JP2006088162A - Linear heating deformation method for steel sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heating deformation method mainly applicable in the case a welded structure for a vessel is produced, where a steel sheet having properties capable of obtaining a large heat deformation quantity in accordance with a heating deformation form even under the same heating conditions is selected, and the steel sheet can be bent to an objective shape at an operating efficiency higher than the conventional case. <P>SOLUTION: Regarding the linear heating deformation method for a steel sheet, in a linear heating deformation method where the surface or back face of a steel sheet is linearly heated by a gas burner and is thereafter water-cooled, so as to be angularly deformed or horizontally deformed, as the steel sheet to be angularly deformed, a steel sheet whose yield strength at 600°C is ≥1/3 of the yield strength in room temperature is used, and, as the steel sheet to be horizontally deformed, a steel sheet whose yield strength in room temperature is ≤80% of its tensile strength is used. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for heating and deforming a steel sheet applied when manufacturing a streamline-shaped welded structure by welding steel sheets having a plurality of curvature surfaces in the shipbuilding field and the like. The present invention relates to a linear thermal deformation method for a steel sheet that improves work efficiency when the back surface is linearly heated and then cooled by water to deform the steel sheet.

  Ship structures such as hulls in the shipbuilding field need to have a smooth surface with a continuous outer surface in order to reduce water flow resistance during voyage. A welded structure having a smooth and continuous curvature surface is formed by welding each other.

  Since this steel plate needs to be bent with a complex and delicate curvature depending on the part of the ship structure, it cannot be handled by simple and uniform press work. Has been done. In this linear heating deformation, the steel sheet is locally heated linearly using a gas burner or the like, and the heated portion is thermally expanded and plastically deformed by restraint from its surroundings. Usually, water cooling is performed immediately after heating to increase work efficiency. It is a method to do.

  In the actual production of ship structures, in order to obtain a smooth curvature surface, a plurality of locations on the steel sheet surface are linearly heated and deformed, and a single linear heating deformation is repeated a plurality of times of linear heating and water cooling. In addition, since these are all performed by the intuition and skill of the skilled person, it may take 5 days or more to bend one steel plate into a predetermined shape. For this reason, from the viewpoint of reducing shipbuilding costs and the number of manufacturing days, improvement of work efficiency and automation in bending work by linear heat deformation of steel sheets have been studied.

  In recent years, with the aim of improving the work efficiency of bending work by linear heat deformation of steel plates, and further aiming for automation, predicting the heat deformation at the time of linear heat deformation of steel plates using numerical analysis by the finite element method (FEM), A method for determining a heating condition for deformation into a target shape has been proposed (see, for example, Patent Document 1 and Patent Document 2). However, since the accuracy of the estimation formula by numerical analysis of the finite element method (FEM) is not sufficient, the target shape may not be obtained under the heating conditions set based on this, and each time according to changes in the work environment and heating conditions. The estimation formula must be corrected, and automation has not yet been realized.

In addition, the relationship between the mechanical properties depending on the composition and structure of the steel sheet and the linear heating deformation has not been elucidated in detail, and even if the linear heating deformation occurs under the same heating conditions, depending on the steel sheet, The actual deformed shape may vary greatly with respect to the shape.
From such a state of the art, there is a demand for a method for stably controlling the heating deformation of the bending process by the linear heating deformation of the steel sheet and further improving the working efficiency.

JP 09-285823 A JP 09-323129 A

  In view of these problems of the prior art, the present invention is mainly applied when manufacturing a marine welded structure having a complicated and delicate curvature surface, and a large amount of thermal deformation is caused depending on the heating deformation form even under the same heating condition. An object of the present invention is to provide a heating deformation method capable of selecting a steel plate having the obtained characteristics and bending the steel plate into a target shape with a higher work efficiency than in the past.

  From the above viewpoint, the present inventors have intensively studied the thermal deformation characteristics of the steel sheet, focusing on the characteristics of the steel sheet, which has never been attempted. And by defining the characteristics of the steel materials that are suitable for thermal processing, the inventors have found an unprecedented highly efficient thermal processing method. This invention is made | formed by such a research, The summary is as follows.

  (1) In a linear heating deformation method in which the surface or the back surface of a steel sheet is linearly heated by a gas burner, and the steel sheet is bent and deformed by water cooling, the yield strength at 600 ° C. is 1/3 or more of the yield strength at room temperature. Using a steel plate, the steel plate surface is linearly heated with the gas burner, and the lateral deformation amount on the heating surface side in the thickness direction in the linear heating region is increased in angular deformation as compared with the non-heating surface side. A method for linearly heating and deforming a steel sheet.

  (2) The method for linearly heating and deforming a steel sheet according to (1), wherein the angularly deformed steel sheet has a structure containing a bainite phase in an area ratio of 70% or more.

  (3) The steel sheet to be angularly deformed contains, in mass%, C: 0.001 to 0.10%, Si: 0.02 to 0.60%, Mn: 0.80 to 3.0%, P: 0.03% or less, S: 0.02% or less, Nb: 0.005-0.20%, Ti: 0.005-0.20%, V: 0.005-0 .20% and Mo: 0.05 to 0.5%, or one or more, and the balance is iron and unavoidable impurities as described in (1) or (2) above A method of linearly heating and deforming steel sheets.

  (4) The steel sheet according to any one of (1) to (3), wherein the steel sheet to be angularly deformed further contains B: 0.0003 to 0.0050% in mass%. Linear heating deformation method.

  (5) The steel sheet according to any one of (1) to (4), wherein the steel sheet to be angularly deformed further contains Al: 0.01 to 0.10% in mass%. Linear heating deformation method.

  (6) The steel plate to be angularly deformed is in mass%, and Cu: 0.5 to 2.0%, Ni: 0.1 to 2.0%, Cr: 0.05 to 0.5%, W : 0.05 to 0.5%, and Zr: 0.05 to 0.5%, or one or more, containing any one of (1) to (5) A method of linearly heating and deforming steel sheets.

  (7) The steel plate to be angularly deformed contains, by mass%, REM: 0.001 to 0.02% and Ca: 0.0005 to 0.02%, or one or two of them. The method of linearly heating and deforming a steel sheet according to any one of (1) to (6), wherein

  (8) In a heating deformation method in which the front or back surface of a steel sheet is linearly heated by a gas burner, and the steel sheet is bent and deformed by water cooling, using a steel sheet whose yield strength at room temperature is 80% or less of the tensile strength, The steel plate surface is linearly heated by the gas burner in a direction substantially perpendicular to one side of the steel plate, and the linear heating region and the non-heated region are formed in the linear heating direction and the vertical direction, and then linear heating is performed. A method of linearly heating and deforming a steel sheet, wherein the transverse deformation is performed so that the amount of lateral shrinkage in the thickness direction in the region is uniform.

  (9) The linear heating of the steel sheet according to (8), wherein the steel sheet to be laterally deformed is a mixed structure of a ferrite pearlite phase and a bainite phase containing a ferrite pearlite phase in an area ratio of 30 to 70%. Deformation method.

  (10) The steel sheet to be laterally deformed contains, in mass%, C: 0.05 to 0.18%, Si: 0.05 to 0.6%, Mn: 0.5 to 2.0%, P: 0.03% or less, S: 0.03% or less, the balance being iron and inevitable impurities, the method for linearly heating and deforming a steel sheet according to (8) or (9) above .

