Method of Heat Treatment of a Metal Material

Abstract

A method of heat treatment of a metal material is disclosed. The method of heat treatment includes heating the metal material to a first temperature through a heating fixture, and reducing the first temperature of the metal material to a second temperature through a cooling apparatus performing a fast cooling operation. The fast cooling operation has a high cooling speed of 80° C./sec to 200° C./sec. As such, the processed metal material can have the required mechanical properties.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

The application claims the benefit of Taiwan application serial No. 104138249, filed on Nov. 19, 2015, and the subject matter of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present disclosure generally relates to a method of heat treatment of a metal material and, more particularly, to a method of heat treatment which changes the mechanical properties of a metal material by controlling the cooling speed.

2. Description of the Related Art

Heat treatment process is able to change the mechanical properties of a metal material during the processing of the metal material. For example, when steel is heated to a predetermined temperature, a cooling apparatus can perform a cooling operation to the steel. The cooling apparatus is able to change the texture of the steel by controlling the cooling temperature of the steel, such that the mechanical properties of the steel will meet the required standards (such as stiffness or ductility).

FIG. 1 shows a machine 9 for producing hot-rolled steel sheets. The machine 9 includes a hot-rolling processing machine 91, an instant cooling machine 92 and a thermal circulation cooling machine 93 which are sequentially arranged in a convoying direction of the steel “S.” The steel “S” is shaped by the hot-rolling processing machine 91 to form a predetermined shape, and then undergoes an instant cooling operation performed by the instant cooling machine 92. Finally, the cooled steel “S” is sent to the thermal circulation cooling machine 93 which adjusts the mechanical properties of the steel “S” by maintaining the steel “S” in a predetermined temperature. Such a method of heat treatment can be seen in Taiwan Patent No. I445581.

However, the mechanical properties of the steel “S” change due to not only the cooling temperature but also the cooling speed. Since the conventional method of heat treatment controls the cooling temperature but does not control the cooling speed, the processed metal material (such as steel) cannot have the required mechanical properties.

In light of this, it is necessary to provide a novel method of heat treatment of a metal material.

SUMMARY OF THE INVENTION

It is therefore the objective of this disclosure to provide a method of heat treatment which changes the mechanical properties of a metal material by controlling the cooling speed. As such, the processed metal material will have the required mechanical properties.

In an embodiment of the disclosure, a method of heat treatment of a metal material is disclosed. The method of heat treatment includes heating the metal material to a first temperature through a heating fixture, and reducing the first temperature of the metal material to a second temperature through a cooling apparatus performing a fast cooling operation. The fast cooling operation has a high cooling speed of 80° C./sec to 200° C./sec. As such, the processed metal material can have the required mechanical properties.

In a form shown, the fast cooling operation includes spraying a coolant to the metal material through a spraying unit of the cooling apparatus. As such, the metal material can be cooled.

In the form shown, the fast cooling operation includes spraying the coolant to the metal material with a high speed ejection flow of 60 L/min to 1000 L/min. As such, the processed metal material can have the required mechanical properties via the fast cooling operation.

In the form shown, the coolant applies a high speed ejection pressure to the metal material at the instant the coolant hits the metal material, and the high speed ejection pressure is 70-300 bars. As such, the processed metal material can have the required mechanical properties via the fast cooling operation.

In the form shown, the method of heat treatment further includes reducing the second temperature of the metal material to a third temperature through the cooling apparatus performing a slow cooling operation. The slow cooling operation has a slow cooling speed of 50° C./sec to 80° C./sec. As such, the processed metal material can have the required mechanical properties through the controlling of the cooling speed.

In the form shown, the slow cooling operation includes spraying the coolant to the metal material through the spraying unit of the cooling apparatus. As such, the metal material can be cooled.

In the form shown, the slow cooling operation includes spraying the coolant to the metal material with a low speed ejection flow of 20 L/min to 60 L/min. As such, the processed metal material can have the required mechanical properties via the slow cooling operation.

In the form shown, the coolant applies a low speed ejection pressure to the metal material at the instant the coolant hits the metal material, and the low speed ejection pressure is 30-70 bars. As such, the processed metal material can have the required mechanical properties via the slow cooling operation.

In the form shown, the method of heat treatment further includes convoying the metal material in a convoying direction through a convoying unit of the cooling apparatus. As such, the metal material can be convoyed.

