Wyniki wyszukiwania - BazTech

1

Effects of steel - applied for large-dimension castings for the power engineering - refining in the ladle-furnace

Kalandyk B., Wojtal W

Archives of Metallurgy and Materials

|

2013

|

Vol. 58, iss. 3

779--783

EN

The changes of a sulphur content during refining in melting low-alloy and high-alloy steels (G17CrMoV5-10; GX12CrMoNiVNbN9-1) applied for large-dimension castings for the power engineering are presented in the hereby paper. The investigated steel was melted in the oxygen-recovery melting technology with an application of maximum 70% of the process scrap. In addition, after steel melting in the electric arc furnace (EAF), the secondary metallurgy was performed in the ladle furnace (LF). It was shown that the application of the secondary metallurgy by a synthetic slag in the ladle furnace and argon bubbling of a metal bath leads to obtaining in the final analysis: 0.0043-0.0046% of sulphur (a decrease of S content during refining in LF reached 40%). Current measurements of FeO in the slag and maintaining its content below 0.8%, support obtaining such low sulphur content in steel. So low level of the slag oxidizing is one of the necessary conditions for a deep desulphurisation of the metal bath. Without the secondary metallurgy the sulphur content in low-alloy cast steel was 0.007%, while 0.01% in high-alloy cast steel. Controlling of the gas (oxygen, nitrogen) content during steel melting and correcting the amount of additions (e.g. deoxidants), allowed to obtain the low oxygen content (below 45 ppm for two investigated steel grades) and nitrogen content (88 ppm for low-alloy steel and 330 ppm for high-alloy steel), which warrants a good combination of strength and plastic properties.

PL

W pracy przedstawiono zmiany zawartosci siarki podczas rafinacji w czasie wytapiania stali nisko- i wysokostopowej (G17CrMoV5-10; GX12CrMoNiVNbN9-1) stosowanej na wielkogabarytowe odlewy dla energetyki. Badana stal wytopiono w technologii odzyskowo-tlenowej z zastosowaniem maksymalnie 70% złomu własnego. Dodatkowo, po wytopieniu stali w piecu łukowym (EAF) przeprowadzono obróbke pozapiecowa w pieco-kadzi (LF). Wykazano, ze zastosowanie obróbki pozapiecowej zuzlem syntetycznym w pieco-kadzi i argonowania kapieli metalowej prowadzi do uzyskania w analizie koncowej 0,0043-0,0046%S (zmniejszenie zawartosci S podczas rafinacji w LF siegało 40%). Uzyskaniu tak niskiej zawartosci siarki w stali sprzyja m.in. biezacy pomiar FeO w zuzlu i utrzymanie jego zawartosci ponizej 0,8%. Tak niski poziom stopnia utlenienia zuzla jest jednym z warunków koniecznym do dobrego odsiarczenia kapieli metalowej. Bez obróbki pozapiecowej zawartosc siarki w staliwie niskostopowym wynosiła 0,007%, natomiast dla staliwa wysokostopowego 0,01%. Kontrola zawartosci gazów (tlenu i azotu) w czasie wytapiania stali i dokonywana korekta ilosci wprowadzanych dodatków (np. odtleniaczy) doprowadziła do uzyskania niskiej zawartosci tlenu (ponizej 45 ppm dla dwóch badanych gatunków stali) i azotu (88 ppm dla stali niskostopowej, 330 ppm dla stali wysokostopowej) gwarantujaca dobra kombinacje własciwosci wytrzymałosciowych i plastycznych odlewów.

2

Nitrogen hardening of creep-resistant G-NiCr28W alloy

Pirowski Z., Wodnicki J., Gwiżdż A.

Archives of Foundry Engineering

|

2010

|

Vol. 10, iss. 3

79--84

EN

In the group of creep-resistant materials, most important are heat-resistant nickel-based alloys. The G-NiCr28W alloy subject to detailed examinations was observed to have two different austenite-like phases. In the interdendritic spaces of alloy matrix, the presence of another phase, also characterised by paramagnetic properties, was detected. Inside this interdendritic phase, local areas of a lamellar structure, composed of both of the above mentioned phases, were present. Nitrogen treatment was observed to raise the microhardness of both these phases. The presence of nitrogen made the regions of a lamellar structure disappear completely. Their place was occupied by precipitates dispersed in the matrix, and occasionally forming large clusters. It has been observed that cold work can harden the G-NiCr28W alloy to a very small degree only, in spite of the fact that hardness is increasing systematically with the increasing degree of cold work. The said alloy, when enriched with nitrogen added as an alloying element, is characterised by hardness higher than the hardness of its nitrogen-free counterpart. The value of hardness is increasing even more under the effect of low-degree cold work, although increasing further the degree of cold work seems to have no effect on hardness increase. The problem faced in nickel-based materials is the possibility of making defect-free castings from alloys with high nitrogen content. Alloys investigated in the present study were remelted, cast and subject to solidification under high nitrogen pressure in the furnace chamber. However, melting carried out under these conditions could not prevent the occurrence of non-metallic inclusions which, while being unable to pass to a riser, formed local clusters or even thin films, resulting in numerous microcracks or discontinuities encompassing large regions of the casting. This problem seems to be of major concern and is the first one to require prompt solution in the currently executed large research project.

3

Effect of melting technology on the properties of G17CrMo5-5 steel for cast turbines

Mańkowski P., Kalandyk B., Zapała R.

Archives of Foundry Engineering

|

2010

|

Vol. 10, iss. 4

133--136

EN

Two technologies of the G17CrMo 5-5 cast steel melting were compared, i.e. the so far used oxygen-recovery melting technology (electric arc furnace + ladle furnace – EAF + LF) and a new recovery melting technology (electric induction furnace + ladle furnace - EIF + LF). The effect of the melting technology on the properties of cast steel for turbine parts was determined. The cast steel was evaluated in term of its metallurgical purity and mechanical properties. During melting of G17CrMo 5-5 steel in induction furnace, lower total content of oxygen in casting was reached, but nitrogen content was higher than it was in the cast steel from arc furnace. Metal refining in LF improved the steel desulphurising degree and contributed to modification of the non-metallic inclusions.

4

Application of cast nickel alloys for parts of electronics characterised by special magnetic properties

Uhl W., Pirowski Z., Kułak A.

Archives of Foundry Engineering

|

2008

|

Vol. 8, iss. 1 spec.

327--330

EN

The theoretical part of the study highlights the origin of the idea to start investigations on alloys of high magnetic permeability, manufactured mainly by companies in the USA and Japan. The said materials are applied for various parts of electronics used by the military industry, e.g. satellite antennas for global communication with submarines, and for research instruments, e.g. ferromagnetic cores. They are characterised by very high magnetic permeability, resistivity and corrosion resistance which make them suitable for operation under extra-trying conditions. Nickel alloys of high magnetic properties are usually manufactured as rolled products. The ambition of the authors of this study is to manufacture them as cast products. The program of research included characteristic of nickel alloys with additions of molybdenum and iron satisfying the above mentioned requirements, with attention focussed on their application for magnetic parts of satellite antennas and ferromagnetic cores. Moulding and casting technologies were proposed to best suit the process of manufacture of these elements. The range of chemical compostion was selected to ensure the required magnetic, mechanical and anti-corrosive properties. A series of melts was prepared and castings of the above mentioned elements were made. The chemical composition of the alloys was analysed along with the structure examinations and quality assessment made by the non-destructive methods. Castings were subjected to the finishing treatment, followed by tests and examinations to enable their practical application.