Mathematical model of the temperature field of a rail and a multinozzle device for induction hardening of rail heads

A mathematical model of the temperature field of a rail is developed for designing optimum regimes for surface hardening of rail heads from induction heating by HFC, and the cooling capacity of media formed in a newly designed multinozzle device is considered. It is established that the process of cooling of rail heads can be controlled by providing a high dispersity of the water-air mixture formed by a multinozzle cooling device with autonomous feeding of the coolant through each nozzle. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 12, pp. 31–35, December, 1999.     

Cooling Characteristic of Polymeric Quenchant: Calculation of HTC and Prediction of Microstructure and Hardness

The present paper discusses the influence of experimental conditions on the quenching performance of poly(2-ethyl-2-oxazoline) (PEOX) aqueous solutions used as cooling medium, using a standard ISO Inconel alloy probe for measurements of cooling rate. The evaluation procedure is demonstrated on characterization of cooling power of water-based polymer (PEOX) solutions by using different concentration, temperatures, and agitation conditions of the cooling media. The results show that the different experimental conditions have a significant effect on the cooling performance. The polymer quenching mechanism and the comparative cooling characteristics of water, and water-based PEOX polymer solution with concentrations from 2.5 to 15 wt.% were discussed. The study involved the assessment of the quenching severity by calculating the hardening power (HP) via empirical equations. Calculation of heat transfer coefficients as well as prediction of microstructural constituents and the hardness profile in a cross-section of steel sample were carried out on the basis of inverse calculation from the recorded cooling curve.     

用冷却曲线估测动态条件下淬火油的淬火烈度

对淬火油在不同流速下的冷却曲线和淬火烈度进行了测量 ,建立了硬化能力、淬火烈度与介质流速三者之间的关系。结果表明 ,淬火油的淬火烈度H值与建立在冷却曲线基础上的硬化能力HP值均随介质流速的增加而增加 ,二者增加的斜率相近。因此 ,在测得冷却曲线的前提下 ,可以估算出淬火油在该流速下淬火烈度的增加值     

双介质淬火冷却时间计算方法的研究

双介质淬火是钢件淬火重要方法之一，在双介质淬火中从一种介质中冷却转至另一种介质冷却的适当时刻是获得良好效果的关键。根据现有淬火介质冷却速度特性曲线，建立数学模型，计算出换热系数h，从而计算出冷却过程的时间，为完善和发展双介质淬火工艺开拓了新的途径。     

油污掺杂对PAG水基淬火液冷却特性的影响

为了探究油污对水基型淬火液冷却性能的影响,测试了不同油浓度下淬火液的冷却速率曲线、硬化能力等,通过分析淬火的具体过程和特性值函数,探讨了油污的掺杂影响淬火液冷却性能的机制。结果表明:当淬火液中油污含量大于0.3%时,淬火液的冷却性能明显变差,具体表现为沸腾阶段延后且高温阶段冷却速率明显下降,淬火液的硬化能力也随之降低;但油污的含量对工件的畸变影响较小。     

水,油等淬火介质淬硬能力的数值评价方法

本文论述了以淬火硬度评定水、油及冷却特性介于水油之间的淬火介质淬硬能力的方法。其基本思路是,钢的连续冷却转变图中的每条曲线代表着钢的某一硬度,反之也可以认为淬火硬度也对应着该图的某一条曲线,代表介质的淬硬能力,从而就可以借助于淬火硬度值来评定水、油等淬火介质的淬硬能力。     

Gas Quenching during Age Hardening of the Aluminium Casting Alloy Al-7Si-0.3Mg

For quenching of age hardenable aluminium alloys today predominantly aqueous quenching media are used,which can lead due to the Leidenfrost phenomenon to a non-uniform cooling of the parts and thus to thermal stresses.Particularly at thin-walled or complex shaped parts local plastic deformations can occur by the uneven thermal stresses. In relation to the conventional quenching procedures in aqueous media, gas quenching exhibits a number of technological,ecological and economical advantages. In comparison to liquid quenching media, gas does not change its phase during quenching. Moreover, the cleaning problem of the parts can be avoided. The quenching intensity can be adjusted by the variable parameters gas pressure and gas speed as well as the kind of gas and thus can be adapted to the requirements of the alloy. By the higher uniformity and the better reproducibility, gas quenching offers a high potential to reduce distortion. The goal of these investigations is to clarify, if the cooling rate during gas quenching is sufficient to obtain the specific required strength after age hardening of the alloy Al-7Si-0.3Mg. For this purpose different tests in high-pressure gas quenching facilities, gas nozzle fields and water quenching baths were performed.     

