Chromium and copper influence on the nodular cast iron with carbides microstructure

Transcription

1 A R C H I V E S of F O U N D R Y E N G I N E E R I N G Published quarterly as the organ of the Foundry Commission of the Polish Academy of Sciences ISSN (8973) Volume Issue 4/ /4 Chromium and copper influence on the nodular cast iron with carbides microstructure G. Gumienny Department of Materials Engineering and Production Systems, Technical University of Łódź Stefanowskiego /5 Street, Łódź, Poland Corresponding author. address: grzegorz.gumienny@p.lodz.pl Received ; accepted in revised form Abstract In this paper chromium to,% and copper to,5% influence at constant molybdenum content of about,5% on the nodular cast iron with carbides microstructure has been presented. It was found, that as a result of synergic addition of above-mentioned elements there is the possibility obtaining an ausferrite in nodular cast iron with carbides castings. Conditions have been given, when in nodular cast iron with carbides at cooling at first in the form, then air-cooling austenite transformation to upper bainite, its mixture with lower bainite, martensite or ausferrite takes place. Transformations proceed during cooling and the crystallization of cast iron have been determined and the casting hardness has been presented. Keywords: Innovative foundry technologies and materials, Ductile cast iron with carbides, Bainite, Ausferrite, TDA method. Introduction In nodular cast iron microstructure there is the possibility obtaining bainite without heat treatment [ 4]. For that purpose to cast iron a molybdenum and nickel in proper amount are added. In [4] paper nickel influence at constant molybdenum content on the nodular cast iron with carbides microstructure has been presented. This paper is an explication and continuation of researching nodular cast iron with different metal matrix microstructure. Chromium and copper influence on the microstructure and hardness of nodular cast iron with carbides containing about,5% Mo is presented in this paper. 2. Work methodology Tested cast iron was melted in the 2 kg, 5 Hz frequency induction furnace. Cast iron was superheated to 53 C, in order to during reaction with magnesium its temperature was amount to about 48 C. It guarantee total magnesium solution in liquid metal and its maximum yield. Nodularization process was made in the mould. The mould scheme and its dimensions are shown in Figure. A master alloy in amount of,% of casting mass was inserted into the reaction chamber. This chamber was located in the gating system behind the sprue. Behind this chamber the mixing and the control chambers were located. Inside the control chamber the thermocouple PtRh-Pt (S type) was placed. It was connected with Cristaldigraph to thermal derivative analysis (TDA) curves recording. After the solidification finish castings were knocking out and free air cooling. The chemical composition was tested with using SPECTRO- MAXx stationary metal analyzer made by Spectro Analytical Instruments GmbH. It is presented in Table together with an equivalent carbon content E c and a degree of eutectic saturation S c. Equivalent carbon content was calculated according to: () A R C H I V E S o f F O U N D R Y E N G I N E E R I N G V o l u m e, I s s u e 4 / 2,

2 295 o t, C o dt/d, C/s A - A E A B D F H K L B B 2 - B - B A 4 Fig.. The scheme of elements spacing inside the mould: experimental casting, 2 mixing chamber, 3 control chamber, 4 reaction chamber, 5 sprue, 6 - thermoelement s shield A Point t, C dt/d, C/s A ,9 B ,37 D 47 4 E 52 42,4 F H ,47 K ,78 L ,6 Table. The chemical composition of tested cast iron, its equivalent carbon content E c and a degree of eutectic saturation S c Chemical composition, % E c, S C Si Mn Mo Cr Cu Mg % c 2,88 2,37,22,44,,,4 3,62,84 4,3 2,6,32,53,,5,5 4,82,3 The average concentration of P and S was amount to properly,4% and,%. Cast iron microstructure was tested on metallographic samples etched by nital, magn. with use of Eclipse MA2 Nikon microscope. Hardness tests were made by use of HPO hardness testing machine for 2,5/87,5/3 conditions. 3. Results In Figure 2 (a, TDA curves of nodular cast iron with carbides containing,5% Mo ( and its microstructure ( are presented. m microstructure: nodular graphite, upper bainite, ferrite, ledeburitic carbides Fig. 2 (a,. TDA curves ( and the microstructure ( of nodular cast iron with carbides containing: 2,98% C, 2,46% Si,,29% Mn,,53% Mo, (E c = 3,72%) It is hypoeutectic cast iron (E c = 3,72%) and its microstructure consists of: nodular graphite, upper bainite, ferrite and small amount of ledeburitic carbides. The average hardness of castings made of that cast iron is amount to 35HB. 48 A R C H I V E S o f F O U N D R Y E N G I N E E R I N G V o l u m e, I s s u e 4 / 2,