In the form shown, the cooling apparatus includes the spraying unit spraying the coolant to the metal material in a spraying direction, and an angle between the convoying direction and the spraying direction is between 15° and 90°. As such, a proper heat exchange effect can be provided between the coolant and the metal material. In addition, the efficiency of the coolant flushing the film on the surface of the metal material during the fast cooling step, as well as the efficiency of the coolant removing the rust scale from the surface of the metal material during the slow cooling step, can be improved.

In the form shown, the angle is 45°. As such, a proper heat exchange effect can be provided between the coolant and the metal material. In addition, the efficiency of the coolant flushing the film on the surface of the metal material during the fast cooling step, as well as the efficiency of the coolant removing the rust scale from the surface of the metal material during the slow cooling step, can be improved.

In the form shown, the method of heat treatment further includes rotating the metal material about an axle parallel to the convoying direction during the convoying of the metal material. As such, a proper heat exchange effect can be provided between the coolant and the metal material. In addition, the efficiency of the coolant flushing the film on the surface of the metal material during the fast cooling step, as well as the efficiency of the coolant removing the rust scale from the surface of the metal material during the slow cooling step, can be improved.

In the above, when the metal material is convoyed in the convoying direction during the cooling operation of the metal material, the convoying unit drives the metal material to rotate about an axle parallel to the convoying direction in order to maintain a proper heat exchange effect. The efficiency of the coolant flushing away the film on the surface of the metal material during the fast cooling step, as well as the efficiency of the coolant removing the rust scale from the surface of the metal material during the slow cooling step, are improved.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will become more fully understood from the detailed description given hereinafter and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present disclosure, and wherein:

FIG. 1 shows a conventional processing machine.

FIG. 2 shows a cooling apparatus performing a method of heat treatment according to an embodiment of the disclosure.

FIG. 3 is a side view of the cooling apparatus performing the method of heat treatment according to the embodiment of the disclosure.

FIG. 4 is an enlarged view of a roller along with a metal material according to the embodiment of the disclosure.

FIG. 5 is a partial view of a spraying unit of the cooling apparatus performing the method of heat treatment according to the embodiment of the disclosure.

In the various figures of the drawings, the same numerals designate the same or similar parts. Furthermore, when the terms “first”, “second”, “third”, “fourth”, “inner”, “outer”, “top”, “bottom”, “front”, “rear” and similar terms are used hereinafter, it should be understood that these terms have reference only to the structure shown in the drawings as it would appear to a person viewing the drawings, and are utilized only to facilitate describing the disclosure.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 2 and 3 show a cooling apparatus performing a method of heat treatment according to an embodiment of the disclosure. The cooling apparatus is used to perform a cooling operation of a metal material “S” and includes a convoying unit 1 and a spraying unit 2. The spraying unit 2 is arranged at one side of the convoying unit 1.

The convoying unit 1 includes a base 11 and a plurality of rollers 12. The base 11 includes a feeding end 111 and a discharging end 112 in which a convoying direction D1 extends from the feeding end 111 to the discharging end 112. The plurality of rollers 12 is arranged on the base 11. Each of the plurality of rollers 12 includes a convoying portion 121 and a shaft 122. The convoying portion 121 has a diameter which reduces from two ends to the center thereof. The shaft 122 extends in an axle direction D2 which is neither parallel nor vertical to the convoying direction D1. The convoying unit 1 further includes a driving motor 13. The shafts 122 of two adjacent rollers 12 are connected together via a transmission unit 14. The driving motor 13 delivers the power to the shafts 122 of the plurality of rollers 12 via the transmission units 14.

Referring to FIG. 4, the convoying portion 121 of the roller 12 has a varying diameter. The convoying portion 121 has an outer face which may form a curved face in linear projection. For example, the outer face of the convoying portion 121 is in the form of a concave curved face. In this arrangement, when the metal material “S” is in the form of a rod and is disposed on the convoying portions 121 of the plurality of rollers 12, the convoying portions 121 may apply a movement force and a rotational force to the metal material “S.” As such, the metal material “S” may move in the convoying direction D1 while rotating in the concave curved faces of the convoying portions 121. Thus, the metal material “S” can have the movement and rotation effects at the same time. The diameter change of the convoying portion 121 is not limited, but may be adjusted according to the shape of the metal material “S.”

