JPH01111848A - Tube stock for use in stabilizer - Google Patents

Abstract

PURPOSE:To manufacture a tubular stabilizer with high reliability by regulating a difference in wall thickness in a bent part and a temp. in a temp. rise by means of electrification, respectively, at the time of bending a tube stock in which composition and shape are specified. CONSTITUTION:A steel plate having a composition consisting of, by weight, 0.10-0.35% C, <=0.35% Si, 0.30-1.20% Mn, 0.10-0.60% Cr, Ti in an amount 4-10 times the total content of inevitably contained N and O, 0.0005-0.009% B, and the balance Fe with inevitable impurities is subjected to butt seam welding, by which a tube stock which has 12-65mmphi outside diameter and arbitrary length and in which the ratio of wall thickness to outside diameter is regulated to 6-25% is formed. In this tube stock, [(the maximum wall thickness in a bent part)-(the minimum wall thickness in a bent part)]/(wall thickness before bending) is regulated to <=18.0% when this tube stock is bent orthogonally at a bending moment in which inside diameter is practically 4 times the outside diameter, and further, the temp. in the bent tube is regulated so that it is not raised up to >=1110 deg.C when the bent tube is electrified from one end to the other end and resistance heating is applied so that the temp. in the straight run of the tube is practically uniformized to 950 deg.C. By using this tube stock, the tubular stabilizer having high reliability can be manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention is used for a pipe-shaped stabilizer as a member for imparting running stability to an automobile. This invention relates to a raw pipe before being processed into a desired stabilizer shape.

[Prior Art] As is well known, a normal automobile is equipped with a stabilizer (anti-roll-bar) in the suspension mechanism of the vehicle body.
r) is attached. This is a component that prevents excessive tilting of the vehicle body when the vehicle turns, improving ride comfort and stability of the vehicle body, and is one of the important components of the vehicle suspension afjl.

Figure 1 shows the relationship between the typical shape and installation of a conventional stabilizer. It is a curved member. At the center of the stabilizer 1, the center portion (a) is attached to the vehicle body via a rubber bush or rubber bushing 4 so that the center portion (a) can rotate around its axis. As a result, when the vehicle body tilts, the center portion (a) of the stabilizer 1 acts as a torsion bar, and a moment for resisting the tilt is transmitted to the suspension arms 5 and 6 via the arm portions (g) at both ends of the stabilizer 9.

Acting as a restoring force, the stabilizer therefore does not provide a spring action when both the left and right wheels move up and down at the same time.

Conventional stabilizers have generally been made by bending a steel bar (round bar) into a desired shape. but.

Recently, from the perspective of reducing the weight of vehicles as much as possible, hollow pipe materials have been used instead of solid steel bars.

In Japanese Patent Publication No. 61-45688, the present inventors proposed a method of manufacturing steel suitable for manufacturing a pipe-shaped stabilizer. What is the outline of the steel manufacturing method disclosed in the publication?

C: 0.35% or less, Si: 0.20% or less, Mn: 0°30 to 1.20%, Cr: 0.60% or less, P: 0.020% or less, S: 0.02
0% or less, sat, Al: 0.10% or less.

N + O: 200 ppm or less, (N +
O) 4 to 10 times, B: 0.0005 to 0.0
09%, the remainder is steel consisting of Fe and unavoidable impurities, and D+(in)=((0,4C+0.06
) x(0,73++1)x(3,33Mn+1)X
(2,16Cr+IN X((1+1.5(0,9-C
) Adjust the contents of C, Si, Mn and Cr in the steel so that the ideal critical diameter (Dl) according to 1 is 1.0 (in) or more, and further.

Ceq, (χ) = C0Mn/6 + S i/24
A slab of steel with the content of C, Mn, Si, and C in the steel adjusted so that the carbon equivalent according to the formula + Cr15 is 0.48% or less is manufactured, and this is hot rolled. This is a method for manufacturing a steel for an electric resistance welded steel pipe for a hollow stabilizer, which comprises controlling the winding temperature to 570 to 690° C. during rolling.

