800MPa级冷轧耐候双相钢连续冷却相变及组织性能研究

为了探索一种800 MPa级冷轧耐候双相钢的连续冷却转变规律及退火后组织性能变化,利用For-master-FⅡ全自动相变仪及连续退火模拟实验机,进行了连续冷却转变(CCT)曲线的测定及连续退火实验.结果表明:实验钢的过冷奥氏体在很低的冷却速度(0.5℃/s)下即可发生马氏体转变,而珠光体转变较少.当冷速为80℃/s时,仅发生马氏体转变;退火后实验钢显微组织中的马氏体呈带状分布,经最优工艺退火后实验钢的显微组织为多边形铁素体(79%)+块状马氏体(16%)+细小的残余奥氏体(5%),残余奥氏体主要分布于马氏体晶粒内部或铁素体的晶界处;实验钢屈服强度为387 MPa,抗拉强度为863 MPa,延伸率为18%,强塑积达到15534.     

高强汽车双相钢的连续退火与组织性能研究

目的 提升高强DP980双相钢的力学性能,优化连续退火工艺。方法 对高强汽车双相钢进行了连续退火处理,研究了连续退火均热温度、均热时间、过时效温度对冷轧双相钢显微组织、物相组织和力学性能的影响。结果 对于不同退火均热温度处理的双相钢,其组织均为铁素体(F)+马氏体(M),随着均热温度从715 ℃升高至865 ℃,残余奥氏体体积分数逐渐减小,抗拉强度、屈服强度先增后减,断后伸长率逐渐减小,在均热温度为815 ℃时,双相钢的抗拉强度和屈服强度达到最大值。随着均热时间从0.5 min延长至5 min,双相钢的晶粒尺寸逐渐增大,残余奥氏体体积分数先减后增,抗拉强度、屈服强度先增后减,断后伸长率先减后增,在均热时间为1.5 min时,抗拉强度和屈服强度达到最大值。随着过时效温度从245 ℃上升至395 ℃,双相钢中的马氏体体积分数逐渐减小,当过时效温度为395 ℃时,出现了贝氏体,奥氏体体积分数先增后减,抗拉强度、屈服强度逐渐减小,断后伸长率逐渐增大。结论 冷轧DP980双相钢适宜的连续退火工艺如下:均热温度为815 ℃、均热时间为3 min、过时效温度为295 ℃。此时双相钢具有较好的强塑性。     

含δ铁素体Mn-Al系TRIP钢冷轧退火过程的组织性能

研究了临界区退火温度和退火时间对含δ铁素体的Mn-Al系冷轧TRIP钢(Fe-0.18C-6.4Mn-2.8Al)的组织和性能演变行为的影响。结果表明,随着临界区退火温度的提高和退火时间的延长,实验钢的残余奥氏体(RA)含量和强塑积呈现先增大后减小的趋势。在750℃退火2 min实验钢的组织由δ铁素体、临界区铁素体及残余奥氏体组成,其RA含量为24.7%,抗拉强度为773 MPa,断后延伸率39.4%,强塑积为30.46 GPa·%。RA主要集中在粗大δ铁素体与原马氏体边界、原马氏体区域内再结晶铁素体晶界周围以及粗大δ铁素体内的亚晶界附近。     

奥氏体化温度对900 MPa级HSLA钢显微组织和晶体学演变的影响

采用OM和SEM研究了奥氏体化温度对HSLA钢组织演变和低温韧性的影响.结果 表明:奥氏体化温度由850℃升高至950℃(实验钢的AC3温度为819℃)并保温30 min后,奥氏体的平均晶粒尺寸由7.22 μm增大到17.39 μm,在850～950℃淬火后的显微组织均为板条马氏体,屈服强度和抗拉强度均呈下降趋势,延伸...     

