JP6187446B2 - Method and apparatus for quenching steel pipe - Google Patents

Description

  The present invention relates to a quenching method and a quenching apparatus that quench and quench a heated steel pipe.

  In recent years, the characteristics (for example, strength, toughness, etc.) required for steel pipes used in various applications (for example, seamless steel pipes, ERW steel pipes, etc.) have become increasingly severe, and in order to obtain steel pipes of good quality Quenching is performed in the manufacturing process, and tempering is also performed as necessary. When quenching, a technique of rapidly cooling (for example, immersing in a cooling water tank) after heating a steel pipe in a heating furnace or the like is widely used. In addition, for seamless steel pipes manufactured by hot piercing and rolling, a technique has been developed in which a high-temperature steel pipe discharged from the piercing and rolling line is quenched and quenched as it is.

  In any quenching, the heated steel pipe needs to be quenched rapidly throughout. In other words, when the cooling rate in the rapid cooling becomes uneven, the toughness of the steel pipe deteriorates at the part where the cooling rate is too high, and the strength of the steel pipe decreases at the part where the cooling rate is too low. Occurs. In addition, if the cooling rate is not uniform, not only a problem related to characteristics but also a problem related to the shape of the steel pipe, such as bending. Therefore, a technique for uniformly quenching when quenching a steel pipe has been studied.

  For example, Patent Document 1 discloses a technique in which a heated steel pipe is immersed in a cooling water tank and further cooling water is circulated inside the steel pipe. However, in this technique, the cooling water flowing inside the steel pipe flows in one direction (that is, from one end face to the other end face), so that the upper part of the inner surface of the steel pipe 1 comes into contact with the cooling water 2 as shown in FIG. As a result, quality variation occurs. Also, since it is necessary to align the axis of the steel pipe and the nozzle (not shown) in the cooling water tank, equipment (such as an arm) for gripping the steel pipe and immersing it in a predetermined position in the cooling water tank is installed. As a result, it is inevitable that the equipment configuration becomes complicated as a result.

  Patent Document 2 discloses a technique for spraying cooling water on the outer surface of a steel pipe while circulating the heated steel pipe and circulating the cooling water inside the steel pipe. However, this technique does not immerse the steel pipe in water, and the cooling water flowing in the steel pipe flows in one direction, so that it is difficult to fill the inside of the steel pipe 1 with the cooling water 2 as shown in FIG. As a result, quality variation occurs. Moreover, since it is necessary to make the axial center of the steel pipe 1 and the nozzle 3 correspond, you have to install the apparatus (for example, pinch roll etc.) for rotating while holding the steel pipe 1 in a predetermined position, As a result, It is inevitable that the construction of the equipment becomes complicated.

  That is, when quenching a steel pipe, a technique for performing uniform rapid cooling with a simple means to obtain a steel pipe with good and uniform quality has not been established yet.

Japanese Patent No. 5071537 Japanese Patent No. 3624680

  The present invention eliminates the problems of the prior art, and quenching method and quenching capable of obtaining a steel pipe of good and uniform quality by performing uniform quenching in the longitudinal direction and circumferential direction of the steel pipe by simple means. An object is to provide an apparatus.

  This inventor examined the technique of injecting cooling water into the inside of a steel pipe from a nozzle, and quenching a steel pipe uniformly. And if the internal volume of a steel pipe is reduced and the flow path through which cooling water circulates in contact with the inner surface of the steel pipe is secured, the cooling water fills the flow path, contacts the entire inner surface, and flows smoothly. Therefore, it turned out that a steel pipe can be cooled rapidly uniformly.

  The present invention has been made based on such knowledge.

That is, the present invention inserts a closing member having a linear protrusion on the outer surface into the steel pipe over a part or the entire length of the heated steel pipe, and provides a gap between the steel pipe and the closing member. Cooling water is injected at a jet flow rate V ₁ (m ³ / sec) from a nozzle arranged with a gap between one end face of the steel pipe, and a part of the cooling water is discharged from the gap between the nozzle and the steel pipe. With the steel pipe quenching method, V ₂ <V ₁ is obtained by flowing the remaining cooling water into the gap between the closing member and the steel pipe and letting it flow out from the other end surface at the outflow flow rate V ₂ (m ³ / sec). is there.

