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1

A Multiscale Model of Heating-Remelting-Cooling in the Gleeble 3800 Thermo-Mechanical Simulator System

Hojny M., Głowacki M., Bała P., Bednarczyk W., Zalecki W.

Archives of Metallurgy and Materials

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2019

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Vol. 64, iss. 1

401--412

EN

The paper presents a multi-scale mathematical model dedicated to a comprehensive simulation of resistance heating combined with the melting and controlled cooling of steel samples. Experiments in order to verify the formulated numerical model were performed using a Gleeble 3800 thermo-mechanical simulator. The model for the macro scale was based upon the solution of Fourier-Kirchhoff equation as regards predicting the distribution of temperature fields within the volume of the sample. The macro scale solution is complemented by a functional model generating voluminal heat sources, resulting from the electric current flowing through the sample. The model for the micro-scale, concerning the grain growth simulation, is based upon the probabilistic Monte Carlo algorithm, and on the minimization of the system energy. The model takes into account the forming mushy zone, where grains degrade at the melting stage – it is a unique feature of the micro-solution. The solution domains are coupled by the interpolation of node temperatures of the finite element mesh (the macro model) onto the Monte Carlo cells (micro model). The paper is complemented with examples of resistance heating results and macro- and micro-structural tests, along with test computations concerning the estimation of the range of zones with diverse dynamics of grain growth.

2

The influence of austenitization temperature on phase transformations of supercooled austenite in low-alloy steels with high resistance to abrasion wear

Białobrzeska B., Dziurka R., Żak A., Bała P.

Archives of Civil and Mechanical Engineering

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2018

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Vol. 18, no. 2

413--429

EN

The paper presents continuous cooling transformation (CCT) diagram of selected low-alloy steel with high resistance to abrasion. Samples were prepared from examined material in as delivered conditions, then were austenitized at 900, 1000, 1100 and 1200 °C for 20 min, and then cooled with the rates of V800–500 = 50, 10, 5, 1, 0.5, 0.1 °C/s. During the dilatometric research, the critical temperatures were defined as well as the critical points specified for different cooling rates were designated. In addition, metallographic documentation of received microstructures after dilatometric investigations was prepared and hardness measurement was performed. The increase in the austenitizing temperature caused changes in the temperature of MS and in the size of the martensite laths. What is more, the increase in the austenitizing temperature in the case of the analyzed steel caused a displacement of the bainitic and diffusion transformations to longer times. During the analysis using the TEM and SEM it was found that the size of the austenite grains is largely controlled by precipitates of the nitrides of AlN, TiN and carbides, mainly Cr7C3 and M23C6.

3

The analysis of the water-expanded rock bolts ruptures during pressure test

Pawłowski B., Krawczyk J., Bała P., Cios G., Tokarski T.

Archives of Mining Sciences

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2017

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Vol. 62, no. 2

423--430

EN

This paper describe the investigation of a water-expanded rock bolts failed during pressure test (inner water pressure of 330 bar). A main objective of this work was to determine the cracks nucleation and propagation mechanism. It was found that the rock bolts failure was promoted by presence of non-metallic inclusions (mainly long sulphide inclusions) but the primary cause of cracking is strain ageing of steel. Suggestions for improving the behaviour of steel used for water-expanded rock belts by the modification of its chemical composition are proposed finally.

PL

W pracy opisano badania rozprężanych wodą kotw górniczych, które uległy pękaniu podczas prób ciśnieniowych (przy ciśnieniu wody wewnątrz kotwy 330 bar). Głównym celem badań było określenie mechanizmu zarodkowania i propagacji pęknięć. Stwierdzono, że propagacji pęknięć sprzyjała obecność wtrąceń niemetalicznych (głównie długich wydzieleń siarczków) ale podstawowym powodem występowania pęknięć jest zjawisko starzenia po zgniocie. W celu zminimalizowania występowania pęknięć, w pracy zaproponowano modyfikację składu chemicznego stali na tego rodzaju kotwy górnicze.

4

Necessary Thermodynamics Factors to Obtain Simple Solid Solutions in High-Entropy Alloys from the Al-Ti-Co-Ni-Fe System

Górecki K., Bała P., Kozieł T., Cios G.

