Two-Stage Quenching Method with the Use of Oils at Optimal Temperature

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1 Proceedings of the 4th WSEAS Int. onf. on HEAT TRANSFER, THERMAL ENGINEERING and ENVIRONMENT, Elounda, Greece, August 1-3, 006 (pp1-5) Two-Stage Quenching Method with the Use of Oils at Optial Teperature Nikolai I.obasko, Volodyyr V.Dobrivecher Intensive Technologies Ltd., yiv, Ukraine Abstract:- Two-step quenching ethod with the use of hot oils is suggested. At the first stage, cooling in hot oil, the transforation of austenite into artensite is suspended. At the second stage intensive cooling within the artensite range and siultaneously washing steel parts are perfored. On the basis of the study of heat transfer processes, the full autoation and optiization of steel heat treatent processes have been suggested. The optiization is based on the deterination of extree values of critical heat flux densities. This advanced technology iproves the quality of products and saves the ecology for the account of lesser oil exhaust eission in atosphere and shorter tie of heat transfer processes. ey words::- Two-step quenching, ritical heat flux densities, Heat transfer coefficients, Autoation, Quality iproveent, Ecology 1 Introduction As is known, parts of coplex geoetry ade out of alloy and high-alloy steels, as a rule, are quenched in ineral oils. As the intensity in oils is not big, the increase in the hardenability is reached for the account of adding alloys. Besides, slow and unifor cooling within the artensite range reduces the distortion and eliinates the possibility of quench crack foration. However, regarding theral and physical processes, not all potentialities of ineral oils have been fully discovered. The authors of this paper optiize the quench cooling processes on the basis of deterining extree (axiu) heat flux densities and heat transfer coefficients obtained through solving inverse heat transfer probles. This approach brings forth the results as follows: More unifor intensive cooling of parts, which results in the increase of hardenability and reduction of distortion. The opportunities of two-stage quenching are extended through the use of hot oils. The service life of parts increases. O eission to atosphere is reduced. The labor productivity increases for the account of reducing the tie of heat treatent process. Extree values of critical heat flux densities For every kind of oil there is extree value of critical heat flux densities, which is due to the oppositely influencing factors: viscosity and underheating. When the teperature drops, underheating increases and at the sae tie oil viscosity drastically increases, which causes the foration of vapor fils and non-unifor cooling. With the increase of the oil teperature, the viscosity of oil decreases, which results in ore intensive and unifor cooling of parts. However, the further increase in teperature of oil results in the reduction of underheating ( Ts T.), and therefore, the appearance of vapor fils, and again, nonunifor cooling. Therefore, there exists the optial teperature of oil at which the ost intensive and unifor cooling of steel parts is reached. The optial teperature of various oil grades can be deterined fro Fig. 1 by axiu of q cr1 [1]. Fig. 1 The first critical heat flux density vs. oil teperature: 1 MZS-10; MS-0; 3 Effectol B; 4 MZM-16 Besides the oil teperature, it is also necessary to optiize the circulation of the oil, which, of course, has effect upon the critical heat flux densities.

2 Proceedings of the 4th WSEAS Int. onf. on HEAT TRANSFER, THERMAL ENGINEERING and ENVIRONMENT, Elounda, Greece, August 1-3, 006 (pp1-5) 3 Heat transfer coefficients obtained on the basis of solving inverse heat transfer probles N.A.Tikhonov created a new direction in ethods of regularizing algoriths, which allowed to solve inverse probles that could not be solved by any other ethod. The first works were devoted to probles that are solvable analytically. For any probles theores of existence and uniqueness of the solution were proved, algoriths of search for the regularization paraeter α were suggested [ - 5]. For the practical probles related to heating and cooling of steel, it is of interest to consider regularizing nuerical algoriths for heat conduction probles in nonlinear stateent. For this kind of probles the ethod of regularization is reduced to the introduction of a regularizing ter into the error functional, which is to be iniized: F α [ u] Au f + = α u, where u is a vector of required paraeters, F is an error functional to be iniized, f is a vector of experiental data, A is a atrix of transition fro required paraeters to estiated values at appropriate points of teperature easureent, is nor in space R, is a nor which is defined as follows: u = ( u, u) 1/, where is a positively deterined atrix. For exaple, it is possible to assue =E, where E is a unit atrix. Tikhonov s ethod was used in the deterination of heat transfer coefficients during steel quenching in cold and hot oils [6]. Fig. presents the dependence of heat transfer coefficient on surface teperature for steel quenching in ineral oil MZM 16. Fig. Heat transfer coefficient vs. surface teperature As Fig. shows, during oil boiling the ean heat transfer coefficient is within the range of W/. Upon the end of boiling, heat transfer coefficient decreases to about 300 W/ and in the further it changes very little. The ean values of heat transfer coefficients for various oil grades are presented in Table 1. It should be noted that heat transfer coefficients depend on the shape and size of parts being quenched, therefore, it is necessary to have the generalization of this function. Table 1 Mean heat transfer coefficients during quenching steel parts in ineral oils, W/ Mean heat Oil grade transfer coefficient for teperatures The sae below 300 о above 300 о, W/ I MS MZM MZM I

