JP2022108357A - Method of carrying metallic material - Google Patents

Abstract

To provide a method of carrying a metallic material capable of reducing bending of a metallic material due to temperature change while carrying the metallic material from a place where it was subjected to heating to a place for where it is subjected to cooling .SOLUTION: A method of carrying a metallic material carries a long-sized metallic material M composed of metal that causes a phase transformation with temperature change after being heated at a heating unit 10 to a cooling unit 40 via a carrying unit 30. The cooling unit 40 cools the metallic material M with higher uniformity than in the carrying unit 30 in a cross section that crosses the metallic material M in the longer direction. In a cross section of the metallic material M upon reaching the cooling unit 40, a first point and a second point positioned on a surface of the metallic material M separated from each other take a uniform phase state fitting in an area corresponding to the same phase in which no phase transformation is occurring in a continuous cooling transformation diagram of the metallic material M.SELECTED DRAWING: Figure 1

Description

TECHNICAL FIELD The present invention relates to a method for transporting a metal material, and more particularly to a method for transporting a metal material from a place where it is heated to a place where it is cooled when manufacturing a long metal material through heating and cooling. is.

BACKGROUND ART When a long metal material such as steel is manufactured through a process involving heating such as hot rolling, the metal material may be bent as the heated metal is cooled. As one method for reducing bending, a method of correcting bending by using a roll straightening machine or the like is used for a bent metal material.

As another method for reducing bending of the metal material, a method of cooling the heated metal material while fixing and holding it in a predetermined state is also used. For example, in Patent Document 1, after a hot rolling process in which a steel billet is shaped into a rail having a high temperature, in a process of cooling the high temperature rail to room temperature, while the temperature of the rail is in a predetermined temperature range , discloses that the rails are held upright on a cooling bed and allowed to cool naturally without either heat retention or accelerated cooling.

JP 2011-73063 A

As described above, it is possible to reduce the bending of metal materials by correcting bending using a roll straightening machine or the like, or by fixing and holding during cooling. In that case, the straightening efficiency tends to change depending on the degree of bending of the metal material. In addition, since bending is corrected by applying an external force, physical properties of the metal material, such as changes in residual stress and hardening of the surface, are likely to be affected.

On the other hand, when the heated steel material is fixed and held in a predetermined state and cooled as in the method described in Patent Document 1, time and place are required for fixing and holding. end up In particular, when manufacturing a large number of steel materials, a long time and a large space are required to naturally cool the metal materials without performing accelerated cooling as described in Patent Document 1.

When a long metal material is manufactured by forging or the like, the place where the metal material is heated and the place where it is cooled are often separated. It will be transported while being cooled. The present inventors have found that the form of temperature change while the metal material is conveyed is a major factor in the bending of the metal material.

The problem to be solved by the present invention is to provide a method for conveying a metal material that can reduce the bending of the metal material due to the temperature change while the metal material is being conveyed from a place where it is heated to a place where it is cooled. to do.

In order to solve the above-described problems, a method for conveying a metal material according to the present invention includes heating a long metal material made of a metal that undergoes phase transformation due to a temperature change in a heating unit, and then cooling the metal material in the conveying unit. In the method for conveying a metal material to a part, the cooling part cools the metal material with higher uniformity in a cross section intersecting the longitudinal direction than the conveying part, and the metal material when it reaches the cooling part In the cross section of the metal material, the first point and the second point located on the surface of the metal material that are spaced apart from each other are the same in the continuous cooling transformation diagram of the metal material without undergoing phase transformation. It is said that it takes a homogeneous phase state that is settled in the phase.

Here, the first point and the second point are preferably positioned to face each other across the center of gravity of the cross section.

The conveying unit is capable of conveying a plurality of the metal materials simultaneously, and for the plurality of metal materials conveyed simultaneously by the conveying unit, the surface temperature of the metal materials when reaching the cooling unit is In the continuous cooling transformation diagram, it is preferable that the region is within the region corresponding to the same phase that has not undergone phase transformation.

The homogeneous phase state may be achieved by retention elimination control for eliminating retention of the metal material in the conveying section.

In this case, a rolling section is provided between the heating section and the conveying section to roll the metal material heated by the heating section and supply it to the conveying section. The metal material can be switched and supplied to the conveying section or a branch line different from the conveying section, and when continuously rolling a plurality of the metal materials in the rolling section, the conveying section The stagnation elimination control may be performed by adjusting at least one of the order and quantity of the metal material supplied to the branch line and the metal material supplied to the branch line.

Further, a temperature measurement unit is provided for measuring the temperature of the surface of the metal material conveyed by the conveying unit, and the state of retention of the metal material in the conveying unit is predicted, and the predicted state of retention and the temperature The retention elimination control may be performed based on the temperature measured by the measuring unit.

It is preferable to provide a heat retaining section for suppressing cooling or heating the metal material conveyed by the conveying section.

It is preferable to achieve the uniform phase state by controlling the heating state in the heating unit.

The cooling unit preferably includes a rotating transfer that conveys the metal material along the longitudinal axis while rotating the metal material in the circumferential direction at angular intervals of 3° or more and 20° or less about the longitudinal axis.

