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1

Microstructural study of the composite nickel based, containing different Al amounts, sintered by an unconventional technique and forged

Bendriss Houceme, Boudebane Said, Lemboub Samia, Benselhoub Aissa

Inżynieria Materiałowa

|

2024

|

Vol. 45, nr 3

8--17

EN

The aluminum-enriched composite with the composition of Udimet 720 alloy was developed using an unconventional two-step sintering process. The first occurred at 1380°C for 0.5 h and the second at 1180°C for 3 h. The sintered material was then forged at 1200°C under a load of 50 kG and with a fall height of 220 mm, in order to achieve the clusters fragmentation of hard components, followed by the homogenization annealing at 800°C for 1.5 h. The consolidation technique included solution treatment at 1080°C and aging at 800°C with various holding times. The investigation techniques by X-ray diffraction analysis (XRD) and observations under a scanning electron microscope (SEM) with semi-quantitative analyses (EDS) have offered the possibility to reveal the aluminum addition’s impact and the holding time aging on the material’s microstructural evolution. The sintered alloy with a high Al content (5.25 %) exhibits a complex structure composed of metallic matrix γ, the chromium carbide Cr23 C6 , and a large variety of binary intermetallics. Despite this, the solution treatment caused an almost complete dissolution of these compounds, and consequently, a saturation of the nickel cubic lattice. An increase in precipitation phenomenon was, due to the formation of the intermetallic γ’ (Ni, Co)3 (Al, Ti), and then, the alloyed chromium carbide (Cr, Co, Ni, Mo, Ti)23 C6 , led to a noticeable hardening of the metal matrix, reaching a microhardness of 700 HV0.1.

PL

Opracowano kompozyt wzbogacony aluminium o składzie stopu Udimet 720 w niekonwencjonalnym dwuetapowym procesie spiekania. Kompozyt spiekano w temp. 1380°C przez 0,5 h, a następnie w temp. 1180°C przez 3 h. Spiekany materiał poddano kuciu w temp. 1200°C pod obciążeniem 50 kG i wysokości opadania 220 mm, w celu uzyskania fragmentacji skupień twardych składników, a następnie wyżarzaniu homogenizującym w temp. 800°C przez 1,5 h. Technika konsolidacji obejmowała obróbkę przesycającą w temp. 1080°C i starzenie w temp. 800°C z różnymi czasami przetrzymywania. Techniki badawcze polegające na analizie dyfrakcji promieni rentgenowskich (XRD) i obserwacje pod skaningowym mikroskopem elektronowym (SEM) wraz z analizami półilościowymi (EDS) umożliwiły ujawnienie wpływu dodatku aluminium i czasu utrzymywania starzenia na ewolucję mikrostruktury materiału. Spiekany stop o wysokiej zawartości Al (5,25%) wykazywał złożoną strukturę, na którą składały się: metaliczna osnowa γ, węglik chromu Cr23 C6 i duża różnorodność binarnych związków międzymetalicznych. Mimo to obróbka roztworowa spowodowała niemal całkowite rozpuszczenie tych związków, a w konsekwencji nasycenie sześciennej sieci niklu. Nasilenie zjawiska strącania osadów spowodowane utworzeniem się międzymetalicznego γ' (Ni, Co)3 (Al, Ti), a następnie stopowego węglika chromu (Cr, Co, Ni, Mo, Ti)23 C6 , doprowadziło do zauważalnego utwardzenia osnowy metalicznej, osiągającego mikrotwardość 700 HV0,1.

2

Influence of ageing on microstructure and mechanical properties of TP347HFG austenitic stainless steel

Golański Grzegorz, Purzyńska Hanna

Bulletin of the Polish Academy of Sciences. Technical Sciences

|

2023

|

Vol. 71, nr 2

art. no. e144607

EN

The paper presents the results of microstructural and mechanical investigation of long-term aged TP347HFG austenitic stainless steel. Ageing was performed at a time of up to 30 000 hours and the temperature of 600 and 650◦C. Ageing was proved to lead to the precipitation of secondary phase particles not only inside grains but also on the boundaries of grains and twins. The MX precipitates were observed inside the grains. However, M23C6 carbides and sigma phase precipitates were observed on grain boundaries. The changes in the microstructure of the examined steel translated into the mechanical properties, i.e. initially observed growth and then the decrease of yield strength and a gradual decrease in impact energy. The overageing process – a decrease in strength properties – was associated with the growth of the size of M23C6 carbides and the precipitation of the sigma phase. The reduction of impact energy in TP347HFG austenitic stainless steel was found to be associated with the precipitation of M23C6 carbides in the case of the 600◦C temperature, and the M23C6 carbides and sigma phase in the case of the 650◦C temperature. The rate of changes in the microstructure and mechanical properties depended on the ageing temperature.

