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Structural and mechanical properties of laboratory rolled steels high-alloyed with manganese and aluminium

Kuc D., Hadasik E., Niewielski G., Schindler I., Mazancova E., Rusz S., Kawulok P.

Archives of Civil and Mechanical Engineering

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2012

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Vol. 12, no. 3

312--317

EN

The paper deals with rolling conditions, microstructure, as well as basic mechanical properties of four different high manganese steels after laboratory melting, casting, and hot and cold rolling. The stacking fault energy of heats was in the interval of 85–114 mJ m−2 thanks to the high aluminium contents. The heats with the lowest sum of (C+Mn) supported the highest ferrite volume fraction (up to 45%), while the highest sum of (C+Mn) led to 10% ferrite formation. With lower Al/(C+Mn) ratio and lower ferrite fraction higher rolling forces were necessary to be used. Due to heterogeneities of matrixes and observed aluminium oxide complexes differences in mechanical properties were detected. The best results showed the heat with 0.65% C−29.5% Mn−9.0% Al and a stacking fault energy 114 mJ m−2.

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Influence of rolling conditions and aging process on mechanical properties of high manganese steels

Mazancova E., Ruziak I., Schindler I.

Archives of Civil and Mechanical Engineering

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2012

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Vol. 12, no. 2

142--147

EN

Three laboratory cast and rolled high manganese steels with different Mn (in the range of 24–28 wt%), C (in the interval of 0.2–1.2 wt%) and Al (from 2.3 wt% to 12 wt%) contents has been investigated. Differences in chemical compositions, rolling conditions and followed by aging process at the temperature of 500 °C and four different aging dwells (in the range of 6 min to 60 min) have led to various k-carbides precipitation. The k-carbides have been responsible for the mechanical properties. The intragranular type of nano-size has increased the strength, respectively hardness level whereas the k-carbides nucleated in the intergranular form have reached size of micrometre and in lower volume fraction have not been importantly able to increase the matrix hardness, especially in case of lower C portion. Balanced Mn, C and Al contents for optimised k-carbides precipitation have been also discussed. The materials were hot rolled to strips of 1.9 mm in thickness from the heating temperature of 1100 °C using the rolling mill Tandem.

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Properties of high manganese Fe-Mn-Al-C alloys

Mazancova E., Rucka Z., Mazanec K.

Archives of Materials Science

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2007

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Vol. 28, nr 1-4

95-99

EN

Acicular ferrite (AF) microstructure represents an excellent contribution of mechanical properties and the toughness level detected in low-alloy steel. Majority of neighbouring plates (laths) have mutual high-angle misorientation in contradistinction to upper bainite (B) microstructure. High-angle interfaces are only formed between B-packets consisting of low-angle plates (laths) set. The cleavage unit crack path (UCP) has been found to be a distance between two grains of high-angle ferrite regions (corresponding to the two crystallographic B-packets boundaries). In the AF the UCP value is defined as a distance between two neighbouring highly misorientated plates. It shows the UCP values are shorter what results in higher deviation frequency and consequently in limited (retarded) cleavage crack propagation. The nucleation AF conditions in austenite matrix after application of an optimized thermomechanically controlled process consisting of the consecutive straining processes realized in recrystallization and in non recrystallization regions have been determined. The applied nucleation mechanism (base on the nucleation process realized in structural matrix) represents the second variant resulting in the AF formation. The beneficial resistance of the AF particles to hydrogen embrittlement can be held for a very important property of this microstructure what demonstrates the valuable contribution of this microstructure to its engineering application. The AF microstructure is associated with effective combination of strength and toughness. The behaviour of this microstructure is compared with upper bainite properties. Following differences between the microstructural parameters are detected. The AF is nucleated on intragranular inclusions. In majority, plates show high-angle arrangement in comparison with upper bainite. Numerous low-angle interfaces are detected within crystallographic upper bainite packets. In AF microstructure the unit crack path is defined as a distance between two neighbouring highly misorientated plates. The AF microstructure contributes to the achievement of high steels resistance to hydrogen induced cracking due to special arrangement of its plates.

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Comparison of microfractographic behaviour of acicular ferrite and bainite and hydrogen cracking resistance

Mazancova E., Jonsta Z., Mazanec K.

Archives of Materials Science

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2007

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Vol. 28, nr 1-4

90-94

EN

Materials characterized as TRIPLEX having decreased density are constituted on the following chemical composition usually: Fe-26/30Al-0.9/1.2C. Alloy microstructure is preferentially based on the FCC arrangement. Further, microstructure consists of nano-size carbides regularly dispersed in the FCC matrix and of low ferritic particle content (8% approximately). The strength level of this material is immediately connected with the solid solution strengthening forming the matrix basis. Besides this effect, it is useful to take into consideration process of its strengthening due to precipitated fine carbides (above mentioned nano-size k-carbides). The preferential effect of this material is connected with its high absorption capacity (double capacity in comparison with the conventional deep drawing steels applied in automotive industry). The formation of uniformly arranged shear bands (SIP effect) has very important influence on the realized deformation process of discussed material and the achieved beneficial technical response. This process is also influenced due to regular distribution of nano-size k-carbides being coherent to the FCC matrix. Owing to the density decrease up to 10-12%, attained strength level (1000 MPa), excellent formability and high resistance to dynamic loading (high absorption and achieved dynamic capacity) the presented high manganese material can be held for perspective type for many applications in automotive industry. Further, this material finds a perspective application in cryogenic technique (transport and storage of liquid gases) and in rotating machine elements, too.