JP5119475B2 - Center pillar reinforcing member and manufacturing method thereof - Google Patents

Description

  The present invention relates to a center pillar reinforcing member provided inside a body side panel of an automobile and a method for manufacturing the same. In particular, the center pillar is excellent in passenger safety when a load is applied from the outside of the automobile. The present invention relates to a reinforcing member and a manufacturing method thereof.

  In recent years, in the automobile field, reducing injury to passengers at the time of collision has become a major issue, and the strength of vehicle body materials has increased due to the strengthening of regulations related to collision safety, particularly side collision safety regulations. Is underway. As described above, as a method for increasing the strength of the vehicle body, for example, a material having high strength in the state of the material is used, or when a heated material is molded, a quenching process is performed by cooling in the mold. Therefore, a method called hot press capable of achieving both formability and high strength is used (see, for example, Patent Document 1).

  However, in the case of a collision on the side surface of the vehicle body, the crushing distance that can be applied to shock absorption is shorter than that of a frontal collision or a rear surface collision, etc. There's a problem. For this reason, as a method of improving the collision safety on the side surface of the vehicle body, it is not sufficient to simply increase the strength of the material to make it difficult to deform, and it is possible to appropriately control the shape of the side surface structure of the vehicle body after deformation. Desired.

In general, the center pillar reinforcing member of an automobile has a narrow and narrow shape in the width direction and thickness direction in the vicinity of the upper part, which is the side window glass region on the side of the vehicle body, from the viewpoint of design and the like. It is configured. In addition, since the body side panel disposed on the surface side of such a center pillar reinforcing member usually has almost no shock absorbing action when a side collision or the like occurs, basically, the center pillar reinforcement It is important to suppress the deformation of the lower part of the member while absorbing the energy while avoiding contact with the passenger at the upper part.
However, when the center pillar reinforcing member is entirely made of the same material, the structural upper portion is relatively weaker than the lower portion in terms of structural strength. For this reason, when a load is applied due to a collision, the deformation starts at the upper part of the center pillar reinforcing member, and this part comes into an undesirably deformed form such as contacting the occupant's body. It was a problem in improving the performance.

  In order to solve the problems associated with the deformation of the upper portion of the center pillar reinforcing member as described above, several methods have been proposed. As one method, for example, a strength enhancing member is provided on the upper portion of the center pillar reinforcing member. It has been proposed to arrange. According to this method, by adjusting the relative strength between the upper part and the lower part of the center pillar reinforcing member, it is possible to suppress the upper part of the center pillar reinforcing member from coming into contact with the occupant's body, and a preferable deformation form is obtained. It is done. However, in such a method, there is a problem that the weight of the strength enhancing member increases, the weight of the vehicle body also increases, and the manufacturing cost also increases.

  In recent years, for example, a so-called tailored blank technique is known in which different kinds of metal materials having different strengths, plate thicknesses, and the like are joined and then integrally formed. By manufacturing a center pillar reinforcing member using this method, selecting an appropriate material and arranging it at the upper and lower portions, the strength and balance of the member can be adjusted. However, in such a method, there is a problem that the manufacturing cost increases in the joining process of the metal materials, and it is difficult to integrally form the metal materials having different strengths. However, there was a limit to the configuration in which a difference in strength was given. In addition, the combination of such tailored blank technology and hot press technology as described above is difficult to form due to deformation concentration at the joints, making it difficult to cope with the ultra-high strength of the vehicle structure. There is a problem that.

Also, in the center pillar reinforcing member made of light alloy, by changing the plate thickness between the upper part and the lower part, or by providing ribs on the upper part, the strength of the upper part with respect to the external force from the outside of the vehicle body Has been proposed to be larger than the strength of the lower part (see, for example, Patent Document 2).
Also, in the center pillar reinforcing member, the lower portion strength is relatively weaker than the upper strength by providing a plurality of concave weak portions formed below the belt line that is a line passing through the lower end of the side window glass. Has been proposed (see, for example, Patent Document 3).

However, in Patent Documents 2 and 3, in the longitudinal direction of the center pillar reinforcing member, when the upper part is high strength and the lower part is low strength, a boundary point of strength displacement is provided regardless of the size and shape of the center pillar reinforcing member. For this reason, the low strength portion may not necessarily be adapted to the shape of the center pillar reinforcing member. In such a case, for example, when a side collision of the automobile occurs, the deformation of the center pillar reinforcing member cannot be properly controlled, and contact with the passenger is prevented depending on the state of the collision. There is a risk that it will be difficult.
Further, in each of Patent Documents 2 and 3, the strength differs between the upper part and the lower part by changing the plate thickness in the longitudinal direction of the center pillar reinforcing member or by providing a rib or a concave weak part. As a result, the material cost increases, and the overall manufacturing cost increases due to an increase in processing steps.
JP 2004-197213 A JP 2001-163257 A JP 2007-55494 A

  The present invention has been made in view of the above problems, and can be reduced in weight, and can effectively absorb energy when a side load of the automobile occurs and a load is applied from the outside. An object of the present invention is to provide a center pillar reinforcing member excellent in collision safety and a manufacturing method thereof.

As a result of extensive research conducted by the present inventors in order to solve the above-mentioned problems, a side collision of the automobile temporarily occurred due to the arrangement of the strength altered portion in the lower part in the longitudinal direction of the center pillar reinforcing member and the optimization of the steel structure. Even in this case, the deformation of the center pillar reinforcing member can be appropriately controlled, and the center pillar reinforcing member and the vehicle body structural member can be effectively prevented from coming into contact with the passenger. Completed the invention.
That is, the gist of the present invention is as follows.

[1] A center pillar reinforcing member made of a steel plate and arranged on the inner side of a body side panel of an automobile, wherein the center moment of the center pillar reinforcing member when the center pillar reinforcing member is divided in the lateral width direction is Strength modified part which is a softened part at a position below the boundary part where the second derivative obtained by second-order differentiation at each position in the direction becomes “0” in the longitudinal direction of the center pillar reinforcing member Furthermore, in the longitudinal direction of the center pillar reinforcing member, the hardness H1 at the position above the boundary is 400 Hv or more, and the ratio between the hardness H2 of the strength-modified portion and the hardness H1 A center pillar reinforcing member, wherein (H2 / H1) is in a range represented by the following formula (H2 / H1 ≦ 0.85) .
[2] The strength altered portion is a softened structure mainly including bainite in a mixed structure of ferrite and pearlite, and the upper side from the boundary portion in the longitudinal direction of the center pillar reinforcing member mainly includes martensite. The center pillar reinforcing member according to [1] above, which is a hardened structure.
[3] The strength altered portion is provided at a position lower than a position corresponding to a door waist reinforcing member provided in a door attached to a body side panel of the automobile in the longitudinal direction of the center pillar reinforcing member. The center pillar reinforcing member according to the above [1] or [2], wherein

