TRATTAMENTI TERMICI from the austenitizing temperature down to the martensite start temperature Ms (often using hot oil or high-concentra- tion water/polymer solutions). There is an insignificant temperature gradient throughout the cross-section of the part within this slow cooling stage. Therefore, the initial tempe- temperature Ms at the beginning of the second stage of coo- However, a limitation of IQ-1 process is that a) quench oils or high-concentrations of aqueous polymer quenchants are used at the first stage of cooling, and b) the second stage of cooling is conducted in a separate chamber. The use of tions (typically 20% to 24%) considerably reduces the har- dening capacity for steel parts. The necessity of a second it difficult to maintain and it is more expensive. IQ-2 is a three-step procedure: a) fast cooling under nuclea- slow cooling in air, and c) convective cooling in the quen- ching tank. During IQ-2, the duration of the unstable film- pidly on the surface. To avoid surface cracking, the fast cooling is interrupted when there is less than 50% of mar- tensite formed in the surface layer of the part and the surface layer is still Ťplastic.Ž The steel part is removed from the After ŤinterruptionŽ of the intensive stage of cooling, the part continues to cool in air. During this second stage of IQ- 2, the part surface layer or ŤshellŽ is self-tempered by the heat coming from the hot core. The temperature of the part equalizes throughout the cross sectional area. Also, in this which are developed in the first stage of cooling are fixed. As a result of self-tempering, the martensitic surface layer strengthens eliminating possible cracking during final stage surface of the part, and to simultaneously obtain an austeni- re in the core of the part. For thin parts, the required high B. MODELING THE INTENSIVE QUENCHING PROCESS almost any steel part [15]. The process begins by analyzing the thermal and stress profiles within the part during quen- ching using a finite element approach [7]. This model inclu- C. EQUIPMENT FOR INTENSIVE QUENCHING Currently there are two general types of equipment for in- tensive quenching. The first type is for the implementation of the IQ-3 quenching technique for a single (part-by-part) TRATTAMENTI TERMICI simulation results in an AISI simulazione del processo di supporto di acciaio AISI 52100. (HP) motors [18]. Asimilar oil-quench tank in an integral props rotating by two 5 HPmotors [18]; c) IQ-2 quenching systems should be equipped with a very fast elevator mecha- nism since the duration of different IQ-2 process cooling steps is usually calculated in seconds. Moving from Ťinten- Intensive Quenching of Automotive and Truck Axles In one application, truck half-axles constructed from AISI nuous process. The half-axles are typically machined to a 2. Use of Intensive Quenching in Nut and Bolt Production special V-Quench tank was developed for the production of small parts such as bolts. [21] The radial flow rate of the ching of the small parts. Figure 3 illustrates an heat treating line utilizing the V-Quench tank. [21] This system is suitable Reduction in electric energy and water consumption. the V-tank with improved physical properties compared to 3. Bearing Production in a Continuous Intensive Quenching System Quenching of bearing parts may also be performed in conti- 4. Die Production by Intensive Quenching TRATTAMENTI TERMICI Fig. 2 – a) Illustration of close die-forging of truck half-axles. b) Illustration of intensive quenching process for truck hal 10 - a plate; 11 - casters; 12 - a fixed door of a quenching chamber; 13 - an induction coil of quenching quality control; 14 - pneumocylinder for the horizontal carriage displacement; 17 and 15 - a lever and pneumocylinder of reloading from a prism of a spring-loaded centers; 24 - a cup-shaped friction; 25 - a drive with an electromotor, a speed reducer and a transmission; 26 - beam; 28 - fixed supports; 29 - a puller; 30 - a pneumatic cylinder. Fig. 2 – a) Illustrazione di fucinatura a stampo di semiassi di autocarro. b) Illustrazione del processo di “Intensive Quench” autocarro. 