3

Structure of the S304H Steel after 20,000 Hours of Ageing

Wersta Robert, Zieliński Adam, Sroka Marek, Puszczało Tomasz, Sówka Karol

Archives of Metallurgy and Materials

|

2022

|

Vol. 67, iss. 2

487--493

EN

The S304H steel is used in the construction of pressure components of boilers with supercritical operating parameters. The paper presents the results of the research on the microstructure after ageing for 20,000 hours at 650 and 700°C. The microstructure examination was performed using scanning and transmission electron microscopy. The precipitates were identifies using transmission electron microscopy. The influence of ageing time on microstructure changes and the precipitation process of the tested steel is described. The presented research results are an element of material characteristics of the new generation of steel, which are used in the design work of pressure devices of steam boilers and in diagnostic work during operation.

4

Structure of 22Cr25NiWCoCu Austenitic Stainless Steel After Ageing

Sroka Marek, Zieliński A., Puszczało T., Sówka K., Hadzima B.

Archives of Metallurgy and Materials

|

2022

|

Vol. 67, iss. 1

175--180

EN

The 22Cr25NiWCoCu austenitic stainless steel was developed by AB Sandvik Material Technology in Sweden. Due to its high creep strength and good corrosion resistance, this material is well suited for use in superheaters in advanced coal-fired power boilers as well as in other types of steam boilers using various types of fuel. The examined material was subject to long-term ageing for the time of annealing up to 20 000 h at 700 and 750°C. Precipitation processes and microstructure stability as-received and after ageing were investigated. Examination of the microstructure was conducted using scanning electron microscopy. The identification of secondary phases was carried out by X-ray phase composition. Using the results of the investigations of precipitation processes in the microstructure, both within the grains and at the grain boundaries, their statistical analysis was carried out. To illustrate this impact, the following parameters were used: surface area and equivalent diameter of precipitates. Based on the surface area measurements, the percentage of the phase in the reviewed photo’s total area was calculated.

5

Analysis of the precipitation process of secondary phases after long-term ageing of the S304H steel

Zieliński Adam, Wersta Robert, Sroka Marek

Bulletin of the Polish Academy of Sciences. Technical Sciences

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2021

|

Vol. 69, nr 5

art. no. e137520

EN

S304H steel is used in the construction of pressure components of boilers with supercritical operating parameters. The paper presents the results of research on the microstructure following ageing for 30,000 hours at 650 and 700°C. Microstructure examination was performed using scanning and transmission electron microscopy. The precipitates were identified using transmission electron microscopy. The paper analyses the precipitation process and its dynamics depending on the temperature and ageing time in detail. MX carbonitrides and the ε_Cu phase were proved to be the most stable phase, regardless of the test temperature. It was also showed that the M₂₃C₆ carbide precipitates in the tested steel and the intermetallic sigma phase (σ) may play a significant role in the loss of durability of the tested steel. This is related to their significant increase due to the influence of elevated temperature, and their coagulation and coalescence dynamics strongly depend on the ageing/operating temperature level. The qualitative and quantitative identification of the secondary phase precipitation processes described in the study is important in the analysis of the loss of durability of the tested steel under creep conditions.

6

The analysis of the post-operation microstructure and mechanical properties of the similar welded joint

Merda Agata, Klimaszewska Klaudia

Biuletyn Instytutu Spawalnictwa w Gliwicach

|

2020

|

Vol. 64, No. 6

37--41

EN

The test material was a specimen sampled from sections of a pipe operated for 41,914 hours at a temperature of 575°C and under a steam pressure of 28.2 MPa. The specimen subjected to metallurgical tests was a welded joint made of austenitic steel TP347HFG. The non-destructive tests and the macroscopic tests confirmed the lack of any welding imperfections. The test joint represented quality level B in accordance with related standard requirements. The microstructural tests of the heat-affected zone (HAZ) revealed the presence of the fine-grained austenitic structure with numerous precipitates on grain boundaries – probably M23C6 carbides. In spite of long-lasting operation, the mechanical properties of the test welded joint were high and did not exceed the standard-related requirements concerning the base material.

