CLIAMS:1. A method of a prevention of distortion, by quenching a microstructure obtained comprising the steps of:
cooling uniformly the microstructure obtained;
quenching the microstructure obtained, in X-direction of the microstructure using at least on fork, at least one latch link, at least one side plate, and at least one upper link.

2. The method of prevention of distortion according to claim 1, wherein the microstructure is obtained by a process of heat treating the at least one piece of carbon steel comprising the steps of:
a marquenching process
heating the at least one piece of carbon steel;
cooling the at least one piece of carbon steel by quenching;
equalizing a temperature throughout the at least one piece of carbon steel thereby
holding the at least one piece of carbon steel in a salt bath;
cooling the at least one piece of carbon steel; and
tampering the at least one piece of carbon steel to obtain the microstructure, wherein the microstructure is a martensite;

3. The method of prevention of distortion according to claim 1, wherein the microstructures is obtained by a process of heat treating the at least one piece of carbon steel comprising the steps of:
an austempering process
heating the at least one piece of carbon steel;
cooling the at least one piece of carbon steel by quenching;
equalizing a temperature throughout the at least one piece of carbon steel thereby
quenching the at least one piece of carbon steel and holding the at least one piece of carbon steel in the salt bath thereby obtaining the microstructure, wherein the microstructure is a bainite;

4. The method of prevention of distortion according to claim 1, wherein the at least one carbon steel comprises of a variable amount of carbon, wherein the variable amount is between 0.2% Carbon to 1.0% carbon.

5. The method of prevention of distortion according to claim 1, wherein the at least one carbon steel is of thickness ranging from 0.5 mm to 3mm.
,TagSPECI:TECHNICAL FIELD
The present subject matter described herein, in general relates to a mar quenching heat treatment of thin walled sheet metal, and more particularly, to reduce the amount of geometrical distortion observed during heat treatment of complex mechanism component of different thickness in metal.

BACKGROUND
The purpose of heat treatment is to cause desired changes in the metallurgical structure and thus increase the properties of metal parts. Heat treatment can affect the properties of most metals and alloys, but ferrous alloys, principally steels, undergo the most dramatic increases in properties, and therefore structural changes in iron–carbon alloys. Heat treatment is used to improve the mechanical properties of steel components, and commonly involves a quenching step which may cause undesired geometrical distortions in the processed parts. The dimensional accuracy of these parts is affected and leads to production and economical losses. Quenching commonly causes a geometric distortion in the parts, associated with the thermal contraction and with the change in the mechanical and geometrical properties.

The main industrial concern for distortion is due to the design and manufacturing. From the manufacturing process it can create distortion in component. Distorted of components can create erosion, noise and non function of the mechanism, that require a heat treatment process to decrease the distortion on the mechanism assembly. The effects of various factors on distortion are residual stress, pre-heating, cracking of steel components, volume change due to phase change on heating and cooling, part geometry, rate of cooling and heating etc.

Potential factor influence distortions are the material, part geometry, residual stress, cutting, grinding, and bending etc., thermal and transformation stress like heating and cooling cycle, etc.

Distortion as an irreversible and usually unpredictable dimensional change in the component during processing from heat treatment and from temperature variations and loading in service. The term dimensional change is used to denote changes in both size and shape. Size distortion, which involves expansion or contraction in volume or linear dimensions without changes in geometrical form; and shape distortion, which entails changes in curvature or angular relations, as in twisting, bending, and/or nonsymmetrical changes in dimensions. Size distortion is the result of a change in volume produced by a change in metallurgical structure during heat treatment. Shape distortion results from either residual or applied stresses. Residual stresses developed during heat treatment are caused by thermal gradients within the metal (producing differing amounts of expansion or contraction), by non uniform changes in metallurgical structure, and by non uniformity in the composition of the metal itself, such as that caused by segregation.

The various processes studied on the complicated sheet metal component to minimize the distortion by controlling the rate of quenching. A martempering and an austempering are the process to reduce the thermal gradient between surface and centre as the part quenched in isothermal temperature and then air cooled to room temperature.

