346 research outputs found
The Characterization of Phase Transformations in Rapidly Solidified Al-Fe and Cu-Fe Alloys through Measurements of the Electrical Resistance and DSC
For the characterization of the phase transformations in the alloys during the heat treatment the various methods of the thermal analyses are available. Thermogravimetry, differential thermal analysis (DTA) and the differential scanning calorimetry (DSC) are the most frequently used methods. The phase transformations proceed in two stages, i.e. nucleation and the growth of the new phase. Both processes are closely linked with the movement of the atoms. Rapidly solidified alloys often contain the elements with the low diffusivity. During the transition from the unstable to the stable state the energy changes are small, therefore the characterization of the changes by DTA, DSC is very difficult and could not be measured. During the heat treatment the phase transformations of the rapidly solidified alloys of Al-Fe and Cu-Fe were successfully detected by the simultaneous measurements of the electrical resistance, and were compared by the DSC method. By determination of the temperature regions of the phase transitions or temperatures, where the dynamics of the changes is maximal, the samples were heat treated and analysed by the scanning and transmission electron microscopy respectively
UÄinkovitost i kvaliteta indukcijskog zagrijavanja i kaljenja osovina startera dizel motora
Presented work discusses a complex process of inductive heating and quenching of carbon steel planetary shafts for diesel engine starters. On the measurements base of temperature fields on the surface of the planetary shafts by thermographic camera and theoretical knowledge, a mathematical model for temperature conditions determination in the shaft during the entire process of heating and quenching was carried out. On the basis of developed mathematical model a computer program was developed, and used for analyses and induction hardening process optimization of planetary shafts.U ovom se radu raspravlja o složenom procesu indukcijskog zagrijavanja i kaljenja osovina iz ugljiÄnog Äelika za pokretanje dizelskih motora. Na temelju rezultata mjerenja temperaturnih polja na povrÅ”ini osovina termografskom kamerom i teorijskih spoznaja, razvijen je matematiÄki model temperaturnih uvjeta tijekom procesa zagrijavanja i kaljenja osovina. Na temelju postavljenog matematiÄkog modela razvijen je raÄunalni program koji je koriÅ”ten za analizu i optimizaciju procesa zagrijavanja osovina
Zona utjecaja topline kod navarivanja kromovog ledeburitnog Äelika
Tools get failured during work; wear is a major factor that contributes to failures. Damaged tools are replaced or filed. This paper describes typical changes that occur in the heat affected zone of tool (HAZ), which was repaired by surfacing with a TIG and with micro-plasma procedure. Microstructure of the steel on the repaired tool was analysed by an optical and scanning electron microscope. The tool was made of chromium ledeburitic steel type W.N. 1.2379 and it was repaired by surfacing steel type W.N. 1.4718. Changes in the HAZ also depend on the type of surfacing. Besides microstructural changes, dissolution of carbides, especially primary carbides. This way the concentration of the carbide-forming elements and carbon is increased in the base around the primary carbides in the HAZ so the result is so-called secondary eutectic or secondary ledeburite.Alat se tijekom rada oÅ”teÄuje. VeÄina oÅ”teÄenja nastaje zbog habanja materiala. OÅ”teÄeni alat se popravlja navarivanjem. U ovom radu opisuju se znaÄajne promjene u zoni utjecaja topline (ZUT) alata koji je obnovljen navarivanjem TIG postupkom i mikroplazmom. Mikrostrukturu Äelika obnovljenog alata analiziralo se pomoÄu optiÄkog i scaning elektronskog mikroskopa. Alati su izraÄeni iz kromovog ledeburitnog Äelika W.N.1.2379, a obnovljeni su navarivanjem Äelika W.N.1.4718. Promjene u zoni utjecaja topline povezane su takoÄer i s naÄinom navarivanja, meÄu mikrostrukturnim promjenama specifiÄno je rastapanje karbida, posebno primarnih. Na takav se naÄin u okolini karbida u ZUT poveÄava koncentracija karbidotvornih elemenata i ugljika toliko, da dolazi do lokalnog taljenja i nastanka t.z. sekundarnog ledeburita