PL

Materiałem badawczym była próbka pobrana z wycinków rury długotrwale eksploatowanej, przez 105 000 godzin w temperaturze 540°C i przy ciśnieniu pary 12,5 MPa. Obszarem przeprowadzonych badań metaloznawczych było złącze spawane ze stali austenitycznej TP347HFG. Badania nieniszczące oraz obserwacje makroskopowe potwierdziły brak niezgodności spawalniczych. Badane złącze uzyskało poziom jakości „B” zgodnie z wymaganiami normatywnymi. Badania mikrostrukturalne strefy wpływu ciepła (SWC) TP347HFG ujawniły występowanie jednego charakterystycznego obszaru o gruboziarnistej strukturze austenitycznej z licznymi wydzieleniami obserwowanymi na granicach ziaren – najprawdopodobniej węglików M23C6. Właściwości mechaniczne badanego złącza mimo długotrwałej eksploatacji, były wysokie i nie przekraczały wymagań normatywnych dla materiału podstawowego.

7

Increased temperature and long-term impact of the ageing process on changes in the microstructure of the HR6W alloy

Kierat Milena, Zieliński Adam

Journal of Metallic Materials

|

2019

|

Vol. 71, no. 2

8--13

EN

The study was carried out to determine the effect of long-term ageing (1,000 and 10,000 hours) at 700°C and 750°C on the microstructure of the HR6W alloy. The study indicates that the long-term effect of high temperature causes significant changes in the microstructure of the examined alloy: • After ageing for 1,000 hours at 700°C, in addition to primary MX and M23C6 precipitations, an increase in the size and number of precipitates was observed both inside and along austenite grain boundaries, and the occurrence of the Laves phase was also observed. • After 10,000 hours at 700°C, a significant increase in M23C6 precipitates was observed, especially inside and along grain boundaries. An increase in the Laves phase in the microstructure was also observed. The effect of the increase in the ageing temperature to 750°C: • It significantly accelerated the precipitation process after just 1,000 hours. • In addition to a network of M23C6 precipitates along austenite grain boundaries, their coagulation and an increase in the size of the Laves phase precipitates inside the austenite grains was observed. • The extension of the ageing time to 10,000 hours at 750°C contributed to a significant increase in the size of Laves phase precipitates inside austenite grains.

PL

W pracy przeprowadzono badania, które miały na celu okre- ślenie wpływu długotrwałego starzenia (1000 oraz 10 000 godzin) w temperaturze 700°C oraz 750°C na mikrostrukturę stopu HR6W. Praca wskazuje, że długotrwałe oddziaływanie wysokiej temperatury powoduje znaczne zmiany w mikrostrukturze badanego stopu: • Po czasie starzenia 1000 godzin w temperaturze 700°C oprócz wydzieleń pierwotnych MX i M23C6 zaobserwowano wzrost wielkości i ilości wydzieleń zarówno wewnątrz jak i po granicach ziarn austenitu oraz występowanie fazy Lavesa. • Natomiast po 10 000 godzin w temperaturze 700°C obserwowano znaczny wzrost wydzieleń M23C6, szczególnie wewnątrz i po granicach ziarn. Zaobserwowano także zwiększony udział fazy Lavesa w mikrostrukturze. Wpływ podwyższenia temperatury starzenia do wartości 750°C: • Spowodowało znaczne przyspieszenie procesu wydzieleniowego już po czasie 1000 godzin. • Oprócz siatki wydzieleń typu M23C6 po granicach ziarn austenitu zaobserwowano ich koagulację oraz wzrost wielkości wydzieleń fazy Lavesa wewnątrz ziarn austenitu. • Wydłużenie czasu starzenia do 10 000 godzin w temperaturze 750°C przyczyniło się natomiast do znacznego wzrostu wielkości wydzieleń fazy Lavesa wewnątrz ziarn austenitu.

