新型H380级别高强度钢轨热处理工艺的数值模拟

通过计算机数值模拟计算对H380级别热处理钢轨的淬火过程进行了分析。钢轨热处理过程是一种鉴于等温转变与连续冷却转变之间的"连续等温转变过程"。计算表明:对于H380级别热处理钢轨温降控制在200～250℃,钢轨轨头相变温度不应超过620℃,轨头抗拉强度取样位置处珠光体组织相变温度不应超过650℃,相变孕育期为22～30 s,在此段加强冷却强度,降低珠光体组织相变开始温度。有利于钢轨轨头淬硬层的深化,提高该级别热处理钢轨抗拉强度。     

The End-Quench as a Screening Tool for Controlled Cooling of Hot-Rolled Plates of Potential Premium Rail Compositions

Abstract

Current alloy premium rail chemistries have a relatively high hardenability which leads to welding problems. However, premium rails with a hardness of ～Rc 38 are necessary in Canada because the high wear rate of standard C- Mn rails is inadequate on curved track under heavy duty conditions. In the present work, potential premium rail steels combining a hardness of Rc 38, a pearlitic microstructure, and acceptable weldability, were screened by end-quench experiments. Thus, 51 eutectoid, mainly lean-alloy steel compositions were evaluated, the results from which enabled a few compositions to be selected that gave a desirable combination of properties, at cooling rates between ～105 and ～180°C min ^?1 at 705°C. One-inch (25.4-mm) thick, hot-rolled plates of these compositions were then cooled, after rolling, at similar rates and their microstructures and mechanical properties determined. The results showed that cooling rates necessary to produce Rc 38 pearlite in the plates were comparable with those indicated by end-quench experiments. The plates had good tensile properties and an impact toughness similar to or better than that of current alloy rails.

Résumé

Les rails, de qualité supérieure, en alliages couramment employés, ont des propriétés de trempe assez élevées. Cela cause des problèmes pour la soudure. Cependant, au Canada, il est nécessaire que les rails de qualité supérieure aient une dureté de ～ Rc38, car les rails communs C-Mn qui ont un taux d'usure élevé, sont inadéquats sur les voies courbées sous des conditions rigoureuses. Dans ce travail, des aciers pouvant produire des rails de qualité supérieure, et qui combinent une dureté de Rc38, une microstructure perlitique et une soudabilité acceptable, ont été evalués par des essais de trempe des extrémités. Cinquante et un eutectoïdes, surtout d'aciers d'alliages pauvres, ont été évalués. Les résultats ont permis de choisir quelques compositions qui donnaient des propriétés désirables, à des taux de refroidissement entre 105 et 180°C min^?1 à 705°C. Des plaques de ces compositions choisies, laminées à chaud à une épaisseur d'un pouce (25.4 mm) on été refroidies à des taux similaires, et leurs microstructures et propriétés mécaniques ont ete determinées. Les résultats ont démontré que des taux de refroidissement necessaires pour produire une microstructure perlitique avec une dureté de Rc38 étaient com parables à ceux indiqués par les essais de trempe des extrémités. Les plaques avaient de bonne résistance à la traction et une tenacité d'impact équivalente ou même supérieure à celle des rails en alliages couramment employés.     

Improved Cold Formability by Thermo‐Mechanical Rod Rolling

Usually, unalloyed medium carbon steels and 1% chromium steels for cold heading applications are produced by hot rolling, subsequent controlled cooling and soft annealing. It is shown that by thermomechanical rod rolling and slow air cooling at the loop cooling conveyor the tensile strength can be lowered to such an extent so that cost‐intensive soft annealing procedures are not required. The effects of the processing parameters on the microstructural evolution and final mechanical properties of steel grades 23MnB4 and 1% Cr‐steels like 32CrB4, 37Cr4 and 41 Cr4 are tested by a Gleeble machine. Using a microstructural process model, called CAROD, the entire rolling and cooling process has been optimized.     

Improvements in the Characteristics of Nodular Graphite Cast Iron for Crankshafts

This study deals with spheroidal graphite cast iron metallurgy for the mass production of engine crankshafts. Pieces have been made in three different grades under industrial conditions. CCT diagrams and micrographs show that it is possible to remove the undesirable “bull's eye” ferrite from the matrix as well as to improve the mechanical properties of series parts by only altering the chemical composition. A 100% pearlitic matrix and up to a 14% increase in the tensile strength have been obtained by lowering the amount of silicon and increasing the share of pearlitizing elements such as copper and manganese without altering the cooling speed of the parts. The effect of the cooling speed on the matrix microstructure and the mechanical features has also been revealed. For an “improved” grade, the matrix is 100% pearlitic, its hardness is about 390Hv30kg for a cooling speed of around 150°C/min.     

