JP2005076047A - Method for manufacturing hollow stabilizer superior in fatigue resistance - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a hollow stabilizer superior in fatigue resistance. <P>SOLUTION: The manufacturing method comprises: heating a mother steel pipe; draw-rolling it at a rolling temperature of 600 to 850°C and with a cumulative diameter reducing rate of 40% or higher into a stock steel pipe; forming the stock steel pipe into such a shape of the stabilizer as to include a portion having a bend radius R of 2D or less when D is defined as an outside diameter of the stock steel pipe, by cold bending; then heating it to a predetermined heating temperature for quenching by electrification; quenching it; and subsequently tempering it. Thereby, the hollow stabilizer acquires less reduced wall thickness and superior fatigue resistance. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method of manufacturing a stabilizer used in a vehicle such as an automobile, and more particularly to improvement of fatigue resistance of a hollow stabilizer.

  Conventionally, most automobiles have been provided with a stabilizer in order to alleviate rolling of the vehicle body during cornering and maintain running stability at high speeds. As this stabilizer, a solid stabilizer using a steel bar has been generally used. However, recently, it has been required to reduce the weight of automobile bodies from the viewpoint of global environmental protection, and the adoption of hollow stabilizers using steel pipes has been considered for stabilizers.

  The hollow stabilizer greatly contributes to the weight reduction of the vehicle body, but since the cross-sectional area is greatly reduced compared to the solid stabilizer, it has characteristics superior in strength and toughness than conventional ones and is bent so that it can be processed into a complicated shape It is required to apply a material having excellent workability and sufficient hardenability to ensure high fatigue strength.

For such requirements, for example, Patent Document 1, using C, Si, Mn, and Cr content, the ideal critical diameter D _I at least 1.0in, the adjusted slab so Ceq is 0.48% or less Thus, a method for producing a steel for an electric-welded steel pipe for a hollow stabilizer has been proposed which is hot-rolled and wound by adjusting the winding temperature to 570 to 690 ° C. According to this technique, it is said that an electric-welded steel pipe having good mechanical properties and heat treatment characteristics can be manufactured, and a highly reliable hollow stabilizer can be manufactured. However, the electric resistance welded steel pipe manufactured by the technique described in Patent Document 1 has a problem that bending workability is insufficient, and it is impossible to form a complicated stabilizer shape with a small curvature radius. For this reason, the further improvement of the bending workability with respect to the steel pipe for stabilizers was requested | required.

  Patent Document 2 proposes a method for manufacturing a hollow stabilizer. The technology described in Patent Document 2 includes a manufacturing process of obtaining a raw pipe by continuously shrinking an electric-welded pipe hot, and a cold drawing process in which the area reduction rate of the raw pipe is 30% or more. A cold drawing step to make a thick pipe material, a forming step for bending the thick pipe material into a desired stabilizer shape cold, and preferably an annealing step and a shot peening step, It is a manufacturing method of the hollow stabilizer which enabled the fleshing.

Patent Document 3 proposes a method for manufacturing a hollow stabilizer. The technique described in Patent Document 3 includes a contraction process in which the ratio of the wall thickness to the outer diameter is reduced to 18 to 35% by hot contracting or warming the electrical resistance pipe, and the contracted electrical resistance pipe This is a method of performing cold forming or hot forming into a stabilizer shape, performing a heat treatment step on the molded stabilizer semi-finished product, and then performing shot peening and coating.
Japanese Patent Publication No.61-45688 JP 2000-233625 A JP 2002-331326 A

  However, in the techniques described in Patent Document 2 and Patent Document 3, there is a limit to the shape of a stabilizer that can be applied because the bending workability of a steel pipe is significantly deteriorated by cold drawing. Further, the techniques described in Patent Document 2 and Patent Document 3 still have a problem that the fatigue resistance is lowered, and further improvement of the fatigue resistance has been demanded.

  An object of the present invention is to advantageously solve the above-described problems of the prior art and propose a method for manufacturing a hollow stabilizer having excellent fatigue resistance.

  In order to achieve the above-described problems, the present inventors diligently studied various factors affecting the fatigue resistance characteristics of the hollow stabilizer. As a result, it was found that the thickness deviation in the processed portion of the hollow stabilizer greatly affects the deterioration of the fatigue resistance characteristics. And it came to mind that this originated in the fall of the bending workability of a raw material steel pipe. The present invention has been completed based on the above findings and further studies.

