THE INFLUENCE OF MEDIUM AND MICROSTRUCTURE ON CORROSION RATE OF DUAL PHASE HIGH-STRENGTH STRUCTURAL STEELS

The corrosion damages significantly reduce the use-value and shorten the life time of various constructions. As a result of corrosion damages occur enormous costs, and sometimes major disasters which can lead to the material costs and also dangerous consequences for human life. With proper selection of structural material and its corrosion protection these unpleasant consequences can be avoided or significantly reduced. Every material has a different corrosion behavior depending on the physical conditions and medium in which it is located. In this work the influence of medium and microstructure on corrosion rate of dual phase high-strength structural steels was studied. The electrochemical measurements revealed that both examined dual phase steels showed lower corrosion rate in the medium of 5 % NaOH, than in the medium of 5 % H2SO4. The metallographic analysis of investigated materials indicated the fact that the amount of martensite phase and morphology of microstructural constituents have a significant effect on the corrosion behavior of dual phase steels. Namely, with decreasing the amount of martensite in dual phase steels corrosion rate increases in both examined media

Influence of microstructure on the resistance of tool steels to local corrosion in 3.5% NaCl medium

In this research, electrochemical and metallographic tests were carried out on tool steel for cold and hot work, as well as steel for cementation, with the goal to obtain corrosion parameters to determine which of the examined samples is more resistant to local pitting corrosion. Electrochemical tests were performed in a medium of 3.5% NaCl, and were based on conducting cyclic anodic polarization in the potential range from -2000 mV to 200 mV vs SCE and vice versa. The results of the research showed that all three samples are subject to pitting corrosion, but the worst was the cementing tool steel sample X19NiCrMo4, which had the lowest pitting potential. The W600 tool steel sample for hot work proved to be the best, with the highest pitting potential. The results of the electrochemical tests coincide with the metallographic tests, because after corrosion in the chloride medium only the beginnings of pitting corrosion are visible on the surface of the W600 sample in the form of partial accumulations of corrosion products, while the X19NiCrMo4 cementing steel sample was completely covered with corrosion products, which means that of the three tested tool steels, cementing steel is the most susceptible to pitting corrosion and is not recommended for use in conditions where it comes into contact with chloride ions. The martensitic microstructure of cementing tool steel is responsible for the very low pitting potential and, consequently, pronounced pitting corrosion. On the other hand, the W600 tool steel showed better corrosion resistance due to its finer grain and uniform carbide distribution

Influence of microstructure on the resistance of tool steels to local corrosion in 3.5% NaCl medium

In this research, electrochemical and metallographic tests were carried out on tool steel for cold and hot work, as well as steel for cementation, with the goal to obtain corrosion parameters to determine which of the examined samples is more resistant to local pitting corrosion. Electrochemical tests were performed in a medium of 3.5% NaCl, and were based on conducting cyclic anodic polarization in the potential range from -2000 mV to 200 mV vs SCE and vice versa. The results of the research showed that all three samples are subject to pitting corrosion, but the worst was the cementing tool steel sample X19NiCrMo4, which had the lowest pitting potential. The W600 tool steel sample for hot work proved to be the best, with the highest pitting potential. The results of the electrochemical tests coincide with the metallographic tests, because after corrosion in the chloride medium only the beginnings of pitting corrosion are visible on the surface of the W600 sample in the form of partial accumulations of corrosion products, while the X19NiCrMo4 cementing steel sample was completely covered with corrosion products, which means that of the three tested tool steels, cementing steel is the most susceptible to pitting corrosion and is not recommended for use in conditions where it comes into contact with chloride ions. The martensitic microstructure of cementing tool steel is responsible for the very low pitting potential and, consequently, pronounced pitting corrosion. On the other hand, the W600 tool steel showed better corrosion resistance due to its finer grain and uniform carbide distribution

The Influence of Hydrogen on the Frangibility of Modern Structural Steels Processed at a CSP-plant

Mehaničkim, metalografskim i SEM ispitivanjima proučavan je utjecaj vodika na krhkost modernih visokočvrstih dvofaznih DP- i višefaznih TRIP-čelika. Rezultati proučavanja mikrostrukturnih i mehaničkih svojstava termomehanički obrađenih TMCP-čelika prije i nakon navodičenja ukazali su na činjenicu da je TRIP-čelik otporniji na vodikovu krhkost, o čemu svjedoči njegova sitnozrnata mikrostruktura bez pukotina te nepromijenjene vrijednosti za mehanička svojstva nakon navodičenja.By mechanical testing, metallographic and SEM analyses, the influence of hydrogen on the frangibility of modern high-strength dual phase DP- and multiphase TRIP-steels was studied. Results of studying of microstructural and mechanical properties of thermomechanically controlled processed TMCP-steels before and after hydrogenation indicate that TRIP-steel has higher resistance to HE, which can be seen from its fine-grained microstructure with no cracks and also from unchanged mechanical performances after hydrogenation

