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23.06.2010 08:10 -
Публикация на д-р инж. Богомил Великов Колев от конгрес в Охрид-Македония
INDEX OF AUTHORS
A
Ackoski T. 323 Andjelic M. 43, 57,477 Andjelic B. 247 Arsenovic M. 99, 365 Asanovic V. 79, 283 Avramovic Lj. 359
B
Bakic G. 63, 247 Bogdanovic D. 489 Bosnjak B. 79, 283 Boyanov B. 231
C
Cocic M. 335 Crnko J. 93 Cvetkovski S. 85 Cvijovic Z. 105
D
Devic S. 335 Delijic K. 443 DenkovskiD. 419 Dimitrievic S. 359 Dimitrov A. 37, 253, 297 DimovaLj. 215 DjokicJ. 163 Djordjevic V. 271 Djukic M. 63, 247 Djurasevic G. 99 Djurovic M. 43, 57,477, 541 Dodok R. 455 DudukovskaM. 169,303 Dudukovski B. 309
E
Efremov A. 135,523
F
Filipovic J. 129
g
Galjak R. 335
Gavrilovski D. 437
Gavrilovski M. 437
Georgievski P. 315 Golubovic S. 477 Golubovic B. 477 GrabulovV. 19,69 GuUsijaR. 271 GulisijaZ. 271 H Had/.i Jordanov S. 37, 253, 297,403 Harding R. 79 Hristova E. 329 HollidayJ. 155 I Hie I. 163 Nicvska M. 323 Hievski R. 155 Ivanovski Z. 403 J Jacovski V. 215,409 Jakimovski V. 323 Janchev S. 329 Janjic J. 533 Jecnicnica D. 433 Jecmcnica M. 433 •Jcvtic R. 433 Joncic N. 265 Jonovic R. 359 Jordovic B. 271 Jovanovic D. 377,455 Jovanovic S. 129 K Kambcrovic Z. 149, 163 KamevT, 155 Kamili I. 34 [ Kolev B. 29 4Q iftQ, 199. 259 Koneska Z. 277 Koprivica A. 541 Kostov A. 99, 283 Kovaccvic K. 43. 57, 477, 541 Krstcvski H. 403 Kukolccal". 175
INFLUENCE OF TEMPERATURE AND HOLDING TIME A QUENCHING AND TEMPERING ON SOME BASIC MECHANIC CHARACTERISTICS DETERMINING THE APPLICATION OF CASTING WEAR-RESISTANT COMPLEX ALLOYS OF THE Fe-Cr-C-(N) SYSTEM Dr.Eng.Bogomil Vclikov Kolcv. Institute of Metal science. BAS. 67 Shipchcnski prohod sir. Sofia 1574. Bulgaria
Summary Hardness (IIRC) and impact straight (a t) are the most -important mechanic characteristics which determine the application of complex alloyed casting alloys of the Fe-Cr-Mn-C-N system. There have been presented graphic regularities about the inlluence of temperature (T"C) during quenching and tempering on (1IRC) and (ak) of some typical casting complex -alloyed wear-resistant alloys of the Fe-Cr-C-N system. An opposite inlluence of T"C during quenching on the variation of HKC and has been determined. This necessitates a choice ol thermal rales i.e. compromise decisions about the values ol HRC and according to working conditions in production, esp.to pressure. 1.Introduction Hardness and impact strength are determining choice of alloys to work in concrete conditions of wear abrasive. hydroabrasie or strike abrasive. Tempered Cr alloyed steels (cast irons) are better m mechanic characteristics and resistance to .fracture them. Grey and modified cast irons with ferrite or perlitc basic matrix . This makes them suitable of phacetics opening (casting) working in these conditions .If hardness is important to wear resistance ol those class easting alloys in practices it is olten to see impact strength determines exploits. These alloys (melts ot them) aren"t used in practices without thermal treatment. Ol importance for it are 5 factors: austenization. duration, situation of critic points and T"C of quenching. First factor depends on alloying degree with elements making solid solutions lor replacement. N doesn"t influence. The rest factors are dependable on N [ 1-2]. Study of . T"C influence on HRC and ak is significant to form reliable and quality melts .for high strike pressure. Dilficult working wilh culling instruments ligature data, esp. opposition to strike destruction of alloys of Fe-Cr-C system are scares and for alloys of Fe-Cr-C-N system there are almost no data [3-5][8|. Aim of this work is to study the effect of T"C of quenching (and tempering) on HRC and ai, of basic characteristic components of alloys of Fe-Cr-C-(N) system to compare these data with some wear-resistant alloys of Fe-Cr-Ni-(Mn)-C system. We know that N. Mn. Ni arc austeniti/ators and N replaces them. Besides N is residue product of many industries. Unlike Ni and Mn it is common and cheap. Study is due to our patent RB 49451. 2.Methods and experimental results-Alloys are obtained obtaining in induction autoclave with basic lining of oven. Pouring in dry sand moulds in samples 14 x 14 x 250 mm. Thermal treatment is in a silite oven. Preliminary annealing is carried in heating regime of (6) to improve machining instruments. Before polishing of auL, we quenched them in oil. Duration- 40 min each T"C of quenching. Before the test of at samples are tempering at 2()0"C-2h. HRC is measured alter a^ tests. Forms are used according to standard methods of BDS. Results are graphically: lor HRC - ((T"C) tempering fig 1-8. for aut-lig 12-15. Duration at T"C quenching tig.9-11. T" C of tempering - fig. 16-22. Duration of tempering fig.23. Results compared to some Ni - containing cast iron: Nicherd and 3fl()Crl4i3Mn4. 315Cr28Ni2 etc.
