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1

Observation of Hot Tearing in Sr-B Modified A356 Alloy

Uludağ M., Çetin R., Dışpınar D.

Archives of Foundry Engineering

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2017

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Vol. 17, iss. 4

165--168

EN

In this work, T-shaped mould design was used to generate hot spot and the effect of Sr and B on the hot tearing susceptibility of A356 was investigated. The die temperature was kept at 250ºC and the pouring was carried out at 740ºC. The amonut of Sr and B additions were 30 and 10 ppm, respectively. One of the most important defects that may exist in cast aluminium is the presence of bifilms. Bifilms can form by the surface turbulence of liquid metal. During such an action, two unbonded surfaces of oxides fold over each other which act as a crack. Therefore, this defect cause many problems in the cast part. In this work, it was found that bifilms have significant effect over the hot tearing of A356 alloy. When the alloy solidifies directionally, the structure consists of elongated dendritic structure. In the absence of equiaxed dendrites, the growing tips of the dendrites pushed the bifilms to open up and unravel. Thus, leading to enlarged surface of oxide to become more harmful. In this case, it was found that these bifilms initiate hot tearing.

2

The Cracking Mechanism of Ferritic- Austenitic Cast Steel

Stradomski G.

Archives of Foundry Engineering

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2016

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Vol. 16, iss. 4

153--156

EN

In the high-alloy, ferritic - austenitic (duplex) stainless steels high tendency to cracking, mainly hot-is induced by micro segregation processes and change of crystallization mechanism in its final stage. The article is a continuation of the problems presented in earlier papers [1-4]. In the range of high temperature cracking appear one mechanism a decohesion - intergranular however, depending on the chemical composition of the steel, various structural factors decide of the occurrence of hot cracking. The low-carbon and low-alloy cast steel casting hot cracking cause are type II sulphide, in high carbon tool cast steel secondary cementite mesh and/or ledeburite segregated at the grain solidified grains boundaries, in the case of Hadfield steel phosphorus - carbide eutectic, which carrier is iron-manganese and low solubility of phosphorus in high manganese matrix. In duplex cast steel the additional factor increasing the risk of cracking it is very "rich" chemical composition and related with it processes of precipitation of many secondary phases.

3

Ocena skłonności do pękania gorącego stali wysokomanganowych z dodatkiem aluminium

Adamiec J., Lalik S., Niewielski G.

Inżynieria Materiałowa

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2012

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Vol. 33, nr 5

396--399

PL

Nowoczesne wysokowytrzymałe gatunki stali dla motoryzacji oprócz technologiczności w wytwarzaniu, powinny minimalizować oddziaływanie na środowisko przez redukcję emisji spalin. Powoduje to konieczność obniżenia masy pojazdów samochodowych, jako jednego z głównych źródeł zanieczyszczenia atmosfery. Nowoczesne stale pozwalają połączyć lekkość z tradycyjną przewagą stali wynikającą z jej niskiej ceny i walorów ekologicznych. Dobre właściwości mechaniczne, mała gęstość oraz zdolnością do absorpcji energii sprawiają, że stal z układu Fe-Mn-Al-C jest jednym z bardziej perspektywicznych materiałów XXI wieku. Ze względu na niskie koszty materiałowe znalazła uznanie i zainteresowanie w przemyśle motoryzacyjnym. Szersze wykorzystanie tych stopów jest związane często z trudnościami w procesach ich wytwarzania i przetwarzania, w tym procesów spawania. Doświadczenia z tymi stalami wykazały, że oczekiwany zestaw właściwości jest możliwy do uzyskania przez kombinację alternatywnych mechanizmów odkształcenia plastycznego, jak np. bliźniakowanie (efekt TWIP), indukowana odkształceniem przemiana martenzytyczna (efekt TRIP), czy plastyczność wywołana ścinaniem pasm austenitu (TRIPLEX efekt SIP). W pracy przedstawiono wyniki badań skłonności do pękania gorącego dwóch gatunków stali wysokomanganowych z efektem umocnienia typu TWIP I TRIP zawierających 3,1 i 5,3% aluminium oraz 17,3% i 23,9% manganu, w warunkach wymuszonego odkształcenia. Dla określenia podatności analizowanych stali do pękania gorącego w procesie spawania wykonano technologiczną próbę Transvarestraint oraz badania metalograficzne. Badania skłonności do pękania gorącego stali wysokomanganowych z dodatkiem aluminium przeznaczonych dla przemysłu motoryzacyjnego w warunkach wymuszonego odkształcenia, które modeluje próba Transvarestraint, wskazują, że stal X20MnAl18-3 o zawartości około 17% manganu i 3% aluminium jest odporna na pękanie gorące podczas przetopienia w warunkach wymuszonego odkształcenia, natomiast stal X55MnAl25-5 o większej zawartości manganu (ok. 24%) i aluminium (5,5%) jest skłonna do pękania gorącego w zakresie od temperatury solidusu do 0,7 temperatury topnienia. Pękanie w tym zakresie jest związane z małą plastycznością i wytrzymałością obszarów międzykrystalicznych w strukturze przetopienia, co jest związane z segregacją pierwiastków w tych obszarach oraz związanymi z procesem spawania odkształceniami całego złącza spawanego. Powstałe w trakcie badań pęknięcia gorące mogą być również wynikiem obecności znacznej liczby wad sieci krystalicznej i dążenia układu do stabilności energetycznej.

