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1

Acicular ferrite and bainite microfractographic behaviour

Mazancová E., Rucká Z., Mazanec K.

Zeszyty Naukowe. Mechanika / Politechnika Opolska

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2009

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z. 95

31-32

2

High manganese Fe-Mn-Al-C alloy and its properties

Mazancová E, Jonšta Z., Mazanec K.

Zeszyty Naukowe. Mechanika / Politechnika Opolska

|

2008

|

z. 92

53-54

EN

Materials characterized as TRIPLEX having decreased density are constituted on the following chemical composition usually: Fe-26/30Mn-9/12Al-0.9/1.2C. Alloy microstructure is preferentially based on the FCC arrangement with annealing twins. Further, microstructure consists of low ferritic particle content 8-10% in maximum and of nano-size carbides regularly dispersed in the FCC matrix being coherent in maximum rate with that one [1]. Their quantity does not exceed 10 % level approximately. The reached carbide size corresponds to 20-30 nm. The k-carbides are nucleated after homogeneous annealing and followed aging at the temperature of about 500 °C - 600 °C. The existence of these particles is very important not only for specific form of deformation process being realized in the high manganese alloy of the TRIPLEX type. 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). In unite k-carbide cell aluminium atoms occupy its corners, manganese with iron are lying in all faces and carbon atom is situated in its body. It is well known the aluminium atomic radius reaches 0.147 nm, what represents greater dimension in comparison with iron atom having that one on the level of 0.126nm. In superposition manganese atom acts like aluminium one, even when its atomic radius only corresponds to 0.134 nm. It means with the higher aluminium and manganese weight fraction the TRIPLEX cell parameter is increased and matrix density is decreased, simultaneously. For example, in case of 12 % aluminium addition the density corresponds to level of 6.5g.cm-3 and represents a reduction of 1.4g.cm-3 in matrix density in confrontation with iron, what means the decrease density up to 10 % [1]. The preferential effect of material TRIPLEX is connected with its high absorption capacity, too. Double absorption capacity has been detected in comparison with the conventional deep drawing steels applied in automotive industry (crash test simulation). TRIPLEX matrix is strong stabilised thanks the high manganese level. Together with aluminium it is reason of a high level of the stacking fault energy (SFE) lying on the 80-110 mJm-2. Further, the stacking fault energy is responsible for the realized deformation process in TRIPLEX matrix being different e.g. to TWIP alloy. In any case none austenite decomposition into e-martensite is realized, as well [2]. In material TRIPLEX formation of uniformly arranged shear bands (SIP effect) is the sole deformation process being of very important influence. This process is accompanied by regular distribution of nano-size k-carbides being coherent to the FCC matrix. The k-carbides guide the shear bands formation as a matter of fact. Deformation process is accompanied by dislocation gliding. Obtained TRIPLEX strength level reaches l000MPa. Material shows an excellent formability and high resistance to dynamic loading (high absorption and achieved dynamic capacity). The presented high manganese alloy can be held for a 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.

3

Increased resistance of acicular ferrite microstructure to hydrogen embrittlement - physical metallurgy cause of this effect

Mazancová E., Slavíková I., Mazanec K.