  (11) The steel plate to be laterally deformed is in mass%, and further, Ni: 0.1 to 2.0%, Cu: 0.1 to 0.5%, Cr: 0.05 to 0.5% 1 The method of linearly heating and deforming a steel sheet according to any one of the above (8) to (10), comprising a seed or two or more kinds.

  According to the present invention, a work process in heating deformation, which is mainly applied when manufacturing a marine welded structure having a complicated and subtle curvature surface, has been required to repeatedly perform many heating and cooling work processes so far. The working efficiency can be dramatically improved as compared with the prior art, and the industrial contribution such as the shipbuilding field according to the present invention is very large.

  The present invention is described in detail below.

  In general, bending by linear heating deformation of a steel plate mainly used in the manufacture of a marine welded structure is performed as follows.

  In other words, a predetermined position on the front or back surface of the steel sheet is usually locally heated linearly to a temperature of 900 ° C. or higher using a heating source such as a gas burner, and the heated portion expands thermally from the surrounding (non-heated portion). It is plastically deformed by restraint. At this time, water cooling is performed after plastic deformation by heating in order to increase normal working efficiency. Under the present circumstances, the plastic deformation of the linear heating part of a steel plate, ie, generation | occurrence | production of a plastic strain, is dependent on the yield strength of the steel plate in a heating temperature range. For example, in the case of a steel plate having a high yield strength at a high temperature, plastic strain hardly occurs even under the same heating conditions, and the steel plate is difficult to deform. In addition, when the heating source is heated and deformed, the shape of the deformation changes depending on the heating conditions such as the strength and moving speed of the heating source, and the heating conditions such as the interval between the heating parts. When manufacturing an actual ship welded structure, it is possible to achieve bending of a desired shape having a smooth curvature surface by repeatedly performing linear heating and water cooling on a plurality of locations on a single steel plate, and bending them by a predetermined amount. .

  In general, deformation forms when a steel sheet is thermally deformed are roughly classified into two types, an out-of-plane deformation and an in-plane deformation. Among these, bending by linear heating mainly uses out-of-plane deformation.

  A representative example of out-of-plane deformation is the angular deformation shown in FIG. 1- (B), and the amount of lateral shrinkage on either one of the steel sheet surfaces is greater than that on the other steel sheet surface side in the sheet thickness direction of the steel sheet. That is, it occurs when the difference in lateral shrinkage between the front and back surfaces becomes relatively large, and the steel sheet bends toward the steel sheet surface side (in this case, the steel sheet surface side) with a relatively large lateral shrinkage. Here, the amount of lateral contraction means contraction in a direction perpendicular to the linear heating direction (lateral direction).

  On the other hand, as a representative example of in-plane deformation, a lateral deformation shown in FIG. 1- (A) is known. In contrast to the case of angular deformation, the lateral deformation is a case where the difference in lateral shrinkage between the front and back surfaces in the sheet thickness direction of the steel sheet is small, that is, the lateral shrinkage in the sheet thickness direction of the steel sheet is substantially uniform. Occurs in some cases. At this time, when the entire length of the steel sheet in the linear heating direction is linearly heated to form a heating region, lateral deformation occurs in the heating region, as shown in FIG. In-plane deformation occurs in which the length in the direction perpendicular to the direction (lateral direction) is shortened.

  However, this lateral deformation can be used to perform out-of-plane deformation, and is used in bending work by linear heating deformation of an actual steel plate. For example, FIG. 2 shows a linear heating in a direction substantially perpendicular to sides 1 and 2 of a rectangular steel plate, and on both sides of sides 1 and 2 except for the central portion (non-heated region) in the linear heating direction. An embodiment in which a linear heating region 3 (hatched portion in the figure) is formed and a plurality of linear heating regions 3 are formed at intervals on both sides of the side 1 and the side 2 is shown. In this case, lateral deformation occurs in the linear heating region 3 formed on both sides of the side 1 and side 2 of the steel plate, and both sides of the side 1 and side 2 of the steel plate (linear shape) with respect to the central portion (non-heating region). Out-of-plane deformation occurs when the length of the heating region 3) in the lateral direction (direction perpendicular to the linear heating direction) becomes relatively short.

  In the embodiment of FIG. 3, an example is shown in which a non-heated region is formed at the center in the linear heating direction, and a plurality of linear heating regions 3 are formed at intervals on both sides of the side 1 and the side 2 of the steel plate. Conditions such as the position of the non-heating region and the linear heating region 3 formed in the linear heating direction, the number of the linear heating regions 3 formed in the lateral direction (a direction perpendicular to the linear heating direction), and the presence or absence of a gap are as follows. What is necessary is just to set suitably according to the target bending shape.

  Thus, the out-of-plane deformation of the steel plate is possible by utilizing the lateral deformation. In the example shown in FIG. 2, when the steel plate shape is observed from the direction 4, the shape shown in FIG. 3 is obtained, which is similar to the angular deformation. Looks like. However, as shown in FIG. 2, the out-of-plane deformation due to the use of the lateral deformation of the steel sheet is shorter due to the lateral deformation in the vicinity of the side 1 and the side 2 as the heating region than in the central part of the steel plate as the non-heating region. Become. On the other hand, the out-of-plane deformation due to the use of the angular deformation of the steel plate, for example, arranges a linear heating region 3 ′ at the center of the steel plate as shown in FIG. When the transverse shrinkage is caused and observed from the direction 4 ', the steel sheet is bent and deformed to the side where the transverse shrinkage is relatively small. For this reason, in FIG. 4, the lengths in the vicinity of the side 1 'and the side 2' with respect to the central portion of the steel plate hardly change. As described above, the out-of-plane deformation by using the lateral deformation of the steel sheet is strictly different from the out-of-plane deformation by using the angular deformation of the steel sheet.

  In the above description, lateral deformation means in-plane deformation in a direction perpendicular to the linear heating direction. In actual linear heating of a steel sheet, in addition to lateral deformation, there is also vertical deformation that means in-plane deformation in the linear heating direction. However, since the longitudinal deformation has a very small in-plane deformation amount compared to the lateral deformation, in order to bend the steel sheet into the target shape, it is only necessary to consider angular deformation and lateral deformation in the linear heating deformation.

  Conventionally, for the purpose of automating the linear heating deformation of the steel plate described above, the deformation amount is predicted from the heating conditions such as the strength and moving speed of the heating source, the heating unit interval, and the deformation characteristics of the steel plate, and bent into the target shape. Attempts have been made to determine the heating conditions necessary for this purpose. However, since the accuracy of the prediction model is not sufficient, most of the current bending work by the steel wire linear heat deformation is performed by the intuition and skill of a skilled person. Moreover, since it is complicated and requires more than 5 days to bend a single steel plate into a smooth curvature shape by linear heating deformation, improvement of work efficiency is desired.

  Based on the above-mentioned present situation, the present inventors pay attention to the influence of the steel sheet characteristics on the heating deformation mode (angular deformation or lateral deformation) that has not been sufficiently studied to control linear heat deformation, Based on the characteristics of the steel plate, we have intensively studied how to improve the working efficiency during linear heating deformation.

  As a result, as shown below, it was found that optimizing the steel sheet characteristics according to the heating deformation mode of angular deformation or lateral deformation is effective for improving the working efficiency in linear heating deformation of the steel sheet.

