JP2006089785A - High-strength steel with excellent toughness for stabilizer, and method for manufacturing stabilizer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide high-strength steel having excellent toughness at ordinary and low temperatures in an as-water-quenched state and used for a stabilizer and also to provide a method for manufacturing a stabilizer. <P>SOLUTION: The steel has a composition which consists of, by mass, 0.05 to 0.20% C, ≤0.60% Si, 0.30 to 1.50% Mn, 0.05 to 0.80% Cr, 0.005 to 0.065% Al and the balance Fe with inevitable impurities and in which 0.0005 to 0.0050% B is added if necessary and, in that case, one or more kinds among 0.005 to 0.050% Ti, 0.005 to 0.050% V and 0.005 to 0.050% Nb are further added. After the steel is subjected to bar rolling at 900 to 1,100°C finish rolling temperature and then to cold forming into a stabilizer shape, the resultant stabilizer is reheated preferably to Ac<SB>3</SB>+50 to Ac<SB>3</SB>+100°C and used in the as-water-quenched state. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a steel for a high strength stabilizer and a method for producing the stabilizer, and more particularly to a steel having excellent room temperature and low temperature toughness as it is water-quenched.

  Stabilizers are important safety parts on the suspension mechanism that reduce the number of rolls when turning a car and improve ride comfort and running stability.

  Since the stabilizer suppresses the inclination of the vehicle body by a spring action, the steel used as the material is required to have sufficient strength and durability.

  Conventionally, a stabilizer is made of hot-rolled steel such as carbon steel such as S48C or spring steel such as SUP9 to a predetermined size, and then hot-forged and bent, and after forming, it is subjected to oil quenching and tempering to obtain a predetermined strength. However, recently, in order to reduce costs, it has been strongly demanded that heat treatment be omitted to improve productivity and rationalization.

Patent Document 1 has a high strength of 120 to 150 kgf / mm ² as it is hot-rolled without performing strong processing or quenching and tempering after hot rolling, and has excellent toughness and can be cold-bended. For non-tempered rolled linear steel or bar steel that can be processed into springs, stabilizers, etc., 0.13-0.35% C-0.1-1.8% Si-0.8-1.8% A steel having a component composition in which Nb, Ti, and B are added to Cr is described.

  Patent Document 2 relates to a non-tempered high strength steel material having a strength of 1150 MPa or more and good cold workability. In order to obtain a desired strength in a non-tempered state as it is hot-rolled, V is the main element. It is described that a steel having a composition added in combination with the precipitation hardening element is cooled at an appropriate cooling rate after hot rolling at a low temperature to obtain a steel material for a buffer / restoration mechanism member such as a stabilizer.

JP-A-11-323495 JP 2000-17390 A

  Recently, in addition to cost reduction, the industrial world has been demanded to reduce the burden on the global environment at the manufacturing site in order to raise awareness of global environmental problems.

  In the case of stabilizers, quenching and tempering by oil quenching is required after hot forming depending on the component composition of the material, but the treatment of oil waste liquid is a burden on the global environment, so the process avoids the use of oil. It is hoped that.

  In addition, when using automobiles, it is necessary to ensure safety in the global environment. For stabilizers that are important safety components, it is important to ensure not only toughness at normal temperature but also low temperature toughness in cold regions.

In the present invention, the water quenching without tempering after water quenching is performed, and the tensile strength and the room temperature toughness of ₈₀₀ N / mm ² are _2U E ₂₀ : 200 J / cm ² or more, and the low temperature toughness is _2U E _-100 : 100 J / cm ^2. It aims at providing the steel for stabilizers which has the above outstanding toughness, and the manufacturing method of a stabilizer.

  As a result of intensive research from the above-mentioned viewpoints, the present inventors have made the component composition low or low C-high Mn-Cr, or low C-high Mn-Cr-B, one or two of Ti, V, and Nb. When the above is added, cold bending can be performed as it is rolled, and after water quenching, mechanical properties equivalent to those obtained by oil quenching and tempering of carbon steel such as S48C can be obtained, particularly excellent in low temperature toughness. I found out.

The present invention has been made on the basis of the above findings and further studies, that is, the present invention,
1% by mass C: 0.05-0.20%, Si: 0.60% or less, Mn: 0.30-1.50%, Cr: 0.05-0.80%, Al: 0.005 High-strength stabilizer that consists of ~ 0.065%, the balance Fe and inevitable impurities, is rolled with a steel bar at a finishing rolling temperature of 900 to 1100 ° C, and has excellent toughness as it is after quenching into reheated water after cold forming Steel.
2% by mass C: 0.05-0.20%, Si: 0.60% or less, Mn: 0.30-1.50%, Cr: 0.05-0.80%, B: 0.0005 ~ 0.0050%, Al: 0.005 to 0.065%, Ti: 0.005 to 0.050%, V: 0.005 to 0.050%, Nb: 0.005 to 0.050% One or more of the above, the balance Fe and unavoidable impurities, rolled steel bar at a finishing rolling temperature of 900-1100 ℃, high strength to obtain excellent toughness as it is quenched in reheated water after cold forming into a stabilizer shape Steel for stabilizers.
3. A steel having a component composition described in 1 or 2 is rolled at a finish rolling temperature of 900 to 1100 ° C., cold formed into a stabilizer shape, reheated to Ac ₃ +50 to Ac ₃ + 100 ° C., and then water-quenched. A high strength stabilizer with excellent toughness.