Zeszyty Naukowe. Mechanika / Politechnika Opolska

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2007

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Vol. 321, z. 89

117-118

EN

The grain refinement leading to the strength and ductility increase represents important parameter resulting in improved achieved physical metallurgy properties. The acicular ferrite (AF) can be held for a promising microstructure contributing to the accomplishment of above mentioned requirement. The AF is initiated in the same temperature range as bainite (B) by the same transformation mechanism. The difference between AF and B consists in their different nucleation sites in steel matrix. In case of B the ferritic grains are nucleated at the austenite (A) grain boundaries. On the contrary, AF plates are nucleated on non-metallic particles which fulfil special conditions of their nucleability. The AF particles exhibit different orientations in the formation of the fine grained interlocking morphology. The bainitic packets consist of parallel plates (laths) having low angle interface orientations. The beneficial mechanical properties of the AF microstructure are related to the high frequency of high angle interfaces acting as effective obstacles to cleavage cracks propagation in contradistinction to the weak influence of the B having low angle plates interfaces. In B, only packets show high angle boundaries what results in larger free path for cleavage crack propagation [1]. The above discussed beneficial AF properties are acting in large scope inclusive of improved resistance of steels to hydrogen induced cracking. The fracture process analysis has shown the strength and toughness behaviour of AF microstructure are different from that conventional microstructure by reason of its particular microstructure characteristics. In the AF microstructures, the density of micro-orientated plates is enhanced by a profused direct intragranular nucleation on non-metallic inclusions. In the bainitic microstructure a decisive role is ascribed to morphological packets representing the microstructure unit that controls the cleavage cracks propagation without their deflecting. In the B microstructure, the morphological packets size (de) is related to the dimension of unit crack path (UCP) corresponding to the distance between neighbouring high angle boundaries [2]. The AF analysis shows, the microstructure unit is directly related to the set of the AF plates having high angle interface, what is corresponding to the unit crack path in the AF microstructure. In the AF, this value is shorter in comparison to the dimension of packets in investigated B. In the AF, it is 4-5 jim while in the B this distance is substantially greater and attains up to 20jam, approximately. Using the UCP value - dB, it is possible to determine the transition behaviour in steel T = To - K.dB"1/2, where K represents constant value, To depends on the tensile strength. Above presented equation shows, the transition temperature is universally proportional to the square root of distance between high angle interfaces. The AF makes the crack propagation difficult due to presence of a great number of high angle interfaces. The presented AF microstructure is stable and is kept after hydrogen charging process. The increased deflection numbers of the AF plates contribute to the achievement of high resistance to hydrogen induced cracking in this microstructure. The positive AF properties on the resistance to hydrogen induced cracking and the SSC formation in oil and gas pipe-line steels (X60-X80) confirm above presented idea [3]. The investigated steel with dominating AF microstructure, having optimum mechanical properties consists of the fine non-equiaxed and interwoven ferritic plates containing the ultra-fine carbonitrides, eventually. In some case the formed small M/A islands are not excluded absolutely. The AF plates formed by displacive transformation mechanism contain increased dislocation densitiy. This substructure contributes to the trapping of hydrogen atoms and in this way limits the detrimental hydrogen effect on steel properties. The combination of increased resistance to cleavage crack propagation and partial limitation of hydrogen activity (due to dislocation trapping of hydrogen atoms) result in the improvement of steel properties. These results demonstrate, the AF microstructure represents a perspective way how to increase steel durability under simultaneous hydrogen action.

4

Evaluation of cracks profile under the Vickers indentation

Blažková K., Jonšta Z., Mazanec K.

Zeszyty Naukowe. Mechanika / Politechnika Opolska

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2007

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Vol. 321, z. 89

85-86

EN

This work is devoted to the investigation of indentation crack profiles under Vickers indentation on two types cutting tool ceramics. First type of ceramics was aluminium oxide with zirconium oxide and the second one was silicon nitride ceramics. Vickers indents are created into the ceramic surface by hardness testing machine with a load of 294 N, loading time of indentations is 10 s. The value of investigated ceramics A12O3 + ZrO2 is equal to 1765 HV and Si3N4 ceramics reaches the average hardness value of 1574 HV. After Vickers indentation a system of initiated cracks and deformed area are initiated. The attention of this work is given up to the experimental technique by using serial sectioning to obtain depth profile of indentation cracks. By using this method it is possible to obtain a complete system of crack profiles under the Vickers indent and shape of deformed area. Serial sectioning methods are consisted of removing thin layers of material by ceramographic polishing. For each layer three polishing steps with diamond suspension 6,3 and 1 nm were performed. Two different processes of removing material method layer-by-layer are used. The first method consists in obtaining depth profile of the crack determined by ablating in steps from the surface into which the indentations was made. Diagonals of Vickers indents are measured before consecutive polishing and between every polishing step. In the case where the indents are already ablated there is no way how to determine the depth of polishing. To prevent to lose the depth reference new indents have to be created into the specimen surface before ablating previous ones, The second technique is based on layer removal from plane perpendicular to the indented surface. According the results the second method is more precise because of easier control of removed material, obtaining real profile of cracks system and deformed area under the Vickers indent.