The specific challenge involved in these processes was to optimize distortion control of the mechanism component fork, latch bracket, upper link and side plate. The goal was to minimize distortion and give good mechanical strength. The martempering and austempering process are quenched in molten salt bath as quenching medium which eliminate the problem of vapor phase barrier during the stage quenching is applied to achieve uniform temperature distribution inside the load while heating up. The design of fixturing and locating for component is one of key importance to minimize distortion during heat and cooling cycle. As in the case of salt bath liquid quenching, proper fixtures and optimized loading of the parts is important for quenching. However after long term service the fixtures tend to deform due to high temperature deformation, which has a negative effect on the distortion of the loaded parts.

Further, the conventional quenching technologies such as oil or polymer quenching exhibit very inhomogeneous cooling conditions. Three different mechanisms occur during conventional liquid quenching: film boiling, bubble boiling and convection. Resulting from these three mechanisms the distribution of the local heat transfer coefficients on the surface of the component is very inhomogeneous. These inhomogeneous cooling conditions cause tremendous thermal and transformation stresses in the component and subsequently distortion.

SUMMARY
This summary is provided to introduce concepts related to a method of heat treatment process for distortion control of complex sheet metal component. This summary is not intended to identify essential features of the subject matter nor is it intended for use in determining or limiting the scope of the subject matter.

In one implementation, the invention eliminates the problem of vapor phase barrier during initial stage quenching. Further, the transfer of heat is rapidly executed.

In one implementation, the invention enables the martempering process, wherein the direction, position and placement of component give the uniformity cooling and decrease the thermal stress.

In one implementation, a method of a prevention of distortion, by quenching a microstructure is disclosed. The method of the prevention of distortion comprises of a cooling uniformly a microstructure obtained. In the next step, after cooling a quenching is performed on the microstructure obtained. The quenching is performed in the X-direction of the microstructure using at least on fork, at least one latch link, at least one side plate, and at least one upper link.

In one implementation the microstructure may be a martensite or a bainite.

In one implementation, the microstructure is obtained by a process for heat treating the at least one piece of carbon steel. The process comprises of a marquenching process, which further comprises of heating the at least one piece of carbon steel, and cooling the at least one piece of carbon steel by quenching. The quenched piece of carbon steel is equalized for the temperature throughout the at least one piece of carbon steel thereby holding the at least one piece of carbon steel in a salt bath and cooling the at least one piece of carbon steel. Further, the cooled piece of carbon steel is tampered to obtain the microstructure, wherein the microstructure is a martensite.

In one implementation, the microstructure is obtained by a process for heat treating the at least one piece of carbon steel. The process comprises of an austempering process which further comprises of heating the at least one piece of carbon steel. The heated piece of carbon steel is then cooled by the quenching process. After quenching the carbon steel is equalized for a temperature throughout the at least one piece of carbon steel thereby quenching the at least one piece of carbon steel and holding the at least one piece of carbon steel in the salt bath thereby obtaining the microstructure, wherein the microstructure is a bainite.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The detailed description is described with reference to the accompanying figures. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the drawings to refer like features and components.

Figure 1 illustrates the top view of component placed in fixture is shown, in accordance with an embodiment of the present subject matter.

Figure 2 illustrates the view position of fork during heat treatment is shown, in accordance with an embodiment of the present subject matter.

Figure 3 illustrates the view position of latch link during heat treatment is shown, in accordance with an embodiment of the present subject matter.

Figure 4 illustrates the view position of side plate during heat treatment is shown, in accordance with an embodiment of the present subject matter.

Figure 5 illustrates the view position of upper link during heat treatment is shown, in accordance with an embodiment of the present subject matter.

Figure 6 illustrates the view position of Latch bracket during heat treatment is shown, in accordance with an embodiment of the present subject matter.

Figure 7 illustrates the result of distortion and tolerance limit after heat treatment of fork is shown, in accordance with an embodiment of the present subject matter.

