DESC:TECHNICAL FIELD OF THE INVENTION
The present invention relates to the carburizing process of latch, and more particular to heat treatment process of mechanism component to increase the service life. The present invention provides a method for carburizes heat treatment of low carbon steel to increase the wear resistance, strength and minimum distortion of component, by carburize in gas.

BACKGROUND AND THE PRIOR ART
The process of heat treatment to component increase the wear resistance and strength for steels and alloys with their standard mechanical characteristics, with the heat treatment and structure, with the purpose of technological in industrial conditions to control the processes capable to influence positively on the wear resistance increase of mechanism parts under mechanical wear conditions. The latch is use in the mechanism component, where it required both wear resistance and strength. The heat treatment process used heat is carburizing to increase the surface resistance.
For wear resistance surface hardening, a process which includes a wide variety of techniques, is used to improve the wear resistance of parts without affecting the softer, tough interior of the part. This combination of hard surface and resistance to breakage upon impact is useful in parts that must have a very hard surface to resist wear, along with a tough interior to resist the impact that occurs during operation.
In the current heat treatment process only the surface resistance increases but the surface crack and distortion in the component. Due to distortion and crack, the component is not use and lot of rejection of component.
US5672216 disclosed a method of fabricating sheet metal parts comprising the steps of: stamping a pair of overlying metal sheets together to form a pair of stampings, heat treating the stampings, clamping the stampings together to correct distortion of the stampings during the heat treatment and welding the clamped stampings together to produce the part.
US4375997 disclosed a surface layer of a thin-walled, hollow, cylindrical steel body is hardened while controlling thermal distortion by first heating with an inductor and quenching in one direction over the surface and then repeating the process in the reverse direction.
US4472209 disclosed a method of carburizing a metal workpiece and a carburizing apparatus in which the workpiece, generally of steel, is introduced into an annealing oven and subjected to a high temperature in the presence of a carbon-containing gas mixture as a result of which the workpiece is hardened. According to the invention, one or more of the carbon-containing gas components of the mixture effective upon the surface of the work-piece, can be periodically and impulsively injected into the gas mixture for sudden increases in carbon potential followed by longer diffusion phase.
To overcome the disadvantages of the prior art/conventional art, the present invention provides a carburizing and marquenching process which gives more strength, wear resistance and distortion free component. Advantage of martempering in molten salt is the control of surface carburizing or decarburizing. Quenching from the austenitizing temperature into a hot fluid medium (hot oil, molten salt, molten metal, or a fluidized particle bed) at a temperature usually above the martensite range (Ms point). Holding in the quenching medium until the temperature throughout the steel is substantially uniform. Cooling (usually in air) at a moderate rate to prevent large differences in temperature between the outside and the center of the section.

OBJECTS OF THE INVENTION
A basic object of the present invention is to overcome the disadvantages/drawbacks of the known art.
Another object of the present invention is to provide a method for carburizes heat treatment of low carbon steel to increase the wear resistance, strength and minimum distortion of component, by carburize in gas.
Another object of the present invention is to provide a method reducing the thermal gradient between surface and centre, therefore preventing the component from distortion and cracks.
These and other advantages of the present invention will become readily apparent from the following detailed description read in conjunction with the accompanying drawings.

SUMMARY OF THE INVENTION
The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the present invention. It is not intended to identify the key/critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concept of the invention in a simplified form as a prelude to a more detailed description of the invention presented later.
In an aspect of the present invention, there is provided a method of heat treatment for a mechanism component, said method comprising steps of: carburizing the surface of said component to form a carburize layer on the surface, quenching said carburize layer on the surface of said component in a bath 1 medium at a temperature range 190-350°C, holding said component after quenching for about 5-90 minute to facilitate uniformity of temperature, and further quenching in a bath 2 medium at an ambient temperature, tempering of said component after quenching at said ambient temperature, therefore forming said component with at least two layer(s) of microstructure, wherein said method increasing the wear resistance and strength of said component and reducing thermal gradient of said component, thereby minimizing the distortion, cracking, and residual stress on said component .
Other aspects, advantages, and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses exemplary embodiments of the invention.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The following drawings are illustrative of particular examples for enabling methods of the present invention, are descriptive of some of the methods, and are not intended to limit the scope of the invention. The drawings are not to scale (unless so stated) and are intended for use in conjunction with the explanations in the following detailed description.
Figure.1 illustrates the side view of the Latch mechanism component
Figure.2 illustrates the flow chart of carburizing heat treatment cycle
Figure.3 illustrates the heat treatment cycle, where carburizing and marquenching or austempering of component to decrease the distortion on component.
Figure.4 illustrates the typical carburizing process, in carburizing process components are quenched to water from carburizing temperature
Persons skilled in the art will appreciate that elements in the figures are illustrated for simplicity and clarity and may have not been drawn to scale. For example, the dimensions of some of the elements in the figure may be exaggerated relative to other elements to help to improve understanding of various exemplary embodiments of the present disclosure.
Throughout the drawings, it should be noted that like reference numbers are used to depict the same or similar elements, features, and structures.