[ 4 ] In the longitudinal direction of the center pillar reinforcing member, the tensile strength TS1 on the upper side from the boundary portion is set to 1200 MPa or more, and the ratio (TS2) between the tensile strength TS2 and the tensile strength TS1 of the strength-modified portion. / TS1) is a range represented by the following formula (TS2 / TS1 ≦ 0.85), and the center pillar reinforcing member according to any one of the above [1] to [3] .
[ 5 ] In the longitudinal direction of the center pillar reinforcing member, the upper side from the boundary where the second derivative is “0” is configured to have a smaller cross-sectional area than the lower side than the boundary. The center pillar reinforcing member according to any one of [1] to [ 4 ], wherein the center pillar reinforcing member is any one of the above.
[ 6 ] The center pillar reinforcing member is formed in a substantially hat-shaped cross section including a horizontal wall portion and a vertical wall portion extending from both side end portions of the horizontal wall portion, and the vertical wall portion includes the center pillar. The above-mentioned [1], characterized in that it is substantially parallel to the load load direction from the outside of the automobile, which is the load load direction with respect to the reinforcing member, and the strength-altered portion is provided on the vertical wall portion. ] To the center pillar reinforcing member according to any one of [ 5 ].

[ 7 ] A method of manufacturing a center pillar reinforcing member made of a steel plate, which is arranged inside a body side panel of an automobile, wherein the center pillar has a cross-sectional secondary moment when the center pillar reinforcing member is divided in the width direction. The second-order differential coefficient obtained by second-order differentiation at each position in the longitudinal direction of the reinforcing member has a strength altered portion at a position below the boundary where the center pillar reinforcing member is “0” in the longitudinal direction. When the steel plate is heated to a temperature range from Ac ₃ point to melting and then subjected to quenching treatment by forced cooling inside the die while forming the steel plate using a die, the steel plate The strength-modified part is formed as a softened part by relatively slowly cooling the cooling rate in at least a part of the lower part than the other part. A method for manufacturing a center pillar reinforcing member .

According to the center pillar reinforcing member of the present invention, in the longitudinal direction of the center pillar reinforcing member, the second derivative obtained by second-order differentiation of the cross-sectional secondary moment of the center pillar reinforcing member at each position in the longitudinal direction. However, a strength altered portion is provided at a position below the position of “0” in the longitudinal direction of the center pillar reinforcing member, and the hardness H1 at a position above the boundary portion in the longitudinal direction of the center pillar reinforcing member. Is 400Hv or more, and the ratio (H2 / H1) of the hardness H2 of the strength altered portion and the hardness H1 is in a range represented by the following formula (H2 / H1 ≦ 0.85) . Even if a side collision of the automobile occurs and a load load is applied from the outside, the deformation form of the center pillar reinforcing member can be properly controlled. It is possible to effectively absorb the ghee. Thereby, it becomes possible to effectively prevent the center pillar reinforcing member and the vehicle body structural member from coming into contact with the passenger. Further, since it is not necessary to increase the thickness of the steel plate or to provide a rib or the like, it is possible to reduce the weight of the center pillar reinforcing member and thus the entire vehicle body. Therefore, the center pillar reinforcing member having excellent collision safety can be realized with an inexpensive configuration.

Further, according to the manufacturing method of the center pillar reinforcing member of the present invention, the second moment of the section of the center pillar reinforcing member is obtained by second-order differentiation at each position in the longitudinal direction in the longitudinal direction of the center pillar reinforcing member. After the strength derivative portion is provided at a position below the position where the second derivative is “0” in the longitudinal direction of the center pillar reinforcing member, and the steel plate is heated to a temperature range from Ac ₃ point to melting Then, when performing quenching treatment by forced cooling inside the mold while forming the steel sheet using a mold, the cooling rate of at least a part of the steel sheet is set to be lower than that of the other parts and relatively slow cooling is performed. By doing so, it is a method of forming the strength altered part as a softened part, so even if a load is applied from the outside of the automobile, the deformation mode can be controlled properly, and the collision A center pillar reinforcing member capable of effectively absorbing the load load energy at the time can be manufactured. Therefore, the center pillar reinforcing member having excellent collision safety can be manufactured with high productivity.

  Hereinafter, embodiments of the center pillar reinforcing member and the manufacturing method thereof according to the present invention will be described with reference to FIGS. 1 (a) and 1 (b) to FIG. In addition, since this embodiment demonstrates in detail in order to make the meaning of the center pillar reinforcement member of this invention and its manufacturing method better understood, unless otherwise specified, this invention is not limited.

  The center pillar reinforcing member according to the present invention is a center pillar reinforcing member 1 made of a steel plate and disposed inside a body side panel 80 of an automobile. The center pillar reinforcing member 1 is a secondary cross section when the center pillar reinforcing member 1 is divided in the lateral width direction. Position where the second derivative (f) obtained by second-order differentiation of the moment (I) at each position in the longitudinal direction of the center pillar reinforcing member becomes “0” in the longitudinal direction of the center pillar reinforcing member 1 The strength altered portion 2 which is a softened portion is provided at a position below the boundary portion K, which is generally configured (see also FIG. 6 for the sectional second moment and the second derivative).

  The center pillar reinforcing member described in the present invention is a member called a so-called center pillar reinforcement outer or the like disposed inside the body side panel 80 of the automobile, that is, the inside of the automobile interior, as shown in the sectional view of FIG. Yes, in the illustrated example, it is formed in a substantially hat-shaped cross section. Further, in the example shown in FIG. 2, a reinforcement member 90 is further arranged inside the center pillar reinforcing member 1, and an inner reinforcing member 95 called a so-called center pillar reinforcement inner is arranged further inside, The inner reinforcing member 95 and the flange portions 41a and 42a of the center pillar reinforcing member 1 are spot-bonded. In the illustrated example, the center pillar reinforcing member 1 has a substantially closed cross-sectional structure together with the above-described reinforcement member 90 and the inner reinforcing member 95.

