DE112011100846T5 - Massive stabilizer, steel material for the solid stabilizer and manufacturing process of the solid stabilizer - Google Patents

Abstract

It is an object to provide a steel material for a solid stabilizer having high bendability, high hardenability, and high resistance to cracking, to provide a solid stabilizer having high strength, and a method of producing the solid stabilizer.
The steel material for the solid stabilizer contains, by mass, 0.24 to 0.40% C, 0.15 to 0.40% Si, 0.50 to 1.20% Mn, 0.03% or less P, 0 , 30% or less Cr, 0.01 to 0.03% Ti and 0.0010 to 0.0030% B. The steel material for the solid stabilizer satisfies a condition of a following formula (1). The hardness in a radial center portion of the steel material for the solid post-annealing stabilizer is 400 HV or more, and a martensite ratio in the center radial portion after annealing is 80% or more. 1.24 <(2C + 0.1Si + 0.4Mn + 0.4Cr) × {1 + (1.5B - 300B ² ) × 240} <1.7 (1)

Description

Technical area

The present invention relates to solid stabilizers that provide stability during vehicle travel, solid state stabilizer steel materials, and solid stabilizer manufacturing methods.

State of the art

Stabilizers connect links or wishbones, which are arranged on both sides of a vehicle in the vehicle transverse direction or vehicle width direction. The stabilizers suppress the rolling of the vehicle while the vehicle is running. The stabilizers include solid stabilizers made of a solid steel material and hollow stabilizers made of a hollow steel material. In recent years, hollow stabilizers have been increasingly used to reduce vehicle weight. For example, Patent Document 1 discloses an electric resistance welded steel pipe for a hollow stabilizer, and Patent Document 2 discloses a manufacturing method of a hollow stabilizer.

Documents of the prior art

Patent documents

• [Patent Document 1]: Japanese Patent Application Laid-Open Publication No. 2004-11009 ( JP 2004-11009 A )
• [Patent Document 2]: Japanese Patent Application Laid-open No. 2005-76047 ( JP 2005-76047 A )

Summary of the invention

[Problem to be Solved by the Invention]

However, the desired strength of the solid stabilizers can be more easily ensured compared to the hollow stabilizers. In addition, the massive stabilizers can be produced at a lower cost. Accordingly, despite the growing need for hollow stabilizers, the solid stabilizers are still often used. The two types of stabilizers differ in that one of the two types of stabilizers has a hollow structure and the other has a solid structure or solid structure. Accordingly, the requirements imposed on the steel material or required properties are also different between the two types of stabilizers. The differences in requirements and required properties will be described in detail below.

A manufacturing method of a stabilizer includes a molding step, a quenching step and an annealing step. In the forming step, a steel material is bent into the shape of a stabilizer. Steel materials for hollow stabilizers have a cavity in their radial cross-sectional center portions. Accordingly, the steel materials for hollow stabilizers have substantially little resistance to flexural deformation. Therefore, the steel materials for the hollow stabilizers on a high flexibility or flexibility. On the other hand, the steel materials for solid stabilizers are solid throughout to their radial center sections. Accordingly, the steel materials for the solid stabilizers have substantially high resistance to flexural deformation. Therefore, the steel materials for the solid stabilizers have little bending deformation and a large amount of springback. Therefore, the requirements for springback in the manufacture of solid stabilizers are more stringent compared to the case of producing hollow stabilizers. In addition, a higher strength is required for the solid stabilizers than for the hollow stabilizers, which increases the resilience of the solid stabilizers.

Consequently, springback in the manufacture of hollow stabilizers is not large enough to cause a problem. However, in the manufacture of the solid stabilizers, a material, etc. must also be selected in view of the amount of springback.

In the hardening step, the steel material that has been bent is hardened. The hollow stabilizers have a cavity in their radial center sections. Therefore, it is not necessary for the steel materials for the hollow stabilizers to have high hardenability. On the other hand, the radial center portions of the solid stabilizers are grooved with steel material. Therefore, the steel materials for the solid stabilizers must have a hardenability high enough that the solid materials can be cured to their radial center portions.

The hollow stabilizers have a cavity in their radial center sections. Accordingly, when the hollow stabilizers are suddenly cooled in the hardening step, the difference in the amount of shrinkage (the difference in the cooling rate) between the outer peripheral surface and the inner peripheral surface is small. Therefore, hardening cracks are less likely to occur in the hollow stabilizers. On the other hand, the radial center sections of the solid stabilizers are grooved with the steel material. Accordingly, when the solid stabilizers are rapidly cooled in the hardening step, the difference in the amount of shrinkage (the difference in the cooling rate) between the outer peripheral surface and the radial center portion is large. Therefore, cracking cracks tend to occur in the massive stabilizers. Consequently, the steel materials for the solid stabilizers must be more resistant to cure cracks than the steel materials for the hollow stabilizers. This means that the steel materials for the solid stabilizers require a higher resistance to hardening cracks than for the steel materials for hollow stabilizers.