Figure 8 illustrates the result of distortion and tolerance limit after heat treatment of Latch Link is shown, in accordance with an embodiment of the present subject matter.

Figure 9 illustrates the result of distortion and tolerance limit after heat treatment of upper link is shown, in accordance with an embodiment of the present subject matter.

Figure 10 illustrates the result of distortion and tolerance limit after heat treatment of latch bracket is shown, in accordance with an embodiment of the present subject matter.

Figure 11 illustrates the result of distortion and tolerance limit after heat treatment of side plate is shown, in accordance with an embodiment of the present subject matter.

DETAILED DESCRIPTION
Preferred embodiments of the present disclosure will be described herein below with reference to the accompanying drawings. In the following description, well-known functions or constructions are not described in detail to avoid obscuring the present disclosure in unnecessary detail.

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, the present invention is a method of heat treatment process for distortion control of complex sheet metal component.

Construction of the connector assembly of the present invention is explained with reference to the accompanying figures.

In one implementation, a method of a prevention of distortion, by quenching a microstructure is disclosed. The method of the prevention of distortion comprises of a cooling uniformly a microstructure obtained. In the next step, after cooling the quenching is performed on the microstructure obtained. The quenching is performed in the X-direction of the microstructure using at least on fork, at least one latch link, at least one side plate, and at least one upper link.

In one implementation the microstructure obtained may be a martensite or a bainite.

In one implementation, the microstructure is obtained by a process for heat treating the at least one piece of carbon steel. The process comprises of a marquenching process, which further comprises of heating the at least one piece of carbon steel, and cooling the at least one piece of carbon steel by quenching. The quenched piece of carbon steel is equalized for the temperature throughout the at least one piece of carbon steel thereby holding the at least one piece of carbon steel in a salt bath and cooling the at least one piece of carbon steel. Further, the cooled piece of carbon steel is tampered to obtain the microstructure, wherein the microstructure is a martensite.
In one implementation, the microstructure is obtained by a process for heat treating the at least one piece of carbon steel. The process comprises of an austempering process which further comprises of heating the at least one piece of carbon steel. The heated piece of carbon steel is then cooled by the quenching process. After quenching the carbon steel is equalized for a temperature throughout the at least one piece of carbon steel thereby quenching the at least one piece of carbon steel and holding the at least one piece of carbon steel in the salt bath thereby obtaining the microstructure, wherein the microstructure is a bainite.

In one implementation, the at least one carbon steel comprises of a variable amount of carbon, wherein the variable amount is between 0.2% Carbon to 1.0% carbon.

In one implementation, the at least one carbon steel is of thickness ranging from 0.5 mm to 3mm.

In an exemplary embodiment of the present invention, the present invention related to the heat treatment of carbon steel 0.2% Carbon to 1.0% carbon. The thickness of material is 0.5 to 3mm and different length of component. The different in thickness, size, shape and mechanical operation component can be heat treated in one heat treatment cycle and also get less distortion. Martempering and austempering are the isothermal heat treatment process to produce martensite and bainite of the carbon steel.

In marquenching process the carbon steel is heated to austenite temperature then quickly cooled by quenching in salt bath just above or just below the martensite starting temperature (Ms) between 160°C to 230°C. The carbon steel is held in the bath long enough to equalize the temperature throughout the component, then air cooled and tempered. Distortion is minimized and cracking is prevented. The hard microstructure structure form martensite through the component.

Austempering involve the quenching of carbon steel from austenitic temperature salt bath at an appropriate temperature between 200°C to 450°C above the martensite start (Ms) temperature. The carbon steel held in the salt bath for sufficient time to complete transformation of austenite to bainite.

The method of prevention of distortion by quenching the component so that the formation of martensite throughout the surface. The inner and outer side of the component cooled uniformly. Distortion depends on the geometry, residual stress and uniformity in cooling of the component. Due to the complicated shape and size of the component, the geometry quench uniformly in all cross sectional area. The fork, latch link and side plate are quenching from the austenitic temperature to martensite, in X-direction of component to increase the uniform cooling and decrease the thermal stress.

