KR102112095B1 - Heat treatment method of low carbon steel - Google Patents

Abstract

The present invention relates to a heat treatment method of low-carbon steel, and more specifically, to a heat treatment method of low-carbon steel, which can increase the surface strength of a low-carbon steel with excellent moldability, and suppress deformation. According to the present invention, the heat treatment method of low-carbon steel comprises: a step of cementation to cement the low-carbon steel; a step of primary quenching to cool the cemented low-carbon steel to a primary quenching temperature; a step of secondary quenching to cool the primarily quenched low-carbon steel to a secondary quenching temperature which is lower than the primary quenching temperature; a step of controlling corrosion to wash and dry the secondarily quenched low-carbon steel in a vacuum; a step of press tempering to maintain the corrosion-controlled low-carbon steel at a temperature and pressure for press tempering for a period for press tempering; a step of post-treatment to perform at least one of short blast and sand blast on the press tempered low-carbon steel; and a step of inspection to inspect the flatness of the post-treated low-carbon steel.

Description

Heat treatment method of low carbon steel {HEAT TREATMENT METHOD OF LOW CARBON STEEL}

The present invention relates to a method for heat treatment of low-carbon steel, and more particularly, to increase the surface strength of low-carbon steel excellent in formability, and relates to a method for heat treatment of low-carbon steel capable of suppressing deformation.

Low carbon steel (low carbon steel) has a carbon content of 0.25% or less, and is highly combustible, so it has excellent porosity and is processed by press, deep drawing, drawing, etc. to build, bridge, thin plate, steel wire, boiler, steel pipe, bolt, Used for nuts, nails, screws, etc.

However, since these low-carbon steels have a problem that the strength is low for use in the above-mentioned applications after molding, heat treatment such as carburizing is performed to improve the strength.

Carburizing is a heat treatment to increase the surface strength by penetrating carbon on the surface after molding, such as low-carbon steel having good moldability, and carburizing-treated low-carbon steel has a high surface strength and also has the advantage of high toughness inside. , Carburized low-carbon steel will have rigidity.

However, such a carburized low-carbon steel has a disadvantage in that it is difficult to use for parts having precise dimensions due to slight deformation of the external shape of the steel sheet in the quenching step.

As a conventional technique for heat treatment, there is Patent Publication No. 10-2000-0037732.

The present invention has been devised to solve the above problems, and it is an object of the present invention to provide a method for heat treatment of low-carbon steel that can suppress deformation of low-carbon steel when carburizing and quenching (??) of low-carbon steel.

In addition, an object of the present invention is to provide a method for heat treatment of low-carbon steel that is easy to handle.

In addition, the present invention aims to provide a method for heat treatment of low-carbon steel capable of simultaneously post-processing a plurality of low-carbon steel molded articles.

The present invention for the purpose of solving the above problems has the following configuration and features.

Carburization step of carburizing low-carbon steel, primary quenching step of cooling carburized low-carbon steel to a first quenching temperature, and secondary cooling of the first quenching low-carbon steel to a secondary quenching temperature lower than the primary quenching temperature Quenching step, anti-rusting step of washing and drying the second-quenched low-carbon steel under vacuum, press-tempering step of maintaining the anti-rusted low-carbon steel at a press tempering temperature and pressure for a press tempering time, shot blasting, sanding on press-tempered low-carbon steel And a post-treatment step in which at least one of the blasts is performed and an inspection step for inspecting a plan view of the post-treated low-carbon steel.

It also includes a transport step of transporting the low-carbon steel through a transport cart, wherein the transport cart has a seating plate with a moving wheel on the lower surface, a rod provided on the seating plate, an outer spring surrounding the rod and extrapolated to the rod. It may be extrapolated to a washer that is coupled to the top of the spring.

Also in the post-treatment step, the shot blasting is performed by a shot machine. A plurality of the press-tempered low-carbon steel is inserted into the shot in a state mounted on a cradle, and the cradle is a shaft frame having a length in a vertical direction, a horizontal frame extending radially from the shaft frame, and a length of the horizontal frame It is provided with a plurality of spaced apart along the direction, and includes a vertical frame extending along the vertical direction and a detachable portion provided at a predetermined distance along the vertical direction in the vertical frame to be detachably coupled to the plurality of press-tempered low carbon steels. can do.