3. Results analysis and discussion. .?.1. Influence of T"C auenchin c on HRC and cit T"C inlluencc on .quenching can be like simultaneous additional alloying (complex) with all elements in carbide (K). nitride K. N. KN [1.2]. c) Right tt) max of HRC. resp. min : C. N content and oilier
alloying elements in austcniic go up, stability in peiiite area
goes up. TC of martensite transformation goes down,
increases ausieniie quantity (quantity of ferromagnetic phase
decreases 11-2) Austcnite stability goes up. ak goes down. d) under N cllect max HRC lends go to lower values of T"C
of quenching. To decrease stabilisation austenite an N-
contauung alloys it needs to austenize i.e. quenching at lower
T"C than non N containing. Reason is decrease of critical
points i.e. changing phase boundaries to lower T"C under N
11-2]. We see trend to shorten T"C interval of aery change
ability in N- containing casting alloys, esp. when they"re not
.additionally alloyed with carbon and nitride-forming (lead to
formation of high thermal-resistant K. N. KN. Probably the
shorter range of temperature is due number of centres of
crystallisation under pressure P, especially taken afterwards N
11-2.7-8). Increased nuclei facilitate a«=>y transition. e) Max HRC of Cr- alloyed casting alloys containing ausieniie
stabilising elements form solid solutions of substitute (Ni. Mn)
lower than alloys of Fe-Cr-C-(N) system. T"C quenching has
smaller influence on HRC, resp. solid phase, reactions
alloying with Mn and Ni than elements in solid solutions of
installation- C. N. Under Ni and Mn influence, max HRC
becomes at slightly lower T"C of quenching. Probably due to
two combined effects. Favouring C solubility in matrix, esp.
lower T"C growing of the HRC. On the other hand Mn and Ni
go up the quantity and stability of ausieniie in that condition
leading to going down of HRC. Oimpaci strength of casting alloys of Fe-Cr-C-N system is comparable (at extreme points) and better at T"C dilferrem from extreme (above 5O-IOO"C) of cast irons: Nicherd, Crl4Ni3Mn4.Cr2SNi2. To regulate HRC. i.e its growing can put in more carbon and nitride forming quality or even quantity thus to stimulate formation of phases like Me7C,. Mc:iCr,. McC esp. Mc(CN). Alloying have to be introduced ballance and depending on aims: introduction of elements able to make wjih C and N easy solutions of K. N. KN at TC quenching of high thermal
resistance. This influences basic matrix as well as added phases. High resislihiliiy can be useful .during crystallisation in the form to refine structure contain grow up of grains under thermal treatment. A,, can be balanced with elements stabilising austcnitizators: N. Mn, Ni. Cu etc. Some of the elements can be used to dispersion strengthen, tempering (annealing) etc. According to patent RB 49451 we introduce. C=0.6-4,2f/r, to 3%S, ).2-9%Mn. 6-35% Cr, 0.02-2.5%N. 0,0l-3%Mo. O.OOI-O.3%B. 0.01-l%Ti. 0.01 -%V. Ni and Cu to 2%. 0,001-1 %W. Ce and Mg and rest Fc to 100%. Elements can go alone or togedher in combinations 2. 3 etc. aiming different requirements practical [6J. 3.2. Diffusion processes in isothermal conditions. Carried out slower depending on T"Cqucnching, composition, samples thickness. For choosed thickness of sample bodies it is determined on many studied alloys that most actively processes (solid phase reachions) go in first 1-2 hours. Additional alloying can continue to 2-4 hours. This reflects regularity HRC= f(T). In next hours process stabilise but we see a trend to decrease I IRC. Probable reason- coagulation of K and KN phases. Duration of austcnization practically doesn"t reflect on N. Choosing T"C tempering is important technology operation. At T"C above l000"C is necessary to count influence of hard activation diffusion process on sample boty surface- decarbonation, denigration etc. Many laboratory and industry tried to show that T"C responding max. HRC shouldn"t be used since a^, smallest. Especially for details cyclically, dinamically. .impact pressured. Lower T"C. left to HRC max. are to be recommended not only by technology of usefulness, but also economic benefit. For Cr alloyed casting alloys (cast iron) containing 12-22%Cr, recommend optimum T"C tempering is in range of 900-930"C to 960"C- IOOO"C. It determined by composition of alloying and most over by Cr. In practices T"C quenching is chosen according to the needs to detail-conditions of work and pressure. This has to make compromise between HRC and aL in choosing T"C of quenching. Choosing cooling medium one has to have in mind foul heat conduction of Cr alloys and their low plasticity. Since using cooling media with high heat conduction (water, oil) recommended are only for thin well details with simple configuration, without complex transitions "thin-thick". Observations show quenching in oil of shovels, scrapers etc. instruments isn"t dangerous. For industry work water is not recommended for use. Can be used only in pulverisation"s together with ventilators and injection of steam (water-air, oil +air. air). Attempts show that thick wall details (above 80-l00mm) like hammers, step plates etc. have affinity to crack-forma-iion. Temperature gradient in section of thick-wall samples and nonsimultenous phase transition in different sections don"t relax in cooling quickly. This leads to destruction of detail. Best cooling down medium is relaxed air. since difference in cool speed in center of sample and surface is practically not existent. We speak about range 75O-5OO"C in which there is cutcctoid disingretation. Long observation on sample bodies with different thickens and configurations (transitions "thin-thick" show heating speed to avoid crack-formation is of great significance. Laboratory and industry tries to show that heating with high speed (e.g.introduction of thick-wall details in hot lurnation.) leads to crack formation too. Not dangerous speed of heating shouldn"t be more than 80-100"C /hour. N decrease trends to slot-formation. T"C of quenching right to max. is not recommended because of above reasons and increasing of austcnitc grains, stabilising austeniic, decrease of HRC, increase of diffusion- surface processes. These T"C can be used in willing for next dispersion solidity trough tempering :singlc or repeating. High- temperature tempering of fashion sample bodies unlike instrumental steels (details) is " not always proved economically. J-J-Heaiine for improvement _of treatalnlitx with cutting instruments.