8

Metallurgical analysis of the causes of failure of the hardening furnace conveyor belt

Merda A., Klimaszewska K., Sroka M., Golański G.

Archives of Materials Science and Engineering

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2019

|

Vol. 98, nr 2

68--73

EN

Purpose: The aim of the tests was to analyze the microstructure and mechanical properties of a section of the hardening furnace conveyor belt serviced at the temperature of 880-920°C in the carburizing atmosphere, in the context of determining the probable causes of its failure. Design/methodology/approach: The scope of performed tests included: chemical composition analysis of the steel and particles, microstructure investigated using optical and scanning electron microscopy, X-ray phase analysis. Findings: The analysis of the chemical composition showed that the examined material was austenitic steel X15CrNiSi25-21 (S310). Performed metallurgical tests showed that after the service the examined steel was characterized by austenitic structure with numerous precipitates of diverse morphology. In the structure the sigma phase particles and probably the M23C6 carbides precipitates were observed. The continuous grid of precipitates on the boundaries of grains (mainly the sigma phase) and the influence of the cyclic changing heat loads (or thermo-mechanical loads) were the main causes of failure of the analysed detail. Research limitations/implications: The aim of the work was to determine the probable causes of damage of the material used for a conveyor belt of a hardening furnace. Practical implications: The results of investigation and analysis of the metallographic of het-resisting austenitic steel X15CrNiSi25-21 (S310) after service at the temperature of 880-920°C are presented. Originality/value: The paper presents the results of research on the microstructure and mechanical properties of the section of hardening furnace conveyor belt made of creepresisting austenitic steel. The aim of the performed tests was to determine the probable causes of damage of the analysed detail.

9

Analysis of the Impact of Modifiers on the Formation of Non-metallic Inclusions During Continuous Casting of CuZn39Pb2 Brass

Bydałek A. W., Kula A., Błaż L., Najman K.

Archives of Foundry Engineering

|

2019

|

iss. 3

21--26

EN

In this paper results of microstructural observations for series of CuZn39Pb2 alloys produced from qualified scraps are presented. The individual alloy melts were differentiated in terms of thermal parameters of continuous casting as well as refining methods and modifications. Structural observations performed by SEM and TEM revealed formation of different types of intermetallic phases including “hard particles”. EDS results show that “hard particles” are enrich in silicon, phosphorus, iron, chromium and nickel elements. Additionally, formation of Al-Fe-Si and Al-Cr in alloy melts was observed as well. It was found that quantity and morphology of intermetallic phases strongly depends upon the chemical composition of raw materials, process parameters, modifiers and refining procedure applied during casting. It was observed that refining process results in very effective refinement of intermetallic phases, whereas modifiers, particularly carbon-based, results in formation of large particles in the microstructure.

10

AFM and nanoindentation study of selected aluminium alloys

Barényi I., Eckert M., Majerík J., Bezecný J.

Zeszyty Naukowe Politechniki Rzeszowskiej. Mechanika

|

2018

|

z. 90 [298], nr 2

143--152

EN

The structure of EN AW 6082 aluminium alloy is investigated in this paper. Atom force microscopy (AFM) is used to identify present phases and their morphology. AFM enabled to observe even the precipitates, their size and distribution. In the next step, some structure constituent described by AFM were evaluated by the nanoindentation process to determine their local mechanical properties, such as nanohardness and reduced modulus.

PL

W artykule opisano strukturę stopu aluminium AW 6082. Mikroskopia sił atomowych (AFM) służy do identyfikacji obecnych faz i ich morfologii. AFM umożliwił obserwację nawet wtrąceń, ich wielkości i rozmieszczenia. W następnym etapie niektóre składniki struktury opisane przez AFM zostały ocenione w procesie nanoindentacji w celu określenia ich lokalnych właściwości mechanicznych, takich jak nanotwardość i zredukowany moduł.

11

Microstructure and mechanical properties of the Sanicro 25 steel after ageing

Merda A., Sroka M., Klimaszewska K., Golański G.