1 – un carrello; 2 – un cilindro pneumatico per lo spostamento verticale del carrello con l’aiuto di un sistema di l supporto (base); 4 – un magazzino; 5 – coltelli per la presa di un assale; 6 – un induttore di circuito longitudinale; 7 - un p orientabili; 9 – un porta inferiore di una camera di raffreddamento; 10 – una piastra; 11 - ruote orientabili; 12 - un porta fi camera di raffreddamento; 13 – spirale a induzione per il controllo della qualitŕ della tempra; 14 – una griglia; 16 - un cilin dro pneumatico per lo spostamento orizzontale del carrello; 17 e 15 – una leva e un cilindro pneumatico di ricarica da un prisma di un mezzo d una vasca di tempra; 18 – Una vasca per il raffreddamento finale degli assali; 19 – uno scivolo di scarico; 20, 27 - blocchi; 2 Fig. 4 – System employing a rotating tions of aqueous PAG quenchant solutions. Currently, dies are quenched in air-water sprays surrounding the entire sur- face. However, the working side of the dies are intensively quenched as shown in Fig.5. The quenching process is inter- low 2 x Ms (martensite start) temperature. This technology Belarus. [23] The distinctive feature of this controlled complicated form is localized. This is a characteristic of the die quenching process. In this process, the cooling of the working face of the die and the back side of the die is perfor- med at different rates in order to provide the desired hard- Hardness,HRC 40Cr (4140)4037 M18 Bolt5160H Bar Oil42.751-4760.4 IQ54.858-6063.4 Part Core Hardness*,HRC OilIQ 5661 45x264 mm kingpin**3048 yway shaft*** 3150 4247 orged wedge 2938 *) Parts were tempered at the same temperature after intensive quen- hing and oil quenching. **) Reference 13; ***) Reference 26 TRATTAMENTI TERMICI ness in these two different areas. D. EXAMPLES OF INTENSIVE QUENCH PROCESSING The patented IntensiQuenchSM intensive quenching pro- cess [2] has been validated by hundreds of laboratory and low. Hardening and Mechanical Property Improvement Fig. 5 – Die quenching using an intensive quenching process with air-water sprays. Fig. 5 – Tempra di uno stampo mediante l’impiego di un processo Fig. 6 – Proposed intensive quenching process for use with high concentration of aqueous PAG polymer solutions. Fig. 6 – Utilizzo del processo di “Intensive Quench” finalizzato all’impiego con una soluzione acquosa di polimero PAG ad alta various types of parts and different steel alloys. As expected, the as-quenched hardness was improved relative to conven- tional quench oil for AISI 4140, and M18 bolts and an AISI 5160H steel bar as shown in Table 1 and no quench cracks The results of a more extensive study comparing the corehardness after quenching and tempering for intensive andconventional quenching processes with a broader range of steel alloys is shown in Table 2 for steel alloys such as: car- bon, medium alloy, boron and bearing steels [25]. Once again, significant improvement in core hardness no cracking was observed with parts produced from an optimized inten- sive quenching process was observed. Another example illu- strating the substantial improvement in through hardening capability relative to conventional oil is provided in Table 3 able 1 – As–quenched Hardness for Different Materials (Parts were through-quenched). ab. 1 – Durezza di diversi materiali allo stato temprato (tempra profonda), able 2 – As-Tempered Core Hardness Improvement. ab. 2 – Incremento di durezza in profonditŕ dopo rinvenimento. Hardness,HRCHardened SurfaceCoreDepth,inch IQ52.050.2Hardened through Oil50.036.51/8Ó Surface5-10%0% Core15-20%2-5% Microstructure empered martensiteTempered martensite with traces and bainiteof bainite in the core Grain SizeASTM 8ASTM 9 TRATTAMENTI TERMICI 86B30 steel. The enhanced hardenability provided by the in- Fig. 7 – a) As-Quenched Hardness Distribution for Ř 73 mm 1547 Steel Cylinder. b) empered Hardness 1547 Steel Cylinder. durezza in un cilindro di b) Distribuzione della durezza in un cilindro di acciaio 1547 Maximum Crack Length,Total crack Area,x106 µ µ OilIntensiveOilIntensive 5,0001.0000 10,0004.45.413.822.4 15,00017.112.4163.894.4 TRATTAMENTI TERMICI surface to -613 MPa at a depth of 0.13 mm from the surface. (The lower values