  In the quenching method of the present invention, the closing member preferably has a helical linear protrusion or a linear protrusion parallel to the axis of the steel pipe. As shown in FIG. 2 (a), the width of the protrusion (that is, the width of the convex portion) is smaller than the distance between the protrusions (that is, the width of the concave portion). The width may be larger than the interval between the protrusions.

Further, the present invention has a gap between a closing member inserted into the inside of the steel pipe over a part or the entire length of the heated steel pipe and having a linear protrusion on the outer surface, and one end face of the steel pipe. A nozzle that is arranged and causes a portion of the cooling water to flow out of the gap by injecting the cooling water and to flow the remainder of the cooling water into the gap between the steel pipe and the closing member, and is injected from the nozzle Cooling water injection flow rate V ₁ (m ³ / second) and cooling water flow rate V ₂ (m ³ / second) flowing out from the other end surface through the gap between the blocking member and the steel pipe satisfy V ₂ <V ₁ This is a steel pipe quenching device.

  In the hardening apparatus of this invention, it is preferable that the obstruction | occlusion member has a linear protrusion parallel to the spiral linear protrusion or the axial center of a steel pipe.

  According to the present invention, uniform quenching can be performed in a longitudinal direction and a circumferential direction of a steel pipe by a simple means, and a steel pipe having a good and uniform quality can be obtained.

It is sectional drawing which shows typically the example of the hardening apparatus to which this invention is applied. It is sectional drawing which expands and shows the obstruction | occlusion member in FIG. It is sectional drawing which shows typically the conventional example of the cooling water which distribute | circulates the inside of a steel pipe. It is sectional drawing which shows typically the conventional example of the cooling water which distribute | circulates the inside of a steel pipe. It is a graph which shows transition of the temperature of a steel pipe, (a) is an example to which the present invention is applied, and (b) is a conventional example. It is a graph which shows the relationship between the flow volume of the cooling water in a cooling water flow path, and the flow velocity. It is a graph which shows the relationship between the flow rate of the cooling water in a cooling water flow path, and the water temperature which a film | membrane boiling generate | occur | produces. It is a graph which shows transition of the temperature of a steel pipe, (a) is an example to which the present invention is applied, and (b) is a conventional example. It is sectional drawing which shows typically the example which displaced the obstruction | occlusion member in FIG. 1 upwards.

  As shown in FIG. 1, the quenching apparatus to which the present invention is applied has a closing member 4 inserted into the steel pipe 1 over the entire length of the heated steel pipe 1, and a gap is formed between the steel pipe 1 and the closing member 4. Have. Or although illustration is abbreviate | omitted, it is not necessary to insert over the full length, You may insert the obstruction | occlusion member 4 in a part of longitudinal direction of the steel pipe 1. FIG. 1A shows an example in which the tip of the closing member 4 having linear protrusions parallel to the axis is cylindrical, and FIG. 1B shows the closing member 4 having linear protrusions parallel to the axis. An example in which the tip is conical, FIG. 1 (c) is an example in which the tip of the closing member 4 having a helical linear protrusion is made cylindrical.

  A linear protrusion (hereinafter referred to as a linear protrusion) is provided on the outer surface of the closing member 4. 2A and 2B show an example in which the closing member 4 in FIG. 1 is enlarged and four linear protrusions 8 are provided in parallel to the axis of the steel pipe 1. Further, as shown in FIG. 1 (c), the linear protrusions 8 may be provided in a spiral shape (not shown). The means for forming the linear protrusion 8 is not particularly limited, and may be formed by a method such as joining to the outer surface of the closing member 4 or cutting the outer surface of the closing member 4.