3 In Figure 3 (a, TDA curves of nodular cast iron with carbides containing,25% Cr ( and its microstructure ( are presented AB DE F H K L Point t, C dt/d, C/s A ,4 B ,33 D E 65 44,5 F 8 45 H ,42 K ,84 L ,8 - Cast iron microstructure consists of: nodular graphite, ferrite, pearlite, upper and lower bainite and ledeburitic carbides. It is hypoeutectic cast iron (E c = 4,2%). Its solidification begins with austenite precipitations in the melt, what causes on the derivative curve AB thermal effect. Next the melt solidifies as an austenite + graphite eutectic mixture (BDEFH thermal effect). Both Mo and Cr are characterized by the straight microsegregationo the remaining liquid is chromium and molybdenum enriched and crystallizes according to the metastable system and creates complex ledeburitic carbides (Fe,Cr,Mo) 3 C at the temperature of t H = 2 C t L = 8 C (Fig. 3. These carbides crystallize on eutectic cells boundaries.,45% Mo and,25% Cr combination cause obtaining unfavourable metal matrix microstructure consisting large amount of ferrite, pearlite and small amount of upper and lower bainite. A large amount of ferrite is caused, like in previous cast iron, by known, molybdenum ferritizing action [5]. The average hardness of castings made of that kind of cast iron is amount to 33HB. Increase of Cr concentration to,5% caused changes of TDA curves and the microstructure presented in Figure 4 (a,. 4 2 DE F H K L - m microstructure: nodular graphite, ferrite, pearlite, upper and lower bainite, ledeburitic carbides Fig. 3 (a,. TDA curves ( and the microstructure ( of nodular cast iron with carbides containing: 3,48% C, 2,46% Si,,27% Mn,,45% Mo,,25% Cr (E c = 4,2%) Point t, C dt/d, C/s D 6 38 E 32 4,2 F H ,2 K ,57 L 38 -,27 A R C H I V E S o f F O U N D R Y E N G I N E E R I N G V o l u m e, I s s u e 4 / 2,

4 m m microstructure: nodular graphite, upper and lower bainite, ferrite, pearlite, ledeburitic carbides Fig. 4 (a,. TDA curves ( and the microstructure ( of nodular cast iron with carbides containing: 3,55% C, 2,5% Si,,3% Mn,,53% Mo,,5% Cr (E c = 4,26%) From TDA curves results, that it is eutectic cast iron (E c = 4,26%)o its solidification begins with the austenite + graphite eutectic mixture forming. Chromium concentration increase to,5% caused decreasing eutectic transformation temperature (Fig. 4. From Fig. 4 b results, that Cr in amount to,5% caused decreasing of ferrite surface fraction compared to cast iron with,25% Cr. It testify, that chromium not only is a part of carbides, but in a certain amount dissolves in austenite and has an influence on its solid-state transition. Carbides surface fraction is increased. It is presented in Figure 5 (a,. The average hardness of castings made of cast iron containing,53% Mo and,5% Cr was amount to 36HB and is higher than hardness of cast iron with,25% Cr. It is caused by increased carbides surface fraction, too (Fig. 5. microstructure: nodular graphite, ferrite, pearlite, upper and lower bainite, ledeburitic carbides m microstructure: nodular graphite, upper and lower bainite, ferrite, pearlite, ledeburitic carbides Fig. 5 (a,. Nodular cast iron microstructure containing,25% Cr ( and,5% Cr ( TDA curves and the microstructure of cast iron containing,% Cr are presented in Figure 6 (a,. 5 A R C H I V E S o f F O U N D R Y E N G I N E E R I N G V o l u m e, I s s u e 4 / 2,

