Flow characteristics and hot workability of a typical low-alloy high-strength steel during multi-pass deformation

Heavy components of low-alloy high-strength(LAHS) steels are generally formed by multi-pass forging. It is necessary to explore the flow characteristics and hot workability of LAHS steels during the multi-pass forging process, which is beneficial to the formulation of actual processing parameters. In the study, the multi-pass hot compression experiments of a typical LAHS steel are carried out at a wide range of deformation temperatures and strain rates. It is found that the work hardening rate of the experimental material depends on deformation parameters and deformation passes, which is ascribed to the impacts of static and dynamic softening behaviors. A new model is established to describe the flow characteristics at various deformation passes. Compared to the classical Arrhenius model and modified Zerilli and Armstrong model, the newly proposed model shows higher prediction accuracy with a confidence level of 0.98565. Furthermore, the connection between power dissipation efficiency(PDE) and deformation parameters is revealed by analyzing the microstructures. The PDE cannot be utilized to reflect the efficiency of energy dissipation for microstructure evolution during the entire deformation process, but only to assess the efficiency of energy dissipation for microstructure evolution in a specific deformation parameter state.As a result, an integrated processing map is proposed to better study the hot workability of the LAHS steel, which considers the effects of instability factor(IF), PDE, and distribution and size of grains. The optimized processing parameters for the multi-pass deformation process are the deformation parameters of 1223–1318 K and 0.01–0.08 s^(-1). Complete dynamic recrystallization occurs within the optimized processing parameters with an average grain size of 18.36–42.3 μm. This study will guide the optimization of the forging process of heavy components.

Recent progress in visualization and digitization of coherent transformation structures and application in high-strength steel

High-strength steels are mainly composed of medium-or low-temperature microstructures,such as bainite or martensite,with coherent transformation characteristics.This type of microstructure has a high density of dislocations and fine crystallographic structural units,which ease the coordinated matching of high strength,toughness,and plasticity.Meanwhile,given its excellent welding perform-ance,high-strength steel has been widely used in major engineering constructions,such as pipelines,ships,and bridges.However,visual-ization and digitization of the effective units of these coherent transformation structures using traditional methods(optical microscopy and scanning electron microscopy)is difficult due to their complex morphology.Moreover,the establishment of quantitative relationships with macroscopic mechanical properties and key process parameters presents additional difficulty.This article reviews the latest progress in microstructural visualization and digitization of high-strength steel,with a focus on the application of crystallographic methods in the development of high-strength steel plates and welding.We obtained the crystallographic data(Euler angle)of the transformed microstruc-tures through electron back-scattering diffraction and combined them with the calculation of inverse transformation from bainite or martensite to austenite to determine the reconstruction of high-temperature parent austenite and orientation relationship(OR)during con-tinuous cooling transformation.Furthermore,visualization of crystallographic packets,blocks,and variants based on actual OR and digit-ization of various grain boundaries can be effectively completed to establish quantitative relationships with alloy composition and key process parameters,thereby providing reverse design guidance for the development of high-strength steel.

Deep decalcification of factory-provided freezing acidolysis solution to achieveα-high-strength gypsum

