Постинг
23.06.2010 14:15 -
Доклад изнесен и публикуван. Международна конференция- Охрид- Македония
Cojy3 на мешалурзише на Македонща, Охрид, 4-6 ма} 2000 Macedonian metallurgists union, Ohrid, May 4-6, 2000
Организатор на трета металуршка конференщца - МЕТАЛУРГША 2000: Cojy3 на металурзите на Македонка Покровител на третата металуршка конференщца: Господин М-р. Борко Андреев, Минисшер за стопанство во Владаша на Република Македонща Организащцата на конференцията беше подржана од: 1. Министерството за екологща на
Република Македонща 2. Министерството за наука 3. Стопанската комора на
Македонща 4. Технолошко-металуршки
факултет, Универзитет "Св.
Кирил и Методщ " Скоще 5. Инженерската институцща на
Македонща
Organizer of 3rd metallurgical conference-METALLURGY 2000: Macedonia Metallurgists Union The 3rd Metallurgical Conference is under high patronage of: Mr. Borko Andreev, M. Sc, Minister of economy in the Government of the Republic of Macedonia The organization of the conference was supported by: 1. Ministry of Ecology of the Republic
of Macedonia 2. Ministry of Science of the Republic
of Macedonia 3. Economic Chamber of Macedonia 4. Faculty of Technology and
Metallurgy, University "St. Kiril
and Metodij" Skopje 5. Engineers Institution of Macedonia
INFLLENCE OF CHEMICAL COMPOSITION ON MECHANIC CHARACTERISTICS OF CASTING WEAR-RESISTANT COMPLEX ALLOYS OF THE Fe-Cr-C-(N) SYSTEM [Eng.Bogomil Velikov Kolev, Metal Science Institute- BAS, 67 Shipchenski prohod str.Sofia 1574, Bulgaria,E-mail; kolev.b.v@abv.bg. Summury There are are results presented of the research on influence on basic components (Cr, C, N) on mechanic feracteristics of alloyed and heat treated wear-resistant complex alloys of the Fe-Cr-C-(N) system: Rockwell"s hardness, strength tensile(σb), strength bending(σbend) and impact strength (ak). Thе regularities drawn during testing enable the right choice of a proper chemical composition for specific ts according to specific working conditions: the type of wearing and pressure. Introduction Thе better part of details in industrial condition work not only under abrasive, hydroabrasive, corrosion chanic wearing but also under complex dynamic wear. That"s why the study of mechanic chararacteristics of these, alloys aiming to search possibilities for their improvement as well as to chose the apropriate composition is very important for the quality and efficiency of the alloys. This is connected with the solving some topical problems: lightening of machines and apparatuses decreasing the need of our. resourses and energy, which become less on the earth Global ecology [1-8]. The mechanic characteristics of Cr alloyed casting alloys depend on many factors of which very important are: chemical composition, crystallization and thermal treatment conditions. These factors derermine the character of the carbide (K) and nitride (N) and carbonitride (KN) phases and the basic metal matrix. The pressure, resp. the absorbed under its influence. N sharply refine structure along with the increase of cooling rate [4]. The information about mechanic characteristics of casting austenite alloys of Fe-Cr-C system connected with influence of chemical composition and thermal treatment is very scarce [2-3] and for casting alloys of Fe-Cr-C-N system there are no data. One of the basic problems is it high C casting alloys of that system N free are difficulty to treating cutting instruments. The long ■rs of observation show that N improves mashinability and sharply decreases the affinity towards Ishes and slots, since under crystallisation N-phases are formed which have bigger hardness than K-phaseslake stresses easily from phase transitions. We suppose that in cutting N phases have an lubricant are very much like graphite. In pattent RB 49451 there is a concrete worked-out regime which allows ping wearing, making hotes, etc. [2-3,5-6]. Experimental methods. Alloys have been obtained in an induction autoclave with milling, drilling, holes, pouring into dry sand halds with different dimension: a) To determine the tensile strength (σB)- diameter=12mm,and lemth= 250. a) To