Computer Simulation of Microstructure Transformation during the Quenching

Transcription

1 Compuer Simulaion of Microsrucure Transformaion during he Quenching B. Smoljan Faculy of Engineering, Chair of Maerials Science and Engineering Vukovarska 58, Rijeka, Croaia ABSTRACT: Compuer simulaion of ausenie decomposiion during he seel quenching has been invesigaed. The inversion mehod of phase porion esimaion in he quenched seel has been esablished. The mehod of predicion of quenched seel microsrucure composiion is based on hardenabiliy curve of Jominy-specimen. The designed mehod of predicion ausenie decomposiion has been used in compuer simulaion of phase porion vs. hardness in quenched specimens of seel 34 Cr 5 and C 45 (DIN). KEYWORDS: Ausenie decomposiion, Compuer simulaion 1 INTRODUCTION Simulaion of phase ransformaion is in he roo of he simulaion seel quenching. A model of quenching would no be considered represenaive of he acual process if i does no incorporae he effecs of phase ransformaions. Phase ransformaion modeling is one of he main challenges in modeling of hea reamen [1]. Simulaion of any one process can be made successfully only if all mechanisms of process are well known and if he appropriae mahemaical mehods are used. Unforunaely he mechanism of phase ransformaions is no fully undersood and ineracive influence of differen elemens, auseniizing emperaure, ec. usually are no aken in accoun. The errors in phase ransformaion calculaion could be exremely grea if a model is based only on grain size of prior ausenie, auseniizing emperaure and elemenal composiion of seel. Phase ransformaion kineic depends also on he degree of soluion of he carbides and i canno be accuraely prediced only from elemenal composiion. The grain size a he auseniizing emperaure mus be known in calculaion of phase ransformaion kineic. Moreover, in pracice numerous phase ransformaions calculaions are based jus on saisic correlaion beween chemical composiion and final microsrucure as resul of quenching. The invesigaions of seel quenching suggess ha choosing a proper represenaive of he cooling phenomenon, which is relevan for srucural ransformaion is one of he mos imporan facors for a good simulaion of hardening [2]. Good resuls in phase ransformaions predicion could be achieved if he predicion is based on coninuous cooling ransformaions diagrams (CCT diagrams) [3]. CCT diagrams are irreplaceable

2 in he clear presenaion of srucural ransformaion during he seel cooling in order o predic srucural consiuion and hardness afer cooling. Moreover, preparing CCT diagrams is raher expensive. They are prepared for sricly deermined elemenal composiion and auseniizing emperaure and hey could be used wih accuracy only for simulaion of seel quenching wih same elemenal composiion, auseniizing emperaure and hisory as were of seel for i he CCT diagram is made. The compuaion of CCT diagrams upon he elemenal composiion has no been sufficienly developed. From anoher poin of view, he kineic of phase ransformaions can be esimaed based on simple experimen. For example, he kineic of phase ransformaions and hardness disribuion can be esimaed based on ime, relevan for srucure ransformaion measured on Jominy specimen [4]. 2 ALGORITHM OF PHASE PORTION PREDICTION Srucure composiion afer cooling is depended of on acual seel hardness. I can be wrien ha he seel hardness generally is equal: HV=((% ferrie) HV (F) + (% pearlie) HV (P) + (% bainie) HV (B) + ( % marensie) HV (M) )/100 (1) In addiion, he all amoun of phases porion is equal uniy:. ((% ferrie + % pearlie) + % bainie + % marensie) / 100 = 1 (2) By he equaions (1) and (2) is no difficul o predic phase fracions. Boh, hardness (HV) of cooling microsrucure wih 90% or 50% of marensie and of 10%, 50% or 90% of (ferrie+pearlie), and hardness of microsrucure consiuens separaely have o be known. Resuls of ausenie decomposiion are depending on he chemical composiion of seel, severiy of cooling, auseniizing emperaure and seel hisory. The ausenie decomposiion resuls can be esimaed based on ime, relevan for srucure ransformaion. The characerisic cooling ime, relevan for srucure ransformaion for mos srucural seels is he ime of cooling from 800 o 500 C (ime 8/5 ) [4]. Involving he ime 8/5 in he mahemaical model of seel quenching, he Jominyes resul can be involved in ausenie decomposiion model. Everyone locaion of Jominy-sample has one characerisic ime 8/5. The diagram cooling ime 8/5 vs. disance from he quenched end of Jominy-specimen (Jominy-disance) is shown in Figure 1 [4].

