Cryogenic Quenching of High Speed Steels after Vacuum Heating

Transcription

1 Proceedings of the 4th WSEAS Int. Conf. on HEAT TANSFE, THEMA ENGINEEING and ENIONMENT, Elounda, Greece, August -3, 006 (pp-6) Cryogenic Quenching of High Speed Steels after acuu Heating N.I.Kobasko,.M.Shulaye Intensie Technologies td., Kyi, Kharki Physics Engineering Institute, UKAINE Abstract:- An adantageous quenching ethod for high-speed steels after acuu heating is suggested. It lies in cooling tools by inert gases fro austenitizing teperature to artensite start teperature Ms, keeping at this teperature for soe tie, and then the transfer of the tool to a cryogenic edia with the regulated cooling rate within the artensite range at supercritical rate. Engineering calculation ethods hae been deeloped for the calculation of theral and physical processes. The software has been deeloped for the control oer the heat treatent process. Key - Words:- acuu heating, Cryogenic quenching, Tool serice life, Ecologically clean technologies, Software. Introduction Due to significant increase in the price of high - speed steels and necessity to eliinate salt and alkali elting, it becae necessary to deelop efficient and ecologically clean technologies of theral strengthening of high-speed steels. The paper presents a new technology of tool quenching, based on the discoered property of aterial superstrengthening when the cooling rate during quenching within the artensite range is ery high [, ]. In these works it has been established that the high cooling rate within the artensite range results in the considerable increase in the serice life of tools. Heating tools is perfored in acuu, and quenching in special cryogenic equipent. The cryogenic equipent allows to adjust the cooling rate within the artensite range. The regularities of cooling and heating tools hae been studied and, as a result, special SOFTWAE for the control of heat treatent processes has been deeloped. acuu and Cryogenic Equipent acuu eleator electric resistor furnace SEG- 5.5/3-IZG is supposed for quenching arious parts ade out of alloy steels by streas of inert gas. The furnace consists of the ain echaniss as follows (see Fig. ): - case with heating odule, - loading echanis, - acuu syste, - syste of gas cooling for cages, - syste of water cooling, - syste of control. The steel furnace case is closed fro two sides by elliptic bottos. Inside the case in its upper part a heating odule is set on special brackets. The theral insulation of the odule and heaters are ade out of carbon-coposite aterials. The oeent of the cage fro the cooling area to the heating odule and back is perfored by eleator echanis with electric gear. The electric furnace control syste operates in both anual and autoatic odes. The lower part of the chaber, if necessary, can be heated to the artensite start teperature, to preent the when the steel is cooled by inert gas. The furnace is equipped with necessary blocking deices preenting the daage of furnace echaniss in case of incorrect actions of an operator. The noinal teperature in the work space is 300 о C. The non-unifority of teperature in the work space is 0 о C. The accuracy of supporting the teperature is plus/inus 5 о C [3]. arious ethods of cryogen cooling of tools hae been deeloped [4, 5]. A principal schee of one of the is presented in Fig. b. In Fig. bell ibrates at resonance frequency and cooled gas is supplied to it. The specified schee was tested in laboratory conditions. For industrial conditions, special cryogen equipent has been deeloped, which are being patented in Ukraine and USA and are Know How. When quenching tool steels in cryogenic systes, cooling rate within the artensite range can be adjusted within the wide range.