In the automobile field, in order to reduce injury to passengers at the time of a collision in an accident or the like, particularly a collision on the side of a vehicle body, the strength of the vehicle body material has been increased. In increasing the strength of such body materials, for example, when forming a heated steel sheet, it is possible to achieve both formability and high strength of the steel sheet by performing quenching treatment by cooling in the mold. Hot press methods are attracting attention.
Further, in order to improve the collision safety on the side surface of the vehicle body, it is necessary to improve the strength of the center pillar (center pillar reinforcing member) disposed between the door and the side window. On the other hand, if the center pillar is deformed and bent indoors during a side collision, the center pillar reinforcing member or other vehicle body member may come into contact with the occupant depending on the deformation, causing injury. There was a problem.
Furthermore, in the automobile field, there is an increasing need to reduce the weight of the vehicle body for the purpose of reducing fuel consumption and reducing carbon dioxide (CO ₂ ) emissions, thereby realizing a vehicle body having high strength and light weight. It is demanded. For this reason, the center pillar reinforcing member disposed on the side surface of the automobile body is also required to satisfy both of high strength and light weight.

As a result of repeated extensive research by the present inventors, as a requirement for reducing the weight while improving the collision safety of the center pillar reinforcing member provided on the side of the automobile,
(1) Optimize the strength distribution in the longitudinal direction of the center pillar reinforcing member, and control the deformed form after the collision to a form that can suppress the member contact to the passenger.
(2) Reducing the plate thickness by using as high a strength material as possible,
I found two points.

In addition, the inventors pay attention to providing a strength altered portion that is a soft portion of low strength at the lower part in the longitudinal direction of the center pillar reinforcing member, and optimizing the arrangement and steel structure of the strength altered portion, It was found that the deformation mode can be controlled by inducing deformation at the site. In addition, in order to increase the strength of the center pillar reinforcing member, a hot press technology is used in which a steel sheet heated to the austenite region is cold-formed to perform a quenching process to form a hardened structure formed of martensite. We focused on the point of use.
Hereinafter, the center pillar reinforcing member of the present invention will be described in detail.

  As shown in FIGS. 1A and 1B, the center pillar reinforcing member 1 described in the present embodiment has an upper end 11 fixed to a roof side rail 60 of an automobile and a lower end 12 arranged at the lower part of the automobile. It is fixed to the sill 70 and has a substantially vertically long shape in plan view. The center pillar reinforcing member 1 in the illustrated example is formed in a substantially hat-shaped cross section including a horizontal wall portion 3 and two vertical wall portions 41 and 42 extending from both side end portions 31 and 32 of the horizontal wall portion 3. ing.

  Further, the center pillar reinforcing member 1 is provided with a strength altered portion 2 that is a softened portion that can be easily deformed at a substantially lower position in the longitudinal direction. In this example, the center pillar reinforcing member 1 is shown in FIGS. As shown, it is provided on the vertical wall portion 41 of the two vertical wall portions 41, 42. Further, these vertical wall portions 41 and 42 are roughly in a load loading direction from the outside of the vehicle, which is a load loading direction with respect to the center pillar reinforcing member 1 when the center pillar reinforcing member 1 is assembled to the vehicle body. It is a wall-shaped part made parallel.

And the strength alteration part 2 is the position of the center pillar reinforcement member 1 in the substantially lower position, and the cross-sectional secondary moment (I) when the center pillar reinforcement member 1 is divided in the lateral width direction A second derivative (f) obtained by second-order differentiation at each position is arranged below the boundary K that is “0” in the longitudinal direction of the center pillar reinforcing member 1.
In the present invention, the strength altered portion 2 which is a low strength softened portion is disposed at the above-described position of the center pillar reinforcing member 1, so that, for example, when an overload due to a collision or the like is applied, Compared to the upper part of the pillar reinforcing member 1, there is an effect that deformation of the lower part is easily started.

The second derivative (f) of the sectional second moment (I) described in the center pillar reinforcing member of the present invention can be obtained by the method described below (also FIGS. 6 (a) and 6 (b)). reference).
First, for each position (Z) in the height direction of the center pillar, a cross-sectional secondary moment (I) in the bending direction applied at the time of collision is calculated. Since the sectional moment (I) has a discrete value with respect to the position (Z), approximation is performed so as to be a continuous function. Any approximation function can be used as long as it can represent the actual distribution, but polynomial approximation as shown in the following general formula (1) is convenient. Accordingly, first, the cross-sectional secondary moment (I) for each position (Z) is calculated by the following general formula (1).

但し、上記一般式（１）中、「Ｚ」はセンターピラーの高さ方向の位置寸法、「ｉ」は１からｎまでの値をとる整数、「ａ_ｉ」は多項式近似の各項の係数を示し、以下の一般式においても同様である。

However, in the above general formula (1), “Z” is the position dimension in the height direction of the center pillar, “i” is an integer having a value from 1 to n, and “a _i ” is a coefficient of each term of the polynomial approximation. The same applies to the following general formula.

  Then, using the obtained sectional second moment (I), a second derivative (f) for each position (Z) is obtained by the following general formula (2).

但し、上記一般式（２）中、「Ｉ」は断面２次モーメントを示す。

However, in the above general formula (2), “I” indicates a sectional second moment.

  Here, the order of the polynomial approximation is usually about 5th order (n = 6), but if the distribution of the cross-sectional secondary moment is complicated, the approximation up to the higher order may be performed accordingly.

  The center pillar reinforcing member 1 in the example shown in FIGS. 1A and 1B has a boundary portion whose upper side from the boundary portion K where the second derivative of the above-described second-order moment is “0” in the longitudinal direction. The cross-sectional area is smaller than the lower side of K, and the upper side is formed thinner than the lower side. In general, in the body of an automobile, a wide area of side window glass is secured from the viewpoint of openness, etc., and from the viewpoint of design, the upper part of the center pillar has a narrow shape that is smaller than the lower part. ing.

The strength altered portion 2 is mainly a softened structure containing a part of bainite in a mixed structure of ferrite and pearlite, and a hardened structure mainly including martensite on the upper side from the boundary K in the longitudinal direction of the center pillar reinforcing member 1 It is preferable that the deformation mode of the center pillar reinforcing member 1 can be controlled better.
In addition, depending on the cooling conditions and components in the manufacturing method described later, almost the entire vertical wall portion in which the strength altered portion is provided may have a bainite structure. In such a case, in order to provide a strength difference between the strength altered portion and another portion, it is preferable that the strength altered portion has a structure mainly composed of ferrite-pearlite.

  Further, as described above, the strength altered portion 2 described in the present invention is a portion that is provided as a soft portion that is easy to start deformation. Examples of such a softness index include hardness (Hv: Vickers) and Tensile strength (MPa) or the like can be used.

  In the present invention, in order for the center pillar reinforcing member 1 to have a sufficient impact absorption capability and be lightweight, the member needs to have high strength as a whole. For this reason, in the present invention, the center pillar reinforcing member 1 preferably has a hardness H1 of 400 Hv or more at a position excluding the strength altered portion 2, particularly at a position above the boundary portion K. Further, since this hardness value (400 Hv) is substantially equivalent to a tensile strength of 1200 MPa or more, similarly, it is preferable that the tensile strength TS1 at the position above the boundary K is 1200 MPa or more.