5

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.

6

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.

7

Resistance of sour grade steels to Hydrogen Induced Cracking (HIC) formation

Mazovcová E., Wyslych P., Mazanec K.

Zeszyty Naukowe. Mechanika / Politechnika Opolska

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2006

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z. 88

81-86

8

Contribution to the Modelling of Processes Controlling the Acicular Ferrite (AF) Formation in C-Mn Steels

Mazancová E., Jonšta Z., Mazanec K.

Machine Dynamics Problems

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2006

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Vol. 30, No. 4

60-67

EN

Due to special morphology, AF microstructure makes possible to obtain a very favourable combination of mechanical properties (strength, ductility and toughness). The significant parameter is the deflection mechanism limiting cleavage crack propagation. Although the nucleation role of fine special non-metallic inclusions as inoculants controlling the austenite (A)-decomposition into ferrite has been described in great number of works, the comprehensive mechanism of these processes has not been developed. Due to large variety of non-metallic particles acting as inoculants in above considered transformation process, this solution is not facile. The nucleation potency of individual phases comprising complex inclusions has not been assessed so far. In the present contribution the investigation will be devoted to the finding of model being able to describe the nucleating behaviour of some complex inclusions based on manganese - silicate (MnO-SiO2) and on the nucleating effect of Mg-addition (MgO) to the basic chemical constitution resulting from deoxidization with Mn/Si/Ti. Among considered mechanism as the most perspective one could be held the formation of Mn-depleted zone being the nucleation site for intragranular A-decomposition into ferrite phase. It has been proposed this zone is formed around inclusion by the subsequent MnS nucleation on it. This process is accompanied with the subsequent Mn-diffusion running in the steel matrix to the MnS-nuclei. The following conclusions can be determined from the achieved results in investigated steel types. The nucleation potency of some inclusions complex represents a decisive initiation parameter in decomposition of A into AF. It has been established the higher density number of dispersed fine intragranular particles (0.5-2.0 µm) is very effective in the refinement of ferrite plates by AF nucleation. The non-metallic inclusions type participating in the considered nucleation process is determined by steel deoxidization. Precipitation of MnS on primary inclusions (investigated influence of Mn/Si and Mn/Si/Ti) has been analyzed. For both examples the same physical metallurgical characteristics leading to the formation of Mn-depleted zone and simultaneously realized MnS nucleation on applied non-metallic inclusions have been found. In case of AF nucleation on inclusions after Mg addition the mechanism of Mn-depleted zone has been also confirmed. The mechanism of AF formation in connection with Mn-depleted zone existence around the primary steel inclusions accompanied with MnS formation has been analyzed in detail. This complex mechanism can be considered as a very attractive model making possible to predict the AF nucleability in austenitic matrix.

9

Evaluation of basic properties of A12O3 tool ceramics usingindent technique

Blažková K., Olejníčková L., Jonšta Z., Mazanec K.

Zeszyty Naukowe. Mechanika / Politechnika Opolska

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2005

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z. 86

101-106

10

Analysis of inclusions effect on acicular ferritze formation

Mazancová E., Wyslych P., Jonšta Z., Mazanec K.

Zeszyty Naukowe. Mechanika / Politechnika Opolska

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2005

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z. 86

159-164

11

Crystalographic analysis of acicular ferrite and bainite microstructure

Mazancová E., Wyslych P., Jonšta Z., Mazanec K.