  (1) Ratio of yield strength (YP) to tensile strength (TS) (YP / TS), that is, a steel sheet with a yield ratio (YR) of 80% or less, compared with the direct heating surface side even under the same heating conditions during linear heating. The amount of plastic strain generated on the non-heated surface side where the temperature decreases is sufficiently increased, and the amount of lateral shrinkage on the front and back sides in the plate thickness direction is increased uniformly in the thickness direction of the linear heating region. Deformation can be generated efficiently. Further, using this steel plate, as shown in FIG. 2, linear heating is performed with a gas burner in a direction substantially perpendicular to any one side of the steel plate, and a linear heating region ( In the case of FIG. 2, after forming a plurality of locations on both ends of the steel plate and a non-heated region (in the case of FIG. 2, formed at the center of the steel plate), the occurrence of lateral deformation in the linear heating region is promoted. Thus, the amount of bending deformation of the steel sheet can be increased. Therefore, by applying a steel sheet having a yield ratio (YR) of 80% or less, it is mainly responsible for lateral deformation of the steel sheet as shown in FIG. 1- (A) without changing the heating conditions during linear heating. It is possible to increase the deformation amount in the linear heating deformation, and to improve the work efficiency of the bending deformation as shown in FIG.

(2) The ratio of the yield strength (YP ₆₀₀ ) at 600 ° C. to the yield strength (YP) at room temperature (YP ₆₀₀ / YP) is 1/3 or more. The amount of plastic strain on the non-heated surface side is relatively reduced while ensuring the minimum amount of plastic strain on the side, and the difference in lateral shrinkage on the front and back sides in the plate thickness direction in the heating region is increased. be able to.

Therefore, by applying a steel plate having a YP ₆₀₀ / YP of 1/3 or more, the angular deformation of the steel plate as shown in FIG. 1- (B) is mainly performed without changing the heating conditions during linear heating. It is possible to increase the deformation amount in the linear heating deformation, and improve the working efficiency of the bending deformation as shown in FIG.

  The present invention has been made on the basis of the above knowledge and technical idea.

  The present invention presupposes a linear heating deformation method that uses a gas burner to linearly heat the front or back surface of a steel sheet, and then water-cools the steel sheet to perform angular deformation or lateral deformation of the steel sheet. The steel sheet to be deformed is optimized from the mechanical characteristics. Below, among the steel plates to be angularly deformed and the steel plates to be laterally deformed, which are the characteristics of the present invention, first, the reasons for limiting the mechanical properties of the steel plates to be angularly deformed, and the preferable structure and composition of the steel plates will be described.

(Mechanical characteristics of steel plate to be angularly deformed)
The present invention is characterized in that a steel sheet having a yield strength at 600 ° C. that is 1/3 or more of the yield strength at room temperature is used as the steel sheet to be angularly deformed in the linear heating deformation method.
In order to generate linear heating deformation mainly composed of angular deformation of a steel sheet as shown in FIG. 1- (B) by linear heating and cooling of the steel sheet, the front and back sides of the steel sheet in the thickness direction of the heating region It is necessary to increase the difference in lateral shrinkage. As a means for this, it is possible to control the heating and cooling conditions to increase or decrease the lateral shrinkage of either one of the steel sheet surfaces, but this complicates the work method and lowers the work efficiency. It is not preferable.

In the present invention, the yield at 600 ° C. with respect to the yield strength (YP) at room temperature in order to generate linear heating deformation mainly consisting of angular deformation without changing the heating and cooling conditions in the linear heating and cooling of the steel sheet. By applying a steel sheet having a strength (YP ₆₀₀ ) ratio (YP ₆₀₀ / YP) of 1/3 or more, the minimum amount of plastic strain on the direct heating surface side is ensured, while the relative non-heating surface side. This reduces the amount of plastic strain generated and increases the difference in lateral shrinkage on the front and back sides of the steel sheet in the thickness direction of the heating region. A steel sheet having a ratio of yield strength (YP ₆₀₀ ) at 600 ° C. to yield strength (YP) at room temperature (YP ₆₀₀ / YP) of less than 1/3 can be subjected to linear heating change mainly due to angular deformation of the steel sheet. The effect of increasing the amount of deformation and improving the working efficiency of bending deformation using angular deformation cannot be obtained sufficiently.

Therefore, in the present invention, the yield strength at room temperature (in order to increase the amount of deformation in linear heating deformation mainly consisting of angular deformation without changing the heating and cooling conditions, and to sufficiently improve the working efficiency industrially, ( The ratio (YP ₆₀₀ / YP) of the yield strength (YP ₆₀₀ ) at 600 ° C. to YP) was limited to a steel sheet having a value of 1/3 or more.

  The yield strength at 600 ° C. of the steel sheet is generally defined as 0.2% proof stress that can be measured industrially, and this measuring method can also be adopted in the present invention.

(Structure of steel plate to be angularly deformed)
As a preferable structure of the steel sheet to be angularly deformed in the present invention, the ratio (YP ₆₀₀ / YP) of the yield strength (YP ₆₀₀ ) at 600 ° C. to the yield strength (YP) at room temperature satisfies 1/3 or more, and It is necessary to have a structure capable of maintaining the toughness as a welded structural steel.

Increasing the martensite phase, which has the highest strength in the microstructure of the steel sheet, can improve the yield strength (YP ₆₀₀ ) at 600 ° C, but increasing the martensite phase ensures the toughness of the steel sheet. This is not preferable. Further, when the bainite phase in the steel sheet structure is less than 70% in area ratio, the ratio (YP ₆₀₀ / YP) of the yield strength (YP ₆₀₀ ) at 600 ° C. to the yield strength (YP) at room temperature is 1 / It becomes difficult to satisfy 3 or more, and the effect of increasing the work efficiency of bending deformation by increasing the amount of deformation in linear heating deformation mainly of angular deformation of the steel sheet during linear heating and cooling cannot be obtained sufficiently. .

For this reason, in the present invention, the ratio (YP ₆₀₀ / YP) of the yield strength (YP ₆₀₀ ) at 600 ° C. to the yield strength (YP) at room temperature as the steel plate to be angularly deformed satisfies 1/3 or more, and is welded. In order to maintain the toughness as structural steel, the preferred structure is limited to a bainite-based structure containing a bainite phase in an area ratio of 70% or more.

  It should be noted that the structure other than the bainite phase in the steel sheet structure is not particularly limited, and can be selected according to other purposes within a range that does not impair the basic characteristics of the present invention.

(Component composition of steel plate to be angularly deformed)
The preferable component composition of the steel sheet to be angularly deformed in the present invention is preferably defined as follows in order to stably secure the mechanical properties and the bainite main structure of the steel sheet.
The reason for limiting the preferred component composition of the steel sheet to be angularly deformed will be described below.

  In the following description, “%” means “% by mass” unless otherwise specified.

  C: C is an element that increases the strength of the steel sheet and increases the hardenability. The lower limit of the C content was set to 0.001% as a minimum value for enhancing hardenability and ensuring a bainite phase of 70% or more in the structure. On the other hand, excessive addition of C increases the problem of increased hardness and reduced toughness by increasing martensite in the steel sheet structure, and further increases the difference in hardness between the front and back surfaces of the steel sheet. The upper limit of the C content is set to 0.10% because it is not preferable for ensuring good characteristics of the steel sheet. In the present invention, the hardenability of the steel sheet can be ensured by addition of Mn, and from the viewpoint of steel sheet mechanical properties, it is preferable to keep the upper limit of the C content low, so the upper limit of the C content is 0.07. % Is more desirable.