The steel plate obtained by this manufacturing method can be manufactured into ERW steel pipes with sound welds, and when this ERW steel pipe material is processed into the shape required as a stabilizer and then quenched, it has sufficient quenching hardness. can get. Therefore, it is a useful steel for manufacturing pipe-shaped stabilizers in place of conventional solid round bars.

[Problems to be Solved by the Invention] Ever since the present inventors proposed the method for manufacturing steel disclosed in Japanese Patent Publication No. 61-45688, the present inventors have continued to strive to obtain a pipe-shaped stabilizer with high layer reliability. Further research has been carried out for this purpose. The stabilizer is a part of the suspension mechanism of the car body that is subjected to repeated stress countless times, and in addition to functioning adequately as a stabilizer, it is also important to ensure safety that it will not break because the life of a single person is at stake. Because it has to be done. In the research process, in the case of a stabilizer made of pipes.

I learned that traditional stabilizers made of solid round bars come with troublesome phenomena that are not seen.

One of these is the change in wall thickness of the bent portion that occurs when the raw pipe is bent. As can be seen in FIG. 1, the stabilizer always has arm portions (arm portions) on both sides of the center portion (a) via bent portions so that the direction of the axis is different from that of the center portion. In other words, there must be a bending section in order to shape the pipe into the shape required for the stabilizer. During bending of this pipe, it is inevitable that the wall thickness of the pipe changes between the inner and outer parts of the nine bends. When bending a pipe, compressive stress is applied on the inside of bend 9 and tensile stress is applied on the outside of bend 9, so the wall thickness is thicker on the inside of bend 1 than the original thickness, and on the contrary, the wall thickness on the outside of bend 5 is the same as the original thickness. This is because it appears as a phenomenon of becoming thinner. In a stabilizer installed in an automobile, stress is particularly concentrated at the bent portion depending on the vertical position of the wheel. Therefore, the pipe-shaped stabilizer is accompanied by the problem that the difference in wall thickness at the bent portion may cause damage to the stabilizer during driving.

The second problem is that a portion of the bent portion of the pipe overheats during the quenching process. In order to impart the spring characteristics necessary for a stabilizer, it is necessary to quench and temper the steel pipe processed into the final stabilizer shape (quenching before processing hardens the steel and makes processing difficult). For heating for the quenching treatment, a well-known electric resistance heating means that is easy to produce and adjust the temperature is used. During electrical resistance heating caused by this current application, a portion of the bent portion of the pipe is heated more than the straight portion. When this excessive heating occurs, the austenite grains in that area locally increase.
The problem is that it may cause fatigue failure due to localized strength reduction at the bent portion.

Therefore, one object of the present invention is to eliminate the above-mentioned factors that impair the safety of the stabilizer that are associated with the production of a pipe-shaped stabilizer.

[Means to solve problems]

When trying to solve the two problems in pipe-shaped stabilizers by targeting electric resistance welded steel pipes manufactured from steel plates within the range of composition proposed in the previous Japanese Patent Publication No. 61-45688, the first requirement (a) is met. It has been found that the requirements of (b) and (b), more preferably, the requirements (C) and (off) may be satisfied together.

(a) When the wire tube is bent 90' at a curvature such that the inner radius is substantially four times the outer diameter.

The wall thickness difference (χ) calculated using the wall thickness formula before bending shall be 18.0% or less.

(b), with the wire tube bent 90' at a curvature such that the inner radius is essentially four times the outer diameter (the tube is straight except for this bend), electricity is applied from one end of the pipe to the other. When resistance heating is performed so that the temperature of the straight portion of the pipe is substantially uniformly 950°C, the temperature of the bent portion does not exceed 1110°C.