3 Fig. 1 Disance from he quenched end of Jominy-specimen vs. cooling ime from 800 o 500 C If oher hea reamen parameers are consan, he ausenie decomposiion resuls in some locaion of a cooled specimen will depend only of he ime 8/5. I could be wrien for Jominy es ha phase hardness depends of chemical composiion (CC) and cooling rae parameer (CRP) ha corresponds o acual disance (d) of Jominy specimen quenched d end. I was adoped ha CRP = log 8 / 5. HV M d M M 8/5d = fm ( CC, CRP) = HVmax K M log ; (3) M 8/5max HV B d B B 8/5d = fb( CC, CRP) = HVmax KB log ; (4) B 8/ 5max P+ F P+ F P+ F 8 / 5N HV d = fp+ F( CC, CRP) = HVN + KP+ F log ; (5) P+ F where N is normalizing, B max is lower bainie. Characerisic value of HV, K and 8/5 in equaions (3), (4) and (5) has o be evaluaed based on chemical composiion for invesigaed seel combined by Jominy es resuls. Hardness of quenched srucures wih 100%, 90% or 50% of marensie can be prediced by using he diagram of hardness a differen percenages of marensie vs. carbon conen afer Hodge and Orehoski [1][5] and Jominy curve, bu he influence of chemical composiion of seel has o be aken in accoun. Disances of quenched end Jominy specimen wih marensie fracion of 90% and 50% can be prediced by he diagram of Jominy curve by conversion hardness resuls o disances. 8 / 5d

4 Disances of 100% marensie and 100% of pearlie can be prediced by he diagram of Jominy curve. The regression relaions beween he cooling ime from 800 o 500 C for cooling srucures of 100%, 50%, 10% and 0% pearlie are esablished. log log log log 100%(P + F) 8 / 5 90%(P + F) = f 90 a 8 / 5 ( CC, T ) 100%(P + F) 8 / 5 50%(P + F) = f 50 a 8 / 5 a ( CC, T ) 100%(P + F) 8 / 5 10%(P + F) = f10 a 8 / 5 a ( CC, T ) 100%(P + F) 8 / 5 = f 0%(P F) 0 a, + 8 / 5 a ( CC, T ) a ; (6) ; (7) ; (8) ; (9) where T a is auseniizing emperaure in K; a is auseniizing ime in h; Characerisic Jominy disances for characerisic ime 8/5 is esimaed using he relaion beween cooling ime and disance from he quenched end of Jominy specimen shown in Figure 1. 3 COMPUTER SIMULATION OF PHASE PORTION The phase porion of Jominy specimen of seel 34 Cr 4 (DIN) and C 45 (DIN) are esimaed by compuer simulaion. An own compuer sofware program was used for compuer simulaion. Elemenal composiion of invesigaed seel 34 Cr 4 was 0.36% C, 0.28% Si, 0.63% Mn, 1.15% Cr. Jominy es resuls of invesigaed seel 34 Cr 4 are shown on Figure 3. Auseniizing emperaure was equal 850 C.

5 Fig. 3 Jominy es resul of seel 34 Cr 4 Diagram of srucure porion for Jominy specimen of seel 34 Cr 4 is shown on figure 4. Fig. 4 Simulaed srucure composiion vs. Jominy disances diagram of seel 34 Cr 4 Elemenal composiion of invesigaed seel C45 was 0.44 % C, 0.28% Si, 0.60% Mn. Jominy es resuls of invesigaed seel C45 are shown on Figure 5. Auseniizing emperaure was equal 850 C.