  In addition, in order for the strength-affected portion 2 to be deformed prior to other portions of the center pillar reinforcing member 1 and to improve the deformation of the entire member, as described above, the cross-sectional secondary moment ( In addition to disposing the strength altered portion 2 below the position where the second derivative (f) of I) is “0”, it is important that the strength ratio between the strength altered portion 2 and other parts is large. It becomes. As a result of intensive studies by the present inventors, in the center pillar reinforcing member 1, the hardness H1 of the portion excluding the strength altered portion 2, particularly the position above the boundary portion K is set to 400 Hv or more, and the hardness H2 of the strength altered portion 2; It has been found that when the ratio (H2 / H1) to the hardness H1 is set to a range represented by the following formula (H2 / H1 ≦ 0.85), a favorable deformation form as illustrated in FIG. 4 can be obtained. It was. Thereby, in this invention, the hardness H1 of the position above the boundary part K is prescribed | regulated to 400 Hv or more.

Furthermore, when the present inventors diligently studied, as in the relationship between the hardness of the strength-modified portion 2 and other portions as described above, in the relationship of the tensile strength between the strength-modified portion 2 and other portions, It became clear that the above proportional relationship was established. That is, the tensile strength TS1 on the upper side from the boundary portion K is set to 1200 MPa or more, and the ratio (TS2 / TS1) between the tensile strength TS2 of the strength altered portion 2 and the tensile strength TS1 is expressed by the following formula (TS2 / TS1 ≦ 0. It was found that a good deformation form as illustrated in FIG. 4 can be obtained by setting the range represented by 85). Thereby, in this invention, the tensile strength TS1 of the position above the boundary part K is prescribed | regulated to 1200 Mpa or more.
In the center pillar reinforcing member 1 of the present invention, by defining the relationship of the hardness or tensile strength between the strength altered portion 2 and the position above the boundary portion K as described above, a favorable deformation form is obtained. Therefore, even when a side collision of the automobile occurs, it is possible to ensure high collision safety.

  As shown in the schematic diagram of FIG. 4, when a large load is applied to the side body panel 80 (see FIG. 3) disposed on the side surface side of the automobile due to a side collision or the like, the side body panel 80 is Along with the deformation toward the vehicle inner side, the center pillar reinforcing member 1 is also given an overload toward the vehicle inner side. At this time, the center pillar reinforcing member 1 is provided with the strength altered portion 2 at the position defined in the above-described range, and the deformation starts at this portion. It becomes a form in which a deformation | transformation to an inner side is suppressed. Thereby, since the center pillar reinforcing member 1, the inner reinforcing member 90, and the like are suppressed from coming into contact with the occupant, it is possible to ensure high collision safety even if a side collision occurs. It becomes.

In general, an automobile has a structure in which the side body panel 80 is inclined toward the inside of the vehicle from the viewpoint of design and aerodynamic characteristics, so that the upper part of the center pillar reinforcing member is more occupant than the lower part. It will be placed at a position very close to. For this reason, when the upper part of a center pillar reinforcement member deform | transforms into a vehicle inside, there exists a possibility of contacting a passenger. Further, in the conventional center pillar supply member, since the center pillar reinforcing member is generally formed with a smaller size toward the upper part, the upper part becomes low in strength, and deformation to the inside of the vehicle at the time of collision is likely to occur. There's a problem.
On the other hand, the center pillar reinforcing member of the present invention is deformed from the strength altered portion 2 provided below the boundary portion K as in the example shown in FIG. It becomes a form and it is suppressed that the center pillar reinforcement member 1, the inner reinforcement member 90, etc. contact a passenger. Thereby, even if a side collision of the automobile occurs, it is possible to effectively prevent the passenger from being injured, and a center pillar reinforcing member having high collision safety can be realized.

As a steel plate used for the center pillar reinforcing member 1 according to the present invention, a steel plate material conventionally used in this field can be used without any limitation. Further, by using such a steel plate, a center pillar reinforcement made of a high strength steel plate such as a 1200 MPa class, a 1500 MPa class, or a 1800 MPa class by performing a quenching process while forming by a hot press method in a manufacturing method described in detail later. A member can be realized.
In the present invention, even if any steel plate is used, the above-described effect can be obtained by providing the strength altered portion 2 by a manufacturing method described later in detail.

In addition, the strength alteration part 2 is the load load direction S (refer FIG. 4) with respect to the center pillar reinforcement member 1 like the example shown in FIG.1 (b) and FIG. It is preferable to be provided in any one or both of the vertical wall portions 41 and 42 that are substantially parallel to each other. This is because the influence on the deformation resistance of the vertical wall portions 41 and 42 is maximized when deformation of the bending main body occurs. Therefore, it is possible to easily control the deformation mode by arranging the strength altered portion 2 in this portion. This is because it is most efficient.
Further, when forming by the hot press method, which will be described in detail in the manufacturing method described later, the lateral wall portion 3 positioned perpendicular to the load direction becomes the bottom of the punch, and contact with the mold from the initial stage of molding is inevitable. Therefore, since the horizontal wall 3 is difficult to be slowly cooled due to heat removal by the mold, the strength altered portion 2 can be disposed on the vertical wall portions 41 and 42 from the viewpoint of manufacturing. preferable.

  Further, in the present invention, the position where the strength altered portion 2 is arranged is optimized according to the structure of the actual center pillar reinforcing member that varies greatly depending on the vehicle type, and is defined within the above range. It is more preferable to arrange the pillar reinforcing member in a range narrower than the lower half of the entire length in the longitudinal direction. If the strength altered portion, which is a softened portion, is disposed in a region other than this range, that is, a region on the upper side in the longitudinal direction of the center pillar reinforcing member, the merit of increasing the strength of the center pillar reinforcing member is lost.

  Further, in the present invention, as shown in FIG. 5, the strength altered portion 2 has a door waist reinforcing member 51 (provided in a door 50 attached to the body side panel 80 of the automobile in the longitudinal direction of the center pillar reinforcing member 1. More preferably, it is provided at a position below the position corresponding to the chain line portion). If the strength altered portion 2 is provided below the position corresponding to the door waist reinforcing member 51 as described above in the longitudinal direction of the center pillar reinforcing member 1, the center pillar reinforcing member 1 is deformed by a side collision. Even in this case, it is possible to more effectively prevent the center pillar reinforcing member and its peripheral members from coming into contact with the passenger. Here, the door waist reinforcement member 51 is a member positioned near the lower end of the side window provided on the door 50, and is a member that reinforces the door 50 by connecting the door panel in the longitudinal direction of the vehicle body.

