JPH0841544A - Quenching of steel pipe - Google Patents

Abstract

PURPOSE:To prevent ununiform cooling caused by float-up of a steel pipe without damaging the steel pipe, in a dipping axial flow quenching method of the inner and the outer surfaces of the steel pipe. CONSTITUTION:In this dipping axial flow quenching method of the steel pipe 21, the water quantity supplied to a dipping vessel 22 is rapidly increased until the one end of the steel pipe 21 charged in the dipping vessel 22 floats up to form a high water level advancing flow 32. When the water surface level of the dipping vessel 22 at one end thereof becomes higher than the level of the floated upper end of the steel pipe, the cross sectional area in the dipping vessel 22 is reduced at the float-up part side of the steel pipe.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a quenching method for steel pipes of the immersion type.

[0002]

2. Description of the Related Art Quenching and tempering treatments are carried out in order to increase the tensile strength and toughness of steel pipes. Steel pipe quenching methods are roughly classified into a spray method and an inner / outer surface immersion axial flow quenching method. From the viewpoints of high cooling capacity and simple device structure, the inner and outer surface immersion axial flow quenching method is superior. The inner / outer surface immersion axial flow quenching method is a method in which a heated steel pipe is put into a dipping tank and immersed, and quenching is performed by giving a cooling water flow (axial flow) along the axial direction to both the inner and outer surfaces of the steel pipe. . One of the problems of this type of quenching method is the occurrence of uneven quenching due to the thin steel pipe floating above the water surface of the dipping tank. That is, in a thin-walled steel pipe, one end of the steel pipe is immersed in the water surface of the dipping tank due to buoyancy until it falls into a predetermined position on the pedestal (or roller) installed in the dipping tank after being immersed in the dipping tank. There is a problem in that a phenomenon of floating above occurs, and the floating portion is insufficiently cooled, and uniform heat treatment cannot be obtained.

Description will be made with reference to FIG. As shown in FIG. 6 (a), cooling water is supplied from the cooling water supply pipe 2 into the immersion tank 1, and a cooling water flow 4 along the axial direction of the steel pipe 10 is formed in the cooling water 3 for firing. The steel pipe 10 to be put is put in this dipping tank in a horizontal posture as shown by an arrow 5. Figure 6 (b)
As shown in, the cooling water flow 4 cools the inner and outer surfaces of the steel pipe 10, but bubbles 6 are generated in the steel pipe, and the bubbles 6 give buoyancy to the steel pipe 10 to cause it to float. As shown in FIG. 6 (c), the bubbles are brought to one end of the steel pipe 10 by the cooling water flow 4, and particularly in a thin-walled steel pipe, the end 11 of the steel pipe 10 is above the water surface 7 of the dipping tank 1. Surface. Therefore, the end portion 11 is not sufficiently cooled and uneven quenching occurs.

As a method for preventing this floating, for example, Japanese Patent Publication No. 60-3
As seen in 9734 and JP-A-60-37859,
Method or device for clamping steel pipe before or after immersion,
Further, as disclosed in Japanese Patent Publication No. 58-55217, a method and an apparatus for covering after immersion are considered to be effective, but there is a problem that the equipment becomes complicated and the cost becomes high. In addition, if the timing of the method of clamping or covering after immersion is inappropriate, the floating steel pipe interferes with the clamp or cover, causing flaws.

In addition to this, as disclosed in Japanese Patent Publication No. 55-32766, a method has been developed in which the speed of entry into the dipping tank is controlled to allow entry at a low speed, but the equipment cost is high. There is a problem that uneven quenching is inevitable.

[0006] Therefore, the applicant of the present invention, when quenching a steel pipe by the inner and outer surface immersion axial flow quenching method, as a method for preventing uneven cooling due to floating of a thin-walled steel pipe, one end of the steel pipe put into a dipping tank floats. It has already been proposed that the amount of water supplied to the immersion tank be increased rapidly to form a high-level progressive flow, and the water level of the immersion tank at that portion is made higher than the floating top of the steel pipe.

[0007]

However, in the prior application technology already proposed by the present applicant, a large amount of water is supplied to the dipping tank in order to form a high water level advancing flow for preventing the floating of the steel pipe. Need to increase rapidly. This large amount of water flow causes the steel pipe to flow in the longitudinal direction in the dipping tank, and there is a disadvantage that the pipe end collides with the inner wall surface of the dipping tank and is scratched.