Iskustva u gospodarenju otpadom koji sadrži azbest u Republici Hrvatskoj

This paper presents an overview of asbestos production data worldwide and in the Republic of Croatia in the period 2000 to 2018 as well as the asbestos consumption data from 1995 to 2010. The results of asbestos waste collection from 1995 to 2018 have been analyzed and the experiences of the Republic of Croatia in the management of asbestos-containing waste have been described in accordance with the applicable national legislation. Although asbestos does not pose a risk if its products do not become damaged by fracture, or during transportation or decomposition, it poses a potential danger to human health. In today\u27s world, every five minutes someone dies from a disease related to asbestos, such as asbestosis and cancer caused by asbestos. For these reasons, most countries adopted the obligation to execute a series of measures to stop using asbestos in 1999, while at the same time in the Republic of Croatia still imported about 4000 tonnes of asbestos per year. In 2006, the Republic of Croatia banned the production, transport, and use of asbestos, and the asbestos objects whose lifetime expired ended up in municipal waste, causing the need for special regulations in order to arrange the management of asbestos containing waste. Over the past ten years, the Republic of Croatia has developed an asbestos waste management system. Regardless of the success of its application, certain improvements are needed, as data on the amounts of reported construction waste, and thus the part containing asbestos, do not coincide with economic and other indicators for the construction sector.U radu je dan pregled podataka o proizvodnji azbesta u svijetu i Republici Hrvatskoj u razdoblju od 2000. do 2017. godine te njegovoj potrošnji, od 1995. do 2010. godine. Analizirani su rezultati sakupljanja otpada koji sadrži azbest od 1995. do 2018. godine i opisana su iskustva Republike Hrvatske u gospodarenju otpadom koji sadrži azbest u skladu s važećom nacionalnom legislativom. Iako azbest ne predstavlja rizik sve dok se njegovi proizvodi ne oštete prilikom loma, tijekom transporta ili raspadanja, on predstavlja potencijalnu opasnost za ljudsko zdravlje. Danas u svijetu svakih pet minuta netko umre od bolesti povezane s azbestom, poput azbestoze i karcinoma uzrokovanog azbestom. Iz ovih razloga je većina država u svijetu još 1999. godine prihvatila obvezu izvršenja niza mjera za prestanak uporabe azbesta, dok se istovremeno u Republiku Hrvatsku još uvijek uvozilo oko 4000 tona azbesta na godinu. Republika Hrvatska je tek 2006. godine zabranila proizvodnju, promet i upotrebu azbesta, a predmeti od azbesta kojima je vijek trajanja istekao, završavali su u komunalnom otpadu, zbog čega se nametnula potreba za donošenjem posebnih propisa kojima je uređeno gospodarenje otpadom koji sadrži azbest. U proteklih desetak godina u Republici Hrvatskoj je razvijan sustav gospodarenja otpadom koji sadrži azbest. Bez obzira na uspješnost njegove primjene, nužna su određena poboljšanja, jer se podaci o količinama prijavljenog nastalog građevnog otpada, a s time i onog dijela koji sadrži azbest, ne podudaraju s gospodarskim i drugim pokazateljima za građevni sektor