  Si: Si acts as a deoxidizing element in steel and as a strength maintaining element. In order to sufficiently obtain the effects of deoxidizing Si and ensuring the strength, the lower limit of the Si content is set to 0.02%. On the other hand, when the Si content exceeds 0.60%, the weld zone toughness deteriorates when the steel sheet is welded, so the upper limit of the Si content is set to 0.60%.

  Mn: Mn is an essential element for ensuring the strength of the steel sheet and for improving the hardenability and increasing the bainite structure efficiently. By these actions, the lower limit of the Mn content was set to 0.8% as a minimum amount for securing a bainite structure of 70% or more in the steel sheet structure. On the other hand, if the Mn content is excessively increased, hardening is significantly enhanced when welding the steel sheet, which deteriorates the toughness of the weld heat affected zone (HAZ), which is not preferable. Therefore, the upper limit of the Mn content is set to 3.0%. .

  P, S: P and S are unavoidable impurities in the steel, and if these elements are contained excessively, the toughness of the HAZ when welding the steel plate and the steel plate deteriorates, so the upper limit of the content of P and S They were limited to 0.03% and 0.02%, respectively.

  Nb, Ti, V, Mo: Nb, Ti, V, and Mo are elements that improve the high-temperature yield strength by precipitation or solid solution in steel, and in order to effectively utilize this action, Each component contains one or more of the following contents.

Nb is an effective element for precipitating as carbide together with C in the steel sheet and improving the high temperature strength of the steel sheet. Nb has the effect of lowering the Ar ₃ transformation temperature and extending the bainite generation range to the low cooling rate side, and is necessary for stably generating the bainite phase. The lower limit of the Nb content is set to 0.005% as a minimum value for sufficiently obtaining the action and effect of the addition of Nb. On the other hand, if the Nb content exceeds 0.20%, the hardness is excessively increased and it is difficult to ensure toughness, so the upper limit of the Nb content is 0.20%.

Ti, like Nb, is an effective element for forming carbides in the steel sheet and increasing the high temperature strength by precipitation hardening. In addition, the Ar ₃ transformation temperature is lowered to contribute to the formation of a bainite structure, and TiN is formed during welding to improve the toughness of the weld heat affected zone. In order to sufficiently obtain these effects, the lower limit value of the Ti content is set to 0.005%. On the other hand, the Ti content exceeding 0.20% is not preferable because it deteriorates toughness, so the upper limit of the Ti content is set to 0.20%.

  V is also a precipitation strengthening element like Nb. In order to increase the high temperature strength by precipitation hardening of carbides in the steel sheet, the lower limit of the V content needs to be 0.005%. On the other hand, even if the content of V exceeds 0.20%, the effect of improving the precipitation strengthening of the steel sheet is saturated and further toughness deterioration is caused. Therefore, the upper limit of the V content is set to 0.20%.

  Mo is an element that has the effect of increasing the yield strength at room temperature and high temperature. In order to sufficiently obtain these strength increasing effects, the lower limit of the Mo content is set to 0.05%. On the other hand, when the Mo content exceeds 0.5%, the weldability deteriorates, so the upper limit of the Mo content is set to 0.5%.

  The above is a basic component as a preferable component composition of the steel sheet to be angularly deformed. In addition to this, the following components can be added for the following reasons.

  B: B is a typical hardenable element, segregates at the austenite grain boundary, and suppresses ferrite transformation therefrom, so that a great improvement in hardenability can be expected with a small addition. Therefore, in the present invention, the lower limit of the B content is set to 0.0003% in order to effectively use this action and ensure hardenability. On the other hand, excessive content of B causes BN to precipitate in the steel and deteriorates weldability, so the upper limit of its content was made 0.0050%.

  Al: Al is a deoxidizing element similar to Si, and in order to effectively obtain the effect of supplementing the deoxidizing action of Si and reducing the oxygen in the steel sheet and ensuring the steel sheet characteristics, the lower limit of the Al content is 0.010. %. On the other hand, excessive addition of Al impairs the weldability of the steel sheet, so the upper limit of Al content is 0.10%.

  Cu, Ni, Cr, W, Zr: Cu, Ni, Cr, W, and Zr are effective elements for improving the strength, and in order to effectively utilize this action, these components are respectively It can contain 1 type (s) or 2 or more types by content.

  Cu is an element that precipitates as a single substance and improves the strength. In this respect, the mechanism for improving the strength is different from the precipitation element that forms carbides such as Nb. In order to precipitate Cu and sufficiently improve the strength, the lower limit of the Cu content needs to be 0.5%. On the other hand, if the Cu content exceeds 2.0%, the toughness of the steel sheet deteriorates rapidly, which is not preferable. Therefore, the upper limit of the Cu content is set to 2.0%.

  Ni is an effective element for improving both strength and toughness of the steel sheet and for preventing Cu cracking during rolling in a steel sheet containing Cu. In order to sufficiently obtain these functions and effects, the lower limit of the Ni content is set to 0.1%. On the other hand, even if Ni is added in excess of 2.0%, the effect is saturated and Ni element is expensive, so the upper limit of Ni content was set to 2.0%.

  Cr has an effect of increasing the strength of the steel sheet, and the lower limit of the Cr content is set to 0.05% as the lowest value at which this effect can be manifested. On the other hand, if Cr is added over 0.5%, the weld toughness deteriorates due to welding, so the upper limit of Cr content was set to 0.5%.

  W has an effect of increasing the high-temperature yield strength of the steel sheet, and the lower limit of the W content is set to 0.05% in order to sufficiently obtain this effect. On the other hand, since W is expensive and the toughness deteriorates when the W content exceeds 0.5%, the upper limit of the W content is set to 0.5%.

  In addition to the effect of increasing the strength of the steel sheet, Zr is an element that has the effect of improving the plating cracking resistance in the case of a steel sheet that has been galvanized. As the lowest value at which these effects can be exhibited, the lower limit of the Zr content was set to 0.05%. On the other hand, if Zr is added over 0.5%, the weld toughness deteriorates due to welding, which is not preferable. Therefore, the upper limit of the Zr content is set to 0.5%.

  REM, Ca: REM and Ca are effective elements for improving the toughness of the weld heat affected zone of the steel sheet by welding, and one or two of REM and Ca can be added.

  REM becomes oxysulfide in the steel sheet, suppresses the grain growth of austenite grains, and improves the toughness of the weld heat affected zone of the steel sheet by welding. In order to sufficiently obtain this effect, the lower limit of the REM content was set to 0.001%. On the other hand, if REM is added over 0.02%, the cleanliness of the steel is impaired, so the upper limit of the REM content is set to 0.02%.

  Ca is effective for improving the toughness of the weld heat-affected zone of the steel sheet by welding, and is effective for improving the material in the thickness direction of the steel sheet by controlling the form of sulfides in the steel. In order to obtain these effects sufficiently, the lower limit of the Ca content is set to 0.0005%. On the other hand, if Ca is added over 0.02%, the amount of non-metallic inclusions in the steel is increased and causes internal defects, so the upper limit of Ca content was made 0.02%.

  The reasons for limiting the mechanical properties of the steel sheet to be angularly deformed and the preferable structure and composition of the steel sheet are as described above.