determine bending strengt (σbend-)- diameter10 x 300 mm, without meching treatment. c)To determined impact strength ak= 12x 250.mmTo improve the treatability with cutting instruments we carried out an intermediatl thermaltreatment according to [2, 3, 5, 6]. After that: other treatments. After quenching tempering and cutting of samples. They have been tested under standart BDS. Investigating mechanic characterictics of casting alloys of those systems it is necessary to have in mind the above mentioned factors determining fuctors. The crystallization conditions are constant study characteristics, it is of primary importance to show the place, resp.alloy in the condition diagram fig-1 ■ Unfortunately, in the Fe-Cr-C-N system are none and this is the future of scientific studies. With our investigation on the contemporary period the necessity of building such [2-7]. Cr, C and N are the basic components in the Fe-C-N system. Results,analysis and discussion. 3.1.Influence of Cr on HRC, ak and σbending It is graphically interpreted fig.2-4. For every point there are 3 to 6 observations.The properties change acording structural changes [2-7]. Recapitulated conclusions:
1.Influence of Cr on HRC, abending and ak is smaller than that of C. Above 16-18%Cr, HRC
haltand decreases because of the change of K phasesI 2. Increasing C and Cr content HRC increases and ak decreases. On the values special influence have I
type of crystal lattice of K, N, KN phases, although there are changes also in the metal matrix esp. I
it is big in the steels. Big influence have K in comparison with N which have less hardness than K. On I
homogenesation and quenching non alloyed alloys of the Fe-Cr-C-N system with big carbo and nitrid
formation show smaller thermodynamic stability towards , K than N. Carbon influence is summed with, the
N towards the matrix and determines the availability of products of non-diffusion processes (martensite I
austenite, products of disintegration [2-3]. Up to 0,2 - 0,4%N tends to increase HRC after which it sharply decreases [2-3].) 3. Cr inffluence of a bending is not yet clear. With increase of its content at low C there is a trent to decrease σbending- The quantity of K phase under influence of Cr increases, although the matrix is s "
determinative. At high C concentrations - trend towards decrease of σbending under influence of(
Determinative is K phase and its characteristics [2-8]. Generally: Ме7Сз and Ме23Сб influence n*
positively than МезС wich increase at high C. Cr and C influence on the eutectic point, which also refflected
on σbending. With Cr increase the eutectic point moves towards lower C. ; 3.2. Influence of C on HRC, σb, σbending, etc. 3.2.1. Influence of C on HRC. Testing after tempering of 950° and 1150°C, t duration= 40 min. and 4 hour Cooling - easy air. Results have been graphically interpreted and for every point there are at least 4 to! observation, fig.5-7. Since there is an opposite dependence between HRC and ak [6]. Then often in practics it is turned
chosing an alloy whose chemical properties and type of thetrmal treatment assure compromise rating
between HRC, σb, σbend- a k- wear resistance, quenching, etc. There are no data about C, C influence)
HRC of casting austenite alloys of the system Fe-Cr-C-N. The role of C is more determinative than Cr. N
a givem sum C+N can be obtained austenite, non-magnetic structure with much higher hardnes than th
of austenite alloys of system Fe-Cr-Mn-C-(N) or Fe-Cr- N-(Mn)-(C)-(N) and even of possibility i;
mechanic treatment which is an advantage of C and N to structure formation and alloys properties of tk
Fe-Cr-C-N system. The results help us make following conclusiuon on structure formation [1-7]. 1.C content increase in N- alloyed alloys of the type Crl3NMnMo2, Crl8NMnM2, Cr22NMo2, HRC.
after quenching of 950°C and 1150°C increases. Because there are big and crude K above some C content
there is decrease of HRC: at 13%Cr (Crl3NMnMo2),- above 3,2-3,3%C, at 18%Cr (Cr22NMo2), -abov
2,8-3%C. 2. Temperature and duration under quenching influence diffusion processes resp. on HRC and ak of the.