The freezing acidolysis solution of the nitric acid-phosphate fertilizer process has a high calcium content,which makes it difficult to produce fine phosphate and high water-soluble phosphate fertilizer products.Here,based on the potential crystallization principle of calcium sulfate in NH_(4)NO_(3)-H_(3)PO_(4)-H_(2)O,the deep decalcification(i.e.calcium removal)technology to achieveα-high-strength gypsum originated from freezing acidolysis-solutions has been firstly proposed and investigated.Typically,calcium can be removed from the factory-provided freezing acidolysis-solution by neutralizing it with ammonia,followed by the addition of ammonium sulfate solution.As a result,the formation of calcium sulfate in the reaction system undergoes the nucleation and growth of CaSO_(4)·2H_(2)O(DH),as well as its dissolution and crystallization into short columnarα-CaSO_(4)·0.5H_(2)O(α-HH).Remarkably,with the molar ratio of SO_(4)^(2-)/Ca^(2+)at 1.8,the degree of neutralization(NH_(3)/HNO_(3) molar ratio)at 1.7,the reaction temperature of 94℃,and the reaction time of 300 min,the decalcification rate can reach 86.89%,of which the high-strengthα-CaSO_(4)·0.5H_(2)O(α-HH)will be obtained.Noteworthy,the deep decalcification product meets the standards for the production of fine phosphates and highly water-soluble phosphate fertilizers.Consequently,the 2 h flexural strength ofα-HH is 5.3 MPa and the dry compressive strength is 36.8 MPa,which is up to the standard of commercialα-HH.

Study on Fracture Delay of High-Strength Bolts in Road Bridge Maintenance

In the maintenance work of highway and bridge engineering structures,the fracture delay of high-strength bolts is a content that needs to be focused on and researched.Based on this,the paper analyzes the fracture delay of high-strength bolts in highway bridge maintenance,including an overview of the fundamental research on fracture delay and related specific studies.It is hoped that this study can provide scientific reference for the reasonable maintenance of high-strength bolts,so as to ensure the overall maintenance effect of highway bridge projects.

Effect of traveling-wave magnetic field on dendrite growth of high-strength steel slab: Industrial trials and numerical simulation

The dendrite growth behavior of high-strength steel during slab continuous casting with a traveling-wave magnetic field was studied in this paper. The morphology of the solidification structure and composition distribution were analyzed. Results showed that the columnar crystals could deflect and break when the traveling-wave magnetic field had low current intensity. With the increase in current intensity, the secondary dendrite arm spacing and solute permeability decreased, and the columnar crystal transformed into an equiaxed crystal. The electromagnetic force caused by the traveling-wave magnetic field changed the temperature gradient and velocity magnitude and promoted the breaking and fusing of dendrites. Dendrite compactness and composition uniformity were arranged in descending order as follows:columnar-toequiaxed transition (high current intensity), columnar crystal zone (low current intensity), columnar-to-equiaxed transition (low current intensity), and equiaxed crystal zone (high current intensity). Verified numerical simulation results combined with the boundary layer theory of solidification front and dendrite breaking–fusing model revealed the dendrite deflection mechanism and growth process. When thermal stress is not considered, and no narrow segment can be found in the dendrite, the velocity magnitude on the solidification front of liquid steel can reach up to 0.041 m/s before the dendrites break.

Hot deformation behavior of novel high-strength Mg-0.6Mn-0.5Al-0.5Zn-0.4Ca alloy

The hot compression behavior of as-extruded Mg-0.6Mn-0.5Al-0.5Zn-0.4Ca alloy was studied on a Gleeble-3500 thermal simulation machine.Experiments were conducted at temperatures ranging from 523 to 673 K and strain rates ranging from 0.001 to 1 s^(-1).Results showed that an increase in the strain rate or a decrease in deformation temperature led to an increase in true stress.The constitutive equation and processing maps of the alloy were obtained and analyzed.The influence of deformation temperatures and strain rates on microstructural evolution and texture was studied with the assistance of electron backscatter diffraction(EBSD).The as-extruded alloy exhibited a bimodal structure that consisted of deformed coarse grains and fine equiaxed recrystallized structures(approximately 1.57μm).The EBSD results of deformed alloy samples revealed that the recrystallization degree and average grain size increased as the deformation temperature increased.By contrast,dislocation density and texture intensity decreased.Compressive texture weakened with the increase in the deformation temperature at the strain rate of 0.01 s-1.Most grains with{0001}planes tilted away from the compression direction(CD)gradually.In addition,when the strain rate decreased,the recrystallization degree and average grain size increased.Meanwhile,the dislocation density decreased.Texture appeared to be insensitive to the strain rate.These findings provide valuable insights into the hot compression behavior,microstructural evolution,and texture changes in the Mg-0.6Mn-0.5Al-0.5Zn-0.4Ca alloy,contributing to the understanding of its processing-microstructure-property relationships.