Zeszyty Naukowe. Mechanika / Politechnika Opolska

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2004

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z. 78

113-118

EN

Acicular ferrite (AF) is known to nucleate at intragranular inclusions. The high toughness of this austenite (A) decomposition product is attributed to the fine grained interlocking arrangement of fine plates growing by displacive mechanism. AF is formed in the same temperature range and by the same transformation type as upper bainite (B). On the contrary to AF, ferrite particles in B are nucleated at A-grain boundaries and form packets in which the plates have parallel arrangement [1]. In medium- and low-carbon steels, the formation of AF is usually associated with a favourable combination of strength and toughness values. The achieved AF microstructure toughness values are related to the increased density of high-angle boundaries (interfaces) characterized for this microstructure. This is beneficial microstructural arrangement because these interfaces act as obstacles to cleavage crack propagation, forcing the cleavage crack to change the microscopic plain of propagation in order to accommodate the new local crystallography. Low-angle boundaries forming B-packets are not effective obstacles and consequently have not influence on the achievement of improved toughness level in steel. This arrangement forms crystallographic packets defined by Gourgues et al. [2] as a continuous set of ferrite plates with crystallographic misorientation lower than a certain level of angle in contradiction to the AF secondary plates nucleation realized at surface of primary AF plates. The fan shaped formation of primary AF plates represents a further favourable parameter contributing to the increase of cleavage fracture resistance of this microstructure [3]. The object of present contribution is to compare the effect of AF and B microstructure parameter in relation to the obtained mechanical properties, especially toughness values in low-carbon steels. This comparison will be based on the misorientation of crystallographic parameters observed in above mentioned microstructure types.

12

Residual Stress Field and Evaluation of Isostress Contours in Ceramics

Horváthová J., Jonšta Z., Mazanec K.

Machine Dynamics Problems

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2004

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Vol. 28, No. 3

125-130

EN

The residual stress field is initiated in the vicinity of sharp indent (Vickers) too. Also to the studying of the residual stress field the special identation technique was applied. Identation technique is a reliably technique, which makes possible to determine the set of mechanical properties of ceramics (brittle) materials. Some cracks are developed near the identation cavity and their parameters reflect except the fracture toughness value and response to the repeated loading the level of residual stresses. Two types of technical ceramics (Al₂O₃ and Si₃N₄ ) with a different level of mechanical properties are the subjects of present study.

13

Využití indentační techniky při hodnocení mechanických vlastností keramických materiálů

Horváthová J., Jonšta Z., Šustai O., Mazanec K.

Zeszyty Naukowe. Mechanika / Politechnika Opolska

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2003

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z. 76

99-104

14

Contribution to the Physical Metallurgy of Acicular Ferrite

Mazancová E., Jonšta Z., Wyslych P., Mazanec K.

Zeszyty Naukowe. Mechanika / Politechnika Opolska

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2003

|

z. 76

121-126

15

Mechanism of idiomorphic ferrite formation

Mazancová E., Wyslych P., Mazanec K.

Zeszyty Naukowe. Mechanika / Politechnika Opolska

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2002

|

z. 75

51-54

EN

Ferrite which grows by a reconstructive mechanismus can be classified into two important forms: allotriomorphic (ATF) and/or idiomorphic ferrite (IDF). The ATF is nucleated at the prior austenite (A) grain boundaries, while the IDF is initiated intragranularly [1]. The study of physical engineering behaviour of the IDF has been very rarely realized in comparison with the number of works devoted to the investigation of ATF properties. For this reason, the purpose of presented work is as to identify the governing factors of the intragranular ferrite (F)-formation so as to define the growing condition of IDF in detail [2].

16

Fyzikálně inženýrské charakteristiky indentačního porušení keramiky

Horváthová J., Olejníčková L., Jonšta Z., Mazanec K.

Zeszyty Naukowe. Mechanika / Politechnika Opolska

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2002

|

z. 75

43-46

17

Contribution to the physical metallurgy of acicular ferrite

Mazancová E., Wyslych P., Mazanec K.

Zeszyty Naukowe. Mechanika / Politechnika Opolska

|

2001

|

z. 72

49-53

18

Contribution to physical metallurgy of hot ductility behaviour of steels

Pavliska J., Jonšta Z., Mazanec K., Mazancová E.

Zeszyty Naukowe. Mechanika / Politechnika Opolska

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2001

|

z. 72

55-58

19

Three-Stagne Heat Treatment of Baintic Steel and ITS Effect on the toughness increase

Mazancová E., Wyslych P., Mazanec K.

Zeszyty Naukowe. Mechanika / Politechnika Opolska

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2000

|

z. 63

107-110

20

Residual elelents and Their effect the susceptibility to transverse cracking in continuously cast steels

Pawliska J., Jonšta Z., Mazanec K.

Zeszyty Naukowe. Mechanika / Politechnika Opolska

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2000

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z. 63

99-102