  In the present embodiment, the center pillar reinforcing member is reduced in size toward the upper portion as shown in FIGS. 1A and 1B and has a hat shape as shown in the sectional view of FIG. Although an example has been described, the present invention is not limited to this. As described above, the strength altered portion having the configuration defined in the present invention can be applied to the center pillar reinforcing member of any shape.

In the present embodiment, only the second moment (I) of the cross section of the center pillar reinforcing member 1 is calculated, the second derivative (f) is obtained, and the boundary K is set, thereby reducing the softened portion with low strength. However, the present invention is not limited to this. For example, in the substantially closed cross-sectional structure as shown in FIG. 2, the center pillar reinforcing member 1, the reinforcement member 90 and the inner reinforcing member 95 are regarded as an integrated structure (substantially closed cross-sectional structure). It is also possible to calculate (I) to obtain the second derivative (f), set the boundary portion, and arrange the strength altered portion. In such a case, for example, the inner reinforcing member is also configured to have a substantially hat-shaped cross section, so that the center pillar reinforcing member and the inner reinforcing member (and the reinforcement member) are regarded as one body, and resistance to bending is increased. Can be configured.
However, the inner reinforcing member generally has a low vertical wall portion, and even when a strength altered portion is provided, the obtained effect is limited. Therefore, in the present invention, only the center pillar reinforcing member 1 is used. A sufficiently large effect can be obtained by providing the strength altered portion.

  As described above, according to the center pillar reinforcing member 1 according to the present invention, in the longitudinal direction of the center pillar reinforcing member 1, the sectional moment (I) of the center pillar reinforcing member 1 is changed to each position in the longitudinal direction. A structure in which the strength altered portion 2 is provided at a position below the boundary portion K where the second derivative (f) obtained by second-order differentiation is “0” in the longitudinal direction of the center pillar reinforcing member 1. By doing so, even if a side collision of the automobile occurs and a load is applied from the outside, the deformation form of the center pillar reinforcing member 1 can be appropriately controlled, so that the load load energy at the time of the collision is reduced. It becomes possible to absorb effectively. Thereby, it is possible to effectively prevent the vehicle body structural members such as the center pillar reinforcing member 1 and the inner reinforcing member 90 from coming into contact with the passenger. Further, in the present invention, it is not necessary to increase the thickness of the steel plate or to provide a rib or the like, so that the center pillar reinforcing member 1 and thus the entire vehicle body can be reduced in weight. Therefore, the center pillar reinforcing member 1 excellent in collision safety can be realized with an inexpensive configuration.

  The center pillar reinforcing member of the present invention uses the second derivative (f) of the second moment of inertia (I) corresponding to the structure of the center pillar reinforcing member, when providing the strength altered portion which is a softened portion of low strength. By defining the arrangement location below the position where the secondary differential coefficient (f) is “0”, it is possible to appropriately control the deformation mode even if the center pillar reinforcing member has any shape and dimension. It becomes possible. Also, even if the thickness of the steel plate forming the center pillar reinforcing member is reduced, sufficient strength and collision safety can be obtained, so that the weight of the center pillar reinforcing member is reduced, and thus the weight reduction of the automobile in which the center pillar reinforcing member is used. Can be realized.

  Further, in the center pillar reinforcing member of the present invention, the strength-modified portion is mainly a softened structure containing a part of bainite in the mixed structure of ferrite and pearlite, and the upper side from the boundary portion in the longitudinal direction of the center pillar reinforcing member mainly. By configuring with a hardened structure containing martensite, the deformation mode can be controlled more appropriately. Such an effect can be obtained by providing the strength altered portion at a position lower than the position corresponding to the door waist reinforcing member provided in the door attached to the body side panel of the automobile in the longitudinal direction of the center pillar reinforcing member. , Become more prominent.

Hereinafter, the manufacturing method of the center pillar reinforcement member 1 provided with the above strength-affected portions 2 will be described.
The manufacturing method of the center pillar reinforcing member 1 according to the present invention is such that the secondary moment (I) of the cross section when the center pillar reinforcing member 1 is divided in the lateral width direction is changed to the second floor at each position in the longitudinal direction of the center pillar reinforcing member. The second derivative (f) obtained by differentiating is provided with a strength altered portion 2 at a position below the boundary portion K which is a position where the center pillar reinforcing member 1 is “0” in the longitudinal direction of the center pillar reinforcing member 1. After heating the steel plate to a temperature range from Ac ₃ point to melting, and then performing a quenching treatment inside the mold while forming the steel plate using a mold, the cooling rate in at least a part of the steel plate, This is a method of forming the strength altered portion 2 as a softened portion by relatively slow cooling at a lower speed than other portions.

  In the manufacturing method of the present invention, the center pillar reinforcing member 1 is so-called hot that forcibly cools the steel sheet by, for example, injecting cooling water into the mold while the heated steel sheet is formed in the mold as described above. Manufactured by pressing. Further, in the present invention, the strength altered portion 2 provided at the lower portion of the center pillar reinforcing member 1 corresponds to a part of the steel plate, that is, the lower portion of the center pillar reinforcing member 1 in the steel plate forming step by the hot press method as described above. It is provided by a method of slowly cooling only the part.

In the process by the hot press method as described above, the steel plate that has been quenched in the mold has a high-strength structure in which a large amount of martensite is generated. Therefore, the center pillar reinforcing member 1 according to the present invention has a high strength. It becomes the member of. On the other hand, a part of the same steel plate that has been slowly cooled, that is, a portion of the strength-affected zone 2 does not undergo martensitic transformation by being slowly cooled (slowly cooled), and therefore is partly in the mixed structure of ferrite and pearlite. It becomes a softened structure containing bainite and becomes a low strength part.
The manufacturing method of the center pillar reinforcing member of the present invention is to obtain the center pillar reinforcing member 1 that is excellent in strength characteristics and capable of appropriately controlling the deformation mode at the time of a side collision by forming a steel sheet under the above conditions. it can.

In the hot press method in which a heated steel plate is cooled while being molded with a mold and subjected to quenching as described above, the final strength is determined by the material, that is, the cooling rate of the steel plate in this example. At this time, for example, an aluminum-plated steel plate or a bare cold-rolled steel plate is selected as the base plate (mainly defining the C content), and a method of applying annealing that locally changes the cooling rate results in low strength. It is possible to provide the strength altered portion which is the softened portion of the material at an arbitrary position. Thus, as a method of providing the strength altered portion on the steel sheet by the annealing treatment that locally lowers the cooling rate, for example, the following methods (1) to (3) are exemplified.
(1) Embed ceramics in a part of the mold and slow down the heat conduction only in this part.
(2) After pre-forming a steel sheet with unevenness locally, final molding is performed using a mold having a recess inside, thereby slowly cooling the location where the voids are formed (inside the steel sheet) Since the heat conduction is 10 times or more between the part closely attached to the mold and the part via the gap, the part via the gap can be formed in the strength altered portion).
(3) Using a water-coolable mold, only the portion of the steel plate that requires high strength, that is, the portion excluding the strength-modified portion is water-cooled.