Archives of Metallurgy and Materials

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2017

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Vol. 62, iss. 4

2141--2145

EN

In this paper findings regarding the design and synthesis of High-Entropy Alloys based on mixing enthalpy, mixing entropy, δ parameter, Ω parameter and valence electron concentration are presented. Four alloys were synthesised with different predicted crystalline structures. Results of the microstructure and crystal structure studies are presented. It was shown that predicted structures as well as complex intermetallic phases exist in the material. The validity of valence electron concentration as well as additional parameters such as mixing enthalpy, mixing entropy and others necessary to obtain only the solid solution in High-Entropy Alloys were examined.

5

Effect of Zr Purity and Oxygen Content on the Structure and Mechanical Properties of Melt-Spun and Suction-Cast Cu46Zr42Al7Y5 Alloy

Kozieł T., Latuch J., Cios G., Bała P.

Archives of Metallurgy and Materials

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2016

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Vol. 61, iss. 2B

1215--1219

EN

The effect of oxygen content in zirconium on the structure and mechanical properties of the Cu46Zr42Al7Y5 alloy, in the form of melt-spun ribbons and suction-cast rods, was investigated. Two types of Zr, rod and crystal bar of different nominal purities and oxygen contents, were used to synthesize the alloy by arc melting. Rapidly solidified ribbons were produced by melt spinning and their amorphous structures were confirmed by X-ray diffractometry (XRD) and differential scanning calorimetry (DSC). Bulk samples in the form of rods were cast using a special water-cooled suction casting unit attached to the arc melting system. XRD and DSC studies proved the amorphous structure of the bulk alloy synthesized from low-oxygen Zr and partial crystallization of the same alloy for high-oxygen Zr. In both bulk samples, uniformly distributed crystalline particles were identified as yttrium oxides. Higher mean compressive strength of amorphous alloy was observed. The hardness of amorphous phase was close to 500 HV1 in both bulk alloys, while the hardness of crystalline dendritic areas, observed in the alloy synthesized from high oxygen Zr, was lower by about 50 HV1.

6

The influence of microstructure of 30MnB4 steel on hydrogen-assisted cracking

Krawczyk J., Bała P., Frocisz Ł., Tokarski T., Pawłowski B.

Metallurgy and Foundry Engineering

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2015

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Vol. 41, no. 4

171--180

EN

This paper analyzes the problem of susceptibility to hydrogen-assisted cracking (fracture behavior) of zinc-coated screws made of 30MnB4 steel. Two samples (screws) were compared after proper and improper heat treatment affecting hydrogen solubility during the further galvanic process and resulting in different fracture modes. Both samples were loaded to failure by torsion. The fracture surface and microstructure of the samples were examined using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS).

PL

Praca dotyczy problemu pękania wspomaganego wodorem. Materiałem do badań były śruby ocynkowane wykonane ze stali 30MnB4. Porównywano dwie próbki po poprawnej obróbce cieplnej, obejmującej hartowanie i niskie odpuszczanie, oraz obróbce polegającej wyłącznie na hartowaniu. Sposób przeprowadzenia obróbki cieplnej skutkował zmianami w rozpuszczalności wodoru w strukturze analizowanej stali. Wodór dostarczony został do materiału podczas procesu elektrolitycznego pokrywania cynkiem. Po procesie cynkowania obie próbki były skręcane do zerwania. Powstałe przełomy i zgłady metalograficzne badanych materiałów obserwowano przy wykorzystaniu skaningowego mikroskopu elektronowego (SEM), dokonano również analizy ich składu chemicznego, wykorzystując metodę spektroskopii rentgenowskiej z dyspersją energii fali (EDS).

7

Microstructural banding in titanium alloys

Krawczyk J., Dąbrowski R., Łukaszek-Sołek A., Frocisz Ł., Górecki K., Cios G., Śleboda T., Kopyściański M., Bała P.