Tool steels - classification and basic properties

U ovom radu dan je pregled proučavanja metalurških procesa naprednih metalnih materijala. Termodinamičke karakteristike procesa obuhvadaju uvjete prema kojima je mogude pratiti odvijanje procesa u željenom pravcu te kinetiku odvijanja procesa. Alatni čelici pripadaju skupini naprednih metalnih materijala od kojih se zahtijevaju posebna svojstva poput visoke tvrdode i otpornosti na trošenje, postojanost čvrstode kod povišenih temperatura, dobro ponašanje pri toplinskoj obradi, korozijska otpornost i dr. Postizanje dobrih svojstava omogudeno je legiranjem kromom, volframom, vanadijem, molidbenom ili kobaltom. Veoma je bitno u kojoj mjeri se dodaju legirajudi elementi i kako teče proces proizvodnje, jer spojevi koji nastaju tijekom proizvodnje mogu se mijenjati i tako utjecati na transformacijske procese te se izlučiti u nepoželjnom obliku. Legirajudi elementi se najčešde spajaju s ugljikom u karbide, ali također mogu dijelom supstituirati u kristalnu rešetku željeza te stvarati nepoželjne intermetalne spojeve. U svrhu poboljšanja svojstava alatnih čelika, teži se pronalasku adekvatnog kemijskog sastava kako bi se omogudilo dobivanje stabilnih termodinamičkih parametara.This paper presents an overview of metallurgical processes of advanced metallic materials. The thermodynamic characteristics of the process include the conditions under which it is possible to follow the process in the desired direction and kinetics of the process. Tool steels belong to a group of advanced metallic materials, which are required by special properties such as high hardness and wear resistance, high strength stability at elevated temperatures, good behavior during heat treatment, high corrosion resistance etc. Achieving good properties is enabled by alloying with chromium, tungsten, vanadium, molybdenum or cobalt. It is very important to what extent the alloying elements are added and how the process of production proceeds, because the compounds formed during the production can be altered, and thus affect the transformation processes, and secreted in an undesirable form. Alloying elements are most often combined with carbon in carbides but can also be partially substituted in the iron crystal lattice and create undesirable intermetallic compounds. In order to improve the properties of tool steels, the aim is to find an adequate chemical composition to enable obtaining stable thermodynamic parameters

Pit nucleation on as-cast aluminiuim alloy AW-5083 in 0.01M NaCl

The use of aluminium alloys in a wide range of technical applications is related mostly to the two facts: they facilitate weight saving of final products (if compared to the steel) and they are prone to spontaneous passivity due to the coherent surface oxide layer which impedes further reaction of aluminium with the environment. Among the commercial Al alloys, EN AW-5083 alloy is a representative non-heat treatable Al-Mg based alloy which possesses many interesting characteristics as a structural material, such as low price, moderately high strength, high formability in conjunction with superplasticity and good corrosion resistance in marine atmospheres. Aiming to enhance the knowledge of possible interactions of studied alloy EN AW-5083 in as-cast condition with chloride media, electrochemical measurements were used to follow the pitting behaviour in 0.01 M NaCl. The results of tests have shown that susceptibility of alloy to pitting corrosion is strongly influenced by the microstructural constituents of the alloy in as-cast condition

Influence of medium on corrosion and microstructural properties of HTCS-130 tool steel for hot work

In this paper the corrosion resistance of tool steel for hot work in the industrial emulsion medium (Lenox Band-Ade semi-synthetic oil + water, in ratio 1:10), water and 3.5% NaCl medium was tested. By Tafel’s extrapolation from polarization curves it was established that the tested tool steel showed extremely high corrosion rate in water and 3.5% NaCl medium in contrast to medium of Lenox BandAde emulsion. The double higher corrosion rate of tool steel is recorded in the chloride medium as opposed to that obtained in water, indicating that the tested steel is more corrosion resistant in water. The obtained results were confirmed by the method of electrochemical impedance spectroscopy. The sample of tool steel in the Lenox Band-Ade emulsion medium showed far greater value of charge transfer resistance Rct than that obtained in the water medium and 3.5% NaCl, which means that the Lenox Band-Ade emulsion formed a thicker oxide layer that has the role of barrier in further penetration of aggressive ions from the solution. The conducted SEM analysis after electrochemical measurements in 3.5% NaCl medium indicate the occurrence of pitting corrosion caused by breaking the passive surface of the material as a result of the action of aggressive ions from the solution. The EDS analysis of formed pits has been shown the increased oxygen content, but also the higher presence of sodium and chlorine, which accumulate in the pits, and come from the medium. Molybdenum and tungsten showed the highest presence in white deposits on the sample surface, which represent parts that did not completely cover with oxide layer, which is why the smallest oxygen content was recorded at these sites. The obtained corrosion rate values in the water medium and the chloride medium indicate that the studied tool steel is poorly stable in water and chloride media, and because of that it can only be used in exceptional cases under conditions in which it will come into contact with water or chloride medium

Influence of medium on corrosion and microstructural properties of HTCS-130 tool steel for hot work

