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1

Effect of heat treatment on the tensile properties of cam shaft made of ductile cast iron

Karaca B., Şimşir M., Akkan H.

Journal of Achievements in Materials and Manufacturing Engineering

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2016

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Vol. 76, nr 1

15--20

EN

Purpose: The aim of this study is to investigate effects of austempering heat treatment on the tensile properties of GGG60 ductile cast iron for cam shaft production. For this purpose, cam shafts have been produced by sand casting method. Design/methodology/approach: For nodulizing process, Fe-Si-Mg alloy has been used and Fe-Si-Ba-Ca-Al alloy for inoculation process. The casting has been done between 1410-1420°C and the pouring time was between 11-13 sec. The casted cam shafts and tensile test samples have been austenitized at two different temperatures (800 and 900°C) and time (60 and 90 min.) under controlled furnace atmosphere. The austenitized cam shafts and tensile test samples have been quenched into the molten salt bath at 360°C temperature and held 90 min. and then cooled in air. By this way, austempering heat treatment has been applied. Microstructure of cam shafts and tensile test samples have been examined by optical and scanning electron microscopy (SEM) and mechanical tests (hardness, and tensile tests) have been performed. Findings: Results show that austempering heat treatment increases the tensile strength of cam shaft as-cast condition. Tensile strength of the cam shaft increases with increasing austenitizing temperature and time. The highest tensile strength, 1165.5 MPa, has been obtained from the cam shaft austenitized at 900°C and 90 min. time. Research limitations/implications: The production of cam shafts used in engines, it is carried out with the casting and machining techniques. Today, cam shafts are produced from gray, nodular graphite cast iron, because of many advantages, and also machining of steel.

2

Microstructure and mechanical properties of ADI depending on austenitization methods and parameters

Giętka T., Szykowny T.

Archives of Foundry Engineering

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2012

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Vol. 12, iss. 2

19-24

EN

Ductile iron was quenched using two-variant isothermal transformation. The first treatment variant consisted of one-phase austenitization at a temperature t = 830, 860 or 900 C, cooling down to an isothermal transformation temperature of 300 or 400 C and holding from 8 to 64 minutes. The second treatment variant consisted of two-phase austenitization. Cast iron was austenitizied at a temperature t = 950 C and cooled down to a supercritical temperature t = 900, 860 or 830 C. Isothermal transformation was conducted under the same conditions as those applied to the first variant. Ferrite cast iron was quenched isothermally. Basic strength (Rp0.2 Rm) and plastic (A5) properties as well as matrix microstructure and hardness were examined. As a result of heat treatment, the following ADI grades were obtained: EN-GJS-800-8, EN-GJS-1200-2 and EN-GJS-1400-1 in accordance with PN-EN 1564:2000 having plasticity of 1.5-4 times more than minimum requirements specified in the standard.

3

Zmiany mikrostruktury i twardości stali 56NiCrMo7 w zakresie temperatur austenityzowania 700÷1000 °C

Dąbrowski R., Dziurka R.

Hutnik, Wiadomości Hutnicze

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2010

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Vol. 77, nr 6

290-296

PL

W artykule przedstawiono wyniki badań wstępnych stali narzędziowej gatunku 56NiCrMo7 do pracy na gorąco. Obejmowały one ocenę punktów przełomowych oraz mikrostruktury w stanie wyżarzonym. Dokonano również analizy zmian twardości oraz zmian zachodzących w mikrostrukturze stali w wyniku zmiany temperatury austenityzowania. Uzyskane wyniki badań stanowią przyczynek do wykonania oryginalnych wykresów CTPc° służących do analizy kinetyki przemian fazowych, zachodzących podczas odpuszczania tej stali uprzednio zahartowanej od wybranej temperatury austenityzowania.

