The present disclosure relates to the field of metallurgy.
DEFINITIONS
As used in the present disclosure, the following terms are generally intended to have the meaning as set forth below, except to the extent that the context in which they are used indicate otherwise.
Relatively inert gas – A relatively inert gas is hereinafter referred to a gas that does not react with a workpiece at the operating temperature.
BACKGROUND
Carburizing is a heat treatment process which is widely used in surface hardening processes in order to achieve hardness of a workpiece made of low carbon steel. In a carburizing process, the workpiece is heated to a high temperature, typically ranging from 880o C to 950o Celsius, in the presence of a carbon carrying gas in a furnace retort. During carburizing, the workpiece absorbs liberated carbon. After carburizing, the workpiece is heated and cooled rapidly, which is known as quenching process. Due to rapid cooling (quenching), higher carbon content surface of the workpiece becomes hard, whereas the core of the workpiece remains soft and tough. Conventionally, after completion of carburizing cycle, air is blown with the help of an air blower over the furnace retort to cool it, which in turn cools the workpiece. This is an indirect cooling of the workpiece. The indirect cooling requires more time to cool the workpiece to a desired temperature, which may result in poor microstructure on the surface of the workpiece. Due to slow cooling process, carbon present in the workpiece is deposited on grain boundaries of workpiece, which results in formation of carbide network. Being brittle in nature, the carbide network can propagate cracks along the grain boundaries which are detrimental for life of the workpiece. Further, the indirect cooling by air affects the visual appearance of the workpiece as it discolors the workpiece. Discoloration of the work piece results in poor surface appearance after grinding on the unground parts.
Therefore, there is felt a need of a process for carburizing of a workpiece that alleviates above mentioned drawbacks.
OBJECTS
Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows:
An object of the present disclosure is to provide a process for carburizing of a workpiece that facilitates effective cooling within a short time period.
Another object of the present disclosure is to provide a process for carburizing of a workpiece that prevents carbide network formation in the workpiece.
Yet another object of the present disclosure is to provide a process for carburizing of a workpiece that prevents discoloration of the workpiece.
Other objects and advantages of the present disclosure will be more apparent from the following description, which is not intended to limit the scope of the present disclosure.
SUMMARY
The present disclosure envisages a process for carburizing of a workpiece. Initially, the workpiece is heated to a temperature above 880o Celsius in a carburizing vessel. After carburizing cycle, the heated workpiece is rapidly cooled to below 700o Celsius within the carburizing vessel in the presence of a relatively inert gas, preferably nitrogen. The external surface of the vessel is cooled with the help of air. The relatively inert gas, preferably nitrogen, is circulated within the carburizing vessel using a fan. The workpiece is supported by at least one mesh basket within the vessel.
In an embodiment, the relatively inert gas is nitrogen.
The present disclosure further envisages an apparatus for carburizing of a workpiece. The apparatus comprises a heating means and a rapidly cooling means. The heating means is configured for heating the workpiece to a temperature ranging from 880o Celsius to 950o Celsius. The rapidly cooling means includes a carburizing vessel and a blower. The carburizing vessel is configured to support the workpiece therewithin. The carburizing vessel has an inlet port for introducing a gas therewithin. The blower is configured to create a flow of air, and direct the flow of air on an outer surface of the carburizing vessel.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
A process for carburizing of a workpiece, of the present disclosure, will now be described with the help of the accompanying drawing, in which:
Figure 1 illustrates a microphotograph of the microstructure on the surface of a workpiece that is carburized by a conventional process;
Figure 2 illustrates a schematic view of a vessel depicting a process of the present disclosure, in accordance with an embodiment of the present disclosure; and
Figure 3 illustrates a microphotograph of the microstructure on the surface of a workpiece that is carburized by the process of the present disclosure.