Can be used ordinary or isothermal heating . Most favourable for treatment is fcrrite (perlile) matrix such structure is obtained in isothermal or slow cooling between Aj and A|. Optimum conditions arc not known .There is possibility basic matrix to go transition in grain perlile. N helps pcrlitize and big decrease of HRC [ 1-2). Pcrlitize can be done alter heating in range 900-950"C and slow cooling (can be stage taking) in rang 820-600"C by speed 50"C/min., after that 550-60O"C air can be used regimes worked out for average of high Cr-alloyed instrumental steels |5j. N containing casting alloys have better trcatability with cutting instruments. Soft nitride phases (towards carbide) encase metal cutting operations. Practically can work out holes to make cutways. Hence we apply: strewing, rattling, etc.. One practical regime is shown in patent RBA 49451 (6). .?,■)".Influence of"tempering (annealing) temperature (tin rat ion) on HRC and a^ Tempering is ending operation of thermal treatment. One basic demands is .removing stresses . in the samples, formed as result of uneven cooling in sections with different thickness"s. We should have in mind pressures of phase trsansilions in cooling. Influence of tempering T,,C (annealing) on HRC and ak is studied in wide spectrum of alloys of different composition of C (N) with or without additional alloying with N. Mo. Cu. V ctc.-after quenching in oil of T"C near to max HRC and tempering (annealing) in range 200-700"C. Changes in HRC after tempering (annealing) don"t respond to structure changes in |l-2]. Summarry shows that to 2()0"C is observed small fall in HRC after removing of quenching stresses. To 400-450"C HRC almost preserves values even shows trend to enhance with some units. In some alloys reach HRC above the values after oil quenching. This shows that in range 400-450"C can be done annealing without danger of deteriorating HRC. N containing alloys show high hardening (secondary) than N free. This effect is characteristic to lower C-alloys (steels) and additional alloying with other elements -Mo. Reason is bigger quantity basic matrix than lower quantity primary K. N. KN. Some casting alloys reach to 65-67HRC. which makes them useful for casting instruments. All studied alloys of system Fe-Cr-C-N have in tempering high HRC than Ni-containing cast irons of type Crl4 Ni3 Mn4. It seems that N can substitute for part of C. Alloy Cll0Cr28 contain 2.08% N after quenching and tempering show considerably high HRC than cast-iron classic C3l5Cr28Ni2 (0.I5N). IC+N is equivalent to 3.15-3,25%C. This show that with N canachicvc very high HRC even more than C. Decrease in HRC above 450-500"C jn all alloys is explained by activation of solid-phase reactions | -2J. HRC at Cr-Mo casting alloys can be increased after tempering if after quenching structure is predominantly austcnite, i.e on the right to max. That"s why helps introduction C and N. HRC increase for account of taking of saturated austcnite of dispersion K, N. KN, followed by martensite transition of austeniic (residual y poorcd by C, N, Cr, Mo, Mn etc. Analogy (similar) processed observed at quenching and tempering of high Cr alloyed instrumental steels [4,5,8]. In practices Cr alloyed casting alloys anneal at 200"C but can use tempering (annealing) at 35O-5OO"C there, where is proved (increase in HRC). Can be applied several limes of tempering it is economically proved. White Cr -alloyed cast alloys (cast irons) are different for high tempering resistance [1-2]. In Cr-Mn cast irons is hindered obtaining of HRC because of big quantity astcnitc. HRC in wear-resistant cast iron have austcnitc structure after quenching can be enhanced to use possibilities of dispcrtion solidifying [7.9]. Example in cast irons C21OCrl5NMn8 and C28OCrl5NMn8 max HRC is obtained after casting at I48O"C and tempering at 75O"C, rcsp. 38-41/56-57 and 45-46/58-60. In numerator- HRC alter casting, in denumerator alter tempering 750oC. after tempering (annealing) 750"C. This way to enhance HRC makes possible to obtain together with manensile other products of pcrlitc disintregalion. since T"C
rof tempering (4h) is directly to the range of pcrlitc transition. If not done such preliminary austcnization (quenching ), tempering can recommed only for samples where structure of "metal matrix is fully austenitc in cast condition (in form) i.e. vonly for thin-wall (shovels some instruments etc.). For other samples containing in structure products of disintegration of Uustenite there"s danger to coagulate K and decrease HRC of .^ferrite-carbide mixture. After first 1-2 hours of tempering HRC is not stable (shows trends to decrease and variance) to initial quenching "condition, probably due to removing the stresses and solid phase reactions at 500"C. We studied some typical alloys with and without N at 200 and 500"C. After 2-3 hours processes die out. Values of variation arc not different and hesitate about practical distractions. At very long duration-ca.50 hours we see some process going to change in HRC probably by coagulation of solid phase reactions [1-2]. Alloys which are Mn and N alloyed exhibit a more stable way of HRC with going up of time of tempering (annealing) C300Crl4Ni3Mn4. At some of them (C315Cr28Ni2) is observed after 5-10 hours trend to go up HRC which once again shows the big stabilising of austcnitc than Mn and N. Possible deprivation of mtermctallids. A,, after tempering is tested on alloy C200Cr200MoCu with different content of N tempered at 1150"C table 1. Content of N almost not influence on HRC. 0.4-0.8%Cu is introduced as substitute for Ni. It smaller range stabilises austcnitc. "*v Introduction of N, Cc and Ti reflects favourably on aw. Favourable influence of Ti is characteristic to low quality (0,1%) N for much bigger it deteriorates. , Conclusions .* 1 The influence of T"C of quenching and tempering on HRC ~. and ak of some typical casting alloys of the Fc-Cr-C-(N ) •" system has been studied and we determined that its influence " is opposite of HRC and ak. a) for every alloy there is T"C of quenching which obtains - max. in HRC and resp. min in ak. This practically imposes the " necessity of compromise choice of the T"C quenching according to the concrete configuration working conditions and sample pressure. , b) N influence comes over C influence. To the right of HRC maximums (min for ak) the austcnite is stabilised by N. c) Increasing T"C of tempering to 4OO-5OO"C there is
almost no deterioration of HRC resp. of ak after which the
lurther increase of HRC decreased and ak is docs not change
and tends to increase. d) N containing casting alloys of Fe-Cr-C-N system tend to
harden in tempering in the range up to 4OO-5OOX in
comparison to N -free and alloyed with austenitc forming Mn.