EN

Modern high-strength types of steel for motorisation should, apart from producibility in manufacturing, minimise the influence on the environment by reducing exhaust fumes emission. It creates the necessity of lowering the weight of car vehicles as one of the main sources of atmosphere pollution. Modern steel types enable to join the lightness with traditional advantages of steel which are low price and ecological qualities. High mechanical properties, low density and ability to absorb energy cause that steel type from Fe-Mn-Al-C set is one of more perspective materials of 21 st century. Due to low material costs it deserved appreciation and interest from automotive industry. Wider use of these alloys is often connected with difficulties in their manufacturing processes, including the welding processes. Experience with those steels has shown that expected set of properties is possible to achieve by a combination of alternative mechanisms of plastic deformation, such as twinning (TWIP effect), strain induced martensite transformation (TRIP effect) or plasticity caused by austenite band shearing (TRIPLEX effect SIP). The paper presents tests results of the susceptibility to hot cracking of two types of high manganese steel with the consolidation effect of TWIP and TRIP which included 3.1 and 5.3% of aluminium and 17.3% and 23.9% of manganese in conditions of extorted strain. In order to determine the susceptibility of analysed steel to hot cracking in welding process a technological Transvarestraint test and metallographic tests were conducted. Tests of susceptibility to hot cracking of high manganese steel types with aluminium addition for the use in automotive industry, in conditions of extorted strain, which is modelled by Transvarestraint test show, that steel X20MnAl18-3 with 17% of manganese and 3% of aluminium is resistant to hot cracking during weld penetration in conditions of extorted strain whereas the steel X55MnAl25-5 with higher content of manganese (about 24%) and aluminium (5.5%) is susceptible to hot cracking in temperature range from solidus to 0.7 of melting point temperature Cracking in this range is connected with low plasticity and strength of intercrystalline areas in weld penetration structure which is connected with segregation of the chemical elements in those are and deformations connected with welding process of the whole welded joint. Hot cracks which were created during tests may also be the result of the presence of large amount of defects of crystal system and the drive of the system to reaching energetic stability.

4

Influence of design factors on weldability of the AZ91E alloy

Adamiec J.

Archives of Foundry Engineering

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2010

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Vol. 10, iss. 1 spec.

339--344

EN

Basic design factors which influence weldability include casting shape, its stiffness and type of welded joint. The influence of casting stiffness on weldability, understood as susceptibility to hot cracking, in conditions of constant joint stiffness has been determined on the basis of the Fisco test results, and in conditions of varying stiffness on the basis of the Houldcroft test.

5

Hot cracking of ZRE1 alloy in constant joint stiffness condition

Adamiec J., Kierzek A.

Archives of Foundry Engineering

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2010

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Vol. 10, iss. 1 spec.

151--156

EN

ZRE1 alloy with addition of Zn, Zr and rare earth elements is gravity casted to sand casting moulds, and is used mainly in aerospace and automotive industries. Magnesium alloy castings often have defects, such as misruns and micro-shrinkage. This defects are repaired with welding and overlay welding techniques. Main practical difficulty during welding of magnesium alloys is their susceptibility to hot cracking in the crystallization process. The paper intends to evaluate susceptibility of magnesium alloys to hot cracking and examine influence of heat treatment on cracking of the ZRE1 magnesium alloy with addition of zinc and rare earth elements during welding in conditions of constant stiffness. The results of tests of susceptibility to hot cracking of repair welding joints of ZRE1 alloy castings have been described. The range of research has included the Fisco test and metallographic tests. It has been observed that heat treatment decreases susceptibility of the ZRE1 alloy to hot cracking.

6

Evaluation of susceptibility of the ZRE1 alloy to hot cracking in conditions of forced strain

Adamiec J.

Archives of Foundry Engineering

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2010

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Vol. 10, iss. 1 spec.