(C), with the wire tube bent 900 degrees with a curvature so that the inner radius is essentially four times the outer diameter (the tube is straight except for this bend), electricity is applied from one end of the pipe to the other. When resistance heating is performed so that the temperature of the straight part of the pipe is substantially uniform at 950°C, the austenite crystal grains in the bent part do not become larger austenite crystal grains than the grain size corresponding to grain size number 6. .

(d) The wire tube has a work hardening index (n value) of L2 or more.

These requirements are that the outer diameter of the electric resistance welded steel pipe used is 12 to 65 m + mφ, and the wall thickness/outer diameter ratio is 6 to 25.
%, this applies to pipes of arbitrary length.

According to the invention, therefore, at 1% by weight, 0. IO~0
．． 35% (7) C, 0, 35% or less (7) S i,
0.30-1.20% Mn, 0, 10-0
, 60% Cr, Tt contained at a rate of 4 to 10 times the total amount of N% and 0% inevitably contained in R, 0.0005 to 0.009% (7) It was manufactured by electric resistance welding a steel plate B and the remainder consisting of Fe and unavoidable impurities. It is used to manufacture pipe-shaped stabilizers as members for providing driving stability for automobiles. A raw pipe before being molded into a desired stabilizer shape.

Outer diameter is 12~65mmφ, wall thickness/outer diameter ratio is 6~25
%, for any length of tube.

When this is bent 90' with a curvature such that the inner radius is essentially four times the outer diameter.

It is a pipe whose wall thickness difference (χ) calculated by the formula is 18.0% or less.

90° with a curvature such that the inner radius is essentially four times the outer diameter
When the pipe is bent (the pipe is straight except for this bent part) and electrical current is applied from one end of the pipe to the other end to heat the pipe resistance so that the temperature of the straight part of the pipe is substantially uniform at 950"C. This is a tube that does not generate heat when the temperature of the bent part exceeds 1110'C.This provides a vibrator tube used in a stabilizer.The vibrator tube preferably has an inner radius that is substantially outside the outer radius. 90 with a curvature that is 4 times the diameter
° When the pipe is bent (the pipe is straight except for this bent part) and electrical current is applied from one end of the pipe to the other end, resistance heating is applied so that the temperature of the straight part of the pipe is substantially uniform at 950°C. It is a pipe in which the austenite crystal grains in the bent portion do not become austenite crystal grains larger than the grain size corresponding to grain size number 6, and the work hardening index (n
value).

[Details of the invention]

Even within the range of the steel composition proposed in Japanese Patent Publication No. 61-45688, as well as within the range of manufacturing conditions proposed in the publication, ERW steel pipes made of that steel meet the above requirements (a).
) to (in some cases, the condition is not satisfied, and in this case, there is a problem in obtaining a pipe-shaped stabilizer that ensures safety.

First, this will be specifically explained based on two test examples conducted by the present inventors.

Test example 1 Steel having the chemical composition shown in Table 1 was melted.

It was hot rolled to a plate thickness of 2.6a+m. Steels B, C, and D in Table 1 are all made by Tokuko Sho 61-45688.
This is the steel described in the publication. During the rolling, the hot rolling finishing temperature was set in the range 1 of 843 to 870°C as shown in Table 2.
Eight hot-rolled coils were manufactured using different hot-rolling and assembling machines by adjusting the hot-rolling coiling temperature within the range of 568 to 680''C. After pickling and slitting these strip steels.

Both steel plates were made using a pipe making machine using high frequency welding to obtain wall thickness (t) = 2.6a+m, outer diameter (D) -22
,2ms+φ, wall thickness/outer diameter ratio kum/D x 100
) = 11.7% ERW steel pipe was manufactured. The welded parts after electric resistance welding were all reheated at a temperature of about 650°C.