EN

Results of preliminary research of a hot-work tool steel, grade 56NiCrMo7, are presented in this paper. The investigations have been focused on measurements of the steel’s critical temperatures and on microstructural analysis after softening annealing. The effect of austenitizing temperature on hardness and development of microstructure also was investigated. On the basis of the obtained results an original CHT (Continuous–Heating–Transformations) diagram will be developed, which can be used for analysis of phase transformations taking place during tempering of previously quenched steel.

4

The effect of thermal treatment on the mechanical properties of vermicular cast iron

Mierzwa P., Soiński M. S.

Archives of Foundry Engineering

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2010

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Vol. 10, iss. 1 spec.

99--102

EN

The work determines the effect of austempering (isothermal quenching) on the basic mechanical properties of cast iron with vermicular graphite. The cast iron has been produced in one of Polish foundries. Copper addition in the amount of about 1% has been introduced to the cast iron in order to obtain the pearlitic matrix. The mechanical properties (Rm, R0,2 , A5, HB) have been determined both for the as-cast state and after austenitizing at 960 °C combined with quenching at 290 °C for 90 minutes, and also after austenitizing at 960 °C followed by isothermal quenching at 290 °C for 150 minutes. It has been found that the thermal treatment, resulting in the cast iron matrix change from the ferritic-pearlitic one to the one composed of acicular precipitates of ferrite and residual austenite, causes a distinct increase in cast iron strength; after the thermal treatment it has reached about 900÷1000 MPa. The examination has been performed using the specimens cut out of the reversed U-block test coupons of walls 25 mm thick and 50 mm high.

5

Predicting ADI mechanical properties

Giętka T., Dymski S.

Archives of Foundry Engineering

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2009

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Vol. 9, iss. 3

267-274

EN

Ductile cast iron was quench-hardened with the isothermal transformation according to two alternatives. The first treatment alternative consisted in the austenitizing process at temperature t\gamma = 830, 860 i 900 oC and annealing at temperature tpi = 400, 350 and 300oC in a period of time up to 240 min. The second treatment alternative consisted in dual-stage austenitizing. The material was annealed in temperature of t\gamma = 950oC and cooled to temperature t\gamma = 900, 860 and 830oC. The isothermal transformation was performed in the same conditions as in the first alternative. The cast iron was ferritizingly annealed before the isothermal quench-hardening. The cast iron matrix after the annealing was ferritic. Metallographic cubic specimens with the size about of 10 mm were quench-hardened with the isothermal transformation. Matrix microstructure, austenite percentage and Vicker's hardness were determined using the specimens. Hardness test results were used to determine, on the base of material coefficients, tensile strength Rm, yield strength Rp0,2 and deformation A5. Tests showed that heat treatment according to two alternatives of the quench hardening led to obtain ADI cast iron with accordance to PN-EN 1564 : 2000 grade: EN-GJS-800-8, EN-GJS-1000-5, EN-GJS-1200-2. Only ausferritic cast iron was assumed as a base of qualification.

6

The influence of saturation of cast iron austenite with carbon on the ausferrite transformation

Giętka T., Szykowny T., Dymski S.

Archives of Foundry Engineering

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2007

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Vol. 7, iss. 3

241-246

EN

Austenitizing during quench hardening of the ductile cast iron influences the content of carbon in austenite depending on the soaking heat. On the other hand, the saturation of austenite impacts its transformation in the ausferritizing process of a metal matrix and forming of microstructure. Ductile cast iron with the ferrite matrix was hardened with isothermal transformation in the range of ausferritizing in temperature [...]. Microstructure was investigated, there were also defined the proportion of austenite in the matrix of the cast iron and the content of carbon in it and hardness and impact strength in unnotched specimens. It was stated, that the precooling temperature deciding on the content of carbon in austenite influences kinetics of the ausferritic transformation, the content of carbon in the [gamma] phase and impact strength and, in a less degree, hardness. As a result of gradual austenitizing the cast iron after quench hardening, in some conditions of treatment, reached mechanical properties corresponding, according to the ASTM A 897 standard, with high grades of ADI. Chilling in the range of austenitizing in temperature 850 and 800 oC led to the decrease of carbon in austenite what influenced positively on the matrix microstructure and properties of the ADI. Investigations in this range will be continued.