Q&P工艺参数对34SiMn2CrNiMo钢组织和力学性能的影响EI北大核心

设计制备一种中碳合金钢34SiMn2CrNiMo,通过对淬火-配分(Q&P)热处理试样的显微组织表征和力学性能测试,建立工艺-组织-性能的关系,结合热膨胀相变行为研究结果,探讨淬火中止温度TQ、加热模式、配分温度TP和配分时间tP对组织演变的影响规律并进行强韧性机理分析。结果表明:实验钢经过Q&P处理后可以获得马氏体+残余奥氏体的复相组织,从而大幅提高强塑性。在最佳处理状态组织中残余奥氏体体积分数约为24%,屈服强度为1053 MPa,抗拉强度为1607 MPa,伸长率为24.9%,强塑积为40.0 GPa·%。为了避免生成块状二次马氏体,实验钢最佳淬火温度应位于马氏体相变开始温度Ms以下150℃左右。实验钢不完全淬火后缓慢加热比快速加热配分能获得更多的残余奥氏体,钢的塑韧性提高更明显。实验钢在400℃配分时Q&P组织和性能相对稳定,而在450℃配分时残余奥氏体体积分数随时间延长而减少,导致屈服强度和伸长率同步下降。     

退火处理对异种钢激光焊接头组织及性能的影响

目的 通过研究相同时间不同退火温度下304/Q345激光焊接头的组织和性能,得到优化后的退火处理制度,为制定异种钢激光焊退火工艺提供一定的理论指导和技术支撑。方法 基于前期大量试验,在激光功率和离焦量不变的情况下,调节焊接速度由15 mm/s到35 mm/s,通过改变焊接速度获得性能优异的焊接接头。由于异种钢物理化学性能差异较大,接头组织不均匀,因此还需对激光焊接头进行退火处理。结果 焊缝区显微组织由板条马氏体与残余奥氏体组成,Q345低碳钢热影响区显微组织为多面体状铁素体与黑色珠光体,其中铁素体含量更多,304奥氏体不锈钢热影响区在奥氏体晶界上析出了铁素体。不同退火温度下碳元素均由Q345低碳钢侧向焊缝迁移,在Q345低碳钢侧形成脱碳层,在焊缝中形成黑色条带状增碳层。随着退火处理温度的升高,峰值温度升高,高温停留时间变长,碳迁移强度随之增加,黑色条带状区域增碳层宽度增大。拉伸性能测试结果表明,试样均断裂于Q345母材一侧,且断口存在韧窝,属于典型韧性断裂。此外,焊缝区硬度(390HV左右)最高,热影响区硬度(300HV)次之,母材的硬度(130HV左右)最低。结论 在给定试验参数范围内,优化后的最佳退火工艺参数为550 ℃-1.5 h。     

低温临界区退火时间对22MnB5钢组织和性能的影响

为了研究22MnB5钢在退火过程中的组织演变规律,细化热冲压成形后马氏体板条束,通过扫描电镜(SEM)、能谱分析、电子背散射衍射(EBSD)分析技术和拉伸实验等方法,研究了不同低温临界区退火时间对22MnB5钢显微组织和力学性能的影响,并阐述了不均匀奥氏体在退火过程中的转变机制及合金元素对粒状珠光体形成的影响.研究表明,经低温临界区不同退火时间保温及随后等温处理后,得到不同的珠光体形态,在770℃保温0.5 h,并在700℃等温处理后,得到铁素体基体上分布颗粒状碳化物的粒状珠光体组织;随着临界区保温时间的延长,奥氏体转变逐渐均匀,使部分奥氏体在随后的等温过程中发生共析转变,得到多边形铁素体+片层状珠光体组织.粒状珠光体组织有利于细化淬火后的马氏体板条束,提高综合力学性能.     

304不锈钢在ECAP过程中形变诱发马氏体的定量计算

利用X射线衍射对经ECAP挤压及退火处理后的304奥氏体不锈钢进行了物相标定及各物相含量的定量计算.结果表明,经ECAP挤压后,不锈钢内明显形成α'和ε两种形变诱发马氏体,且α'马氏体含量高于ε马氏体含量.挤压后的不锈钢经退火处理后,α'马氏体含量显著下降,ε马氏体含量相对增加.奥氏体含量在第一道次挤压后明显下降,以后道次的挤压和退火处理对其影响较小.     