studied typical casting alloys according to structure changes [2, 3, 6]. -At 950°C 4 hours favours to obtain max hard basic matrix and secondary K, N, KN. There is higher HR( in comparison with 40 min. duration. -At 1150°C, 4 hours favours the release of max (resp. hard) austenite, because of the sharp dissolvimg o: primary and secondary K and N phase and stabilising of the solid solution. We obtained lower HRC ir comparison with 40 min. duration. 3.2.2. Influence of C (N) on ak. Studies after 950°C and 1150°C, duration 4 hours cooling - easy air Tempering 200°C. Results are interpreted graphically. For every point-2 to 4 observations, fig. 18-19. On the basis of the above and studies in [2, 3, 5-7] can be drawn the fallowing conclusions. 1.Increasing C content in casting alloys of the type Crl3NMnMo3, Crl8NMnMo2, Cr22NMo2, ak
decreases, because of increase of K phase and change of its quality and quantity characteristics. 2. N in studied content 0,2 to 0,9% influences slowly on ak (alloy of C200Cr22MoCu type) and moves in
the range 0,37- 0,65.10-5, j/m2, 1150°C, 2h., air, 200°C, 500°C, 700°C, 2h., fig. 14. Up to 0,1- 0,15%N
there is a trend to increase ak, after which it tails down and again slowly increases reaching 0,7% the value
at 0,1 %N introducing 0,1 %Ti increases ak in the range 0,l-0,9%N with 0,05-0,15.10-5,j/m2. Tempering
of 500 and 700°C preserves the ak values or practically there is slow increase [6]. N influence is result of
summary effect: hardening action of introduce atomic N in solid solution, increasing quantity and stability
of austenite (1150°C) and decreasing the quantity of martensite and of products of diffusion disintegration as well as of secondary K, N, KN [2, 3, 6]. 3.T°C of quenching and duration influence significantly diffusion processes resp. HRC and a* of the studied alloys after quenching (low-T°C tempering 200°C). Increasing T°C of quenching and τdUration quantity and stability of residual austenite increase, i.e., HRC decreases, ak increases importantly at steels with low C and no so much in last iron. 4.Since there is opposite dependence between HRC and ak [6] under influence of C in practics there should be compromise decisions on C content and regimes of thermal treatment in dependance of concrete conditions and pressure of samples N doesn"t deteriorate ak. 3..З. Influence ofC (N) on Obending and aB of some typical alloys. Having in mind influence of basic factors determining mechanic properties of casting alloys of the above systems we determine that comparing result of scarce data of different authors for base system Fe-Cr-C is difficult because of absence of data for previous above conditions for treatment and crystallizations (cooling) of alloys or samples: shape, type of forming materials, metallurgical treatment, ToC of casting, velocity of crystallization (cooling) connected with the size of samples, shape and configuration of samples for strength tests etc. [2-8]. There aren"t sure data and standard methodics for strength testing for these alloys, probably because of present working in recent, 1-2 decades. Tested are samples with and without mechanic treatment. The used samples of clinched probes or cast samples with d= 30 mm aren"t very good to use because of its big contraction, non homogeneous structure towards center due to different cooling . Hence, becouse of obtaining of structures with products which have non diffusion and diffusion character. Velocity of cooling and crystallization conditions together with chemical composition influence on characteristics of matrix and carbide phase [2-9]. Big part of problems ofstudies on strength characteristics come out of cutting instruments treatment, esp. N free alloys since determinative application are very HRC and ak, probably authors for that reason prefer less strength indicators [2-9]. Above mentioned differrent characteristics and obtaining conditions, casting and crystallization, treatment and testing of alloys of that system become the reason for antithesises between authors. For strength charactericics of Fe-Cr-C-N system we haven"t got data. The aim is to give fuller characteristics of casting alloys of the studied system giving results of abending, Rb etc. according to patent RB 49451. [5]. Alloys were obtained by method above -described; σbending is tested in cast condition after crystallization inmould and after quenching of 950°C, 40 min., oil, tempering 200°C, 2 hours σв is tested after mechanic treatment following thermal treatment: quenching of 950—1150°C, 45 min, oil, tempering 2 hours -200°C. Strength test on machine "Amsler" according to BDS standart. Results are shown graphically as for every point there are 3 to 5 observations, fig.20-22 for bending and fig.23-24 for σb show: aving Having in mind the above in [2-9] we determine: 1. Increasing C content in some typical casting wear -resistant alloys of Fe-Cr-C-N system σbend and σb decrease. C influence on σbending and σBis stronger than that of Cr ( point 4.1). σbending