Ni. The effect of hardening in tempering is bigger in low C
steels, those containing N. N replaces C. 2. We studied the influence of holding time (of quenching)
and tempering (annealing) on HRC (ak) and determined that
the first 1-2 hours carry out active diffusion processes
connected, with solid-phase reactions reflecting in the change
of HRC in variation of values. After 2-4 hours HRC values are
retained and are practically constant (samples 14 xl4). 3. The influence of increasing T"C of quenching and time of
tempering (holding time) can be said to be simultaneous
complex alloying of the matrix with all elements included in
carbide, nitride, karbonitridc. 4. The studied casting alloys of the Fc-Cr-C-(N) system have
resp. better HRC and ak after quenching and tempering
(annealing) compared to classic wear resistant with Mn, Ni:
Nicherd, cast iron of the Fe-Cr-Ni-(Mn)-C system:
C300C414Ni3Mn4, C3l5Cr28Ni2. This show that the alloys
of studied system can be replace these alloys, resp. for casting
of details working in abrasive and hydroabrasivc wear and
impact loading.
References I.Kolcv B.V.Izslcdvania varchu structurata sled cristalli/a-tchia vav format I sled term.obrabotka na liati stomani ot sistcmata Fc-Cr-C-N.NTConf. s .mcid. ulchastie. Mctalozna-nic I term, ohrahoivanc na mctalitc. Dokladi, Sny.opol.1998 2.Kolev B.V.Izslcdvane na tchugunot systemala Fc-Cr-C-N sled kristallizatchia vav formaia i sled term.obrabotka. NT.Conf. s mejd. utchaslie. Dokladi. Sozopol. 1998. 3.E.Pivovarskii.Vaissokokatchcstvcnii tchugun. Mctallurgia, M.. 1965. 4.Gcller U.A.Instumcntalnic stali. Mctallurgia M.,1983. 5.Rashkov N.D. Termichno obrabotvane na Spetchialni stomani. Technika, Sofia 1993. 6.Dimov I.N.. B.V.Kolev and all. Iznosoustoitchiva splav na Fc-C osnova.. Patent RB 49451. 7.Kolcv B.V. Vazmojnosli za polutchavanc, structuroobra/.u-vane I svoistva na niakoi Iciarski splavi na Fe-C osnova legirani s azot. Disscrtazia. IM-BAN. Sofia. 1985. S.Kolcv. B.V. Effects of pressure and N on structure formation of some Fc-C based casting alloyis. Theoretical ana-lis. lntcm.Congr. Mech.Engin..Techn.-99. Proc, Sofia, 1999. 9.Rashcv Ts.V. Baisokoa/.otistic stalli.Mctallurgia pod davlenicm. Izdatclsvo BAS,"prof.M.Drinov". Sofia ,1995. lO.Kolcv B.V.Tcrmichna mctastabilnost pri nagriavanc I ochlajdane na miakoi liati austcnitni splavi na Fe osnova. Teoret. osnovi. Intern, congr. Mech. Eng. Techn.-97 Proc, vol.2. Sofia. 1997. and Thermal metastabi-lity in heating and cooling of some austcnitic Ferrous alloys -Thcorct. founda-tions.-Vth ltcm.Congr. HNS-98, Stokholm and Hclzinki, "98, and Intern Workshop "Diffusion and diffusional phase transformations in alloys.Diftrans-98. Cherkasy, Ukraine, 1998. Figures fig. 1-7. HRC=f(T"C quenching) figl.C300Crl4MnMo:1.0.02%N:2.0.45%N:3.C300Crl4Ni3Mn4 fig2.C300Crl4Mo2:1.0.0254%N:2.0.3827rN:3.C300Crl4Ni3Mn fig3.C2-10Crl4:1.0.048%N;2.0.450%N;3.C300CrI4Ni3Mn4 fig4.C300Crl7Mo3:1.0.037%N:2.0.537%N;3.C300Crl4Ni3Mn4 fig5.C260Crl3MnMo;1.0.031%N;2.0.408%N; 3.C300Crl4Ni3Mn4 fig6.CI50Cr20Mo2:1.0.026%N;2.0.917%N;3.C300Crl4Ni3Mn4 fig7.CI 10Cr28M.N=2.08%. fig8.1.C300Cr30Ni3(0.099%N):2.C240Crl4Mnl2(0.923%N). fig9-l l:HRC=f(t)-duralion at T"C of quenching. fig9.IOOOvC:240Crl4;1.0.084l5N;2.0.614%N; 3.C3OOCrl4Ni3Mn4 figl0.950"C:CI50Crl4Mo2:1.0.08415N;2.0.6145N. figll..95O"C:1.30OCrl4Ni3Mn4;2.Nichard. fig. 12-15:Ak=f(T"C of quenching) figl2.CI50Cr!4Mo2:1.0.084 5N: 2.0.6I45N; 3.C300Crl4Ni3Mn4. figl3.Cl50Cr20Mo2;I.0.0262%N:2.0.917%N; 3.C300Cr!4Ni3Mn4 fig. 14.C240Cr20; 1.0.088%N :2.0.89%N :3 .C300Cr 14Ni3Mn4. fig. 15.30OCr 14MnMo; 1.0.02%N:2.0.453%N figl6-22:HRC=f(T"C of tempering). fig.23.HRC=f(t of duration at T"C of tempering) fig.24.HRC=f(Mn).C300Crl69N=0,2-0.3%).2h.air. Note:Thc work has been carried out under Contract TH 717/97 of the Ministry of Edicsation and Science.