  If the height H (mm) of the linear protrusion 8 is too low, the effect of smoothly circulating the cooling water 2 described later in the steel pipe 1 cannot be obtained. On the other hand, if it is too high, the diameter D of the closing member 4 must be reduced, and the strength of the closing member 4 cannot be ensured. Therefore, the height H of the linear protrusion 8 is preferably within the range of D / 1 to D / 4 with respect to the diameter D (mm) of the closing member 4.

  If the width W (mm) of the linear protrusion 8 is too narrow, the linear protrusion 8 may be damaged. Therefore, the width W is preferably 5 mm or more. On the other hand, if the width W of the linear protrusion 8 is too wide, the gap between the closing member 4 and the steel pipe 1 is reduced, so that the circulation of the cooling water 2 described later in the steel pipe 1 is hindered. Therefore, the width W is preferably smaller than the interval between the linear protrusions 8.

  1 and 2 show an example in which four linear protrusions 8 are provided at equal intervals (90 ° intervals), the number of linear protrusions 8 is not particularly limited. However, if the number of the linear protrusions 8 is too small, the effect of smoothly circulating the cooling water 2 described later in the steel pipe 1 cannot be obtained. On the other hand, when too much, the distribution | circulation in the steel pipe 1 of the cooling water 2 mentioned later is inhibited. Therefore, the number of the linear protrusions 8 is preferably in the range of 2 to 8, and is preferably arranged at equal intervals.

  Thus, the space formed by the steel pipe 1, the closing member 4, and the linear protrusion 8 becomes a flow path for the cooling water 2 described later. And the nozzle 3 for injecting the cooling water 2 to the one side of the steel pipe 1 is arrange | positioned. A gap is provided between the nozzle 3 and the end surface 5 (hereinafter referred to as nozzle-side end surface) of the steel pipe 1 on the nozzle 3 side. Further, the closing member 4 is inserted into the steel pipe 1 from an end surface 7 (hereinafter referred to as an outflow side end surface) on the side from which the coolant 2 flows out.

When quenching the heated steel pipe 1, the nozzle 3 and the closing member 4 are arranged in this way on the steel pipe 1, and the cooling water 2 is injected from the nozzle 3. Let the amount of water jetted from the nozzle 3 be V ₁ (m ³ / sec). At this time, in order to distribute the cooling water 2 uniformly in a space 6 (hereinafter referred to as a cooling water flow path) formed by the steel pipe 1, the closing member 4 and the linear protrusion 8, the steel pipe 1, the closing member 4 and the nozzle 3 It is preferable to match the axes.

However, when the diameter of the closing member 4 is smaller than the inner diameter of the steel pipe 1 and the closing volume ratio described later is small, it becomes difficult to fill the inside of the steel pipe 1 with the cooling water 2, and as a result, the upper portion of the steel pipe 1 is rapidly cooled. Be inhibited. Therefore, in that case, as shown in FIG. 9, it is preferable to displace the shaft core of the closing member 4 upward from the shaft core of the steel pipe 1. In that case, the lower side in the width of the gap formed between the closing member 4 and the steel pipe 1 and d ₁ and (mm), the width of the upper gap as _{d 2 (mm), d 1} / d 2 value Is preferably displaced within a range of 2 or less.

That is, since the d ₁ / d ₂ value is 1 when the axis of the steel pipe 1, the closing member 4, and the nozzle 3 coincide with each other, the shaft of the closing member 4 is within the range where the d ₁ / d ₂ value is 1 to 2. The core is displaced and adjusted so that the cooling water 2 fills the cooling water flow path 6.

  A part of the cooling water 2 sprayed from the nozzle 3 collides with the closing member 4, flows out from the gap between the nozzle side end surface 5 of the steel pipe 1 and the nozzle 3, and the remaining part flows into the cooling water flow path 6. The nozzle 3 side tip of the blocking member 4 may protrude from the nozzle side end surface 5 of the steel pipe 1 in the direction of the nozzle 3. In that case, the closing member 4 exists inside the steel pipe 1 over the entire length of the steel pipe 1.

  Further, when the closing member 4 is buried in the inner part of the steel pipe 1, the nozzle 3 side tip of the closing member 4 may be disposed within 100 mm on the inner side from the nozzle side end surface 5 of the steel pipe 1. In that case, the closing member 4 exists in a part of the longitudinal direction of the steel pipe 1.