In addition, as described above, a desired strength of the solid stabilizers can be more easily ensured as compared with the hollow stabilizers. Therefore, the massive stabilizers are often used for vehicles requiring high strength. However, in order to increase the strength, the content of C, etc., which is effective in increasing the strength, must be increased, causing a decrease in flexibility and resistance to cracking. Consequently, the intended properties can not be achieved if the same technique used for the hollow stabilizers is also used for the preparation of the solid stabilizers which have a higher strength than that of the hollow stabilizers.

As described above, the properties required of the steel materials for the hollow stabilizers are completely different from those required for the steel materials for the solid stabilizers. Accordingly, even if the same steel materials are used for the hollow stabilizers as the steel materials for the solid stabilizers, not all the requirements of the properties such as bendability, hardenability and resistance to cracking cracks can be satisfied.

A solid stabilizer, a steel material for the solid stabilizer and a production method for the massive stabilizer according to the present invention were completed in view of the above-mentioned problems. It is an object of the present invention to provide a solid stabilizer which has high strength and does not cause the above-mentioned problems in bendability, hardenability and resistance to cracking during its production, a steel material for the solid stabilizer and a production method for the to provide massive stabilizer.

Means of solving the task

• (1) In order to achieve the above-described object, a solid stabilizer according to the present invention is a solid stabilizer prepared by cold-forming, hardening and annealing a steel material for the solid stabilizer. The massive stabilizer is characterized by containing the steel material for the solid stabilizer, in mass%, 0.24 to 0.40% C, 0.15 to 0.40% Si, 0.50 to 1.20% Mn, 0 , 03% or less P, 0.30% or less Cr, 0.01 to 0.03% Ti, and 0.0010 to 0.0030% B, and satisfies the condition of the following formula (1), wherein the balance of the steel material for the solid stabilizer of Fe and an unavoidable impurity, and wherein the hardness in a radial center portion of the solid stabilizer after annealing is 400 HV or more, and a martensite ratio in the radial center portion of the solid stabilizer after annealing 80 % or more. 1.24 <(2C + 0.1Si + 0.4Mn + 0.4Cr) × {1 + (1.5B - 300B ² ) × 240} <1.7 (1)
• (2) Preferably, in the above configuration of (1), a lower limit of the C content is 0.25%, an upper limit of the Mn content is 1.00%, and a lower limit of the formula (1) is 1, 4th
• (3) Preferably, in the above configuration of (1) or (2), a condition of the following formula (2) is satisfied: (Si / C) <1.5 (2)
• (4) Preferably, in the above configuration according to each of (1) to (3) after the tempering, the tensile strength is 1,200 MPa or more, the 0.2% proof stress is 1,100 MPa or more, and a notched impact strength at room temperature 70 J / cm ² or more. According to this configuration, a solid stabilizer having both high strength and high toughness can be obtained.
• (5) In order to achieve the above object, a steel material for a solid stabilizer is characterized in that the steel material for the massive stabilizer contains, in mass percentage, 0.24 to 0.40% C, 0.15 to 0.40 % Si, 0.50 to 1.20% Mn, 0.03% or less P, 0.30% or less Cr, 0.01 to 0.03% Ti, and 0.0010 to 0.0030% B, and satisfies a condition of the following formula (1), wherein the remainder of the steel material for the solid stabilizer is Fe and an unavoidable impurity, and wherein the steel material for the solid stabilizer is in finish-rolling at a heating temperature of 1,000 C. or less, and the hardness of the steel material for the solid post-rolling stabilizer is 200 HV or less. 1.24 <(2C + 0.1Si + 0.4Mn + 0.4Cr) × {1 + (1.5B - 300B ² ) × 240} <1.7 (1)
• (6) Preferably, in the above configuration of (5), a lower limit of the C content is 0.25%, an upper limit of the Mn content is 1.00%, and a lower limit is the formula (1) 1.4.
• (7) Preferably, in the above-described configuration of (5) or (6), a condition of the following formula (2) is satisfied. (Si / C) <1.5 (2)
• (8) In order to achieve the above-described object, a method for producing a solid stabilizer according to the present invention is characterized by comprising: a forming step of cold bending a steel material for the massive stabilizer containing, in mass percentage, 0.24 to 0.40% C, 0.15 to 0.40% Si, 0.50 to 1.20% Mn, 0.03% or less P, 0.30% or less Cr, 0.01 to 0.03 % Ti, and 0.0010 to 0.0030% B, and which satisfies a condition of the following formula (1), wherein the balance of the steel material for the solid stabilizer is Fe and an unavoidable impurity, and wherein the steel material is for the solid stabilizer in finish-finishing rolling at a heating temperature of 1,000 ° C. or less, and a hardness of the steel material for the solid stabilizer after rolling is 200 HV or less, the method further comprising: a curing step of curing St ahlmaterials for the massive stabilizer after molding; and an annealing step of tempering the steel material for the solid stabilizer after curing. 1.24 <(2C + 0.1Si + 0.4Mn + 0.4Cr) × {1 + (1.5B - 300B ² ) × 240} <1.7 (1)
• (9) Preferably, in the above configuration of (8), a lower limit of the C content is 0.25%, an upper limit of the Mn content is 1.00%, and a lower limit of the formula (1) is 1, 4th
• (10) Preferably, in the above configuration of (8) or (9), a condition of the following formula (2) is satisfied. (Si / C) <1.5 (2)