Referring FIGS. 2 and 3 again, the spraying unit 2 includes a plurality of nozzle units 21 arranged between the feeding end 111 and the discharging end 112 of the base 11. Each of the plurality of nozzle units 21 includes a plurality of nozzles 211 facing the metal material “S” that is convoyed by the convoying portions 121 of the plurality of rollers 12. The plurality of nozzles 211 is able to spray a coolant which may be any working fluid with a heat exchange function. In the embodiment, the coolant may be water but is not limited thereto. The spraying unit 2 further includes a support 22 coupled with the base 11 of the convoying unit 1. The plurality of nozzle units 21 is arranged on the support 22. The support 22 may be used as a coolant transmission pipe for transmission of the coolant. In this regard, the plurality of nozzle units 21 may intercommunicate with the coolant transmission pipe such that the coolant in the coolant transmission pipe may be sprayed out by the plurality of nozzle units 21.

Referring to FIG. 5, the arrangement of the plurality of nozzle units 21 is not limited. The plurality of nozzle units 21 may be parallel to the convoying direction D1. As such, the coolant will be sprayed by the plurality of nozzle units 21 in a spraying direction D3 vertical to the convoying direction D1. Alternatively, as shown in the embodiment, the plurality of nozzle units 21 may be arranged in an inclined manner between the feeding end 111 and the discharging end 112. As a result, the spraying direction D3 of the coolant will contain a horizontal component and a vertical component (according to the orientation of the cooling apparatus in the drawing). The horizontal component of the spraying direction D3 is opposite to the convoying direction D1, such that the coolant of the plurality of nozzles 211 will apply a larger impact force to the metal material “S” moving in the convoying direction D1. Therefore, the film or rust scale on the surface of the metal material “S” may be flushed by the coolant. Therefore, the heat treatment process is smooth.

The method of heat treatment of a metal material according to the embodiment of the disclosure includes a heating step and a fast cooling step.

In the heating step, a heating fixture is used to heat the metal material “S” to a first temperature. The type of the metal material “S” is not limited, and the first temperature may be flexibly adjusted according to the type of the metal material “S.” In the embodiment, the metal material “S” is steel and the first temperature is between 800° C.-1200° C. When the metal material “S” is to be heated to the first temperature, the first temperature is the surface temperature of the metal material “S.”

In the fast cooling step, the cooling apparatus performs a fast cooling operation to the metal material “S” to reduce the temperature of the metal material “S” to a second temperature. The fast cooling step reduces the temperature of the metal material “S” in a high cooling speed, which is between 80° C./sec to 200° C./sec.

Specifically, the spraying unit 2 performs the fast cooling operation by spraying the coolant. In the fast cooling operation, each of the plurality of nozzles 211 has a high speed ejection flow during the spraying of the coolant. The high speed ejection flow is between 60 L/min to 1000 L/min. The coolant from the spraying unit 2 applies a high speed ejection pressure to the metal material “S” at the instant the coolant hits the metal material “S.” The high speed ejection pressure is about 70-300 bars. In the arrangement, not only the mechanical properties of the metal material “S” can be adjusted by improving the heat change effect through the use of a large amount of coolant, but also the film that is generated on the surface of the metal material “S” during the heating step may be flushed by the high pressure cooling flow of the coolant. Advantageously, the processed metal material “S” will have the required mechanical properties through the fast cooling process, and the surface integrity of the metal material “S” can be maintained.

The second temperature may be flexibly adjusted according to the type of the metal material “S.” In the embodiment, when the metal material “S” is steel, the second temperature is a phase-change critical temperature of the steel. In the fast cooling step, the mechanical properties of the steel can be adjusted by reducing the temperature of the steel to the phase-change critical temperature in a cooling speed. As such, the processed steel will have the required mechanical properties.

The method of heat treatment according to the embodiment of the disclosure may further include a slow cooling step. In the slow cooling step, the cooling apparatus performs a slow cooling operation to the metal material “S,” reducing the temperature of the metal material “S” in a low cooling speed. The low cooling speed is between 50° C./sec to 80° C./sec.