  In the manufacturing method of the present invention, each of the above methods can be appropriately selected and adopted while taking into account, for example, mold manufacturing costs and the like. Here, for example, when the method (2) is adopted, the average cooling speed is 100 ° C./sec or more at the contact portion between the mold and the steel plate, and 50 ° C./sec or less at the portion where the die is not in contact. By using this, the strength alteration part can be appropriately arranged by controlling the components and heating temperature of the steel sheet so that the critical cooling rate of the martensitic transformation is 50 ° C./sec or more and 100 ° C./sec or less. Is possible.

According to the manufacturing method of the center pillar reinforcing member of the present invention as described above, the second moment of the cross section of the center pillar reinforcing member in the longitudinal direction of the center pillar reinforcing member 1 is increased to the second floor at each position in the longitudinal direction. The second derivative is obtained by providing a strength altered portion 2 at a position below the boundary K where the center pillar reinforcing member becomes “0” in the longitudinal direction of the center pillar reinforcing member, and the steel plate is melted from Ac ₃ points. After heating to the temperature range up to then, when performing quenching treatment inside the mold while forming the steel sheet using the mold, the cooling rate in at least a part of the steel sheet is set to be slower than other parts Since the strength-affected zone 2 is formed as a softened part by relatively slow cooling, even when a load is applied from the outside of the automobile, the deformation mode can be controlled appropriately. The center pillar reinforcing member 1 capable of effectively absorbing the load load energy at the time of the collision can be manufactured. Therefore, the center pillar reinforcing member 1 having excellent collision safety can be manufactured with high productivity.

  Hereinafter, the examples of the center pillar reinforcing member and the manufacturing method thereof according to the present invention will be described to explain the present invention more specifically. However, the present invention is not limited to the following examples from the beginning. The present invention can be carried out with appropriate modifications within a range that can be adapted to the gist of the present invention, and these are all included in the technical scope of the present invention.

[Steel component]
In this example, steel plates a to e having the component compositions as shown in Table 1 below were prepared and used as raw materials for each sample. Table 1 below also shows the temperatures of _three Ac points that are the austenite single-phase regions of these steel plates a to e. In the case of performing molding using the hot press method, it is necessary to heat to a temperature of Ac ₃ point or higher to form an austenite single layer before molding. Further, the strength of the steel sheet after the quenching treatment mainly depends on the C amount.

  The steel plates a, b, and e in Table 1 below are adjusted so as to have high strength of about 1200 MPa class, 1500 MPa class, and 1800 MPa class, respectively, after the quenching treatment. The steel sheet c has substantially the same ultimate strength as the steel sheet b, but has improved hardenability by increasing the amount of Mn added. The steel plate d is not added with Si, and the hardenability is almost the same as that of the steel plate b.

[Forming steel plates by hot pressing]
Using each steel plate shown in Table 1, forming was performed using a hot press method as described below, and a sample of the center pillar reinforcing member was produced. Moreover, as a steel plate used for forming the center pillar reinforcing member, a steel plate having a thickness of 1.8 mm was used.

  Here, the shape and dimensions of the center pillar actually used in the automobile vary depending on the vehicle type. In this embodiment, as a sample to be a model member, FIGS. 8A and 8B (FIG. 1). Various tests were performed using the shapes and dimensions shown in (a) and (b). In this example, in all the evaluation tests, the outer side center pillar reinforcing member and the inner side inner pillar member used were members produced by a hot press method. Further, the hot press forming conditions were such that the steel plate was heated to 900 ° C. before forming and the temperature at the start of hot press forming did not fall below 850 ° C.

Further, the strength altered portion 2 provided in the sample of the center pillar reinforcing member was provided in the vertical wall portion 41 of the outer side center pillar reinforcing member, as shown in FIGS. Moreover, the arrangement position of the strength altered portion 2 was determined based on the calculation result of the cross-sectional second moment of the center pillar reinforcing member as shown in FIGS. 6 (a) and 6 (b). Here, each dimension value shown in FIG. 6A indicates the position (Z) in the height direction of the center pillar, and the vertical axis in the graph of FIG. 6B indicates the center shown in FIG. The coordinates of the longitudinal direction of the pillar reinforcing member 1 are shown.
As shown in FIGS. 6 (a) and 6 (b), the cross-sectional secondary moment calculated at 100 mm intervals in the longitudinal direction of the center pillar reinforcing member 1 is large at the upper part and becomes larger toward the lower part. It shows that the small upper part is easier to bend with lower strength than the lower part. Similarly, FIG. 6B shows the second derivative obtained by second-order differentiation of the second moment of section with respect to the position (longitudinal coordinate). As shown in FIG. 6B, the second derivative of the sectional second moment becomes “0” at a position of about 700 mm from the lower end 12. It can be seen that the rate of change of moment takes an extreme value. That is, it is clear that this boundary portion K is a portion where the ease of bending changes most steeply in the longitudinal direction of the center pillar reinforcing member 1.

  In this example, steel plates having various component compositions as shown in Table 1 were used for the outer side center pillar reinforcing member, but the inner side inner reinforcing member had a component composition approximate to that of the steel plate b. The steel plate (C = 0.22, Si = 0.25, Mn = 1.20, Al = 0.03, the unit is mass%) was used. In this example, the inner reinforcing member was not provided with a strength altered portion, but this was due to the restrictions in the method for forming the strength altered portion adopted in this example, and it was not located at a position other than the vertical wall portion. This is because it is difficult to provide the strength-affected portion, and the effect is limited in the inner reinforcing member having a small depth of the vertical wall portion. In this embodiment, the method of controlling the formation of the strength altered portion by the presence or absence of water cooling as described below is adopted, but the strength altered portion in the present invention is, for example, embedded with a ceramic having a low thermal conductivity. It is also possible to adopt a method using a metal mold, and in this case, it is possible to arrange the strength-modified part on the inner reinforcing member including the position other than the vertical wall part.