In the method for conveying a metal material according to the above invention, the metal material is allowed to cool while being conveyed by the conveying unit. Both the first point and the second point located at mutually spaced locations in the cross section of are in the region corresponding to the same phase that is not undergoing phase transformation in the continuous cooling transformation diagram. In other words, the first point and the second point are cooled in the cooling section from a state in which they are in the same phase without undergoing phase transformation. If uneven cooling of the metal material causes a difference in the timing of phase transformation within the cross section, the metal material tends to bend due to the expansion and contraction behavior associated with the phase transformation, but it is transported in a transport section with low cooling uniformity. By suppressing the temperature gradient in the cross section and making the first and second points of the surface take the same phase, bending of the steel material due to expansion and contraction due to phase transformation should be reduced. can be done. In this state, the steel material can be cooled in a state in which bending is less likely to occur by introducing the steel material into the cooling section that can perform cooling with higher uniformity than the conveying section.

Here, when the first point and the second point are located opposite to each other across the center of gravity of the cross section, if there is a large temperature gradient between the two points in such a positional relationship, Although this tends to lead to bending of the metal material, bending of the metal material can be effectively suppressed by suppressing the temperature gradient between these two points and maintaining a homogeneous phase state.

The conveying section can convey a plurality of metal materials simultaneously, and for the plurality of metal materials conveyed simultaneously by the conveying section, the temperature on the surface of the metal materials when reaching the cooling section is, in the continuous cooling transformation diagram, When the metal materials are contained in the regions corresponding to the same phase in which no phase transformation has occurred, bending can be suppressed in the metal materials simultaneously conveyed by the conveying unit. In addition, the distribution of physical properties and product shapes among individuals can be kept small. Furthermore, the fact that the temperature distribution among multiple metal materials that are conveyed at the same time is kept small is an indicator that the temperature gradient within each individual is small, and that the temperature distribution between the pieces can be kept small. , which also leads to minimizing the bending of each individual.

When a homogeneous phase state is achieved by retention elimination control that eliminates retention of the metal material in the conveying section, the metal material stays in the conveying section for a long time and is allowed to cool for a long time, so that the cross section of the metal material It becomes easy to avoid the increase in the temperature gradient at and the resulting bending of the metal material.

In this case, a rolling unit is provided between the heating unit and the conveying unit to roll the metal material heated by the heating unit and supply it to the conveying unit. or a branch line different from the conveying unit, and when continuously rolling a plurality of metal materials in the rolling unit, the metal material supplied to the conveying unit and the metal supplied to the branch line By adjusting at least one of the order and quantity of the metal materials, according to the configuration in which the retention elimination control is performed, the metal materials are distributed to the branch lines, and the retention of the metal materials in the conveying section is effectively suppressed. can do. For example, if metal materials are expected to stagnate in the conveying section, the supply order and quantity of metal materials distributed to the conveying section and branch lines are adjusted so that a large amount of metal materials are supplied to the branch line. As a result, it is possible to lengthen the time interval at which the metal material is supplied to the conveying section and prevent the metal material from stagnation in the conveying section.

In addition, a temperature measurement unit is provided to measure the temperature of the surface of the metal material conveyed by the conveying unit, and the state of retention of the metal material in the conveying unit is predicted. According to the configuration in which retention elimination control is performed based on the temperature of the metal material, the retention elimination control is performed while actually monitoring the temperature of the metal material, and by predicting the retention status of the metal material in advance. By suppressing retention of the metal material in the portion, the temperature gradient of the cross section of the metal material can be effectively reduced.

In the case of providing a heat retaining part for suppressing or heating the metal material conveyed by the conveying part, the cooling speed of the metal material while being conveyed by the conveying part is reduced. In particular, a temperature gradient is less likely to occur in the cross section of the metal material.

When a uniform phase state is achieved by controlling the heating state in the heating unit, for example, by introducing the metal material heated to a high temperature into the conveying unit, the metal material is conveyed while the temperature is high. It is possible to carry out the transportation in the department. This makes it easier to maintain the surface of the metal material in a state where the influence of phase transformation due to cooling is small even when the metal material reaches the cooling portion.

In the case where the cooling unit includes a rotating transfer that conveys the metal material along the longitudinal axis while rotating the metal material in the circumferential direction at an angular interval of 3° or more and 20° or less around the longitudinal axis, the metal material can be conveyed while being cooled with high uniformity.

1 is a block diagram showing an example of a rolling line for carrying out a metal material conveying method according to an embodiment of the present invention; FIG. (a) is a figure which shows the state of the steel material in a conveyance part. (b) is a diagram showing the temperature gradient in the steel material, and (c) is a diagram showing the bending of the steel material due to the temperature gradient. 1 is a model diagram for explaining a continuous cooling transformation diagram, showing a mode of cooling across a phase boundary L between a phase A and a phase B according to two cooling curves C1 and C2. FIG. FIG. 2 is a diagram showing measurement results of hardness of each part of (a) a steel material that is not bent (sample 1) and (b) a steel material that is bent (sample 2). The unit of hardness is HRC. 4 shows microstructure observation images of each part of the cross section of Sample 1 and Sample 2 with an optical microscope. The reference numerals attached to each image correspond to the measurement positions indicated by the reference numerals in FIG.

Hereinafter, a method for conveying a metal material according to one embodiment of the present invention will be described in detail with reference to the drawings. In a method for conveying a metal material according to one embodiment of the present invention (hereinafter sometimes simply referred to as a conveying method), a long metal material such as a steel material is heated by hot rolling or the like. from a location to a location to receive cooling.