[Effects of the Invention]

In the solid stabilizer steel material according to the present invention, the constituents thereof are optimized, whereby a performance which satisfies the mechanical properties such as strength, toughness, etc., while ensuring the required hardenability, resistance to cracking and flexibility, can be obtained , The performance level of the steel material for the solid stabilizer according to the present invention is not necessarily obviously higher than that of conventional steels when the bendability, the resistance to cracking and the mechanical properties of the steel material according to the present invention with those from conventional steels individually. While the conventional steels meet the required levels of some of the properties, they do not necessarily meet other properties. In contrast, the most notable feature of the present invention is that an optimal product design has been developed that achieves all the required properties.

Short description of the drawing

1 FIG. 12 is a perspective view of a solid stabilizer according to an embodiment of the present invention. FIG.

Ways of carrying out the invention

An embodiment of a solid stabilizer, a steel material for the solid stabilizer and a production method for the massive stabilizer according to the present invention will be described below.

<Steel material for the massive stabilizer>

[Content of Each Constituent in Steel Material for Massive Stabilizer]

First, the content of each component in the steel material for the massive stabilizer will be described.

(C)

C is a constituent which is essential to ensure strength, which is required as a solid stabilizer after curing and tempering. The C content is 0.24 mass% (hereinafter abbreviated as "%" if necessary) or more for the following reasons. If the C content is less than 0.24%, the strength of the solid stabilizer is lowered, and also the hardenability of a steel material for the solid stabilizer is reduced. For similar reasons, it is preferable that the C content is 0.25% or more. The C content is 0.40% or less for the following reasons. When the C content exceeds 0.40%, the resistance of the steel material to the solid stabilizer against hardening cracks is lowered, and also the toughness after annealing is lowered. In addition, the hardness of the steel material for the solid stabilizer is increased after finish-finishing (before cold-working), and flexibility during cold-forming is reduced.

(Si)

Si acts as a deoxidizer at the time of steelmaking. The Si content is 0.15% or more for the following reasons. When the Si content is less than 0.15%, the hardenability of the steel material for the solid stabilizer is lowered, and the strength of the solid stabilizer is also lowered. The Si content is 0.40% or less for the following reasons. If the Si content exceeds 0.40%, the durability of the steel material for the solid stabilizer is lowered against hardening cracks. Moreover, the hardness of the steel material for the solid stabilizer is increased after finish-rolling (before cold-working), and the flexibility during cold-forming is reduced.

(Mn)

Mn is added to improve the hardenability of the steel material for the solid stabilizer. The Mn content is 0.50% or more for the following reasons. When the Mn content is less than 0.50%, the hardenability of the steel material for the solid stabilizer is lowered, and the strength of the solid stabilizer is also lowered. The Mn content is 1.20% or less for the following reasons. When the Mn content exceeds 1.20%, the durability of the steel material for the solid stabilizer is lowered against hardening cracks. Moreover, the hardness of the steel material for the solid stabilizer is increased after finish-rolling (before cold-working), and the flexibility during cold-forming is reduced. For similar reasons, it is preferable that the Mn content is 1.00% or less.

(P)

It is preferred that the P content is as low as possible. The P content is 0.03% or less for the following reason. When the P content exceeds 0.03%, the toughness after annealing is lowered.

(Cr)

Like Mn, Cr is added to improve the hardenability of the steel material for the solid stabilizer. The Cr content is 0.30% or less for the following reason. When the Cr content exceeds 0.30%, the durability of the steel material for the solid stabilizer is lowered against hardening cracks. Moreover, the hardness of the steel material for the solid stabilizer is increased after finish-rolling (before cold-working), and the flexibility during cold-forming is reduced.

(B)

Like Mn and Cr, B has an effect of improving the hardenability of the steel material for the massive stabilizer. In addition, B has an effect of improving grain boundary strength. The B content is 0.0010% or more for the following reasons. When the B content is less than 0.0010%, the hardenability of the steel material for the solid stabilizer is lowered, and the strength of the solid stabilizer is also lowered. The B content is 0.0030% or less for the following reason. The effects resulting from the addition of B (the effect of improving the hardenability and the effect of improving the strength) gradually become saturated even if the amount of B added is increased. Therefore, the effects saturate when more than 0.0030% B is added. In this respect, in the formula (1) described below, in addition to a linear term for the B content, a quadratic term is also included.

(Ti)

B tends to bond with the N contained in the steel. When B combines with N to produce BN, the effects achieved by the addition of B are not obtained. Accordingly, Ti is added to cause Ti and N to form TiN, thereby ensuring the effects obtained by the addition of B.