It is an object of the present invention to prevent uneven cooling due to floating of the steel pipe in the axial-flow quenching method of immersing the inner and outer surfaces of the steel pipe without scratching the steel pipe.

[0009]

According to the present invention as set forth in claim 1, when a steel pipe is put in a horizontal position in a dipping tank and a water flow in the axial direction of the pipe is used to perform inner and outer surface dipping axial flow quenching treatment, the dipping tank is used. In the quenching method of the steel pipe, the amount of water supplied to the dipping tank is rapidly increased until one end of the steel pipe put in The cross-sectional area of the immersion tank is reduced on the floating side of the steel pipe.

The present invention according to claim 2 is the same as the invention according to claim 1, wherein the internal cross-sectional width of the dipping tank is made smaller on the floating side of the steel pipe.

According to a third aspect of the present invention, in addition to the first aspect of the present invention, the depth of the internal cross section of the dipping bath is made smaller on the floating side of the steel pipe.

[0012]

According to the present invention, in the quenching treatment of the inner and outer surfaces of the steel pipe by the axial flow quenching method, after the steel pipe is immersed in the immersion tank, the amount of water supplied to the immersion tank is rapidly increased to form a high water level progressive flow. Then, the water amount of the axial water flow is rapidly increased at a predetermined water amount Q ₂ (m ³ / H), a pressure P ₂ (MPa) and a predetermined injection start time T _F so that the water level at the floating top of the steel pipe becomes high. And then jet. At this time, the injection start time T _F is set to satisfy the following condition.

[0013] _{0 <f T1 (D, t} , v) - (T F -T in)
-F _T2 (Q, P, L) However, T _in : Time of immersing the steel pipe in the dipping tank _TF : Time of injection start with water amount Q ₂ and pressure P ₂ D: Steel pipe outer diameter t: Steel pipe wall thickness v: Velocity of Steel Pipe Penetration into Immersion Liquid L: Distance from Jet Port to Other End of Steel Pipe f _T1 : Function of Time (D, t, v) from Immersion of Steel Pipe to Immersion Liquid f _T2 : Water Quantity Q ₂ , after starting the injection at pressure P ₂ , distance L
It is a function of the time (Q, P, L) until the water level at the position rises. Under the above conditions, the high water level advancing flow is set to have a higher water level than the floating upper end of the steel pipe before one end of the steel pipe put into the immersion tank floats.

In the above formula of the injection start time T _F , the time f _T1 from the time when the steel pipe enters the immersion liquid to the time when it floats up, and
The time f _T2 from the start of injection with the water amount Q ₂ and the pressure P ₂ to the rise of the water level at the distance L position is
It depends on the size of the steel pipe, the speed at which the steel pipe penetrates the immersion liquid, the amount of water before and after the immersion of the steel pipe, the pressure, the distance from the injection port to the other end of the steel pipe, and the like. However, these can be determined for the immersion tank and the steel pipe by simulation or experiment. Therefore, the injection start time T _F can be determined.

FIG. 4 is a time chart showing the injection start time. The time T _in when the steel pipe is dipped in the dipping tank is the starting point, and the time T _E after the time f _T1 from the time when the steel pipe is dipped in the dipping tank until the steel pipe floats is the end point. The injection is started with the water amount Q ₂ and the pressure P ₂ at the injection start time T _F which is in time for the arrival time T _M which is earlier than the end time T _E by a minute time ΔT. The injection start time T _F is determined by knowing the time f _T2 from when the injection is started with the water amount Q ₂ and the pressure P ₂ until the water level at the distance L increases.

The time f _T1 is a function of the outer diameter D of the steel pipe, the wall thickness t of the steel pipe, and the speed v at which the steel pipe penetrates into the immersion liquid, and can be determined if these conditions are determined. The time f _T2 is
Since it is a function of the dimensions of the immersion tank, the amount of water Q, the pressure P, and the distance L from the injection port to the other end of the steel pipe, it can be determined if these are determined. Therefore, the relationship between the two times T _in and T _F is uniquely determined according to the conditions. In practice, these may be determined by simulation or experiment. By storing the data of these conditions in the control computer, it is possible to easily and accurately control the water amount and the injection start time according to the conditions.