The present invention having the above structure and features includes an effect of being able to improve dimensional precision by suppressing deformation of low-carbon steel after carburization by including a first quenching step and a press tempering step.

In addition, the present invention has the effect of easy storage, transport and withdrawal of the low-carbon steel by including a transport step of transporting the low-carbon steel through a transport cart.

In addition, the present invention has the effect that the low-carbon steel in the post-processing step is introduced into the shot in a state mounted on the cradle, so it is possible to perform a post-processing step for a plurality of low-carbon steel targets to shorten the process time.

1 is a flowchart schematically showing a heat treatment method of low-carbon steel according to an embodiment of the present invention.
2 is a view for explaining a carburizing furnace and a press tempering furnace.
3 is a view for explaining the rust preventive device.
4 is a view for explaining a short machine.
5 is a view for explaining the inspection machine.
6 is a view showing the external state of the ultra-low carbon steel prior to the carburizing step in this example.
7 is a view showing the external state of the ultra-low carbon steel after the carburizing step, the first quenching step, and the second quenching step.
8 is a view showing the external state of the ultra-low carbon steel subjected to the press tempering step.
9 is a view for explaining a transport truck.
10 is a view showing a further embodiment of the present invention.

The present invention can be applied to a variety of changes and can have a variety of forms, the implementation (態 樣, aspect) (or embodiments) to describe in detail in the text. However, this is not intended to limit the present invention to a specific disclosure form, and it should be understood that it includes all modifications, equivalents, and substitutes included in the spirit and scope of the present invention.

The terminology used herein is only used to describe a specific embodiment (sun, 態 樣, aspect) (or embodiment), and is not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In the present application, terms such as ~ include ~ or ~ consist of ~ are intended to designate the existence of features, numbers, steps, operations, components, parts or combinations thereof described in the specification, and one or more other features. It should be understood that the existence or addition possibilities of fields or numbers, steps, actions, components, parts or combinations thereof are not excluded in advance.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by a person skilled in the art to which the present invention pertains. Terms such as those defined in a commonly used dictionary should be interpreted as having meanings consistent with meanings in the context of related technologies, and should not be interpreted as ideal or excessively formal meanings unless explicitly defined in the present application. Does not.

~ 1 ~, ~ 2 ~, etc. described in this specification will only refer to different components, and are not limited to the order in which they are manufactured, and the names in the detailed description and claims of the invention It may not match.

1 is a flowchart schematically showing a method of heat treatment of low-carbon steel according to an embodiment of the present invention, and FIG. 2 is a view for explaining a carburizing furnace and a press tempering furnace.

Hereinafter, the heat treatment method of low-carbon steel in one embodiment of the present invention will be referred to as a 'this method' for convenience of description.

1 and 2, the present method (heat treatment method of low carbon steel) is a carburizing step (S1), a first quenching step (S2), a second quenching step (S3), a rust prevention step (S4), and a press tempering step ( S5), a post-treatment step (S6) and an inspection step (S7).

First, in the carburizing step (S1), the low-carbon steel is carburized. When the low-carbon steel is required to be processed, such as turning, it is preferably performed before the carburizing step (S1). That is, in the carburizing step (S1), the low carbon steel may be a processed low carbon steel product.

In order to improve moldability, the low carbon steel preferably has a carbon content of less than 0.3% by weight, and more preferably 0.1% by weight or less. In addition, it is preferable to be a steel sheet having a thickness of 2 mm to 5 mm, but is not necessarily limited to the thickness range.

Carburizing step (S1) may be performed through a carburizing furnace (1). Exemplarily, the carburizing step (S1) may be performed by forming a carburizing atmosphere and maintaining the carburizing furnace 1 into which the low-carbon steel is introduced at 750 ° C to 850 ° C (hereinafter, a carburizing temperature) for several hours.

