Claims:We claim:
1. A method (600) for determining Finish Rolling Temperature (FRT) of hot roll mill based on non-recrystallization temperature (Tnr) of steel, the method (600) comprising:
generating (601), based on multi-deformation test, a relationship between stress and strain;
generating (602) a relationship (MFS Vs 1/T) between Means Flow Stress (MFS) and inverse absolute temperature based on the relationship between the stress and the strain; and
determining (603) the non-recrystallization temperature (Tnr) based on the relationship between the MFS and the inverse absolute temperature.
2. The method (600) as claimed in claim 1, wherein the method (600) further comprises:
determining (604) range of non-recrystallization temperature (Tnr) by changing parameters of the multi-deformation test.
3. The method (600) as claimed in claim 1, wherein the method further comprises:
determining (605) the FRT based on the determined non-recrystallization temperature (Tnr).
4. The method (600) as claimed in claim 1, wherein the step of determining (605) comprises:
calculating the non-recrystallization temperature (Tnr) when change in the relationship between the MFS and the inverse absolute temperature is detected.
5. The method (600) as claimed in claim 2, wherein the parameters are reheating temperatures, pass strain and strain rates.
6. The method (600) as claimed in claim 1, wherein the multi-deformation test is torsion test.
7. A system (500) to determine Finish Rolling Temperature (FRT) of hot roll mill based on non-recrystallization temperature (Tnr) of steel, the system (500) comprising:
a data processing module (505) coupled with a processor (501) and a memory (503) to:
generate a relationship between stress and strain based multi-deformation test;
generate a relationship between Means Flow Stress (MFS) and inverse absolute temperature based on the generated relationship between the stress and the strain; and
a non-recrystallization temperature (Tnr) determining module (506) coupled to the processor (501) and the memory (503) to:
determine, based on the generated relationship between the MFS and the inverse absolute temperature, the non-recrystallization temperature (Tnr).
8. The system (500) as claimed in claim 7, wherein the non-recrystallization temperature (Tnr) determining module (506)
determines range of non-recrystallization temperature (Tnr) by changing parameters of the multi-deformation test.
9. The system (500) as claimed in claim 7, wherein the non-recrystallization temperature (Tnr) determining module (506)
determines, based on the determined non-recrystallization temperature (Tnr), the FRT.
10. The system (500) as claimed in claim 7, wherein the non-recrystallization temperature (Tnr) determining module (506)
calculates the non-recrystallization temperature (Tnr) when change in the relationship between the MFS and the inverse absolute temperature is detected.
11. The system (500) as claimed in claim 8, wherein the parameters are reheating temperatures, pass strain and strain rates.
12. The system (500) as claimed in claim 7, wherein the multi-deformation test is torsion test.
, Description:A METHOD FOR DETERMINING FINISH ROLLING TEMPERATURE OF HOT ROLL MILL BASED ON NON-RECRYSTALLIZATION TEMPERATURE OF STEEL
FIELD OF INVENTION:
[001] The present subject matter described herein, relates to a method and a system for determining of finish rolling temperature (FRT) for steels through determining the non-recrystallization temperature (Tnr) using torsion test procedure.
BACKGROUND AND PRIOR ART AND PROBLEM IN PRIOR ART:
[002] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
[003] The non-recrystallization temperature (Tnr) is measured below which theoretically static recrystallization remains incomplete. Therefore, if the material is deformed below this particular temperature, there will be a definite chance of strain accumulation in the structure. As a result, pancaking and deformation bands can be visible in the structure. In recrystallized structure, ferrite nucleation usually occurs at the prior austenite grain boundaries. However, in the deformed structure, the same can also happen in the dislocation bands. This will lead to a finer grain size. This is explained in Figs. 1 and 2 [1].
[004] Unlike an evaporation temperature, Tnr is not a fixed temperature. Static recrystallization occurs in between two hot rolling passes. When hot rolling is conducted below Tnr, this recrystallization does not go to completion.