That is, the gist of the present invention is as follows.
(1) In the method of manufacturing a hollow stabilizer, in which a raw steel pipe is sequentially subjected to a forming step of forming into a stabilizer shape by cold bending and a heat treatment step of quenching and tempering the formed steel pipe. However, the steel tube is excellent in fatigue resistance, characterized by being subjected to heat treatment, and then subjected to drawing rolling at a rolling temperature of 600 to 850 ° C. and a cumulative diameter reduction ratio of 40% or more. Manufacturing method of hollow stabilizer.
(2) The method for manufacturing a hollow stabilizer according to (1), wherein a bending radius R of the cold bending process has a portion that is 2D or less with respect to the raw steel pipe outer diameter D.
(3) In (1) or (2), the base steel pipe is, by mass%, C: 0.2 to 0.38%, Si: 0.35% or less, Mn: 0.3 to 1.5%, P: 0.025% or less, S: 0.005 %, Al: 0.1% or less, Ti: 0.005 to 0.1%, B: 0.0005 to 0.005%, a welded steel pipe having a composition consisting of the remaining Fe and inevitable impurities .
(4) The method for manufacturing a hollow stabilizer according to any one of (1) to (3), wherein the temperature of the heat treatment is a temperature in a range of 800 to 1000 ° C.

  According to the present invention, a hollow stabilizer having excellent fatigue resistance can be manufactured by an inexpensive method, the durability of the stabilizer can be remarkably improved, the weight of the automobile body can be reduced, and the industrial effect is remarkable. Play.

  An example of a hollow stabilizer is shown in FIG. In the example shown in FIG. 1, the hollow stabilizer 1 includes a torsion part 11 that extends in the width direction of the vehicle body, and a pair of arm parts 12 and 12 that are connected to both ends of the torsion part 11. The torsion part 11 is attached to the vehicle body via bushes 11a. The end portions 12a and 12a of the arm portion 12 are connected to a suspension mechanism or the like via a stabilizer link or the like (not shown). A torsion part 11 and a part of the arm part 12 have a bending part 13 processed with a bending radius R.

  In the method for manufacturing a hollow stabilizer of the present invention, a raw steel pipe is sequentially subjected to a forming process for forming into a stabilizer shape by cold bending, and a heat treatment process for quenching and tempering the formed steel pipe.

  In the present invention, a steel pipe obtained by subjecting the base steel pipe to a heat treatment and then subjecting the base steel pipe to drawing rolling at a rolling temperature of 600 to 850 ° C. and a cumulative diameter reduction ratio of 40% or more is used.

  As a base steel pipe, it is mass%, C: 0.2-0.38%, Si: 0.35% or less, Mn: 0.3-1.5%, P: 0.025% or less, S: 0.005% or less, Al: 0.1% or less, Ti: 0.005 It is preferable to use a welded steel pipe having a composition comprising -0.1%, B: 0.0005-0.005%, and remaining Fe and inevitable impurities.

  The reason why the composition of the mother pipe is limited to the above range is as follows. Hereinafter, mass% is simply expressed as%.

C: 0.2-0.38%
C is an element that improves the hardenability of the steel and increases the strength of the steel pipe, and is preferably contained in an amount of 0.2% or more in order to ensure a desired stabilizer strength. On the other hand, if the content exceeds 0.38%, the strength becomes too high, the ductility is lowered, the weld hardenability is increased, and the weld steel pipe properties are adversely affected. Therefore, C is preferably limited to a range of 0.2 to 0.38%.

Si: 0.35% or less
Si acts as a deoxidizer and dissolves in the matrix to improve the hardenability of the steel and increase the strength of the steel pipe. Such an effect is recognized at 0.01% or more, and more preferably at 0.10% or more. However, when the content exceeds 0.35%, the ductility is remarkably reduced. Because of this, Si
It is preferable to limit it to 0.35% or less.

Mn: 0.3-1.5%
Mn is an element that improves the hardenability of the steel and increases the strength of the steel pipe, and is preferably contained in an amount of 0.3% or more in order to ensure a desired stabilizer strength. On the other hand, if the content exceeds 1.5%, the weld hardenability increases remarkably with the decrease in ductility, and the soundness of the welded portion decreases. For this reason, Mn is preferably 0.3 to 1.5%.

P: 0.025% or less P increases the strength of the steel by solid solution, but reduces ductility, segregates at the grain boundaries, and tends to promote low temperature temper embrittlement after heat treatment. In the present invention, it is preferably limited to 0.025% or less.

S: 0.005% or less S exists as a sulfide in steel, and deteriorates cleanliness and lowers ductility. In order to improve the workability of the raw steel pipe, it is desirable to reduce S of the base steel pipe as much as possible at 0.005% or less.