Development of high-strength magnesium alloys with excellent ignition-proof performance based on the oxidation and ignition mechanisms: A review

High reactivity and ease of ignition are the major obstacles for the application of Mg alloys in aerospace.Thus,the ignition mechanisms of Mg alloys should be investigated systematically,which can guide the ignition-proof alloy design.This article concludes the factors influencing the ignition resistance of Mg alloys from oxide film and substrate microstructure,and also the mechanisms of alloying elements improving the ignition resistance.The low strength is another reason restricting the development of Mg alloys.Therefore,at the last section,Mg alloys with the combination of high strength and good ignition-proof performance are summarized,including Mg-Al-Ca based alloys,SEN(Mg-Al-Zn-Ca-Y)alloys as well as Mg-Y and Mg-Gd based alloys.Besides,the shortages and the future focus of theses alloys are also reviewed.The aim of this article is to promote the understanding of oxidation and ignition mechanisms of Mg alloys and to provide reference for the development of Mg alloys with high strength and excellent ignition-proof performance at the same time.

ZK60 based alloys with high-strength and high-ductility:A review

Wrought magnesium alloys with high-strength and high-ductility property have been attracting more and more interest in automotive and aerospace industries,and the conventional Mg-Zn based alloys are widely accepted as the representative one.Development of Mg-Zn based alloys with rare earth(RE)element additions and with modified preparation processes domains the evolution of their potential structural applications.Nonetheless,their highest tensile yield strength(TYS)is still in the order of 400 MPa,clearly lower than that of the Mg-RE based alloys,in the order of 500 MPa,much less compared with the high-strength aluminum alloys and titanium alloys.According to many previous investigations,two relatively efficient methods to improve mechanical properties of ZK based alloys were revealed as:alloying by RE and optimizing wrought processes.However,comprehensive combinative investigation was hitherto not conducted to date.Thus,it is imperative in the next work to further improve the yield strength to the order of 500 MPa or much higher,and simultaneously modify the tension-compression strength asymmetry of the ZK series alloys.Maybe,developing novel wrought processes for ZK60(+RE)alloys or exploring appropriate pre-dealing treatments before or after the wrought processes might be an important approach to accomplish a much higher level of balance of high-strength and high-ductility.

Packer同径止水技术在彬长矿区多含水层分层抽水试验中的应用

彬长矿区含水层厚度大,矿井防治水难度高,为准确获取地下水的水力学参数、水文地质条件,需对煤层上方各含水层进行分层抽水试验。传统的异径套管分层止水方法操作难度大,扩孔费用高,止水效果一般。为准确获取不同层位含水层水力学参数,彬长矿区引入Packer同径止水技术代替传统异径套管分层止水方法进行分层抽水试验,有效的解决了传统钻孔抽水试验中分层抽水止水难题。研究表明:采用Packer系统可轻松实现在第四系松散岩类及洛河组含水层钻孔中同径止水,具有实施过程简化、安全、高效、便捷的优点,并且可以检查止水效果,能够更加准确有效地获取各含水层的水文地质参数。

Microstructure Distribution Characteristics of High-Strength Aluminum Alloy Thin-Walled Tubes during Multi-Passes Hot Power Backward Spinning Process

The microstructure of the thin-walled tubes with high-strength aluminum alloy determines their final forming quality and performance. This type of tube can be manufactured by multi-pass hot power backward spinning process as it can eliminate casting defects, refine microstructure and improve the plasticity of the tube. To analyze the microstructure distribution characteristics of the tube during the spinning process, a 3D coupled thermo-mechanical FE model coupled with the microstructure evolution model of the process was established under the ABAQUS environment. The microstructure evolution characteristics and laws of the tube for the whole spinning process were analyzed. The results show that the dynamic recrystallization is mainly produced in the spinning deformation zone and root area of the tube. In the first pass, the dynamic recrystallization phenomenon is not obvious in the tube. With the pass increasing, the trend of dynamic recrystallization volume percentage gradually increases and extends from the outer surface of the tube to the inner surface. The fine-grained area shows the states of concentration, dispersion, and re-concentration as the pass number increases. .

