Darko Landek

University of Zagreb · Materials Science

This paper presents a Computational Fluid Dynamics (CFD) simulation of the quenching process based on ISO 9950, focusing on the heat flux and heat transfer coefficient integrated over a metal specimen. The numerical method, which employs the two-fluid VOF method and frozen turbulence approach (Cukrov et al., Appl. Sci. 2023, 13, 9144), is used for...

Boronizing is a type of thermal diffusion with the primary goal of increasing the surface hardness, wear and corrosion resistance. The wear resistance of boronized parts depends on the type of borides that form on the steel surface and their thickness. This study investigated the properties of boride layers formed on X90CrMoV-18 martensitic stainle...

The computational model that is able to estimate the temperature distribution inside a solid specimen during the film boiling phase of immersion quenching (water entry) process has been presented in this paper. It is based on the prescribed initial temperatures of the solid specimen and the liquid quenchant. In addition, the turbulence effects have...

The paper investigates the effects of DC plasma nitriding on surface roughness, hardness, microstructure, micro-abrasion, and corrosion resistance of AISI 316L Austenitic Stainless (AS) steel. The nitriding has been conducted for durations ranging from 4 to 24 h at a temperature of 430 °C in a commercial vacuum furnace, Rübig PN90/70. Micro-abrasio...

The computational model that is able to estimate the temperature distribution inside a solid specimen during the film boiling phase of immersion quenching (water entry) process has been presented in paper, and it is based on the prescribed initial temperatures of the solid specimen and the liquid quenchant. In addition, the turbulence effects have...

The volume erosion rate of the slip cast monolithic and composite ceramics was studied using SiO2 and SiC particles as erodents, under different impact angles (30°, 60°, 90°), at room temperature. Therefore, three groups of samples were prepared: (i) monolithic alumina (Al2O3); (ii) composite alumina–zirconia (Al2O3–ZrO2) containing 99 wt-% Al2O3 a...

The contribution compares the abrasion and erosion resistance of two high-alloy tool steels, X153CrMoV12‑1 and Böhler K390 Micro Clean, coated with multilayer coatings TiN/TiCN and TiN/Ti-B‑N. Multilayer coatings were applied to hardened and tempered samples by pulsed direct current (DC) plasma-assisted chemical-vapour deposition (PACVD) process in...

Tribological coatings are found on machine elements (e [...]

In this work, alumina (Al2O3) ceramics were prepared using an environmentally friendly slip casting method. To this end, highly concentrated (70 wt.%) aqueous suspensions of alumina (Al2O3) were prepared with different amounts of the ammonium salt of a polycarboxylic acid, Dolapix CE 64, as an electrosteric dispersant. The stability of highly conce...

The purpose of this investigation was to compare the wear of diamond-coated dental burs applied on specimens made of four different materials used in dental prosthetics. Cutting was performed using a dental air turbine handpiece. Identical coarse-grit diamond burs were mounted on the handpiece and subjected to a 1.5 N load. Dental burs were divided...

Two different steel substrates were coated with the same gradient multilayer TiN/TiCN coating in the plasma‐assisted chemical vapor deposition (PACVD) process. The multilayer TiN/TiCN coatings on the substrate of the X37CrMoV5‐1 tool steel and the X22CrMoV12‐1 stainless steel were analyzed by scanning electron microscopy (SEM), energy dispersion sp...

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 investigat...

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 wat...

This paper investigates the abrasion and erosion wear resistance of the multilayer coating within the system Ti-B-N applied to samples made of two hardened and tempered tool steels: Böhler grades K390 MC and X155CrVMo12-1. The multilayer coating consists from the thin interlayer TiN deposited directly on steel substrate and the Ti(B,N) coating, wit...

A barrel is one of the most tribologically and thermally loaded parts of artillery weapons. The influence of the salt bath nitrocarburizing and hard-chrome plating of three steels used for artillery barrels on their abrasion resistance is studied in this paper. The tested steels are 42CrMo4, 30CrNiMo8, and 36CrNiMo4 in the initial quenched and temp...

T This paper examines the abrasive and erosive wear of duplex multilayer TiN/TiCN and TiN/TiBN coatings deposited on quenched and tempered hot work tool steel grade X37CrMoV5-1. The coatings were produced by duplex method composed of a plasma nitriding and pulsed direct current (DC) plasma-assisted chemical-vapor deposition (PACVD). Measurements of...

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....

Predicting thermal distortions and residual stresses after steel heat treatment is a complex task in which the solution involves the use of a number of process parameters and nonlinear variation of steel properties. Former investigations in transformation-free cooling processes of long cylindrical work pieces in a gas nozzle field showed a typical...

A series of quenching experiments was performed according to the ISO 9950, ASTM 6200-01, and ASTM D6482-06 standards. Water based nanofluids with 0.01, 0.1, and 0.2 g/L TiO2 were prepared using a two-step method and ultrasonic homogenization. The nanofluids were tested to see the possibility of their application as high temperature heat transfer fl...