7

Parametry stereologiczne węglików w żeliwie chromowym w stanie surowym i austenityzowanym

Przybył M., Studnicki A.

Archiwum Odlewnictwa

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2004

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R. 4, nr 14

430-437

PL

W pracy przebadano wytopy żeliwa chromowego zawierające około 7; 12 i 22 %Cr oraz 1.8 i 2.6 %C. Określono powierzchnie, obwody wydzieleń węglików oraz ich udział objętościowy w stanie surowym i po austenityzowaniu w 900 i 1000°C. Przedstawiono w sposób graficzny empiryczny oraz funkcyjny rozkład ilości węglików i udziału objętościowego w klasach ich powierzchni.

EN

In this paper stereological parameters of carbides of chromium cast iron has been presented. Chromium cast iron in as-cast and after austenitizing 900°C and 1000°C have been examined.

8

Wpływ temperatury austenityzowania na charakterystyczne temperatury przemian w stopie Fe-30%Ni

Ciura F., Michta G., Osuch W.

Inżynieria Materiałowa

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2003

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R. XXIV, nr 6

260-263

PL

Badaniom poddano próbki ze stopu Fe-30%Ni różniące się morfologią i ilością martenzytu otrzymanego na drodze odkształcenia oraz w wyniku hartowania w ciekłym azocie. Zastosowanie metod magnetycznych pozwoliło na określenie charakterystycznych temperatur przemian fazowych oraz udziału poszczególnych faz powstałych w wyniku odkształcenia plastycznego oraz podczas chłodzenia w ciekłym azocie, a także podczas przemiany odwrotnej alfa'->gama w zakresie temperatur pomiędzy As i Af. W pracy podjęto również próbę określenia wpływu temperatury austenityzowania na charakterystyczne temperatury przemian w stopie Fe-30%Ni, wiążąc je ze strukturą badanego stopu.

EN

The specimens of the alloy Fe-30%Ni with different martensite morphology and content were achieved by deformation and quenching at temperature of liquid nitrogen. By means of magnetic methods the temperatures of phase transformations and the phase contents at the particular steps of treatment (i.e. after plastic deformation quenching in liquid nitrogen and reverse transformation between As and Af temperatures) were determined. The microstructural investigations enabled the determination of the influence of the austenitizing temperature on the transformations temperatures.

9

Effect of austenitizing parameters on dissolution of carbides in gamma solution and chemical composition of matrix in the hardened steel of 2% C and 12% Cr type with additives of W, Mo, V

Nykiel T., Hryniewicz T.

Advances in Materials Science

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2003

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Vol. 3, nr 2(4)

49--60

EN

The NCWV/D3 tool steel was the subject of the study. In the course of the investigation carried out it was found that during austenitizing of the steel the carbides contents decreased from 24.84 wt% in the annealed state down to 13.33 wt% after austenitiz-ing at 1150 °C during 30 minutes. It was also stated that the carbides contents in the quenched steel after austenitizing in the temperature range from 900 to 1150 °C during 30 minutes may be determined from the relationship cb[wt%] = 28.60 - 0,46e 0.003T Dissolution of carbides during austenitizing brings about the increase of elements Cr, W, and V contents in austenite up to 7.27%, 1.06%, and 0.086%, respectively, after austenitizing at 1150 °C during 30 minutes. It was also noticed that there is a rectilinear correlation between the contents of dissolved carbides in austenite and the contents of Cr and W in matrix of the tool steel quenched after austenitizing in the temperature range from 900 to 1150 °C and constant time of 30 minutes.

10

Wpływ zgniotu powierzchniowego na skutki azotowania jonowego stali NC11LV o różnej strukturze.

Berkowski L., Borowski J., Majchrzak W., Rybak Z., Stefko A.