  In the present invention, the method of manufacturing the angularly deformed steel sheet need not be particularly limited in order to achieve the object of the present invention. For example, the steel sheet having the above mechanical properties and structure can be easily manufactured by the following method. Is possible.

  That is, after heating the steel slab containing the above-described component composition to a temperature of Ac3 to 1350 ° C., the rolling is finished at an austenite non-recrystallization temperature range of 800 ° C. or more at a rolling reduction of 30% or more, and then 0.1% By cooling at a cooling rate of ˜80 ° C./s, a steel sheet having a structure containing 70% or more of a bainite phase can be produced. In addition, although these rolling conditions and cooling conditions are set for the following reasons, in order to achieve the objective of this invention, it does not limit to these.

The heating temperature of the steel slab, the temperature range for the steel structure and the austenite single tissue, ie the Ac ₃ transformation temperature or more and the upper limit of the heating temperature is suppressed excessive waste of energy, in consideration of the saturation of the heating effect 1350 It is desirable that the temperature is not higher than ° C.
The rolling end temperature is preferably set to 800 ° C. or higher in order to obtain the effect of rolling in an austenite non-recrystallized region, refining the bainite structure by introducing work dislocations, and improving toughness.
Further, the rolling reduction at this time is preferably 30% or more so that the effect of improving toughness becomes remarkable.

  The cooling after the end of rolling may be either air cooling or accelerated cooling. The cooling rate is set to 0.1 ° C./s or more in order to suppress the formation of ferrite pearlite and increase the bainite phase, and the bainite is increased by increasing the cooling rate. -In order to increase the strength of the lath interval and suppress the deterioration of the toughness of the base metal, it is preferably 80 ° C./s or less.

  Furthermore, in order to produce a steel sheet with improved high-temperature yield strength, it is preferable to perform precipitation treatment of the precipitation strengthening element by any one of the following heat treatment or cooling after the rolling in the above method. The following two types of precipitation treatment methods may be appropriately selected in consideration of various manufacturing circumstances.

  In the first precipitation treatment method, the steel sheet obtained under the above rolling and cooling conditions is reheated at a heating temperature of less than 500 to 800 ° C. and held to precipitate the precipitation strengthening element in the steel sheet. The reheating temperature is preferably 500 ° C. or higher in order to sufficiently form precipitates, and is preferably less than 800 ° C. in order to prevent the bainite phase introduced by excessive heating from being altered.

  In the second precipitation treatment method, after rolling under the same rolling conditions as described above, accelerated cooling is performed at a cooling rate of 0.1 to 80 ° C./s to a temperature range of less than 500 to 800 ° C., and then 30 seconds or more in this temperature range. In this temperature range, the precipitation strengthening element in the steel sheet is subjected to precipitation treatment by cooling at a cooling rate of 1 ° C./s or less and a cooling time of 30 seconds or more.

  The cooling rate to a temperature range of 500 to less than 800 ° C. after the end of rolling is set to 0.1 ° C./s or more in order to suppress the formation of ferrite pearlite and increase the bainite phase. In order to increase the strength of the gaps and suppress the deterioration of the toughness of the base material, the temperature is preferably set to 80 ° C./s or less.

  It is desirable that the isothermal holding time in the temperature range below 500 to 800 ° C. be 30 s or longer in order to precipitate the precipitation strengthening element in the steel sheet.

  The cooling rate and cooling time in the temperature range of 500 to 800 ° C. should be 1 ° C./s or less and the cooling time should be 30 s or more in order to obtain the same effect as the above isothermal holding. Is desirable.

  Next, the reason for limiting the steel sheet to be laterally deformed, which is a feature of the present invention, and the preferable structure and composition of the steel sheet will be described.

(Mechanical properties of steel plate to be laterally deformed)
In the present invention, a steel sheet having a yield strength (YP) ratio to a tensile strength (TS) (YP / TS), that is, a yield ratio (YR) of 80% or less is used as a steel sheet to be laterally deformed in the linear heating deformation method. It is characterized by.

  In order to generate linear heating deformation mainly composed of lateral deformation of the steel sheet as shown in FIG. 1- (A) by linear heating and cooling of the steel sheet, the front and back surfaces in the thickness direction in the linear heating region It is necessary to uniformly increase the lateral shrinkage on the side. As a means for this, it is possible to increase the lateral shrinkage of the front and back surfaces of the steel sheet by controlling heating and cooling conditions, but this is not preferable because it complicates the work method and lowers work efficiency.

  In the present invention, in order to generate bending deformation using lateral deformation by linear heating deformation mainly in the lateral deformation without changing the heating and cooling conditions in the linear heating and cooling of the steel sheet, the tensile strength (TS) By applying a steel sheet having a yield strength (YP) ratio (YP / TS), that is, a yield ratio (YR) of 80% or less, the yield strength at high temperatures is reduced, so the temperature is higher than that on the direct heating surface side. It is possible to sufficiently increase the amount of plastic strain generated on the non-heated surface side where the temperature decreases, and to uniformly increase the amount of lateral shrinkage in the thickness direction in the linear heating region. In addition, the upper limit of the yield ratio (YR) allows the yield strength at high temperatures to be kept low by reducing the yield strength at room temperature while maintaining the tensile strength level at room temperature required as a steel material for welded structures. It becomes possible. In a steel sheet having a yield ratio (YR) exceeding 80%, the lateral shrinkage generated on the non-heated surface side where the heating temperature is relatively lower than that on the heated surface side is reduced, and the lateral deformation in the linear heating region is uniform. It will be difficult to increase. For this reason, it is not possible to sufficiently obtain the effect of increasing the amount of deformation in the linear heating deformation mainly including the lateral deformation of the steel sheet and improving the work efficiency of the bending deformation using the lateral deformation.

  Therefore, in the present invention, the tensile strength (in order to increase the deformation amount in the linear heating deformation mainly composed of lateral deformation without changing the heating and cooling conditions and to sufficiently improve the work efficiency of the bending deformation industrially, The ratio (YP / TS) of the yield strength (YP) to TS), that is, the yield ratio (YR) was limited to 80% or less.

  In the present invention, the lower limit of the yield ratio (YR) does not need to be specified in particular. However, the manufacturing conditions for realizing the steel sheet become strict and the cost increases. Therefore, in the present invention, the yield ratio ( The lower limit of YR) is preferably 60%.

(Structure of steel plate to be laterally deformed)
As a preferable structure of the steel sheet to be laterally deformed in the present invention, the ratio (YP / TS) of the yield strength (YP) to the tensile strength (TS), that is, the yield ratio (YR) satisfies 80% or less, and for the welded structure. It is a structure that can maintain the tensile strength and toughness of steel.