Gas Quenching during Age Hardening of the Aluminium Casting Alloy AI-7Si-0.3Mg

For quenching of age hardenable aluminium alloys today predominantly aqueous quenching media are used.which can lead due to the Leidenfrost phenomenon to a non-uniform cooling of the parts and thus to thermal stresses.Particularly at thin-walled or complex shaped parts local plastic deformations can occur by the uneven thermal stresses. In relation to the conventional quenching procedures in aqueous media, gas quenching exhibits a number of technological.ecological and economical advantages. In comparison to liquid quenching media, gas does not change its phase during quenching. Moreover, the cleaning problem of the parts can be avoided. The quenching intensity can be adjusted by the variable parameters gas pressure and gas speed as well as the kind of gas and thus can be adapted to the requirements of the alloy. By the higher uniformity and the better reproducibility, gas quenching offers a high potential to reduce distortion. The goal of these investigations is to clarify, if the cooling rate during gas quenching is sufficient to obtain the specific required strength after age hardening of the alloy A1-7Si-0.3Mg. For this purpose different tests in high-pressure gas quenching facilities, gas nozzle fields and water quenching baths were performed.     

Criteria for evaluating the cooling capacity of quenching media

Numerous criteria have been suggested for evaluating the cooling capacity of quenching media. Although the cooling capacity of a medium can hardly be evaluated by a single number, such data can be helpful in the initial stage of choosing the medium for quenching a specific part. Various criteria for evaluating the cooling capacity of polymer quenching media have been analyzed within the developed international standard based on ISO 9950 (for industrial quenchants). Those that can be calculated from results of tests of a medium by means of a Wolfson gauge, recommended by the ISO 9950 standard, have been chosen. The aim of the present work consists in determining the correlation between the criteria suggested by various researchers for various domestic and foreign quenching liquids on a polymer base. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 10, pp. 18–21, October, 1998.     

DISTRIBUTIONS OF MICROSTRUCTURES IN QUENCHED STEELS AS REVEALED BY COMPUTER SIMULATION

1.IntroductionPhasesandmicrostructuresformedincoolingofausteniteofsteels(quenching)havebeenextensivelystudiedandagreatamountofdatalikeisothermaltransformationcurves(TTTcurves)andcontinuoscoolingtransformationcurveshaveestablished.However,itisdifficulttousethesedatatopredictdistributionofmicrostructuresofaquenchedsteelstructureduetothefactthatthetransformationoccursinaunknownchangingfieldoftemperature.Acomputersimulationtoolcombiningthetransformationkineticsandthermalevolutionruleshouldbeanide…     

由“冷却模型”到“冷却工程”的演进

冷却方式决定热处理工艺的类型。淬火是金属热处理中具有标志性的核心技术,其中最关键的操作环节是冷却。通过冷却曲线分析提出了钢探头在有物态变化介质中冷却时的主、辅界面模型。分析了钢在奥氏体化后冷却转变的物理冶金学现象与工程实际所能提供的冷却环境之间的联系。概述了淬火介质与冷却技术的研究现状与发展动态,特别指出了新的冷却技术及其装备开发的重要性。总之,从单纯的冷却模型研究到冷却工程的实现将是一大跨越。     

两种真空高压气淬炉淬火工艺的数值模拟及验证

对管道式和压入式真空高压气淬炉中实施的高压气淬工艺进行了数值模拟和实物验证试验。研究结果表明,在相同的冷却压力下,管道式真空高压气淬炉的冷却速度比压入式真空高压气淬炉快,小型工件更适宜在管道式真空高压气淬炉中进行淬火。     

淬火工件内温度场的计算机模拟

根据实测的淬火介质冷却速度曲线推导了淬火冷却过程换热系数h值的数学表达式,研究了圆柱体工件内淬火过程中瞬变温度场的数学模型及其数值解.利用计算机计算淬火过程中工件内瞬变温度场,在实际生产中取得了满意的结果.     

Effect of composition on oil quenchant performance

Abstract

Quenching is the most common method of hardening metals and involves continuous cooling from a given austenitising temperature to achieve full transformation into a martensitic structure. The cooling rate depends mainly on the thermal characteristics of the metal, the section thickness of the workpieces and the heat removal properties of the quenching medium. Oils, when used as quenching media contain a base oil and different types of additives according to the application requirements. As the base oil, it is possible to use mineral, synthetic and natural oils, either separately or in combination. Mineral base oils are widely used because of their advantages in stability in comparison with natural oils, or lower price in comparison with synthetic oils. There are numerous additives available for use but, besides functional properties, the environmental and safety requirements have to be considered in their selection, e.g. barium additives must be replaced with less harmful compounds. Additionally, petroleum derivatives should be replaced by renewable base stocks that are biodegradable, which is a general trend in lubricant development. By changing the composition of the base oils and additives, heat transfer characteristics are also changed. This study presents the results of the analysis of physical and chemical properties, as well as of cooling characteristics of new quenching oils with different compositions. Cooling curves have been evaluated according to ISO 9950 standard.     