The carburizing atmosphere may be formed by introducing a carburizing agent into the carburizing furnace 1 such as charcoal or by introducing carburizing gas such as CH3OF, methane, CH3 into the carburizing furnace 1. Since these conditions are well known to those of ordinary skill in the present invention, detailed descriptions are omitted.

1 and 2, the first quenching step (S2) is a step of rapidly cooling the carburized low-carbon steel after the carburizing step (S1) to the first quenching temperature. Illustratively, the first quenching step S2 may be performed by adjusting the temperature of the carburizing furnace 1.

The primary quenching temperature may be provided for 10 minutes to several tens of minutes, starting at 700 ° C to 800 ° C, which is slightly lower than the carburizing temperature in the carburizing step (S1), but is not limited thereto. That is, in the first quenching step (S2), the first quenching temperature and the holding time can be performed in various situations depending on the type of low-carbon steel, the use, and the conditions during the carburizing reaction, and these conditions are those skilled in the present invention. Since it is a well-known configuration, detailed description is omitted.

The method has the advantage of suppressing the deformation of the low-carbon steel after the carburizing step (S1) and the low-carbon steel of the secondary quenching step (S3) described later by including the first quenching step (S2).

1 and 2, in the second quenching step (S3), the low quenching steel first quenched after the first quenching step (S2) is cooled to a second quenching temperature lower than the first quenching temperature.

By way of example, the first quenched low-carbon steel may be drawn out from the carburizing furnace 1 and introduced into oil or the like that maintains the second quenching temperature. At this time, the second quenching temperature may be 100 ° C to 200 ° C. The first quenched low-carbon steel is preferably performed for about 20 to 30 minutes at the second quenching temperature, but is not necessarily limited to the above conditions (secondary quenching temperature and holding time).

3 is a view for explaining the rust preventive device.

1 and 3, the rust prevention step (S4) is a step of washing and drying the low-quenched steel, which is second-quenched after the second quenching step (S3), in vacuum.

The anti-rusting step (S4) suppresses the occurrence of rust in the secondary-quenched low-carbon steel by washing the surface in a vacuum atmosphere by introducing the secondary-quenched low-carbon steel into the anti-corrosive device (4). Since the rust preventive device 4 is obvious to a person skilled in the art, a more detailed description will be omitted.

1 and 2, the press tempering step (S5) is a step of maintaining the rust prevented low-carbon steel at a press tempering temperature and a press tempering pressure for a press tempering time. Exemplarily, the press tempering step (S5) may be performed by the press tempering furnace (5), after which the rust prevented low carbon steel is introduced into the press tempering furnace (5) to press the tempering step (S5). Is to do

The press tempering temperature is a temperature below the transformation point of the low carbon steel, the press tempering time is less than a few minutes, and the press tempering pressure may be about 100 cm ² / Kg. However, it is not necessarily limited to the press tempering temperature, press tempering time, and press tempering pressure.

As an example, the press tempering step (S5) is preferably performed multiple times. At this time, the press pressure may be 50 to 120 cm ² / Kg, and the press tempering time may be 15 to 40 seconds. However, when the press tempering time is lengthened, the press tempering step S5 may be performed only once.

As described above, the present method can suppress deformation of low-carbon steel by including a press-tempering step (S5) that maintains at a tempering temperature while applying a constant pressure to the low-carbon steel instead of the tempering normally used after quenching (? Qing). There is an advantage.

4 is a view for explaining a short machine.

1 and 4, the post-treatment step (S6) is a step in which at least one of shot blasting and sand blasting is performed on the low-carbon steel that is press-tempered after the press tempering step (S5). The shot blasting is performed by the short machine 6 and the sand blasting is performed by a sand blasting machine (not shown).

The shot machine 6 and the sand blast machine (not shown) each spray hard particles (short balls) and sand on the surface of the low-carbon steel, which is the object of the present invention, using compressed air or the like, foreign substances on the surface of the low-carbon steel, It is performed to remove paint and the like, and to increase the surface strength.

5 is a view for explaining the inspection machine.

1 and 5, the inspection step (S7) inspects the plan view of the low-carbon steel after the post-treatment step (S6). It may be performed by the inspection machine 7 of the inspection step (S7). In this regard, since it is apparent to a person skilled in the art, a more detailed description is omitted.