in casting non thermal treated samples is higher than σbending of tempered at 950°C. Increasing content this difference decreases and at C above 2,8- 3,2% it is fully deceased. Probably these differenees are due to to-eutectic alloys in which the influence of structure changes in basic matrix are significant. At thin-wall samples where velocity of cooling is high there is fine-grain structure which strengthens matrix N and pressure act in the same way, esp. N [4-7]. In thin wall high pressure samples to 10-15min cannot apply additional extremely exspensite operation of thermal treatment if there are no special requirements for wear resistance. Besides, thermal treatment detremines the influence of low C steels since there the important role has the matrix and not K, N, KN unlike cast iron. Hence, thin-wall samples of cast iron can do without thermal treatment if strength of bending is very important for sample forthick-wall samples thermal treatment is necessary. The quality is determined by its, temperability etc. Non-homogeneous structure after castingis absolutely necessary to obtain necessary properties [2, 3, 5]
σB at ca 3%C (Crl3Mo3Mn) shows sharper decrease under influence of C. This probably due to above eutectic crude K. Increasing Cr content in different typical alloys the curves of adding decreases under influence of C. This is due to the change of type and other K phases characteristics. 3. Increasing N content in different types casting alloys of studied system σb increases by 1-3.107Pa every 0,1 %N. This effect is reflected in alloys containing below 2-2,2%C. σBaccording to patent RB 49451in the range 50-100.10"7Pa Conclusions We studied the influence of basic components Cr, C and N on mechanic characteristics of casting allo of Fe-Cr-C-N system and determined: 1.HRC increases whil tensile strentgh σв, bending strength - σbend and impact strength- ak decrease whe
the content of C increases from 1 to 4% in the under eutectic alloys of the system Fe-Cr-C-N- 12-14%Cr. 2. N up to 0,2-0,4% tends to increase HRC by some units after quenching. In further its increase HRC
decreases due to increase of quantity and stability of austenite. In spite of that fact ak, tends to preserve
constant values of N content increase of content up to the studied values -0,89% in alloy;
C200Cr20MoCu. We obtained casting austenite (non magnetic) alloys of the Fe-Cr-C-N system which
have higher HRC and mechanic characterictics, than cast austenite alloys of the Fe-Cr-Mn-(Ni)-C-N, Fe
Cr-Ni-C systems. This makes them competitive even to replace some traditional steel instruments:
Advantage is the good machinability compared to austenite Cr-Mn steels for details that require high
mechanic workability. 3. N increase hardness of casting austenite alloys of the system with 1-3.10-7 Pa every 0,1 %N after
quenching of 950-1000°C and low treatment. Basic influence has according to conclusions 1 and 2 C and
Cr content neverttheless N increases carbide (K), nitrides(N), carbonitrides (KN) quantity. The change in.
type, shape, size, quantity, distribution. C influence is bigger than N and Cr, because the K phase role is
determined than that of the N phases. The problem of KN remains open. 4. Increasing C content the basic role of the basic matrix on mechanic characteristics decreases and
increases the role of K, N and KN phases with their characteristics. The bearing cross-section of the tested
samples decreases and hardness characteristic deteriorate. Nitrides are more soft than K. 5. T°C quenching and increase quantity and holding times and C, N increase quantity and stability of
austenite-changes that reflect in properties. 6. The invers relationship between HRC and ak influenced by C necesitates taking compromise decisions
about C content at (12-24%Cr) and thermal treatment regime as a function of concret demands of practice
and esp. loading of casting in use. References l.Kolev B.V.Basic results from the production, research and application of new Fe-based Nitrogen alloys. directionand development, forcasts on the 21-st century. Development of metallurgy in the Balkans at the beginningof the XXIst century. Reports and final documents , Varna, 1996. Kolev B.V. The fundamental philosophical resources of material science and metallurgy in explanation of some processes and phenomenain supreme modes of the mater"s motion, iae oai-Varna, 1996. Kolev B.V. Reference to the positionof the metallurgical sciences (materialscience) in the contamporary classification of the sciences and their role for resolving. Global fundam. -philosoph
Организатор на трета металуршка конференщца - МЕТАЛУРГША 2000: Cojy3 на металурзите на Македонка Покровител на третата металуршка конференщца: Господин М-р. Борко Андреев, Минисшер за стопанство во Владаша на Република Македонща Организащцата на конференцията беше подржана од: 1. Министерството за екологща на
Република Македонща 2. Министерството за наука 3. Стопанската комора на
Македонща 4. Технолошко-металуршки
факултет, Универзитет "Св.