  In order to satisfy the yield ratio (YR) of 80% or less and maintain the tensile strength as a welded structural steel, the microstructure is a mixed structure of a low-strength ferrite pearlite phase and a high-strength bainite phase. It is effective to introduce plastic strain into the ferrite pearlite phase on the relatively low strength side and to ensure the overall tensile strength with a high strength bainite phase. When the content of the ferrite pearlite phase in the steel sheet structure is less than 30% in terms of area ratio, the yield region with low stress becomes small, and it becomes difficult to make the yield ratio (YR) 80% or less. The amount of plastic strain introduced at the time of linear heating and cooling is reduced, and as a result, the amount of deformation in linear heating deformation mainly in the lateral deformation of the steel sheet is increased, and the work efficiency of bending deformation using lateral deformation is increased. The effect of improving is not sufficiently obtained. For this reason, the content of the ferrite pearlite phase in the steel sheet structure is set to 30% or more by area ratio. On the other hand, when the ferrite pearlite phase exceeds 70% in area ratio, a martensite phase having a higher strength than bainite must be used as a high-strength structure in order to ensure tensile strength. When the martensite phase increases in the steel sheet structure, the base material toughness deteriorates, and it becomes difficult to secure the toughness required for welded structural steel, so the upper limit of the ferrite pearlite phase content is 70 in area ratio. %.

  For these reasons, in the present invention, as a steel sheet to be laterally deformed, the above yield ratio (YR) satisfies 80% or less, and a preferable structure for maintaining the tensile strength as a welded structural steel is ferrite. It is limited to a mixed structure of a low-strength ferrite pearlite phase and a high-strength bainite phase containing 30 to 70% of the pearlite phase by area ratio.

(Component composition of steel plate to be laterally deformed)
The preferable component composition of the steel sheet to be laterally deformed in the present invention is preferably defined as follows in order to stably ensure the mechanical properties of the steel sheet and the mixed structure of the ferrite pearlite phase and the bainite phase.

  The reason for limiting the preferred component composition of the steel sheet to be laterally deformed will be described below.

  In the following description, “%” means “% by mass” unless otherwise specified.

  C: C is an element that increases the tensile strength of the steel sheet, and the lower limit of the C content is 0.05% in order to fully utilize the effect. On the other hand, if C increases excessively, the weldability of the steel sheet is hindered, so the upper limit of the C content is 0.18%.

  Si: Si is an element effective as a deoxidizing element in steel. In order to sufficiently obtain this effect, the lower limit of the Si content is set to 0.05%. On the other hand, if the amount of Si is excessively increased, the weldability of the steel sheet is hindered, so the upper limit of the Si content is set to 0.6%.

Mn: Mn is necessary for securing the tensile strength of the steel sheet, and the lower limit of the Mn content is set to 0.5% in order to sufficiently obtain the tensile strength improvement effect. On the other hand, if Mn is excessively increased, the weldability of the steel sheet is hindered, so the upper limit of the Mn content is set to 2.0%.
P, S: P and S are unavoidable impurities in the steel, and if these elements are contained excessively, the toughness of the HAZ when welding the steel sheet and the steel sheet deteriorates, so the upper limit of the content of P and S is Both are limited to 0.03%.

  The above is the basic component as a preferable component composition of the steel sheet to be laterally deformed (shrinked). In addition to this, the following components can be added for the following reasons.

  Ni, Cu, Cr: Ni, Cu, and Cr are effective elements for improving strength toughness, and in order to effectively utilize this action, each of these components is used in the following content, or It can contain 2 or more types.

  Ni is an effective element for improving both strength and toughness of the steel sheet and for preventing Cu cracking during rolling in a steel sheet containing Cu. In order to sufficiently obtain these functions and effects, the lower limit of the Ni content is set to 0.1%. On the other hand, even if Ni is added in excess of 2.0%, the effect is saturated and Ni element is expensive, so the upper limit of Ni content was set to 2.0%.

  Cu is an element that precipitates alone and improves the strength. In order to sufficiently improve the steel plate strength by the precipitation of Cu, the lower limit of the Cu content needs to be 0.1%. On the other hand, when the Cu content exceeds 0.5%, the strength of the soft ferrite pearlite is unnecessarily improved, and the effect of increasing the deformation amount in linear heat deformation mainly composed of lateral deformation (shrinkage) of the steel sheet is reduced. . Moreover, since the toughness of the welded portion deteriorates due to an increase in Cu, it is not preferable. For these reasons, the upper limit of the Cu content is set to 0.5%.

  Cr has the effect of increasing the strength of the steel sheet. In order to sufficiently improve the steel sheet strength, the lower limit of the Cr content needs to be 0.05%. On the other hand, if Cr is added in excess of 0.5%, the steel sheet precipitates and hardens, unnecessarily improves the strength of the soft ferrite pearlite, and the amount of deformation in linear heating deformation mainly composed of lateral deformation (shrinkage) of the steel sheet is reduced. The effect of increasing is reduced. Moreover, since the weld toughness deteriorates due to an increase in Cr, it is not preferable. For these reasons, the upper limit of the Cr content is set to 0.5%.

  The reasons for limiting the mechanical properties of the steel sheet to be laterally deformed and the preferred structure and composition of the steel sheet are as described above.

  In the present invention, the method for producing a laterally deformed steel sheet need not be particularly limited in order to achieve the object of the present invention. For example, a steel sheet having the above mechanical properties and structure can be easily produced by the following method. Is possible.

That is, after heating the steel slab containing the above-described component composition to a temperature of Ac _{3 to} 1350 ° C., rolling was completed at an austenite recrystallization temperature range of Ar ₃ ° C. to 900 ° C. at a rolling reduction of 25% or more, and then Ar ₃ Mixing of ferrite pearlite phase and bainite phase containing 30% to 70% ferrite pearlite phase by area ratio by cooling to a temperature range of 400 to 600 ° C. at a cooling rate of 5 to 20 ° C./s from a temperature of 5 ° C. or higher. Steel sheets with a structure can be manufactured. In addition, although these rolling conditions and cooling conditions are set for the following reasons, in order to achieve the objective of this invention, it does not limit to these.

The heating temperature of the steel slab, the temperature range for the steel structure and the austenite single tissue, ie the Ac ₃ transformation temperature or more and the upper limit of the heating temperature is suppressed excessive waste of energy, in consideration of the saturation of the heating effect 1350 It is desirable that the temperature is not higher than ° C.

  The rolling end temperature is preferably 900 ° C. or lower in order to perform rolling in an austenite recrystallization region of Ar 3 ° C. or higher, to refine the crystal grains of the austenite single phase structure and to obtain appropriate hardenability. In addition, the rolling reduction at this time is preferably 25% or more so that the effect of refining austenite crystal grains becomes remarkable.

  Cooling after the end of rolling starts cooling from an austenite single phase temperature range of Ar 3 ° C. or higher, a cooling rate of 5 ° C./s or higher in order to appropriately generate a bainite phase, and to secure a ferrite pearlite phase The cooling rate is preferably 20 ° C./s or less. The cooling stop temperature is preferably 400 ° C. or higher in order to suppress a decrease in toughness due to the formation of island sites, and 600 ° C. or lower in order to suppress a decrease in strength due to an increase in ferrite pearlite phase.

  Other methods described above include reheating the hot-rolled steel sheet to a two-phase region of austenite and ferrite and then air-cooling, or air-cooling to a two-phase region of austenite and ferrite after hot rolling, and then water-cooling, etc. There is. In these methods, the hot rolled steel sheet is once brought into a two-phase state of austenite and ferrite, and the austenite phase is transformed into a bainite phase in the subsequent cooling process to obtain a steel sheet having a mixed structure of ferrite phase and bainite phase.

Example 1
Based on the following examples, the method of the present invention improves the work efficiency of bending deformation using angular deformation by increasing the amount of deformation in linear heating deformation mainly consisting of angular deformation without changing the heating and cooling conditions. The effect will be described.