Here, as the metal material to be conveyed by the conveying method according to the present embodiment, steel material will be described as an example below, but it is not limited to steel material. It doesn't matter what it is. In the following, pearlite transformation (γ→P transformation), which is a phase transformation from γ phase to pearlite phase, is given as a specific example of phase transformation, but the type of phase transformation is not particularly limited either. In addition to the phase transformation of interest (here, pearlite transformation), another phase transformation may occur under conditions other than the conditions of interest (temperature, cooling rate, etc.). Another phase transformation is a bainite transformation (γ→B transformation) in which a bainite structure is formed from a γ phase.

[Overview of rolling line]
First, an outline of an example of a rolling line will be described as an apparatus capable of implementing the conveying method according to one embodiment of the present invention. In the rolling line, a billet is heated, rolled, conveyed while undergoing processing such as cutting, and finally cooled.

The outline of the rolling line 1 is shown in FIG. The rolling line 1 has a heating section 10 , a rolling section 20 , and a refinement section including a conveying section 30 and a cooling section 40 .

The heating unit 10 is composed of a heating furnace, and heats the steel slab to a predetermined temperature required for each steel type. Then, the heated billet is rolled in the rolling section 20 . In the rolling unit 20, multistage rolling is performed by a roughing row rolling mill, an intermediate row rolling mill, and a finishing row rolling mill (all not shown). to divide and cut.

The steel material M that has undergone rolling and division in the rolling section 20 is introduced into the conveying section 30 . Two cutting machines 32 and 34 are provided in the middle of the conveying section 30, and the long steel material M introduced from the rolling section 20 cuts a predetermined length while being conveyed through the conveying section 30. is severed.

The conveying path 30 conveys the steel material M along the conveying direction D with the longitudinal axis of the steel material M arranged substantially parallel to the conveying direction D. The conveying unit 30 can convey a plurality of steel materials M while arranging them in the width direction intersecting the conveying direction D, as shown in FIG. 2(a). The conveying portion 30 has side walls 30b that rise upward from the conveying surface 30a on both sides in the width direction of the conveying surface 30a.

The steel material M conveyed by the conveying section 30 while being cut to a predetermined length is introduced into a rotating transfer 40 as a cooling section. The rotary transfer 40 conveys the steel material M whose longitudinal axis is oriented substantially perpendicular to the conveying direction D along the conveying direction D while rotating it in the circumferential direction about the longitudinal axis. During this transportation, the steel material M is cooled. The turning of the steel material M is performed at predetermined angular intervals. In the rotating transfer 40, the steel materials M are conveyed while rotating the steel materials M, and by conveying a plurality of steel materials M while being separated from each other, the steel materials M are allowed to cool in the conveying section 30. It is possible to cool the steel material M with higher uniformity in the cross section intersecting the longitudinal direction of the steel material M, that is, in the circumferential direction than when the steel material M is cooled. The angular interval for turning the steel material M is preferably in the range of 3° to 20° in consideration of cooling with high uniformity along the circumferential direction centering on the longitudinal axis of the steel material M. More preferably, it should be in the range of 4° to 10°, for example 6°.

The steel material M conveyed while being cooled by the rotary transfer 40 is accumulated in the accumulation section 60 . Then, it is appropriately subjected to post-stage processing such as shape correction by a roll straightening machine.

Further, in the rolling line 1 , a branch line 50 that branches off from the line extending from the rolling section 20 to the conveying section 30 and is different from the conveying section 30 is provided. The branch line 50 branches off within the rolling unit 20 and runs parallel to the conveying unit 30. Although illustration after the branching unit is omitted, the branch line 50 conveys, cuts, and cools the steel material M independently of the conveying unit 30. It can be performed. A line switching unit 51 is provided at a location where the branch line 50 branches, and the steel material 20 rolled by the rolling unit 20 is switched to the conveying unit 30 or the branch line 50 by the line switching unit 51. can supply. For example, when the line from the rolling unit 20 to the conveying unit 30 is configured as a thick round line for processing a rolled material that has been rolled to a diameter larger than a predetermined diameter, the branch line 50 is used for rolling to a diameter smaller than the predetermined diameter. It can be configured as a thin round line for processing rolled material.

[Temperature change of steel material in rolling line]
Next, the temperature change of the steel material M in each part of the rolling line 1 described above and its influence will be described.

Here, description will be made based on the continuous cooling transformation diagram schematically shown in FIG. Here, phase A and phase B are assumed as phases of the metal structure. Phase A is generated at a higher temperature than phase B, and when each part of the billet M heated to a high temperature is cooled along the cooling curve, phase A and phase A are generated as the temperature decreases. A phase transformation from phase A to phase B occurs when the phase boundary L between B is crossed. As described above, the specific phases corresponding to phase A and phase B are not particularly limited. Let us assume A and phase B. Here, as an example, it is assumed that the phase A is the γ phase and the phase B is the pearlite phase.

As described above, in the heating section 10 , the raw steel billet is sufficiently heated and introduced into the rolling section 20 . The heating temperature in the heating section 10 is set so that the temperature of the steel material M falls within the region corresponding to the phase A in the entire region at the time when the steel material M is introduced into the conveying section 30 after being rolled and divided in the rolling section 20. ing. Therefore, the steel material M is in the phase A over the entire area when it is introduced into the conveying unit 30 . If the entire steel material M is in phase A at the time of entering the conveying unit 30, even if it has already undergone some phase transformation and reached the phase A by cooling after leaving the heating unit 10 good.