The difference in thickness, size and mechanical operation component may be heat treated in one heat treatment cycle. The direction of quenching in the component is the important for the distortion in quenching. The quenching of component are first the legs of the component. If the bend area quench initially, it increases the distortion. When the components depend on the component and decrease the thermal shock at the bend cross sectional area. The features in the quenching arrangement are that, the component cooling is achieved in both tangential and longitudinal axes.

Figure 2 Figure 3, Figure 4 and Figure.5 show the placement and direction of component in the fixture and the further process in the marquenching process. The direction of quenching is in X- axis. The fork may be of 1.5mm thickness, the latch link may be of 1.2 mm of thickness, the side plate may be of 1.0 mm of thickness and the upper link may be of 1.0 mm of thickness that may have different thickness, shape, and size and have different mechanical operation during manufacturing. This X-direction marquenching process gives minimum distortion in the component.

The fork, latch link, side plate and upper link may be placed, position and direction as shown in figure. The fixture with components are placed in stress relieved, martempering furnace and quenching as shown in the figure 1. After the marquenching process, the tempering of components in tempering furnace may be performed.

Referring now to figure 1 illustrates a top view of component placed in fixture is shown, in accordance with an embodiment of the present subject matter. In an embodiment of the present invention, the detailed description of figure 1 is as given above.

Referring now to figure 2 illustrates the view position of fork during heat treatment is shown, in accordance with an embodiment of the present subject matter. In an embodiment of the present invention, the detailed description of figure 2 is as given above

Referring now to figure 3 illustrates the view position of latch link during heat treatment is shown, in accordance with an embodiment of the present subject matter. In an embodiment of the present invention, the detailed description of figure 3 is as given above.

Referring now to figure 4 illustrates the view position of side plate during heat treatment is shown, in accordance with an embodiment of the present subject matter. In an embodiment of the present invention, the detailed description of figure 4 is as given above.

Referring now to figure 5 illustrates the view position of upper link during heat treatment is shown, in accordance with an embodiment of the present subject matter. In an embodiment of the present invention, the detailed description of figure 5 is as given above.

Referring now to figure 6 illustrates the view position of Latch bracket during heat treatment is shown, in accordance with an embodiment of the present subject matter. In an embodiment of the present invention, the detailed description of figure 6 is as given above

Figure 7, Figure 8, Figure 9, Figure 10 and Figure11 shows the result after heat treatment. All the components are have minimum distortion and are within the given tolerance limit.

In one implementation, the method of heat treatment to get high strength, high wears resistance and minimum distortion on the carbon steel sheet components, is disclosed. The components are manufactured by cutting, punching, shearing, bending, blanking mechanical operation and create residual stress. The difference in thickness, size, shape and mechanical operation component can be heat treated in one heat treatment cycle. The components are placed transverse or X-direction in figure of part is quenched to give the less distortion in component. The components are quenching in molten salt bath during quenching in the X-direction that to decrease the stress raiser develops during quenching. The components are placed in X-direction which give stable and relieve residual stress.

In one implementation, the heat treatment of carbon steel 0.2% Carbon to 1.0% carbon is performed.

In one implementation, the thickness of material is 0.5 to 3 mm and length of component is 0.1to 15 mm.

In one implementation, the components are stress relieved to a temperature to 400-450° C for 5-60 minute. The stress relieved component are positioned and placed in X-direction. The stress relieved component are then heated to 800-900° C for 5-30 minute and quenched to salt bath of temperature 160-400° C The components are martempering and austempering heat treatment process to produce martensite and bainite of the carbon steel. The quenching medium is salt bath of temperature 160-400° C. The steel components are tempered at 250-450° C for 60-180 minute.

Exemplary embodiments discussed above may provide certain advantages. Though not required to practice aspects of the disclosure, these advantages may include those provided by the following features:

One feature of the invention is that, during marquenching in molten salt bath the quenching medium eliminates the problem of vapor phase barrier during initial stage quenching. The heat transfer is rapidly executed, and further, the viscosity achieved due to the product is uniform over a wide range of temperature. It remains stable at operating temperature and is completely soluble in water, thus facilitate subsequent cleaning operations. This result a much more homogenous in cooling conditions and gives less distortion.