Each of the obtained pipes was bent by 90°. Figure 2 shows the state of the cross section along the pipe axis of the bent part, and Figure 3 shows the cross section taken along line xx' (450 line) in Figure 2 (45° cross section of the bent part perpendicular to the pipe axis). The condition was shown. In Fig. 3, (goods) indicates a welded part.In the case of 900 bending, the radius of curvature of the outer surface r at the inside (in) of the bent part is the initial outer diameter D.
(actually 22.6 mm).

In case of any pipe.

The wall thickness on the inside (in) of the bent part became thicker than the original pipe wall Ftt, and the wall thickness on the outside (out) of one bent part became thinner than t. Each pipe was cut at a 45° cross section of the bent portion, and the thickness at each position; ~vi in FIG. 3 was measured. An example of the measured values is shown in FIG. The measured values in Figure 4 are:
This is about the pipe of Test Demon 2 in Table 2. Then, the wall thickness difference (χ) was calculated as a percentage of the difference between the maximum value and the minimum value of each measured value divided by the initial thickness t.

The pipe of test Nα2 was calculated to have a wall thickness difference (χ) of -19.1%. Similarly, the wall thickness difference (χ
) were measured and the results shown in Table 2 were obtained.

The results in Table 2 show that a difference in the composition of 1 wJ and, even if the composition is the same, a difference in the fiber composition of the steel brings about a large change in the wall thickness difference (χ). In particular, test magnets 2 and 3 using the same rope B. Even in tests Nα5 to Nα7 using the same steel, an interesting fact can be seen that when the hot rolling conditions differ, the wall thickness difference (χ) varies greatly.

On the other hand, a pipe made of the same steel and bent at 90° is shown in 5.
2 to 950°C for Nf16 and Nα7.
After heating in an atmosphere furnace for 0 minutes, quenching in water,
After tempering at ℃ for 30 minutes, repeated stress of each product size was applied using a fatigue testing machine, and a repeated rupture test was performed until rupture occurred. The results are shown in FIG. From the results shown in Figure 5, the pipes on floors 6 and 7 with a wall thickness difference (χ) of 18% or less will break even if they are subjected to a stress of 40 kg/-m'' over a million times. There isn't, but
Seed 5 pipes with a wall thickness difference (χ) greater than 18% are 4
It can be seen that there is a possibility of rupture even if a stress of 0 kg/+c++ is applied approximately 100,000 times.

In addition, both the pipes of test wall 1 and test wall 8 have a wall thickness difference (
χ) exceeds 18%. The cause of this is the chemical composition of the steel, and with such steel it is difficult to reduce the wall thickness difference (χ) to 18% or less even if hot rolling conditions are controlled. It can be said that it is not suitable in the first place.

Table 2 also shows the work hardening index (n value) of the hot rolled steel sheet from which each pipe was made, and for pipes with a wall thickness difference of 18% or less, the n value of the material steel is 0. You can see that it is given by 2 or more.

Test Example 2 All of the eight pipes manufactured in Test Example 1 were subjected to the same 90° bending process as in Test Example 1 at two locations to form bent pipes 11 having a shape as shown in FIG. Then, energizing terminals 14 and 15 are attached to the end portions of the two bent parts 12 and 13, and these terminals are connected to the a! 16 and connect terminals 14 and 15
A test was conducted in which the pipe between the two was electrically heated and resistively heated. The energization condition is 950° for straight pipe parts other than bent parts 12 and 13.
The conditions were set to maintain C.

Then, the surface temperature of the bent inner parts (the side indicated by (in) in FIG. 2) of the bent parts 12 and 13 was measured while the straight pipe part was maintained at 950°C. The results are shown in Table 3.

As can be seen from the results in Table 3, even though raw pipes of the same shape and size are used and the temperature of the straight pipe part is the same, the temperature inside the bent part of each pipe is different. There is. This can be considered to be caused by the difference in wall thickness of each pipe at the bent portion.