2 Proceedings of the 4th WSEAS Int. Conf. on HEAT TANSFE, THEMA ENGINEEING and ENIONMENT, Elounda, Greece, August -3, 006 (pp-6) Fig. acuu furnace a) and cryogenic equipent b) for cryogenic quenching of High-Speed Tool steels: - ibrating bell for the supply of cooled gas, gas bubbles, 3 a part to be quenched, 4 a therostat containing a cryogen liquid. а) b) 3 Matheatical Description of Heating and Cooling Processes For approxiate calculation of the heating and cooling tie for parts of arious configuration generalized dependence () can be used [4]. More precise calculations are ade by coputer siulation with the use of appropriate experiental databases. Databases are created through soling inerse and reerse heat transfer probles. For this purpose there are special software [6]. t kbi Bi T T + ln T T = 0 C C K akn Here t is tie of cooling of steel parts; Bi is generalized Biot nuber; () K is Kondratje for coefficient; Kn is Konddratje nuber; T C is ediu teperature; a is theral diffusiity; T o is initial teperature. Table Kondratje for coefficients K for bodies of a siple configuration No. Shape of the S Coefficient K,, - part. Plate of thickness. Cylinder of radius Square infinite 4 pris with equal sides of Cylinder of radius and height Z + Z Finite cylinder, =Z 5 65 Finite cylinder =Z 8. 5 Finite square plate with sides of,, Z 4 3 ( ) 3 S K, 0,346 Z ( + Z ) 5.784Z

3 Proceedings of the 4th WSEAS Int. Conf. on HEAT TANSFE, THEMA ENGINEEING and ENIONMENT, Elounda, Greece, August -3, 006 (pp-6) Nu = 0.0 e Pr (Pr Pr ) ε, () wd where Nu is Nusselt nuber, e = is aynolds nuber, Pr = is Prandtle nuber. a Correctional function ε = f ( λ λ, e) depends on d the correlation of the length to diaeter. If λ d > 50, thenε e =. When λ d < 50, tabulated alues are used. sf e Heat transfer coefficient for cooling tools in strea of neutral gases is deterined by equation forula (), then the generalized Biot nuber is deterined, which is placed in equation (). Haing nuerical alues of K and Kn, it is easy to deterine the tie of tool cooling fro austenitizing teperature to artensite start teperature. The aerage alues of heat transfer coefficients for cooling in cryogen equipent with liquid nitrogen are presented in Table. Table Heat transfer coefficients with regard to the state of the quenchant [5] Quenchant Mediu Cooling ibration ibrator α, teperature, conditions frequency, Hz acceleration, W/ K o C g/g o iquid nitrogen -96 No ibration iquid nitrogen and nitrogen apor iquid nitrogen and apors of nitrogen and heliu - 96 ibration agitation -96 Airing, ibration agitation The cooling rate for tools of arious configuration within the artensite range can be deterined by equation (3) as follows: a Kn = ( T T ), (3) K where is cooling rate ( o C/s); a is aerage theral diffusiity ( /s); T is current teperature ( о C); T is teperature of ediu. As is known, Kondratje for coefficient for cylinder-shaped bodies is D K = or K =, therefore, equation (3) can be presented as follows: Table 3 presents results of calculation of cooling rates within the artensite range (00 о C) for cooling cylinder-shaped speciens of 6- and - diaeter. It shows that cooling rate within the artensite range significantly increases if a cryogen ediu is used instead of ineral oil. This is reached ainly for the account of big difference of teperatures between the part s teperature and liquid nitrogen boiling point (see equation (3)). Table 3 Cooling rate of the core of cylindershaped speciens of 6- and - diaeter during their cooling in oil Houghton K, haing teperature 43 о C, and ibrated liquid nitrogen. Diaeter of specien, Cooling rate in oil, С/s Cooling rate in nitrogen, C/s 6 6 = 3.3 α Kn D ( T T )