Al: 0.1% or less
Al acts as a deoxidizer and has the effect of refining crystal grains. In order to refine crystal grains, Al is preferably contained in an amount of 0.001% or more. However, if the content exceeds 0.1%, the amount of oxygen-based inclusions increases and the cleanliness decreases. For this reason, it is preferable to limit Al to 0.1% or less.

Ti: 0.005-0.1%
Ti combines with N to form TiN, contributes to refinement of crystal grains, and fixes nitrogen to effectively improve the hardenability of B. In order to acquire such an effect, it is preferable to contain 0.005% or more. On the other hand, if the content exceeds 0.1%, the ductility decreases and the workability of the steel pipe deteriorates. For this reason, it is preferable to limit Ti to 0.005 to 0.1%. In addition, More preferably, it is 0.01 to 0.05%.

B: 0.0005-0.005%
B is an element that greatly improves the hardenability of the steel by containing a small amount. In order to obtain such an effect, B is preferably contained in an amount of 0.0005% or more. On the other hand, if the content exceeds 0.005%, the hardenability decreases. For this reason, it is preferable to limit B to 0.0005 to 0.005%.

  The balance other than the above components is Fe and inevitable impurities, and N: 0.005% or less and O: 0.005% or less are acceptable as the inevitable impurities.

  The manufacturing method of the mother steel pipe is not particularly limited, but it is preferable to use a welded steel pipe from the viewpoint of manufacturing cost. As a method for manufacturing a welded steel pipe, any known method can be applied, in which a steel strip is formed by forming and a seam portion is manufactured by electro-welding. There is no problem even if seamless steel pipes are used.

  In the present invention, a steel pipe formed by subjecting the base steel pipe having the above composition to heat treatment and drawing at a rolling temperature of 600 to 850 ° C. and a cumulative diameter reduction ratio of 40% or more is used as the raw steel pipe.

  The temperature at which the mother steel pipe is heated is preferably 800 to 1000 ° C. If the heating temperature is less than 800 ° C, it is not possible to ensure an appropriate rolling temperature for drawing. On the other hand, when the heating temperature exceeds 1000 ° C., the surface properties deteriorate, austenite grains become coarse, and the ductility of the material steel pipe decreases. The method for heating the mother steel pipe is not particularly limited, but it is preferable to use induction heating.

  The heated mother pipe is then subjected to drawing rolling. The drawing rolling is preferably rolling by a plurality of (a plurality of stands) continuous rolling mills called reducers.

  Drawing rolling is performed at 600 to 850 ° C. or less in the austenite temperature range. By carrying out drawing rolling in this temperature range, the rolling texture develops and as a result, the r value increases and the workability of the steel pipe is significantly improved. When the rolling temperature of drawing rolling is less than 600 ° C., deformation resistance is high and rolling becomes difficult, or recrystallization becomes insufficient, so that processing strain remains, ductility decreases, and bending workability deteriorates. On the other hand, when the rolling temperature of the drawing rolling is higher than 850 ° C., the growth of crystal grains becomes remarkable, the formation of the rolling texture becomes insufficient, and the ductility and bending workability are lowered. For this reason, the rolling temperature of drawing rolling was limited to the temperature range of 600-850 degreeC. In addition, Preferably it is 700-800 degreeC.

Further, the cumulative diameter reduction ratio in the drawing rolling is 40% or more. The cumulative diameter reduction rate is
Cumulative diameter reduction rate (%) = {(base pipe outer diameter-steel pipe outer diameter after rolling) / base pipe outer diameter} x 100%
Defined by

  If the cumulative diameter reduction ratio is less than 40%, the diameter reduction ratio is too small, and the effect of the above-described drawing rolling cannot be expected. There is also a problem that productivity is low when the cumulative diameter reduction is less than 40%. By setting the cumulative diameter reduction ratio to 40% or more, the refinement of the structure and the formation of the texture become remarkable, and the bending workability is remarkably improved. For this reason, it is preferable that the cumulative diameter reduction ratio of the base steel pipe drawing rolling is 40% or more. The cumulative diameter reduction rate is more preferably 50% or more.

  In the present invention, the raw steel pipe obtained under the above-described conditions is subjected to a forming process and a heat treatment process to obtain a hollow stabilizer.

