase and released active oxygen which can react with base steel easily. So the inner oxidation layer became the second source of oxidizing agent besides atmosphere. Internal stress at austenite grain boundary caused local oxide to fragment. So the scale/steel interface appeared to be network. Liquid Si-rich phase formed at sufficient ly high temperature. Penetration of the liquid Si-rich phase along austenite grain enhanced austenite grain oxidizing.

Ni segregation and thermal stability of reversed austenite in a Fe–Ni alloy processed by QLT heat treatment

High-resolution transmission electron microscopy(HRTEM) and X-ray diffraction(XRD) were used to investigate Ni segregation and thermal stability of reversed austenite(RA) in a Fe–Ni alloy processed by quench–lamellarize–temper(QLT) heat treatment. The results show that the 77 K impact energy of the alloy increases with RA content increasing. As an austenite-stabilizing element, Ni is found to segregate in RA, though Ni is not evenly distributed within RA. The amount of segregations increases near the boundary(twice as high as the balanced content)and decreases to some extent in the center of the RA regions. Ni concentration in matrix near the boundary is lower than that in matrix far from the boundary because of Ni atom transportation from a to c near the boundary. RA in this alloy has high heat and mechanical stability but is likely to lose its stability and transform to martensite when a mechanical load is applied at ultralow temperatures(77 K), which induces plasticity.

Precipitation Behavior of V-N Microalloyed Steels during Normalizing

The precipitation behavior of V-N microalloyed steel during normalizing process was studied by physicochemical phase analysis and transmission electron microscopy（TEM）. The effect of precipitation behavior on mechanical properties was investigated by theoretical calculations. The results showed that 32.9% of V（C,N） precipitates remained undissolved in the austenite during the soaking step of the normalizing process. These precipitates prevented the growth of the austenite grains. During the subsequent cooling process, the dissolved V（C,N） re-precipitated and played a role in precipitation strengthening. The undissolved V（C,N） induced intragranular ferrite nucleation and refined the ferrite grains. Consequently, compared with hot-rolled steel, the normalized steel exhibited increased grain-refining strengthening but diminished precipitation strengthening, leading to an improvement of the impact energy at the expense of about 40 MPa yield strength.

Corrosion behavior of low alloy steel for cargo oil tank under upper deck conditions

A simulated corrosion test apparatus was used to investigate the corrosion behavior of a low alloy steel under simulated upper deck conditions in a cargo oil tank. The estimated corrosion loss of conventional E36 class ship plate steel is 4.27 mm, which is clearly inadequate compared with the standard adopted by International Maritime Organization. Outer rust layer of specimens starts to peel off after 77 days and becomes fragmented after 98 days. X-ray diffraction, scanning electron micros- copy, and Raman spectroscopy revealed that the resulting rust is composed of σ-FeOOH （the main protective phase）, Fe2O3, FeS, elemental S, and FeSO4. FeSO4 in the interface of the base and rust layer leads to localized corrosion. Elemental sulfur forms on the surface of σ-FeOOH, and the quantity and size thereof increase with increasing corrosion time. Furthermore, layered elemental sulfur promotes fracture and peels off the rust layer.

Effect of Cr on Characteristic of Rust Layer Formed on Low Alloy Steel in Flow-accelerated Corrosion Environment

The flow-accelerated corrosion experiments were carried out to research the effect of Cr on the rust layers formed on the carbon steel and Cr-containing steel,as well as the structure of rust layer of the two experimental steels.The influence of Cr on the flow-accelerated corrosion resistance and the corrosion morphology of inner rust layer formed on the Cr-containing steel were studied by the methods of polarization curves,scanning electron microscope,transmission electron microscope,and X-ray photoelectron spectroscope.The distribution of Cr and its form of existence in the inner rust layer were analyzed.The results show that corroded mass loss of Cr-containing steel is lower than that of carbon steel and its inner rust layer is compact.Cr exists in the form of Fe2CrO4 and is enriched in the inner rust layer.This concentration could make the inner rust layer exhibit the tendency of amorphous.This phenomenon is related to fine Fe2CrO4.The inner rust layer becomes more compact because of the formation of fine Fe2CrO4,and the protectiveness of inner rust layer could be improved remarkably.

Effect of Heat Input on Cleavage Crack Initiation of Simulated Coarse Grain Heat-affected Zone in Microalloyed Offshore Platform Steel

The combined effects of martensite-austenite（MA）constituent and pearlite colony on cleavage crack initiation in the simulated coarse-grained heat-affected zone（CGHAZ）of V-N-Ti microalloyed offshore platform steel under different heat inputs were investigated.The results of welding simulation,instrumented impact test,and quantitative analysis indicated that the size of the MA constituent decreased with the increase in cooling time,and by contrast,the size of the pearlite colony increased.According to Griffith theory,the critical sizes of cleavage microcracks were calculated.With the increase of cooling time,the calculated microcrack size could be characterized by the size of the MA constituent first,and then fitted with the size of the pearlite colony.Moreover,the calculated microcrack size variation was opposite to the microcrack initiation energy.This phenomenon is probably due to the combined effects of the MA constituent and pearlite colony with increasing the cooling time of the specimen′s temperature from800 to 500 ℃.

Effect of modifying matrix microstructures and nanosized precipitates on strengthening mechanisms and ductile-to-brittle-transitiontemperature in a 1000 MPa Ni-Cr-Mo-Cu steel

A superior combination of yield strength(1001 MPa)and-20℃ impact toughness(166 J)was obtained in Nb-V-Timicroalloyed Ni-Cr-Mo-Cu steel treated by direct quenching and tempering route(DQT).The tested steels treated by DQT route and re-austenitization and tempering route(QT)were compared with each other in terms of mechanical properties and microstructures characterized by optical microscopy,transmission electron microscopy,X-ray diffraction,electron back-scattered diffraction method and so on.Strength and Vickers hardness of the tested steel treated by the above two routes vary with isothermal aging temperature(400-600℃),shown as under-aged state,peak-aged state and overaged state.All DQT specimens show higher strength and Vickers hardness than QT specimens with the same aging condition.Furthermore,the largest difference of yield strength between DQT and QT specimens was shown in DQT600 and QT600 specimens.DQT600 or QT600 specimens refers to direct quenched(DQ)or quenched(Q)specimens isothermally aged at 600℃.The main disparities in quenched microstructure between DQ and Q specimens are mainly in morphology of prior austenite grains,dislocation density of martensite matrix and solution amount of Nb and Mo elements dissolving in martensite matrix,which play key roles in affecting microstructure and mechanical properties of DQT and QT specimens.Higher dislocation density of matrix and finer average diameter of both MC(M is any combination of Nb,Mo and V)and Cu-rich particles were shown in DQT600 specimens than in QT600 specimens.Strengthening from dislocations and nanosized MC and Cu-rich particles mainly leads to the largest difference of yield strength between DQT600 and QT600 specimens.In addition,strong dislocation strengthening and precipitation strengthening in DQT600 specimen also elevated its ductile-to-brittle-transition-temperature,compared with QT600 specimen.