Development and application of alternate timed quenching by water and air

Abstract

Water and air are commonly used quench media with very different quenching powers; further, they are environmentally friendly and of very low cost. Theoretically, alternate quenching by water and air can produce any desired cooling rate between those of each medium alone. While this technology has not been practicable due to the difficulties in process design and control, the recent development of numerical simulation and processing control techniques has established a solid base for its industrial application. A new technology, alternate timed quenching by water and air (AT-quenching), is proposed. The technology has been applied to a medium carbon low alloy steel, the mechanical properties of which do not meet specification after oil quenching, but which suffers cracking after water quenching. The key points are to design the process by computer simulation and to realise it with digitally controlled quenching equipment. The technology has been successfully employed in production of large forged blocks of die steel for plastics moulding, long shaft forgings and forgings for marine crankshaft, effectively solving the difficulties that traditional processes and quenchants encounter.     

Effect of hardening conditions on mechanical properties of high speed steels

Abstract

Hardness and toughness are the main properties determining wear resistance and performance of high speed steel tools. The objective of the present paper was to study the effect of hardening conditions on the toughness of high speed steels, mainly concerning the hardening temperature and cooling rate during quenching. Several conditions were simulated in laboratory and industrial heat treatment furnaces and toughness was evaluated through the static bend test. Under the same tempering condition, the higher the hardening temperature, the higher the attained hardness. The results also point out a compromise situation between hardness and toughness, until 1200°C hardening temperature is reached; for temperatures over this value, the loss in toughness become more accentuated, without a considerable increase in hardness. The present paper also describes the mechanical properties of M2 high speed steel heat treated to lower hardness, necessary in some cold work tooling applications. In this case, hardening at lower temperatures and tempering close to the peak hardness has shown the best results. And lastly, regarding cooling conditions during nitrogen hardening in a vacuum furnace, the results point out that low quenching pressures might reduce the cooling rate and decreases material toughness, but the differences are very small for pressures between 6 and 9 bar.     

A comparative study on determination method of heat transfer coefficient using inverse heat transfer and iterative modification

The distortion control of heat-treated steel parts is a main consideration when dealing with hardening by quenching process. Before implementing this heat treating process, prediction of distortion is necessary to be done by experiment and computer simulation for determining a quenching technique which gives the smaller distortion. Temperature-dependent heat transfer coefficient (HTC) estimated from SUS304 cylinder can be determined by both iterative modification of lumped heat capacity method (LumpHC) and inverse heat transfer method (InvHT). Predicted HTC from silver probe is needed for the LumpHC, whereas initial set of assumption is needed for the InvHT. The zone-based HTC estimated from SUS304 cylinder then is employed on S45C cylinder. The prediction accuracy results from both methods are evaluated. As expected, stir quenching gives less distortion than that of still quenching. More accurate prediction of cooling curves, cooling rate curves, and distortion is achieved by employing the LumpHC than that by the InvHT. All analyses were performed by DEFORM-HT 2D.     

FEM modeling of induction hardening processes in steel

A modeling system for analyzing the integrated induction hardening processes was developed based on a general-purpose finite element program, with the capability to analyze the whole process from electromagnetic-induced thermal heating to final hardening. A coupled electromagnetic-thermal model was applied to study the induction heating process, which includes consideration of nonlinear material characteristics on temperature. Also, arrangement of AC current density distribution was conducted to simulate practical induction coil structure and magnetic concentrator effects to achieve desired heating patterns for later quenching and hardening analysis. Quenching analysis can provide cooling curve at any location in a heat-treated workpiece based on heat transfer principles. In hardening analysis, phase transformation was studied and an algorithm was developed to determine volumetric content of micro-structural constituents formed from austenitized phase in quenching process, based on analysis of the interaction between cooling curve and material time-temperature-transformation (TTT) diagram. Finally, hardness value was converted from martensite content based on a developed formulation. Validation was preliminary conducted based on comparison of hardening pattern of induction hardening of an automotive spindle with complex surface.     

一种新型淬火冷却技术的研发和应用

淬火油是热处理淬火过程中应用最广的冷却介质,同时也是最重要的污染源和火灾隐患。近年来,由于热处理数值模拟虚拟系统和精确控制技术的完善和应用,使以水代油淬火冷却技术得以实现。该技术以数据挖掘型模拟系统为工具,以优化的工艺数据库为核心,通过具有灵活切换和调整冷却能力功能的工艺装备,形成以水代油淬火冷却的智能化系统技术,从而实现淬火冷却的节能、环保、安全目标。