Development of Dual Phase and Multiphase High Strength Steels by Using a New Cooling Technology: The Howaq‐Twice Process

In order to develop low alloy dual and multiphase high strength steels, CRM and Arcelor implemented the Howaq‐twice process in a continuous annealing line. This new equipment combines a slow primary cooling with a fast secondary cooling. Various cooling strategies were investigated in regard to microstructure and mechanical properties of low alloyed steels. Depending on the cooling rate and the quenching temperature, the microstructure varied between fully martensitic, ferritic‐martensitic, and ferritic‐martensitic‐bainitic. The associated tensile strengths reached from 720 to 1100 MPa.     

Calculation of temperature and heat flux in quenched cylinders for different wetting processes

The cooling of pieces being quenched in evapourable fluids is mainly determined by the process of wetting, which is defined as the sequence of the three known cooling stages film boiling, nucleate boiling and convective heat transfer. All these determine the properties of the finished product. The effect of different wetting processes and heat transfer coefficients on the time-dependent distribution of temperature and heat flux in quenched cylinders was examined using numerical methods. Only transformation-free quenching was considered. When the three cooling stages simultaneouly take place on the sample's surface the radial heat fluxes are superimposed by high axial heat fluxes, which could not be pointed out experimentally before. The consequences may be great axial differences of structure and hardness, especially for steels with low hardenability, as well as residual stresses. The axial temperature gradients can be reduced by producing high wetting velocities. An optimum wetting process involves a very fast breakdown of the vapour envelope on the whole surface of the quenched piece.     

百米U75V钢轨矫直前冷却过程温度场的有限元分析

通过研究U75V钢轨冷却过程的热边界条件,采用三维瞬态非线性有限元法计算了百米钢轨矫直前845～150℃冷却过程的温度场。结果表明,在冷却过程中的钢轨横截面不同位置的温度下降速率不同,在冷却初期(200～2 000s),每条冷却温度线都出现一个温度降低缓和的"平台"阶段,如轨底边部冷却速度最快,开始相变时间最早;在冷却2 500～3 000s时,轨头、轨腰、轨底中心的温度迅速下降,轨头与轨底边部的温差约5℃,在冷却5 000～7 000s时,各部位温差趋于一致;计算温度值和现场实测值差别小于50℃。     

The Increasing Demands on the Serviceability of Rail Steels

Abstract

Increasing freight car weight, an unbroken upward trend for the past 20 years, has placed new and severe demands on railway rails. The recent performance and metallurgy of carbon steel rails are reviewed, and projections of its future behaviour are made using the Canadian Institute for Guided Ground Transport (CIGGT) wear and AAR fatigue models.

The metallurgical development and performance of improved fine pearlitic heat-treated and alloy rail steels are discussed in respect to their comparative behavior on heavy-haul Canadian and Australian mining railroads with general North American Freight Service.

The metallurgist engaged in the development of rail steels will therefore be presented with a set of goals and requirements for the direction of his work.

Résumé

Le poids augmente des wagons de marchandises a la hausse depuis 20 ans, fait les exigencies nouvelles et rigoureuses sur les rails du voies ferreés. Le comportement recente et la metallurgie des rails en acier au carbone sont passe en revue, et des previsions des possibilites de ce materiau sont faites, d'apres un modele de l'usure propose par le Canadian Institute for Guided Ground Transport (CIGGT) et un modele de la fatigue propose par l'AAR.

Le developpement metallurgique et le comportement des aciers a rail traites thermiquement, ou d'alliage, a perlite fine, sont discutes afin de comparer leur comportement sous les poids lourds des routes ferroviaires des compagnies minieres Canadiennes et Australiennes, et dans le service normal de fret en Amerique du Nord.

Nous presentons donc, au metallurgiste qui travaille dans le developpement des aciers a rail, des buts et des exigences pour diriger ses travaux.     

20CrMoA抽油杆杆头板手方部校直断裂原因分析

20CrMoA抽油杆头板手方部在校直过程中发生断裂,通过对断口进行宏观和微观分析,结果表明原材料中的气泡缺陷所造成的微小孔洞和材料本身非金属夹杂物含量高导致抽油杆在锻造时开裂并在随后的校直过程中断裂。     

冷却系统在铜炉渣缓冷工艺中的应用

介绍了铜炉渣的缓冷工艺特点、影响因素及缓冷效果的衡量标准;简述了冷却系统的工艺流程和工作原理;描述了冷却塔的工作机理、结构组成和在冷却系统中的作用;通过对冷却系统扩建前后炉渣缓冷效果进行的对比实验,进一步论证了冷却系统对炉渣缓冷及浮选指标的影响     

XRD Analysis of Local Strain Fields in Pearlitic Steels ‐ towards the Fast Examination of Microstructure after Hot Rolling