Journal of Achievements in Materials and Manufacturing Engineering

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2018

|

Vol. 91, nr 1

5--11

EN

Purpose: The purpose of the research was to determine and analyse the changes in the microstructure and mechanical properties of the Sanicro 25 steel in the as-received condition and after ageing at 600, 650 and 700°C for up to 10,000 hours. Design/methodology/approach: The scope of the investigations included: microstructural investigation – SEM microscopy, analysis of precipitation performed using TEM microscopy, investigation of mechanical properties, Vickers hardness measurement. Findings: In the as-received condition, the Sanicro 25 steel was characterised by austenitic microstructure with annealing twins and numerous primary precipitates. The analysis of Sanicro 25 steel microstructure after ageing at 600 and 700°C for up to 10,000 hours revealed significant changes in the microstructure consisting mainly in a tendency to create unfavourable morphology of secondary precipitates – M23C6 carbides that form continuous carbide systems along the grain boundaries. The observations have shown that during long-term ageing the secondary carbides were also precipitated inside the grains and at the interface of three grain boundaries – σ phase. Research limitations/implications: The analysis of the microstructure of the examined steel using SEM and TEM was performed to determine the influence of ageing on the processes of changes in the precipitate morphology. Practical implications: The results obtained based on the performed research constitute a building block for the degradation characteristics of the microstructure and mechanical properties of the 23/25-type austenitic steels. Originality/value: The results of the investigation and analysis of the metallographic and mechanical properties of the Sanicro25 austenitic steel in as-received condition and after ageing are presented.

12

Forecasting the distribution of precipitate diameters in the presence of changes in the structure of the material

Zieliński A., Miczka M., Golański G.

Archives of Metallurgy and Materials

|

2017

|

Vol. 62, iss. 1

273--280

EN

The results of investigations on the microstructure of T23 and T24 low-alloy steels as well as P91 and P92 high-chromium steels in the as-received condition and after 70.000 h annealing at 550-650°C are presented. The quantitative analysis of the existing precipitates was performed for representative images of microstructure. The statistical analysis of collected data allowed the parameters of a selected theoretical statistical distribution to be estimated. A forecast of average precipitate diameter and standard deviation of such a distribution for the time of 100,000 hours at 550 and 600°C for T23 and T24 steels and at 600 and 650°C for P91 and P92 steels was calculated. The obtained results of investigations have made it possible to compare changes in the microstructure of various steel grades due to long-term impact of elevated temperature. They have also confirmed the possibility of using, in evaluating the degradation degree of materials in use, the forecasting methods that derive from mathematical statistics, in particular the theory of stochastic processes and forecast by analogy methods. The presented approach allows the development of a forecast of precipitate diameter probability density under the microstructure instability conditions for selected steel grades. The assessment of material condition that takes into consideration, but is not limited to, the precipitate diameter measurement is useful as an assessment component in estimating the time of safe service of power unit elements working under creep conditions.

13

Phase identification of nanometric precipitates in Al-Si-Cu aluminum alloy by HR-STEM investigations

Pawlyta M., Labisz K., Matus K.

Archives of Metallurgy and Materials

|

2016

|

Vol. 61, iss. 3

1303--1308

EN

Aluminium recycling is cost-effective and beneficial for the environment. It is expected that this trend will continue in the future, and even will steadily increase. The consequence of the use of recycled materials is variable and difficult to predict chemical composition. This causes a significant reduction in the production process, since the properties of produced alloy are determined by the inicrostructure and the presence of precipitates of other phases. For this reason, the type and order of formation of precipitates were systematically investigated in recent decades. These studies involved, however, only the main systems (Al-Cu. Al-Mg-Si, Al-Cu-Mg, Al-Mg-Si-Cu), while more complex systems were not analysed. Even trace amounts of additional elements can significantly affect the alloy inicrostructure and composition of precipitates formed. This fact is particularly important in the case of new technologies such as laser surface treatment. As a result of extremely high temperature and temperature changes after the laser remelting large amount of precipitates are observed. Precipitates are nanometric in size and have different morphology and chemical composition. A full understanding of the processes that occur during the laser remelting requires their precise but also time effectively phase identification, which due to the diversity and nanometric size, is a major research challenge. This work presents the methodology of identification of nanometer phase precipitates in the alloy AlSi9Cu, based on the simultaneous TEM imaging and chemical composition analysis using the dispersion spectroscopy using the characteristic X-ray. Verification is performed by comparing the simulation unit cell of the identified phase with the experimental high-resolution image.

