Uniform and Intense Cooling During Hardening Steel in Low Concentration of Water Polymer Solutions

The possibility of decreasing water polymer concentration, decreasing alloy elements in steel, decreasing distortion of steel parts, and increase service life of machine components and tools during quenching is widely discussed in this paper based on achievements of modern physics. Instead of quenching alloy and high alloy steel in oils or high concentration of water polymer solutions, the quench of the optimal hardenability steel in low concentration of inverse solubility polymers in water is proposed. Physics of the new approach and new technologies is explained by author. It consists in creation of a thin polymeric insulating layer during quenching of steel parts in low concentration of inverse solubility polymers in water that decreases initial heat flux density below its critical value. Due to this fact, the film boiling during quenching is completely absent and it allows use of the optimal hardenability steel instead of alloy steels containing costly alloy elements. Accelerated cooling of the optimal hardenability steel in low concentration of water polymer solution results in creation of high surface compressive residual stresses and super strengthening of material that increases service life of machine components and tools. It is underlined in the paper that along with the use of a thin polymeric insulating layer, the resonance effect can be used for destroying the film boiling process based on implementation differernt kinds of hydrodynamic emitters. The proposed new technology saves materials, increases service life of steel parts and improves environment condition in heat treating industry. The patented technologies and processes can be used by engineers and scientists and can bring the great benefits if widely implemented in the practice.

www.videleaf.com achievements of modern physics. Instead of quenching alloy and high alloy steel in oils or high concentration of water polymer solutions, the quench of the optimal hardenability steel in low concentration of inverse solubility polymers in water is proposed. Physics of the new approach and new technologies is explained by author. It consists in creation of a thin polymeric insulating layer during quenching of steel parts in low concentration of inverse solubility polymers in water that decreases initial heat flux density below its critical value. Due to this fact, the film boiling during quenching is completely absent and it allows use of the optimal hardenability steel instead of alloy steels containing costly alloy elements. Accelerated cooling of the optimal hardenability steel in low concentration of water polymer solution results in creation of high surface compressive residual stresses and super strengthening of material that increases service life of machine components and tools. It is underlined in the paper that along with the use of a thin polymeric insulating layer, the resonance effect can be used for destroying the film boiling process based on implementation differernt kinds of hydrodynamic emitters. The proposed new technology saves materials, increases service life of steel parts and improves environment condition in heat treating industry. The patented technologies and processes can be used by engineers and scientists and can bring the great benefits if widely implemented in the practice.

Introduction
For the wide implementation of intensive quenching processes into practice, two companies were established in 1999 and 2000 dealing with intensive quenching processes. The first company was established in 1999 in Akron, Ohio, USA and its name is IQ Technologies Inc (IQT). The second company was established in 2000 in Kyiv, Ukraine and its name is Intensive Technologies www.videleaf.com Ltd (ITL). A continuous cooperation between both companies has been lasting since 2000. The aim of IQT is design of equipment and commercialization of intensive quenching processes worldwide while ITL pays its main attention to academic investigations and designing appropriate software for controlling and governing intensive quenching processes in the practice. The IQT company made a great progress in hardening the small and average machine components and tools while ITL is developing new technologies for more larger steel components and tools which cannot be quenched in developed by IQT fixtures. Currently, there are several Ukrainian Patents which make a green pass for their implementation in the USA if properly developed and tested [1][2][3]. This paper discusses the physics of accelerated cooling in water solutions of low concentration polymers and provides possibilities for intense hardening of large wind gears, rollers, large shafts and rotors, made of optimal hardenability steel, to save energy, materials, increase their service life and improve environment condition.