5 4 DE F H K L from it, that in cast iron with,% Cr molybdenum amount equals,5% did not caused austenite transformation to upper or lower bainite during permanent cooling. Carbides amount is similar, like in cast iron with,5% Cr. It is presented in Figure Point t, C dt/d, C/s D 5 38 E 32 4,2 F 6 43 H 277 -,3 K ,62 L ,37 m microstructure: nodular graphite, pearlite, ledeburitic carbides, ferrite Fig. 7. Nodular cast iron microstructure containing,% Cr The average hardness of pearlitic-ferritic cast iron with carbides is amount to 37HB. In Figure 8 (a, TDA curves of nodular cast iron with carbides containing,49% Mo and,5% Cu ( and its microstructure ( are presented. 4 E AB D F H K L 2 - m microstructure: nodular graphite, pearlite, ledeburitic carbides, ferrite Fig. 6 (a,. TDA curves ( and the microstructure ( of nodular cast iron with carbides containing: 3,56% C, 2,5% Si,,27% Mn,,5% Mo,,% Cr (E c = 4,27%) From Fig. 6 a results, that chromium content increase to,% did not caused eutectic transformation temperature change. Temperature recalescence was increased of about C compared to cast iron with,5% Cr and amount to 5 C. Metal matrix microstructure of cast iron changes essentially. It consists of pearlite, ledeburitic carbides and small amount of ferrite. Results Point t, C dt/d, C/s A ,4 B 9 2,4 D E 48 6,2 F 53 6 A R C H I V E S o f F O U N D R Y E N G I N E E R I N G V o l u m e, I s s u e 4 / 2,

6 H ,86 K ,9 L ,23 The average hardness of cast iron with about,5% Mo and,5% Cu was amount to 328HB. Increase of copper content to,% caused in cast iron changes presented in Figure (a,. 4 E ABD F H K L 2 - m microstructure: nodular graphite, upper and lower bainite, ferrite, pearlite, ledeburitic carbides Fig. 8 (a,. TDA curves ( and the microstructure ( of nodular cast iron with carbides containing: 4,3% C, 2,5% Si,,24% Mn,,49% Mo,,5% Cu (E c = 4,82%) From TDA curves results, that it is hypereutectic cast irono its solidification begins with the nodular graphite precipitation (AB thermal effect). Copper addition caused increase of austenite + graphite eutectic mixture crystallization temperature (BDEFH thermal effect) compared to cast iron with chromium. Molybdenum presence causes, like in previously described cast irons, solidification of the remaining liquid according to the metastable system and (Fe,Mo) 3 C carbides forming. Compared with cast iron containing,53% Mo and,5% Cr it has reduced amount of carbides and similar amount of ferrite and pearlite. It is exemplary presented in Figure Point t, C dt/d, C/s A 39 56,4 B ,3 D E 73 53,9 F H ,6 K ,77 L ,24 m m microstructure: nodular graphite, upper and lower bainite, ferrite, pearlite, ledeburitic carbides Fig. 9. Nodular cast iron microstructure containing,5% Cu microstructure: nodular graphite, upper and lower bainite, martensite, ferrite, ledeburitic carbides, retained austenite Fig. (a,. TDA curves ( and the microstructure ( of nodular cast iron with carbides containing: 3,5% C, 2,49% Si,,32% Mn,,5% Mo,,% Cu (E c = 4,32%) 52 A R C H I V E S o f F O U N D R Y E N G I N E E R I N G V o l u m e, I s s u e 4 / 2,