  Table 1 shows the components of the steel slab. A steel plate was produced from the steel bills of this component system under the production conditions shown in Table 2. Table 3 shows the combinations of steel slabs and manufacturing conditions and the characteristics of the steel sheets. Steel sheet properties are fracture surface transition temperature (vTrs), yield strength (YP), tensile strength (TS) and yield strength at 600 ° C. The yield strength at 600 ° C. was defined as 0.2% proof stress. The present invention relates to a high-efficiency thermal processing method in which a steel sheet is angularly deformed by performing burner heating and subsequent water cooling using a predetermined steel sheet, and is not simply a technique for providing the steel sheet itself. Therefore, it is not possible to judge whether the steel sheet is within the scope of the present invention only with the steel sheet in Table 3, but for reference, the remarks column in Table 3 shows whether the steel is within the scope of the present invention. .

  Table 4 shows the results of measuring the amount of splashing that occurred when the steel materials listed in Table 3 were subjected to thermal processing with gas burner heating and water cooling. The heating method and measured values are shown in FIG. That is, it heats with the gas burner 6 along the centerline of a steel plate, and sprays the cooling water 7 after that. As shown in FIG. 6, the heating region 8 was continuously performed from one side of the steel plate to the other side. Heating was performed three times for each steel plate, and after that, the steel plate itself was cooled to room temperature, and then the amount of splash h: 9 was measured. The definition of the amount of splash h is shown in FIG. This value corresponds to the amount of angular deformation, and the effect of the present invention can be examined by relatively comparing the measured values. In addition, about No19 and 20 of Table 4, it is the example which was not water-cooled.

  In Table 4, Nos. 1 to 15 are examples when the heating rate is 15 cm / min and the distance between the burner heating position and the water cooling position is 10 cm. In the comparative example of No1, the amount of protrusion is 3.6 mm, and the amount of protrusion is considerably lower than 6.0 mm of No2 which is an example of the present invention. The steel material used in the No. 1 example is the S1 steel material in Table 3, and this is because the steel sheet component is included in the example of the present invention, but the bainite structure ratio is outside the range of the example of the present invention. This is a small example. In the No. 3 example, since the bainite ratio and Nb, Ti, V, and Mo were all outside the range of the present invention example, the high-temperature strength was insufficient and the amount of splash was small. On the other hand, No. 4, 6, 7, 8, 10, 11, 12, 14, and 15 all have the amount of splash exceeding 6 mm, and can be efficiently angularly deformed. On the other hand, No1, 3 and 9 which are comparative examples all have the amount of protrusion less than 4 mm, and the amount of protrusion is smaller than the example of this invention. In No5 and No13, the amount of splash h is an example of the present invention and is sufficiently higher than that of the comparative example. However, the steel material of No5 is an example in which C is outside the scope of claim 3, and the steel material of No13 has a bainite ratio of claim 2. The steel is out of range. In these examples, when the cooling rate is as high as 75 ° C./second, martensite is partially generated, and as a result, the base material vTrs is higher than other steel materials. Therefore, in order to have a large amount of splash and vTrs sufficiently low, that is, to have good base material toughness, it is necessary to be within the range of not only Claim 1 but also Claim 2 and below.

  Examples 16, 17, and 18 in Table 4 are cases where the heating rate was set to 20 cm / min. However, No15 and 16 examples of the present invention had a larger amount of protrusion than the No16 example that was a comparative example. Efficient thermal processing is possible.

  Examples No. 19 and 20 in Table 4 are cases where water cooling is not performed, and in particular, No. 20 has a steel plate component and a bainite ratio within the scope of the present invention. However, since it is not water-cooled, it is not the high-efficiency thermal processing method according to the present invention. In particular, the amount of splash is 4.0 to 4.5 mm for both No. 19 and 20, and there is not much difference between the two. In Example No19 which uses S1 which is outside the steel plate range of the example of the present invention, the amount of protrusion is larger than No1 which is a condition with water cooling. For this reason, it is possible to expect an effect of increasing the amount of deformation by simply stopping the water cooling for the thermal processing method currently practiced in the industry. However, since it was not water-cooled, the time to reach the final shape, that is, to cool to room temperature, was as long as about 1 hour. In general, since the worker performs the work while confirming the shape of the steel sheet during the construction, that is, during the construction, it is very problematic in terms of work efficiency that the cooling time is close to one hour. In this case, the time required to finish to the final shape can be shortened by using Example No1 with a small amount of protrusion in one construction. From the viewpoint of high efficiency, the No1 Example is rather superior. .

  The above is an example of the amount of splash when the heating is performed three times. Table 4 also shows the number of times of heating necessary to obtain the amount of splash exceeding 6 mm. The fact that the number of times of heating is small means that a sufficient amount of splashing, that is, a deformation amount can be obtained in such a short time, and it is understood that the heat deformation processing is efficient. About No2,4,6-8,10-15,17,18 which is an example of this invention, the frequency | count of a heating is few with 2-4, and No1,3,9,16,19,20 which is a comparative example is It can be seen that the number of times of heating is as large as 5-8. That is, the example of the present invention is an efficient thermal processing method.

(Example 2)
Based on the following examples, the method of the present invention improves the work efficiency of bending deformation using lateral deformation by increasing the amount of deformation in linear heating deformation mainly in lateral deformation without changing the heating and cooling conditions. The effect will be described.

  Table 5 shows the billet components. A steel plate was produced under the production conditions shown in Table 6 for this component steel slab. Table 7 shows the combination of steel slabs and manufacturing conditions and the characteristics of the steel sheet. The steel sheet characteristics are YP, TS, YR, ferrite pearlite texture and vTrs.

  The present invention provides a method for efficiently laterally deforming a steel sheet by performing burner heating and subsequent water cooling using a predetermined steel sheet, and is not simply a technique for providing the steel sheet itself. Therefore, it is not possible to judge whether the steel sheet is within the scope of the present invention only with the steel sheet in Table 7, but for reference, the remarks column in Table 7 shows whether the steel sheet is within the scope of the present invention. .

  FIG. 7 is a conceptual diagram showing a heating / cooling method and a lateral deformation amount W. In FIG. 7, the heating region 8 ′ is continuously performed from side to side of the steel plate. This is to facilitate comparison of the lateral deformation amount W. When bending deformation is given to the steel sheet, it is said that the heating region is interrupted in the middle, and the results for that will be described later. Table 8 shows the lateral deformation measurement result (W) generated at the time when the steel plate shown in Table 7 was subjected to thermal processing with gas burner heating 6 'and water cooling 7'. In the same manner as in Example 1, the gas burner was heated three times, and then the lateral deformation amount W: 10 was measured. In Table 8, Nos. 21 to 30 are examples when the heating rate is 15 cm / min and the distance between the burner heating position and the water cooling position is 10 cm. No. 21 to 24, 27 and 30 are examples of the present invention, and the lateral deformation W is as large as 0.86 to 1.14 mm, but No. 28 and 29 which are comparative examples have W of 0.53 and 0.58 mm. small. Moreover, No25 is a comparative example when W exceeds 1 mm. The steel material used in No25 is S25 in Table 7, and when YR exceeds 80%, W equivalent to the present invention example is obtained, so TS is 425 MPa, lower than S21 to S24, and the present invention example. It can be seen that the use of this steel material ensures the strength and the lateral deformation is larger. No. 26 is an example in which W is 1.89 mm, which is an example outside the component range of claim 9 in the present invention. Therefore, the strength of the steel material S26 of No. 26 is lower than that of S21 to S24 of the example of the present invention. If this strength can ensure the required strength of the structure, it is desirable to use this steel material. These choices can be determined by those skilled in the art according to the situation. In the example of the present invention, in No. 30 example, the steel sheet is S30, and YR is within the scope of claim 1 of the present invention, but the ferrite pearlite structure ratio is outside the scope of claim 8. Since YR is suppressed under these conditions, a hard structure such as martensite is introduced into the base material, and as a result, the base material vTrs is as low as −25 ° C. That is, the base material toughness is inferior to that of other steel materials of the present invention and there is no structural problem. However, when a problem occurs, it is desirable to employ a steel material that satisfies claim 8.