Experimental Example

A specific example of heat-treating low-carbon steel according to a preferred embodiment of the method will be described below.

First, as a sample, 0.01% by weight of carbon was included, a thickness of 0.1mm, and a very low-carbon steel having a flatness of 0.15mm was prepared, and a carburizing step (S1) was performed. In the carburizing step (S1), the carburizing temperature was performed at 805 ° C for 120 minutes. In addition, during the carburizing reaction, the inside of the carburizing furnace 1 was maintained at 2800 cc / hr of CH3OH, 7 ml / min of C3H8, and 3.0 ml / min of NH3, and an exemplary carbon atmosphere of 0.9% was maintained.

Next, a first quenching step (S2) was performed. Specifically, the internal temperature of the carburizing furnace 1 was lowered to 760 ° C for 20 minutes, and the internal temperature of the carburizing furnace 1 was lowered to 150 ° C. In addition, during the first quenching step (S2), the inside of the carburizing furnace 1 was kept the same as during the carburizing reaction.

A second quenching step (S3) was performed. The first quenched low-carbon steel was maintained at about 150 ° C for about 30 minutes.

Next, a press tempering step (S5) was performed. Specifically, the press tempering step (S5) was performed by heating the second quenched low-carbon steel to 430 ° C. and then pressurizing it at a pressure of about 100 cm ² / Kg for 25 seconds, and the pressurization was performed a total of 3 times.

According to the experimental example, the ultra-low carbon steel is only before press tempering (before the press tempering step (S5)), that is, as in the conventional carburizing step (S1), the first quenching step (S2), and the second quenching step (S3) When performed, the ultra-low-carbon steel, which had an initial flatness of 0.15 mm, showed flatness of about 0.6 mm to 0.7 mm, but after performing a press tempering step (S5) according to a preferred embodiment of the present invention, 0.2 mm It was confirmed that it had a flatness of. Here, the flatness may be a value measured through the inspector 7 in the above-described inspection step (S7). That is, when performing the press tempering step (S5) according to a preferred embodiment of the present invention, it means that it is possible to suppress deformation such as warping of low-carbon steel due to carburizing and quenching.

6 is a view showing the external state of the ultra-low-carbon steel before the carburizing step in this experimental example, FIG. 7 is a view showing the external state of the ultra-low-carbon steel after the carburizing step, the primary quenching step, the secondary quenching step, and 8 is a view showing the external state of the ultra-low carbon steel subjected to the press tempering step.

As shown in Figure 2, the carburizing step (S1), the first quenching step (S2), the second low quenching carbon steel (S3) that performs the quenching step (S3) is performed in the initial carburization step (S1) is significantly deformed compared to the previous one, but the ultra-low carbon steel subjected to the press tempering step (S5) after the carburizing step (S1), the first quenching step (S2), and the second quenching step (S3) is shown in FIG. 3. As can be seen, the deformation was greatly reduced.

9 is a view for explaining a transport truck.

Meanwhile, the method may include a transport step (not shown) of transporting the low-carbon steel through the transport truck 8.

The conveying step (not shown) is a step (carburizing step (S1), primary quenching step (S2), secondary quenching step (S3), anti-rusting step (S4), press tempering step (S5), respectively) in the present method. It may be performed before the processing step (S6), the inspection step (S7), or after each step.

Referring to FIG. 9, the transport vehicle 8 is a seating plate (not shown) equipped with a moving wheel on the lower surface, a rod 81 provided on the seating plate (not shown), and an extrapolated rod 81 It may be extrapolated to the spring 82 and the rod 81, but may include a washer 83 coupled to the top of the spring 82. The lower end of the spring 82 may be coupled to the seat plate (not shown) or a stepped protrusion protruding from the lower end of the rod 81.

As described above, since the low-carbon steel has increased strength after the carburizing step (S1), it was said that it can be processed into a molded article before the carburizing step (S1), and the molded article may be hollow. The molded article of may be seated on a seating plate (not shown) in a state inserted into the rod 81 (see FIG. 9).