[005] Commonly, Tnr is determined experimentally. This is done by simulating the rolling passes and generate the stress-strain diagrams for each and individual passes. From there after calculating the mean flow stress (MFS) values, these are plotted against the inverse of absolute temperature. The Tnr is determined from the first inflection point in the curve. This is illustrated in more details below.
[006] After reheating, a sample is given multi pass deformation with a specific inter-pass time. For each pass a specific stress-strain diagram is generated. An example is given in Fig. 3 (a) [2]. Different regions in this diagram are identified based on the change in slope of the curve. This is very well manifested in Fig. 3(b) where MFS is plotted against inverse of absolute temperature. From region I to region II, the slope increases before it drops in region III, and again increases in region IV. It is important to note that from one region to the next, the temperature is dropping continuously. In the experimental simulations, the pass strains, strain rates, cooling rates and inter-pass times are always kept constant.
[007] From Fig. 3(b), four different zones can be distinguished:
i. In region I, since the temperature is high, austenite recrystallizes completely between passes and thus the change in MFS is solely due to the change in temperature.
ii. In region II, the slope increases rather quickly due incomplete recrystallization which leads to some sort of retained work hardening in the material.
iii. In region III, a significant drop in MFS indicates the formation of ferrite in the microstructure.
iv. In region IV, due to warm rolling of ferrite, slope increase slightly.
[008] Now the intersection of the regressions lines which can be fitted to regions I and II is defined as Tnr and the same for regions II and III determines the Ar3 [3]. Similar remarks apply to the Ar1, for regions III and IV. The MFS versus 1/T relationship in Fig. 3(b) is little curved around Tnr which implies the transition is more gradual.
[009] Since Tnr depends on inter-pass time, the simulations which involve 10 s and 20 s do not applicable for 1 s inter-pass time. In case of shorter inter-pass time (like 1 s) which usually happens in strip mill conditions, carbonitride precipitation does not play a significant role. Instead solute drag inhibited the recrystallization phenomenon [4].
[0010] For the quantification of the recrystallization behaviour, direct observation methods such as optical microscopy [5, 6] and indirect mechanical methods, such as multi-deformation tests can be employed [7-19]. The former is little tedious and time consuming. For this reason, the later technique is preferred.
[0011] Technical objective: To improve mechanical properties of hot rolled steel without changing chemical composition. It has been observed that rolling parameters has great impact on mechanical properties of the hot rolled steel. One of the parameter is Finish Rolling Temperature (FRT) which has direct relationship with mechanical properties of the hot rolled steels.
[0012] The information disclosed in this background of the disclosure section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.
OBJECTS OF THE INVENTION:
[0013] It is therefore the object of the present subject matter to overcome the aforementioned and other drawbacks in prior method/product/apparatus.
[0014] The principal objective of the present subject matter is to develop a method and a system to determine the non-recrystallization temperature (Tnr) during hot rolling for steels using torsion test procedure.
[0015] Another object of the present subject matter is to develop a method and system to determine finish rolling temperature (FRT) during hot rolling steels based on the determined non-recrystallization temperature (Tnr).
[0016] These and other objects and advantages of the present subject matter will be apparent to a person skilled in the art after consideration of the following detailed description taken into consideration with accompanying drawings in which preferred embodiments of the present subject matter are illustrated.
SUMMARY OF THE INVENTION:
[0017] One or more drawbacks of conventional method for determining of finish rolling temperature, and additional advantages are provided through the method as claimed in the present disclosure. Additional features and advantages are realized through the technicalities of the present disclosure. Other embodiments and aspects of the disclosure are described in detail herein and are considered to be a part of the claimed disclosure.
[0018] The present subject matter relates to a method for determining Finish Rolling Temperature (FRT) of hot roll mill based on non-recrystallization temperature (Tnr) of steel. The method comprises generating a relationship, i.e., plot between stress and strain based on multi-deformation test and generating a relationship (i.e., plot or graph MFS Vs 1/T) between Means Flow Stress (MFS) and inverse absolute temperature based on the generated relationship between the stress and the strain. Further, determining the non-recrystallization temperature (Tnr) based on the generated relationship between the MFS and the inverse absolute temperature.