  In this example, whether or not to form a strength altered portion was controlled by the presence or absence of water cooling. For this reason, the mold clearance of the vertical wall portion was set as wide as 200% with respect to the plate thickness. In addition, by providing a water channel on the mold surface in a portion other than the strength altered portion, by securing a sufficient cooling rate by water cooling, it is possible to cause almost 100% martensitic transformation. Strength was secured. On the other hand, part of the vertical wall that is not cooled with water is martensite because there is a clearance between the mold and the bottom dead center, so the heat is not removed by the mold and is slowly cooled. Transformation became difficult to occur, and as a result, the martensite and bainite partially mixed with the mixed structure of ferrite and pearlite, resulting in a low strength part.

  In addition, about the sample using the steel plate a and the steel plate b, the center pillar reinforcement member from which various intensity | strength alteration parts differed was obtained by changing the position of water cooling (sample No. 1-10 in Table 2). Moreover, about the sample using the steel plates c, d, and e, both what provided the strength alteration part and what did not provide were produced, and the evaluation test was done. In addition, in this embodiment, since the components (especially C content) differ for every used steel plate, the ultimate ultimate strength obtained when it becomes a hardened structure differed. Further, as the strength of each part of the center pillar reinforcing member, a Vickers hardness test was performed at a total of 5 points at the strength altered portion and other portions, and a list of the average values is shown in Table 2 below. Here, about the sample using the steel plate c, since Mn which improves hardenability was added, the change in hardness due to the presence or absence of water cooling was smaller than that of the sample using other steel plates, but the strength In the sample intended for the altered portion, a hardness difference of 20% or more was obtained. In this example, a sufficient effect was obtained even with a hardness difference of about 20%. However, in the present invention, the hardenability of the steel sheet can be adjusted according to the method for producing the strength-affected portion under more severe conditions. In this case, it can be easily performed by adjusting the amount of Mn.

  In addition, as will be described in detail later, each sample is fixed to a member having a uniform cross section imitating the upper side of the roof side rail, and similarly to a member imitating the lower part of the sill, as in the case of an actual automobile. The test was carried out in a fixed manner. Further, at this time, an inner reinforcing member (inner side: plate thickness 1.2 mm) was arranged inside the center pillar reinforcing member (outer side: plate thickness 1.8 mm), that is, inside the vehicle.

[Evaluation test method]
The roof side rails and sills used in this example were all made of 590 MPa grade steel plates (JSH 590Y) having a plate thickness of 3.2 mm. Each member was joined by spot welding at intervals of about 50 mm.

The evaluation test in this example was performed under conditions simulating actual side collision.
First, the roof side rail and the left and right ends of the sill (lateral width direction in FIG. 1A) were fixed with a jig.
Next, a hemispherical jig (R = 1000 mm, 125 kg) was moved from the side with the apex located at a height of 500 mm in the coordinates shown in FIGS. 6 (a) and 6 (b). It was made to collide from the center pillar reinforcement member 1 side at 15 m / s. At this time, the reaction force generated in the hemispherical jig is measured, and the positions of the marks provided at intervals of about 100 mm are sequentially measured on the ridge lines of the inner reinforcing member arranged on the inner side of the center pillar reinforcing member. It was used as an index of the amount of intrusion.

  Moreover, as an index of collision safety on the side of an automobile, an average reaction force obtained by averaging reaction force generated in a hemispherical jig in a certain section (0-20 msec and 10-20 msec), and an intrusion amount at 20 msec It evaluated by the deformation | transformation form by (mark position of an inner reinforcement member).

  Table 2 below shows a list of the strength altered portions and the results of each test of the sample of the center pillar reinforcing member produced in this example.

[Evaluation results]
Hereinafter, the evaluation results of this example will be described with reference to Table 2 and each drawing as appropriate.
The graph of FIG. 7 shows a modified form of the sample using the steel plate b. The graph of FIG. 7 is No. which is a comparative example having no strength altered portion. No. 6 and No. 6 which is an example of the present invention in which a strength alteration portion is provided in a vertical wall portion at a height of 500 to 250 mm at the height shown in FIGS. 10 (corresponding to FIG. 3), the amount of penetration of the inner reinforcing member into the vehicle when 20 msec elapses is compared. As shown in FIG. In the sample No. 6, deformation was concentrated on the upper part where the cross-sectional strength was relatively low, and the member was bent on the upper part (near the position of 1100 mm from the lower end). On the other hand, no. In sample 10, the part (near 1100mm from the lower end) was preferentially deformed and absorbed the energy, and as a result, no folds occurred because the deformation concentration did not occur in the upper part. The member shape when 20 msec passed is No. Compared with the sample of 6, it became a preferable form near vertical. In order to evaluate the verticality of such a member, the horizontal difference between the position of the uppermost mark at 20 msec and the position of the lower mark at 20 msec is calculated, squared, and summed. The square root was calculated and shown in Table 2 as the degree of verticality (a numerical value having a dimension of mm). If the horizontal positions of the marks are the same, the calculated value is 0, indicating that the shape of the inner reinforcing member is vertical after the collision. That is, it is considered that the smaller the numerical value of the verticality, the more preferable characteristics as the center pillar reinforcing member. When the verticality is determined for the member form after the collision shown in FIG. For the 10 samples, 86, no. It can be quantified as 110 in 6 samples.

  Moreover, the average reaction force (average value of 0-20 msec) indicating the shock absorbing ability of the center pillar reinforcing member is No. 6 and no. 10 is 93.6 kN and 97.3 kN, respectively. Ten samples show higher values. Further, when the average load (10-20 msec) in the latter half is compared, the difference becomes very large. 6, 60.4 kN, 10 was 74.9kN. This is because of no. In No. 6, it is considered that the upper part is bent at a certain timing after the start of deformation, and the load transmission efficiency is greatly reduced. On the other hand, no. In No. 10, since such a fold does not occur, it is considered that the overall shock absorption capability is increased.

  No. 2-5 and no. Each sample of 7-10 is a sample which changed the position of the strength alteration part variously using the steel plate a and the steel plate b, respectively. Although each sample has a different steel plate strength, the value of the average reaction force is different, but it is clear that the deformation forms are similar when compared between samples having a strength altered portion at the same position. First, in the range from 1000 to 250 mm from the lower end, No. 1 in which the strength altered portion is arranged on the vertical wall portion. 2 and no. In the sample No. 7, there was a slight crease at the top. On the other hand, when the average reaction force is used for evaluation, no. 1, no. Compared to 5, the reaction force in all sections, especially in the latter half, was improved, and it was found that a certain effect was exhibited. No. 3-5 and no. The samples 8 to 10 have a strength lower than the boundary K (about 700 mm from the lower end) where the second derivative of the sectional second moment calculated based on FIGS. 6A and 6B is 0. This is an example in which an altered portion is arranged. In these samples, no. 2 and no. Unlike the case of No. 7, the evaluation of the deformed form was not broken at the upper part, and the average reaction force was also superior to that without the strength altered portion.