基于双重介质渗流-应力耦合模型的高压压水试验渗透参数反演

高压压水试验过程中岩体易发生水力劈裂产生裂隙,岩体内部孔隙、裂隙双重导水,渗流场和应力场相互作用,导致岩体渗透参数的时空变异性。基于高压压水试验反演渗透参数需考虑双重介质渗流-应力耦合作用下产生裂隙前后渗透系数的变化规律,利用渗流-应力耦合数值模型结合工程现场高压压水试验数据进行参数反演,计算得到不同压力阶段下灰岩岩体渗透率。主要结论如下:发生水力劈裂前,随着注液压力的增大,渗透率及孔隙水压力在不同压力阶段之间分界明显,渗透率反演值与规程公式计算值相近;发生水力劈裂后,岩体渗透率增大约2倍,孔隙介质渗透率和通过的流量出现陡减现象。

一种新型钾基磷酸盐无固相高密度封隔液

高温高密度封隔液是高温高压井完井关键技术之一,目前密度超过1.60 g/cm 3无固相盐水封隔液只有溴盐、锌盐或者甲酸铯溶液,溴盐毒性大,锌盐高温腐蚀性难以控制,而甲酸铯价格昂贵,难以满足高温高压井完井技术要求,开发针对高温高压井的新型无固相高密度清洁盐水封隔液势在必行。以磷酸三钾TKP为主剂并添加其他处理剂优化而成可溶性盐SW4,研发了一种新型钾基磷酸盐无固相高密度封隔液,测试了其密度调节能力、水溶液的流变性和流变模式、金属腐蚀性、高温稳定性、生物毒性等性能。结果表明,SW4封隔液常温条件下最大密度可达1.90 g/cm 3;随密度增大,其水溶液黏度上升,其流变模式为牛顿流体;密度1.85 g/cm 3的封隔液在150℃、7 d条件下对A3钢、N80钢、TN110Cr13S和TN110Cr13M钢的腐蚀速率均小于0.076 mm/a,N80钢在1.80 g/cm 3 SW4封隔液中的腐蚀性明显低于同等条件下的溴化钠、溴化钙和溴化锌,与甲酸铯相当;在同等加量条件下,SW4能够提供更多的K+,具有更优异的防膨性;高温稳定性强,能够满足高温高压井完井工况需求;生物毒性低,具有环境可接受性,可以满足作为无固相高密度封隔液加重剂的技术要求。

连续管磨损对防喷盒胶筒密封性能的影响

为研究连续管磨损对防喷盒胶筒密封性能的影响,归纳连续管常见磨损形式并构建其磨损几何模型,以通径为38.1 mm防喷盒胶筒为例,通过实验得到其材料本构模型参数,建立防喷盒胶筒密封连续管的有限元模型;以有效接触应力和最大Mises应力为指标,分析连续管的磨损形式、磨损深度、磨损长度以及偏磨角度对胶筒密封性能的影响。结果表明:连续管偏磨形式对胶筒密封性能影响较大,连续管偏磨段长度大于胶筒高度且偏磨深度大于1 mm时,胶筒密封能力会出现不能满足井口密封要求的情况;偏磨角度会影响胶筒的应力分布,从而影响密封性能。