  Even if the end of the closing member 4 is cylindrical as shown in FIG. 1A, the cooling water 2 is smoothly guided to the cooling water flow path 6 by the linear protrusions 8. However, as shown in FIG. 1B, the cooling water 2 is more smoothly guided to the cooling water flow path 6 by making the tip of the closing member 4 conical. Further, the same effect can be obtained even if the tip of the closing member 4 is a spherical curved surface (not shown).

Here, when the internal volume of the steel tube 1 and M _P (mm ^3), and M _Q (mm ³⁾ the volume of the closing member 4 which is inserted into the steel pipe 1 linear projections 8 also including a cooling water flow path The volume of 6 can be calculated by the following equation (1). In other words, the volume of the cooling water passage 6 because it decreases than the internal volume M _P of the steel tube 1, easily coolant 2 is filled in the cooling water passage 6, and flows at a high speed. Therefore, the heat of the heated steel pipe 1 can be discharged efficiently and stably, and uniform quenching can be performed in the longitudinal direction and the circumferential direction of the steel pipe 1. In order to exert such an effect, the internal volume M _P (mm ³ ) of the steel pipe 1 and the volume M _Q (mm ³ ) of the closing member 4 inserted into the steel pipe 1 are expressed by the following equation (2). It is preferable that the calculated closed volume ratio is 15% or more.
Cooling water channel volume = M _P -M _Q (1)
Blocking volume ratio (%) = 100 × M _Q / M _P (2)
On the other hand, if the closed volume ratio is too large, the cooling water flow path 6 becomes narrow and the flow of the cooling water 2 is hindered, so that uniform rapid cooling of the steel pipe 1 becomes difficult. Therefore, the closed volume ratio is preferably 70% or less.

Thus, if the outflow rate of the cooling water 2 flowing out from the outflow side end face 7 of the steel pipe 1 through the cooling water flow path 6 is V ₂ (m ³ / sec), the following equation (3) is established. By satisfying this relationship, the cooling water 2 fills the cooling water channel 6. As a result, the cooling water 2 comes into contact with the entire inner surface of the steel pipe 1 and uniform cooling in the circumferential direction is possible (see FIG. 5 (a)). And it is not necessary to immerse the steel pipe 1 in a cooling water tank, and it can quench by a simple means. In the present invention, uniform quenching is also possible in the longitudinal direction of the steel pipe 1, which will be described later with reference to FIG. If the linear protrusions 8 are provided in a spiral shape, the circumferential uniformity is further improved.
V ₂ <V ₁ (3)
On the other hand, when V ₂ = V ₁ , the upper part of the steel pipe 1 is hardly cooled as shown in FIGS. 3 and 4 (see FIG. 5B).

That is, the present invention enables uniform rapid cooling of the steel pipe 1 by using the closing member 4 to satisfy V ₂ <V ₁ . Preferably V ₂ <0.9 × V ₁ .

The inventor then inserts a blocking member 4 having a linear protrusion 8 parallel to the axis of the steel pipe 1 and having a cylindrical tip over the entire length of the steel pipe 1 (inner diameter 130 mm, pipe length 9000 mm) (FIG. 1 (a )) And the experiment conducted without using the closing member 4, the flow rate of the cooling water 2 flowing through the cooling water flow path 6, that is, V ₂ (m ³ / sec) and the flow velocity (m / The relationship with (second) is as shown in FIG.

  As apparent from FIG. 6, the flow rate of the cooling water 2 flowing through the cooling water flow path 6 is increased by inserting the closing member 4 into the steel pipe 1. When the flow rate of the cooling water 2 is increased, the heat of the steel pipe 1 is easily discharged, so that film boiling is difficult to occur. That is, as shown in FIG. 7, the water temperature at which film boiling occurs increases. On the other hand, the cooling water flow path 6 when the closing member 4 is not used is the entire inside of the steel pipe 1, and the flow rate of the cooling water 2 becomes slow, so that the water temperature at which film boiling occurs is lowered as shown in FIG. .