Georgievski P. 315 Golubovic S. 477 Golubovic B. 477 GrabulovV. 19,69 GuUsijaR. 271 GulisijaZ. 271 H Had/.i Jordanov S. 37, 253, 297,403 Harding R. 79 Hristova E. 329 HollidayJ. 155 I Hie I. 163 Nicvska M. 323 Hievski R. 155 Ivanovski Z. 403 J Jacovski V. 215,409 Jakimovski V. 323 Janchev S. 329 Janjic J. 533 Jecnicnica D. 433 Jecmcnica M. 433 •Jcvtic R. 433 Joncic N. 265 Jonovic R. 359 Jordovic B. 271 Jovanovic D. 377,455 Jovanovic S. 129 K Kambcrovic Z. 149, 163 KamevT, 155 Kamili I. 34 [ Kolev B. 29 4Q iftQ, 199. 259 Koneska Z. 277 Koprivica A. 541 Kostov A. 99, 283 Kovaccvic K. 43. 57, 477, 541 Krstcvski H. 403 Kukolccal". 175
INFLUENCE OF TEMPERATURE AND HOLDING TIME A QUENCHING AND TEMPERING ON SOME BASIC MECHANIC CHARACTERISTICS DETERMINING THE APPLICATION OF CASTING WEAR-RESISTANT COMPLEX ALLOYS OF THE Fe-Cr-C-(N) SYSTEM Dr.Eng.Bogomil Vclikov Kolcv. Institute of Metal science. BAS. 67 Shipchcnski prohod sir. Sofia 1574. Bulgaria
Summary Hardness (IIRC) and impact straight (a t) are the most -important mechanic characteristics which determine the application of complex alloyed casting alloys of the Fe-Cr-Mn-C-N system. There have been presented graphic regularities about the inlluence of temperature (T"C) during quenching and tempering on (1IRC) and (ak) of some typical casting complex -alloyed wear-resistant alloys of the Fe-Cr-C-N system. An opposite inlluence of T"C during quenching on the variation of HKC and has been determined. This necessitates a choice ol thermal rales i.e. compromise decisions about the values ol HRC and according to working conditions in production, esp.to pressure. 1.Introduction Hardness and impact strength are determining choice of alloys to work in concrete conditions of wear abrasive. hydroabrasie or strike abrasive. Tempered Cr alloyed steels (cast irons) are better m mechanic characteristics and resistance to .fracture them. Grey and modified cast irons with ferrite or perlitc basic matrix . This makes them suitable of phacetics opening (casting) working in these conditions .If hardness is important to wear resistance ol those class easting alloys in practices it is olten to see impact strength determines exploits. These alloys (melts ot them) aren"t used in practices without thermal treatment. Ol importance for it are 5 factors: austenization. duration, situation of critic points and T"C of quenching. First factor depends on alloying degree with elements making solid solutions lor replacement. N doesn"t influence. The rest factors are dependable on N [ 1-2]. Study of . T"C influence on HRC and ak is significant to form reliable and quality melts .for high strike pressure. Dilficult working wilh culling instruments ligature data, esp. opposition to strike destruction of alloys of Fe-Cr-C system are scares and for alloys of Fe-Cr-C-N system there are almost no data [3-5][8|. Aim of this work is to study the effect of T"C of quenching (and tempering) on HRC and ai, of basic characteristic components of alloys of Fe-Cr-C-(N) system to compare these data with some wear-resistant alloys of Fe-Cr-Ni-(Mn)-C system. We know that N. Mn. Ni arc austeniti/ators and N replaces them. Besides N is residue product of many industries. Unlike Ni and Mn it is common and cheap. Study is due to our patent RB 49451. 2.Methods and experimental results-Alloys are obtained obtaining in induction autoclave with basic lining of oven. Pouring in dry sand moulds in samples 14 x 14 x 250 mm. Thermal treatment is in a silite oven. Preliminary annealing is carried in heating regime of (6) to improve machining instruments. Before polishing of auL, we quenched them in oil. Duration- 40 min each T"C of quenching. Before the test of at samples are tempering at 2()0"C-2h. HRC is measured alter a^ tests. Forms are used according to standard methods of BDS. Results are graphically: lor HRC - ((T"C) tempering fig 1-8. for aut-lig 12-15. Duration at T"C quenching tig.9-11. T" C of tempering - fig. 16-22. Duration of tempering fig.23. Results compared to some Ni - containing cast iron: Nicherd and 3fl()Crl4i3Mn4. 315Cr28Ni2 etc.