注氮气机抽防腐防垢一体化管柱的研制与应用

针对塔河油田注氮气机抽井井筒及井下工具严重腐蚀结垢,易造成抽油泵卡泵、封隔器解封困难等井下故障的问题,在现有技术的基础上,优化改进结构、技术创新,研制了一种注氮气防腐防垢机抽一体化管柱。该管柱包括注气防垢杆式泵、防腐封隔器等关键工具,注气防垢杆式泵优化改进了柱塞和泵筒的结构,泵筒上部设计注气孔、下部设计封堵筒,柱塞下部设计密封堵头,注气时柱塞下部堵头将进油通道密封,能防止高压油液倒灌进入泵腔发生腐蚀结垢,消除柱塞下放失败的风险;防腐封隔器采用新型护肩式的胶筒组件及双“O”型圈、双向支撑密封结构、分级解封机构和分体式双向卡瓦锚定结构,提高封隔器胶筒的耐腐蚀性能、降低上提解封力和保证卡瓦锚定性能。经过理论校核和室内模拟试验均满足现场需求,现场应用表明,该管柱坐封、解封及注气均正常,转采成功率100%,满足开发需求,解决了注气腐蚀结垢卡泵和封隔器解封困难的工程难题,具有很高的推广价值。

深水测试密闭环空压力变化下的封隔器胶筒性能分析

为探讨深水测试双封隔器由密闭环空压力变化引起的变形与强度问题,建立双封隔器胶筒结构的力学分析模型。根据工作过程中封隔器间密闭环空压力的变化,对胶筒的密封性能进行分析,得到各胶筒的应变量、等效应力以及接触应力的变化情况。分析采用胶筒不同圆形倒角参数时封隔器胶筒与套管的接触特性,研究胶筒倒角参数对封隔器密封性能的影响,得出封隔器的优化结构参数。结果显示:各胶筒的应变量、等效应力以及接触应力均随密闭环空压力的增大而增大,其中下胶筒的增大幅度最明显;各胶筒变形量随着胶筒倒角的增大无明显变化,但等效应力随着胶筒倒角的增大均减小,而随着胶筒倒角的增大上胶筒和中胶筒的接触应力均增大,下胶筒的接触应力先增大后减小。因此,一定程度上增大胶筒倒角有利于提升封隔器的密封性能,倒角半径为0.75 mm时为最优结构。

双封隔取样压力数据深入解释方法研究

双封隔器是一种地层测试测压取样工具,取样过程通常需要泵抽几小时甚至十几小时,取得地层流体样品,获得压力和流量数据,但无法真实反映地层渗透率的探测范围。利用油藏模拟软件模拟双封隔器泵抽取样过程,引入Schroeter算法和Levitan算法这两种压力/流量数据反褶积算法,反演渗透率参数波及半径从几厘米到上百米,并使用数值模拟案例验证了只利用取样完成后的压力恢复数据进行反褶积方法的准确性和合理性。该研究应用于双封隔现场测井数据,采用反褶积方法得到渗透率探测半径31m,反褶积处理后的数据可用于产能预测,对正确认识油气藏具有重要意义。

W形密封结构金属封隔器性能研究

针对橡胶封隔器难以适应150℃、70 MPa以上环境的缺点,设计一种适用于230℃、70 MPa工况,两端传递载荷,中间中空促进径向变形的W形密封结构的金属封隔器,并研究其密封性能。根据工况需求,以温度依赖性和超弹性激发应力选择β-NiTi合金作为W形密封结构材料,以W形结构坐封后产生的接触应力评价其密封性能,以工作承压后W形结构的弹性-超弹性应变率评价其解封性能,分析W形密封结构半径、壁厚及壁厚比对其密封性能的影响,并对设计优化后的W形结构进行密封性能仿真分析。结果表明:结构半径对W形密封结构的密封性能和解封性能影响较小,而壁厚与壁厚比均显著影响密封性能和解封性能;随着壁厚的增加,W形密封结构的密封性能逐渐下降但解封性能逐渐上升,随着壁厚比的增加,密封性能逐渐下降解封性能先上升后下降。对设计优化后的W形结构进行密封性能仿真分析,结果表明,基于β-NiTi合金材料的W形密封结构金属封隔器完全可以适用于高温高压环境,其在230℃、70 MPa的工况下坐封载荷为220 kN,弹性-超弹性应变率达90%以上。