345--350

EN

Nowadays, magnesium alloys are used for casting into sand moulds of huge dimensional castings, high-pressure castings and precise casings. In castings of magnesium alloys defects or inconsistencies often appear (like casting misrun, porosities and cracks) particularly in the huge dimensional castings. Such defects are mended with the use of padding and welding. The welding techniques can be applied by using weld material consisting of magnesium alloy, as well as for regeneration of alloys after excessive wear. Nevertheless, the number of the repaired castings, which were permitted for use, is not satisfactory for a profitable production. The main reasons for wear are the cracks appearing during welding in brittleness high-temperature range. This work in combination with industrial tests of casting welding show that the causes of high-temperature brittleness are the partial tears of the structure and the hot cracks of both the castings and the welded and padded joints. Such phenomena should be treated as irreversible failures caused by the process of crystallisation that is in the area of co-existence of the solid and liquid structural constituent. The assessment of the resistance to hot fractures was conducted on the basis of the transvarestriant trial. The transvarestriant trial consists in changing of strain during welding It was stated that the range of the high-temperature brittleness is very broad, which significantly limits the application of the welding techniques to join or mend the elements made of alloy ZRE-1. The brittleness is caused mainly by metallurgical factors, i.e., precipitation of inter-metal phases from the solid solution.

7

Brittleness temperature range of Fe-Al alloy

Adamiec J., Kalka M.

Journal of Achievements in Materials and Manufacturing Engineering

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2006

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Vol. 18, nr 1-2

43--46

EN

Purpose: The purpose of this paper was to experimentally determine the brittleness temperature range of an alloy based on the intermetallic FeAl phase matrix. This was done in order to evaluate the applicability of the said alloy for bonding using welding methods, and specifically, whether the character of the brittleness temperature range of the material indicates susceptibility to hot cracking. Design/methodology/approach: The research was executed using a Gleeble 3800 type simulating device. A simulation of the heating process at a set rate of 20ºC/s was conducted in order to determine the NST and then NDT temperatures during the heating stage, followed by the determination of DRT temperature during the cooling stage. This allowed to evaluate the brittleness temperature range. Findings: The executed tests allowed to determine the brittleness temperature range for the examined FeAl alloy which was found to be situated between 1320°C and the liquidus temperature for the heating stage, and down to 1330°C for the cooling stage. The index of hot cracking resistance was found to be 0.05. Research limitations/implications: The method of simulating the flow of a welding process using the Gleeble 3800 simulator allows to simply and effectively determine the characteristic temperatures of the process and the susceptibility of a given alloy to hot cracking. Originality/value: Using a Gleeble 3800 type simulator for the examination of an FeAl alloy in a semi-solid state enables one to evaluate the material’s suitability for permanent bonding, eg. welding. Such data is indispensable for a technologist or a constructor designing components made of an alloy based on the FeAl phase.

8

Wysokotemperaturowy zakres kruchości staliwa

Telejko I.

Archiwum Odlewnictwa

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2003

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R. 3, nr 10

261--266

PL

Zakres temperatur kruchości jest tożsamy z zakresem pękania na gorąco odlewanej, a także spawanej stali. Szerokość tego zakresu dla tego samego gatunku staliwa zależy przede wszystkim od jego niższej temperatury - rzeczywistej temperatury solidus – która może się wahać od odczytanej z układu równowagi Fe-C, (segregacja składników ograniczona do węgla, manganu i krzemu) do określonej dla staliwa zawierającego silnie segregującą domieszkę o bardzo małej rozpuszczalności w fazie stałej. We wszystkich gatunkach staliwa węglowego i niskostopowego domieszką taką jest siarka, w staliwie Hadfielda – fosfor. W wyniku dodatku pierwiastka zapobiegającemu wzrostowi przed frontem krzepnięcia stężenia siarki możliwe jest podwyższenie rzeczywistej temperatury solidus staliwa nawet do wartości bliskiej równowagowej. Efektem jest znaczne ograniczenie pękania stali przy jej odlewaniu i spawaniu.

EN

Cracking susceptibility of alloys depends mainly on the brittleness solidification range BTR. As the process of microsegregation of elements of steel is negligible during the early period of solidification, the upper limit of BTR changes mainly with the change in carbon content. The transition from brittle state to ductile appears when the liquid phase disappears from the grain boundaries. Under the conditions of non-segregation, the brittle-ductile transition temperature (the end of BTR) is very close to solidus calculated from an Fe-C diagram. Under segregate conditions (a real condition of solidification of industrial steel) the composition of liquid during the final period of solidification is closed to Fe-C-S. The brittle-ductile transition temperature is equal to the solidification temperature of the sulphides.

9

Powierzchniowy charakter pękania na gorąco siluminów niskokrzemowych

Mutwil J.

Archiwum Technologii Maszyn i Automatyzacji

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2001

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Vol. 21, Nr 1

107-115

PL

Przedstawiono ilustracje rozwoju sił skurczowych powstających w okresie krzepnięcia i studzenia aluminium oraz siluminów dwuskładnikowych: AlSiO,85, AlSil,65, AlSi5,18. Określono temperaturę pękania na gorąco. Zamieszczono skaningowe ilustracje przełomów.

EN

The development of shrinkage forces appearing in time of solidification and cooling of alumi-num and binary aluminum - silicon alloys: AlSiO.85, AlSil.65, AlSi5.18 has been presented. The hot cracking temperature has been determined. The SEM microfractographs have been presented.