at the surface are due to the occurrence of shown in Figure 8b. Although Figure 8c shows that shot Similar results were obtained for AISI 5160H automotive leaf springs (76 mm wide, 16 mm thick leafs formed with 44 fatigue life for the intensively quench leafs was about 45% Fatigue tests showed that, on average, the intensively quen- PropertyOil QuenchIntensive QuenchImprovement(%) Yield Strength (MPa)830-1050140033.3 ensile Strength (MPa)950-1125150033.3 Impact Strength 20ˇC (J)30-60100-13066.7-116.7 Elongation (%)12-1815---- Reduction in Area (%)50-6563---- property comparison of ab. 5 – Confronto delle forcelle in 15B35H, temprate in olio o con processo IQ. improvement due to improved mechanical properties and the presence of compressive surface stresses. Table 6 provi- des a summary of the improvement of the service life of the cularly noteworthy is the average improvements achievable using parts made of plain carbon steel which is 7.6-8.0 times steel and quenched in oil. This means that by using an inten- 2. Reduction of Part Distortion The effect of intensive quenching on hardness and distortion ruck half-axles4340 (oil quench)1045 (intensive quench)76024 Shafts81B40 (oil quench)1045 (intensive quench)80025 PunchesShock-resisting S5100- PunchesHigh-speed steel (equivalent to M2)50-10026 Dies5210050-10027 orklift forks 15B35H20- Automotive coil springs925930- Automotive leaf springs516085- Pulverize coil springs8660300- Note:*) Based on actual cycle test data able 6 – Comparison of Sealed QuenchSealed Quench Furnace Heated/Furnace Heated/ Hot Oil QuenchedIntensively Quenched HRC Surface43.251.457.4 HRC Core32.131.050.0 Distortion (mm)0.20-0.360.25-0.510.08-0.12 TRATTAMENTI TERMICI using feeler gauges as shown in Fig. 9. The accuracy of the- se measurements was ±0.025 mm. The results of this study are summarized in Table 8. The da- greatest surface and core hardness. Also, the intensively quenched shafts exhibited substantially less distortion than 3. Intensive Quenching of Carburized Parts These results have shown that typically carburization cycles N In summary, intensive processes have been shown to increa- se part hardness and strength, while at the same time provi- ding less part distortion on typical products made of various Fig. 9 – Measurement of keyway shaft distortion. Fig. 9 – Misura della distorsione di un albero con intaglio. Fig. 10 – Hardness distribution throughout 8617 bearing cage ab. 8 – Misura della durezza albero (lega 1045, mm, intaglio 6.4 X 6.4 mm ). TRATTAMENTI TERMICI Fig. 11 – Hardness distribution throughout 4137 forged “Shoe” Cross section of 110x116 mm and case depth of 1.5-2.0 mm. Fig. 11 – Distribution della durezza entro un forgiato di 4137 con sezione trasversale di 110x116 mm e profonditŕ steel types. Computer process modelling may be used to fa- cilitate the design of intensive quenching processes. Some REFERENCES [1] N. I, KOBASKO AND N. I., PROKHORENKO, ŤQuenching Cooling Rate Effect on Crack Formation Case DepthCycle Time (mm)Reduction (%) Universal joint cross86201.540 Bearing cage86171.850 Crankshaft86201.540 Railroad part41302.050 Railroad part41382.0Comp.elimin. able 9 – Carburization cycle reduction for different parts. TRATTAMENTI TERMICI B.L. FERGUSON, A.M. FREBORG AND G.J. PE- TRUS, ŤModeling to Investigate Sensitivities to Heat reat Process Variables, in Heat Treating … Procee- dings of the 21st Conference, Eds. S. Shrivastava and Specht, 5-8 November, 2001, ASM International, [18] M.A. ARONOV, N.I. KOBASKO, J.A. POWELL, AND D.V. LIPNICKI, ŤPeculiarity of Intensive Quen- ching Processes and EquipmentŽ, IFHTSE 2002 Con- gress, Columbus, Ohio, 2003, ASM International, Ma- [19] E.I. NATANZON, V.I. ZILBERBERG AND V.F. LY- SENKO, ŤClose-Die Forging of Half-Axles on the au- tomatic LineŽ, Automotive Industry, 1977, Vol. 2, p. [20] K.Z. SHEPELYAKOVSKY, Hardening of Parts by Ca- se Hardening Using Induction Heating, Mashionstroe- nie, Moscow, 1972, p. 287. ABSTRACT MIGLIORAMENTO NELLA PRODUZIONE DI PARTI AUTOMOBILISTICHE MEDIANTE ILPROCESSODIŤINTENSIVE QUENCHŽ ole chiave: trattamenti termici, processi Il processo di “Intensive Quench - IQ” offre enormi vantag-