  Example No 31-35 is a result at the time of setting a burner speed to 20 cm / min. The examples of the present invention were Nos. 31 and 32, and the lateral deformations were 0.98 mm and 0.92 mm, whereas Nos. 33 and 34 as comparative examples were as small as 0.51 mm and 0.54 mm. Moreover, No33 is an example in which the lateral deformation was the largest, but the steel plate strength was low, and there was a problem in securing the strength as a structure.

  The above is an example in which the number of heating is fixed to 3 and linear heating is performed from one side of the steel plate to the opposite side. In order to bend and deform the steel plate using the lateral deformation W, the linear heating may be interrupted halfway. Therefore, as shown in FIG. 8- (A), the heating region 11 was set almost vertically inward from two opposing sides, and the bending deformation HW12 of the steel sheet was measured. FIG. 8- (B) is a conceptual diagram illustrating the HW 12. Moreover, the combination of the steel plate, the heating rate, and the burner water cooling distance was the same as in Table 8 described above, and each heating region 11 was linearly heated until the HW was 15 mm or more, and the number of times was measured.

  Table 8 shows the measurement results. In the case of the present invention example, the HW can be increased to 15 mm or more by the number of heating times of 4 times or less. On the other hand, in comparative example No28, 29, 34, 35, the frequency | count of a heating of 6 times or more was required. No. 25 and 33 with a low heating frequency in the comparative example are those when the steel plate strength is low.

  Example Nos. 36 and 37 are cases where water cooling is not performed, but the lateral deformation W was not significantly different between the steel plates S21 and S29. Moreover, since it is not water-cooled, it takes a long time to complete the cooling, and it cannot be said that the efficiency is high. Furthermore, in order to make the bending deformation HW 15 mm or more, it is necessary to increase the number of times of linear heating to 8 times or more. From this point of view, it cannot be said that the efficiency is high.

It is a conceptual diagram explaining the heat deformation in the case where the lateral deformation is large (A) and the case where the angular deformation is large (B). It is a conceptual diagram explaining the angular deformation which the difference of the length of a center part and a side forms. It is a conceptual diagram explaining the shape of a steel plate. It is a conceptual diagram which shows the angular deformation which the difference of the horizontal contraction of the front and back forms. It is a conceptual diagram explaining the mechanism in which the difference in lateral shrinkage of the front and back surfaces forms angular deformation. It is a conceptual diagram explaining the heating-cooling method and the amount of jumps (h). It is a conceptual diagram explaining the heating-cooling method and lateral deformation (W). It is a conceptual diagram explaining the bending method (HW) of a heating method and a steel plate.

Explanation of symbols

1, 1 ′, 2, 2 ′: Sides of a rectangular steel plate to be linearly heated 3, 3 ′, 8, 8 ′, 11: Linear heating region 4, 4 ′: Steel plate shape observation direction 5, 5 ′: Deformation Direction 6, 6 ': Gas burner 7, 7': Cooling water 9: Splashing amount, h
10: lateral deformation, W
12: Bending deformation, HW

Claims (11)

  In a linear heating deformation method in which the front or back surface of a steel sheet is linearly heated with a gas burner, and the steel sheet is bent and deformed by water cooling, a steel sheet having a yield strength at 600 ° C. of 1/3 or more of the yield strength at room temperature The steel sheet surface is linearly heated by the gas burner, and the steel sheet is subjected to angular deformation in which the amount of lateral shrinkage on the heating surface side in the thickness direction in the linear heating region increases compared to the non-heating surface side. Linear heating deformation method.   The method for linearly heating and deforming a steel sheet according to claim 1, wherein the steel sheet to be angularly deformed has a structure containing a bainite phase in an area ratio of 70% or more.   The steel sheet to be angularly deformed contains, in mass%, C: 0.001 to 0.10%, Si: 0.02 to 0.60%, Mn: 0.80 to 3.0%, P: 0 0.03% or less, S: limited to 0.02% or less, Nb: 0.005 to 0.20%, Ti: 0.005 to 0.20%, V: 0.005 to 0.20% And Mo: 0.05 to 0.5% of one or more, and the balance is iron and inevitable impurities, the linear heat deformation of the steel sheet according to claim 1 or 2 Method.   The method for linearly heating and deforming a steel sheet according to any one of claims 1 to 3, wherein the steel sheet to be angularly deformed contains, in mass%, B: 0.0003 to 0.0050%.   The method for linearly heating and deforming a steel sheet according to any one of claims 1 to 4, wherein the angularly deformed steel sheet further contains Al: 0.01 to 0.10% in mass%.   The steel plate to be angularly deformed is in mass%, and Cu: 0.5 to 2.0%, Ni: 0.1 to 2.0%, Cr: 0.05 to 0.5%, W: 0.00. The linear heat deformation of the steel sheet according to any one of claims 1 to 5, characterized by containing one or more of 05 to 0.5% and Zr: 0.05 to 0.5%. Method.   The steel sheet to be angularly deformed is mass% and further contains one or two of REM: 0.001 to 0.02% and Ca: 0.0005 to 0.02%. The method for linearly heating and deforming a steel sheet according to any one of claims 1 to 6.   In a heating deformation method in which the front or back surface of a steel sheet is linearly heated by a gas burner, and the steel sheet is bent and deformed by water cooling, a steel sheet having a yield strength at room temperature of 80% or less of the tensile strength is used. After heating linearly with the gas burner in a direction substantially perpendicular to any one side of the steel sheet, forming a linear heating region and a non-heating region in the linear heating direction and the vertical direction, the thickness in the linear heating region A method of linearly heating and deforming a steel sheet, wherein the transverse deformation is performed so that the amount of lateral shrinkage in the direction becomes uniform.   9. The method of linearly heating and deforming a steel sheet according to claim 8, wherein the laterally deformed steel sheet is a mixed structure of a ferrite pearlite phase and a bainite phase containing a ferrite pearlite phase in an area ratio of 30 to 70%.   The steel sheet to be laterally deformed contains, in mass%, C: 0.05 to 0.18%, Si: 0.05 to 0.6%, Mn: 0.5 to 2.0%, P: 0 The linear heat deformation method for a steel sheet according to claim 8 or 9, characterized by being limited to 0.03% or less and S: 0.03% or less, and the balance being iron and inevitable impurities.   The steel plate to be laterally deformed is in mass%, and further, Ni: 0.1 to 2.0%, Cu: 0.1 to 0.5%, Cr: 0.05 to 0.5%, one or two The linear heating deformation method of the steel sheet according to any one of claims 8 to 10, comprising at least one seed.

Images