However, in the present invention, "to reduce the internal cross-sectional area of the immersion tank on the floating side of the steel pipe", specifically "to reduce the internal cross-sectional area of the immersion tank on the floating side of the steel pipe". ,
Alternatively, it is characterized in that "the depth of the cross section of the immersion tank is reduced on the floating side of the steel pipe". According to this, in order to form the high water level advancing flow for preventing the floating of the steel pipe, the amount Q ₂ of water supplied to the immersion tank can be reduced. That is, a high water level advancing flow necessary and sufficient to prevent the floating of the steel pipe can be formed with a small amount of water Q ₂ . The decrease in the amount of water Q ₂ prevents the steel pipe from traveling in the longitudinal direction in the dipping tank, and prevents the pipe end from colliding with the inner wall surface of the dipping tank and being damaged.

[0018]

1 is a schematic view showing an embodiment of the present invention, FIG.
Is a schematic view showing a transverse section of the immersion tank, FIG. 3 is a schematic view showing a vertical section of the immersion tank, FIG. 4 is a jet start time chart, FIG. 5 is a schematic view showing an inner and outer surface immersion axial flow quenching apparatus, and FIG. [Fig. 6] is a schematic view showing a conventional example. As shown in FIG. 5, the quenching apparatus 20 puts a heated steel pipe 21 into a dipping tank 22 to immerse the steel pipe 21 and applies quenching to both inner and outer surfaces of the steel pipe 21 by applying a cooling water flow (axial flow) along the axial direction thereof. It is something to do. In FIG. 5, 23
Is a steel pipe kick-in device, 24 is a water injection port, 25 is a water circulation path, and 26 is an axial flow cover.

That is, in the quenching apparatus 20, the immersion tank 2
2 is supplied with cooling water from a water injection port 24 to form a cooling water flow 27 along the axial direction of the steel pipe 21 in the immersion tank 22, and the steel pipe 21 to be quenched is horizontally immersed in the immersion tank by a kick-in device 23. Put in 22. The steel pipe 21 is covered with an axial flow cover 26 in a state in which the floating posture prevention method described in detail later is applied and the immersion posture in the immersion tank 22 is leveled, and the inner and outer surfaces of the steel pipe 21 are cooled by a cooling water flow 30 and quenched. To be done.

At this time, the immersion tank 22 is set so that the internal cross-sectional area of the immersion tank 22 becomes smaller on the floating side of the steel pipe. Specifically, (1) reduce the cross-sectional width of the immersion tank 22 on the floating side of the steel pipe (Fig. 2), or (2) decrease the cross-sectional depth of the immersion tank 22 on the floating side of the steel pipe. (FIG. 3).

The method of preventing the steel pipe 21 from rising in the immersion tank 22 is as follows (a) to (d). (a) The water level of the cooling water surface 28 in the immersion tank 22 is adjusted to 150 mm or less from the upper end of the injection port 24 of the cooling water supply pipe, and the cooling water flow 27 in the axial direction of the steel pipe 21 is set in the immersion tank 22. Let it form.

(B) The steel pipe 21 to be quenched is placed in the immersion tank 22 in a horizontal posture. The cooling water flow 27 cools the inner and outer surfaces of the steel pipe 21.
9, and the bubbles 29 give buoyancy to the steel pipe 21 to try to float. At this time, at a predetermined injection start time, the cooling water flow 30 supplied from the injection port 24 of the cooling water supply pipe to the immersion tank is rapidly increased to generate the high water level advancing flow 32 that advances in the direction of the arrow 31 at a high water level. . Water amount Q ₂ (m ³ / H), pressure P ₂ (MPa), injection start time T at this time
_F is stored in the computer in advance according to the conditions.

(C) The bubbles 29 generated in the steel pipe 21 try to float the end of the steel pipe 21 above the water surface 28 of the dipping tank 22, but at this time, they are traveling in the direction of the arrow 31. The high water level advancing flow 32 raises the water level of the steel pipe end so that the end of the steel pipe 21 does not come out above the water surface. Therefore, the steel pipe 21
Does not allow its end to float above the water surface 28, and the arrow 33
Settle in the direction indicated by.