Analysis of the crystallographic anisotropy of the lattice strains, i.e. the analysis of the dependence of the lattice strain on the crystallographic direction, is discussed to be an efficient method for getting information about the mesoscopic local strains and microscopic local strain fields in dual‐phase materials. This technique is illustrated on the example of hot‐rolled pearlitic steels containing ferritic lamellae separated by cementite from each other. In these samples, the information about the local strain fields was further used to build a microstructure model that describes the interaction between crystallites of different phases on the microscopic scale. Such a microstructure model is quite appropriate for examination of the correlations between the structure and properties of the pearlitic steels, because it links the microstructure parameters obtained using X‐ray diffraction on the atomic level with the interaction between the crystallites or grains of different phases, which can more directly be related to the macroscopic mechanical properties of the materials. The second important result of this study was the detection and explanation of several correlations between individual microstructure parameters, which are obtained from X‐ray diffraction. This offers a possibility to use the X‐ray diffraction for a fast microstructure analysis of pearlitic steels, or generally for a fast microstructure analysis of dual‐phase steels, after or even during the rolling processes.     

低温钢筋穿水冷却工艺

 根据低温钢筋穿水冷却工艺特点,利用现场实测数据并结合理论分析得到不同规格低温钢筋穿水冷却过程中的对流换热系数。采用MSC Marc有限元软件与现场试制结果对低温钢筋穿水冷却过程进行了研究。研究了冷却水流量、终轧温度、穿水时间等工艺参数对低温钢筋温度场和组织演变的影响。模拟结果表明：当冷却水流量为120 m3/h时,钢筋芯部开始有珠光体转变;当冷却水流量为400 m3/h时,钢筋芯部无铁素体转变;冷却水流量为160～200 m3/h时,所获得的组织为针状铁素体与贝氏体。终轧温度增加50 ℃,出水冷装置后钢筋表面温度约增加10 ℃,返红温度约增加30 ℃;在200 m3/h水流量下冷却1.2 s,终轧温度为1 050 ℃时,其芯部组织为针状铁素体与细小的贝氏体。在相同水压与水流量条件下,随着穿水速度的增加,淬透层深度减小,返红温度增加。     

Induction Hardening of Spur Gearwheels Made from 42CrMo4 Hardening and Tempering Steel by Employing Spray Cooling

As a rule, induction surface hardening is carried out industrially by employing polymer solutions since these ensure a more homogeneous quench than immersion cooling in water. Besides reproducing the quenching process, the intention here is to minimise the hardening defects and the distortions arising from the heat treatment. Polymer solutions also have a few disadvantages which include, among others, poor environmental compatibility and handleability. Quenching by means of spray cooling provides an effective alternative. The purpose of the current investigation is to substitute the polymer solution by a water‐air spray in induction hardening equipment for surface hardening spur gearwheels made of 42CrMo4 hardening and tempering steel. The suitability of spray cooling was assessed by means of hardness measurements, residual stress conditions, distortion measurements and by metallographic examinations. Based on the analyses currently carried out, it was possible to show that the two‐phase spray cooling represents an alternative quenching method which produces comparable component properties.     

Influence of stresses on the kinetics of pearlitic transformation during continuous cooling

The effect of stress/strain on the kinetics of pearlitic transformation is reviewed. Our results on the pearlitic transformation of an eutectoïd carbon steel under applied uniaxial tensile stresses are analyzed. From these results, we have modelized the effect of the internal stresses, generated during cooling in a solid specimen, on the transformation kinetics. This model is based on a shifting in time of the IT curves of the steel as a function of the internal stress condition (deviatoric part of the stress tensor). A coupled thermal, phase transformation, stress calculation, which includes this model, is applied to the cooling of an eutectoïd carbon steel cylinder. The calculated results show that the internal stresses have an important effect on the kinetics of transforamtion and on the temperature evolutions. The calculated cooling laws are compared with those obtained by experiment and the validity of the model is discussed.     

用循环阳极极化曲线评价Al6061/SiCP复合材料表面稀土转化膜耐腐蚀性能的研究

本文提出了利用循环阳极极化曲线研究转化膜耐腐蚀性能的方法。介绍了 Al60 61 /Si CP复合材料表面稀土转化膜工艺。将稀土转化膜与其它转化膜的耐腐性能进行了比较。利用循环阳极极化曲线的“相对环面积”研究转化膜耐腐蚀性能能够得出很好的规律性。     

Modelling the Temperature Distribution along the Length of Strip during Hot Rolling Process