  When the center pillar reinforcing member having a member shape as shown in FIGS. 1A and 1B is used as in the present embodiment, the strength change is minimal (position from the lower end is 500 to 250 mm). Even with the setting of the part, the effect was hardly changed. On the other hand, it is necessary to examine this result in consideration of the cross-sectional shape of the center pillar reinforcing member.

  No. 11-No. No. 16 compares the difference between the samples produced using the steel plates c, d, and e depending on the presence / absence of the strength altered portion. As described above, in the sample using the steel plate c having good hardenability, the hardness of the strength altered portion was high and the difference from the general portion tended to be small (No. 12). No effect was seen. As for the average reaction force, the effect of improving the reaction force in the latter half is slightly small, but No. Compared to 11, it was improved. Moreover, about the sample using the steel plates d and e, it became clear that the hardness difference of a sufficient general part and a strength altered part was obtained, and the effect obtained by providing a strength altered part is large.

  From the results of the embodiments described above, the center pillar reinforcing member of the present invention can appropriately control the deformation form of the center pillar reinforcing member even if a side collision of the automobile occurs. It has become clear that the vehicle body structural member can be effectively prevented from coming into contact with the passenger.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which illustrates typically an example of the center pillar reinforcement member which concerns on this invention, (a) is the schematic which shows the state which attached the center pillar reinforcement member to the roof side rail and sill of a motor vehicle, (b) is ( It is a side fracture view of a). It is a figure explaining typically an example of the center pillar reinforcement member concerning the present invention, and is a sectional view showing the state where the center pillar reinforcement member and the inner reinforcement member are arranged inside the body side panel. It is a figure which explains typically an example of the center pillar reinforcement member concerning the present invention, and is a schematic diagram showing the strength alteration part provided in the vertical wall part of the center pillar reinforcement member. It is a figure which illustrates typically an example of the center pillar reinforcement member which concerns on this invention, and is the schematic which shows the deformation | transformation form of the center pillar reinforcement member with respect to a load load. It is a figure explaining typically an example of the center pillar reinforcement member concerning the present invention, and is a schematic diagram showing arrangement relation of a strength alteration part provided in a center pillar reinforcement member, and a door waist reinforcement member provided in a door of a car. is there. It is a figure explaining typically the Example of the center pillar reinforcement member which concerns on this invention, (a) is the schematic which shows the parting position of the center pillar reinforcement member at the time of calculating | requiring a cross-sectional secondary moment, (b) is ( It is a graph which shows the relationship between the cross-sectional secondary moment of the center pillar reinforcement member divided | segmented in the position of a), and a secondary differential coefficient. It is a figure explaining the Example of the center pillar reinforcement member which concerns on this invention, and is a graph which shows the penetration | invasion dimension to the vehicle inside at the time of the deformation | transformation by a collision test. It is a figure explaining the Example of the center pillar reinforcement member which concerns on this invention, and is the schematic which shows the dimension of the member to which the produced sample and this sample were attached.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Center pillar reinforcement member, 2 ... Strength change part, 41, 42 ... Vertical wall part, 50 ... Door, 51 ... Door waist reinforcement member, 80 ... Body side panel (automobile), I ... Secondary moment of section, f ... Second derivative, K ... Boundary, H1, H2 ... Hardness, TS1, TS2 ... Tensile strength

Claims (7)

A center pillar reinforcing member made of a steel plate, arranged inside the body side panel of an automobile,
The second derivative obtained by differentiating the second moment of the section when the center pillar reinforcing member is divided in the transverse direction at the respective positions in the longitudinal direction of the center pillar reinforcing member has a second derivative of the center pillar reinforcing member. In the longitudinal direction, a strength altered portion that is a softened portion is provided at a position below the boundary portion that becomes “0” ,
Furthermore, in the longitudinal direction of the center pillar reinforcing member, the hardness H1 on the upper side from the boundary portion is set to 400 Hv or more, and the ratio (H2 / H1) between the hardness H2 of the strength altered portion and the hardness H1 is A center pillar reinforcing member characterized by being in a range represented by the following formula (H2 / H1 ≦ 0.85) .   The strength-altered part is a softened structure mainly containing bainite in a mixed structure of ferrite and pearlite, and a hardened structure mainly containing martensite on the upper side from the boundary part in the longitudinal direction of the center pillar reinforcing member. The center pillar reinforcing member according to claim 1, wherein the center pillar reinforcing member is provided.   The strength altered portion is provided at a position below a position corresponding to a door waist reinforcing member provided in a door attached to a body side panel of the automobile in the longitudinal direction of the center pillar reinforcing member. The center pillar reinforcing member according to claim 1 or 2.   In the longitudinal direction of the center pillar reinforcing member, the tensile strength TS1 on the upper side from the boundary portion is set to 1200 MPa or more, and the ratio of the tensile strength TS2 of the strength altered portion and the tensile strength TS1 (TS2 / TS1) Is a range represented by the following formula (TS2 / TS1 ≦ 0.85), The center pillar reinforcing member according to any one of claims 1 to 3. In the longitudinal direction of the center pillar reinforcing member, the upper side from the boundary where the second derivative is “0” is configured to have a smaller cross-sectional area than the lower side than the boundary. The center pillar reinforcing member according to any one of claims 1 to 4 . The center pillar reinforcing member is formed in a substantially hat-shaped cross section including a horizontal wall portion and a vertical wall portion extending from both side end portions of the horizontal wall portion, and the vertical wall portion is formed with respect to the center pillar reinforcing member. a load application direction, which are generally parallel with respect to the load application direction from outside the vehicle, according to claim 1 to 5, characterized in that the strength deterioration zone is provided in the vertical wall portion The center pillar reinforcing member according to any one of the preceding claims. A method of manufacturing a center pillar reinforcing member made of a steel plate, arranged inside a body side panel of an automobile,
The second derivative obtained by differentiating the second moment of the section when the center pillar reinforcing member is divided in the transverse direction at the respective positions in the longitudinal direction of the center pillar reinforcing member has a second derivative of the center pillar reinforcing member. A strength altered portion is provided at a position below a boundary portion that becomes “0” in the longitudinal direction, the steel plate is heated to a temperature range from Ac ₃ point to melting, and then the steel plate is used using a mold. When performing quenching treatment by forced cooling inside the mold while forming the mold, the strength altered portion is obtained by relatively slowly cooling the cooling rate of at least a part of the steel sheet as a lower speed than other parts. A method of manufacturing a center pillar reinforcing member, wherein the center pillar reinforcing member is formed as a softened portion .

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