LIST OF REFERENCE NUMERALS
100 – Carburizing vessel
110 – Workpiece
120 – Fan
125 – Mesh basket
130 – Inlet
135 – Blower
DETAILED DESCRIPTION
Conventionally, in order to make a workpiece surface harder, the workpiece is heated to a high temperature in presence of a carbon carrying gas. The workpiece is made of low carbon steel. This process is known as carburizing. Carburizing is a heat treatment process widely used to achieve hardening of a workpiece. The workpiece is heated to a high temperature, typically ranging between 880o Celsius to 950o Celsius, in the presence of the carbon carrying gas. Typically, the carbon carrying gas is Methane, carbon monoxide, or liquid petroleum gas (LPG). High temperature and long carburizing time increases the depth of carbon diffusion. Following equation, also known as Harris formula, is used to determine time required for carburizing.
Time required for carburizing=[(Required case depth*?10?^((3722/temperature)) )/803]^0.5
In aforementioned equation, the time required for carburizing is in hours, required case depth is in mm, and the temperature is in Kelvin. Further, the active cycle is carried out for 75% of the total time, and the diffusion cycle is carried out for 25% of the total time required for carburizing.
Conventionally, the temperature of the workpiece is maintained at 950o C in a furnace. An endothermic gas and a liquid petroleum gas (LPG) are introduced in the furnace in which the workpiece is disposed. More specifically, the endothermic gas is introduced in the furnace when the temperature of the workpiece is 700o Celsius, and the liquid petroleum gas (LPG) is introduced in the furnace when the temperature of the workpiece is 880o Celsius. The workpiece is heated to 950o Celsius in the presence of the endothermic gas and the liquid petroleum gas (LPG). Further, after completion of carburizing process, the flow of the liquid petroleum gas within the furnace is stopped. The workpiece is then cooled by blowing atmospheric air on the retort using a blower to reduce temperature of the workpiece below 700o Celsius. The endothermic gas is fed in the furnace till the workpiece achieves the temperature of 700o C, and is stopped as soon as the workpiece achieves temperature of 700o Celsius. The endothermic gas prevents the scale formation on the workpiece, which occurs when the workpiece comes in contact with atmospheric air. However, air requires more time to cool the workpiece to a desired temperature, which may result in poor microstructure. Further, due to slow cooling process, carbon present in the workpiece is deposited on grain boundaries of workpiece, which results in formation of carbide network. Being brittle in nature, the carbide network can propagate cracks along the grain boundaries which are detrimental for life of the workpiece. Further, cooling by air affects the visual appearance of the workpiece as it discolors the workpiece. Figure 1 illustrates a microphotograph of the microstructure on the surface of the workpiece that is cooled by air. The carbide network can be clearly seen in figure 1. The workpiece carburized by the conventional process needs to undergo reworking to dissolve the carbide network. This reworking increases the overall cost of carburizing, and consumes lot of time.
The present disclosure envisages a process for carburizing of a workpiece, which facilitates effective cooling within a short time period, and prevents carbide network formation.
The process, of the present disclosure, is now described with reference to figure 2 and figure 3. Figure 2 illustrates a schematic view of a carburizing vessel 100 depicting a process of the present disclosure, in accordance with an embodiment of the present disclosure.
Initially, a workpiece 110 is heated inside the carburizing vessel 100 to a temperature ranging from 880o Celsius to 950o Celsius. Typically, the carburizing vessel 100 is a retort furnace, and is disposed within a pit type gas carburizing furnace. The workpiece 110 is supported by at least one mesh basket 125 within the carburizing vessel 100. A fan 120 is disposed in the carburizing vessel 100.
In an exemplary embodiment, the workpiece 110 is heated to a temperature of 950o Celsius. An endothermic gas and a liquid petroleum gas (LPG) are introduced in the carburizing vessel 100 in which the workpiece 110 is disposed. More specifically, the endothermic gas is introduced in the carburizing vessel 100 when the temperature of the workpiece 110 is 700o Celsius, and the liquid petroleum gas (LPG) is introduced in the carburizing vessel 100 when the temperature of the workpiece 110 is 880o Celsius. The workpiece 110 is heated to 950o Celsius in the presence of the endothermic gas and the liquid petroleum gas (LPG).
In an exemplary embodiment, the carburizing cycle is carried out to achieve case depth of 2 mm, and the workpiece 110 is heated to a temperature of 950o Celsius (1223 Kelvin). The total time required for carburizing is calculated by aforementioned equation, and is approximately 8 hours. The active cycle is carried out for 6 hours, and the diffusion cycle is carried out for 2 hours. In an exemplary embodiment, all the process parameters, such as temperature, time, and carbon potential, are controlled by Eurotherm Program Controller used in Auto mode.