奥氏体化条件对675装甲钢中马氏体相变的影响

利用高分辨热膨胀仪,结合显微组织分析,研究了奥氏体化过程中奥氏体化加热温度和保温时间两个重要参数对675装甲钢快速冷却中马氏体相变的影响,包括原奥氏体晶粒尺寸、马氏体显微组织形态和马氏体相变点(Ms)。结果表明:奥氏体化温度对原奥氏体晶粒尺寸的影响程度远大于保温时间;奥氏体化过程中,675装甲钢中钒微合金碳化物(V4C3)在大约1000℃能全部溶入到奥氏体中,从而失去钉扎奥氏体晶界的作用,致使晶粒开始粗化;随原奥氏体晶粒尺寸增大,快速冷却得到的马氏体尺寸迅速增大,表现出对原奥氏体晶粒的组织遗传现象;马氏体相变点(Ms)受到奥氏体晶粒尺寸和钒微合金碳化物向奥氏体中溶解程度两个因素综合作用。     

奥氏体不锈钢晶粒细化对形变机制和力学性能的影响

利用相逆转变原理采用冷变形使得亚稳奥氏体转变为形变马氏体,采用不同温度和时间退火分别获得纳米晶/超细晶和粗晶奥氏体不锈钢。通过拉伸实验得到不同晶粒尺寸的奥氏体不锈钢力学性能,采用透射电镜观察形变组织结构并利用扫描电镜观察断口特征。结果表明:高屈服强度纳米晶/超细晶奥氏体不锈钢通过形变孪晶获得优良塑性;而低屈服强度的粗晶奥氏体不锈钢发生形变诱导马氏体效应,得到良好的塑性;两组具有不同形变机制的奥氏体不锈钢拉伸断口均为韧性断裂。形变机制由形变孪晶转变为形变诱导马氏体归因于晶粒细化导致奥氏体稳定性大幅度提高。     

Insertion of triangulated surfaces into a meccano tetrahedral discretization by means of mesh refinement and optimization procedures

In this paper, we present a new method for inserting several triangulated surfaces into an existing tetrahedral mesh generated by the meccano method. The result is a conformal mesh where each inserted surface is approximated by a set of faces of the final tetrahedral mesh. First, the tetrahedral mesh is refined around the inserted surfaces to capture their geometric features. Second, each immersed surface is approximated by a set of faces from the tetrahedral mesh. Third, following a novel approach, the nodes of the approximated surfaces are mapped to the corresponding immersed surface. Fourth, we untangle and smooth the mesh by optimizing a regularized shape distortion measure for tetrahedral elements in which we move all the nodes of the mesh, restricting the movement of the edge and surface nodes along the corresponding entity they belong to. The refining process allows approximating the immersed surface for any initial meccano tetrahedral mesh. Moreover, the proposed projection method avoids computational expensive geometric projections. Finally, the applied simultaneous untangling and smoothing process delivers a high‐quality mesh and ensures that the immersed surfaces are interpolated. Several examples are presented to assess the properties of the proposed method.     

Certification Institutions Expected to Update and Transfer Information on Present Standards

Standards are the basis for production enterprises to organize production, ex-factory inspection, trade (delivery) and technical exchanges, product certification, quality arbitration and supervision.……     

From Industry 4.0 to Research 4.0. Development of High Performance Fibers in the Light of Digitization

We associate a variety of innovations with the term ＂Industry 4.0＂. The pioneer of many 4.0 modifications forms the basisfor the trend towards the integrated di...     

Flow calorimeter for enthalpy increment measurements on condensed gases

A flow calorimeter for enthalpy increment measurements on condensed gases is presented. A better knowledge of the properties of the liquefied natural gas is needed, and therefore a liquid loop has been designed for our flow calorimeter. The fluid loop in the calorimeter is designed in order to avoid the two-phase region, since two phases would give compositional disturbances in the measurements. The avoidance of the two-phase region is made possible by increasing the pressure of the test fluid after the measurement section, then heating the fluid at super-critical pressure past the critical point. Finally, the fluid is throttled to the low-pressure gas state at the inlet condition of the compressor that circulates the fluid. To perform the pressure increase, a new cryogenic pump has been designed. To evaluate the new equipment, measurements were taken on liquid ethane over the temperature range 146–256 K at pressure between 0.9 and 5.1 MPa.     