At this time, the outer diameter of the washer 83 described above is formed to be larger than the inner diameter of the hollow of the molded article, when the molded article is extrapolated to the rod 81, the washer 83 supports the molded article, and the molded article delivered by the washer 83 By the weight of the spring 82 is compressed a number of molded products hollow can be extrapolated to the rod 81. That is, as the number of molded articles extrapolated to the rod 81 increases, the spring 82 is further compressed by the weight of the loaded molded article so that the elastic modulus of the spring 82 is such that the molded article does not deviate from the rod 81. It is desirable to be determined.

At this time, when a molded product fitted to the rod 81 is pulled out by an operator or the like, the molded product moves to the upper side of the rod 81 by the elastic force of the spring 82, and the molded product (processed low-carbon steel) inserted into the rod 81 is viewed. It has the advantage of being able to withdraw conveniently.

1 and 4, it has been described above that in the post-processing step (S6), the shot blasting may be performed by the shot machine (6).

At this time, a plurality of press-tempered low-carbon steel (press-tempering step (S5 after the low-carbon steel)) is introduced into the shot machine 6 while being mounted on a cradle (HD). More specifically, the cradle (HD), the cradle (HD) is an axis frame (not shown) having a length in the vertical direction, a horizontal frame (HD1), extending radially from the top of the axis frame (not shown), horizontal A plurality of spaced apart along the longitudinal direction of the frame (HD1) is provided, a predetermined distance along the vertical direction in the vertical frame (HD2) and the vertical frame (HD2) extending along the vertical direction (e.g., the lower direction) It may include a detachable portion (HD3) provided to be detachably coupled to a plurality of press-tempered low-carbon steel (low-carbon steel after the press tempering step (S5)).

It was said that the low-carbon steel may be processed and formed into a molded article before the carburizing step (S1). When the molded article is to form a hollow, the detachable part HD3 is protruded from the vertical frame HD2, but is inclined upward. It can be a ring.

As described above, since the method includes a cradle (HD), a large amount of press-tempered low-carbon steel is introduced into the shot machine (6) to efficiently perform shot blasting, thereby reducing the cost of performing shot blasting. There is an advantage.

10 is a view showing a further embodiment of the present invention.

1, 4 and 10, the shot machine 6 sprays hard particles (short balls) onto the surface of the low carbon steel. Therefore, the shot machine 6 is required to suppress the outflow of the injected hard particles to the outside, thereby making it necessary to make the environment of the work site where the post-treatment step S6 (short blasting) is performed.

In addition, the shot machine 6 is a spraying device (not shown) for spraying hard particles, and the shot machine 6 is a separation device (not shown) for separating foreign particles and hard particles separated from low-carbon steel, and the separation device (not shown) ) May include a transport device (not shown) for transporting the separated hard particles for reuse.

In summary, the shot machine 6 includes a working space for installation of the above-described spraying device (not shown), separation device (not shown), transfer device (not shown), protective film (not shown), and the like. It is required to seal the space so that hard particles do not flow out of the shorter 6.

As a means for solving the above problem, the short machine 6 is coupled to the main body H1 having the opening H11 and the interior space H12 on one side, and the main body H1 to cover the opening H11. And (H2) and a housing (H) including a hermetic coupling means (C) for coupling and sealing the main body (H1) and the cover (H2).

 The sealing engagement means (C) is a binding groove (C1) formed along the circumference of the main body (H1), an extension groove (C2) formed on the wall surface of the binding groove (C1), and a cover (H2) on the wall surface of the extension groove (C2) It is provided along the circumference of the entrance hole (C3), the cover (H2) formed in the side and inserted into the binding groove (C1), provided along the circumference of the cover (H2) and corresponding to the entrance hole (C3) Locking pin (C5) formed in the position, the sealing member (C6) provided on the outer surface of the binding projection (C4) and the lock pin that is accommodated in the access hole (C3) to move back and forth and the front end is inserted into the lock groove (C5) (C7),

 The sealing member C6 includes a heating part C61 that generates heat by an impact of a threshold value or more, and an expansion part C62 that is provided outside the heating part C61 to expand by heat generation.