The Ti content is 0.01% or more for the following reason. When the Ti content is less than 0.01%, it is difficult to secure the effects obtained by the addition of B. The Ti content is 0.03% or less for the following reason. When the Ti content exceeds 0.03%, coarse TiN tends to be generated, and the toughness is lowered.

In addition to the above-mentioned ingredients, the steel material for the solid stabilizer according to the present invention may also contain, as an impurity, an amount of Al (about 0.040% or less) required for a deoxidation process, which is essential for steelmaking.

[Formula 1)]

Formula (1) will be described below. Formula (1) is an empirical formula obtained by multivariate analysis of experimental data. The hardenability and resistance of the steel material for the solid stabilizer to cure cracks can be optimized by adjusting the content of each ingredient according to formula (1).

The numerical value obtained by substituting the content of each component (the value in%, for example, 0.25 in the case of 0.25%) in formula (1) is higher than 1.24 for the following reasons. When this numerical value is 1.24 or less, the hardenability is not high enough for use as a solid stabilizer, and it is difficult to ensure a martensite ratio of 80% or more continuously up to the radial center portion after curing the strength of the solid stabilizer is reduced. For similar reasons, it is preferable that the numerical value of the formula (1) is higher than 1.4. The numerical value obtained by substituting the content of each component in formula (1) is less than 1.7 for the following reason. If this is numeric When the value is 1.7 or more, there is a possibility that curing cracks can not be completely avoided in the case of producing solid stabilizers which are more susceptible to hardening cracks than hollow stabilizers for the reason described above. Therefore, by using the formula (1), acceptable levels of hardenability and resistance to curing cracks can be secured in the preparation of the solid stabilizers.

[Formula (2)]

Formula (2) will be described below. Formula (2) is an empirical formula obtained by multivariate analysis of experimental data. The surface hardness of the steel material for the solid stabilizer can be optimized by adjusting the contents of Si and C of the formula (2).

The numerical value of formula (2) is less than 1.5 for the following reasons. When this numerical value is 1.5 or more, the content of Si relative to C is relatively large, whereby decarburization tends to appear. That is, the strength of the surface of the solid stabilizer becomes lower compared to the hardness of the inner part of the solid stabilizer. Thus, a reduction in the strength of the surface of the solid stabilizer can be suppressed by using the formula (2).

[Heating temperature, hardness after rolling]

The heating temperature during the finishing rolling is 1,000 ° C or less for the following reason. If the heating temperature is higher than 1,000 ° C, the hardness after rolling is increased, and the cold bendability of the steel material for the solid stabilizer is lowered. In particular, the springback is increased, which increases a variation in shape after bending. The hardness after rolling is 200 HV or less for the following reason. When the hardness after rolling is 200 HV or less, the amount of springback during bending may be reduced to a target value or less.

<The massive stabilizer>

The content of each ingredient, formula (1) and formula (2) of the steel material for the stabilizer as a material for the solid stabilizer are as described above.

1 FIG. 15 is a perspective view of the solid stabilizer according to the embodiment of the present invention. FIG. As in 1 is the overall shape of a massive stabilizer 1 a U-shape. The massive stabilizer 1 includes a torsion section 10 and a pair of arm sections 11 , The torsion section 10 extends in a vehicle transverse direction. The pair of arm sections 11 is at the two axial ends of the Torsionsabschnitts 10 coupled. A pair of rings 12 is near both ends in the vehicle transverse direction of the torsion portion 11 fixed by crimping. A pair of sleeves or sockets 13 is on the outer sides in the vehicle transverse direction of the pair of rings 12 attached. The pods 13 are attached to a vehicle body (not shown). Eye-shaped sections 110 are at the respective distal ends of the pair of arm sections 11 arranged. The pair of eye-shaped sections 110 is each coupled to a handlebar (not shown).

[Hardness after annealing, martensite ratio]

The hardness after annealing and the martensite ratio are determined in the radial center portion for the following reasons. The solid stabilizers must have a structure whose radial center sections are hardened. If the hardenability is not high enough, the solid stabilizers do not have a structure whose radial center portions are hardened, thereby reducing the hardness of the solid stabilizers. Accordingly, when the solid stabilizers have both an acceptable structure and an acceptable hardness in their radial center portions, a martensite ratio of 80% or more can be secured in the portions other than the radial center portion such as the surface.

The hardness in the radial center portion after annealing is 400 HV or more for the following reason. Since the object of the present invention is to ensure the strength which is the same as or higher than that of conventional hollow stabilizers, the hardness is less than 400 HV not high enough to ensure strength. Similarly, the martensite ratio in the radial center portion after annealing is 80% or more for the following reason. If this martensite ratio is less than 80%, the intended strength can not be obtained.

[Tensile strength, 0.2% proof strength, notch toughness]

The tensile strength is 1,200 MPa or more, the 0.2% proof stress is 1,100 MPa or more, and a notched strength at room temperature is 70 J / cm ² or more for the following reason. When the tensile strength, 0.2% proof stress and notched toughness are lower than these lower limits, high strength and high toughness required for solid stabilizers can not be achieved simultaneously.