Analiza meÄupovrÅ”ine eksplozijski zavarenih ploÄa iz niskougljiÄnog Äelika i titana
On the basis of experimentally obtained data, it was established that a very thin layer of a melt is generated at the explosive welding of two metals at the bond interface within which impurities flow at the bond during melting. Rapid cooling after the collision generates an alloy of different structure and very small grains of an average thickness approximately 1 to 2 mm. The generation of such an amorphous layer in the bond area has been noticed with various metal combinations and represents a fundamental mechanism of explosive welding of metals. Using the metallographic analysis, the development of the vortices which were formed by the explosive welding of low-carbon steel and titanium plates is described in the paper.Na osnovi eksperimentalnih rezultata utvrÄeno je da pri eksplozijskom zavarivanju dvaju metala na meÄupovrÅ”ini spoja nastaje veoma tanki sloj rastaljenog metala unutar kojeg dolazi do istjecanja neÄistoÄa tijekom taljenja. Velika brzina hlaÄenja nakon sudara dovodi do nastanka sitnozrnate legure drugaÄije strukture s projeÄnom veliÄinom od 1 do 2 mm. Zapaženo nastajanje amorfnog sloja na podruÄju spoja kod razliÄitih kombinacija metalnih materijala predstavlja temeljni mehanizam eksplozijskog zavarivanja metala. Primjenom rezultata metalografske analize u radu je opisan razvoj vrtloga koji su nastali eksplozijskim zavarivanjem ploÄa iz niskougljiÄnog Äelika i titana
Examination of weld defects by computed tomography
Defects in metal arc gas (MAG) welds made in S235JR low carbon steel of 6 mm thickness were examined. A sample containing lack of fusion (LOF) and pores was examined by computed tomography ā CT. The computed tomography examination was performed in order to define LOF size and position as well as dimensions and distribution of accompanying pores in the weld metal
UvoÄenje tehnologije eksplozijskog platiranja u postupku izrade hidrauliÄkih cilindara
The microhardness, microstructure and bond strength of the interface of a bi-metallic joint on the cross-section of the testing hydraulic cylinder were investigated. Experimental findings of related to both method of cladding obtained with metallographic and mechanical investigations of the interface between the CuSn6 bronze and the TS5 (Ä.1213) steel cylinder, are given.Istraživani su mikrotvrdoÄa, mikrostruktura i ÄvrstoÄa veze meÄupovrÅ”ine bimetalnog spoja po popreÄnom presjeku ispitivanog hidrauliÄnog cilindra. Na osnovi metalografskih i mehaniÄkih ispitivanja meÄupovrÅ”ine izmeÄu CuSn6 bronce i ÄeliÄnog cilindra TS5 (Ä.1213) usporedno su prikazani odgovarajuÄi rezultati ovih dviju tehnologija platiranja
Ispitivanje greŔaka zavara kompjutorskom tomografijom
Defects in metal arc gas (MAG) welds made in S235JR low carbon steel of 6 mm thickness were examined. A sample containing lack of fusion (LOF) and pores was examined by computed tomography ā CT. The computed tomography examination was performed in order to define LOF size and position as well as dimensions and distribution of accompanying pores in the weld metal.Ispitivane su greÅ”ke u zavarenom spoju niskougljiÄnog Äelika S235JR debljine 6 mm zavarenog MAG postupkom. Uzorak koji sadrži greÅ”ke naljepljivanja i pore je ispitivan kompjutorskom tomografijom - KT. Programskom analizom tomografa je odreÄena veliÄina i pozicija greÅ”aka naljepljivanja kao i dimenzije i raspored prateÄih pora u zavarenom spoju
Effect of nonmetallic inclusions on steel welds metal hot cracking
Intercrystally distributed nonmetallic inclusions greatly increase weld susceptibility to hot cracking. Oxide and sulphide inclusions are the result of contaminated base material or its highly oxidised surfaces and they can be a consequence of metallurgical reactions between welding slag and remelted base material, while carbide inclusions can occur due to the mixing of high-carbon base and low-carbon filler material. All welding surfaces must thus be cleaned before welding and the least possible mixture of base with filler material must be enusured during welding
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