Journal of Achievements in Materials and Manufacturing Engineering

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2015

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Vol. 72, nr 1

5--13

EN

Purpose of this paper was to investigate the phenomenon of microstructural banding in three titanium alloys: Ti-6Al-4V, Ti-10V-2Fe-3Al and Ti-3Al-8V-6Cr-4Mo-4Zr. Design/methodology/approach: The microstructure of the investigated materials in as-delivered condition was characterized. Compression tests were performed on Gleeble thermomechanical simulator to investigate banding phenomena occurring in the microstructure of each studied alloy. Moreover, banding phenomena was also investigated in the case of forging obtained from Ti-6Al-4V alloy. Heat treatment conditions allowing to reduce banding in the microstructure of the investigated alloys were also determined. Findings: Thermomechanical processing leading to dynamic recrystallization in the investigated alloys restricts the formation of bands in their microstructure. Homogenizing treatment can also reduce banding in such alloys. Research limitations/implications: Future research should concern the investigations of grain size in the recrystallized alloys and in the alloys subjected to homogenizing heat treatment. Practical implications: The results of this research should allow obtaining homogenous microstructure in titanium alloys studied in this paper. Originality/value: The range of the temperature and strain rate for dynamic recrystallization restricting banding in the microstructure in the investigated alloys was determined. In the case of Ti-3Al-8V-6Cr-4Mo-4Zr alloy the range of the temperature and time of annealing leading to homogenization of the material was identified.

8

The Characterization Of Cast Fe-Cr-C Alloy

Wieczerzak K., Bała P., Stępień M., Cios G., Kozieł T.

Archives of Metallurgy and Materials

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2015

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Vol. 60, iss. 2A

779--782

EN

The paper presents the results of the characterization of alloy from Fe-Cr-C (carbon content 0.79 wt.%) system including the microstructure, phase analysis, morphology and hardness in as cast state. The chemical composition was designed to create chromium-rich ferritic matrix with high volume fraction of carbides in form of interdendritic eutectics. The research was carried out on the cross section of the ingot, synthesized in an arc furnace under high purity argon atmosphere and crystallized on water-cooled copper mould. Microstructural characterization was carried out by light microscopy and scanning electron microscopy (SEM). Phase identification was performed by X-Ray diffraction (XRD). The microstructure of the investigated alloy is composed of primary and secondary dendrites Fe-Cr solid solution and complex M23C6 and M7C3 carbides in interdendritic areas. Segregation of Cr and C during crystallization causes precipitation of M7C3 carbides. The average hardness of the alloy is 205±12 HV10.

PL

W pracy dokonano analizy mikrostruktury, faz oraz wybranych właściwości stopu w stanie lanym z układu Fe-Cr-C (stężenie węgla 0,79% mas.). Skład chemiczny zaprojektowano tak, aby uzyskać osnowę ferrytyczną bogatą w chrom z dużym udziałem objętościowym węglików eutektycznych. Badania przeprowadzono na przekroju poprzecznym wlewka wykonanego w piecu łukowym w atmosferze ochronnej argonu, krystalizującego na miedzianym łożu, chłodzonym wodą. Obserwacje mikrostruktury przeprowadzono z wykorzystaniem mikroskopii świetlnej oraz skaningowej mikroskopii elektronowej (SEM). Identyfikację faz wykonano za pomocą rentgenowskiej analizy fazowej. Mikrostruktura badanego stopu składa się z dendrytów pierwszo i drugorzędowych roztworu stałego chromu w żelazie α oraz węglików złożonych M23C6 i M7C3, powstałych w obszarach międzydendrytycznych. Segregacja Cr i C podczas krystalizacji, sprzyja wydzielaniu węglików typu M7C3. Średnia twardość stopu wynosi 205±12 HV10.

9

Microstructure of Cast Ni-Cr-Al-C Alloy

Cios G., Bała P., Stępień M., Górecki K.

Archives of Metallurgy and Materials

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2015

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Vol. 60, iss. 1

145--148

EN

Nickel based alloys, especially nickel based superalloys have gained the advantage over other alloys in the field of high temperature applications, and thus become irreplaceable at high temperature creep and aggressive corrosion environments, such as jet engines and steam turbines. However, the wear resistance of these alloys is insufficient at high temperatures. This work describes a microstructure of a new cast alloy. The microstructure consists of γ matrix strengthened by γ’ fine precipitates (dendrites) improving the high temperature strength and of Chromium Cr7C3 primary carbides (in interdendritic eutectics) which are designed to improve wear resistance as well as the high temperature strength.

PL

Stopy na osnowie niklu, a w szczególności superstopy na osnowie niklu zyskały przewagę w stosunku do innych stopów metali na polu zastosowań w wysokiej temperaturze. Są niezastąpione w warunkach pełzania wysokotemperaturowego, a także agresywnym środowisku korozyjnym silników odrzutowych czy tez turbin parowych. Jednakże odporność na ścieranie tych stopów jest niewystarczalna do zastosowania tych materiałów w wysokiej temperaturze i warunkach ścierania. W niniejszej pracy opisano mikrostrukturę nowego stopu. Składa się ona z osnowy γ umocnionej fazą γ’ (dendryty) - zwiększającą wytrzymałość wysokotemperaturową, a także z pierwotnych węglików chromu Cr7C3 (w eutektykach międzydentrytycznych) - mających na celu zwiększyć zarówno odporność na ścieranie jak i wytrzymałość wysokotemperaturową.