Intense Quenching when Cooling in Low Concentration of Water Polymer Solutions
As known, the real heat transfer coefficient during transient nucleate boiling process is evaluated as a ratio of the heat flux density produced by bubbles to the overheat of the boundary layer [4,5], i.e.
It cannot be used for correct temperature gradients calculation during transient nucleate boiling process. As seen from Table 1, the real HTC is almost 7 times larger as compared with the effective HTC [4,6]. According to author [4], the average heat flux density q during nucleate boiling is proportional to the cube of temperature difference is small from the very beginning of cooling. Table 2 shows the real heat transfer coefficients in W/m 2 K which are responsible for developing temperature gradients during quenching of steel parts. Calculations of HTCs were made for maximal critical heat flux density of water salt solutions which was equal to 15 MW/ m 2 [4]. Dimensionless correlations of authors [4,6] were used for this purpose. www.videleaf.com Results of calculations presented in Table 2 actually are experimental data because dimensionless equations of Tolubinsky and Shekriladze are based on thousand of accurate experiments [4,6].
As seen from Table 2, real HTCs are very large when heat flux density approaches the critical value 15 MW/m 2 . It means that in the Inconel 600 standard probe 12.5 mm in diameter maximal temperature gradients are formed because Biot number Bi tends to infinity (see Table 3). It is very important to calculate temperature gradient during quenching small and large steel parts. As an example, let's consider quenching truck semi-axle 40 mm (0.04 m) in diameter which is cooled in water flow of 8 m/s and large roller 1 m in diameter which is cooled in still water at 30 o C where natural convection takes place. Cooling steel parts in water flow was discussed in previous published papers [7][8][9]. Heat transfer coefficients for quenching cylindrical steel parts in water flow in round fixture one can find in Ref. [7,10] (see Table 4). Heat transfer coefficients (HTCs) of natural convection during quenching large steel parts in still water were calculated using well known Eq. (4) [10]:  Table 4). Having these accurately calculated data, we'll investigate temperature gradients in semiaxle and roller during their hardening in water flow and still water. Since during quenching HTCs are a little bit variable, depending on size of semi-axle and water temperature, we'll use for quenching in still water and 25000   for quenching in water flow of 8 m/s. For calculating temperature gradients in semiaxle and roller during quenching, one can use universal correlation (5) [11,12]  61 . Cooling semiaxle in water flow 8 m/s provides very intensive quenching creating huge temperature gradient in semiaxle. The same huge temperature gradient is formed during quenching of large roller in still water. It means that for big roller during quenching in still water, the cooling process for it is also very intensive quenching. This conclusion is extremely important because customers don't need very expensive and complicated equipment. The cooling process of large steel parts can be performed just in large quench water tanks without complicated and costly equipment. However, there is a trick here. During immersion large steel parts into liquid, developed film boiling starts immediately, making cooling process slow. One should eliminate film boiling process from the very beginning of cooling prior to provide intensive quenching for large steel parts in still water. Very cheap and simple method www.videleaf.com of eliminating film boiling process during quenching is discussed below.

Elimination Film Boiling Process by Creation a Thin Surface Insulating Layer
The idea on elimination film boiling during quenching via creation artificial surface insulating layer before quenching was forwarded by authors in 1987 [13]. In 1996 authors [14] discovered that low concentration (1%) of inverse solubility polymer in water provides very intensive and uniform cooling even during testing of silver spherical probe 20 mm in diameter. In 2012 author [15] explained this unusual fact by considering Eq. (6): In the paper is considered an initial heat flux density during quenching of cylindrical specimen received by solving inverse problem (IP). Results of calculations are presented in Figure 1. www.videleaf.com Let's consider now how the thickness of insulating polymeric layer  decreases initial heat flux density q in . Table 5 provides the value  depending on thickness of insulating layer .  Table 6 shows decrease of maximal initial heat flux density q max depending on thickness of insulating layer  . It was assumed that thermal conductivity of insulating layer was 0.2 W/mK. www.videleaf.com  19 15.8 13.6 11.9 10.5 Tolubinsky studied extreme transient nucleate boiling processes and he came to conclusion that the well known ratio (7) q q cr cr 2 1 0 2  .
is true during conventional processes. In extreme condition during shock boiling the well known ratio (7), depending on extreme cooling rate, can be [4]: For conventional processes, according to Tolubinsky and Kutateladze [4,5], the first critical heat flux densities for water depending on the underheat  uh S m T T   are provided in Table 7.  [14] (see Table 8). Authors [16] used the same idea for eliminating film boiling process during quenching steel parts in mineral oil adding to it low amount of PIB. Fig. 2 clearly shows decreasing duration of film boiling process when concentration of PIB in mineral oil increases and disappear completely at concentration 3% PIB in mineral I-20A oil. www.videleaf.com It means that insulating layer is excellent tool for eliminating film boiling processes during quenching steel parts in different liquid quenchants.