As described above, by having the opening H11 of the housing H, accessibility to the internal space H12 (the working space) is improved, so that work on the internal configuration, such as assembly, wiring, replacement, and soldering, is easy. . In addition, it is possible to fundamentally prevent the deterioration of the sealing performance due to taking the powder bonding form in order to have the opening H11 described above by the sealing coupling means C, without additional equipment, additional tools, and skilled techniques. H11) and the cover (H2) can improve the bonding force and holding force.

(In the following description, for convenience of explanation, the upper, lower, left, and right sides will be described based on FIG. 10. This direction specification should not be interpreted as an element limiting the scope of the present invention. .)

Referring to Figure 10, more specifically, first, the binding groove (C1) is a groove formed along the circumference of the body at the end side of the body (H1), the overall shape of the binding groove (C1) is the shape of the body Follow. The binding groove (C1) is formed by being recessed downward along the circumference of the main body (H1) from the top.

And the extended groove (C2) is a groove formed on the wall surface (side wall of the drawing reference) of the binding groove (C1), also the overall shape (H1) of the extended groove (C2) follows the shape of the body. The binding groove (C1) and the extension groove (C2) has a continuous groove structure along the circumference of the body.

And the entrance hole (C3) is formed to the cover (H2) side from the wall surface of the extension groove (C2). For example, the access hole C3 may be a through hole penetrating the upper wall surface adjacent to the cover H2 and the upper end of the main body H1 in the extension groove C2.

And the binding projection (C4) is provided to protrude from the bottom to the bottom along the circumference of the cover (H2) is inserted into the binding groove (C1) when the coupling between the main body (H1) and the cover (H2).

And the locking groove (C5) is a groove recessed upward from the bottom of the cover (H2), similarly formed at a position corresponding to the exit hole (C3) along the perimeter of the cover (H2).

And the sealing member (C6) is provided on the outer surface of the binding projection (C5). The sealing member C6 includes a heating part C61 that generates heat by an impact of a threshold or higher, and an expansion part C62 provided outside the heating part C61 to expand by heat generation. In more detail, the heating part C61 includes 50 parts by weight of water compared to 80 parts by weight of sodium acetate, and is accommodated in the heat conductor C63. The heating part C61 may be provided by dissolving sodium acetate in supersaturated water.

The heat generating portion C61 is heated by receiving a shock of a threshold or higher while being pressed by the lower wall of the cover H2 and the binding groove C1 during the coupling process between the cover H2 and the main body H1, and the heat generation temperature It is about 50 ~ 90 ℃.

The expanded part (C62) is characterized in that it further comprises 1 part by weight of polyol di (meth) acrylate and 13 parts by weight of hydrofluoric ether, relative to 100 parts by weight of cellulose ester.

In the above, cellulose ester is used as a thermoplastic polymer constituting the polymerizable monomer, and the glass transition temperature is 30 to 120 ° C., but the glass transition temperature is lowered to 55 ° C. by a crosslinking agent described later. The other composition of the expanded portion (C62) is based on 100 parts by weight of this cellulose ester.

Polyol di (meth) acrylate is added as a crosslinking agent, and the molecular weight between the crosslinking points is large, thereby increasing the viscosity of the expanded portion (C62) without deteriorating the foaming properties of the hydrofluoric ether without excessively increasing the crosslinking density of the polymer resin. In addition, the glass transition temperature of the expansion portion C62 is lowered to enable foaming at a low temperature. If the polyol di (meth) acrylate is too small, the thickening effect is insignificant and can be easily torn during foaming. If excessive, the crosslinking density is excessively high, thereby deteriorating the foaming magnification. As a result of repeated experiments, the content showing optimal foaming properties was 4 parts by weight.

The hydrofluor ether is added as a blowing agent, and the content is preferably 13 parts by weight. When the expansion portion (C62) is heated by the heating portion (C61), the thermoplastic polymer softens, and at the same time, the internal pressure of the blowing agent rises to expand the volume.

And the locking pin (C7) is accommodated in the access hole (C3) to move forward and backward (up and down based on the drawing), the front end is inserted into the locking groove (C5). Description of the specific matters in which the locking pin C7 is accommodated in the entrance hole C3 is omitted, and it is assumed that normal knowledge is followed.