Кирил и Методщ " Скоще 5. Инженерската институцща на
Македонща
Organizer of 3rd metallurgical conference-METALLURGY 2000: Macedonia Metallurgists Union The 3rd Metallurgical Conference is under high patronage of: Mr. Borko Andreev, M. Sc, Minister of economy in the Government of the Republic of Macedonia The organization of the conference was supported by: 1. Ministry of Ecology of the Republic
of Macedonia 2. Ministry of Science of the Republic
of Macedonia 3. Economic Chamber of Macedonia 4. Faculty of Technology and
Metallurgy, University "St. Kiril
and Metodij" Skopje 5. Engineers Institution of Macedonia
INFLLENCE OF CHEMICAL COMPOSITION ON MECHANIC CHARACTERISTICS OF CASTING WEAR-RESISTANT COMPLEX ALLOYS OF THE Fe-Cr-C-(N) SYSTEM [Eng.Bogomil Velikov Kolev, Metal Science Institute- BAS, 67 Shipchenski prohod str.Sofia 1574, Bulgaria,E-mail; kolev.b.v@abv.bg. Summury There are are results presented of the research on influence on basic components (Cr, C, N) on mechanic feracteristics of alloyed and heat treated wear-resistant complex alloys of the Fe-Cr-C-(N) system: Rockwell"s hardness, strength tensile(σb), strength bending(σbend) and impact strength (ak). Thе regularities drawn during testing enable the right choice of a proper chemical composition for specific ts according to specific working conditions: the type of wearing and pressure. Introduction Thе better part of details in industrial condition work not only under abrasive, hydroabrasive, corrosion chanic wearing but also under complex dynamic wear. That"s why the study of mechanic chararacteristics of these, alloys aiming to search possibilities for their improvement as well as to chose the apropriate composition is very important for the quality and efficiency of the alloys. This is connected with the solving some topical problems: lightening of machines and apparatuses decreasing the need of our. resourses and energy, which become less on the earth Global ecology [1-8]. The mechanic characteristics of Cr alloyed casting alloys depend on many factors of which very important are: chemical composition, crystallization and thermal treatment conditions. These factors derermine the character of the carbide (K) and nitride (N) and carbonitride (KN) phases and the basic metal matrix. The pressure, resp. the absorbed under its influence. N sharply refine structure along with the increase of cooling rate [4]. The information about mechanic characteristics of casting austenite alloys of Fe-Cr-C system connected with influence of chemical composition and thermal treatment is very scarce [2-3] and for casting alloys of Fe-Cr-C-N system there are no data. One of the basic problems is it high C casting alloys of that system N free are difficulty to treating cutting instruments. The long ■rs of observation show that N improves mashinability and sharply decreases the affinity towards Ishes and slots, since under crystallisation N-phases are formed which have bigger hardness than K-phaseslake stresses easily from phase transitions. We suppose that in cutting N phases have an lubricant are very much like graphite. In pattent RB 49451 there is a concrete worked-out regime which allows ping wearing, making hotes, etc. [2-3,5-6]. Experimental methods. Alloys have been obtained in an induction autoclave with milling, drilling, holes, pouring into dry sand halds with different dimension: a) To determine the tensile strength (σB)- diameter=12mm,and lemth= 250. a) To determine bending strengt (σbend-)- diameter10 x 300 mm, without meching treatment. c)To determined impact strength ak= 12x 250.mmTo improve the treatability with cutting instruments we carried out an intermediatl thermaltreatment according to [2, 3, 5, 6]. After that: other treatments. After quenching tempering and cutting of