14

Forecasting the Particle Diameter Size Distribution in P92 (X10CrWMoVNb9-2) Steel After Long-Term Ageing at 600 and 650°C

Zieliński A., Sroka M., Miczka M., Śliwa A.

Archives of Metallurgy and Materials

|

2016

|

Vol. 61, iss. 2A

753--760

EN

The investigations on microstructure of P92 steel in the as-received condition and after 105h ageing at 600 and 650°C were carried out. For the recorded images of microstructure, the quantitative analysis of precipitates was performed. On that basis, a statistical analysis of collected data was made with the aim of estimating parameters of selected theoretical statistical distribution. Then, the forecast for average precipitate diameter and standard deviation of such a distribution for the time of 1,5*105h at 600 and 650°C was calculated. The obtained results of investigations confirm the possibility of using, in evaluation of degradation degree for materials in use, the forecasting methods derived from mathematical statistics, in particular the theory of stochastic processes and methods of forecasting by analogy.

15

Evaluation of Precipitates Type in Brasses as a Function of Charge Material

Bydałek A. W., Najman K., Kula A., Biernat S., Błaż L., Wołczyński W.

Archives of Foundry Engineering

|

2016

|

Vol. 16, iss. 3

19--24

EN

Trial series of cast alloy MO59 obtained from qualified scrap was investigated. SEM and TEM of resulting precipitates were conducted. The SEM analysis demonstrated the dependence of silicon, phosphorus, iron, chromium and nickel in the composition of the so-called hard precipitates. TEM analysis showed the formation of phase AlFeSi and AlCr. Made studies have shown the important role of the composition of the batch melts brass CuZn39Pb2 type. The analysis of SEM and TEM resulting precipitates pointed to the formation of various forms of divisions, only one of which was described in the literature character of the so-called hard inclusions. The SEM studies demonstrated the dependence of the occurrence of inclusions rich in silicon, phosphorus, iron, chromium and nickel. In contrast, additional TEM analysis indicated the formation of AlFeSi phase type and AlCr. The results of the analyses referred to the structure of the batch. Due to the difficulty of obtaining recycled materials that do not contain these elements necessary to carry out further analyzes in the direction of defining the role of phosphorus in the formation of the so-called hard inclusions.

16

Tem Observation Of Precipitate Structures In Al-Zn-Mg Alloys With Additions Of Cu/Ag

Watanabe K., Matsuda K., Ikeno S., Yoshida T., Murakami S.

Archives of Metallurgy and Materials

|

2015

|

Vol. 60, iss. 2A

977--979

EN

Al-Zn-Mg alloy has been known as one of the aluminum alloys with the good age-hardening ability and the high strength among commercial aluminum alloys. The mechanical property of the limited ductility, however, is required to further improvement. In this work, three alloys, which were added Cu or Ag into the Al-Zn-Mg alloy, were prepared to compare the effect of the additional elements on the aging behavior. The content of Ag and Cu were 0.2at.% and the same as, respectively. Ag or Cu added alloy showed higher maximum hardness than base alloy. The particle shape and rod shape precipitates were observed in all alloys peak-aged at 423K. According to addition of Ag or Cu, the number density of the precipitates increased higher than that of base alloy.

PL

Al-Zn-Mg jest stopem, który można efektywnie poddawać procesowi utwardzania wydzieleniowego. Spośród różnorodnych stopów aluminium charakteryzuje się bardzo wysoką wytrzymałością mechaniczną, jednak jego ograniczona plastyczność jest cechą wymagającą poprawy. W toku prac przygotowano trzy stopy: stop bazowy Al-Zn-Mg oraz stopy zawierające dodatki Cu lub Ag, dla porównania wpływu tych dodatków na starzenie się materiału. Zawartość Ag i Cu wynosiła odpowiednio 0,2% at. Stopy z dodatkiem Ag lub Cu wykazywały większą twardość maksymalną w porównaniu ze stopem bazowym. We wszystkich stopach starzonych w temperaturze 423K obserwowano charakterystyczne wydzielenia, a ich koncentracja była odpowiednio większa dla stopów z dodatkiem Ag lub Cu.

17

Microsegregation and Precipitates in Inconel 625 Arc Weld Overlay Coatings on Boiler Pipes

Rozmus-Górnikowska M., Blicharski M.

