Darko Landek

Effect of Deep-Cryogenic Treatment on High Speed Steel Properties

Advantages of deep-cryogenic treatment over standard heat treatment of high speed steels for the purpose of obtaining better properties are quoted in an increasing number of scientific articles. This article deals with the most important improvements of high speed steel properties achieved by using deep-cryogenic treatment. The effect of deep-cryogenic treatment on impact and fracture toughness, on erosion wear resistance, and on the material microstructure has been tested on samples made of the PM S390 MC high speed steel. A set of test samples was heat treated by conventional methods (hardened and three times high temperature tempered), and the other set was deep cryogenic treated. From the results, it can be concluded that the application of deep-cryogenic treatment results in significantly higher wear resistance of high speed steels, but no significant improvements in toughness have been observed.

The effect of TiO2 nanoparticles on fluid quenching characteristics

AbstractNanofluids are colloidal suspensions of nanoparticles in base fluids. Some of the particles used in recent research are metal oxide and carbide particles, such as SiC, CuO, Al2O3 and TiO2, graphite and carbon nanotubes and particles. Quenching in such colloids results in better cooling abilities, higher impact toughness and smaller dimension changes of steels, compared with pure quenching media. In this investigation, nanofluids with TiO2 powders of 50 nm average particle size were investigated. Base fluids of primary interest were deionised (DI) water, some commercial quenching oils and polyalkylene glycol water solution of various polymer concentrations, 5–30 vol.-%. The investigated fluids were prepared with the addition of the same TiO2 powder with different concentrations, from extremely low, 10 mg nanopowder per litre to 1 g L−1. The cooling characteristics of these colloids were compared with the results of base fluids, but also with the results of previous measurements carried out on the f...

Systematic analysis of cooling curves for liquid quenchants

This investigation suggests and describes a systematic approach to the analysis of liquid quenchant characteristics using a standard ISO Inconel alloy probe. A new systematic mathematical model for the cooling curve analysis has been developed. The model allows for a more precise determination of quenching parameters and links certain parameters with a mathematical model for microstructure prediction and properties of quenched workpieces. Besides the usual technological parameters (cooling rate at 700°C, maximum cooling rate, cooling time from 800 to 500°C, cooling rate at 300°C, quenching intensity H), the heat transfer coefficient is determined using the following methods: the lumped heat capacity method, the Kobasko method and the inverse heat transfer method according to ‘SQIntegra’ software. The results of the heat transfer coefficient calculation according to the aforementioned methods are compared and verified with the ISO Inconel alloy probe cooling curve analysis for quenching in water, industria...

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.

Effects of thermochemical treatments on properties of maraging steels

Abstract Effects of such thermochemical processes as carburising, nitriding and boriding on properties of maraging steel grades have been investigated. Despite certain improvements in the properties of the obtained surface, at present, carburising and boriding cannot be recommended owing to problems in the layer quality and difficulties in dimension control processes. Nitriding has proved to be the most suitable process and subsequent surfacing with a TiN layer on the previously nitrided substratum of maraging steel provided additional improvement in properties.

A Prediction of Quenching Parameters Using Inverse Analysis

The cooling curves of still water and of water-based polymer quenchant polyalkylene glycol (PAG) were recorded with the ISO Inconel 600 probe with 12.5 diameter and 60 mm length equipped with a type K thermocouple inserted into the probes geometric center. The research included recording of cooling curves for still water in temperature range from 20 to 60°C, as well as quenching experiments with water based polymer solutions with concentration from 10 to 30 vol. % of PAG. The possibility of a new cooling curve determination method for any given water temperature based on interpolation model and experimental data for cooling curves at three different water temperatures was tested. Surface temperature, heat flux density, and heat transfer coefficient (HTC) were estimated based on the recorded cooling curve at the center of the ISO Inconel 600 probe using the solutions of inverse heat conduction problem (IHCP). The results of the inverse heat transfer analysis of the ISO Inconel 600 probe cooling in water and water based polymer solutions were compared to the results of the commercial software ivf SQintegra ver4.0 for the same cooling experiments. The proposed inverse determination of HTC can be used for the specification of boundary conditions in numerical simulations of quenching axisymmetric work pieces with similar dimensions to the ISO Inconel 600 probe.

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).

An analysis of induction hardening of ferritic ductile iron

Achievements of the induction hardening of ferritic ductile iron were investigated. Ductile iron is not advisable for use in induction hardening because of the small carbon content in the metal matrix of ferritic ductile iron. The carbon content in the metal matrix of ductile iron can be increased by additional preparation of metal matrix before final induction heat hardening. Wear resistance of the induction hardened ferritic ductile iron can increase as result of increased carbon content of the metal matrix and higher hardness after induction hardening. Some heat pretreatments for metal matrix preparation were applied before the induction hardening of ferritic ductile iron. The process parameters of the induction hardening heat pretreatment were analyzed and optimized. According to recommended elemental composition of ferritic ductile iron and required mechanical properties, the process parameters of the investigated induction heat pretreatment were optimized. The efficiency of pretreatment processes of induction hardening was analyzed. Applicability and manufacture ability of engineering components by proposed heat pretreatments were investigated. The limitations of the investigated heat pretreatment applications were estimated by the comparison of mechanical properties of heat-treated specimens.

Influence of Steel Substrate on the Properties of PACVD Gradient Multilayer TiCN Coating

Titanium-based hard coatings are known for increasing both hot work and cold work tool steel performance in terms of wear and corrosion resistance. In this paper, the influence of different steel substrates on the properties of plasma-assisted chemical vapor deposition (PACVD) gradient multilayer titanium carbo-nitride (TiCN) coating was investigated. The same gradient multilayer TiCN coating was deposited by pulsed direct current (dc) PACVD on a hot work tool steel grade X37CrMoV5-1 and two Bohler cold work tool steels K390 PM and K110. Hardened samples of each steel were also included in the investigation. The coating-substrate systems have been characterized with respect to their chemical composition, thickness, adhesion, and resistance to electrochemical corrosion, abrasion, erosion, and dry sliding wear. The results show an increased wear and corrosion resistance of TiCN-coated specimens compared with noncoated and prehardened specimens. The application of gradient multilayer TiCN coating on different steel substrates shows the different behavior of TiCN coating. Therefore, besides the coating itself, the base material on which the coating is applied has a significant influence on the tool properties.

Application of Ultrasound Stirring for Quenching in a Liquid Medium

This paper investigates an application of ultrasonic stirring in water and oil-immersion quenching of a medium carbon steel sample. By developing a pressure acoustic simulation, the distribution of ultrasound pressure and acceleration in quenching media was predicted. By using the standard temperature probe of Inconel 600, the cooling curves of water and quench oil were recorded with and without ultrasound agitation. Using the same conditions, a quenching of the steel cylinders made for carbon steel C45 was performed. The experimental results have shown a significant impact of ultrasound agitation on cooling curve parameters, sample distortions, and surface hardness distribution and its hardenability.