samples. They have been tested under standart BDS. Investigating mechanic characterictics of casting alloys of those systems it is necessary to have in mind the above mentioned factors determining fuctors. The crystallization conditions are constant study characteristics, it is of primary importance to show the place, resp.alloy in the condition diagram fig-1 ■ Unfortunately, in the Fe-Cr-C-N system are none and this is the future of scientific studies. With our investigation on the contemporary period the necessity of building such [2-7]. Cr, C and N are the basic components in the Fe-C-N system. Results,analysis and discussion. 3.1.Influence of Cr on HRC, ak and σbending It is graphically interpreted fig.2-4. For every point there are 3 to 6 observations.The properties change acording structural changes [2-7]. Recapitulated conclusions:
1.Influence of Cr on HRC, abending and ak is smaller than that of C. Above 16-18%Cr, HRC
haltand decreases because of the change of K phasesI 2. Increasing C and Cr content HRC increases and ak decreases. On the values special influence have I
type of crystal lattice of K, N, KN phases, although there are changes also in the metal matrix esp. I
it is big in the steels. Big influence have K in comparison with N which have less hardness than K. On I
homogenesation and quenching non alloyed alloys of the Fe-Cr-C-N system with big carbo and nitrid
formation show smaller thermodynamic stability towards , K than N. Carbon influence is summed with, the
N towards the matrix and determines the availability of products of non-diffusion processes (martensite I
austenite, products of disintegration [2-3]. Up to 0,2 - 0,4%N tends to increase HRC after which it sharply decreases [2-3].) 3. Cr inffluence of a bending is not yet clear. With increase of its content at low C there is a trent to decrease σbending- The quantity of K phase under influence of Cr increases, although the matrix is s "
determinative. At high C concentrations - trend towards decrease of σbending under influence of(
Determinative is K phase and its characteristics [2-8]. Generally: Ме7Сз and Ме23Сб influence n*
positively than МезС wich increase at high C. Cr and C influence on the eutectic point, which also refflected
on σbending. With Cr increase the eutectic point moves towards lower C. ; 3.2. Influence of C on HRC, σb, σbending, etc. 3.2.1. Influence of C on HRC. Testing after tempering of 950° and 1150°C, t duration= 40 min. and 4 hour Cooling - easy air. Results have been graphically interpreted and for every point there are at least 4 to! observation, fig.5-7. Since there is an opposite dependence between HRC and ak [6]. Then often in practics it is turned
chosing an alloy whose chemical properties and type of thetrmal treatment assure compromise rating
between HRC, σb, σbend- a k- wear resistance, quenching, etc. There are no data about C, C influence)
HRC of casting austenite alloys of the system Fe-Cr-C-N. The role of C is more determinative than Cr. N
a givem sum C+N can be obtained austenite, non-magnetic structure with much higher hardnes than th
of austenite alloys of system Fe-Cr-Mn-C-(N) or Fe-Cr- N-(Mn)-(C)-(N) and even of possibility i;
mechanic treatment which is an advantage of C and N to structure formation and alloys properties of tk
Fe-Cr-C-N system. The results help us make following conclusiuon on structure formation [1-7]. 1.C content increase in N- alloyed alloys of the type Crl3NMnMo2, Crl8NMnM2, Cr22NMo2, HRC.
after quenching of 950°C and 1150°C increases. Because there are big and crude K above some C content
there is decrease of HRC: at 13%Cr (Crl3NMnMo2),- above 3,2-3,3%C, at 18%Cr (Cr22NMo2), -abov
2,8-3%C. 2. Temperature and duration under quenching influence diffusion processes resp. on HRC and ak of the.