分体式自适应分支井主井眼支撑系统研制

分支井主井眼支撑工具是满足分支井窗口支撑与分支井眼钻井的核心工具,包括可回收式斜向器、打捞钩、定向锚定封隔器及定向插头等。针对常用配套工具存在的锚定性能差、地面定向难度大、斜向器可取性差等问题,研发了分体式自适应分支井主井眼支撑系统。该系统以大通径锚定封隔器作为井下定位单元,具备轴向及周向锚定功能,可取式钻井导向器可在井下实现自动找正对接,从而建立牢固的窗口支撑系统,配套打捞钩具备定向打捞功能;该系统也可为后期井眼选择性重入及生产提供大通径机械通道。对主井眼窗口支撑系统关键部件进行了有限元分析,并对支撑系统的锚定、抗扭及自动对接等性能进行了测试。分析及测试结果表明:大通径锚定封隔器双向锚定能力1200 kN,环空封隔能力80 MPa;钩式打捞器可实现导向器的定向锁定。所得结果可为分支井设计及工具选择提供参考。

高温高压高产气体封隔器卡瓦力学行为的分析与实验

为了提高海上“三高”气井管柱的安全性,确保卡瓦良好的工作性能,以HPC070401封隔器双向筒式卡瓦为例,将滑移线理论法、数值模拟和实验法相结合,研究卡瓦咬入过程的力学行为,分析卡瓦与套管的接触应力分布规律、卡瓦牙咬入套管的深度和疲劳寿命,建立了封隔器卡瓦系统工作可靠的充分必要准则。研究结果表明:坐卡压力增加,卡瓦牙咬入套管的深度也随之增加,在坐卡压力为35、42、48、55 MPa时,卡瓦咬入套管深度为0.25993、0.29425、0.32353、0.36561 mm;坐卡压力增加,卡瓦牙尖局部塑性变形增大,在坐卡压力35、42、48、55 MPa下,对称循环波动20%时,卡瓦疲劳循环次数为951110、789540、717160、629260;通过高温高压封隔器卡瓦锚定实验,卡瓦咬入套管的实测深度介于0.350~1 mm之间,与有限元模拟结果较吻合;结合评价准则和高温高压封隔器疲劳实验可知,套管因疲劳累积损伤产生的应力松驰系数为0.18。

气体封隔器密封单元的增强方法与安全分析

气体封隔器胶筒是实现气井分层分段开采的关键部件。常规三胶筒结构在坐封时易发生初始破坏,导致胶筒整体应力水平降低,密封安全性储备不足。为此,提出一种多材料组合式密封单元的增强方法,用于HPHT105-232-V0型含硫化氢高温高压气体封隔器密封单元的设计;基于拉伸试验和Yeoh理论获得橡胶的本构模型参数;在温度204℃、坐封力200 kN和环空压力70 MPa下,分析了胶筒的应力和变形规律;试验测试了增强单元的密封安全性。分析结果表明:HPHT105-232-V0型封隔器密封单元胶筒的最大变形量为94.785 mm,最大接触应力为240 MPa,位于金属护环与套管接触区域。根据API标准,对HPHT105-232-V0型封隔器实物进行测试试验,坐封时胶筒未发生初始破坏,密封单元的整体应力水平提高;稳压过程胶筒压降幅度小于1%;整个试验测试过程中,密封单元无气泡溢出,封隔器卸载后胶筒结构无明显的塑性变形。研究结果表明,采用该增强方法所设计的多材料组合式密封单元具有良好的密封性能,满足极端环境下的密封安全性要求。