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1

Observation of Hot Tearing in Sr-B Modified A356 Alloy

100%

Uludağ M. , Çetin R. , Dışpınar D.

Archives of Foundry Engineering

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2017

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tom 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

100%

Stradomski G.

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tom 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

Brittleness temperature range of Fe-Al alloy

100%

Adamiec J. , Kalka M.

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tom 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.

4

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

100%

Adamiec J.

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2010

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tom 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.

5

Hot cracking of ZRE1 alloy in constant joint stiffness condition

80%

Adamiec J. , Kierzek A.

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2010

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tom 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.