Another feature of the invention is that, in the martempering process, the direction, position and placement of component gives the uniformity cooling, and decreases the thermal stress. The X-direction of quenching in the figure gives the minimum distortion. The variations in thickness of component also give minimum distortion during the X-direction of quenching.

Still another feature of the invention is that, the marquenching or martemper treatment uses an elevated temperature quench. The components are heated to the austenitizing temperature range and quenched, normally in molten salt at a temperature above the martensitic transformation start point (Ms). Molten salt is used for martempering in the range of 160 to 400 °C. Components are held in the quenching medium for sufficient time until the temperature of the component is uniform and then air cooled through the martensite formation range. This is effectively hardened and tempers operation at the same time, keeping distortion to a minimum. Subsequent tempering is carried out to improve the materials toughness. This process minimizes the distortion, cracking, and residual stress.

In one implementation, the benefit of the proposed invention is that, the control heat treatment is used to improve the mechanical properties of steel components, and commonly involves a quenching step which decreases the geometrical distortions in the processed parts. The dimensional accuracy of these parts is to improve, less rejection and increases the production and economical benefit to industry.

The advantage of marquenching lies in the reduced thermal gradient between surface and core as the part is quenched to the isothermal temperature and then is air cooled to room temperature. Residual stresses developed during marquenching 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 the final transformation and thermal changes occur throughout the part at approximately the same time. Marquenching also reduces susceptibility to cracking. Marquenching is an interrupted quench from the austenitizing temperature of certain alloy, mild steel, 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 primary martensitic that is untempered and brittle.

The process provides immersion recommendations for parts with complex shapes, where cracking potential is minimum and maximum. The conditions for quench cracking are most favorable if parts are immersed into the quenchant, so the perimeter of the stress raiser simultaneously touches the liquid along the entire length. In the case where the perimeter of the stress raiser slowly touches the quenchant at the moment of immersion in individual regions, quench cracking is reduced substantially.

In one implementation, during marquenching in molten salt bath quenching medium which eliminate the problem of vapor phase barrier during initial stage quenching. It heat transfer heat rapidly, its viscosity gives uniform over a wide range of temperature. It remains stable at operating temperature and is completely soluble in water, thus facilitate subsequent cleaning operations. This result a much more homogenous in cooling conditions and gives less distortion.

In the martempering process, the direction, position and placement of component gives the uniformity cooling and decrease the thermal stress.

Marquenching or Martemper treatment uses an elevated temperature quench. The components are heated to the austenitizing temperature range and quenched, normally in molten salt at a temperature above the martensitic transformation start point (Ms). Molten salt is used for martempering in the range of 160 to 400 °C. the components are held in the quenching medium for sufficient time until the temperature of the component is uniform and then air cooled through the martensite formation range. This is effectively a hardened and tempers operation at the same time, keeping distortion to a minimum. Subsequent tempering is carried out to improve the materials toughness. This process minimizes the distortion, cracking, and residual stress.

In one implementation, the process provided immersion recommendations for parts with complex shapes, where cracking potential is minimum and maximum. Conditions for quench cracking are most favorable if parts are immersed into the quenchant, so the perimeter of the stress raiser simultaneously touches the liquid along the entire length. In the case where the perimeter of the stress raiser slowly touches the quenchant at the moment of immersion in individual regions, quench cracking is reduced substantially.

Although implementations for a method of heat treatment process for distortion control of complex sheet metal component have been described in language specific to structural features and/or the methods, it is to be understood that the appended claims are not necessarily limited to the specific features or methods described. Rather, the specific features are disclosed as examples of, the method of heat treatment process for distortion control of complex sheet metal component.

It is intended that the disclosure and examples above be considered as exemplary only, with a true scope and spirit of disclosed embodiments being indicated by the following claims.