The steel material M introduced from the rolling unit 20 to the conveying unit 30 is allowed to cool while being conveyed and cut in the conveying unit 30 . However, in the conveying method according to the present embodiment, the steel material M is in a homogeneous phase state at the time when it is introduced into the cooling unit 40 after being conveyed by the conveying unit 30 . The homogeneous phase state means that, in the cross section of the steel material M, the first point and the second point located on the surface of the steel material M, which are separated from each other, form a phase in the continuous cooling transformation diagram (CCT diagram) of the steel material M It refers to the state of being settled in the region corresponding to the same phase that has not undergone transformation. Here, the phase in which no phase transformation has occurred means the phase in which the focused phase transformation has not occurred. In FIG. 3, the state in which both the first point and the second point fall within the region corresponding to phase A that has not undergone phase transformation to phase B across phase boundary L is the homogeneous phase state. Become.

In the CCT diagram of FIG. 3, a cooling curve C1 representing cooling at a certain cooling rate and a cooling curve C2 representing cooling at another higher cooling rate are set, and the steel material M heated to a temperature that takes phase A is cooled at a cooling rate between cooling curve C1 and cooling curve C2. The cooling curve C2 crosses the phase boundary L at an earlier time than the cooling curve C1. , the phase transformation from phase A to phase B occurs even if the elapsed time is short.

In the homogeneous phase state of the present embodiment, the first and second points located on the surface of the steel material M separated from each other while the steel material M is being conveyed and cut in the conveying unit 30 are shown in the CCT diagram. , remains in the region corresponding to the same phase A. That is, when cooling is performed at a cooling rate between the cooling curve C1 and the cooling curve C2, at both the first point and the second point on the steel surface, the region corresponding to the phase B across the phase boundary L prevent entry. For example, if a first point cools along cooling curve C1 and a second point cools along cooling curve C2, at time t1 both the first point and the second point are in phase. It is in the region corresponding to A (intersection points p1 and p2) and has a homogeneous phase state. On the other hand, at time t2, which is later than time t1, the first point remains in the region corresponding to phase A (point of intersection p3), while the second point crosses the phase boundary L and corresponds to the region corresponding to phase B. (intersection point p4) and is not in a homogeneous phase state.

In the rolling line 1 , the steel material M heated by the heating section 10 is allowed to cool while being conveyed by the conveying section 30 . Even if it is left to cool, if it remains in the region corresponding to phase A in the CCT diagram, the phase transformation from phase A to phase B will not occur, but the temperature within the region corresponding to phase B will not occur. If this occurs, a phase transformation to phase B will occur. At this time, if the cooling occurs unevenly (uneven cooling) in a cross section that intersects the longitudinal direction of the steel material M, a part of the same cross section will remain in the region corresponding to phase A, and phase transformation will occur. A situation can occur in which the phase A is maintained without causing phase A, but the region shifts to a region corresponding to phase B at another site, undergoes a phase transformation, and adopts phase B. Then, structures of different phases coexist within the same cross section. If the phases are distributed symmetrically outward from the center of the cross section, the phase distribution is unlikely to lead to deformation of the steel material M. However, if the phase distribution occurs asymmetrically with respect to the center of the cross section, Due to the difference in the crystal structure of each phase before and after the transformation, here phase A and phase B, the steel material M may undergo local contraction or expansion, and deformation such as bending may occur. In addition, on the surface of the steel material M, physical properties such as hardness may be distributed depending on the part.

However, in the conveying method according to the present embodiment, the first point and the second point located on the surface of the steel material M separated from each other in the same cross section both remain in the region corresponding to the phase A. By being in the phase state, the distribution of phases is less likely to occur in the cross section intersecting the longitudinal direction of the steel material M while being conveyed by the conveying unit 30 . As a result, deformation such as bending and physical property distribution due to phase distribution are less likely to occur. The transportation by the transportation unit 30 is finished until the time when the phase boundary L is crossed and the phase B is entered in a part of the cross section where the cooling rate is relatively high, such as the time t2 in FIG. Otherwise, a non-uniform phase distribution will occur in the cross section. However, if the transfer by the transfer unit 30 can be completed within the time during which the phase A remains in the entire cross section where the cooling rate is between the cooling curve C1 and the cooling curve C2, as in the time t1, the phase in the cross section distribution is unlikely to occur.

If the steel material M is introduced into the cooling unit 40 while the steel material M is being transported by the transporting unit 30 without forming a non-uniform distribution of phases in the cross section of the steel material M, the cooling unit 40 will reduce the steel material more than the transporting unit 30. Because of the high uniformity of cooling for M, the entire cross-section of steel M will be cooled with high uniformity. Then, the phase transformation proceeds with high uniformity over the entire cross section of the steel material M. In this case, deformation such as bending and distribution of physical properties are less likely to occur in the steel material M.

The first point and the second point for determining whether the homogeneous phase condition is satisfied in the steel M are spaced apart from each other on the surface of the steel M in a cross section intersecting the longitudinal axis of the steel M. However, they are set at positions facing each other across the center of gravity (point b) of the cross section, such as points a and c shown in FIG. preferably. This is because the difference in temperature is most likely to occur between the parts facing each other across the center of gravity due to the form of transport by the transport unit 30 as shown in FIG. 2(a). Also, such two points are the farthest point in one cross section, and if there is a temperature gradient between those points, it is likely to lead to large bending of the steel material M. On the other hand, if those points satisfy the homogeneous phase state, it can be said that there is a high probability that the uniformity of the temperature distribution is high over the entire surface of the steel material in that cross section. Preferably, the homogeneous phase state is satisfied regardless of how the first point and the second point are set in a certain cross section. Further, when any cross section is taken in one steel material M, it is preferable that the uniform phase state is satisfied in any cross section.

