Božidar Liščić

Quenching Theory and Technology, Second Edition

Hardening of Steels, L. de C.F. Canale and G.E. Totten Quenching of Aluminum Alloys, R.T. Shuey and M. Tiryakiogliu Quenching of Titanium Alloys, L. Meekisho, X. Yao, and G.E. Totten Mechanical Properties of Ferrous and Nonferrous Alloys after Quenching, H.-J. Spies Thermo- and Fluid-Dynamic Principles of Heat Transfer during Cooling, F. Mayinger Heat Transfer during Cooling of Heated Metals with Vaporizable Liquids, R. Jeschar, E. Specht, and C. Kohler Wetting Kinematics, H.M. Tensi Wetting Kinetics and Quench Severity of Selected Vegetable Oils for Heat Treatment, K.N. Prabhu Residual Stresses after Quenching, V. Schulze, O. Vohringer, and E. Macherauch Effect of Workpiece Surface Properties on Cooling Behavior, F. Moreaux, G. Beck, and P. Archambault Determination of Quenching Power of Various Fluids, H.M. Tensi and B. Liscic Types of Cooling Media and Their Properties, W. Luty Gas Quenching, G. Belinato, L. de C.F. Canale, and G.E. Totten Techniques of Quenching, H.E. Boyer, P. Archambault, and F. Moreaux Intensive Steel Quenching Methods, N.I. Kobasko Prediction of Hardness Profi le in Workpiece Based on Characteristic Cooling Parameters and Material Behavior during Cooling, H.M. Tensi and B. Liscic Simulation of Quenching, C. Simsir and C. Hakan Gur Appendices Index

Relations between fracture toughness, hardness and microstructure of vacuum heat-treated high-speed steel

Abstract When modelling the fracture toughness of the investigated AISI M2 high-speed steel, the stress-modified critical strain criterion was used. The very important influence of microstructural parameters such as the volume fraction of undissolved eutectic carbides, their mean diameter, and the mean distance between the carbides, as well as the volume fraction of retained austenite in the matrix, was also taken into account. The influence of yield stress and fracture ductility was expressed in terms of the hardness of the steel. It was found that the plastic zone which develops, during fracture toughness measurements, ahead of the fatigue crack tip, was, as a rule, smaller than the prior austenite grain size, so that, in the case of the investigated high-speed steel, the size of these grains did not have any influence on the measured fracture toughness value. However, importantly, the calculated fracture toughness values, which were derived using a newly developed semi-empirical equation, agreed well with the experimental results obtained by the authors, as well as with results obtained by other authors.

Heat Transfer Control During Quenching

The aim of this article is to discuss the measures to control the dynamic of heat extraction by changing some parameters during quenching. This is possible for workpieces of not too small a cross-section size, because transformation of the microstructure proceeds gradually from the surface to the core only when a particular point attains the temperature A 1. Differences between calculation of the temperature dependent heat transfer coefficient (HTC) for laboratory specimens and for real workpieces, taking into account the damping effect, the time lag, and the thermocouple response time, have been discussed. High Pressure Gas Quenching (HPGQ) in vacuum furnaces is especially prone to changing some parameters during quenching. To increase its quenching intensity, in order to attain high enough hardness in the core, the gas pressure and/or its flow velocity can be increased. When this measure is combined with the transient spraying of liquid nitrogen, a new Controllable Heat Extraction (CHE) Technology can be developed. Moreover, if the furnace is provided with a necessary control system and software program, fully automatic control of the heat extraction during quenching, which guarantees repeatable hardness results, is possible.

System for Process Analysis and Hardness Prediction when Quenching Axially-Symmetrical Workpieces of any Shape in Liquid Quenchants

A new Temperature Gradient System has been designed for practical use when quenching real workpieces in any kind of liquid quenchants. The main hardware component of the system is a cylindrical probe of 50 mm Dia. × 200 mm assembled with three thermocouples, and the tem-perature data acquisition unit for automatic drawing of cooling curves. The accompanying software-package consists of three modules: The first one for calculation of the heat transfer coefficient, the second one for quenching process analysis by graphical presentation of different thermodynamic functions, and the third one for hardness distribution prediction on the axial section of axially-symmetrical workpieces of any complex shape. The hardness prediction 2-D program is based on a Finite Volume Method, by which cooling curves in every particular point of the axial workpiece section are calculated, and cooling times from 800 °C to 500 °C (t8/5) determined. Using the known relation between the cooling time (t8/5) and the distance from the quenched end of the Jominy spe-cimen, for the relevant steel, the hardness can be predicted, at once, in every particular point of the axial workpiece section, which is the unique feature of this system. The system itself is designed to: record, evaluate and compare real quenching intensities during the whole quenching process, when different liquid quenchants with different conditions are used, and different quenching techniques have been applied.