[0019] In an aspect, the present method determines range of non-recrystallization temperature (Tnr) by changing parameters of the multi-deformation test.
[0020] In an aspect, the present method further determine the FRT based on the determined non-recrystallization temperature (Tnr).
[0021] In an aspect, the present method calculates the non-recrystallization temperature (Tnr) when change in the relationship between the MFS and the inverse absolute temperature is detected
[0022] In another embodiment, the present subject matter discloses a system to determine Finish Rolling Temperature (FRT) of hot roll mill based on non-recrystallization temperature (Tnr) of steel. The system includes a data processing module and a non-recrystallization temperature (Tnr) determining module coupled with a processor and a memory. The data processing module generate a relationship between stress and strain based multi-deformation test and generate a relationship between Means Flow Stress (MFS) and inverse absolute temperature based on the generated relationship between the stress and the strain. The non-recrystallization temperature (Tnr) determining module determine the non-recrystallization temperature (Tnr) based on the generated relationship between the MFS and the inverse absolute temperature.
[0023] In an aspect, the non-recrystallization temperature (Tnr) determining module determines the FRT based on the determined non-recrystallization temperature (Tnr).
[0024] It is to be understood that the aspects and embodiments of the disclosure described above may be used in any combination with each other. Several of the aspects and embodiments may be combined to form a further embodiment of the disclosure.
[0025] The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] It is to be noted, however, that the appended drawings illustrate only typical embodiments of the present subject matter and are therefore not to be considered for limiting of its scope, for the invention may admit to other equally effective embodiments. The detailed description is described with reference to the accompanying figures. In the figures, a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the figures to reference like features and components. Some embodiments of system or methods or structure in accordance with embodiments of the present subject matter are now described, by way of example, and with reference to the accompanying figures, in which:
[0027] Fig. 1 illustrates Rolling above Tnr results complete static recrystallization of austenite between rolling passes i and i+1 [1];
[0028] Fig. 2 illustrates rolling below Tnr, results partial recrystallization of austenite between rolling passes i and i+1: [1];
[0029] Fig. 3(a) illustrates stress-strain curves obtained from the test;
[0030] Fig. 3(b) illustrates mean flow stress (MFS) versus inverse absolute temperature plot;
[0031] Fig. 4 illustrates deformation schedule for the 13-pass torsion test;
[0032] Fig. 5 illustrates system for determining non-recrystallization temperature (Tnr), in accordance with an embodiment of the present subject matter;
[0033] Fig. 6 illustrates a method for determining non-recrystallization temperature (Tnr), in accordance with an embodiment of the present subject matter;
[0034] Fig. 7(a) illustrates Stress-strain curves obtained from the torsion test and fig. 7(b) illustrates mean flow stress (MFS) versus inverse absolute temperature plot for Steel 1;
[0035] Fig. 8(a) illustrates stress-strain curves obtained from the torsion test and Fig. 8(b) mean flow stress versus inverse absolute temperature plot for Steel 2;
[0036] Fig. 9(a) illustrates Stress-strain curves obtained from the torsion test and Fig. 9(b) illustrates mean flow stress (MFS) versus inverse absolute temperature plot for Steel 3;
[0037] Fig. 10(a) illustrates Stress-strain curves obtained from the torsion test and Fig. 10(b) illustrates mean flow stress (MFS) versus inverse absolute temperature plot for Steel 4;
[0038] Fig. 11 illustrates effect of reheating temperature on the Tnr values for the 4 investigated steels where all the experiments were carried out at a von Mises strain of 0.3 and at a strain rate of 10 s-1;
[0039] Fig. 12 illustrates effect of von Mises equivalent strain on the Tnr values for the 4 investigated steels where all the experiments were carried out at a reheating temperature of 1200°C and at a strain rate of 0.5 s-1; and
[0040] Fig. 13 illustrates Effect of strain rate on the Tnr values for the 4 investigated steels where all the experiments were carried out at a reheating temperature of 1200°C and at a strain of 0.3.