After carburizing cycle, the flow of the endothermic gas and the liquid petroleum gas (LPG) within the carburizing vessel 100 is stopped. Further, the workpiece 110 is rapidly cooled within the carburizing vessel 100 with the help of a relatively inert gas, preferably nitrogen, until the temperature of the workpiece 110 is reduced below 700o Celsius. As soon as the temperature of the workpiece 110 reduces below 700o Celsius, the flow of the relatively inert gas within the carburizing vessel 100 is stopped. In an embodiment, the relatively inert gas, preferably nitrogen, is introduced in the carburizing vessel 100 from an operative top end thereof. The carburizing vessel 100 is configured with an inlet 130 to facilitate introduction of the relatively inert gas, preferably nitrogen, into the carburizing vessel 100. In an embodiment, the inlet 130 is in the form of port through which a gas pipe can be inserted. The workpiece 110 is exposed to the relatively inert gas. More specifically, the relatively inert gas, preferably nitrogen, is purged over the workpiece 110, which reduces the temperature of the workpiece 110 below 700o Celsius. The relatively inert gas is circulated within the carburizing vessel 100 via the fan 120. The mesh basket 125 is configured to facilitate maximum exposure of the workpiece 110 to the relatively inert gas.
In an embodiment, the relatively inert gas, preferably nitrogen, is introduced in the carburizing vessel 100 at a temperature ranging from 20o Celsius to 40o Celsius.
Generally, the scaling may take place due to the atmospheric air coming in contact with the workpiece 110. The relatively inert gas, preferably nitrogen, protects the workpiece 110 from scale formation as it does not allow the workpiece 110 to come in contact with the atmospheric air.
In an embodiment, the relatively inert gas is an endothermic gas, typically an inert gas. In a preferred embodiment, the inert gas is nitrogen. Nitrogen facilitates fast cooling, and effectively avoids scale formation. In an embodiment, the temperature of the workpiece 110 is reduced from 950o C to 600o C in 2 hours using nitrogen as the inert gas. In conventional processes, it takes 3.5 hours to reduce the temperature of the work piece 110 from 950o C to 600o C.
Further, while purging the relatively inert gas, preferably nitrogen, over the work piece 110, an external surface of the carburizing vessel 100 is cooled with the help of air. The external surface of the carburizing vessel 100 is exposed to a flow of air. More specifically, a blower 135 is configured proximal to an outer surface of the carburizing vessel 100 to create and direct maximum flow of air towards the carburizing vessel 100. The flow of air reduces the temperature of the carburizing vessel 100, which further reduces the temperature of the work piece 110. As the flow of air is directed on the outer surface of the carburizing vessel 100, air does not come in direct contact with the work piece 110, thereby preventing scale formation.
The work piece 110 is made of any carbon deficient metallic material. In an embodiment, the work piece is of a material selected from the group consisting of steel, alloys of steel, and iron.
The workpiece carburized and cooled by the process disclosed in the present disclosure is analyzed on the basis of the parameters such as percentage of carbon, effective case depth, and microstructure formed on the surface of the workpiece. After carburizing, the percentage of carbon is measured at a depth of 500 microns from the carburized surface. After hardening and tempering of carburized surface, the effective case depth is measured. Further, the microstructure is analyzed after completion of hardening and tempering of carburized surface using an optical microscope. All the aforementioned parameters are found in order with the standard values.
The present disclosure further envisages an apparatus for carburizing of a work piece. The apparatus comprises a heating means and a rapidly quenching means. The heating means is configured for heating the work piece to a temperature ranging from 880o Celsius to 950o Celsius. The rapidly quenching means includes the carburizing vessel 100 and the blower 135. The carburizing vessel 100 is configured to support the work piece therewithin. The carburizing vessel 100 has an inlet port 130 for introducing a gas therewithin. The blower 135 is configured to create a flow of air, and direct the flow of air on an outer surface of the carburizing vessel 100. The carburizing vessel includes the mesh basket 125 which supports the work piece within the carburizing vessel 100.