Archives of Metallurgy and Materials

|

2015

|

Vol. 60, iss. 4

2599--2606

EN

The aim of this work was to investigate the microsegregation and precipitates formed due to segregation in Inconel 625 arc weld overlay coatings on boiler pipes. Examination of microsegregation and precipitates were carried out by means of a scanning electron microscope (SEM) equipped with an EDS detector as well as a transmission electron microscope (TEM) equipped with a HAADF (STEM) and an EDS detectors. The presence of precipitations in the weld overlay was also confirmed with X-ray diffraction analysis (XRD) of residue in the form of powder that remained after the electrolytic dissolution of weld overlay matrix. The investigations showed that the interdendritic regions were considerably enriched during microsegregation with Nb, and less so with Mo. The distribution of Cr and Fe in the weld overlay is relatively uniform. The value of the partition coefficient k for Mo and Nb is lower than 1. Therefore, these elements segregate during solidification into the liquid and, once solidification is finished, the interdendritic regions are considerably enriched with these elements. The value of k for Cr, Ni and Fe are only slightly higher than 1. Though the Inconel 625 is a solid-solution strengthened alloy, precipitation of secondary phases occurs in weld overlays. Precipitations were identified as a Laves phase and carbonitrides (Nb, Ti)(C, N).

PL

Celem pracy była ocena segregacji dendrytycznej (mikrosegregacji) oraz identyfikacja wydzieleń w napoinach ze stopu Inconel 625 napawanych metodą CMT na rury kotłowe. Badania segregacji dendrytycznej oraz składu chemicznego wydzieleń w napoinach ze stopu Inconel 625 prowadzono za pomocą mikroskopu elektronowego skaningowego NanoSEM 450 firmy FEI wyposażonego w detektor EDS firmy EDAX oraz za pomocą mikroskopu elektronowego transmisyjnego (TEM, TECNAI GF20) wyposażonego w detektor HAADF do badań techniką skaningowo - transmisyjną STEM, jak również zintegrowany spektrometr promieniowania rentgenowskiego do analizy składu chemicznego firmy EDAX. Obecność wydzieleń została potwierdzona za pomocą rentgenowskiej analizy fazowej (XRD) cząstek proszku osadu uzyskanego w wyniku elektrolitycznego rozpuszczenia osnowy napoiny. Badania wykazały, że w wyniku mikrosegregacji zachodzącej podczas krzepnięcia napoin następuje znaczne wzbogacenie obszarów międzydendrytycznych tj. obszarów między ramionami dendrytów w Nb a mniejsze w Mo. Wartość równowagowego współczynnika rozdziału k dla Mo i Nb jest mniejsza od 1, dlatego podczas krystalizacji pierwiastki te segregują do cieczy, a zatem, po zakończeniu krystalizacji obszary międzydendrytyczne są znacznie wzbogacone w w/w pierwiastki. Pomimo, że stop Inconel 625 jest stopem umacnianym roztworowo to w napoinach występowały wydzielenia. Na podstawie wyników analizy składu chemicznego, jak również rentgenowskiej analizy fazowej wydzielenia te zidentyfikowano jako fazę Lavesa oraz (Nb, Ti)(C, N).

18

Influence of Degree of Deformation and Aging Time on Mechanical Properties and Microstructure of Aluminium Alloy with Zinc

Jarzębska A., Bogucki R., Bieda M.

Archives of Metallurgy and Materials

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2015

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Vol. 60, iss. 4

3023--3028

EN

In order to investigate the influence of the deformation degree and aging time on the mechanical properties and microstructure of AA7050 alloy static tensile test, microhardness measurements, calorimetric analysis and observations of the microstructure in the transmission and scanning electron microscope were carried out. For study a series of cylindrical specimens with an initial diameter of about 3 mm were used. The samples were saturated at a temperature of 470° C for 1 hour and quenched in water. The samples were then subjected to deformation up to the three levels: 0%, 5% and 10%. Deformed samples was artificially aged at 120°C for 6 hours, 12 hours, 24 hours and 72 hours. The results showed that the increase in the degree of deformation caused an increase in yield strength and a decrease in ductility. The longer aging time influenced on an increase in tensile strength, yield stress and microhardness and a decrease in ductility. An analysis of the precipitates present in the material was conducted. The highest value of yield strength equal 538 MPa with elongation 9.2% were obtained for sample pre-strained to 10% and aged for 24 hours. The obtained results showed that prolongation in aging time and use of pre-strain were beneficial for precipitation processes courses, consequently, for optimal mechanical properties of alloy 7050.