Specifically, the spraying unit 2 performs the slow cooling operation by spraying the coolant. In the slow cooling operation, each of the plurality of nozzles 211 has a low speed ejection flow during the spraying of the coolant. The low speed ejection flow is between 20 L/min to 60 L/min. The coolant of the spraying unit 2 applies a low speed ejection pressure to the metal material “S” at the moment the coolant hits the metal material “S.” The low speed ejection pressure is about 30-70 bars. The third temperature may be flexibly adjusted according to the type of the metal material “S.” In this arrangement, the heat exchange process can be slowed down through a smaller amount of the cooling flow. As a result, not only the mechanical properties of the metal material “S” can be adjusted by slowing down the heat exchange process through the use of a smaller amount of coolant, but also the film on the surface of the metal material “S” may be flushed by the cooling flow that has a proper pressure. Advantageously, the processed metal material “S” will have the required mechanical properties through the slow cooling process, and the film on the surface of the metal material “S” can be removed.

Furthermore, before the fast cooling step, the method of heat treatment according to the embodiment of the disclosure may further include a temperature maintaining step after the heating step is performed. In the temperature maintaining step, after the metal material “S” is heated to the first temperature, the metal material “S” is maintained in the first temperature for a predetermined period of time. In the embodiment, the metal material “S” is steel, the first temperature is 800-1200° C., and the predetermined period of time is 10-60 min. Based on the above steps, the mechanical properties of the steel can be adjusted as required.

Referring to FIGS. 2 and 3 again, the plurality of nozzle units 21 may spray the coolant according to the fast cooling step and the slow fast cooling step. As a preferred case in FIG. 2, the part of the plurality of nozzle units 21 that is adjacent to the feeding end 111 is used to perform the fast cooling step, whereas the part of the plurality of nozzle units 21 that is adjacent to the discharging end 112 is used to perform the slow cooling step. Thus, the fast cooling step and the slow cooling step can be performed in sequence as the metal material “S” is convoyed by the convoying unit 1. As a result, the processed metal material “S” will have the required mechanical properties under the fast cooling step and the slow cooling step sequentially performed.

Referring to FIG. 5 again, during the fast cooling step and the slow cooling step, the convoying unit 1 convoys the metal material “S” in the convoying direction D1, and the spraying unit 2 sprays the coolant in the spraying direction D3. In this regard, there is an angle A1 between the convoying direction D1 and the spraying direction D3. The angle A1 is between 15° and 90°, which is preferably 45° in the embodiment. In this arrangement, not only the coolant and the metal material “S” can have a proper heat exchange effect therebetween, but also the efficiency of the coolant flushing the film on the surface of the metal material “S” during the fast cooling step, as well as the efficiency of the coolant removing the rust scale from the surface of the metal material “S” during the slow cooling step, can be improved.

In other words, when the fast cooling step and the slow cooling step are performed under the cooling apparatus according to the embodiment of the disclosure, if the metal material “S” is in the form of a rod, the plurality of rollers 12 is able to convoy the rod-shaped metal material “S” in the convoying direction D1 while the metal material “S” is able to rotate about an axle parallel to the convoying direction D1 via the concave curved faces of the convoying portions 121 of the plurality of rollers 12. Thus, the coolant can be uniformly sprayed on the metal material “S,” which not only provides a proper heat exchange effect between the coolant and the metal material “S,” but also improves the efficiency of the coolant flushing the film on the surface of the metal material “S” during the fast cooling step, as well as the efficiency of the coolant removing the rust scale from the surface of the metal material “S” during the slow cooling step.

In order to prove that the method of heat treatment according to the embodiment of the disclosure has the ability to process the metal material with the required mechanical properties, the rod-shaped steel with the diameter of 60 mm (SCM440) is used in the experiment. The obtained mechanical properties are listed in Tables 1 and 2 below.