10

The analysis of phase transformation of undercooled austenite and selected mechanical properties of low-alloy steel with boron addition

Łętkowska B., Dziurka R., Bała P.

Archives of Civil and Mechanical Engineering

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2015

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Vol. 15, no. 2

308--316

EN

The paper presents continuous cooling transformation (CCT) diagram of selected low-alloy boron steel with high resistance to abrasion. Tests were performed on samples with dimensions of Ø 3 mm × 10 mm. Samples were prepared from examined material in as – delivery conditions, then were austenitized at 930 °C for 20 min, and then cooled with the rates of V800-500 = 0.17, 0.33, 1, 5, 10, 25 and 47 °C/s. During the dilatometric research, the critical temperatures were defined as well as the critical points specified for different cooling rates were designated. In addition, metallographic documentation of received microstructures after dilatometric investigations was prepared and hardness measurement was performed. Moreover, examinations of the basic parameters of strength, impact test and abrasion resistance test were performed and a tendency to brittle fracture was analyzed. The studies show big differences of the analyzed parameters depending on the applied heat treatment, which should provide guidance to users to specific applications of this type of steel.

11

Influence of solution heat treatment on the microstructure and hardness of the Ni-Ta-Al alloy with a high carbon content

Bała P.

Inżynieria Materiałowa

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2014

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Vol. 35, nr 2

78--81

EN

The main purpose of the hereby paper was to determine temperature and time of solution heat treatment influence on a microstructure and hardness of the newly designed model alloy for operations at high temperature. A test melt of a mass of approximately 1 kg was performed in a vacuum furnace, and cast into a ceramic mould. The microstructure of the investigated material was examined by means of the Axiovert 200 MAT light microscope and the FIB Zeiss NEON 40EsB CrossBeam scanning electron microscope. Samples for investigations were solution heat treated in the temperature range 1020÷1170°C. After heating to the desired temperature they were hold at this temperature for 0.5 or for 2 hours and then water-cooled. The main constituents of the microstructure of the Ni-Ta-Al-C alloy in as-cast state are: the γ phase, which constitutes the matrix, the γ' phase (γ' phase occurs as fine globular precipitates) as well as primary Ta carbides of MC type. Primary carbides of irregular shapes are uniformly distributed not forming agglomerates. Solution heat treatment of the investigated alloy from higher and higher temperature causes a slow increase of a graphite fraction. Taking into account the chemical composition of the investigated alloy the possibility of improving its properties by means of the heat treatment should not be expected. In the first place the fraction of carbide forming elements should be increased to eliminate graphite, and secondly the fraction of elements forming γ' phase should be increased to obtain the possibility of the modification of properties by means of solution heat treatment and aging. Nonetheless, the achieved results will be utilised at the chemical composition modification of Ni-based alloys of a high carbon content.

PL

W pracy opisano wpływ temperatury i czasu przesycania na mikrostrukturę i twardość stopu modelowego na osnowie niklu, o dużym stężeniu węgla (0,81%), przewidywanego do pracy w wysokiej temperaturze. Wytop próbny o masie około 1 kg wykonano w piecu próżniowym i odlano do ceramicznej formy. Obserwacje mikrostruktury wykonano za pomocą mikroskopu świetlnego Axiovert 200 MAT oraz elektronowego mikroskopu skaningowego FIB Zeiss NEON 40EsB CrossBeam. Próbki do badań przesycano z zakresu temperatury 1020÷1170°C. Po nagrzaniu do określonej temperatury próbki wygrzewano przez 0,5 godz. lub 2 godz., a następnie chłodzono w wodzie. Dla każdej próbki określono udział objętościowy węglików oraz grafitu. Mikrostruktura badanego stopu w stanie po odlaniu jest złożona z osnowy γ, fazy γ' oraz rozmieszczonych w obszarach międzydendrytycznych węglików pierwotnych tantalu typu MC. Węgliki pierwotne o nieregularnym podłużnym kształcie i zróżnicowanej wielkości są rozmieszczone równomiernie, nie tworząc aglomeratów. Opisano wpływ temperatury i czasu przesycania na mikrostrukturę oraz twardość badanego stopu. Stwierdzono, że przesycanie badanego stopu z coraz to wyższej temperatury powoduje rozpuszczanie węglików pierwotnych tantalu, rozrost byłych obszarów dendrytycznych, pozostaje jednak bez wyraźnego wpływu na udział grafitu, który tylko nieznacznie zwiększa się w odniesieniu do stanu po odlaniu. Badany stop jest stopem modelowym. Jego skład chemiczny nie pozwala na poprawę jego własności za pomocą obróbki cieplnej. Aby uzyskać możliwość modyfikacji jego własności w wyniku obróbki cieplnej w pierwszej kolejności należałoby zwiększyć udział pierwiastków węglikotwórczych, aby wyeliminować grafit, a w drugiej udział pierwiastków tworzących fazę γ'. Wyniki badań osiągnięte w pracy posłużą do projektowania nowych stopów na osnowie niklu o dużym stężeniu węgla.