The above-described sealing engagement means (C) largely provides two effects, one is to completely close the gap occurring in the coupling portion between the main body (H1) and the cover (H2), and the other body (H1) ) And improves the binding force between the cover (H2), the holding force and the shaking of the cover.

Summarizing the operation and effects of the hermetic coupling means (C) with reference to FIG. 10, in the state of FIG. 10 [A], the heat generating part (C61) is an impact applied upon coupling between the main body (H1) and the cover (H2). As the heat is generated, the expansion part C62 is expanded, and thus, a gap between the main body H1 and the cover H2 is filled as shown in FIG. And in this process, the expansion portion (C62) is expanded and filled in the extension groove (C2), thereby advancing the locking pin (C7) so that the locking pin (C7) is inserted into the locking groove (C5), the main body (H1) And the locking structure between the cover H2 and the cover H2.

The present invention described above with reference to the accompanying drawings can be variously modified and changed by a person skilled in the art, and such modifications and variations should be interpreted as being included in the scope of the present invention.

Carburizing furnace: 1 Hearing aid: 4
Press tempering furnace: 5 Short machine: 6
Holder: HD Horizontal frame: HD1
Vertical frame: HD2 Detachable part: HD3
Checker: 7 Carrier: 8
Rod: 81 Spring: 82
Washers: 83

Claims (4)

Carburizing step of carburizing the low carbon steel;
A first quenching step of cooling the carburized low carbon steel to a first quenching temperature;
A second quenching step of cooling the first quenching low carbon steel to a second quenching temperature lower than the first quenching temperature;
Rust prevention step of washing and drying the second quenched low-carbon steel in a vacuum;
A press tempering step of maintaining the rust prevented low carbon steel at a press tempering temperature and pressure for a press tempering time;
A post-treatment step in which at least one of shot blasting and sand blasting is performed on the press-tempered low-carbon steel; And
An inspection step of inspecting a plan view of the post-treated low-carbon steel;
Including,
A transport step of transporting the low-carbon steel through a transport cart,
The carriage is characterized in that it comprises a seating plate provided with a moving wheel on the lower surface, a rod provided on the seating plate, a spring wrapped around the rod and extrapolated to the rod, but a washer coupled to the top of the spring. Low carbon steel heat treatment method.
delete The method according to claim 1,
In the post-treatment step, the shot blasting is performed by a shot machine.
A plurality of the press-tempered low-carbon steel is introduced into the shorter while mounted on a cradle,
The cradle includes an axial frame having a length in a vertical direction, a horizontal frame extending radially from the axial frame, a plurality of spaced apart spaces along the longitudinal direction of the horizontal frame, and a vertical frame extending in the vertical direction and the vertical frame Heat treatment method of a low-carbon steel, characterized in that it comprises a detachable portion which is provided at a predetermined interval along the vertical direction to be detachably coupled to a plurality of the press-tempered low-carbon steel.
The method according to claim 3,
The short machine includes a housing having an opening and an internal space on one side, a cover coupled to the main body to cover the opening, and a housing including a sealing coupling means for coupling and sealing the main body and the cover,
The sealing coupling means, a binding groove formed along the circumference of the main body, an extension groove formed on the wall surface of the binding groove, an entrance hole formed toward the cover side from the wall surface of the extension groove, is provided along the circumference of the cover and the binding groove The binding protrusion inserted into the cover, provided along the periphery of the cover, a locking groove formed in a position corresponding to the entrance hole, a sealing member provided on the outer surface of the binding protrusion, and accommodated in the entrance hole to move back and forth and shear when advancing. The locking pin is inserted into the locking groove,
The sealing member includes a heat generating part that generates heat by an impact of a threshold value or more, and an expansion part that is provided outside the heat generating part to expand by heat generation,
The heating portion contains 50 parts by weight of water compared to 80 parts by weight of sodium acetate,
The expansion portion is a heat treatment method of low-carbon steel, characterized in that it further comprises 1 part by weight of polyol di (meth) acrylate and 13 parts by weight of hydrofluoric ether, compared to 100 parts by weight of cellulose ester.

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