3 Proceedings of the 4th WSEAS Int. onf. on HEAT TRANSFER, THERMAL ENGINEERING and ENVIRONMENT, Elounda, Greece, August 1-3, 006 (pp1-5) 4 onveyer line for the ipleentation of two-stage quenching with the use of hot oils The tie of heating and cooling for bodies of any geoetry and speeds of conveyor oveent are deterined on the basis of diensionless equation [7]: k Bi v Fov n= + lnθ (1) Biv Here t and τ are tie of heating and cooling of the steel parts; Bi v is generalized Biot nuber; is ondratjev for factor; n is ondratjev nuber; T o is initial teperature before cooling; T c is quenchant teperature. depends on shape and size of steel part. n depends on cooling capacity of quenchant. Fig. 3 Industrial installation for the ipleentation of IQ- technology [4] І loading steel parts to conveyor for their heating in heater 1; II chute with intensive cooling devices; ІІІ loading of quenchant to quenching tank with two conveyors; ІV unloading of steel parts fro heater ; TR1, ТR, ТR3, ТR4, ТR5 speed control units for conveyors 1,, 3, 4 and 5 operated by the control device; HT1, HT heaters 1 and ; WQ1 washing and quenching device; PM1, PM pups 1 and ; L1, L coolers 1 and ; F1 filter; BX1 container for quenched parts Table Martensite start teperature and teperature at which 5% artensite is fored, for various steel grades, о Steel grade M S, AISI/ o GOST Austeni tizing teperature, arbon content in steel, % T1/R % arten site teper ature E5100/ Shh15 A485()/ Shh15SG L/ 9h / arburized 0hNM W1/ U W1/ U The process can be fully autoated on the basis of known equation [8]: L aln W = = () τ ( Ω+ b lnθ ) The above-entioned conveyor line is universal in the sense that it allows to apply various quenchants: aqueous salt solutions of optial concentration, aqueous polyer solutions exhibiting inverse solubility and foring the optial depth of polyer fil, hot oils at optial teperature, and so on. Hot oils have one iportant advantage that lies in their high boiling point (see Table 1). It follows that hot oil at optial teperature not only speed up cooling process in coparison with cold oils, but also delays the transforation of austenite into artensite, since in the ajority of cases, the optial teperature of oil is greater than or equal to

4 Proceedings of the 4th WSEAS Int. onf. on HEAT TRANSFER, THERMAL ENGINEERING and ENVIRONMENT, Elounda, Greece, August 1-3, 006 (pp1-5) artensite start teperature. The artensite start teperature for soe steels is presented in Table. When the transforation of austenite into artensite is delayed at the first stage, and a part is intensively cooled in the artensite range at the second stage (where washing and intensive cooling coincide), it is possible to significantly increase the strength properties of aterial. At each step the tie and speed of conveyor is calculated by the progra, which includes the database of ondratjev for coefficients, heat transfer coefficients and quenchant properties. The window of choosing the part s shape and sizes is presented below: Heat transfer coefficients for sprayer cooling can be deterined by known forula [9, 10] as follows: N u= 1 Re Pr, (3) where H / D 1 = 1+ f ; 0.6 f (1. f ) = ; 1+ 0.( H / D 6) f ( π ) D f = 4 ; A square ( hexagon) D is a diaeter of a nozzle in sprayer ; H is a distance fro a nozzle (aperture) to a surface to be quenched; A is the area of the square, hexagon. Diensionless nubers 1 also are connected with geoetry and arrangeent of nozzles with respect to the surface to be quenched. Reynolds nuber Re is connected with the speed of the quenchant in the beginning of the outlet fro a nozzle, and the nuber Pr characterizes physical properties of the quenchant. The diensionless equation of siilarity (6) is fair within the boundaries of the following values and given paraeters: 000 Re ; f 0.04 ; H 1. D 5 Discussion The authors are adherents of intensive steel quenching ethods. In the near future, in the ajority of cases, alloy and high-alloy steels will be replaced with plain carbon steels of low hardenability. Oils and high-concentration polyer quenchants substituting the will be replaced with plain water, that is, intensive water streas or jets. It becae possible due to the discovered property of aterial superstrengthening and foration of high copressive stresses at the surface of parts quenched [8]. Since the ipleentation of intensive quenching ethods in production is delayed because of the lack of appropriate equipent and sufficient availability of low-hardenability steels, the authors consider it their duty to start the optiization of usual processes of alloy-steel quenching in usual oils. As it is entioned above, the optiization solves, to soe extent, ecological probles and increases the service life of steel parts due to intensive cooling within the artensite range, when at the sae tie the parts are washed. It should be noted that washing steel parts becoes essentially easier due to lesser viscosity of hot oils, which considerably reduces the aount of oil carried out together with the part when it is taken out of the quenchant. When quenching is perfored in cold oil, such aount of oil carried out significantly increases, and washing becoes ore coplicated. Therefore, the optial teperature of oil not only iproves the quality of parts, reduces the O eission to the atosphere, but also saves quench oils due to the lesser aount carried out of the quench tank during unloading parts. In our opinion, if there is the faintest chance to solve ecological probles and iprove the quality of products at the sae tie, it ust be done iediately. Finally, by such efforts of any