(D) Therefore, as shown in FIG. 1 (d), the steel pipe 21 is uniformly quenched in the water by the cooling water flow 30, and uneven quenching does not occur.

Inventive Examples 1 and 2 are shown in Table 1 together with a conventional example and a comparative example.

[Table 1]

Example 1 of the present invention has an outer diameter of 406.44 mmφ and a wall thickness of 9.52.
A steel pipe of carbon steel of mm was quenched by the method of the present invention, and in particular, the cross sectional width of the dipping tank 22 was set as shown in FIG. 2, and L ₁ = 2860 mm, L ₂
= 1800 mm.

Inventive Example 2 has an outer diameter of 406.44 mmφ and a wall thickness of 9.52.
A steel pipe of carbon steel of mm was quenched by the method of the present invention, and in particular, the depth of the internal cross section of the dipping bath 22 was as shown in FIG. 3, and H = 500 mm.

In the comparative example, the internal cross-sectional area of the dipping tank 22 is made constant, and a high water level advancing flow is formed. The conventional example does not form a high water level advancing flow.

In Example 1 of the present invention, the injection start time T _{F at} which the high water level advancing flow 32 is generated with respect to the steel pipe immersion time T _in is 0.2.
Seconds, water quantity Q ₁ = 1500 m ³ / H, water quantity Q ₂ = 5000 m ³ / H
Has rapidly increased. ΔT = 0.2 seconds.

In Example 2 of the present invention, the injection start time T _{F at} which the high water level advancing flow 32 is generated with respect to the steel pipe immersion time T _in is 0.1.
Seconds, water quantity Q ₁ = 1500 m ³ / H water quantity Q ₂ = 6000 m ³ / H
Has rapidly increased. ΔT = 0.2 seconds.

In the comparative example, the injection start time T _F for generating the high water level advancing flow 32 with respect to the steel pipe immersion time T _in is 0 seconds, and the water amount Q ₁ = 1500 m ³ / H is the water amount Q ₂ = 8000 m ³ / H. Has rapidly increased. ΔT = 0.2 seconds.

In Examples 1 and 2 of the present invention, the amount of water Q ₂ could be greatly reduced as compared with the comparative example. And in the invention examples 1 and 2,
Tensile strength TS after tempering at the end and middle of the steel pipe
Regarding the yield strength YS, the same strength as in the comparative example could be secured. That is, uniform quenching without quenching unevenness could be realized while reducing the water amount Q ₂ .

[0033]

As described above, according to the present invention, it is possible to prevent uneven cooling due to floating of the steel pipe in the axial immersion quenching method of the inner and outer surfaces of the steel pipe without causing any flaws in the steel pipe.

[Brief description of drawings]

FIG. 1 is a schematic view showing an embodiment of the present invention.

FIG. 2 is a schematic view showing a cross section of an immersion tank.

FIG. 3 is a schematic view showing a vertical section of an immersion tank.

FIG. 4 is an injection start time chart.

FIG. 5 is a schematic view showing an inner and outer surface immersion axial flow quenching apparatus.

FIG. 6 is a schematic view showing a conventional example.

[Explanation of symbols]

 20 Quenching device 21 Steel pipe 22 Immersion tank 24 Water injection port 27, 30 Cooling water flow 28 Water surface 32 High water level advancing flow

Claims (3)

[Claims] 1. When a steel pipe is placed in a dipping tank in a horizontal posture and subjected to an axial dipping axial flow quenching treatment by a water flow in the axial direction of the pipe,
Quenching of a steel pipe that increases the amount of water supplied to the immersion tank rapidly until one end of the steel pipe put into the immersion tank rises to form a high-level progressive flow, and raises the water level of the immersion tank above that part of the steel pipe In the method, a method for quenching a steel pipe is characterized in that the internal cross-sectional area of the immersion tank is reduced on the floating side of the steel pipe. 2. The method for quenching a steel pipe according to claim 1, wherein the internal cross-sectional width of the dipping bath is reduced on the side where the steel pipe floats. 3. The method for quenching a steel pipe according to claim 1, wherein the depth of the internal cross-section of the dipping bath is reduced on the floating side of the steel pipe.