Here, temperature gradients that typically occur in steel materials will be described. As shown in FIG. 2(a), when the steel material M is conveyed in the conveying unit 30 with its longitudinal direction facing the conveying direction D, a plurality of steel materials M are aligned in the width direction of the conveying surface 30a. There are many cases. In this case, in one steel material M, the part facing inward in the row of the steel materials M, that is, the opposite inner part M1, which is the part away from the side wall 30b, is in contact with or close to the other steel material M. Due to the effect of On the other hand, in the portion facing the outside of the row of the steel materials M, that is, in the portion close to the side wall 30b to the outside M2, cooling occurs more easily than to the inside M1.

As a result, as shown in FIG. 2(b), a temperature gradient occurs in a cross section intersecting the longitudinal direction in one steel material M, in which the inside M1 has a high temperature and the outside M2 has a low temperature. . Due to this temperature gradient, the pair inside M1 kept at a high temperature stays in the region corresponding to phase A in the CCT curve and maintains phase A, while the pair outside M2 cooled down to a low temperature rises to the phase boundary L into the region corresponding to phase B and transform into phase B. Then, as described above, in the cross section of the steel material M, a region having the phase A and a region having the phase B coexist. As a result, due to the difference in crystal structure between the phase A and the phase B, there is a possibility that the shrinkage behavior of the material will differ between the interior M1 and the exterior M2, and the steel material M will bend. For example, when phase A is a γ phase and phase B is a pearlite phase, as shown in FIG. On the other hand, the contraction S of the material occurs in the external M2 which assumes the phase B (pearlite phase). This is because the lattice constant of the bcc lattice included in the pearlite phase is smaller than that of the fcc lattice of the γ phase. When such local shrinkage S occurs, the steel material M bends with the side where the shrinkage S occurs inside.

When the steel material M is bent due to such phase distribution while the steel material M is being conveyed in the conveying section 30, even if the phase transformation further progresses in the cooling section 40 thereafter, at least a part of the bending is maintained. There are many. Due to the contraction (or expansion) of the structure that undergoes phase transformation first, tensile (or contraction) stress is applied to the untransformed structure. This is because phase transformation occurs. If the steel material M remains bent in this way, it becomes necessary to mechanically correct the bend using a roll straightening machine or the like. If the bending is large, it may become difficult even to install the steel material M in a roll straightening machine or the like. The distribution of phases in the cross section of the steel material M leads not only to the bending of the steel material M but also to the distribution of physical properties such as hardness on the surface of the steel material M.

In particular, in the conveying unit 30, the heated steel M does not exist adjacent to the outside M2 in the steel M positioned on the outermost side of the row of the plurality of steels M. As shown in c), the external side M2 directly contacts or abuts the cold side wall 30b. Then, the difference in temperature between the inside M1 and the outside M2 becomes large, and the distribution of bending and physical properties tends to become remarkable.

However, in the conveying method according to this embodiment, in the cross section of one steel material M, both the inner side M1 and the outer side M2 are in the region corresponding to the phase A in the CCT diagram. Conveyance in the conveyance section 30 is performed. As a result, while the steel material M is being conveyed through the conveying section 30, a temperature gradient such as that shown in FIG. As a result, due to the temperature gradient, the bending of the steel material M as shown in FIG.

The steel material M conveyed through the conveying section 30 while remaining in the region corresponding to phase A both to the interior M1 and to the exterior M2 is introduced into the cooling section 40 and is cooled with a higher uniformity than in the conveying section 30. , a phase transformation occurs with respect to both the inner M1 and the outer M2. The phase transformation that occurs in the cooling section 40 may be the phase transformation itself (transformation from phase A to phase B; in the example, pearlite transformation) that should be avoided in the conveying section 30, or other phase transformation (for example, bainite transformation). good too. In the cooling part 40, due to the high uniformity of the cooling, the temperature gradient and the resulting phase distribution are generated between the mutually spaced regions of the surface, such as the inner side M1 and the outer side M2. unlikely to occur. Therefore, in the cooling in the cooling unit 40, bending of the steel material M and distribution of physical properties on the surface of the steel material M are less likely to occur. Therefore, in the conveying unit 30, the temperature gradient on the surface of the steel material M is suppressed, and the distribution of bending and physical properties is suppressed, so that the bending and distribution of physical properties are suppressed in the steel material M finally manufactured in the rolling line 1. be able to.

If the steel material M cannot maintain a uniform temperature state while being transported by the transport unit 30, and phase transformation occurs in a part of the surface area, the steel material M may be bent or have physical properties of the surface. Even if a distribution occurs, it may sometimes be possible to eliminate or reduce the bending using a roll straightener or the like. However, even if the bending as an appearance can be eliminated, the non-uniform distribution of the phases on the surface of the steel material M and the resulting distribution of physical properties such as hardness cannot be eliminated. Therefore, even if the steel material M does not have a curved appearance, it can be evaluated whether or not a uniform temperature state is maintained during transportation by the transportation unit 30 by observing the structure and evaluating the physical properties. .