That is, the massive stabilizers are often used for vehicles that require high strength and high toughness compared to hollow stabilizers. Accordingly, if the tensile strength, 0.2% proof stress and notched toughness are lower than the above lower limits, there is a possibility that the strict requirements for the solid stabilizers can not be satisfied.

<Production method for the massive stabilizer>

The production method of the solid stabilizer includes a molding step, a curing step and an annealing step. In the forming step, the steel material for the solid stabilizer after finish-finishing rolling is subjected to cold bending such that the steel material for the solid stabilizer has a shape of the solid stabilizer to be produced. In the curing step, the steel material for the solid stabilizer is first heated to austenitize the structure of the steel material, and then rapidly cooled to obtain a hard martensite structure. The subsequent annealing step improves the toughness of the steel material for the solid stabilizer.

The content of each constituent in the steel material for the solid stabilizer, the formula (1), the formula (2), the heating temperature during the finish-rolling, and the hardness after the finish-rolling are as described above.

<More>

The embodiment of the solid stabilizer, the steel material for the solid stabilizer, and the production method of the solid stabilizer according to the present invention have been described above. However, the embodiments are not particularly limited to the above embodiment. Various modifications and improvements may be made by those skilled in the art.

For example, although a heating method in the curing step of the solid stabilizer manufacturing method is not particularly limited, furnace heating, electric heating, etc. may be used as the heating method. Although a cooling medium for rapid cooling in the curing step is not particularly limited, water, a polymer solution, etc. may be used as the cooling medium. The temperature patterns of heating and cooling in the curing step and in the tempering step are not particularly limited. Moreover, the bending in the molding step is not particularly limited. For example, cold bending may be performed by using an NC bending device, a bending mold, etc.

[Example 1]

Hereinafter, the evaluation tests for the resistance to cracking, the cold bendability, the strength, the durability, and the toughness performed on the stabilizers and the steel materials for the stabilizers will be described.

<Production Method of Examples>

First, a production method of samples (stabilizers of Examples 1 to 8 and Comparative Examples 1 to 7, 9 to 13) will be described. The manufacturing process for the samples includes one Hot forging step, a forming step, a hardening step, an annealing step and a finishing step.

In the hot forging step, a steel material was first cut to a predetermined length. Then, both axial ends of the cut steel material were heated and hot forged, and holes were formed therein. As it is in 1 has been shown, the pair of eye sections or eye-shaped sections 110 formed at both axial ends of the steel material in this way.

In the forming step, the steel material was subjected to cold bending. In particular, the steel material was bent into a U-shape. As it is in 1 has been shown, the Torsionsabschnitt 10 and the pair of arm sections 11 formed in this way.

In the hardening step, the pair of eye-shaped sections 110 initially clamped in steel material. Then there was a current between the pair of eye-shaped sections 110 applied to heat the steel material to a curing temperature of 970 ° C. Thereafter, the steel material was rapidly cooled with water.

In the tempering step, the steel material was reheated and slowly cooled. The highest heating temperature (tempering temperature) was set so as to attain a target hardness of 420 HV in the radial center portion of the steel material after annealing. However, the hardness in Comparative Example 10 described below increased to only 320 HV in the curing step. Accordingly, it was found that it would be impossible to set the hardness to 420 HV in the annealing step. Since there was a possibility that the annealing could further reduce the hardness and thus increase the difference between the actual hardness and the target value, tempering in Comparative Example 10 was not performed. In Example 7, a painting step which comprises heating the steel material was also performed as the annealing step. The painting temperature, namely the tempering temperature, was 200 ° C.

In the post-processing step, the shape of the steel material was first finely adjusted, and then the surface of the steel material was subjected to shot peening or shot peening. Thereafter, the surface of the steel material was painted. Finally, as it was in 1 Shown is the pair of rings 12 by crimping to the torsion section 10 attached. The samples were prepared in this way.

Comparative Example 8 is a sample used to evaluate the difference in the possibility of curing cracks between the hollow stabilizers and the solid stabilizers. For Comparative Example 8, only the resistance to the curing cracks was evaluated. An evaluation method will be described below.

<Compositions of the samples>

The compositions of the samples are described below. Table 1 shows data on ingredients, production conditions, evaluation items (resistance to curing cracks, cold bendability, strength, durability and toughness) of Examples 1 to 8 and Comparative Examples 1 to 13.

In the table, the numerical values marked with the symbol "*" indicate that they are outside the ranges for numerical values of the constituents and properties defined in the claims. The numerical values marked with the symbol "#" mean that the assigned properties, although not defined by the claims, have a very unfavorable value.