[0041] The figures depict embodiments of the present subject matter for the purposes of illustration only. A person skilled in the art will easily recognize from the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the disclosure described herein.
DESCRIPTION OF THE PREFERRED EMBODIMENTS:
[0042] While the embodiments of the disclosure are subject to various modifications and alternative forms, specific embodiment thereof have been shown by way of example in the figures and will be described below. It should be understood, however, that it is not intended to limit the disclosure to the particular forms disclosed, but on the contrary, the disclosure is to cover all modifications, equivalents, and alternative falling within the scope of the disclosure.
[0043] The terms “comprises”, “comprising”, or any other variations thereof used in the disclosure, are intended to cover a non-exclusive inclusion, such that a device, system, assembly that comprises a list of components does not include only those components but may include other components not expressly listed or inherent to such system, or assembly, or device. In other words, one or more elements in a system or device proceeded by “comprises… a” does not, without more constraints, preclude the existence of other elements or additional elements in the system or device.
[0044] In the present subject matter, non-recrystallization temperature (Tnr) is considered as an important factor to decide finish rolling temperature. Further, the finish rolling temperature (FRT) has great impact on mechanical properties of hot rolled steel, such as bar. The non-recrystallization temperature (Tnr) is a temperature below which static recrystallization in a material remains incomplete which leads to a pancaked or deformed structure at high temperature during hot rolling. This type of structures helps in developing fine grained microstructure when the material is cooled to room temperature. Finer structure shows better mechanical properties in comparison to a coarse-grained structure. Therefore, finish rolling below the non-recrystallization temperature (Tnr) is one of the ways to produce high strength material without changing the composition. Thus, knowing the Tnr range for a particular steel assists in deciding the finish rolling temperature (FRT) during hot rolling.
[0045] It should be noted that the description and figures merely illustrate the principles of the present subject matter. It should be appreciated by those skilled in the art that conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present subject matter. It should also be appreciated by those skilled in the art that by devising various arrangements that, although not explicitly described or shown herein, embody the principles of the present subject matter. Furthermore, all examples recited herein are principally intended expressly to be for pedagogical purposes to aid the reader in understanding the principles of the present subject matter and the concepts contributed by the inventor(s) to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions. The novel features which are believed to be characteristic of the present subject matter, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures.
[0046] These and other advantages of the present subject matter would be described in greater detail with reference to the following figures. It should be noted that the description merely illustrates the principles of the present subject matter. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described herein, embody the principles of the present subject matter and are included within its scope.
[0047] Referring to Figure 5 illustrating a system 500 for determination of non-recrystallization temperature (Tnr) and determining Finish Rolling Temperature (FRT) based on determined Tnr range to improve mechanical properties of hot rolled steel in hot rolling process according to an embodiment of present invention. The system 500 includes a processor(s) 501, an interface(s) 502, and a memory 503. The processor(s) 501 may be implemented as one or more microprocessors, microcomputers, microcontrollers, digital signal processors, central processing units, logic circuitries, and/or any devices that manipulate data based on operational instructions given or stored in the memory 503. Among other capabilities, the one or more processor(s) are configured to fetch and execute computer-readable instructions and one or more routines stored in the memory. The memory 503 may store one or more computer-readable instructions or routines, which may be fetched and executed to determine probability of clogging over a network service. The memory 503 may include any non-transitory storage device including, for example, volatile memory, such as RAM, or non-volatile memory, such as EPROM, flash memory, and the like.
[0048] The interface(s) 502 may include a variety of interfaces, for example, interfaces for data input and output devices referred to as I/O devices, storage devices, and the like. The interface(s) 502 may facilitate communication of the system 500 with various devices, such as display unit 508 and torsion test machine. The interface(s) 502 may also provide a communication pathway for one or more components to communicate with torsion test machine which are used for conducting research related to steel rolling. In an implementation, the present system 500 may be implemented in the torsion test machine. In another implementation, the system 500 may be implement away from the torsion test machine and input data from the torsion test machine is inserted into the system 500 for further processing.