As described above, in the conveying method according to the present embodiment, the first point and the second point located on the surface of the steel material M in the cross section are separated from each other in one steel material M. However, when a plurality of steel materials M are simultaneously conveyed side by side on the conveying section 30, the surface of each of the plurality of steel materials M may be in the area corresponding to the phase A when conveyed by the conveying section 30. 3 and is introduced into the cooling section 40, it should be in a region corresponding to the same phase (phase A in FIG. 3) that has not undergone phase transformation. As a result, the surface temperature distribution between individual pieces of the steel material M, such as between the inner side and the outer side of the row when being conveyed by the conveying unit 30, is suppressed to be small. It is possible to manufacture a steel material M with less variation in properties. In addition, since the distribution of the surface temperature among the individuals is small, the probability that the gradient of the surface temperature within each individual is also small increases. For each individual, the temperature is evaluated at one point on the surface, or at multiple points, such as the first and second points above, and the values are compared between the individuals, all of which are in the same phase. It should be within the corresponding area.

[Means for achieving homogeneous phase state]
As described above, in the conveying method according to the present embodiment, while the steel material M is conveyed by the conveying unit 30, in the cross section intersecting the longitudinal direction of the steel material M, the By maintaining a uniform phase state in which the first point and the second point both correspond to the same phase in which phase transformation has not occurred, the bending of the steel material M and the distribution of physical properties on the surface are suppressed. Means for achieving this homogeneous phase state are not particularly limited, but the following means can be exemplified. Each means can also be applied in combination.

(1) Retention Elimination Control When the steel material M stays in the conveying unit 30 for a long period of time, the steel material M is allowed to cool for a long period of time. transition from phase A to phase B in FIG. 3) is more likely to occur. Therefore, it is preferable to shorten the stay time of the steel material M in the transport section 30 . For that purpose, for example, at the stage of rolling in the rolling unit 20 before the steel material M is introduced into the conveying unit 30, the steel material M can be distributed to another line, and the distribution can be used. Thus, it becomes effective to eliminate the retention of the steel material M in the conveying unit 30 .

The stagnation of the steel material M in the conveying unit 30 is a state in which the conveying of the steel material M is temporarily stopped or a state in which the conveying speed is temporarily slowed down. The stagnation of the steel materials M in the conveying section 30 is caused, for example, by the time it takes for the cutting machines 32 and 34 provided in the middle of the conveying section 30 to cut the steel materials M when a large number of steel materials M are sequentially supplied to the conveying section 30 . is generated by requiring As in the rolling line 1 described above, if the steel material M rolled by the rolling unit 20 can be switched between the conveying unit 30 and the branch line 50 and supplied, the distribution of the steel material M to the branch line 50 can be used. Therefore, the stagnation of the steel material M in the conveying section 30 can be alleviated. The order in which the steel materials M are supplied to the conveying section 30 and the steel materials M are supplied to the branch line 50 so that the steel materials M do not stagnate in the conveying section 30 when continuously rolling a large number of steel materials M in the rolling section 20. and quantity should be adjusted. In other words, the order in which the rolled steel materials M are to be supplied to the conveying unit 30 and the branch line 50, respectively, and the number of steel materials M to be continuously supplied to each are planned. It should be formulated.

For example, when the conveying section 30 constitutes a thick round line and the branch line 50 is a thin round line, the distribution of the steel material M to the branch line 50 is used to avoid stagnation in the conveying section 30. Second, the rolling unit 20 sets the order and quantity of the large-diameter rolled material to be supplied to the conveying unit 30 and the small-diameter rolled material to be supplied to the branch line 50, and the line switching unit 51 You can control the action. In addition, in the thin round line, since the diameter of the steel material M to be processed is smaller than in the thick round line, cooling progresses faster, and in many cases, unevenness occurs before the steel material M is cut. Subject to cooling that can produce a distribution of phases. Therefore, in the thin round line, a rotary transfer similar to the rotary transfer 40 in the large round line is provided prior to the cutting machine, or as disclosed in US Pat. It is preferable to have facilities that can

As described above, to eliminate stagnation using the adjustment of the rolling order, the stagnation state of the steel material M in the conveying unit 30 is predicted in advance at the stage before rolling, and the stagnation is eliminated preventively. is preferred. In other words, based on experience and the like, information is accumulated in advance as to how many pieces of steel material M should be supplied to the conveying unit 30 and how much accumulation will occur in the conveying unit 30 . Then, at a certain point in time, with reference to the information on the number of steel materials M being transported in the transport section 30, it is predicted whether or not the steel materials M that are scheduled to be supplied from the next time onward will cause stagnation in the transport section 30. do it. Then, when it is predicted that stagnation will occur, the stagnation can be eliminated by adjusting the order of rolling.

It is preferable to predict the staying state of the steel material M in combination with measuring the temperature of the surface of the steel material M in the conveying unit 30 . It is necessary to eliminate the stagnation in the conveying unit 30 so that the steel material M conveyed by the conveying unit 30 can maintain a homogeneous phase state. If it is relatively difficult to maintain a homogeneous phase, even small stagnation should be eliminated efficiently. On the other hand, from the viewpoint of maintaining the production efficiency of the steel material M, it is preferable to keep the retention within the range necessary for maintaining the homogeneous phase state, and when it is relatively easy to maintain the homogeneous phase state. , it is better not to be so rigorous about clearing stagnation. In other words, while actually measuring the temperature of the surface of the steel material M, comparing it with the required homogeneous phase state, and estimating how much retention is required to maintain or achieve the homogeneous phase state. , retention can be eliminated within a necessary and sufficient range to satisfy the homogeneous phase state.