In this paper the corrosion resistance of tool steel for hot work in the industrial emulsion medium (Lenox Band-Ade semi-synthetic oil + water, in ratio 1:10), water and 3.5% NaCl medium was tested. By Tafel’s extrapolation from polarization curves it was established that the tested tool steel showed extremely high corrosion rate in water and 3.5% NaCl medium in contrast to medium of Lenox BandAde emulsion. The double higher corrosion rate of tool steel is recorded in the chloride medium as opposed to that obtained in water, indicating that the tested steel is more corrosion resistant in water. The obtained results were confirmed by the method of electrochemical impedance spectroscopy. The sample of tool steel in the Lenox Band-Ade emulsion medium showed far greater value of charge transfer resistance Rct than that obtained in the water medium and 3.5% NaCl, which means that the Lenox Band-Ade emulsion formed a thicker oxide layer that has the role of barrier in further penetration of aggressive ions from the solution. The conducted SEM analysis after electrochemical measurements in 3.5% NaCl medium indicate the occurrence of pitting corrosion caused by breaking the passive surface of the material as a result of the action of aggressive ions from the solution. The EDS analysis of formed pits has been shown the increased oxygen content, but also the higher presence of sodium and chlorine, which accumulate in the pits, and come from the medium. Molybdenum and tungsten showed the highest presence in white deposits on the sample surface, which represent parts that did not completely cover with oxide layer, which is why the smallest oxygen content was recorded at these sites. The obtained corrosion rate values in the water medium and the chloride medium indicate that the studied tool steel is poorly stable in water and chloride media, and because of that it can only be used in exceptional cases under conditions in which it will come into contact with water or chloride medium

Influence of medium and microstructure on corrosion behavior of gray cast iron

U ovom radu ispitana je korozijska otpornost sivog lijeva u mediju umjetne kiše i mediju 0,5 M H2SO4 te utjecaj mikostrukture na njegovo korozijsko ponašanje u navedenim medijima. Tafelovom ekstrapolacijom polarizacijskih krivulja je ustanovljeno da ispitani sivi lijev pokazuje izrazito veliku brzinu korozije u kiselom mediju za razliku od ispitivanja u mediju umjetne kiše, gdje brzina korozije poprima znatno manju vrijednost. Međutim, u usporedbi s rezultatima ranijih istraživanja dobivenim za nodularni lijev te su vrijednosti trostruko vede, što upuduje na činjenicu da je nodularni lijev ipak korozijski otporniji u uvjetima atmosferske korozije te stoga i prihvatljiviji za izradu dijelova za poljoprivredne strojeve. Dobiveni rezultati su potvrđeni i metodom elektrokemijske impedancijske spektroskopije, pri čemu je u mediju umjetne kiše za sivi lijev registriran manji otpor prijenosu naboja od nodularnog lijeva. To ukazuje na činjenicu da se na sivom lijevu formirao tanji sloj, koji predstavlja slabu barijeru prema prodiranju agresivnih iona iz otopine. Dobiveno korozijsko ponašanje sivog lijeva u ispitanim medijima može se povezati i s njegovom mikrostrukturom. Naime agresivni ioni iz primijenjenih medija napadaju metalnu osnovu ispitanih materijala, dok grafit zadržava svoj prvobitni oblik. Pri usporedbi s nodularnim lijevom, nodule su se pokazale kao povoljniji oblik izlučenog grafita jer bolje prekrivaju površinu uzorka i slijedom navedenog izoliraju uzorak u procesu elektrokemijske korozije.This paper investigated the corrosion resistance of gray cast iron in the medium of artificial rain and 0.5 M H2SO4 medium and the effect of microstructure on its corrosion behavior in the mentioned media. By Tafel's extrapolation of the polarization curves, it was found that the examined gray cast iron shows an extremely high corrosion rate in the acidic medium, as opposed to the artificial rain test, where the corrosion rate is much lower. However, compared with the results of earlier researches obtained for nodular cast iron these values are three times higher, indicating that the nodular cast iron is more corrosion-resistant to atmospheric corrosion and therefore more acceptable for the manufacture of parts for agricultural machines. The obtained results were confirmed by the method of electrochemical impedance spectroscopy, where in the medium of artificial rain lower value of charge transfer resistance of gray cast iron was registered in opposite to nodular cast iron. These points to the fact that a thin layer formed on the gray cast iron, which represents a weak barrier to penetrating aggressive ions from the solution. The corrosion behavior of the gray cast iron in the tested media can also be related to its microstructure. Namely, aggressive ions from the applied media attack the metal matrix of the examined materials, while the graphite retains its original form. When compared to nodular cast iron, the nodules seems to be a more favorable form of precipitated graphite due to better sample surface covering and therefore the insulation in electrochemical corrosion process