12

The Dilatometric Analysis of the High Carbon Alloys from Ni-Ta-Al-M System

Bała P.

Archives of Metallurgy and Materials

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2014

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Vol. 59, iss. 3

977--980

EN

In the following work presents results of high carbon alloys from the Ni-Ta-Al-M system are presented. The alloys have been designed to have a good tribological properties at elevated temperatures. Despite availability of numerous hot work tool materials there is still a growing need for new alloys showing unique properties, which could be used under heavy duty conditions, i.e. at high temperatures, in a chemically aggressive environment and under heavy wear conditions. A characteristic, coarse-grained dendritic microstructure occurs in the investigated alloys in the as-cast condition. Primary dendrites with secondary branches can be observed. Tantalum carbides of MC type and graphite precipitations are distributed in interdendritic spaces in the Ni-Ta-Al-C and Ni-Ta-Al-C-Co alloys, while Tantalum carbides of MC type and Chromium carbides of M3C2 type appeared in the Ni-Ta-Al-C-Co-Cr and Ni-Ta-Al-C-Cr alloys. In all alloys γ’ phase is present, however, its volume fraction in the Ni-Ta-Al-C and Ni-Ta-Al-C-Co alloys is small. During heating from as-cast state in Ni-Ta-Al-C and Ni-Ta-Al-C-Co alloys, the beginning of the tantalum carbides precipitation process (MC type) followed (or simultaneous) by the intermetallic phase precipitation (γ’ – Ni3(AlTa)) was stated, while in Ni-Ta-Al-C-Co-Cr and Ni-Ta-Al-C-Cr alloys, besides Tantalum carbides also the Chromium carbides precipitation occurred. It means that the investigated alloys were partially supersaturated in as-cast state. Above 1050°C in all investigated alloys the γ’ phase is dissolving. In addition, the precipitation of secondary carbides during slow cooling was occured.

PL

W pracy przedstawiono wyniki badań nowych stopów z układu Ni-Ta-Al-M o dużym stężeniu węgla. Stopy te zostały zaprojektowane do pracy w wysokiej temperaturze i w warunkach silnego zużycia tribologicznego. Pomimo, że istnieje wiele materiałów narzędziowych do pracy na gorąco wciąż istnieje silna potrzeba poszukiwania nowych materiałów o unikatowych własnościach, które mogłyby pracować w bardzo trudnych warunkach, tj. wysokiej temperaturze, agresywnym chemicznie środowisku i w warunkach silnego zużycia tribologicznego. W stanie po odlaniu badane stopy cechują się charakterystyczną budową dendrytyczną. Widoczne są pierwszo i drugorzędowe dendryty. W stopach Ni-Ta-Al-C i Ni-Ta-Al-C-Co w obszarach międzydendrytycznych rozmieszczone są węgliki tantalu typu MC oraz grafit, natomiast w stopach Ni-Ta-Al-C-Co-Cr i Ni-Ta-Al-C-Cr węgliki tantalu typu MC oraz węgliki chromu typu Cr7C3. We wszystkich stopach występuje faza γ’, choć jej udział objętościowy w stopach Ni-Ta-Al-C i Ni-Ta-Al-C-Co jest nieduży. Podczas nagrzewania ze stanu lanego w stopach Ni-Ta-Al-C i Ni-Ta-Al-C-Co stwierdzono wydzielanie węglików wtórnych tantalu typu MC z następnym (lub równoczesnym) wydzielaniem fazy (γ’ – Ni3(AlTa)). Natomiast w stopach Ni-Ta-Al-C-Co-Cr i Ni-Ta-Al-C-Cr oprócz węglików wtórnych tantalu wydzielają się węgliki wtórne chromu. Oznacza to, że badane stopy w stanie po odlaniu były w stanie częściowego przesycenia. Powyżej 1050°C we wszystkich badanych stopach rozpuszczają się wydzielenia fazy γ’. Wtórne wydzielanie węglików stwierdzono również podczas wolnego chłodzenia od temperatury 1200°C.