Difference between IQ-2 and IQ -3 Processes
From the point of practical use, it is very important to find out what is difference between IQ-2 and IQ -3 processes when switching from one to another depending on their size and condition of cooling. As known, when initial austenitizing temperature is fixed at 850 o C and bath temperature at 20 o C, then duration of transient nucleate boiling process can be presented by simplified Eq. (7) [17,18]: In this case, the value  function of the convection Biot number Bi [19,20] and duration of transient nucleate boiling process can be formulated as follows. Duration of transient nucleate boiling is proportional to square of thickness of steel part, inversely proportional to thermal conductivity of steel, depends on configuration of steel part quenched and cooling characteristics of quenchant if austenitizing and bath temperatures are fixed. During transient nucleate boiling surface temperature of steel part maintains at the level of boiling point of a liquid insignificantly differs from it. The established new characteristics were used for developing austempering process via cold liquids [6] for reconstruction of surface temperature during nucleate boiling and for estimation the cooling difference between IQ-2 and IQ -3 processes (see Figure 1 a) Table 9, temperature difference between IQ -2 and IQ -3 processes is insignificant.  Table 10) that significantly differs these two situation from each other. When performing intensive quenching IQ -2 or IQ -3 processes, engineers every time must take into account martensite start temperature M S .

Optimal Hardenability Steel
Optimal hardenability steel was invented to provide optimal hardened layer during quenching in any cooling condition. In early patented! Q -3 technology optimal hardened layer in trough hardened steel was achieved by interruption intensive quenching at proper time using Eq. (10)  . . (13) Note that low hardenability steel of authors [26] can be used for intensive quenching of small steel parts and cannot be used for large steel parts. Moreover, technological process is expensive and complicated. Optimal hardenability steel makes technological process very simple, cheap and it can be used for any size and form of steel part. For this purpose the special software is used which was designed by Intensive Technologies Ltd. For designing such software a huge amount of experiments were carried out to calculate dimensionless number Kn which is presented in Eq. (13).
Difference between intensively quenched low hardenability steel and optimal hardenability steel quenched in any condition is shown in Figure 4 [27,28]. As one can see from Eq. (13) and Fig. 4 ...... (14) Effect the form of steel part on chemical composition of optimal hardenability steel is discussed in the Ukrainian Patent No. 114174 [2].