In addition, each bending vibrator was subjected to resistance heating in which the straight pipe part was maintained at 950°C for 1 minute, then quenched in water, and tempered by holding it at 350°C for 30 minutes. Then, specimens were taken from the inside of the bent portion where the heating temperature reached the highest, and each specimen was observed under a microscope to examine the crystal grain size. As a result (austenite grain size number according to JIS standard), the grains become larger in the 0-bending portion which is also shown in Table 3 and is subjected to excessive heating.

Note that, as a matter of course, the larger the grain size number, the smaller the crystal grains.

FIG. 7 shows the results of a fatigue fracture test on the bent portion of N115, 6.7 pipes that were quenched and tempered in this test. 7th
As can be seen from the results in the figure, even though the material pipe is made of the same rope, the one with larger austenite crystal grains has a shorter number of fatigue failures even under the same repeated stress, which poses a safety problem as a stabilizer. I understand that.

Table 3 also lists the results of flattening tests performed on the pipes before zero bending and quenching and tempering. This flattening test is carried out on a flat plate 17 as shown diagrammatically in FIG.
and 18 (with the welded part W located in the center between the plates), stress is applied between the plates to crush the pipe, and the distance H between the plates at the time when 1 crack occurs is used as an evaluation index. It is expressed as a relative proportion to the diameter. The flat test results also show that the Nα3 pipe of the same B111, and the Nα6 and 7 pipes of the same D, show good results. Therefore, these pipes that showed good results can be crimped at the ends.

Test example 3 Steel having the chemical composition shown in Table 4 was melted.

It was hot rolled to a plate thickness of 3.5 cm. Steels G and H in Table 4 are the steels described in Japanese Patent Publication No. 61-45688. During this rolling, as shown in Table 5, the hot rolling finishing temperature was set in the range of 850 to 873°C, and the hot rolling winding temperature was set at 4°C.
Six hot-rolled coils with different hot-rolled structures were manufactured by adjusting the temperature within the range of 70 to 620°C. These steel strips are pickled and
After slitting, both steel plates were machined using high-frequency welding to produce wall thickness (1) = 3.5+*s, outer diameter (D) -25.4 mmφ, wall thickness/outer diameter ratio (t/D
X 100) -13.8% electric resistance welded steel pipe was manufactured.

In addition, the temperature for the welded part after electric resistance welding is approximately 650°C.
Reheating treatment was performed at a temperature of .

Each of the resulting pipes was heated for 20 minutes in a salt bath maintained at 950°C without bending, quenched in water, and then tempered in a salt bath at 350°C for 30 minutes to determine its tensile strength. It was subjected to a test. The results are shown in Table 5. It can be seen that the material pipe made of steel G and WaH can secure a tensile strength of 100 kgf/mm, which is necessary for the stabilizer, by heat treatment.

In addition, the quenching heating temperature in the salt bath was set to 850°C.
Each pipe was water quenched at 000℃, and the hardness at that time (
H*c) and grain size were investigated. The results are also shown in Table 5, and even when heated to 850°C, among the pipes made of the same steel H, Nα12 and 13 have a hardness of Hc45, but even with the same H steel, the hardness of the 14th pipe and Gfi The pipe of No. 11 is inferior in hardness. Regarding the crystal grain size, the pipe materials had a crystal grain size number of 8 or more in all cases, and sufficiently fine crystal grains were obtained.

In addition, Table 5 shows the structure of the pipe before being subjected to heat treatment (
The results of examining the actual structure of the steel plate using a metallurgical microscope are also included. From this result, it can be seen that the pipes that had good hardness in this test corresponded to those with a high pearlite area ratio, and that the pipes were sufficiently hardened even at a low hardening heating temperature.

The above test examples 1.2 and 3 are 9th Special Publication No. 61-4568.
Even when using the steel proposed in Publication No. 8, the above-mentioned (a)
It has been proven that satisfying the requirements in ) and ■), as well as the requirements in (C) and (d), is important in ensuring the safety of the stabilizer.