[0049] The system 500 includes module(s) 504 and data 507. The module(s) 504 and the data 507 are communicatively coupled with the processor 501 for processing of the instructions. The modules 504 further includes a data processing module 505 and a non-crystallization temperature (Tnr) determining module 506 that may be implemented as a combination of hardware and programming (for example, programmable instructions) to implement one or more functionalities. In examples described herein, such combinations of hardware and programming may be implemented in several different ways. For example, the programming for the processing module 505 and the non-crystallization temperature (Tnr) determining module 506 may be processor executable instructions stored on a non-transitory machine-readable storage medium. In the present examples, the machine-readable storage medium may store instructions that, when executed by the module(s) 504, provides range of non-crystallization temperature (Tnr) based on input parameters and output of the torsion test machine.
[0050] In operation, the data processing module 505 receives the data related to stress and strain from the torsion test machine and generates a relationship, i.e., a plot a curves of stress-strain. Further, the data processing module 505 generate a relationship (MFS Vs 1/T), i.e., a graph in between the Means Flow Stress (MFS) and inverse absolute temperature (I/T) based on the generated relationship between the stress and the strain for steel.
[0051] The non-recrystallization temperature (Tnr) determining module (506) determine the non-recrystallization temperature (Tnr) based on the generated relationship between the MFS and the inverse absolute temperature. The non-recrystallization temperature (Tnr) determining module (506) calculates the non-recrystallization temperature (Tnr) when a change is observed in the slope of the plot of MFS Vs 1/T. In the present subject matter, it is observed that reheating temperature, stress and strain rate impacts the non-recrystallization temperature (Tnr) of the hot rolled steel. Accordingly, the non-recrystallization temperature (Tnr) determining module (506) determines range of the non-recrystallization temperature (Tnr) by changing parameters, such as reheating temperature, stress, and strain rate of the torsion test.
[0052] The non-recrystallization temperature (Tnr) determining module (506) determine or predict the finish rolling temperature (FRT) of the steel being hot rolled based on the range of non-recrystallization temperature (Tnr).
[0053] The determined range of non-recrystallization temperature (Tnr) is displayed in the display unit 508 coupled to the system 500. The display unit 508 may be display unit of the torsion machine.
[0054] FIG. 6 illustrates a method 600 for determining non-recrystallization temperature (Tnr) of steel being hot rolled, according to an implementation of the present disclosure. The order in which the method 600 is described is not intended to be construed as a limitation, and any number of the described method blocks can be combined in any appropriate order to carry out the method 600 or an alternative method. Additionally, individual blocks may be deleted from the method 600 without departing from the scope of the subject matter described herein.
[0055] At step 601, data related to stress and strain of the steel is received by the data processing module 505. Further, a relationship between stress and strain is generated for further processing.
[0056] At step 602, generated relationship between the stress and strain is used to generate a relationship between Means Flow Stress (MFS) and inverse absolute temperature (1/T).
[0057] At step 603, change in the relationship between the MFS and 1/T is detected to determine the non-recrystallization temperature (Tnr) of the steel. Further, at step 604, a range of non-recrystallization temperature (Tnr) is determined by varying the parameters, such as reheating temperature, stress, and strain rate of the torsion test.
[0058] At step 605, the finish rolling temperature (FRT) is decided based on the determined range of the non-recrystallization temperature (Tnr) of the steel to improve mechanical properties of the hot rolled steel.
[0059] The present invention was performed on the four different steels to calculate their non-crystallization temperature (Tnr) using torsion test. The experimental parameters namely reheating temperatures, pass strain and strain rates were varied in order to see the changes in Tnr. For Steel 1, Steel 2, Steel 3 and Steel 4 the experimental Tnr values varies in the range 850 - 924°C, 846 - 895°C, 876 - 917°C and 863 - 910°C, respectively. It is observed in the present subject matter that the reheating temperature has a positive influence on the Tnr values while the strain and strain rates have the opposite effect. From these Tnr values for different steels, finish rolling temperatures can be decided.