studied typical casting alloys according to structure changes [2, 3, 6]. -At 950°C 4 hours favours to obtain max hard basic matrix and secondary K, N, KN. There is higher HR( in comparison with 40 min. duration. -At 1150°C, 4 hours favours the release of max (resp. hard) austenite, because of the sharp dissolvimg o: primary and secondary K and N phase and stabilising of the solid solution. We obtained lower HRC ir comparison with 40 min. duration. 3.2.2. Influence of C (N) on ak. Studies after 950°C and 1150°C, duration 4 hours cooling - easy air Tempering 200°C. Results are interpreted graphically. For every point-2 to 4 observations, fig. 18-19. On the basis of the above and studies in [2, 3, 5-7] can be drawn the fallowing conclusions. 1.Increasing C content in casting alloys of the type Crl3NMnMo3, Crl8NMnMo2, Cr22NMo2, ak
decreases, because of increase of K phase and change of its quality and quantity characteristics. 2. N in studied content 0,2 to 0,9% influences slowly on ak (alloy of C200Cr22MoCu type) and moves in
the range 0,37- 0,65.10-5, j/m2, 1150°C, 2h., air, 200°C, 500°C, 700°C, 2h., fig. 14. Up to 0,1- 0,15%N
there is a trend to increase ak, after which it tails down and again slowly increases reaching 0,7% the value
at 0,1 %N introducing 0,1 %Ti increases ak in the range 0,l-0,9%N with 0,05-0,15.10-5,j/m2. Tempering
of 500 and 700°C preserves the ak values or practically there is slow increase [6]. N influence is result of
summary effect: hardening action of introduce atomic N in solid solution, increasing quantity and stability
of austenite (1150°C) and decreasing the quantity of martensite and of products of diffusion disintegration as well as of secondary K, N, KN [2, 3, 6]. 3.T°C of quenching and duration influence significantly diffusion processes resp. HRC and a* of the studied alloys after quenching (low-T°C tempering 200°C). Increasing T°C of quenching and τdUration quantity and stability of residual austenite increase, i.e., HRC decreases, ak increases importantly at steels with low C and no so much in last iron. 4.Since there is opposite dependence between HRC and ak [6] under influence of C in practics there should be compromise decisions on C content and regimes of thermal treatment in dependance of concrete conditions and pressure of samples N doesn"t deteriorate ak. 3..З. Influence ofC (N) on Obending and aB of some typical alloys. Having in mind influence of basic factors determining mechanic properties of casting alloys of the above systems we determine that comparing result of scarce data of different authors for base system Fe-Cr-C is difficult because of absence of data for previous above conditions for treatment and crystallizations (cooling) of alloys or samples: shape, type of forming materials, metallurgical treatment, ToC of casting, velocity of crystallization (cooling) connected with the size of samples, shape and configuration of samples for strength tests etc. [2-8]. There aren"t sure data and standard methodics for strength testing for these alloys, probably because of present working in recent, 1-2 decades. Tested are samples with and without mechanic treatment. The used samples of clinched probes or cast samples with d= 30 mm aren"t very good to use because of its big contraction, non homogeneous structure towards center due to different cooling . Hence, becouse of obtaining of structures with products which have non diffusion and diffusion character. Velocity of cooling and crystallization conditions together with chemical composition influence on characteristics of matrix and carbide phase [2-9]. Big part of problems ofstudies on strength characteristics come out of cutting instruments treatment, esp. N free alloys since determinative application are very HRC and ak, probably authors for that reason prefer less strength indicators [2-9]. Above mentioned differrent characteristics and obtaining conditions, casting and crystallization, treatment and testing of alloys of that system become the reason for antithesises between authors. For strength charactericics of Fe-Cr-C-N system we haven"t got data. The aim is to give fuller characteristics of casting alloys of the studied system giving results of abending, Rb etc. according to patent RB 49451. [5]. Alloys were obtained by method above -described; σbending is tested in cast condition after crystallization inmould and after quenching of 950°C, 40 min., oil, tempering 200°C, 2 hours σв is tested after mechanic treatment following thermal treatment: quenching of 950—1150°C, 45 min, oil, tempering 2 hours -200°C. Strength test on machine "Amsler" according to BDS standart. Results are shown graphically as for every point there are 3 to 5 observations, fig.20-22 for bending and fig.23-24 for σb show: aving Having in mind the above in [2-9] we determine: 1. Increasing C content in some typical casting wear -resistant alloys of Fe-Cr-C-N system σbend and σb decrease. C influence on σbending