In the raw pipe for the stabilizer of the present invention, the chemical composition value of the steel of the pipe material is from 0.10 to 0.10 in weight%.
0.35% C, 0.35% Si, 0.30
~1.20% Mn, 0, 10~0, 60%
Cr, N% and 0, which are inevitably contained in steel.
Ti contained at a rate of 4 to 10 times the total amount of %
, B is defined in the range of 0.0005 to 0.009%, but the present invention was made for the steel proposed in the publication.

Although some of the reasons for limiting the upper and lower limits of each component range are substantially the same as those described in the publication, it is necessary to further limit the ranges to the above ranges for the reasons described below.

In other words, if C is less than o,io%, the tensile strength after heat treatment, which is necessary as a stabilizer characteristic, is 100 kgf/
If it exceeds 0.35%, the strength of the material steel plate becomes too high, making roll forming during pipe manufacturing difficult, and the hardness of the welded bead of the ERW steel pipe increases. Bending workability and bendability of the pipe deteriorate.St
0.35% is necessary for deoxidation during steel manufacturing, but adding too much increases the hardness of the steel and deteriorates workability during pipe making and processing into stabilizers.
Limited to the following.

Mn improves the hardenability of pipes, but if it increases too much, the structure of the hot-rolled sheet tends to form bump knot stractures, which reduces toughness and makes roll forming during pipe manufacturing difficult due to high strength. Furthermore, since the hardness of the weld bead becomes excessively high and deteriorates the bending workability into a stabilizer, it is necessary to keep the hardness at 1.20% or less.

Cr is an element that improves hardenability without impairing the ductility of the material, and is one of the preferred elements to ensure workability of the electric resistance welded steel pipe and to obtain high strength after hardening.

However, if the amount of Cr added exceeds 0.6%, penetrators are likely to occur in the welded part during pipe making and the bending properties of the stabilizer during processing will deteriorate, so the upper limit should be set at 0.6%.
However, if Cr1l is less than 0.1%, no hardenability improvement effect is observed, so the lower limit is set to 0.10%.
limited to. Ti is added to deoxidize and denitrify steel, and B
It works effectively to stably and effectively improve hardenability by addition. on the other hand.

Small-diameter ERW steel pipes are heated to 100°C during welding.
With the temperature raised above, the pipe is passed through a sizing machine to form the outer diameter within tolerances and to make it perfectly round and straight, but it is subjected to processing distortion during this process. For this reason, the ductility of electrical resistance welded steel pipes for ships is significantly reduced due to the strain age hardening phenomenon caused by solid solution nitrogen. On the other hand, steel denitrified with Ti suppresses the decrease in ductility due to strain age hardening, and can produce electrical resistance welded steel pipes with good elongation, a large n value, and good workability. However, the amount of N in steel and 0
If the amount of Ti added is less than 4 times the total amount, it will not be possible to ensure sufficient hardenability and prevent the decrease in ductility due to strain age hardening, and if the amount is more than 10 times the amount, the effect will be saturated. ,
On the contrary, the processability of the electric resistance welded steel pipe deteriorates, such as increasing the strength of the hot-rolled material due to precipitation hardening due to the formation of TiC. For these reasons, it is necessary to make the addition range of Ti 4 to 10 times the total amount of N and O in the steel. Adding a small amount of B can greatly improve the hardenability of steel materials, but if the amount added is less than 0.000%, it has no effect on hardenability, and if it exceeds 0.009%, it has no effect on hardenability. Since it tends to decrease, it is set in the range of 0.0005 to 0.009%. By treating molten steel with Ca, the spherical inclusions extending in the rolling direction can be changed to spherical inclusions, and the ductility and toughness in the direction perpendicular to the rolling direction are significantly improved. The characteristics are improved. Therefore, it is preferable to perform Ca treatment during melting of steel. Spherical inclusions are present in the impurities of this Ca-treated steel. However, Ca1l in steel is 2
If it exceeds 00 ppm, the amount of inclusions will increase and the improvement effect will not be seen, so it is preferable to limit Cal to 200 pp+s or less.