13

Improper Interpretation of Dilatometric Data for Cooling Transformation in Steels

Pawłowski B., Bała P., Dziurka R.

Archives of Metallurgy and Materials

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2014

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Vol. 59, iss. 3

1159--1161

EN

Dilatometry is the most commonly method of producing CCT diagrams and analyzing phase transformations during cooling (as well as transformations during heating) and it permits the real-time monitoring of the extent of reaction in terms of dimensional changes due to phase transformation. All modern dilatometers are fitted with computerised systems which collect dimensional change signals versus temperature to plot a dilatometric curve and also to calculate and plot the derivative of the relative dimensional change with respect to temperature. Unfortunately, elaborated by dilatometers manufacturers software, in many cases could lead to wrong interpretation of phase transformations during cooling.

PL

Dylatometria jest najczęściej stosowana technika badawczą przy tworzeniu wykresów CTPc i analizie przemian fazowych podczas chłodzenia oraz nagrzewania. Umożliwia również śledzenie na bieżąco postępu przemiany dzięki rejestracji zmian wymiarów próbki w trakcie przemiany. Wszystkie współczesne dylatometry są wyposażone w systemy komputerowe sterowania i akwizycji danych pomiarowych umożliwiające obserwację dylatogramu w trakcie chłodzenia czy nagrzewania jak również obliczenie i narysowanie po zakończeniu eksperymentu wykresu różniczki (pierwszej pochodnej) w funkcji temperatury. Niestety, fabryczne oprogramowanie w wielu przypadkach może prowadzić do błędnej interpretacji zjawisk podczas przemian fazowych w trakcie chłodzenia.

14

The influence of the heat treatment on the microstructure and tribological properties of mottled cast iron

Krawczyk J., Pacyna J., Pawłowski B., Madej M., Bała P.

Journal of Achievements in Materials and Manufacturing Engineering

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2013

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Vol. 57, nr 1

15--22

EN

Purpose: The objective of this work was to determine the influence of microstructure changes on GJS-HV300(SiNiCr2-3) cast iron tribological properties. Modification of the investigated cast iron microstructure was carried out by the heat treatment. Design/methodology/approach: The tribological tests were performed on the T05 tester at a load of 100 N. Bearing steel 100Cr6 of a hardness of 57 HRC was applied as a counter sample. The test duration time was 2000 s. During the tribological test the continuous measurements of the friction coefficient were carried out and the friction products were being removed from the counter sample surface. The tribological tests were performed at a room temperature. A stereological analysis of volume fractions of structural components (VV) was performed by means of the point method, with the application of a network deposited on the microstructure photographs. For each variant of the heat treatment 30 depositions of the network were performed. Measurements were done on microphotographs obtained by using an objective of 50 times magnification. The network with 200 measurement points was applied. Findings: Predicting of wear resistance only on the basis of hardness is unappropriate. The main factor here is the mechanism of wear, which is influenced mainly by the microstructure. Research limitations/implications: The relationship between the hardness resulting from the microstructure and the wear resistance of the investigated cast iron was presented. This supplements the knowledge concerning the role of the microstructure in the formation of tribological properties of cast iron. Practical implications: Predicting of the tribological properties of mill rolls. Originality/value: Heat treatment resulting in decrease of volume fraction of ledeburitic cementite and increase of volume fraction of graphite decreases wear resistance of investigated material.

15

Effect of microstructural banding in hot-work tool steel on thermal expansion anisotropy

Pawłowski B., Bała P., Dziurka R., Krawczyk J.