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 probe's geometric center. The research included recording of cooling curves for still water in temperature range from...

Quenching steel parts by immersing them in liquid quenchants is still the most used method for hardening carbon and low alloyed structural and tool-steels. The achieved hardness, residual stresses and distortion of a workpiece depend on the selection of the quenchant, the phenomena of nonlinear heat transfer and on used cooling parameters. The non-...

The main goal of the investigation is to define the quenching characteristics of standard quenching oil with ultrasonic agitation and addition of nanoparticles. The tested quenching oil was Fuchs Thermisol QH 120. The tested quenchant temperatures were set at 20 and 60°C. This oil type was previously tested within the Liquid Quenchant Database proj...

Advantages of applying deep cryogenic treatment (DCT) after the quenching of high speed steels are well documented in references. But still there are no fully established methods for testing wear resistance that would clearly distinguish the impact of DCT from the impact of other stages in the heat treatment process on the steel tribological proper...

Nitrocarburizing is one of the frequently applied processes that significantly improve the service life of steel parts in the complex activities of mechanical loads, wear and corrosion damages. Characterization and confirmation of the quality of a nitrided/nitrocarburized layer is a prescribed norm including a determination of the surface hardness,...

Introducing nanofluids as liquid quenchants in order to improve the heat-transfer characteristics is a novel approach in heat treatment. These new liquid quenchants are called nanoquenchants and are colloid suspensions of nanoparticles in the base fluid (BF). For the purpose of this research standard liquid quenchants, such as water and polymer sol...

Advantages of deep cryogenic treatment (DCT) over the standard heat treatment of high speed steels for the purpose of obtaining better properties are quoted in an increasing number of scientific papers to be found in literature. This paper deals with the improvements in high speed steel properties achieved by using DCT on test samples made of PM S3...

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 wi...

Nanofluids 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 change...

In this paper, the effect of the heating rate on the process of tempering and the obtained hardness of the DIN 100 V1 (AISI W2) carbon tool steel has been investigated and determined. Steel specimens in two initial states were investigated: after quenching and after quenching and deep-cryogenic cooling. The specimens were submitted to tempering in...

Hardenability is an inherent property of every steel, usually characterized by the Jominy end-quenched test. For steel grades quenched in liquid quenchants this test is enough selective, and for them a good fixed correlation between cooling time from 800 to 500 o C (t 8/5) and the distance from the quenched end can be established. For steel grades...

Low-carbon, high-alloy, precipitation hardening MARAGING steels have been developed in the early sixties of the last century as a high strength structural materials for application in aeronautical and missile engineering. Due to their excellent properties, such as: high hardenability, good toughness, and high resistance to thermal fatigue, and due...

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 com...

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-cryog...

Former investigations in transformation-free cooling processes of long cylindrical workpieces in a gas nozzle field showed a typical behaviour of the dimensional changes, which correlated to only few dimensionless numbers. These numbers are created by the following parameters: shape and dimensions of component, its initial temperature, temperature...

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...

The surface of the non-alloyed carbon steel was subjected to thermochemical modification by salt bath nitrocarburizing with or without post-oxidation based on the Tenifer procedure in order to improve mechanical properties, corrosion and wear resistance. Nitrocarburized layers were characterized by testing their basic properties (compound layer thi...

The rule of Ameen whereby steel made cylinders with no phase transformations during quenching approach the spherical shape is contrary to the finding of Berger, who observes an elongation of thin and long work pieces. If the prediction of Ameen is correct, cylinders should decrease in length during heat treatment. This paper describes a first step...

The computer simulation of electromagnetic, thermodynamic and microstructural transformations in the treated workpiece is usually recommended for the exact definition of working parameters in process planning of the induction hardening processes. A special simulation program has been developed for the axially symmetric workpieces. The simulation pr...

To achieve a higher quality process planning and a more flexible execution of induction hardening computer Simulation Of electromagnetic and thermodynamic processes as well as microstructural transformation is recommended. This paper describes and suggests an own simulation model of the induction hardening process and explains a special Simulation...

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 fi...

In order to achieve higher quality and a more flexible execution of the induction hardening process, a computer assisted program for undertaking and controlling of this process is needed. This paper proposes and describes a model for the induction hardening process, the application of which achieves a specified quality of the hardened layer, within...

Nanofluids are the new quenching media with colloidal suspensions of nanoparticles in base fluids, offering new possibilities for enhancement of the heat transfer characteristics. The recent investigations show that the addition of the metals oxides particles, such as CuO, Al2O3 and TiO2, or graphite particles result in better cooling abilities and...

Investigations of transformation free cooling processes of long cylindrical workpieces in a gas nozzle field conducted at project SFB 570, at research Centre for Distortion Engineering University of Bremen, Germany, indicated a specific behavior of the dimensional changes. It is find that the dimension changes are correlated to only a few dimension...