The raw pipe of the present invention is made by electric resistance welding of steel sheet materials with each component adjusted as described above, and has an outer diameter (D) in the range of 12 to 65 steel Akebono φ, a wall I ¥ (1) and an outer diameter (D ) with a ratio t/D in the range of 6 to 25%. Outer diameter is 1
If the diameter is less than 2 mm and t/D is less than 6%, the pipe will become too small and the strength that satisfies the stabilizer properties will not be obtained.If the outer diameter is > 65a+m and t/D is > 25%, the pipe will become too thick and have a large diameter, making it difficult to bend. In addition to making processing difficult, cooling water does not come into direct contact with the inner surface of the tube during the quenching process after it is processed into a stabilizer with both tube ends sealed. It becomes difficult to obtain a martensitic structure.

The fatigue properties after tempering will deteriorate. On the other hand, it is difficult to roll form a small-diameter, thick-walled electric resistance welded steel pipe with an outer diameter of less than 121φ and a t/D of more than 25%, making it difficult to form the pipe. Also, the outer diameter exceeds 65IIIlφ and t/D is 6
Thin-walled, large-diameter ERW steel pipes with a thickness of less than % will not have the strength to satisfy the stabilizer characteristics.

For a pipe material having such a steel composition and size range, the requirement is that the wall thickness difference (χ) according to the above-mentioned 2 when bent 90 degrees so that the inner radius is -4XD is 18% or less. As demonstrated in the above test example, it is important to use only those that satisfy the requirements for the stabilizer in order to achieve the object of the present invention. The bent shape of the stabilizer to be mounted varies depending on the vehicle model, but we conducted a 90' bending test so that the inner radius = 4XD and found a material with a wall thickness difference (χ) of 18% or less. If it's a tube.

All you need to do is process the raw tube into the desired stabilizer shape for mounting.
This is because the bend is often 0°, and bending of 90° or more is rarely performed except in very special cases.

In addition, when heating a pipe bent by direct current heating to the quenching heating temperature, the bent part is bent by 90° so that the inner radius = 4XD, and the temperature of the straight pipe part is maintained at 950°C. In order to achieve the purpose of the present invention, it is important to use only pipes with an inner temperature that does not exceed 1110°C as stabilizers, but only pipes with a temperature difference of less than 160°C as a result of this heating test should be used. can be used as a stabilizer for mounting.

In a sense, it is unavoidable that the wall thickness difference (χ) and temperature difference in the bent part will change in various ways when the component values and dimensions differ in the steel composition range and size range mentioned above. However, it is possible to manufacture a steel sheet that satisfies the requirements defined by the present invention as much as possible during the manufacturing process of the steel sheet. This is to accurately understand the relationship between specific component values and the structure of the steel sheet within the above component range using the hot rolling coiling temperature as a variable. One of the preferable m-weave steel sheets is a structure in which the pearlite area ratio exceeds 50% as shown in Test Example 3 above, and the hot-rolling and winding temperature should be set so as to obtain such a structure. It is. According to experiments conducted by the present inventors, when the coiling temperature is lower than around 600°C in the above composition range, a structure with a pearlite area ratio of more than 50% tends to be formed, and in this case, during heating during quenching, Carbides are easily dissolved into austenite, and high quenching hardness can be obtained even at low quenching temperatures, thereby preventing the austenite crystal grains from increasing.

