Iva Nováková

The Selection of Appropriate Process Parameters of Diffusion Bonding in Heterogeneous Weld of 355J2/AISI 316L Steels

The aim of this article is to present possibilities of diffusion bonding utilization at creation heterogeneous joints where strength properties are taken into account. The joint was implemented to low-alloy structural ferrite-pearlite S355J2 steel and high-alloy austenitic AISI 316L steel. The fundamental theory of diffusion and also design and realisation of experimental creation of diffusion joint in thermal-mechanical simulator Gleeble 3500 is described in the article. Furthermore, procedure of technological parameters selection, when optimisation of strength properties of heterogeneous joint including metallographic evaluation are taken into account, are presented.

APPLICATION OF NUMERICAL SIMULATIONS ON X10CRWMOVNB9-2 STEEL MULTILAYER WELDING

Creep-resistant martensitic steel X10CrWMoVNb9-2 (P92) is suitable for high-temperature application used in the ultrasupercritical (USC) power plants at temperatures within the limits from 600 to 620°C and pressures about 26 MPa. It is steel alloyed with vanadium and with controlled content of boron and nitrogen. The aim of this paper is to describe how can be optimized welding processes by means of the numerical simulations mainly with respect to the structural changes and hardness in the HAZ. On the real multilayer weld will be described how to arrange whole experiment in order to obtain not only relevant input data but also verification data. Additional aim of this paper is to propose mathematical description of the computational model that is usable for simulation computations of welding and heat treatment of real structure components.

Application of Numerical Simulations on 10GN2MFA Steel Multilayer Welding

10GN2MFA steel is used to produce wire and manufacturing of steam generators, pressure compensators, collectors and other equipment for nuclear power plants. In this area, there is no place to do any mistakes during manufacturing or carrying out extensive tests and producing a lot of prototypes. It is the main reason why we used modern software for numerical simulation of welding and heat treatment processes also on the very early stage of development. The aim of this paper is to describe how can welding processes be optimized by means of the numerical simulations mainly with respect to the structural changes, stresses and hardness distribution in the Heat Affected Zone (HAZ). On the real multilayer weld how to arrange whole experiment in order to obtain not only relevant input data but also verification data will be described. Additional aim of this paper is to propose mathematical description of the computational model that is usable for simulation computations of welding and heat treatment of real structure components.

APPLICATION POSSIBILITIES OF THE DIFFUSION BONDING FOR MATERIAL 10GN2MFA USED IN THE NUCLEAR POWER INDUSTRY

The aim of this paper is to demonstrate the application possibilities at using diffusion bonding for creation the homogenous joints regarding their strength properties in comparison with the fusion MMAW method and with the parent material. Connection was carried out for low-alloyed bainitic steel 10GN2MFA that is designed for production shells and bodies of the primary steam-generators collectors which are used in the nuclear power industry. In the paper are theoretically described the basics of diffusion. Moreover, there is described also the proposal and optimization of the diffusion bonding process parameters and optimization of the thermal treatment procedure. Experiments were carried out by means of the thermal-mechanical simulator Gleeble 3500. Welded joints were subsequently evaluated in light of mechanical properties by hardness measurement and metallography.

The Increase in Effectivity of Material Processing with Employment of Liquid CO 2 during Aluminium Die Casting

The article is focused on monitoring the cooling effect of the liquid CO2. This unconventional cooling system was used as a supplement method added to the standard tempering system of the die casting mould particularly intended for aluminium alloy castings. Standard tempering system of die casting moulds enables preheating the mould to operating temperature before the particular production starts and then the tempering system regulates the temperature balance between the mould and the casting during individu al production cycles. Conventional cooling system is based on drilled or milled interconnected channels with predominantly parallel orientation to the parting line, through which a tempering medium (oil, water etc.) flows. This system has some limitations that can be overcame with utilizing of special approaches. One of these approach is employment of liquid CO2.This study revealed the positive impact of this additive cooling on homogeneity of temperature field distribution on the mould cavity surface, which assures first of all the uniform coating the cavity surface by separating agent and sticking the melt on the cores. The products were analysed using the metallographic and CT analyses and the leak tightness was tested.