Therefore, when the result of the experiment shown in FIG. 6 is analyzed, when the flow rate of the cooling water 2 is 0.1 m ³ / sec and the flow velocity is sufficiently high (that is, 10.5 m / sec), the nozzle side end surface 5 of the steel pipe 1 and the outflow The transition of the temperature at the side end face 7 is as shown in FIG. 8 (a), and it can be seen that uniform rapid cooling in the longitudinal direction of the steel pipe 1 is possible. On the other hand, when the flow rate of the cooling water 2 is also 0.1 m ³ / sec but the flow velocity is slow (ie 7.5 m / sec), the nozzle-side end face 5 of the steel pipe 1 is cooled, but the cooling water flow path 6 In this case, film boiling occurs and the outflow side end face 7 is hardly cooled as shown in FIG.

  As described above, the present invention fills the cooling water flow path 6 with the cooling water 2 by inserting the closing member 4 having the linear protrusions 8 parallel to the axis of the steel pipe 1 into the steel pipe 1, and Rapid cooling is performed by increasing the flow rate of the cooling water 2. When the cooling water 2 is filled, uniform quenching in the circumferential direction is possible, and when the flow rate of the cooling water 2 is increased, uniform quenching in the longitudinal direction is possible. When the linear protrusions 8 are provided in a spiral shape, the uniformity in the circumferential direction is further improved.

  In order to easily and quickly perform the operation of inserting and removing the closing member 4 from the steel pipe 1, it is preferable to reduce the weight of the closing member 4 (for example, to make the inside hollow). Moreover, the effect which makes the temperature deviation of the circumferential direction still smaller by rotating the steel pipe 1 in the case of rapid cooling is acquired.

  The billet heated in the heating furnace was subjected to hot piercing and rolling to obtain a seamless steel pipe (inner diameter 130 mm, pipe thickness 40 mm, pipe length 8000 mm). Cooling water was sprayed from the nozzle onto the seamless steel pipe (temperature 1150 ° C) to rapidly cool to 850 ° C. The conditions set at that time are as shown in Table 1. The diameter of the nozzle used is 110 mm. Hereinafter, a seamless steel pipe will be described as a steel pipe 1 with reference to FIGS.

In Invention Example 1, the shaft core of the closing member 4 in which the two spiral linear protrusions shown in FIG. 1C are provided at equal intervals (ie, 180 ° intervals) is located above the axis of the steel pipe 1. In this example, the displacement (see FIG. 9) is set to d ₁ / d ₂ = 2 and the closing member 4 is inserted over the entire length of the steel pipe 1 to set the closing volume ratio to 15%, and the steel pipe 1 is rapidly cooled without rotating. . As shown in Table 1, V ₂ <V ₁ was satisfied, and the inside of the steel pipe 1 was 100% filled with the cooling water 2, and the flow rate of the cooling water 2 in the steel pipe 1 was 8.5 m / sec. And the temperature deviation of the circumferential direction of the steel pipe 1 was restrained to 8 degreeC, and the temperature deviation of the longitudinal direction was restrained to 14 degreeC. Although the steel pipe 1 was not rotated, the temperature deviation in the circumferential direction was almost the same as that in the case where the steel pipe 1 was rotated (Comparative Example 2).

  In addition, the obstruction | occlusion area rate shown in Table 1 is the value computed as a ratio (%) of the cross-sectional area of the obstruction | occlusion member 4 with respect to the pipe end opening area of the steel pipe 1. FIG. The degree of fullness is a value calculated by photographing the outflow side end face 7 during rapid cooling, obtaining the area occupied by the cooling water 2 from the image, and calculating the ratio (%) to the cross-sectional area of the cooling water flow path 6. The temperature deviation is the difference between the maximum value and the minimum value when the temperature of the steel pipe 1 is measured using a non-contact type radiation thermometer on the exit side of the quenching device (8 places in the circumferential direction and 4 places in the longitudinal direction). It is.