Another preferable steel sheet structure is a ferrite+pearlite structure, which is adjusted by controlling the hot rolling winding temperature to a ferrite+pearlite structure such that the n value of the steel sheet is 0.2 or less. This is because if the n value is 0.2 or more, the wall thickness difference is likely to be 18% or less as shown in Test Example 1 above. According to tests conducted by the present inventors, it has been found that it is preferable for such a composite fiber to have a hot rolling winding temperature higher than around 600°C. In this way, the hot rolling winding temperature is 6
Preferably lower than 00°C and 600″C
There are cases where it is preferable to control the temperature higher than the above, but if a specific component is selected within the above range of component composition, which winding temperature satisfies both the wall thickness difference requirement and the temperature difference requirement. It is only necessary to understand in advance which relationship is most preferable.

In any case, the present invention is the first to clarify that it is important for pipes used in stabilizers to satisfy the above-mentioned requirements (a) and (b) regarding wall thickness difference and temperature difference. Steel that easily satisfies these requirements can be manufactured with moderate predicted values by appropriately adjusting the manufacturing conditions of the steel sheet within the range of the composition.

[Brief explanation of the drawing]

Figure 1 is a perspective view showing the relationship between the shape and installation of a conventional stabilizer, Figure 2 is an axial cross-sectional view of the bent part of the pipe-shaped stabilizer, and Figure 3 is a direction transverse to the axis of the bent part of the pipe-shaped stabilizer. Fig. 4 is a diagram showing the change in wall thickness at the bent part, Fig. 5 is a diagram showing the relationship between the repeated stress and the number of repeated fractures of a pipe with a bent part, and Fig. 6 is a diagram showing the relationship between the repeated stress and the number of times of rupture of a pipe with a bent part. Figure 7 is a diagram showing the relationship between the installation of equipment when a pipe is subjected to an electrical heating test. FIG. 8 is a schematic cross-sectional view showing the condition of a flat pipe test. 1. Stabilizer, 2. Wheels. in... Inside the bent part of the pipe. out...Outside of the bent part of the pipe.

Claims (4)

[Claims] (1) In weight%, 0.10 to 0.35% C, 0
．． 35% or less Si, 0.30-1.20% Mn, 0
．． 10 to 0.60% Cr, Ti contained at a rate of 4 to 10 times the total amount of N% and O% inevitably contained in steel, and 0.0005 to 0.009% Desired stabilizer shape used to manufacture a pipe-shaped stabilizer as a member for imparting driving stability to an automobile, manufactured by electric resistance welding of steel plates B and the remainder consisting of Fe and unavoidable impurities. A raw pipe with an outer diameter of 12 to 65 mm before being molded into
φ, the wall thickness/outer diameter ratio is 6 to 25%, and the length is arbitrary, and when this is bent by 90 degrees with a curvature such that the inner radius is essentially 4 times the outer diameter, , The wall thickness difference (%) calculated by the formula {(maximum wall thickness of bent portion - minimum wall thickness of bent portion)/thickness before bending}×100 is 18.
0% or less, and the pipe is bent 90 degrees with a curvature that makes the inner radius substantially four times the outer diameter (the pipe is straight except for this bend), and the pipe is bent from one end to the other. A raw pipe for use in a stabilizer, which is a pipe that does not generate heat to a temperature of 1110° C. or higher at a bent portion when it is resistively heated to a substantially uniform temperature of 950° C. in a straight portion of the pipe when energized. (2) The raw pipe has an inner radius that is substantially the same as the outer diameter.
With the pipe bent at 90 degrees with a curvature that doubles (the pipe is straight except for this bend), electricity is applied from one end of the pipe to the other, and the temperature of the straight part of the pipe becomes substantially uniform at 950°C. The stabilizer according to claim 1 is a tube in which the austenite crystal grains in the bent portion do not become austenite crystal grains larger than the grain size corresponding to grain size number 6 when resistively heated as described above. Pipe material. (3) Work hardening index (n value) of raw pipe is 0.2 or more
A pipe material used in a stabilizer according to claim 1 or 2, which is a pipe having: (4) The stabilizer according to claim 1, 2, or 3, wherein the steel material is Ca-treated steel during melting, and spherical inclusions are present among the impurities in the steel plate. The raw pipe used.