3. Results analysis and discussion. .?.1. Influence of T"C auenchin c on HRC and cit T"C inlluencc on .quenching can be like simultaneous additional alloying (complex) with all elements in carbide (K). nitride K. N. KN [1.2]. c) Right tt) max of HRC. resp. min : C. N content and oilier
alloying elements in austcniic go up, stability in peiiite area
goes up. TC of martensite transformation goes down,
increases ausieniie quantity (quantity of ferromagnetic phase
decreases 11-2) Austcnite stability goes up. ak goes down. d) under N cllect max HRC lends go to lower values of T"C
of quenching. To decrease stabilisation austenite an N-
contauung alloys it needs to austenize i.e. quenching at lower
T"C than non N containing. Reason is decrease of critical
points i.e. changing phase boundaries to lower T"C under N
11-2]. We see trend to shorten T"C interval of aery change
ability in N- containing casting alloys, esp. when they"re not
.additionally alloyed with carbon and nitride-forming (lead to
formation of high thermal-resistant K. N. KN. Probably the
shorter range of temperature is due number of centres of
crystallisation under pressure P, especially taken afterwards N
11-2.7-8). Increased nuclei facilitate a«=>y transition. e) Max HRC of Cr- alloyed casting alloys containing ausieniie
stabilising elements form solid solutions of substitute (Ni. Mn)
lower than alloys of Fe-Cr-C-(N) system. T"C quenching has
smaller influence on HRC, resp. solid phase, reactions
alloying with Mn and Ni than elements in solid solutions of
installation- C. N. Under Ni and Mn influence, max HRC
becomes at slightly lower T"C of quenching. Probably due to
two combined effects. Favouring C solubility in matrix, esp.
lower T"C growing of the HRC. On the other hand Mn and Ni
go up the quantity and stability of ausieniie in that condition
leading to going down of HRC. Oimpaci strength of casting alloys of Fe-Cr-C-N system is comparable (at extreme points) and better at T"C dilferrem from extreme (above 5O-IOO"C) of cast irons: Nicherd, Crl4Ni3Mn4.Cr2SNi2. To regulate HRC. i.e its growing can put in more carbon and nitride forming quality or even quantity thus to stimulate formation of phases like Me7C,. Mc:iCr,. McC esp. Mc(CN). Alloying have to be introduced ballance and depending on aims: introduction of elements able to make wjih C and N easy solutions of K. N. KN at TC quenching of high thermal
resistance. This influences basic matrix as well as added phases. High resislihiliiy can be useful .during crystallisation in the form to refine structure contain grow up of grains under thermal treatment. A,, can be balanced with elements stabilising austcnitizators: N. Mn, Ni. Cu etc. Some of the elements can be used to dispersion strengthen, tempering (annealing) etc. According to patent RB 49451 we introduce. C=0.6-4,2f/r, to 3%S, ).2-9%Mn. 6-35% Cr, 0.02-2.5%N. 0,0l-3%Mo. O.OOI-O.3%B. 0.01-l%Ti. 0.01 -%V. Ni and Cu to 2%. 0,001-1 %W. Ce and Mg and rest Fc to 100%. Elements can go alone or togedher in combinations 2. 3 etc. aiming different requirements practical [6J. 3.2. Diffusion processes in isothermal conditions. Carried out slower depending on T"Cqucnching, composition, samples thickness. For choosed thickness of sample bodies it is determined on many studied alloys that most actively processes (solid phase reachions) go in first 1-2 hours. Additional alloying can continue to 2-4 hours. This reflects regularity HRC= f(T). In next hours process stabilise but we see a trend to decrease I IRC. Probable reason- coagulation of K and KN phases. Duration of austcnization practically doesn"t reflect on N. Choosing T"C tempering is important technology operation. At T"C above l000"C is necessary to count influence of hard activation diffusion process on sample boty surface- decarbonation, denigration etc. Many laboratory and industry tried to show that T"C responding max. HRC shouldn"t be used since a^, smallest. Especially for details cyclically, dinamically. .impact pressured. Lower T"C. left to HRC max. are to be recommended not only by technology of usefulness, but also economic benefit. For Cr alloyed casting alloys (cast iron) containing 12-22%Cr, recommend optimum T"C tempering is in range of 900-930"C to 960"C- IOOO"C. It determined by composition of alloying and most over by Cr. In practices T"C quenching is chosen according to the needs to detail-conditions of work and pressure. This has to make compromise between HRC and aL in choosing T"C of quenching. Choosing cooling medium one has to have in mind foul heat conduction of Cr alloys and their low plasticity. Since using cooling media with high heat conduction (water, oil) recommended are only for thin well details with simple configuration, without complex transitions "thin-thick". Observations show quenching in oil of shovels, scrapers etc. instruments isn"t dangerous. For industry work water is not recommended for use. Can be used only in pulverisation"s together with ventilators and injection of steam (water-air, oil +air. air). Attempts show that thick wall details (above 80-l00mm) like hammers, step plates etc. have affinity to crack-forma-iion. Temperature gradient in section of thick-wall samples and nonsimultenous phase transition in different sections don"t relax in cooling quickly. This leads to destruction of detail. Best cooling down medium is relaxed air. since difference in cool speed in center of sample and surface is practically not existent. We speak about range 75O-5OO"C in which there is cutcctoid disingretation. Long observation on sample bodies with different thickens and configurations (transitions "thin-thick" show heating speed to avoid crack-formation is of great significance. Laboratory and industry tries to show that heating with high speed (e.g.introduction of thick-wall details in hot lurnation.) leads to crack formation too. Not dangerous speed of heating shouldn"t be more than 80-100"C /hour. N decrease trends to slot-formation. T"C of quenching right to max. is not recommended because of above reasons and increasing of austcnitc grains, stabilising austeniic, decrease of HRC, increase of diffusion- surface processes. These T"C can be used in willing for next dispersion solidity trough tempering :singlc or repeating. High- temperature tempering of fashion sample bodies unlike instrumental steels (details) is " not always proved economically. J-J-Heaiine for improvement _of treatalnlitx with cutting instruments.