TABLE 1
	Tensile Strength	Yield Strength
Metal Material	(MPa)	(MPa)	Hardness
SCM440	924	730	41
S1-1	A	1866	1492	56.9
	B	1816	1463	53.3
S1-2	A	1772	1334	53.2
	B	1817	1410	52.0
S1-3	A	1870	1390	53.1
	B	1806	1305	52.9
S1-4	A	1827	1342	53.0
	B	1865	1274	51.5

	TABLE 2
	Hardness (HRC)
Metal	Depth	Depth	Depth	Depth
Material	(30 mm)	(15 mm)	(7.5 mm)	(1 mm)
S1-1	53.6	54.3	55.5	55.4
S1-2	53.2	55.7	57.2	55.8
S1-3	56.7	55.2	56.6	56.2
S1-4	51.4	52.9	55.0	54.8

Tables 1 and 2 show the mechanical properties obtained by the steps of heating 4 types of SCM440 steel rods to 1100° C. (first temperature), maintaining the steel rods in the first temperature for a period of time, convoying the steel rods in a speed, and reducing the temperature of the steel rods to Martensite formation temperature (second temperature) with a coolant having an ejection flow of 1000 L/min and an ejection pressure of 120 bar. The steel No. S1-1 is maintained in the first temperature for 30 min, the one No. S1-2 is 35 min, the one No. S1-3 is 15 min, and the one No. S1-4 is 20 min. The steel No. S1-1 is convoyed in a speed of 5 M/min, and the rests are convoyed in a speed of 7 M/min. “A” and “B” represent two different sampling points on the same steel. The depth represents the distance from the surface of the steel to a central axle of the steel. It can be known from Tables 1 and 2 that the mechanical properties of the steel (tensile strength and yield strength) may be improved by 40% or more and the hardness of the steel may be improved by 20% or more using the method of heat treatment according to the embodiment of the disclosure. Therefore, it is proven that the method of heat treatment according to the embodiment of the disclosure is capable of processing the metal material with the required mechanical properties.

In summery, the method of heat treatment according to the embodiment of the disclosure changes the texture of the metal material “S” by reducing the temperature of the metal material “S” in a certain cooling speed. As such, the processed metal material “S” will have the required mechanical properties.

Although the disclosure has been described in detail with reference to its presently preferable embodiments, it will be understood by one of ordinary skill in the art that various modifications can be made without departing from the spirit and the scope of the disclosure, as set forth in the appended claims.

Claims

1. A method of heat treatment of a metal material, comprising: heating the metal material to a first temperature through a heating fixture; andreducing the first temperature of the metal material to a second temperature through a cooling apparatus performing a fast cooling operation, wherein the fast cooling operation has a high cooling speed of 80° C./sec to 200° C./sec.

2. The method of heat treatment of the metal material as claimed in claim 1, wherein the fast cooling operation comprises spraying a coolant to the metal material through a spraying unit of the cooling apparatus.

3. The method of heat treatment of the metal material as claimed in claim 2, wherein the fast cooling operation comprises spraying the coolant to the metal material with a high speed ejection flow of 60 L/min to 1000 L/min.

4. The method of heat treatment of the metal material as claimed in claim 2, wherein the coolant applies a high speed ejection pressure to the metal material at the instant the coolant hits the metal material, and wherein the high speed ejection pressure is 70-300 bars.

5. The method of heat treatment of the metal material as claimed in claim 1, further comprising reducing the second temperature of the metal material to a third temperature through the cooling apparatus performing a slow cooling operation, wherein the slow cooling operation has a slow cooling speed of 50° C./sec to 80° C./sec.

6. The method of heat treatment of the metal material as claimed in claim 5, wherein the slow cooling operation comprises spraying a coolant to the metal material through a spraying unit of the cooling apparatus.

7. The method of heat treatment of the metal material as claimed in claim 6, wherein the slow cooling operation comprises spraying the coolant to the metal material with a low speed ejection flow of 20 L/min to 60 L/min.

8. The method of heat treatment of the metal material as claimed in claim 6, wherein the coolant applies a low speed ejection pressure to the metal material at the instant the coolant hits the metal material, and wherein the low speed ejection pressure is 30-70 bars.

9. The method of heat treatment of the metal material as claimed in claim 1, further comprising convoying the metal material in a convoying direction through a convoying unit of the cooling apparatus.

10. The method of heat treatment of the metal material as claimed in claim 9, wherein the cooling apparatus comprises a spraying unit spraying a coolant to the metal material in a spraying direction, and wherein an angle between the convoying direction and the spraying direction is between 15° and 90°.

11. The method of heat treatment of the metal material as claimed in claim 10, wherein the angle is 45°.

12. The method of heat treatment of the metal material as claimed in claim 9, further comprising rotating the metal material about an axle parallel to the convoying direction during the convoying of the metal material.