[Table 1]

The characteristics of Examples 1 to 8 and Comparative Examples 1 to 13 will be briefly described below. Examples 1 to 8 are massive stabilizers according to the present invention. In Comparative Example 1, the C content is higher than the upper limit of the range of the composition according to the present invention. In Comparative Example 2, the Cr content is higher than the upper limit of the range of the composition according to the present invention, and the numerical value of the formula (1) is larger than the upper limit of the range of the composition according to the present invention. In Comparative Example 3, the Si content is higher than the upper limit of the range of the composition according to the present invention. In Comparative Example 4, the numerical value of the formula (1) is larger than the upper limit of the range of the composition according to the present invention. In Comparative Example 5, the Ti content is higher than the upper limit of the range of the composition according to the present invention. In Comparative Example 6, the numerical value of the formula (1) is less than the lower limit of the range of the composition according to the present invention. Comparative Example 6 is a solid stabilizer made using the same material as the steel material conventionally used generally for solid stabilizers. In Comparative Example 7, the Mn content is higher than the upper limit of the range of the composition according to the present invention, and the numerical value of the formula (1) is larger than the upper limit of the range of the composition according to the present invention. Comparative Example 7 is a solid stabilizer formed of the same steel material as that of a base steel pipe C in Table 1 of Patent Document 2. That is, substantially the same steel material as that described in Patent Document 2 as a solid material was produced Stabilizer is disclosed, and the massive stabilizer was made of this steel material. Comparative Example 8 will be described below. In Comparative Example 9, the C content is less than the lower limit of the range of the composition according to the present invention, and the numerical value of the formula (2) is larger than the upper limit of the range of the composition according to the present invention. In Comparative Example 10, the contents of Ti and B are lower than their respective lower limits of the range of the composition according to the present invention, and the numerical value of the formula (1) is less than the lower limit of the range of the composition of the present invention. Comparative Example 10 is a solid stabilizer formed of a steel material having a JIS carbon steel S33C equivalent. In Comparative Example 11, the C and Cr contents are higher than their respective upper limits for the range of the composition according to the present invention, and the contents of Ti and B are lower than their respective lower limits for the range of the composition according to the present invention Invention, and the numerical value of the formula (1) is greater than the upper limit of the range of the composition according to the present invention. Comparative Example 11 is a solid stabilizer which is formed of a steel material which has a JIS spring steel SUP9 equivalent. Comparative Example 12 is a solid stabilizer formed of the same steel material as that of Example 1. The heating temperature during the finish rolling of the steel material is higher than the upper limit of the present invention. Comparative Example 13 is a solid stabilizer formed of the same steel material as that of Example 3. The heating temperature during the finish rolling of the steel material is higher than the upper limit of the present invention.

Although not shown in Table 1, all of the steel materials used for the examples are deoxidized steel materials and therefore contain a small amount (0.010 to 0.035%) of Al. Although not shown in Table 1, all steel materials used for the examples contain 0.03% or less of P.

<Evaluation items and evaluation procedures>

The evaluation items and the evaluation method will be described below with reference to Table 1. For Comparative Example 8, only the resistance to cracking cracks was evaluated.

[Resistance to hardening cracks]

Resistance to creep cracking was evaluated by using thirty test pieces (which had a diameter of 26 mm and a length of 100 mm, and a V-shaped notch or a 1-mm depth cut), which consisted of a steel material have been cut out after finishing rolling. That is, thirty test pieces were used per sample. Thirty test pieces each having a diameter of 26 mm and a length of 100 mm, a V-shaped notch having a depth of 1 mm and a thickness of 4 mm in the radial direction were used for Comparative Example 8.

The thirty test pieces were first held at a curing temperature of 970 ° C for 30 minutes and then cooled with water. After cooling with water, the test pieces were examined. The symbol "×" represents the case where hardening cracks have been observed in at least one of the thirty test pieces, and the symbol "o" represents the case where no hardening cracks have been observed in any of the thirty test pieces.

The V-shaped notch was formed in the test pieces for the following reason. Basically, cracking cracks are unacceptable, even if they occur only in some of the mass-produced products and tend to occur infrequently. Therefore, in the case where a small number of test pieces are used, no difference between them may occur. In addition, in many cases actual cracking cracks due to cracks, such as small cuts, occur. Therefore, it is necessary that no hardening crack occurs in the products, even if they have such a breakage.

[Cold bending properties]

(Hardness after rolling)

The hardness of the steel material after rolling was determined by the Vickers hardness ( JIS Z 2244 HV 10 ) of the test pieces cut from the steel materials after finish-finishing rolling.

(Spring back)

The cold bendability was evaluated by the springback. This is because a variation in shape after bending increases as the springback increases, as described above.

The springback was made by using a ratio (actual angle / design angle) of an actual angle between the torsion portion 10 and the arm section 11 after actually bending to a rotation angle of a bending head of an NC bending apparatus (a planned angle between the torsion portion 10 and the arm section 11 ) when a bending operation of the steel material is performed.