Inżynieria Materiałowa

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1999

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R. XX, nr 5

232-236

PL

W referacie przedstawiono wyniki badań wpływu powierzchniowego odkształcenia plastycznego na strukturę oraz twardość stali NC11LV po azotowaniu jonowym. Badano próbki o różnej strukturze. Próbki austenityzowano w temperaturach 900-1200 stopni Celsjusza. W rezultacie uzyskano struktury o różnym składzie fazowym, od węglików na tle martenzytu, do praktycznie czystego austenitu z niewielką ilością węglików. Partie próbek o najniższej i najwyższej twardości , austenityzowano w temperaturach odpowiednio 1150 i 1020 stopni Celsjusza, nagniatano ślizgowo nagniatakiem diamentowym, stosując dwie wartości docisku: 150 i 400 N. Przedstawiono struktury stref przypowierzchniowych po nagniataniu. Tak przygotowane próbki azotowano jonowo. Azotowanie przeprowadzono przy stałym czasie - 4h, stosując trzy różne temperatury procesu: 400, 440 i 480 stopni Celsjusza. Skutki nagniatania i azotowania oceniano za pomocą pomiarów twardości HK0,1, oraz poprzez obserwację warstw azotowanych pod mikroskopem świetlnym na zgładach metalograficznych. Przedstawiono wyniki pomiarów twardości, a struktury zaobserwowane w próbkach nagniatanych i azotowanych. W wyniku badań stwierdzono, że nagniatanie stali NC11LV spowodowało utwardzenie stref przypowierzchniowych. Szczególnie dotyczy to próbek o strukturze austenitycznej. Wygrzewanie tych próbek w czasie i temperaturze azotowania spowodowało spadek twardości tych stref o ok. 200 HK0,1. Po azotowaniu wyższą twardość przekraczającą 1200 HK0,1, stwierdzono w próbkach o strukturze martenzytycznej, gdy tymczasem próbki o strukturze austenitycznej wykazały twardość maksymalną ok. 1000 HK0,1. Nagniatanie stali o strukturze martenzytycznej jak i austenitycznej spowodowało istotny wzrost twardości stref przypowierzchniowych w stosunku do stali nienagniatanej przed azotowaniem. Niezależnie od struktury hartowanej stali NC11LV (martenzytyczna lub austenityczna osnowa) nagniatanie spowodowało wzrost twardości stref przypowierzchniowych po azotowaniu ionowym.

EN

The results of investigations for surface plastic strain influence on ionitrided NC11LV steel hardness and structure are presented in this paper. The samples of different structure were investigated. Temperatures 900-1200 degrees centigrade for austenitizing were used. In the result, following structures were obtained: from carbides exsisting in martensite matrix, until pure austenite with reduced quantity of carbides. Two batches of samples, representing the highest and the lowest hardness (austenitized respectively at 1150 and 1020 degrees centigrade), to the operation of slide burnishing by diamond burnisher, with application of pressure forces 150 and 400 N, were undertaken. Structures of sub-surface layers after burnishing are shown. The samples in the above described state were ionitrided. This operation was carried out in constant time, however for different temperatures 400, 440 and 480 degrees centigrade. The results of burnishing and ionitriding by HK0,1 hardness measurements, and by nitrided layer structure investigations were assessed. Hardness measurement results are presented. Microstructures obtained for burnished and nitrided samples are shown. It was stated, that burnishing operation for NC11LV steel results in sub-surface layers hardening. Especially this fact is well marked for the samples having austenitic microstructure. The heating of these samples during nitriding process resulted in hardness decrease by about 200 HK0.1. After nitriding, higher hardness over 1200 HK0,1 for the martensitic sample was established, whilst for austenitic samples 1000 KH0,1 hardness was only reached. Burnishing operation, both for austenitic, and for martenitic structures caused an visible hardness increase for sub-surface layer, regarding to non-burnished steel before nitriding. Irrespective of heat treated NC11LV steel structure (martensitic or austenitic matrix), burnishing operation resulted in sub-surface layers hardness increase, after ionitriding.