PL

W celu zbadania wpływu stopnia odkształcenia i czasu starzenia na właściwości mechaniczne i mikrostrukturę stopu AA7050 przeprowadzono statyczną próbę rozciągania, badania mikrotwardości, analizę kalorymetryczna oraz obserwacje mikrostruktury w transmisyjnym i skaningowym mikroskopie elektronowym. Do badań wykorzystano serię cylindrycznych próbek o średnicy początkowej równej około 3 mm. Próbki do badań poddano procesowi przesycania w temperaturze 470°C przez 1 godzinę i szybko schłodzono w wodzie. Następnie próbki poddano wstępnemu odkształcaniu o trzy różne stopnie: 0%, 5% i 10%. Później zastosowano proces sztucznego starzenia w temperaturze 120°C w czasie: 6 godzin. 12 godzin. 24 godzin i 72 godzin. Wyniki badań wykazały. że wzrost stopnia odkształcenia powodował wzrost granicy plastyczności i spadek plastyczności. Wydłużenie czasu starzenia wpłynęło na wzrost wytrzymałości na rozciąganie. granicy plastyczności i mikrotwardości oraz na spadek plastyczności. Przeprowadzono analizę występujących w materiale wydzieleń. Najwyższą wartość granicy plastycznej równą 538 MPa przy wydłużeniu 9,2 % osiągnięto dla próbki odkształconej o 10 % i starzonej 24 godziny. Wydłużenie czasu starzenia i stopień odkształcenia wpłynęły korzystnie na poprawę właściwości mechanicznych stopu z gatunku 7050.

19

Back-Diffusion In Crystal Growth. Eutectics

Wołczyński W.

Archives of Metallurgy and Materials

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2015

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Vol. 60, iss. 3

2403--2407

EN

Solute segregation/redistribution model for some eutectic alloys is presented. The differential equation for the solute micro-segregation during solidification accompanied by the back-diffusion is formulated. The solution to this equation results in the definitions of: solidification path, solid/liquid (s/l) interface path and redistribution path. An equation for the estimation of the amount of equilibrium and non-equilibrium precipitates is also delivered. It is proved that the current model is universal one. Thus, the model reduces perfectly, mathematically to both description of diffusion-less solidification and model of equilibrium solidification.

PL

Przedstawiono model segregacji/redystrybucji składnika dla stopów eutektycznych. Sformułowano równanie różniczkowe dla mikrosegregacji składnika podczas krystalizacji, której towarzyszy dyfuzja wsteczna. Rozwiązanie tego równania pozwoliło na zdefiniowanie ścieżek: krystalizacji, frontów krystalizacji i redystrybucji. Sformułowano równanie dla oceny ilości wydzieleń równowagowych i nierównowagowych. Pokazano, że model jest uniwersalny. Dlatego, redukuje się perfekcyjnie, matematycznie do opisu krystalizacji bez dyfuzji a także do modelu krystalizacji równowagowej.

20

Evaluation of post weld heat treatment quality of modified 9Cr–1Mo (P91) steel weld by magnetic coercive force measurements

Sudharsanam V., Senthilkumar V., Raju N., Vetriselvan R.

Archives of Civil and Mechanical Engineering

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2015

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Vol. 15, no. 4

847--853

EN

This paper presents a novel technique for evaluation of quality of post weld heat treatment (PWHT) of modified 9Cr–1Mo (P91) steel weld by correlation with its magnetic coercive force (MCF). The MCF of modified 9Cr–1Mo steel was studied in respect of different PWHT cycles involving ordered variations of soaking temperature unto 770 °C and soaking time unto 140 min. It was observed that MCF of the weld metal reduced with increase in both the soaking temperature and soaking time of PWHT. The drop in MCF of welds after PWHT was found to be dependent on the drop in the hardness of the weld and on the degree of carbide precipitations seen in the weld microstructure. Based on the study, a criterion was evolved for evaluation of heat treatment quality of the weld.