Experimental Materials
[0060] In the current study four different grades of steels were investigated. The chemical compositions of the steels are given in Table 1. Initially the steels were cast in a vacuum induction furnace. In order to break the cast structure subsequently they were forged. From these forged specimens, torsion samples were machined.
[0061] Table 1. Chemical compositions (wt. %) of the investigated steels.
Steel C Mn Si Nb Cr Al Mo V
1 0.18-0.22 1.5-1.6 0.9-1.1 0.03-0.05 0.9-1.1 - 0.05-0.15 -
2 0.13-0.17 4.45-4.55 0.9-1.1 - - 0.3-0.4 - -
3 0.02-0.06 1.3-1.4 0.3-0.4 0.02-0.03 0.5-0.7 - - -
4 0.03-0.07 1.2-1.3 0.35-0.45 - - 0.03-0.1 0.1-0.2 0.2-0.3

[0062] Torsion testing:
[0063] The torsion testing is performed on known torsion testing machine to determine the non-crystallization temperature (Tnr).
[0064] Theory and understanding:
[0065] In the torsion test, the strain varies linearly from zero along the axis to a maximum at the surface. As calculated by Nadai [20], the shear stress, t, at the surface is given by:
t = (1/2pr3)(3T+ ? dT/d?) ….(1)
where T is the torque, dT/d? the slope of the torque-twist curve, r the radius of the specimen and ? the amount of twist in the specimen (radians).
[0066] Later, Fields and Backofen [21] proposed that dT/d? = (T/?)(n+m). Here n is the twist sensitivity coefficient and m the twist rate sensitivity coefficient. This leads to:
t = (1/2pr3)T(3+n+m) ….(2)
[0067] Now at temperatures above 500°C, n is negligible and m can be taken as approximately 0.3. Therefore,
t = 3.3T/2pr3 ….(3)
[0068] Again t = s/v3 where s is the von Mises equivalent stress.
[0069] Therefore, s = 3.3v3T/2pr3 ….(4)
[0070] The equivalent strain e = r?/v3L ….(5)
where L is the length of the specimen. Despite claims to the contrary [22], the von Mises description is the best suited for torsion experiments [23-25 reference].
Thermomechanical Schedule
[0071] The thermomechanical schedule that is followed in the current study is depicted in Fig. 4. Initially the samples were heated up to the reheating temperature zone at a heating rate of 5°C/s. Three different temperatures, namely 1100, 1200 and 1250°C were chosen for this purpose. At these temperatures, they were soaked for 5 mins. After that they were cooled at a cooling rate of 5°C/s till the temperature reached at 1075°C. Here the samples were held for 10 s and then the first deformation was employed. For the subsequent deformations 25°C temperature intervals were selected. Since for this simulation a 13 pass deformation cycle was picked, the last pass was given at 875°C temperature. For every 13 pass cycle the von Mises equivalent strain and strain rates were kept constant to a particular value. A wide range of equivalent strain and strain rates were tried. The different strain and strain rate values were 0.1, 0.2, 0.3, 0.4 and 0.01, 0.5, 10 s-1 respectively. Likewise, the inter-pass time was also kept constant for a particular simulation. Here the resultant cooling rate became a function of interpass time. In other words, higher the interpass time lower was the cooling rate between two consecutive passes and vice versa. This was altered between 1 to 5°C/s. It is important to note that the experimental parameters, namely reheating temperatures, pass strain and strain rates were varied in order to see the changes in Tnr.
Determination of Tnr from the Torsion Test
[0072] Torsion tests were performed in order to obtain MFS vs. l/T information under continuous cooling conditions. Calculation of the MFS from stress-strain data (obtained using equations (4) and (5)) was done by evaluating the area under the curve by numerical integration which is then normalized by strain. It is calculated by summing, over the entire deformation, the product of strain increment for each data reading, ?e, and the average stress in that increment sav [26, 27]:
….(6)
where ea and eb denote the beginning and end of the strain interval, respectively. The MFS vs. 1/T plot so generated is used to identify the Tnr temperature.