DETAILED DESCRIPTION OF THE INVENTION
The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of exemplary embodiments of the invention as defined by the claims and their equivalents. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope and spirit of the invention. In addition, descriptions of well-known functions and constructions are omitted for clarity and conciseness.
The terms and words used in the following description and claims are not limited to the bibliographical meanings, but, are merely used by the inventor to enable a clear and consistent understanding of the invention. Accordingly, it should be apparent to those skilled in the art that the following description of exemplary embodiments of the present invention are provided for illustration purpose only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.
It is to be understood that the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise.
By the term “substantially” it is meant that the recited characteristic, parameter, or value need not be achieved exactly, but that deviations or variations, including for example, tolerances, measurement error, measurement accuracy limitations and other factors known to those of skill in the art, may occur in amounts that do not preclude the effect the characteristic was intended to provide.
Accordingly, present invention provides a carburizes heat treatment process of low carbon steel to increase the wear resistance, strength and minimum distortion of component, by carburize in gas.
The present invention is reducing and eliminating the susceptibility to cracking and providing advantage of in molten salt is the control of surface carburizing or decarburizing. The advantage of in the reduced thermal gradient between surface and center as the part is quenched to the isothermal temperature and then is air cooled to room temperature. Residual stresses developed during martempering are lower than those developed during conventional quenching because the greatest thermal variations occur while the steel is in the relatively plastic austenitic condition and because final transformation and thermal changes occur throughout the part at approximately the same time.
In the heat treatment process carburize the surface of component by carburizing process at temperature 800-1000°C with a methane containing carburization atmosphere for time to form carburize layer on surface. The carburize component quenched to 190-350°C just above the martensite start temperature and hold then quenched to ambient temperature. After marquenching or austempering process components are cooled in air. By this carburizing process the components are carburize and through harden. By this process the surface layer increase the wear resistance and on cooling to martensite temperature it increase strength of component. The advantage of this process is to reduce thermal gradient between surface and center as the part is quenched to the isothermal temperature and then is air cooled to room temperature. In conventional carburizing process components are distorted and cracked due to high thermal gradient and high carbon percentage on surface.
Quenching from the austenitizing temperature into a hot fluid medium (hot oil, molten salt, molten metal, or a fluidized particle bed) at a temperature usually above the martensite range (Ms point). Holding in the quenching medium until the temperature throughout the steel is substantially uniform. Cooling (usually in air) at a moderate rate to prevent large differences in temperature between the outside and the center of the section.
The advantage of martempering lies in the reduced thermal gradient between surface and center as the part is quenched to the isothermal temperature and then is air cooled to room temperature. Residual stresses developed during martempering are lower than those developed during conventional quenching because the greatest thermal variations occur while the steel is in the relatively plastic austenitic condition and because final transformation and thermal changes occur throughout the part at approximately the same time. Martempering also reduces or eliminates susceptibility to cracking. Another advantage of martempering in molten salt is the control of surface carburizing or decarburizing
In the heat treatment process of low carbon steel to increase the strength and wear resistance and minimum distortion, by carburize in gas. The carburize part is quenched from carburizing temperature 800-950C to martempering temperature190-350C, and hold the component for 5-90 minute for uniformity in temperature. The components are cooled to ambient temperature. The components are tempered to 250-450C for 0.5-5 hours. The component formed two layer of microstructure, outer martensite and bainite structure and inner carburize layer.
The quenched bath 1 medium is salt bath or oil bath. The quenched bath temperature is 190-350°C. The quenched bath 2 medium is oil, water or air. The quenched bath temperature is ambient temperature. The components are hold just above martensite start and then quenched to ambient temperature to form martensite, the process is called marquenching. The components are hold just above martensite start for longer time to form completely bainite then air cooled, the process is called austempering. By this process the surface layer increase the wear resistance and on cooling to martensite temperature it increase strength of component. The advantage of this process reduced thermal gradient between surface and center as the part is quenched to the isothermal temperature and then is air cooled to room temperature.
For strength marquenching or austempering is a term used to describe an interrupted quench from the austenitizing temperature of certain alloy, cast, tool, and stainless steels. The purpose is to delay the cooling just above the martensitic transformation for a length of time to equalize the temperature throughout the piece. This will minimize the distortion, cracking, and residual stress. The microstructure after martempering is essentially primary martensitic that is untempered and brittle. After austempering the microstructure is bainite.
The heat treatment process is either of carburizing, carbonitriding or nitrocarburizing for the wear resistance and strength of component. The atmosphere is carburize or both carburize and nitride. The quenching medium is salt bath. The purpose is to delay the cooling just above the martensitic transformation for a length of time to equalize the temperature throughout the piece. This will minimize the distortion, cracking, and residual stress. The microstructure after martempering is essentially primary martensitic that is untempered and brittle
,CLAIMS:1. A method of heat treatment for a mechanism component, said method comprising steps of:
carburizing the surface of said component to form a carburize layer on the surface,
quenching said carburize layer on the surface of said component in a bath 1 medium at a temperature range 190-350°C,
holding said component after quenching for about 5-90 minute to facilitate uniformity of temperature, and further quenching in a bath 2 medium at an ambient temperature,
tempering of said component after quenching at said ambient temperature, therefore forming said component with at least two layer(s) of microstructure
wherein said method increasing the wear resistance and strength of said component and reducing thermal gradient of said component, thereby minimizing the distortion, cracking, and residual stress on said component .

2. The method as claimed in claim 1, wherein carburizing said component at a temperature range of 800-1000o C with a methane containing carburization atmosphere for a time period to form said carburize layer on the surface of said component.
3. The method as claimed in claim 1, wherein tempering said component at a temperature range 250-450oC for about 0.5-5hours.
4. The method as claimed in claim 1, wherein said component having an outer said layer of microstructure is a martensitic structure or a bainite structure.
5. The method as claimed in claim 1, wherein said component having an inner said layer of microstructure is a carburize structure.
6. The method as claimed in claim 1, wherein said bath 1 medium is selected from a group comprising of salt bath, oil bath.
7. The method as claimed in claim 1, wherein said bath 2 medium is selected from a group comprising of oil, water or air.
8. The method as claimed in claim 1, wherein said component is made up of a iron alloy.
9. The method as claimed in claim 1, wherein said iron alloy is a low carbon steel.