7 In this cast iron eutectic transformation takes place in the temperature of 7 C less, than in cast iron with,5% Cu, but it is still higher than in cast iron with chromium. Molybdenum presence caused ledeburitic carbides forming (HKL thermal effect, Fig.. Copper increase caused small amount of martensite forming, but did not change significantly carbides amount. It is important, that ferrite amount is decreased and pearlite disappeared in cast iron metal matrix microstructure. The average hardness of castings made of cast iron containing about,5% Mo and,% Cu was amount to 379HB and it is 5HB higher, than hardness of castings made of cast iron containing,5% Cu. TDA curves and the microstructure of cast iron containing,5% Mo and,5% Cu is presented in Figure (a,. 4 DE F H K L m Point t, C dt/d, C/s D 3 57 E 23 58,2 F 4 59 H ,52 K ,69 L ,23 - microstructure: nodular graphite, martensite, upper and lower bainite, ledeburitic carbides, retained austenite Fig. (a,. TDA curves ( and the microstructure ( of nodular cast iron with carbides containing: 3,39% C, 2,54% Si,,29% Mn,,5% Mo,,5% Cu (E c = 4,26%) It is eutectic cast iron and its microstructure consists of: nodular graphite, martensite, upper and lower bainite, ledeburitic carbides and retained austenite. Eutectic transformation temperature in this cast iron is similar to the temperature of this transformation in cast iron with,5% Cu (DEFH thermal effect, Fig. and it is higher than in cast iron with chromium. Compared with cast iron containing,% Cu this cast iron has got increase martensite surface fraction and decrease upper and lower bainite. Results from it, that in cast iron with,5% Mo copper causes hardenability increase. Carbides amount is similar to previously described cast irons with Cu. The average hardness of castings made of cast iron containing about,5% Mo and,5% Cu was amount to 493HB. Metal matrix microstructure consisting an ausferritie and carbides was obtained in cast iron with,5% Cr,,5% Mo and,% Cu (Figure 2. A R C H I V E S o f F O U N D R Y E N G I N E E R I N G V o l u m e, I s s u e 4 / 2,

8 o t, C o dt/d, C/s 4 2 A B DEF H K L - From Fig. 2 a results, that it is hypoeutectic cast iron (E c = 4,9%). Eutectic transformation temperature is similar to the temperature of this transformation taking place in cast iron with chromium and molybdenum and without copper. Cast iron microstructure consist of: nodular graphite, ausferrite and ledeburitic carbides. Ausferrite is highly advisable phase in wear resistant materials, because of its possibility to pressure hardening [6]. Carbides presence should cause high wear and adhesive resistance. The average hardness of casting made of ausferritic cast iron with carbides was amount to 34HB Point t, C dt/d, C/s A ,2 B 6 7 -,93 D 77 4 E 88 4,6 F 2 4 H ,9 K ,68 L 392 -, 4. Conclusions Results have indicated the following: metal matrix microstructure consisting large amount of ferrite and pearlite and small amount of upper and lower bainite is obtained in cast iron containing,45% Mo and,25% Cr, increase of chromium content to,5% decreases ferrite amount and increases carbides amount in cast iron with about,5% Mo,,% chromium addition makes impossible obtain bainite ascast in cast iron with,5% Mo, a presence of small amount of lower bainite and pearlite and decrease of ferrite amount is caused by,5% Cu addition in cast iron with molybdenum, austenite stability is increased because of,5% Cu addition, synergic addition of,5% Mo,,% Cu and,5% Cr make possible to obtain an ausferrite in metal matrix microstructure of nodular cast iron with carbides. Scientific project financed from means of budget on science in years as research project N m microstructure: nodular graphite, ausferrite, ledeburitic carbides Fig. 2 (a,. TDA curves ( and the microstructure ( of nodular cast iron with carbides containing: 3,32% C, 2,48% Si,,24% Mn,,5% Mo,,5% Cr,,% Cu (E c = 4,9%) References [] S. Pietrowski, G. Gumienny, Carbides in Nodular Cast Iron with Cr and Mo, Archives of Foundry Engineering, Vol. 7, Issue 3 (27) [2] S. Pietrowski, G. Gumienny, Crystallization of nodular cast iron with carbides, Archives of Foundry Engineering, Vol. 8, Issue 4 (28) [3] G. Gumienny, Bainitic nodular cast iron with carbides obtaining with use of Inmold method, Archives of Foundry Engineering, Vol. 9, Issue 3 (29) [4] G. Gumienny, Bainitic-martensitic nodular cast iron with carbides, Archives of Foundry Engineering, Vol., Issue 2 (2) [5] The Sorelmetal Book of Ductile Iron, Metals Minerals, Warsaw, 26. [6] E. Guzik, Ausferritic cast iron and its kinds structure and selected properties, Production system optimization tendencies in foundries, Katowice-Gliwice 2, A R C H I V E S o f F O U N D R Y E N G I N E E R I N G V o l u m e, I s s u e 4 / 2,