In order to measure the temperature of the surface of the steel material M, the transfer unit 30 may be provided with a temperature measurement unit. The temperature measuring unit may be provided at any position in the conveying unit 30, but it is necessary that the steel material M satisfies the homogeneous phase state when it is introduced into the cooling unit 40 after being conveyed by the conveying unit 30. Since this is important, it is preferable to provide a temperature measuring section at least in the vicinity of the area immediately before the cooling section 40 in the line of the conveying section 30 . The temperature measurement unit may be of any type as long as it can measure the surface temperature of the metal material. It is preferable to be measurable.

(2) Installation of Heat Retaining Section In the conveying section 30, if the cooling speed of the steel material M is reduced to make it difficult for the steel material M to cool, it becomes easier to maintain a homogeneous phase state during conveyance. Therefore, it is conceivable to provide the conveying section 30 with a heat retaining section capable of suppressing cooling or heating the steel material M.

As a specific configuration of the heat retaining section, it is conceivable to provide a heat retaining hood surrounding the outer periphery of the conveying section 30 . As a result, the heat transfer loss due to contact of the steel material M with the outside air can be reduced, and the heat lost by radiation can be confined in the conveying unit 30, so that the cooling speed of the steel material M can be reduced.

It is conceivable to provide a reheating heater in the middle of the conveying section 30 instead of or in addition to the heat retaining hood. Even if the steel material M introduced into the conveying unit 30 in a high temperature state is allowed to cool while being conveyed by the conveying unit 30 within a range that satisfies the homogeneous phase state, it is heated again during the conveying. As a result, the steel material M can be brought back to a high temperature state, and the uniform phase state can be easily maintained in the subsequent transportation process. Also, when using a reheating heater, the degree of heating should be controlled by referring to the result of temperature measurement of the surface of the steel material M by the temperature measurement means provided in the transfer unit 30, as in the above-described retention elimination control. is preferred.

(3) Control of heating state If the temperature of the steel material M is sufficiently high when it is introduced into the conveying unit 30, even if it is allowed to cool while being conveyed by the conveying unit 30, it will eventually reach the cooling unit 40. The temperature of each part of the steel material M becomes high when it is introduced, and it is easy to achieve a homogeneous phase state. If the rolling and division/cutting are performed in the rolling section 20 while being heated to a high temperature in the heating section 10, the temperature of the steel material M can also be raised when it is introduced into the conveying section 30. FIG.

By controlling the heating state of the steel material M in the heating unit 10 in this way, it is possible to achieve a homogeneous phase state in the steel material M conveyed through the conveying unit 30 . At this time, for the setting of specific heating conditions in the heating unit 10 such as the heating temperature, refer to the result of temperature measurement of the surface of the steel material M by the temperature measuring means provided in the conveying unit 30, as in the above-described retention elimination control. It is preferable to

Examples of the present invention are shown below. However, the present invention is not limited to these examples.

<Test method>
Using a rolling line as shown in FIG. 1, a steel material made of steel grade SCM435 was rolled, cut, and cooled. At this time, the temperature of the surface of the steel material was measured at an arbitrarily selected point on the surface after cutting by the second cutting machine (34) and at the inlet of the rotary transfer (40).

The appearance of the steel material after cooling in the rotating transfer was completed was visually observed to evaluate the presence or absence of bending. A steel material without bending was extracted as sample 1, and a steel material with bending as sample 2.

Then, each of the samples 1 and 2 was cut along the longitudinal direction, and the hardness was measured and the structure was observed in the cross section.

A Rockwell C scale was used to measure hardness. As shown in FIG. 4, the measurement was performed for each of Samples 1 and 2 at two points: the center of the cross section (center of gravity; points b and e) and the surface of the steel material facing each other across the center (point a, c, d, f). Here, for the sample 2 in which the steel material is bent, the point d corresponds to the inside of the bend, and the point f corresponds to the outside of the bend.

Observation of the structure was performed by microstructure observation with an optical microscope. Observations were made at positions corresponding to points a to f where the hardness was measured above for each of Samples 1 and 2.

<Test results>
Temperatures measured at the rolling line were 690° C. at the second cutter and 645° C. at the inlet of the rotary transfer for unbent Sample 1. For bent Sample 2, it was 570°C at the second cutter and 520°C at the rotary transfer inlet. Thus, the temperature of sample 1 is higher than that of sample 2 at any position.

FIG. 4 shows numerical values (unit: HRC) of the hardness measured at each position of the cross section of sample 1(a) and sample 2(b). According to this, in sample 1, the surface hardness is almost the same at point a and point c. Also, the hardness of these surfaces is higher than the hardness at the central point b. On the other hand, in sample 2, the surface hardness differs greatly between point d and point f. That is, the hardness of point d on the inside of the bend is lower than the hardness of point f on the outside of the bend. Moreover, the hardness of these surfaces, especially the hardness at the point d, is not as high as in the case of the sample 1 compared to the center point e.

FIG. 5 shows microstructure observation images at each point of samples 1 and 2 by an optical microscope. In sample 1, similar observed images are obtained at points a and c on the surface. A texture with many elongated crystals can be associated with the bainite phase. At the central point b, although the display of the observed image is omitted, bainite with more ferrite than the surface is generated.