Journal of Achievements in Materials and Manufacturing Engineering

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2013

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Vol. 56, nr 1

14--19

EN

Purpose: The objective of the present work was to study the effect of the microstructural banding on the thermal anisotropy of hot-work tool steel used for die for aluminium alloy die-casting. In particular, the major purpose of this research was to find possible correlation between geometrically oriented thermal expansion coefficient values and the presence of number of parallel cracks on the working surface of die. Design/methodology/approach: The studies were performed on the specimens which were cut from the failed prematurely die along the three axes of the coordinate system (X-axe was parallel to the cracks direction). Macroscopic, metallographic, SEM and dilatometric examination were made. Findings: Surface cracks of die are parallel to the microstructural banding orientation. Differences in the values of thermal expansion coefficient determined along the three axes of the coordinate system probably promote cracks propagation direction. Research limitations/implications: Studies were performed on the single prematurely failed die for economic reason. This work findings should be compared to the similar examinations results obtained for the another failed dies. Practical implications: The incorrect microstructural banding orientation of the die core and related differences in the values of thermal expansion coefficient promote crack propagation. Originality/value: This show the relationship between microstructural banding and the thermal anisotropy of hot-work tool steel used for die for aluminium alloy die-casting.

16

Premature cracking of dies for aluminium alloy die-casting

Pawłowski P., Bała P., Tokarski T., Krawczyk J.

Archives of Metallurgy and Materials

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2013

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Vol. 58, iss. 4

1275--1279

EN

Two identical dies for aluminium alloy die-casting failed prematurely because of a number of parallel cracks on the working surface. These cracks were of a mechanical nature related to incorrect microstructural banding orientation of the die core and related to improper heat treatment. The microstructural banding orientation was determined by metallographic examination of the specimens, which were cut from the dies along the three axes of the coordinate system. Scanning electron microscopy (SEM) examination of the fracture surfaces and along the crack path (including energy dispersive spectroscopy (EDS) analysis) indicated that the root cause of the premature cracking of the dies was improper heat treatment (quenching and tempering conditions). Additionally, resistance to fracture of the investigated specimens, as measured by the Charpy V-notch test, was five times lower than that required for the desired hardness.

PL

Dwie identyczne matryce do ciśnieniowego odlewania stopów aluminium zostały przedwcześnie wycofane z eksploatacji z powodu wystąpienia na ich powierzchniach roboczych szeregu równoległych pęknięć. Kierunek propagacji pęknięć pokrywał się z kierunkiem pasmowości mikrostrukturalnej a samo tworzenie się pęknięć było skutkiem niewłaściwej obróbki cieplnej matryc. Stwierdzono nieprawidłową orientację geometryczną matrycy względem kierunku włókien struktury pierwotnej. Badania przy użyciu skaningowego mikroskopu elektronowego z wykorzystaniem techniki EDS wykazały, że przyczyną powstawania pęknięć matryc była nieprawidłową przeprowadzona obróbki cieplna matryc.

17

The influence of continuous heating rate on the austenite formation in the medium carbon TRIP steel

Kokosza A., Pacyna J., Bała P., Dziurka R.

Archives of Materials Science and Engineering

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2013

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Vol. 62, nr 1

22--27

EN

Purpose: The purpose of the hereby work was to determine the influence of heating rate on the austenite formation range and to draw the time-temperature-austenitizing diagram at continuous heating for TRIP 41MnSi6-5 steel. Design/methodology/approach: The dilatometric analysis was applied as the basic investigation method. Samples of the tested steel were heated to 1100°C with various heating rates. Changes in the relative elongation (ΔL) were recorded as a temperature function (T), during heating. On the basis of analysing such dependencies, for each heating rate the critical temperatures were determined. Findings: It was found, that during heating of the 41MnSi6-5 steel the austenite formation starts at the higher temperature the faster is the heating. It was observed, that directly before the start of the austenite formation, an unidentified (in the presented here investigations) transformation occurs in the investigated steel, causing its volume increase. Research limitations/implications: The performed investigations indicate that during heating of elements of small thickness or cross-sections - within the critical temperature range - the method of their heating to the required temperature becomes very important. At short heating times incorrectly selected the heating conditions can be the reason of significant errors of the heat treatment. Practical implications: The developed diagram: time-temperature-austenitizing, at a continuous heating (CHT), can be a useful tool supporting the proper selection of heating parameters within the critical temperature range. Originality/value: The dependence of the heating rate and the temperature range, in which austenite is formed in the tested 41MnSi6-5 steel, was found. It was observed that heating of the investigated steel with rates lower than 1°C/s has an insignificant influence on the temperature range within which the austenite formation occurs.