Benefits providing by Intensive Quenching in Low Concentration of Polymers
Currently, IQ -3 technology is successfully used in the USA [7]. However, it is rather complicated and costly and it is a reason for headache when thin holes are present in steel parts which endorse quench crack formation, especially in hardened layer. Engineers try to plug holes or use some special tricks which eliminate crack formation during quenching. However, such operation makes technological process more costly and not enough convenient. Instead of costly and complicated process IQ -3, the new technology is discussed in this paper which was developed by Intensive Technologies Ltd, Kyiv, Ukraine. It allows cardinally simplify technological process, make technology cardinally cheaper and repeatable During quenching steel parts with thin holes in low concentration of water polymer solutions, the thin holes are partially plugged automatically due inverse solubility phenomenon. The simple and universal quench tank for performing such operation is shown in Figure 5. www.videleaf.com Figure 5: Prinsipal scheme of performing IQ -2 and IQ -3 processes with use of low concentration polymers: 1 is quench tank; 2 is level quenchant in a tank; 3 is steel parft (large gear or large bearing ring); 4 is surface polymeric layer; 5 is liquid stream; 6 is hydrodynamic emitter; 7 is holder; 8 is outlet tube; 9 is pump.
Agitation of quenchant 2 in quench tank 1 is provided by hydrodynamic emitters that generate resonance frequency to eliminate effectively film boiling process during quenching steel parts in liquid media. Along with generating the resonance effect, pumping of liquid in quench tank creates turbulent that significantly increases convective heat transfer coefficients during quenching. Note that it can be used different kinds of hydrodynamic emitters which were discussed by authors [3,27]. Agitation of liquid should be not enough strong to prevent dissolving of insulating polymeric layer that eliminates film boiling process during quenching. One of them is shown in Figure 6 [3]. 4a generator of waves in liquid; 5a regulator of the wave frequency;6a water flow combined with the generated waves and directed to load being quenched [3,27].
Exploring the low concentration of water polymer solutions combined with the use of emitters, providing resonance waves for eliminating film boiling, it is possible to create high enough temperature gradients in quenched steel parts because transient nucleate boiling process. After such intensive cooling, if surface temperature of steel parts during selfregulated thermal process is below the martensite start temperature M S , the high compressive residual stresses are formed and superstrengtheing of material takes place. As known, very large wind gears (see Figure 7) are made of carburized high alloy steel [29]. It is possible to make wind gears (see Figure 7) exploring optimal hardenability steel containing 0.6% C,wt with the significantly reduced alloy elements in it. Benefits of intensive quenching processes are provided in Table 7 and Table 8 [7,26,30].
. www.videleaf.com  The accurate experimental results on essential benefits of intensively quenched steel parts made from low hardenability steel [26] (see Table 8) can be extended for larger steel parts if www.videleaf.com Eq (13) is satisfied. In this case, surface hardened layer should be thicker to provide the same surface residual stresses and supertrengthening effect after intensive quenching of larger steel parts. Table 9 shows the benefits of new technology.  [1][2][3]. Transient nucleate boiling process during quenching of steel parts in water and water solutions is very intensive by itself due to intense acting of thousands vapor bubbles [4,5]. New characteristics of transient nucleate boiling process were discovered by author [17,18] which were also used for designing new technology. Engineers in heat treating industry, as a rule, considered effective heat transfer coefficients during nucleate boiling which can differ from real HTCs ten times showing always slow cooling [15]. It was widely shared a wrong opinion that nucleate boiling cannot provide enough intensive quenching that is why very powerful and costly pumps were used to agitate quenchants in quench tanks. It is shown in this paper that destroying film boiling process provides intensive quenching during hardening of steel parts. If so, the technological process become very simple and cheap that can make it widely used globally. One more thing is connected with the proposed new technology. Optimal hardenability steel provides optimal hardened layer and maximal surface compressive residual stresses even after complete cooling. It means that process of cooling can be interrupted at proper time to create nano-bainitic microstructure at the core of steel parts [31][32][33][34]. In this case additional strengthening of steel parts will be accumulated. This problem was discussed in the recently published paper [8]. ITL Co is developing software for governing new technological processes and is planning to organize small teams of engineers in different countries to start saving material, energy increasing service life of steel parts and decreasing cost of their production and simultaneously improving environment condition. .

Conclusion
Large steel parts, beginning from thickness 50 mm (0.050 m) and larger, can be intensively and uniformity quenched in slowly agitated by hydrodynamic emitters of the low concentration of inverse solubility water solution polymer that eliminates completely film boiling making cooling process intensive.
In this case the high surface compressive residual stresses and super strengthening effect in quenched steel parts are achieved due to use patented in Ukraine the optimal hardenability steel www.videleaf.com tolerated to size and form of hardened component. The proposed new technology saves materials, due to low concentration water polymer solution and reduced percentage of alloy elements in steel, decreases corrosion due to elimination carburization process, increases service life (due to high surface compressive residual stresses and super strengthening effect) and improves environment condition. Along with the mentioned benefits the proposed technology and equipment is significantly cheaper as compared with the existing IQ processes and is rather simple in implementation in heat treating industry. Since the new technology can bring very huge benefits, it makes sense to start testing it in shops of big companies.