Hot strip rolling process includes four main stages, which are reheating process, roughing and finishing process, laminar‐cooling process, and coiling process respectively. Temperature is the most sensitive parameter and has direct effect on the microstructural evolution and further the mechanical properties, and the accurate control of temperature guarantees the quality of products and homogeneity of properties along the strip length. However, for the conventional hot strip rolling process, thermal history along the strip length is very complex, the related temperature variation concerns air cooling, water cooling, heat transmission by roll contact, heat generation by deformation and friction. Based on the actual hot strip mill, the thermal models are established in this paper to simulate the temperature distribution along the whole strip length from the reheating furnace exit to the down coiler. Different interface heat transmission coefficients are selected for the scale breaking and spray water‐cooling process, and a self‐learning algorithm is thus employed to improve the calculation accuracy. This model is characterized as simple and fast, and convenient for on‐line/off‐line prediction of temperature. Finally the simulated results are verified by the on‐line temperature detection at typical points such as roughing exit (RT2), finishing exit (FT7) and coiling position (CT).     

一种Fe-C-Si-Mn-Cr-Mo钢碳配分行为对组织的影响

 利用Formastor-FⅡ全自动相变仪模拟研究了一种Fe-0.24C-0.3Si-1.0Mn-0.56Cr-0.17Mo（质量分数,%）钢在冷却过程中的碳配分行为及其对马氏体和残余奥氏体的影响,用扫描电镜、透射电镜进行微观组织表征,用X射线衍射法和电子背散射衍射法测定残余奥氏体体积分数。结果表明,试验钢分别经末段慢冷和直接快冷工艺冷却后均获得马氏体＋残余奥氏体两相组织,其中直接快冷工艺所得马氏体相对杂乱,尺寸较小,残余奥氏体体积分数较少;而末段慢冷工艺所得马氏体板条较长,且发生了碳的配分,残余奥氏体体积分数较多,以薄膜状分布在马氏体板条间,板条内部含有高密度位错。     

Analysis of Microstructure and Mechanical Properties of Different Hot Stamped B‐bearing Steels

Hot stamping is a technique to produce ultra high strength automobile components. The common material used in hot stamping process is coated and/or uncoated 22MnB5 boron alloyed steel. Ferritic‐pearlitic microstructure in as‐delivered sheets is transformed to fully lath martensitic after hot stamping. In the present research, hot stamping under water or nitrogen cooling media was investigated using different boron alloyed steel grades. Microstructural analyses, linear and surface hardness profiling as well as tensile tests of hot stamped samples were performed. Various microstructures of fully bainitic and/or fully martensitic were produced. The resulting microstructures provided yield strengths of 650–1370 MPa and tensile strengths of 850–2000 MPa. There is an optimum carbon equivalent content for which the highest formability index value, UTS × A₂₅, is achieved. Using a nitrogen cooled punch resulted in higher yield strength without significant changes in ultimate tensile strength. It is concluded that a wide range of B‐bearing steels having an extended carbon equivalent range with an acceptable formability index value can be used by increasing the cooling rate in the die assembly.     

Development and Application of On-Line Solution Annealing Process for 304 Austenitic Stainless Steel

After hot rolling, 304 austenitic stainless steel requires a solution annealing treatment to prevent intergranular corrosion and eliminate work hardening effects. Compared to traditional offline processes, on-line solution annealing offers advantages in terms of cost and time savings. However, both recrystallization behavior and M₂₃C₆ carbide precipitation behavior are significantly influenced by the cooling process after rolling, which poses conflicting requirements. This study investigates the precipitation behavior of M₂₃C₆ carbides and the recrystallization softening behavior during the continuous cooling process of hot-rolled samples. The kinetics equations are derived using the Scheil's additivity rule. The temperature profiles in different regions of the plate are studied using finite element analysis. A practical approach for online solution annealing is proposed and applied in industrial testing.     

Induction Heat Treatment of Sheet‐Bulk Metal‐Formed Parts Assisted by Water–Air Spray Cooling

In order to produce components with massive secondary functional elements from sheet metal bulk forming operations, termed sheet‐bulk metal forming, can be applied. Owing to high, three‐dimensional stress and strain states present during sheet‐bulk metal forming, ductile damage occurs in the form of micro‐voids. Depending on the material flow properties, tensile residual stresses can also be present in the components' formed functional elements. During service, the components are subjected to cyclic loading via these functional elements, and tensile residual stresses exert an unfavorable influence on crack initiation and crack growth, and therefore on the fatigue life. Following the forming process, temperature and microstructurally related compressive residual stresses can be induced by local heat treating of the surface. These residual stresses can counteract potential crack initiation on the surface or in the subsurface regions. In the present study, the adjustability of the residual stress state is investigated using a workpiece manufactured by orbital cold‐forming, which possesses an accumulation of material in its edge region. Based on residual stress measurements in the workpiece's edge region using x‐ray diffractometry, it is possible to verify the compressive residual stresses adjusted by varying the cooling conditions.