Dependence of the Heat Transfer Coefficient at Quenching on Diameter of Cylindrical Workpieces

For computer simulation of a quenching process, the fundamental prerequisite is to have the relevant heat transfer coefficient (HTC) calculated as function of workpiece’s surface temperature and time respectively. In order to calculate the HTC, experimental measurement of the temperature-time history (cooling curve) near the workpiece surface is necessary. In this investigation, cylindrical probes of 20, 50, and 80 mm diameter are used. The cooling curve was measured always at 1 mm below the surface of the probe. Special care has been taken to keep all other factors (design of the probes, temperature measurement, quenching conditions, and calculation procedure), which can influence on the calculated HTC, constant to assure that the only variable is the diameter of the probe. Supposing a radially symmetrical heat flow at half length of the probe, the HTC was calculated using one-dimensional (1-D) inverse heat conduction method. The unexpected striking result of this investigation is the fact that for biggest probe diameter (80 mm), the calculated HTC as function of surface temperature does not show the film boiling phase. A plausible explanation of this effect is given based on the critical heat flux density. The possibility to establish a simple fixed relation (a correction factor) between the HTC and the diameter of cylinders is discussed.

Hardenability Testing and Simulation of Gas-Quenched Steel

The aim of a joint project between the Stiftung Institut für Werkstofftechnik, Bremen (IWT), the company Ipsen International, and the Faculty of Mechanical Engineering and Naval Architecture (FMENA), the University of Zagreb is to develop a computer program for prediction of hardness on the axial section of axially-symmetrical workpieces of any complex shape, thereupon high pressure gas quenching. The hardenability for the specimens made of tool steel grade EN-90MnCrV8 and the cooling dynamics under two gas pressures are measured using the unique facility at IWT. With developed computer simulation model, the cooling curves at different positions (J) along the end-quenched specimen are determined. Based on them, the cooling time from 800 to 500°C (t 8/5) is determined, and the curves J = f(t 8/5) are derived for different quenching conditions. This curves together with curves of hardness distributions along the end-quenched specimens can serve for the prediction of hardness distribution on the cross-sections of a batch of workpieces cooled in vacuum furnace.

Der Wärmeentzug beim Härten

Kurzfassung Diese Übersichtsarbeit zeigt zuerst die drei gegenseitig bedingten Abschreckprozessteile, nämlich den thermodynamischen, den werkstoffkundlichen und den mechanischen Prozess. Weiter wird die Problematik der Wärmeübergangskoeffizienten beim Abschrecken in flüssigen Mitteln diskutiert. Methoden für die Beurteilung der Abschreckintensität im Labor wie auch in der Praxis werden dargestellt. Die Möglichkeiten für eine absichtliche Änderung der Wärmeentzugsdynamik werden an Beispielen der Intensiven Abschreckung und des Verzögerten Abschreckens dargestellt. Beim Hochdruckgasabschrecken in Vakuumöfen wird eine automatische Steuerung des Wärmeentzugs vorgeschlagen, bzw. eine neue Technologie, die Gesteuerte Wärmeentzugs-Technologie (GWE), eingeführt.

Current Investigations at Quenching Research Centre

Quenching Research Centre (QRC) was established at the beginning of 2010 through the financial support for excellence of the Ministry of Science Education and Sport, of the Republic of Croatia. The main investigation and research possibilities and potentials of the QRC are: quenching in liquids or in a salt bath and cooling by high pressure gases. As a result of long term research, the Temperature Gradient System has been designed, together with a unique cylindrical probe of 50 mm diameter by 200 mm instrumented with three thermocouples. Another device used at the Centre was the IVFSmartQuench® system according to ISO 9950, using a quenching device with agitation according to the ASTM D6482 standard. That equipment is used to investigate liquid quenchants and process parameters, including development of new quenchants: water, oil, and polymer based nanofluids, agitated by ultrasonic vibrations as a novel technology. QRC is also equipped with unique high pressure gas quenching facilities, providing the hardware for controllable heat extraction. The aim of using that equipment is to develop the method for measuring hardenability of high-alloyed steels when they are gas quenched and where a Jominy test is not applicable. QRC is also one of the initiators and an active participant in the project Global database on cooling intensities of liquid quenchants, which is coordinated and conducted by International Federation for Heat Treatment and Surface Engineering (IFHTSE).

Prediction of Quench-Hardness within the Whole Volume of Axially-Symmetric Workpieces of any Shape

A quench probe, based on temperature gradient method was used to measure and record cooling curves when quenching real axially symmetric workpieces of any complex shape in liquid quenchants. Calculation of relevant heat transfer coefficients (HTC) is based on the cooling curve measured just below surface of the cylindrical probe of 50 mm diameter. A 2-D computer program, based on the cooling time from 800 to 500°C (t8/5), and the Jominy hardenability curve of the steel grade in question, is used to predict the hardness distribution within the whole volume of the workpiece, all at once, which is a unique feature of this method.

Gas quenching with controllable heat extraction

High pressure gas quenching became a modern way of quenching finally machined engineering components,having many advantages compared to quenching in liquid quenchants.The main shortcoming of this technology is the problem of achieving adequate hardness in the core of bigger workpieces,because of inadequate quenching intensity.Due to the possibility to change gas pressure and its flow velocity,combined with transient spraying of liquid nitrogen during the quenching process ,the intensity of cooling can be instantly increased during selected time intervals.In this way the heat extraction dynamics can be automatically controlled,and a predetermined path of the heat transfer coefficient can be followed.Preliminary experiments show that using the controllable heat extraction(CHE) technology, the mentioned shortcoming can be eliminated.Theoretical background of the CHE technology is described,with particular attention to the depth of hardening,and to residual stresses.Possibilities and prerequisite conditions for application of the CHE technology in vacuum furnaces,and for automatic heat extraction control,are discussed.