5 Proceedings of the 4th WSEAS Int. onf. on HEAT TRANSFER, THERMAL ENGINEERING and ENVIRONMENT, Elounda, Greece, August 1-3, 006 (pp1-5) people, the environent cleansing will occur and the quality of products will grow up. 6 onclusions 1. The optiized two-stage quenching process with the use of hot oils possessing the axiu value of the first critical heat flux density is proposed.. At the first stage, parts are cooled to the teperature of hot oil with the delay of artensite transforations. At the second stage the parts are both washed and intensively cooled within the artensite range. 3. The axiu value of the first critical heat flux density reduces the distortion, increases hardenability and reduces O eission to atosphere, provides ore unifor cooling. 4. The optiization of cooling processes on the basis of deterining optial critical heat flux densities essentially iproves the quality of parts at the iniu cost and without radical changes in the production lines. 5. It is iportant to start the study of the effect of all possible additions to oils upon the absolute value of critical heat flux densities. 6. The Software has been developed, which is based on generalized criterion functions, for the control of industrial heat treatent processes. 7. The new conditions of aterial heat treatent are exacted and perfected on the basis of coputer siulation of all heat treatent processes taking place in practice. References 1. Nikolai obasko, ritical heat flux densities and their easureents, Proc. Of the 6 th International onference Equipent and Technologies for Metal and Alloy Heat Treatent, OTTOM 6, harkiv, Ukraine, 16-0 May, 005, pp A.N.Tikhonov, V.Ya.Arsenin. Methods of Solving Incorrect Probles, Moscow, Nauka, 1986, 88 p. 3. A.N.Tikhonov. On Solving Incorrectly Set Probles and Regularization Method, Journal Doklady AN USSR, Vol. 151, No. 3, 1963, pp A.N.Tikhonov, V.B.Glasko, On Approxiate Solving of Integral Fredhol Equations of the First ind, Journal ''oputational Matheatics and Matheatical Physics'', Vol. 4, No. 3, 1964, pp A.N.Tikhonov, V.A.Morozov. Methods of Regularization of Incorrectly Set Probles, Journal ''oputational Methods and Prograing'', Issue 35, 1981, pp V.V.Dobrivecher, N.I.obasko, E.N.Zotov, W.S.Morhuniuk, Yu.S.Sergeyev, Software IQLab (coercially available fro Intensive Technologies Ltd., yiv, Ukraine, iqlab@itl.kiev.ua, 7. Nikolai obasko, Siplified ethod of calculation for engineers dealing with quench design processes, Proc. Of the 7 th International onference Equipent and Technologies for Metal and Alloy Heat Treatent, OTTOM 7, harkiv, Ukraine, 4-8 April 006, pp N.I.obasko, Patent of Ukraine H.Martin, Ipinging Jets, in Heisphere Handbook of Heat Exchanger Design, oordinating Editor J.F. Hewit, New York, Heisphere Publishing orporation, 1990, p., H.Martin, and E.U.Schlünder, Optiierung von Schlitzdüsentrocknern auf Irund neuer Versuchsergebnisse über den Wäre - und Stoffübergang in solchen Apparaten, he. Ing. Tech., Vol.45, 1973, p 90 94