  In the forming process, cold bending is applied to the raw steel pipe to form a stabilizer shape. For molding, it is preferable to use an NC bender that can be molded into a substantially arbitrary shape. In addition, you may shape | mold using a bending die. In the present invention, since a material steel pipe having a high workability is used, a reduction in the thickness of the outside of the processed part, particularly the bent part can be suppressed. In this invention, even if it has the part whose bending radius R of a cold bending process is 2D or less with respect to the raw steel pipe outer diameter D, thickness reduction is small.

  The molded product formed in the stabilizer shape is then heated to a predetermined temperature (quenching temperature), and then subjected to a quenching process in which it is put into a quenching tank and rapidly cooled. The method of conducting heating by clamping both ends of the molded product with electrodes and energizing is preferable because the molded product is less deformed and inexpensive. The refrigerant in the quenching tank is preferably water or quenching oil. The predetermined quenching temperature is determined depending on the composition of the steel pipe.

  The quenched molded product is then tempered. By tempering, unstable grain boundary carbides precipitate in the grains, and the toughness is remarkably improved. The tempering temperature is preferably 180 to 400 ° C.

  ERW steel pipe (88mmφ x thickness 7.5mm) with the composition shown in Table 1 is used as the base steel pipe, and the base steel pipe is subjected to drawing rolling under the conditions shown in Table 2 to obtain a raw steel pipe (25.4mmφ x thickness 7mm). did. The base steel pipe used was a hot-rolled steel sheet that was cold-formed to form an open pipe, and the end was electro-welded and made into an electric-welded steel pipe.

  The obtained material steel pipe is cut into a predetermined length, subjected to a forming process by cold rotary drawing bending, and formed into a predetermined stabilizer shape as shown in FIG. 1, and a molded product (minimum bending radius R: 40 mm) ). In addition, the arm part edge part was shape | molded in the crushed state. Subsequently, both ends of the molded product were clamped and heated to 950 ° C. by energization, and then subjected to a quenching treatment to be put into a quenching tank (refrigerant: water). After the quenching treatment, a tempering treatment was performed by tempering at 350 ° C. to obtain a product (hollow stabilizer).

  The obtained product was subjected to a fatigue test in which the bush was fixed and both ends of the arm portion were moved up and down in the opposite direction, the number of repetitions until the occurrence of cracking was determined, and the fatigue resistance was evaluated.

  Other conditions of the fatigue test were as follows.

・ Load stress: 700MPa as the surface stress of the bent part
・ Repetition rate: 2Hz
In addition, a test piece was collected from the bending portion of the obtained product, and the reduction rate (%) of the tube section outer wall thickness was investigated. The thickness reduction rate is defined by the following equation.

Thickness reduction rate = {{(Raw steel pipe wall thickness)-(Bend outer steel pipe wall thickness)} / (Raw steel pipe wall thickness)} x 100%
The obtained results are shown in Table 2.

  In all of the examples of the present invention, the thickness reduction rate of the processed part is small, and the fatigue resistance is remarkably improved. On the other hand, in the comparative example using the raw steel pipe outside the scope of the present invention, the thickness reduction rate of the processed part is increased, and the fatigue resistance is also deteriorated.

It is a schematic diagram which shows an example of a stabilizer shape.

Explanation of symbols

1 Hollow stabilizer
11 Torsion club
11a Bush
12 Arm
12a Arm end
13 Bending part

Claims (4)

In a method for manufacturing a hollow stabilizer, in which a raw steel pipe is sequentially subjected to a forming step of forming a stabilizer shape by cold bending into a stabilizer shape and a heat treatment step of quenching and tempering the formed steel pipe. A hollow stabilizer with excellent fatigue resistance, characterized by being a steel pipe that has been subjected to heat treatment and then subjected to drawing rolling at a rolling temperature of 600 to 850 ° C. and a cumulative diameter reduction ratio of 40% or more. Production method. 2. The method for manufacturing a hollow stabilizer according to claim 1, comprising a portion in which a bending radius R of the cold bending process is 2D or less with respect to the outer diameter D of the raw steel pipe. The base steel pipe is in mass%, C: 0.2 to 0.38%, Si: 0.35% or less, Mn: 0.3 to 1.5%, P: 0.025% or less, S: 0.005% or less, Al: 0.1% or less, Ti: 0.005 The manufacturing method of the hollow stabilizer of Claim 1 or 2 which is a welded steel pipe which has a composition which contains -0.1%, B: 0.0005-0.005%, and consists of remainder Fe and an unavoidable impurity. The method for producing a hollow stabilizer according to any one of claims 1 to 3, wherein a heating temperature of the heat treatment is set to a temperature in a range of 800 to 1000 ° C.

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