Results for Steel 1
[0073] Table 2 shows the different experimental parameters used to calculate the Tnr for Steel 1. The corresponding Tnr values are given in the last column of the Table 2. Figure 7(a) and 7(b) depicts a typical MFS vs. (1/T) plot for this particular steel. From Table 2 it can be observed that the experimentally calculated Tnr for Steel 1 varies between 850 - 924°C temperatures under different experimental conditions i.e. in other words under different hot rolling parameters. The reheating temperature, pass strain, strain rates and interpass time were maintained at 1200°C, 0.1, 0.5 s-1 and 5 s respectively.
[0074] Table 2. Different experimental parameters and their corresponding Tnr values for Steel 1.
Reheating temperature (°C) von Mises equivalent strain von Mises equivalent strain rate Inter-pass time Tnr (°C)
1100 0.3 10 5 850
1200 0.1 0.5 910
1200 0.1 10 880
1200 0.2 0.5 870
1200 0.2 10 863
1200 0.3 0.01 924
1200 0.3 0.5 863
1200 0.3 10 855
1200 0.4 10 850
1250 0.3 10 890

Results for Steel 2
[0075] Table 3 illustrates the experimental parameters for Steel 2. The corresponding Tnr values are given in the last column of the Table 3. Figure 8(a) and 8(b) displays a typical MFS vs. (1/T) plot for this particular steel. It can be seen from Table 3 that the Tnr for Steel 2 varies between 846 - 895°C temperatures under different experimental conditions. The reheating temperature, pass strain, strain rates and interpass time were maintained at 1250°C, 0.2, 0.5 s-1 and 5 s respectively
[0076] Table 3. Different experimental parameters and their corresponding Tnr values for Steel 2.
Reheating temperature (°C) von Mises equivalent strain von Mises equivalent strain rate Interpass time Tnr (°C)
1100 0.3 10 5 846
1200 0.1 0.5 883
1200 0.1 10 869
1200 0.3 0.01 883
1200 0.3 0.5 863
1200 0.3 10 856
1250 0.2 0.5 895
1250 0.2 10 879
1250 0.3 10 871
Results for Steel 3
[0077] Table 4 demonstrates the various experimental parameters for determining the Tnr for Steel 3. The corresponding Tnr values are shown in the last column of the Table 4. Figure 9(a) and 9(b) display a typical MFS vs. (1/T) plot for this particular steel. It can be seen from Table 4 that the Tnr for Steel 3 varies between 876 - 917°C temperatures under different experimental conditions. The reheating temperature, pass strain, strain rates and interpass time were maintained at 1250°C, 0.3, 10 s-1 and 25 s respectively.
[0078] Table 4. Different experimental parameters and their corresponding Tnr values for Steel 3.
Reheating temperature (°C) von Mises equivalent strain von Mises equivalent strain rate Interpass time Tnr (°C)
1100 0.3 10 25 880
1200 0.1 3.33 903
1200 0.1 10 895
1200 0.2 6.67 903
1200 0.2 10 890
1200 0.3 0.5 896
1200 0.3 10 890
1200 0.4 10 876
1250 0.3 10 917

Results for Steel 4
[0079] Finally, Table 5 exhibits the experimental parameters for Steel 4. Likewise, the corresponding Tnr values are shown in the last column of the Table 5. Figure 10(a) and 10(b) represents a typical MFS vs. (1/T) plot for this particular steel. It can be seen from Table 5 that the Tnr for Steel 4 varies between 863 - 910°C temperatures under different experimental conditions. The reheating temperature, pass strain, strain rates and inter-pass time were maintained at 1200°C, 0.3, 0.5 s-1 and 5 s respectively.
[0080] Table 5. Different experimental parameters and their corresponding Tnr values for Steel 4.