and σBis stronger than that of Cr ( point 4.1). σbending in casting non thermal treated samples is higher than σbending of tempered at 950°C. Increasing content this difference decreases and at C above 2,8- 3,2% it is fully deceased. Probably these differenees are due to to-eutectic alloys in which the influence of structure changes in basic matrix are significant. At thin-wall samples where velocity of cooling is high there is fine-grain structure which strengthens matrix N and pressure act in the same way, esp. N [4-7]. In thin wall high pressure samples to 10-15min cannot apply additional extremely exspensite operation of thermal treatment if there are no special requirements for wear resistance. Besides, thermal treatment detremines the influence of low C steels since there the important role has the matrix and not K, N, KN unlike cast iron. Hence, thin-wall samples of cast iron can do without thermal treatment if strength of bending is very important for sample forthick-wall samples thermal treatment is necessary. The quality is determined by its, temperability etc. Non-homogeneous structure after castingis absolutely necessary to obtain necessary properties [2, 3, 5]
σB at ca 3%C (Crl3Mo3Mn) shows sharper decrease under influence of C. This probably due to above eutectic crude K. Increasing Cr content in different typical alloys the curves of adding decreases under influence of C. This is due to the change of type and other K phases characteristics. 3. Increasing N content in different types casting alloys of studied system σb increases by 1-3.107Pa every 0,1 %N. This effect is reflected in alloys containing below 2-2,2%C. σBaccording to patent RB 49451in the range 50-100.10"7Pa Conclusions We studied the influence of basic components Cr, C and N on mechanic characteristics of casting allo of Fe-Cr-C-N system and determined: 1.HRC increases whil tensile strentgh σв, bending strength - σbend and impact strength- ak decrease whe
the content of C increases from 1 to 4% in the under eutectic alloys of the system Fe-Cr-C-N- 12-14%Cr. 2. N up to 0,2-0,4% tends to increase HRC by some units after quenching. In further its increase HRC
decreases due to increase of quantity and stability of austenite. In spite of that fact ak, tends to preserve
constant values of N content increase of content up to the studied values -0,89% in alloy;
C200Cr20MoCu. We obtained casting austenite (non magnetic) alloys of the Fe-Cr-C-N system which
have higher HRC and mechanic characterictics, than cast austenite alloys of the Fe-Cr-Mn-(Ni)-C-N, Fe
Cr-Ni-C systems. This makes them competitive even to replace some traditional steel instruments:
Advantage is the good machinability compared to austenite Cr-Mn steels for details that require high
mechanic workability. 3. N increase hardness of casting austenite alloys of the system with 1-3.10-7 Pa every 0,1 %N after
quenching of 950-1000°C and low treatment. Basic influence has according to conclusions 1 and 2 C and
Cr content neverttheless N increases carbide (K), nitrides(N), carbonitrides (KN) quantity. The change in.
type, shape, size, quantity, distribution. C influence is bigger than N and Cr, because the K phase role is
determined than that of the N phases. The problem of KN remains open. 4. Increasing C content the basic role of the basic matrix on mechanic characteristics decreases and
increases the role of K, N and KN phases with their characteristics. The bearing cross-section of the tested
samples decreases and hardness characteristic deteriorate. Nitrides are more soft than K. 5. T°C quenching and increase quantity and holding times and C, N increase quantity and stability of
austenite-changes that reflect in properties. 6. The invers relationship between HRC and ak influenced by C necesitates taking compromise decisions
about C content at (12-24%Cr) and thermal treatment regime as a function of concret demands of practice
and esp. loading of casting in use. References l.Kolev B.V.Basic results from the production, research and application of new Fe-based Nitrogen alloys. directionand development, forcasts on the 21-st century. Development of metallurgy in the Balkans at the beginningof the XXIst century. Reports and final documents , Varna, 1996. Kolev B.V. The fundamental philosophical resources of material science and metallurgy in explanation of some processes and phenomenain supreme modes of the mater"s motion, iae oai-Varna, 1996. Kolev B.V. Reference to the positionof the metallurgical sciences (materialscience) in the contamporary classification of the sciences and their role for resolving. Global fundam. -philosoph
Тайната на математическия ребус 6:2(1+2)
Преди 100 години избухва Балканската вой...
Петър Стоянов - Президентът, който още с...
Преди 100 години избухва Балканската вой...
Петър Стоянов - Президентът, който още с...
Няма коментари
Вашето мнение
За да оставите коментар, моля влезте с вашето потребителско име и парола.