On the other hand, in the sample 2, the state of the observed image differs between the points d and f on the surface. In other words, at the point f, the bainite phase having elongated crystals occupies the majority, and the ferrite in a slightly massive form is observed. On the other hand, since the observation image of point d is mainly composed of the ferrite phase and the pearlite phase, it can be associated with the ferrite/pearlite structure. At the central point e, although the display of the observed image is omitted, a bainite structure is generated in the same manner as at the point b of the sample 1. FIG. However, the ratio of ferrite is higher than that of sample 1 at point b.

As described above, in Sample 1, which had a high surface temperature during transportation, no bending occurred in the steel material, and hardness and structure that were very close to each other were obtained at the two observation points on the surface. As for the structure, the bainite phase containing a part of ferrite is generated at the center of the steel material, while the bainite phase is generated uniformly at the surface regardless of the position. As a result, a uniform higher hardness is obtained at the surface than at the center. Also, no bending occurs in the steel material. It is presumed that the temperature gradient on the surface is small due to the high temperature of the surface during transportation, and as a result, non-uniform phase transformation occurs due to the temperature gradient on the surface during transportation in the transportation section. It is thought that the phase transformation to the bainite phase occurred uniformly on the surface after moving to the rotational transfer.

On the other hand, in sample 2, which had a low surface temperature during transportation, the steel material was bent, and the hardness and the state of the structure differed greatly between the inside and outside of the bend. As for the structure, on the outside of the bend, a structure containing mainly bainite and a small amount of ferrite was obtained, whereas on the inside of the bend, ferrite and pearlite were the main components. As a result, the hardness is lower, particularly at the inner surface of the bend, than at the core, which is composed of the ferrite-rich bainite phase. It is presumed that the temperature gradient on the surface is large due to the low temperature of the surface during transportation. A metamorphosis may have occurred. After that, after cooling in the rotary transfer, a ferrite-pearlite structure is formed in the part where pearlite transformation occurred in the transfer part, and mainly bainite and a small amount of ferrite are included in the part where pearlite transformation did not occur. It is thought that an organization was formed. Due to this structure distribution, it is interpreted that the part that has undergone pearlite transformation exhibits low hardness and shrinks, causing the steel material to bend with this part inside.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments, and various modifications are possible without departing from the gist of the present invention. In the above, a steel material such as SCM435 is assumed as the metal material, the phase A is the γ phase, the phase B is the pearlite phase, and the phase transformation is the pearlite transformation. , depending on the conditions during rolling, the configuration of the transport section, etc., various phase transformations that can occur during transport and which should be avoided can be treated similarly.

1 Rolling line 10 Heating unit 20 Rolling unit 30 Conveying unit 30a Conveying surface 30b Side walls 32, 34 Cutting machine 40 Turning transfer (cooling unit)
50 branch line (thin round line)
D Conveying direction M Steel material (metal material)
M1 vs. internal M2 vs. external S Contraction C1, C2 Cooling curve L Phase boundary

Claims (9)

In a method for conveying a metal material in which a long metal material made of a metal that undergoes phase transformation due to a temperature change is heated in a heating unit and then conveyed to a cooling unit by a conveying unit,
The cooling unit cools the metal material with higher uniformity in a cross section intersecting the longitudinal direction than the conveying unit,
The temperature at a first point and a second point spaced apart from each other and located on the surface of the metal material in the cross section of the metal material when it reaches the cooling portion is the continuous cooling transformation diagram of the metal material. 2. A method of conveying a metal material characterized by taking a homogeneous phase state in a region corresponding to the same phase in which phase transformation has not occurred. 2. The method of conveying a metal material according to claim 1, wherein the first point and the second point are positioned to face each other across the center of gravity of the cross section. The transport unit can simultaneously transport a plurality of the metal materials,
Regarding the plurality of metal materials simultaneously transported by the transport unit, the temperature at the surface of the metal materials when reaching the cooling unit corresponds to the same phase that has not undergone phase transformation in the continuous cooling transformation diagram. 3. The method for conveying a metal material according to claim 1 or 2, wherein the metal material is contained in a region where the metal material is formed. 4. The method for conveying a metal material according to claim 1, wherein the uniform phase state is achieved by retention elimination control for eliminating retention of the metal material in the transport section. A rolling unit is provided between the heating unit and the conveying unit to roll the metal material heated by the heating unit and supply it to the conveying unit,
The metal material rolled by the rolling unit can be switched and supplied to the conveying unit or a branch line different from the conveying unit,
By adjusting at least one of the order and quantity of the metal materials supplied to the conveying section and the metal materials supplied to the branch line when the plurality of metal materials are continuously rolled in the rolling section 5. The method for conveying a metal material according to claim 4, wherein the retention elimination control is performed. A temperature measurement unit is provided for measuring the temperature of the surface of the metal material conveyed by the conveying unit, and the state of retention of the metal material in the conveying unit is predicted, and the predicted state of retention and the temperature measurement unit are provided. 6. The method for conveying a metal material according to claim 4, wherein the retention elimination control is performed based on the temperature measured by the. 7. The method for conveying a metallic material according to claim 1, further comprising providing a heat retaining section for suppressing cooling or heating the metallic material conveyed by the conveying section. 8. The method for conveying a metal material according to claim 1, wherein the uniform phase state is achieved by controlling the heating state in the heating unit. The cooling unit includes a rotating transfer that conveys the metal material along the longitudinal axis while rotating the metal material in the circumferential direction at angular intervals of 3° or more and 20° or less about the longitudinal axis. The method for conveying a metal material according to any one of claims 1 to 8.

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