The mechanics behind formation of secondary ledeburite during tool steel welding

U ovom prilogu opisujemo mikrostrukturne promjene u zoni toplinskog utjecaja (ZTU) alatnog čelika W. Nr. 1.2379, koji je bio navaren ili zavaren po postupku zavarivanja pod praškom s različitim parametrima zavarivanja. Mikrostrukturu zavara i navara analizirali smo pomoću optičnog i rasterskog (skenirajućeg) elektronskog mikroskopa. U analiziranju smo posebno utvrđivali mikrostrukturne promjene u okolini primarnih kromovih karbida u zoni toplinskog utjecaja i njihov utjecaj na kristalizaciju zavara. Utvrdili smo, da su temperature u zoni toplinskog utjecaja za vrijeme zavarivanja dovoljno visoke da se za vrijeme rastapanja primarnih karbida u okolnoj matici do te mjere povećala koncentracija karbidotvornih elemenata i ugljika, da je nastala tz. talina eutektičnog sastava, koja se stvrdnula u sekundarni eutektik (ledeburit), na kojemu se na granici ZTU/zavara pokrene kristalizacija zavara.In this article we describe the microstructural changes in the heat affected zone (HAZ) of the tool steel W. Nr. 1.2379, which was surfaced or welded by the submerged arc welding technique (SAW) with different welding parameters. Microstructure of the welds and of the surfacing welds was analysed by optical and scanning electron microscope. In this research, we particularly studied microstructural changes in the area of primary chromium carbides in the HAZ and their effect on the weld crystalization. We came to the conclusion that the temperature in the HAZ is high enough during the welding process that it caused primary carbides to dissolve and concentration of the carbide-forming elements and carbon increased in the surrounding austenite matrix area to eutectic composition, which remelts and solidified as secondary eutectic (ledeburite)

Industrial control measurements of high chromium steel rolls heat treatment

In this paper, industrial control measurements of the heat treatment of high chromium steel (HCS) rolls is presented. Measurements of the gas fired car bottom chamber furnace Bosio PP- KP 70/1150 were carried out in the company Valji d. o. o., Štore, Slovenia. Temperature in the individual heating zones of the furnace, temperatures of the roll surface, furnace external walls, and gas consumption was monitored throughout the whole process of heat treatment. The temperature profile of the rolls cross-section was calculated using computer simulation. Periodical measurements of CO and NOx emissions were also carried out with the aim of combustion evaluation and ecological integrity. The successfulness of heat treatment was examined through microstructure observation, hardness measurement, and the amount of retained austenite in the heat treated rolls

Industrial control measurements of high chromium steel rolls heat treatment

In this paper, industrial control measurements of the heat treatment of high chromium steel (HCS) rolls is presented. Measurements of the gas fired car bottom chamber furnace Bosio PP- KP 70/1150 were carried out in the company Valji d. o. o., Štore, Slovenia. Temperature in the individual heating zones of the furnace, temperatures of the roll surface, furnace external walls, and gas consumption was monitored throughout the whole process of heat treatment. The temperature profile of the rolls cross-section was calculated using computer simulation. Periodical measurements of CO and NOx emissions were also carried out with the aim of combustion evaluation and ecological integrity. The successfulness of heat treatment was examined through microstructure observation, hardness measurement, and the amount of retained austenite in the heat treated rolls

Thermal characteristics of enamels and enamelled metal sheets

The main task of the research was to find out why sometimes cracking of the enamelled layer occur and to what extent enamel layer affects the heat transfer in the cooking oven. The samples of the enamelled streel sheet were metallographically analysed by scanning electron microscopy (SEM-EDX) and optical microscopy (OM). Measurements of the thermal properties of two types of enamels, which are used for oven interior enamelling was carried out in accordance with the standard ISO 22007-2 by transient planar heat source method (TPS Hot Disk 2200). To ensure proper measurement conditions, the samples of the enamels were prepared in the form of thick layers. The results show that enamel density has significant influence on its thermal properties. An assessment of the influence of the thermal conductivity of the enamel layer on the heat transfer in the oven is also given

Corrosion properties of aluminized 16Mo3 steel

Chromium-molybdenum steel (16Mo3) is widely used in petroleum, gas, automotive, and construction industries due to its good oxidation resistance and mechanical properties at moderately elevated temperatures. The aim of the research was to evaluate the corrosion susceptibility of 16Mo3 steel in hot rolled and aluminized states. Aluminization was performed by diffusion pack aluminization process at 900°C/2h and 730°C/4h, respectively. Electrochemical corrosion testing included measuring open circuit potential (EOCP), linear polarization resistance (LPR), potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS) in potassium phosphate buffer (KH2PO4, pH = 7). Optical microscopy (OM), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS) were used for surface layer microstructure characterization before and after corrosion tests. It was demonstrated that corrosion resistance of aluminized steel increased substantially. Corrosion properties were related to the structure and properties of intermetallic phase (FeAl, FeAl2 and Fe2Al5) that formed on the surface of 16Mo3 steel

FOUNDRY WASTE MANAGEMENT

Waste management in foundries is gaining a higher ecological and economical importance. Waste is becoming an increasingly traded product, where excellent profits can be made. Due to the cost reduction and successful business operation in companies, waste has to be regenerated and used again as a material to the maximum possible extent. Such research is long lasting and expensive and is a great challenge for companies. In the frame of our research, a total waste management case study for the Slovenian foundry Feniks was carried out. From the sustainable development point of view, waste management is most suitable, since it ensures the material utilization of waste, reduces the consumption of natural renewable or non-renewable resources and makes efficient production capacity utilization possible. Properly treated ecologically safe waste with a suitable physical characteristic, long-term existence, is a substitute for natural materials. Sand, dust, slag and other mineral waste from foundries are increasingly being used as materials in other industries. The foundry Feniks was awarded with certification of the environmental management system according to the standard SIST EN ISO 14001 and confirmed its environmental credentials

Synthesis and characterization of hardened Cu-Fe-Ni-P alloy

In the manufacturing industry of electrical contacts, the prohibition of the use of toxic metals (Cd, Be), and desire to avoid the alloying with precious metals (Ag) has created a need for new alloys with good electrical conductivity and high mechanical properties at elevated temperatures. As a potentially useful material for this purpose, we have analyzed the continuously cast Cu-Fe-Ni-P alloy in various heat treatment conditions. Sequence of phase transformations during heat treatment was followed by 4 point D.C. electrical resistivity measuring method, and analyzed by scanning (SEM) and transmission (TEM) electron microscopy. Measurements of Vickers hardness and electrical conductivity after various heat treatment procedures indicate on high potential of Cu-Fe-Ni-P alloys as a material for electrical contacts

FOUNDRY WASTE MANAGEMENT -CASE STUDY

ABSTRAC

Mechanism of the Mg3_3Bi2_2 phase formation in Pb-free aluminum 6xxx alloy with bismuth addition

In the present work, free-cutting aluminum alloy AA6026 with 1.1 wt.% bismuth addition was fabricated by different melt preparation methods in order to investigate whether the melt preparation route affects the solidification sequence and thus has an influence on the machinability of the alloy. All experiments were designed to simulate variable industrial conditions: addition of bismuth in an induction melting furnace, addition of bismuth in an electric resistance holding furnace, addition of bismuth together with grain refiner, effect of holding time and melt temperature before casting. Detailed thermodynamic analyses (DSC, Thermo-Calc) and microstructural characterization (SEM-EDS, XRD) have been performed to explain the solidification sequence, microstructure development and especially formation of the intermetallic Mg$_3$Bi$_2$ phase