4 Proceedings of the 4th WSEAS Int. Conf. on HEAT TANSFE, THEMA ENGINEEING and ENIONMENT, Elounda, Greece, August -3, 006 (pp-6) 4 esults of Field Testing By the present there are a lot of data accuulated that confir the faorable ipact of intensie cooling within artensite range upon the serice life of tools ade out of high-speed tool steels. Many authors hae noted the increase in serice life of tools by or 3 ties [7, 8]. Soe data on tests with a punch (Fig.) are presented in Table 4. cryogenic quenching increases by or 3 ties, the consuption of expensie etals is reduced by or 3 ties, which akes lesser containations in the enironent. At the present serious attention is paid to ecologically clean technologies. So, WSEAS and other authority organizations deliered the initiatie of soling ecological probles on the Earth (see Fig. A punch ade out of High-Speed Tool Steel. Table 4 Field trial of wear iproeents in deep cold treated of tools ade of high speed M steels Tool Type Tool Material Punch M 300 Drill M 00 Milling cutters M7 50 Iproeent in wear rate (%) 5 Discussion The distinctie feature of the cooling process is that the acuu furnace proides keeping a high-speed tool at teperature M S for soe tie after cooling by neutral gas. The transforation of austenite into artensite takes place outside the acuu furnace in cryogen liquid at supercritical cooling rate within the artensite range. The fact that it is possible to hae such a process is proed on the basis of CCT diagra, which presented in Fig. 3. The diagra shows that there is enough tie to ipleent twostage cooling process with the delay of artensite transforations at the first stage of cooling. The process suggested by this technology is ecologically clean since it becoes unnecessary to use elted salt or alkali, or quench oils as quenchants. Since the serice life of tools after sec in hrs Fig. 3 CCT diagra for steel 8. Heating is to 90 о C. At the first tie notion of critical cooling rate within the artensite range and super strengthening of a aterial was forulated by author [8]. It was noted further that quenching in liquid nitrogen increases serice life of tools [9]. Explanation of this phenoenon is proided in [4]. Here cooling rate adjustent within the artensite range is widely discussed. 6 Conclusions. acuu equipent has been created for heating High-Speed Tool Steels in acuu with their further cooling in neutral gases. Cooling in neutral gases occurs fro austenitizing teperature to artensite start teperature M S.. The equipent allows to keep parts for soe tie at this teperature.. Special equipent has been deeloped for cryogenic quenching of High-Speed Tool Steels in conditions of regulated cooling within the artensite range. 3. The serice life of High-Speed Tool Steels increases for the account of quite high (supercritical) cooling rate within the artensite range.

5 Proceedings of the 4th WSEAS Int. Conf. on HEAT TANSFE, THEMA ENGINEEING and ENIONMENT, Elounda, Greece, August -3, 006 (pp-6) 4. The critical cooling rate in the artensite range, which proides superstrengthening, depends on the content of carbon and alloy eleents in steel. eferences: [] N.I.Kobasko, Steel Superstrengthening Phenoenon, Journal of ASTM, February 005, ol., No, Paper ID JAI 84, pp. - 3, Aailable online at [] N.I.Kobasko, Steel Superstrengthening Phenoenon, Part I, Int. J. Materials and Product Technology, ol. 4, No 4, 005, pp [3].M.Shulaye, F.M.Poliako, Energy- Saing Electric esistor Furnaces of Periodic Action, Kharki, NSC KPEI, 003, 9 p. [4] N. I. Kobasko, Steel Quenching in iquid Media under Pressure, Kyi, Naukoa Duka, 980, 06p [5].F.Ganie, N.I.Kobasko,..Kulik, et al., Oscillation phenoena in ulti-phase edia and their use in technology, Kie, Tekhnika, 980, 4 p. [6]..Dobriecher, N.I.Kobasko, E.N.Zoto, W.S.Morhuniuk, Yu.S.Sergeye, Software 5. Special Software has been deeloped for the control of heat treatent processes IQab (coercially aailable fro Intensie Technologies td., Kyi, Ukraine, iqlab@itl.kie.ua, [7] P.F. Stratton, Process optiization for deep cold treatent of tool steels, Proc. of the st Int. Conference on Heat Treatent and Surface Engineering of Tools and Dies (IFHTSE 005), Pula, Croatia, 08- June, 005. [8] N.I.Kobasko, Effect of Structural and Theral Stresses Upon Crack Foration During Steel Quenching, in a Book: All- Union Conference on Increase in Productiity and Profitability of Heating Furnaces, Dnipropetros k, 967, p 6-7 [9] Е.S. Zhud, Inentor s Certificate # 4856 (USS), A Heat Treatent Method of Tools, Published in B.I., 975, 35.