18

Własności tribologiczne stopów z układu Ni-Ta-Al-M o dużej zawartości węgla

Bała P., Krawczyk J., Madej M.

Tribologia

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2012

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nr 3

21-28

PL

W niniejszej pracy przedstawiono ocenę własności tribologicznych stopów z układu Ni-Ta-Al-M o dużej zawartości węgla. Materiały te zaprojektowano do pracy w wysokich temperaturach w warunkach silnego zużycia tribologicznego oraz agresywnego chemicznie środowiska. Omówiono mikrostrukturę badanych stopów po odlaniu i po obróbce cieplnej oraz określono rodzaj i udział objętościowy węglików. Badania tribologiczne wykonano w temperaturze pokojowej, w stanie po odlaniu oraz po obróbce cieplnej celem określenia roli węglików w mechanizmie zużycia. Określono wpływ obciążenia i czasu trwania próby na parametry tribologiczne ww. stopów. Dla wszystkich wariantów testów tribologicznych wyznaczono wielkość zużycia, współczynnik tarcia oraz określono mechanizm zużycia.

EN

In the paper, the two alloys from Ni-Ta-Al-M system with high carbon content, strengthened by intermetallic compounds, are presented. The chemical compositions of the new materials were designed in such a way as to obtain matrix strengthening by means of the precipitation of intermetallic compounds rich in Ni as well as Al and Ta and having the carbide fraction above 20%. Carbides should remain stable in the microstructure, regardless of the heat treatment, since they favourably influence an abrasion resistance. Tools use for special application made of these materials should primarily have good tribological properties at elevated temperatures. The microstructures and carbides volume fraction of investigated alloys are described. The tribological tests were performed at ambient temperature to determined the role of the carbides in the wear mechanism. The wear level, coefficient of wear, and wear mechanism for all investigated alloys, are described.

19

Analiza przyczyn pęknięć w złączu rura płuczkowa-zwornik w wiertnictwie

Pawłowski B., Krawczyk J., Bała P., Parzych S.

Przegląd Spawalnictwa

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2012

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R. 84, nr 6

42-46

PL

W pracy omówiono przyczyny występowania pęknięć złączy rura-zwornik podczas eksploatacji rur płuczkowych. Na podstawie badań stwierdzono niewłaściwy sposób wykonania złącza – elektrody zostały źle dobrane i sprzyjały powstawaniu pęknięć. Ujawniono również wykorzystanie do produkcji rur płuczkowych niewłaściwego gatunku stali. Dla porównania przedstawiono zmiany właściwości i mikrostruktury złącza rura zwornik wykonanego metodą zgrzewania tarciowego.

EN

The paper presents analysis of the causes of cracks in the pipe-nipple joint region of the drill pipes occurred during service. The results of performed examinations showed the wrong way of making the pipe-nipple joint by welding instead of friction welding. In addition, electrodes used for welding were incorrect and favored crack nucleation and propagation in the heat affected zone of nipple joint. Also discloses the use of the drill pipe of the wrong steel grade. The changes in hardness and microstructure of the pipe-nipple joint properly made by friction welding were shown for comparison.

20

Wpływ procesu kucia matrycowego na mikrostrukturę stopu Ti-6Al-4V

Śleboda T., Krawczyk J., Bała P., Łukaszek-Sołek A., Paćko M.

Inżynieria Materiałowa

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2012

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Vol. 33, nr 4

275--279

PL

W ramach przedstawionych badań analizie poddano zmiany w mikrostrukturze odkształcanego w procesie kucia na gorąco stopu Ti-6Al-4V. Po wygrzaniu w piecu elektrycznym komorowym, wsad w formie walca był odkształcany w temperaturze 950°C. Temperatura wygrzewania, odkształcania oraz chłodzenia była w sposób ciągły monitorowana. Kształtowanie badanego stopu było poprzedzone badaniami dylatometrycznymi stopu oraz analizą numeryczną wariantów kucia, co pozwoliło na precyzyjne określenie parametrów odkształcania w warunkach rzeczywistych.

EN

This research focuses on the development of the microstructure in the hot forged Ti-6Al-4V alloy. After heating in an electric chamber furnace, a billet was forged at 950°C. The temperature of heating, forging and cooling of the billet was constantly monitored. Processing of the investigated alloy in industrial conditions was preceded by dilatometric analysis of the investigated alloy as well as by numerical modelling of the forging modes, which enabled precise determination of the forging parameters.