Reheating temperature (°C) von Mises equivalent strain von Mises equivalent strain rate Interpass time Tnr (°C)
1100 0.3 10 5 863
1200 0.1 0.5 910
1200 0.1 10 890
1200 0.2 0.5 890
1200 0.2 10 883
1200 0.3 0.5 903
1200 0.3 10 880
1200 0.4 10 876

Effect of Reheating Temperature on Tnr
[0081] Figure 11 portrays the effects of reheating temperature on the Tnr values. All the experiments were carried out at a von Mises strain of 0.3 and at a strain rate of 10 s-1. The trend remains more or less same for all the steels. In other words, as the reheating temperature increases Tnr temperature also increases to the higher values. Here it is important to note that all the experiments were carried out at a von Mises strain of 0.3 and at a strain rate of 10 s-1. This could be explained in the following manner. Increase in soak temperature increases the grain size increases. These may increase from 100 µm at a reheat temperature of 1000°C to 200 µm at 1100°C and about 350 µm at 1250°C. Therefore, higher the starting grain size, grain boundary area will decrease and difficult it would be for the steel to recrystallize. Subsequently, the Tnr value will increase.
Effect of Strain on Tnr
[0082] The effect of strain on Tnr is displayed in Fig. 12. All the experiments were carried out at a reheating temperature of 1200°C and at a strain rate of 0.5 s-1. Here it can be seen that the strain has a negative influence on Tnr, i.e., as the strain increases Tnr drops to a lower value. It is worth mentioning that all the experiments were carried out at a reheating temperature of 1200°C and at a strain rate of 0.5 s-1. The reason could be higher strains provide more nuclei for recrystallization. Thus, the process of recrystallization gets accelerated and Tnr decreases. Abad et al. [28] showed that Tnr e -0.072, where temperature is in °C and e is the pass strain. The effect of higher strain is depicted as higher stress in the material. This corresponds to higher dislocation density in the material. It is of considerable importance to evaluate this quantity as accurately as possible [29].
Effect of Strain Rate on Tnr
[0083] The changes in Tnr with strain rate can be visualized from Fig. 13. All the experiments were carried out at a reheating temperature of 1200°C and at a strain of 0.3. Here also it can be observed that with the increasing strain rate Tnr value decreases. Higher strain rates lead to less restoration by dynamic recovery. Therefore, driving force for static recrystallization increases by highly work hardened austenite. This is manifested by lowering of Tnr at higher strain rates.
[0084] It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases “at least one” and “one or more” to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim recitation to inventions containing only one such recitation, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g., “a” and/or “an” should typically be interpreted to mean “at least one” or “one or more”); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of “two recitations,” without other modifiers, typically means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogous to “at least one of A, B, and C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, and C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those instances where a convention analogous to “at least one of A, B, or C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, or C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase “A or B” will be understood to include the possibilities of “A” or “B” or “A and B.”
[0085] It will be further appreciated that functions or structures of a plurality of components or steps may be combined into a single component or step, or the functions or structures of one-step or component may be split among plural steps or components. The present invention contemplates all of these combinations. Unless stated otherwise, dimensions and geometries of the various structures depicted herein are not intended to be restrictive of the invention, and other dimensions or geometries are possible. In addition, while a feature of the present invention may have been described in the context of only one of the illustrated embodiments, such feature may be combined with one or more other features of other embodiments, for any given application. It will also be appreciated from the above that the fabrication of the unique structures herein and the operation thereof also constitute methods in accordance with the present invention. The present invention also encompasses intermediate and end products resulting from the practice of the methods herein. The use of “comprising” or “including” also contemplates embodiments that “consist essentially of” or “consist of” the recited feature.
[0086] Although embodiments for the present subject matter have been described in language specific to structural features, it is to be understood that the present subject matter is not necessarily limited to the specific features described. Rather, the specific features and methods are disclosed as embodiments for the present subject matter. Numerous modifications and adaptations of the system/component of the present invention will be apparent to those skilled in the art, and thus it is intended by the appended claims to cover all such modifications and adaptations which fall within the scope of the present subject matter.
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