INFLUENCE OF THE PRESSURE TANKS REPEATED ENAMELLING ON THE BASIC MATERIAL DEGRADATION

Pressure tanks with the enamel surfaces play an important role mainly in the food industry and pharmacy. As the best advantage of these enamels there is very good resistance against aggressive environment at keeping the required mechanical properties of low-alloyed steels which are used for these applications. Enameling is generally applied as several particular layers whereas every of these layers has to undergo the pre-defined temperature cycle. Because of increasing device service life there is very often applied repeated enameling. The paper deals with the monitoring influence of the temperature exposition on the change of mechanical properties and structure of the basic material P265GH regarding its initial properties. The aim was to identify whether and eventually how these repeated emailing can influence the basic material degradation and based upon this to determinate their possible maximal number.

Cooling Thin Parts of Pressure Casting Moulds by Means of Liquid CO2

To ensure optimal temperature conditions during casting cycle the pressure casting moulds are equipped with cooling systems. These days the cooling systems used in the most of Czech foundry plants enable pre-heating of pressure casting moulds to the working temperature before start-up of production and during casting operation to keep optimal temperature balance among the casting and the mould. Pressure casting mould temperature balance is provided by system of mutually connected channels which are mostly parallel with parting line and inside those the heat transfer medium flows. However such a system allows removal only limited heat amount from the most overheated places of the casting mould and does not allow heat removal from cores of small diameters. This inhomogeneous heat removal causes porosity of the casting in certain areas and also lifetime of the pressure casting mould is dramatically reduced. Cooling by means of liquid CO2 was developed as one of the new cooling possibilities for such places in the pressure casting mould where the heat is concentrated and for standard cooling systems it is too complicated to fully control the heat processes there. The paper deals with the behaviour monitoring of the new cooling system utilizing the potential of liquid CO2. This system was applied into pressure casting mould core and its final impact on the casting quality in the close surrounding was observed.

Comparison of Dilatometry Results Obtained by Two Different Devices when Generating CCT and In Situ Diagrams

For understanding and describing the materials behaviour during phase transformations, dilatometer measurements are commonly used in the scientific community. Generally, standard CCT diagrams are generated by means of dilatometer experiments. However, in many cases, real weld cycles are more suitable for studying the materials behaviour instead of using CCT diagrams. In this regard we talk about so-called in-situ diagrams.In this work, two different devices have been used to obtain CCT as well as in-situ diagrams of a low alloyed steel 10GN2MFA. The goal was to compare the results obtained on the one hand by using a widely used standard dilatometer (Bähr DIL-805A/D) and on the other hand by the usage of a thermomechanical simulator called Gleeble®3800. The paper should finally show advantages as well as disadvantages of using different devices and to keep in mind that the optimal measurement method depends on different parameters. Realized experiments also have revealed the range of operational and diagnostic potential of used devices.

Observation of Impact of Progressive Cooling System on Temperature Field Distributions on Surfaces of Injection Moulded Plastic Parts

Cooling the injection moulds with using of liquid CO2 is rated among progressive and innovative tempering systems nowadays. In the ideal case this cooling method is chosen in combination with conventional drilled or milled tempering channels where the heat transfer medium flows. These wide-spread ways of cooling are not very often effective enough and they do not provide required accuracy of heat transfer control during production by injection moulding technology. Implementation of capillary tubes that bring the liquid CO2 to critical zones enables local increasing of heat transfer. Regulation of liquid CO2 amount that is injected into mould enables removal of required heat quantity in a very short time period. In this way the homogenous rate of part cooling can be achieved which is very difficult when producing the parts with complex geometry or with combination of various wall thickness. The final mechanical and physical properties of moulded parts accrue from properties of polymer material, part design and used technological parameters. This article deals with evaluation of technological parameters, concretely the cooling parameters of both the conventional cooling method and the system utilizing the cooling potential of liquid CO2. The analysis is focused on observation of temperature field distribution on injected part surfaces.

New Methods of Obtaining Input Data of Numerical Computations by Using Heat Treatment Simulator

This paper aims to present completely new method of processing experiments which leads to obtaining input data for numerical simulations of heat treatment of large scale parts. Owing to stated method it will be possible, by using experiments on small tested sample, to simulate cooling conditions comparable with cooling of large scale parts. Apart from that this method of testing makes current boundary conditions during real cooling process more accurate, but it also multiplies stated conditions e. g. by effect of movement of cooling part in hardening media. In the paper we will also present the experimentally obtained difference in cooling rates measured by normalized quench test, standard way of hardening and a method according to newly suggested methodology.