In particular, the amount of springback in the case where a solid stabilizer has been produced using Comparative Example 6, which is a typical example of conventionally used steel material for hollow stabilizers, has been defined as R01, and the amount of springback of Comparative Example 11, which is the most average ingredient of the conventionally used JIS spring steel SUP9 is defined as R02. The mean value of R01 and R02 is defined as R0. The amount of springback of each sample is defined as R1. The ratio of R1 to R0, R1 / R0, is shown in Table 1.

As described above, a variation after bending increases as springback increases. Therefore, a target value of this variation was set to 1.0 or less, and the evaluation of the springback was performed based on this target value. This is because it is known from earlier actual manufacturing data that the variation to an acceptable level or less in the bending process during the production of the solid stabilizers can be suppressed when the amount of springback is at most about the average of the amount of springback of the steel material for hollow stabilizers, such as Comparative Example 6, and the amount of springback of the JIS spring steel SUP9 , as for example Comparative Example 11, can be reduced.

[Strength]

(Surface hardness)

The surface hardness of the stabilizer was determined by the Vickers hardness ( JIS Z 2244 HV 10 ) of the test pieces cut from the stabilizers.

(Hardness)

The hardness of the stabilizer was determined by the Vickers hardness ( JIS Z 2244 HV 10 ) of the test pieces cut from the stabilizers.

(Martensite) ratio

The martensite ratio was evaluated by examining the structures of the center radial portions of the test pieces cut from the stabilizers with an optical microscope (400 ×).

(0.2% proof stress)

As with the tensile strength described below, a tensile test ( JIS Z 2241 ) with the test pieces ( No. 14A test pieces, JIS Z 2201 ), which had been cut from the stabilizers, and the 0.2% proof stress was evaluated by the stress, which caused 0.2% of the load on removal of the load.

(Tensile strenght)

The tensile strength was determined by performing a tensile test ( JIS Z 2241 ) with the test pieces ( No. 14A test pieces, JIS Z 2201 ), which have been cut from the stabilizers, evaluated.

[Durability]

Durability was evaluated by a durability test applied to the stabilizers. As it is in 1 is shown, the stabilizer 1 a diameter of 26 mm. The distance between the pair of sleeves 13 is 490 mm. The distance between the pair of eye-shaped sections 110 is 820 mm.

The durability test was the pair of sleeves 13 initially attached to a tensioning device (not shown). Then the pair of eye-shaped sections 110 alternately vibrated in the opposite vertical directions. The vibration frequency was 2 Hz. The vibration swing (between the bottom dead center and the top dead center) was 70 mm. Durability was evaluated by the number of cycles until the stabilizer broke.

[Toughness]

Toughness was measured by performing a Charpy impact test ( JIS Z 2242 ) at 20 ° C with the test pieces ( JIS No. 3, 2 mm test pieces with U notch ) cut from the stabilizers were evaluated.

<Test results>

The test results will be described below with reference to Table 1. According to Examples 1 to 8, satisfactory evaluation results were achieved for all the evaluation items in both the steel materials and the stabilizers.

In contrast, according to Comparative Examples 1 to 13, satisfactory evaluation results were achieved in some of the evaluation items but not in all of the evaluation items. This will be briefly described below. The cold bendability was low in Comparative Example 1. The toughness was also low in Comparative Example 1. In Comparative Example 2, hardening cracks occurred. The cold bendability was low in Comparative Example 3. In Comparative Example 4, cracking cracks occurred. The springback was large in Comparative Example 5. In addition, the toughness of Comparative Example 5 was low. The martensite ratio was low in Comparative Example 6. The 0.2% proof strength and the durability were also low in Comparative Example 6. In Comparative Example 7, cracking cracks occurred. Moreover, in Comparative Example 7, the hardness after rolling was high and the cold bendability was low. The 0.2% proof strength was low in Comparative Example 9. The durability was also low in Comparative Example 9. The strength (hardness, martensite ratio, 0.2% proof stress and tensile strength) was low in Comparative Example 10. Durability and toughness were also low in Comparative Example 10. at Comparative Example 11, the hardness after rolling was high, and the cold bendability was low. Moreover, in Comparative Example 11, the toughness was low. In Comparative Example 12, the hardness after rolling was high and the cold bendability was low. In Comparative Example 13, the hardness after rolling was high and the cold bendability was low.

From Comparative Examples 1 to 13, Comparative Example 6 is a solid stabilizer made using the steel material used for hollow stabilizers. This shows that satisfactory evaluation results are not obtained for each evaluation subject, even if the same steel material is used for hollow stabilizers as for solid stabilizers.

A hollow test piece using the same steel material as that of Comparative Example 7 was prepared to evaluate the resistance of Comparative Example 8 to curing cracks. According to the evaluation result, hardening cracks occurred in the massive Comparative Example 7, while no hardening cracks occurred in the hollow Comparative Example 8. This shows that, in the case of using the same steel material, cracking cracks can occur in solid stabilizers even if no hardening cracks occur in hollow stabilizers. In the present invention, the ingredients were also designed in view of the fact that curing cracks are more likely to occur in the solid stabilizers than in the hollow stabilizers as described above. Therefore, the present invention is designed such that no curing cracks occur while satisfying the strength properties as described above. The effect of the present invention is extremely significant in the preparation of massive stabilizers.