Inventive Example 2 is a case where the shaft core of the closing member 4 provided with four linear protrusions 8 parallel to the shaft core of the steel pipe 1 at equal intervals (ie, 90 ° intervals) is aligned with the shaft core of the steel pipe 1 d _1. This is an example in which / d ₂ = 1, the steel pipe 1 is further rotated, and the others are set in the same manner as in Example 1 to perform rapid cooling. As shown in Table 1, the temperature deviation of Invention Example 2 was 7 ° C. in the circumferential direction of the steel pipe 1 and 13 ° C. in the longitudinal direction. This means that the circumferential uniformity is improved by rotating the steel pipe 1 during rapid cooling, and the longitudinal uniformity is improved by setting d ₁ / d ₂ = 1.

  Inventive Example 3 is an example in which a closing member 4 provided with eight spiral linear protrusions at equal intervals is used, and other settings are performed in the same manner as in Inventive Example 2 for rapid cooling. As shown in Table 1, the temperature deviation of Invention Example 3 was 6 ° C. in the circumferential direction of the steel pipe 1 and 13 ° C. in the longitudinal direction, and the temperature deviation in the circumferential direction was smaller than that of Invention Example 2. This means that the uniformity in the circumferential direction is improved by providing the occluding member 4 with spiral linear protrusions.

  In Comparative Example 1, the closing member 4 without the linear protrusion 8 is used, the axis of the steel pipe 1 and the closing member 4 are aligned, the steel pipe 1 is not rotated, and the other settings are the same as in Example 2 for rapid cooling. This is an example. As shown in Table 1, the temperature deviation of Comparative Example 1 was 10 ° C. in the circumferential direction of the steel pipe 1 and 15 ° C. in the longitudinal direction, which was the largest among the inventive examples and comparative examples in Table 1.

  Comparative Example 2 is an example in which a closing member having no linear protrusion was used, and the other settings were quenched as in Invention Examples 2 and 3. As shown in Table 1, the temperature deviation of Comparative Example 2 was 7 ° C. in the circumferential direction of the steel pipe 1 and 15 ° C. in the longitudinal direction, and the temperature deviation in the circumferential direction was greater than that of Invention Examples 2 and 3.

DESCRIPTION OF SYMBOLS 1 Steel pipe 2 Cooling water 3 Nozzle 4 Blocking member 5 Nozzle side end surface 6 Cooling water flow path 7 Outflow side end surface 8 Linear protrusion

Claims (4)

A closing member having a linear protrusion on the outer surface is inserted into the steel pipe over a part or the entire length in the longitudinal direction of the heated steel pipe, and a gap is provided between the steel pipe and the closing member, and the steel pipe The cooling water is injected at a jet flow rate V ₁ (m ³ / sec) from a nozzle disposed with a gap between one end face of the nozzle and the cooling water is drawn from the gap between the nozzle and the steel pipe. V ₂ <V ₁ by letting the remainder of the cooling water flow into the gap between the closing member and the steel pipe while flowing out a part, and let it flow out from the other end surface at an outflow flow rate V ₂ (m ³ / sec). A method for quenching a steel pipe, characterized by that.   The method for quenching a steel pipe according to claim 1, wherein the closing member has the linear protrusion or the linear protrusion parallel to the axis of the steel pipe. A gap is provided between a closing member inserted into the steel pipe and having a linear protrusion on the outer surface thereof and a part of one end face of the steel pipe over a part or the entire length of the heated steel pipe in the longitudinal direction. A nozzle that causes a portion of the cooling water to flow out of the gap by injecting the cooling water and to flow the remainder of the cooling water into a gap between the steel pipe and the closing member, and from the nozzle An injection flow rate V ₁ (m ³ / sec) of the injected cooling water and an outflow rate V ₂ (m ³ / sec) of the cooling water flowing out from the other end face through the gap between the closing member and the steel pipe A steel pipe quenching device satisfying V ₂ <V ₁ .   The steel pipe hardening apparatus according to claim 3, wherein the closing member includes the spiral linear protrusion or the linear protrusion parallel to the axis of the steel pipe.

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