Can be used ordinary or isothermal heating . Most favourable for treatment is fcrrite (perlile) matrix such structure is obtained in isothermal or slow cooling between Aj and A|. Optimum conditions arc not known .There is possibility basic matrix to go transition in grain perlile. N helps pcrlitize and big decrease of HRC [ 1-2). Pcrlitize can be done alter heating in range 900-950"C and slow cooling (can be stage taking) in rang 820-600"C by speed 50"C/min., after that 550-60O"C air can be used regimes worked out for average of high Cr-alloyed instrumental steels |5j. N containing casting alloys have better trcatability with cutting instruments. Soft nitride phases (towards carbide) encase metal cutting operations. Practically can work out holes to make cutways. Hence we apply: strewing, rattling, etc.. One practical regime is shown in patent RBA 49451 (6). .?,■)".Influence of"tempering (annealing) temperature (tin rat ion) on HRC and a^ Tempering is ending operation of thermal treatment. One basic demands is .removing stresses . in the samples, formed as result of uneven cooling in sections with different thickness"s. We should have in mind pressures of phase trsansilions in cooling. Influence of tempering T,,C (annealing) on HRC and ak is studied in wide spectrum of alloys of different composition of C (N) with or without additional alloying with N. Mo. Cu. V ctc.-after quenching in oil of T"C near to max HRC and tempering (annealing) in range 200-700"C. Changes in HRC after tempering (annealing) don"t respond to structure changes in |l-2]. Summarry shows that to 2()0"C is observed small fall in HRC after removing of quenching stresses. To 400-450"C HRC almost preserves values even shows trend to enhance with some units. In some alloys reach HRC above the values after oil quenching. This shows that in range 400-450"C can be done annealing without danger of deteriorating HRC. N containing alloys show high hardening (secondary) than N free. This effect is characteristic to lower C-alloys (steels) and additional alloying with other elements -Mo. Reason is bigger quantity basic matrix than lower quantity primary K. N. KN. Some casting alloys reach to 65-67HRC. which makes them useful for casting instruments. All studied alloys of system Fe-Cr-C-N have in tempering high HRC than Ni-containing cast irons of type Crl4 Ni3 Mn4. It seems that N can substitute for part of C. Alloy Cll0Cr28 contain 2.08% N after quenching and tempering show considerably high HRC than cast-iron classic C3l5Cr28Ni2 (0.I5N). IC+N is equivalent to 3.15-3,25%C. This show that with N canachicvc very high HRC even more than C. Decrease in HRC above 450-500"C jn all alloys is explained by activation of solid-phase reactions | -2J. HRC at Cr-Mo casting alloys can be increased after tempering if after quenching structure is predominantly austcnite, i.e on the right to max. That"s why helps introduction C and N. HRC increase for account of taking of saturated austcnite of dispersion K, N. KN, followed by martensite transition of austeniic (residual y poorcd by C, N, Cr, Mo, Mn etc. Analogy (similar) processed observed at quenching and tempering of high Cr alloyed instrumental steels [4,5,8]. In practices Cr alloyed casting alloys anneal at 200"C but can use tempering (annealing) at 35O-5OO"C there, where is proved (increase in HRC). Can be applied several limes of tempering it is economically proved. White Cr -alloyed cast alloys (cast irons) are different for high tempering resistance [1-2]. In Cr-Mn cast irons is hindered obtaining of HRC because of big quantity astcnitc. HRC in wear-resistant cast iron have austcnitc structure after quenching can be enhanced to use possibilities of dispcrtion solidifying [7.9]. Example in cast irons C21OCrl5NMn8 and C28OCrl5NMn8 max HRC is obtained after casting at I48O"C and tempering at 75O"C, rcsp. 38-41/56-57 and 45-46/58-60. In numerator- HRC alter casting, in denumerator alter tempering 750oC. after tempering (annealing) 750"C. This way to enhance HRC makes possible to obtain together with manensile other products of pcrlitc disintregalion. since T"C
rof tempering (4h) is directly to the range of pcrlitc transition. If not done such preliminary austcnization (quenching ), tempering can recommed only for samples where structure of "metal matrix is fully austenitc in cast condition (in form) i.e. vonly for thin-wall (shovels some instruments etc.). For other samples containing in structure products of disintegration of Uustenite there"s danger to coagulate K and decrease HRC of .^ferrite-carbide mixture. After first 1-2 hours of tempering HRC is not stable (shows trends to decrease and variance) to initial quenching "condition, probably due to removing the stresses and solid phase reactions at 500"C. We studied some typical alloys with and without N at 200 and 500"C. After 2-3 hours processes die out. Values of variation arc not different and hesitate about practical distractions. At very long duration-ca.50 hours we see some process going to change in HRC probably by coagulation of solid phase reactions [1-2]. Alloys which are Mn and N alloyed exhibit a more stable way of HRC with going up of time of tempering (annealing) C300Crl4Ni3Mn4. At some of them (C315Cr28Ni2) is observed after 5-10 hours trend to go up HRC which once again shows the big stabilising of austcnitc than Mn and N. Possible deprivation of mtermctallids. A,, after tempering is tested on alloy C200Cr200MoCu with different content of N tempered at 1150"C table 1. Content of N almost not influence on HRC. 0.4-0.8%Cu is introduced as substitute for Ni. It smaller range stabilises austcnitc. "*v Introduction of N, Cc and Ti reflects favourably on aw. Favourable influence of Ti is characteristic to low quality (0,1%) N for much bigger it deteriorates. , Conclusions .* 1 The influence of T"C of quenching and tempering on HRC ~. and ak of some typical casting alloys of the Fc-Cr-C-(N ) •" system has been studied and we determined that its influence " is opposite of HRC and ak. a) for every alloy there is T"C of quenching which obtains - max. in HRC and resp. min in ak. This practically imposes the " necessity of compromise choice of the T"C quenching according to the concrete configuration working conditions and sample pressure. , b) N influence comes over C influence. To the right of HRC maximums (min for ak) the austcnite is stabilised by N. c) Increasing T"C of tempering to 4OO-5OO"C there is
almost no deterioration of HRC resp. of ak after which the
lurther increase of HRC decreased and ak is docs not change
and tends to increase. d) N containing casting alloys of Fe-Cr-C-N system tend to
harden in tempering in the range up to 4OO-5OOX in
comparison to N -free and alloyed with austenitc forming Mn.