Refrigerators Enter a New Era of Health Preservation Frestech initiates the establishment of China's first standard for household sterilization refrigerators

On November 30, 2007, the China Association for Standardization (CAS) held a press conference at Beijing Diaoyutai State Guest House. Leaders from the China Household Electric Appliance Research Institute, the China Household Electric Appliance Association, and the China Consumers' Association attended and made speeches.……     

Roman iron and steel: A review

ABSTRACT

The production of ferrous metal increased during the Roman Late Republican period, Principate and Empire. The direct bloomery process was used to extract the metal from its ores using slag-tapping and slag-pit furnaces. The fuel was charcoal and an air blast was introduced by bellows-operated tuyères. Iron formed as a bloom, often as a spongy mass of metal, which contained impurities from the smelting process, including unreacted ore, fuel, slag and fragments from the furnace walls, while the metal was often inhomogeneous with varied carbon contents. Blooms were either smithed directly into bars or ingots or they were broken up, which also allowed the removal of gross impurities and a selection of pieces with similar properties to be made. These could then be forge-welded together and formed into characteristically shaped ingots. Making steel in the furnace seems to have been achieved: it depended on the ore and the furnace and conditions within it. Surface carburization was also carried out. Iron and steel were used extensively in construction and for tools and weapons. Fire welding was often used to add pieces of steel to make the edges of tools and weapons, which could be heat-treated by quenching to harden them.     

Optimum-Simulation von Ernteprozessen

Zusammenfassung Bei der Gestaltung von Ernteprozessen — beispielsweise des Prozesses Mähdrusch, Körnertransport und -abnahme — als transportverbundene Fließarbeitsverfahren mit mindestens zwei verschiedenen Arbeitsmitteln gibt es einen großen Optimierungsspielraum. Solche Prozesse sind mehrstufige Bedienungsprozesse mit gemischter Anordnung der Bedienungseinrichtungen. Außerdem besitzen sie stark ausgeprägte räumliche Aspekte. Es wird vor allem gezeigt, welche Merkmale solcher Prozesse in Simulationsmodellen abgebildet sein müssen, welche Zielgrößen in Abhängigkeit von welchen Einflußgrößen unter Berücksichtigung welcher Prozeßbedingungen ermittelt werden sollten und wie der Bewertungsprozeß zur Ermittlung der gewünschten Informationen gestaltet werden muß.     

A study of centrifugal cast high boron high speed steel

In the present study a high‐boron high speed steel (HSS) roll material was designed. Many expensive alloy elements have been substituted by cheap boron alloy, and high‐boron high speed steel roll has been manufactured by centrifugal casting method. The microstructures, mechanical properties and wear resistance of centrifugal casting high‐boron high speed steel roll have been investigated by optical microscopy (OM), scanning electron microscopy (SEM), and X‐ray diffraction (XRD) analysis, hardness test, impact test and wear test. The results indicated that the solidification microstructures of high‐boron high speed steel roll consisted of M₂(B,C), (W,Mo)₂(B,C), M₃(B,C), M₂₃(B,C)₆ type borocarbides and martensite, a small amount of retained austenite. Borocarbides were continuously distributed over the grain boundary. After quenching from 1050 °C, local broken network appeared in partial borocarbides, and fine secondary borocarbide precipitated from the matrix. After tempering from 525 °C, the amount of precipitated borocarbide increased significantly. After heat treatment, the hardness of high‐boron high speed steel roll excelled 60 HRC, and its impact toughness excelled 8.0 J/cm². The single groove steel rolling amount of high‐boron high speed steel rolls increases by 500% than that of bainite cast iron roll, when the rolls are used in K₁ mill housing of bar mill.     

Thixotropy of Systems with Shear Thinning and Plastic Flow Behavior

The definition of the thixotropy is a decrease in viscosity with time in shear and a subsequent recovery of viscosity after the shear deformation is removed.We ...