6 Fig. 5 Jominy es resul of seel C45 Diagram of srucure porion for Jominy specimen of seel C45 is shown on figure 6. Fig. 6 Simulaed srucure composiion vs. Jominy disances of seel C45 If he hardness in quenched specimen poins is known and if he phase disribuion vs. Jominy disances is known i is no difficul o predic he phase disribuion in quenched seel specimen. Phase disribuion in quenched seel specimen can be calculaed by numerical mehods [6] from ime 8/5 or by empirical mehods using he diagram on figure 1 and Crafs - Lamon diagrams [5].

7 The calculaed hardness disribuion and phase disribuion in quenched cylindrical seel specimen of 50 mm Dia. of seel C 45 is shown on figure 7. Hea reamen of quenching was: heaing o 850 C for 30 min and quenching in agiaed waer wih severiy of quenching H=1.4. Fig. 7 Simulaed srucure composiion of cylindrical specimen of seel C45. 4 CONCLUSION Simulaion of phase ransformaion is in he roo of he simulaion seel quenching. A model of quenching would no be considered represenaive of he acual process if i does no incorporae he effecs of phase ransformaions. Phase ransformaion modeling is one of he main challenges in modeling of hea reamen. The ausenie decomposiion resuls can be esimaed based on ime, relevan for srucure ransformaion. The characerisic cooling ime, relevan for srucure ransformaion for mos srucural seels is he ime of cooling from 800 o 500 C (ime 8/5 ). The inversion mehod of compuer simulaion of ausenie decomposiion and evaluaion of quenched phase porion was esablished. In he esablished mahemaical model he numerical measure of specimen cooling kineic was ime 8/5. For he calculaion of microsrucure composiion, he hardness in specimen poins, Jominy es resuls and chemical composiion of seel mus be known. The esablished mahemaical model was applied in compuer simulaion of microsrucure ransformaion in Jominy and cylindrical specimens of seel. I can be concluded, ha by proposed mehod microsrucure composiion in quenched seel specimen can by successfully calculaed.

8 REFERENCES 1. K. Funaani and G. Toen, Presen Accomplishmens and Fuure Challenges of Quenching Technology, The 6h Inernaional Seminar of IFHT, Kyongju, (1997). 2. B. Lišćić e al, Workshop Designed Sysem for Quenching Inensiy Evaluaion and Calculaion of Hea Transfer Daa, Proc. of he 1s Iner. Conf. on Quenching & Conrol of Disorion, Chicago, Vol. 1, pp , Theory and Technology of Quenching, eds. B. Liščić, H. Tensi and W. Luy, Springer Verlag, (1992). 4. A. Rose e al, Alas zur Wärmebehandlung der Sähle I, Verlag Sahleisen, Düsseldorf, S. Hoy, Meal Daa, Columbus, Ohio, B. Smoljan, Numerical Simulaion of Seel Quenching, Journal of Maerials Engineering and Performance, Vol. 11(1), (2002), pp B. Smoljan, Compuer Simulaion of ausenie decomposiion, proceedings of he Inernaional Conference on Advanced Maerials processing echnologies (AMPT 01), ed. J. M. Toralba, Univ. Carlos III de Madrid, Vol. 2., pp , M. Lusk and Y. Lee, A Global Maerial Model for Simulaing The Transformaion Kineics of Low Alloy Seels, Proceedings of he 7 h Seminar of IFHT, Budapes, (1999). 9. J. Cbrera, J. Ponce and J. Prado. Modeling Thermomechanical Processing of Ausenie, Inernaional Conference on Advanced Maerials Processing Technologies (AMPT 01), ed. J. M. Toralba, Univ. Carlos III de Madrid, Vol. 2., pp , 2001.