[Description of reference numbers]

• 1 : massive stabilizer, 10 : Torsion section, 11 : Arm section, 12 : Ring, 13 : Sleeve, 110 : eye-shaped section

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• JP 2004-11009A [0003]
• JP 2005-76047 A [0003]

Cited non-patent literature

• JIS carbon steel S33C [0050]
• JIS spring steel SUP9 [0050]
• JIS Z 2244 HV 10 [0056]
• JIS spring steel material SUP9 [0059]
• JIS spring steel material SUP9 [0060]
• JIS Z 2244 HV 10 [0061]
• JIS Z 2244 HV 10 [0062]
• JIS Z 2241 [0064]
• No. 14A test pieces, JIS Z 2201 [0064]
• JIS Z 2241 [0065]
• No. 14A test pieces, JIS Z 2201 [0065]
• JIS Z 2242 [0068]
• JIS No. 3, 2 mm test pieces with U notch [0068]

Claims (10)

A solid stabilizer made by cold forming, curing and annealing a steel material for the solid stabilizer, the solid stabilizer being characterized in that the steel material for the solid stabilizer contains, by mass, 0.24 to 0.40% C, 0.15 to 0.40% Si, 0.50 to 1.20% Mn, 0.03% or less P, 0.30% or less Cr, 0.01 to 0.03% Ti, and 0.0010 to 0, 0030% B, and satisfies a condition of the following formula (1), the remainder of the steel material for the solid stabilizer is Fe and an unavoidable impurity, and a hardness in a radial center portion of the solid stabilizer after annealing is 400 HV or more and a martensite ratio in the radial center portion of the solid stabilizer after annealing is 80% or more. 1.24 <(2C + 0.1Si + 0.4Mn + 0.4Cr) × {1 + (1.5B - 300B ² ) × 240} <1.7 (1) A massive stabilizer according to claim 1, characterized in that a lower limit of the C content is 0.25%, an upper limit of the Mn content is 1.00%, and a lower limit of the formula (1) is 1.4. Massive stabilizer according to claim 1 or 2, characterized in that a condition of a following formula (2) is satisfied. (Si / C) <1.5 (2) A massive stabilizer according to any one of claims 1 to 3, characterized in that after annealing, the tensile strength is 1,200 MPa or more, the 0.2% proof stress is 1,100 MPa or more, and a notched strength at room temperature is 70 J / cm ² or more. A steel material for a solid stabilizer containing, by mass, 0.24 to 0.40% C, 0.15 to 0.40% Si, 0.50 to 1.20% Mn, 0.03% or less P , 0.30% or less of Cr, 0.01 to 0.03% of Ti, and 0.0010 to 0.0030% of B, and which satisfies a condition of the following formula (1), wherein the balance of the steel material for the solid Stabilizer is formed of Fe and an unavoidable impurity, and in the finishing rolling, the steel material for the solid stabilizer is rolled at a heating temperature of 1,000 ° C or less, and a hardness of the steel material for the solid stabilizer after rolling is 200 HV or less , 1.24 <(2C + 0.1Si + 0.4Mn + 0.4Cr) × {1 + (1.5B - 300B ² ) × 240} <1.7 (1) A steel material for the massive stabilizer according to claim 5, characterized in that a lower limit of the C content is 0.25%, an upper limit of the Mn content is 1.00%, and a lower limit of the formula (1) 1, 4 is. A steel material for the solid stabilizer according to claim 5 or 6, characterized in that a condition of the following formula (2) is satisfied. (Si / C) <1.5 (2) A method for producing a solid stabilizer, comprising: a forming step of cold bending a steel material for the massive stabilizer containing, in mass%, 0.24 to 0.40% C, 0.15 to 0.40% Si, 0.50 to 1.20% Mn, 0.03% or less P, 0.30% or less Cr, 0.01 to 0.03% Ti, and 0.0010 to 0.0030% B, and which is a condition of a following formula (1) wherein the remainder of the steel material for the solid stabilizer is formed of Fe and an unavoidable impurity, and in the finishing rolling, the steel material for the solid stabilizer is rolled at a heating temperature of 1,000 ° C or less, and a hardness of The steel material for the solid post-rolling stabilizer 200 is HV or less, the method further comprising: a hardening step of hardening the steel material for the solid stabilizer after molding; and an annealing step of tempering the steel material for the solid stabilizer after curing. 1.24 <(2C + 0.1Si + 0.4Mn + 0.4Cr) × {1 + (1.5B - 300B ² ) × 240} <1.7 (1) A method for producing the massive stabilizer according to claim 8, characterized in that a lower limit of the C content is 0.25%, an upper limit of the Mn content is 1.00%, and a lower limit of the formula (1) is 1 , 4 is. A method for producing the solid stabilizer according to claim 8 or 9, characterized in that a condition of the following formula (2) is satisfied. (Si / C) <1.5 (2)

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