Ni. The effect of hardening in tempering is bigger in low C
steels, those containing N. N replaces C. 2. We studied the influence of holding time (of quenching)
and tempering (annealing) on HRC (ak) and determined that
the first 1-2 hours carry out active diffusion processes
connected, with solid-phase reactions reflecting in the change
of HRC in variation of values. After 2-4 hours HRC values are
retained and are practically constant (samples 14 xl4). 3. The influence of increasing T"C of quenching and time of
tempering (holding time) can be said to be simultaneous
complex alloying of the matrix with all elements included in
carbide, nitride, karbonitridc. 4. The studied casting alloys of the Fc-Cr-C-(N) system have
resp. better HRC and ak after quenching and tempering
(annealing) compared to classic wear resistant with Mn, Ni:
Nicherd, cast iron of the Fe-Cr-Ni-(Mn)-C system:
C300C414Ni3Mn4, C3l5Cr28Ni2. This show that the alloys
of studied system can be replace these alloys, resp. for casting
of details working in abrasive and hydroabrasivc wear and
impact loading.
References I.Kolcv B.V.Izslcdvania varchu structurata sled cristalli/a-tchia vav format I sled term.obrabotka na liati stomani ot sistcmata Fc-Cr-C-N.NTConf. s .mcid. ulchastie. Mctalozna-nic I term, ohrahoivanc na mctalitc. Dokladi, Sny.opol.1998 2.Kolev B.V.Izslcdvane na tchugunot systemala Fc-Cr-C-N sled kristallizatchia vav formaia i sled term.obrabotka. NT.Conf. s mejd. utchaslie. Dokladi. Sozopol. 1998. 3.E.Pivovarskii.Vaissokokatchcstvcnii tchugun. Mctallurgia, M.. 1965. 4.Gcller U.A.Instumcntalnic stali. Mctallurgia M.,1983. 5.Rashkov N.D. Termichno obrabotvane na Spetchialni stomani. Technika, Sofia 1993. 6.Dimov I.N.. B.V.Kolev and all. Iznosoustoitchiva splav na Fc-C osnova.. Patent RB 49451. 7.Kolcv B.V. Vazmojnosli za polutchavanc, structuroobra/.u-vane I svoistva na niakoi Iciarski splavi na Fe-C osnova legirani s azot. Disscrtazia. IM-BAN. Sofia. 1985. S.Kolcv. B.V. Effects of pressure and N on structure formation of some Fc-C based casting alloyis. Theoretical ana-lis. lntcm.Congr. Mech.Engin..Techn.-99. Proc, Sofia, 1999. 9.Rashcv Ts.V. Baisokoa/.otistic stalli.Mctallurgia pod davlenicm. Izdatclsvo BAS,"prof.M.Drinov". Sofia ,1995. lO.Kolcv B.V.Tcrmichna mctastabilnost pri nagriavanc I ochlajdane na miakoi liati austcnitni splavi na Fe osnova. Teoret. osnovi. Intern, congr. Mech. Eng. Techn.-97 Proc, vol.2. Sofia. 1997. and Thermal metastabi-lity in heating and cooling of some austcnitic Ferrous alloys -Thcorct. founda-tions.-Vth ltcm.Congr. HNS-98, Stokholm and Hclzinki, "98, and Intern Workshop "Diffusion and diffusional phase transformations in alloys.Diftrans-98. Cherkasy, Ukraine, 1998. Figures fig. 1-7. HRC=f(T"C quenching) figl.C300Crl4MnMo:1.0.02%N:2.0.45%N:3.C300Crl4Ni3Mn4 fig2.C300Crl4Mo2:1.0.0254%N:2.0.3827rN:3.C300Crl4Ni3Mn fig3.C2-10Crl4:1.0.048%N;2.0.450%N;3.C300CrI4Ni3Mn4 fig4.C300Crl7Mo3:1.0.037%N:2.0.537%N;3.C300Crl4Ni3Mn4 fig5.C260Crl3MnMo;1.0.031%N;2.0.408%N; 3.C300Crl4Ni3Mn4 fig6.CI50Cr20Mo2:1.0.026%N;2.0.917%N;3.C300Crl4Ni3Mn4 fig7.CI 10Cr28M.N=2.08%. fig8.1.C300Cr30Ni3(0.099%N):2.C240Crl4Mnl2(0.923%N). fig9-l l:HRC=f(t)-duralion at T"C of quenching. fig9.IOOOvC:240Crl4;1.0.084l5N;2.0.614%N; 3.C3OOCrl4Ni3Mn4 figl0.950"C:CI50Crl4Mo2:1.0.08415N;2.0.6145N. figll..95O"C:1.30OCrl4Ni3Mn4;2.Nichard. fig. 12-15:Ak=f(T"C of quenching) figl2.CI50Cr!4Mo2:1.0.084 5N: 2.0.6I45N; 3.C300Crl4Ni3Mn4. figl3.Cl50Cr20Mo2;I.0.0262%N:2.0.917%N; 3.C300Cr!4Ni3Mn4 fig. 14.C240Cr20; 1.0.088%N :2.0.89%N :3 .C300Cr 14Ni3Mn4. fig. 15.30OCr 14MnMo; 1.0.02%N:2.0.453%N figl6-22:HRC=f(T"C of tempering). fig.23.HRC=f(t of duration at T"C of tempering) fig.24.HRC=f(Mn).C300Crl69N=0,2-0.3%).2h.air. Note:Thc work has been carried out under Contract TH 717/97 of the Ministry of Edicsation and Science.
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