Figure 3 illustrates a microphotograph of the microstructure formed on the surface of a work piece that is carburized by the process of the present disclosure. It is clearly observed that there is no trace of the carbide network on the surface of the work piece. As there is no formation of carbide network, the work piece carburized by the process of the present disclosure does not require any rework to dissolve the carbide network, thereby reducing cost and time required for the process. Further, the process prevents the discoloration of the workpiece, thereby improving the visual appearance of the work piece.
The process, of the present disclosure, facilitates reduced heat rejection due to carbide network. The heat rejected due to carbide network is 0% in the process of the present disclosure as compared to 12% heat rejection in the conventional process.
The process, of the present disclosure, facilitates faster cooling of the work piece 110. Further, the process protects the work piece 110 from scaling. Further, the process prevents formation of the carbide network.
TECHNICAL ADVANCEMENTS
The present disclosure described herein above has several technical advantages including, but not limited to, the realization of a process for carburizing of a work piece that:
Facilitates effective cooling within short time period;
Prevents carbide network formation on the surface of the work piece; and
Prevents discoloration of the work piece.
The disclosure has been described with reference to the accompanying embodiments which do not limit the scope and ambit of the disclosure. The description provided is purely by way of example and illustration.
The embodiments herein and the various features and advantageous details thereof are explained with reference to the non-limiting embodiments in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.
The foregoing description of the specific embodiments so fully revealed the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.
Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.
The use of the expression “at least” or “at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the disclosure to achieve one or more of the desired objects or results.
Any discussion of documents, acts, materials, devices, articles or the like that has been included in this specification is solely for the purpose of providing a context for the disclosure. It is not to be taken as an admission that any or all of these matters form a part of the prior art base or were common general knowledge in the field relevant to the disclosure as it existed anywhere before the priority date of this application.
The numerical values mentioned for the various physical parameters, dimensions or quantities are only approximations and it is envisaged that the values higher/lower than the numerical values assigned to the parameters, dimensions or quantities fall within the scope of the disclosure, unless there is a statement in the specification specific to the contrary.
While considerable emphasis has been placed herein on the components and component parts of the preferred embodiments, it will be appreciated that many embodiments can be made and that many changes can be made in the preferred embodiments without departing from the principles of the disclosure. These and other changes in the preferred embodiment as well as other embodiments of the disclosure will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation.

Claims:1. A process for carburizing of a workpiece, said process comprising the following steps:
rapidly cooling a heated workpiece (110) to below 700o Celsius within a carburizing vessel (100) with the help of a relatively inert 5 gas preferably nitrogen; and
cooling the external surface of said vessel (100) with the help of air.
2. The process as claimed in claim 1, which includes the step of heating said workpiece (110) to a temperature above 880o Celsius in said carburizing 10 vessel (100).
3. The process as claimed in claim 1, which includes a step of introducing said relatively inert gas, preferably nitrogen, at a temperature ranging from 20o to 40OC Celsius into said carburizing vessel (100).
4. The process as claimed in claim 1, wherein said process includes a step of 15 circulating said relatively inert gas, preferably nitrogen, within said vessel (100) via a fan (120).
5. The process as claimed in claim 1, wherein said relatively inert gas is nitrogen.
6. The process as claimed in claim 1, wherein said workpiece (110) is of a 20 material selected from the group consisting of steel, alloys of steel, and iron.
7. The process as claimed in claim 1, wherein said process includes the step of supporting said workpiece (110) by at least one mesh basket (125) within said carburizing vessel (100). 25
14
8. The process as claimed in claim 1, wherein a blower (135) is configured to direct flow of air onto said vessel (100).
9. An apparatus for carburizing of a workpiece, said apparatus comprising:
a heating means for heating a workpiece (110) to a temperature ranging from 880o Celsius to 950o Celsius; and 5
a rapidly cooling means having:
a carburizing vessel (100) configured to support said workpiece (110) therewithin, said carburizing vessel (100) having an inlet port (130) for introducing a gas therewithin; and 10
a blower (135) configured to create flow of air and direct said flow of air on the external surface of said carburizing vessel (100). ,