According to the present invention, after forming into a stabilizer shape by cold working, a steel for stabilizers having excellent room temperature and low temperature toughness with TS800 N / mm ² grade, with a reheated water quenching, and a method for producing a stabilizer can be obtained. Very useful for environment and industry.

  The reason for limiting the components in the present invention will be described.

C
C is effective in increasing the strength of the steel, and is set to at least 0.05% or more in order to ensure a tensile strength of 800 N / mm ² after water quenching. On the other hand, if added over 0.20%, the bending workability to obtain a stabilizer shape is inferior, and the toughness is also reduced, so 0.05 to 0.20%.

Si
Si is necessary for deoxidation at the time of melting, and is effective for enhancing the solid solution strengthening of the base and improving the sag resistance as a spring, so 0.60% is added as the upper limit.

Mn
Mn works with Si as a deoxidizer during melting and is added in an amount of 0.30% or more in order to improve the hardenability of the steel. On the other hand, if added over 1.50%, segregation increases, bending workability and toughness deteriorate, so 0.30 to 1.50%.

Cr
Cr, like Mn, improves hardenability and is effective in preventing decarburization, so 0.05% or more. On the other hand, if added over 0.80%, segregation increases and bending workability and toughness deteriorate, so 0.05 to 0.80%.

Al
Al is made 0.005% or more in order to make the base material a fine structure and improve toughness. On the other hand, if added over 0.065%, oxide inclusions increase and the toughness decreases, so 0.005 to 0.065%.

  The present invention has the above component composition, steel bars are rolled at a finish rolling temperature of 900 to 1100 ° C., and after cold forming into a stabilizer shape, high strength and excellent low temperature toughness can be obtained with reheating water quenching. In the case of improving, B can be added, and further one or more of Ti, V and Nb can be added.

B
B is very small and improves hardenability and improves strength and toughness. Therefore, when B is added, the content is made 0.0005 to 0.0050%.

Ti, V, Nb
All of these elements refine crystal grains and precipitate carbonitride to improve toughness and strength. Therefore, when added, Ti: 0.005 to 0.050%, V: 0.005 to 0.005. One or two or more of 050% and Nb: 0.005 to 0.050% are added.

  When the steel having the above-described component composition is rolled into a steel bar, the finish rolling temperature is 900 to 1100 ° C. When it is lower than 900 ° C., the hot deformation resistance is large, and the life of the rolling mill is reduced. On the other hand, if it exceeds 1100 ° C., fine hot cracks and the like are generated during rolling, and since it becomes coarse particles, when cold forming into a stabilizer shape, a shape defect occurs, so the finish rolling temperature is set to 900 to 1100 ° C.

The heating temperature at the time of water quenching should be not less than a temperature at which carbide is sufficiently dissolved and not more than a temperature at which toughness does not decrease due to coarsening of austenite crystal grains. In the case of a stabilizer, Ac ₃ + 50 ° C. or more, Ac ₃ + 100 ° C. The following.

When manufacturing a stabilizer using the steel of the present invention, a steel bar rolled material having a finish rolling temperature of 900 to 1100 ° C. is cold-formed into a stabilizer shape, reheated to Ac ₃ + 50 ° C. or higher and Ac ₃ + 100 ° C. or lower and then water-quenched The stabilizer of 800 N / mm ² class tensile strength and room temperature toughness of _2U E ₂₀ : 200 J / cm ² or more and low temperature toughness of _2U E _-100 : 100 J / cm ² or more with water quenching without tempering Is obtained.

  A 160 mm square billet was rolled from a bloom obtained by melting and continuously casting steel having the composition shown in Table 1 and rolled to a diameter of 22 mm to obtain a test material. The composition of the test material is steel No. 1-20 within the scope of the present invention, Steel No. 21 to 32 were out of the scope of the present invention. Steel No. 33 is the component composition of S48C of current steel.

These specimens were cold formed into a stabilizer shape, then reheated and quenched, and subjected to a tensile test and an impact test. Table 2 shows the finish rolling temperature in bar rolling, the heating temperature for reheating and quenching, and the Ac ₃ transformation point measured with an automatic transformation point measuring device. Reheating quenching was performed by water quenching after heating to a predetermined temperature and holding for 60 minutes.

  In Table 2, steels having a component composition within the range of the present invention were rolled into a steel bar at a finish rolling temperature of 900 to 1100 ° C., which was within the range of the present invention, and then reheated and water-quenched were used as Examples 1 to 80 of the present invention. Comparative examples 1 to 28 were used in which the composition or the steel bar finishing rolling temperature deviated from the scope of the present invention.

  In Comparative Examples 1 to 16, the component composition is within the range of the present invention but the steel bar finish rolling temperature is outside the range of the present invention. In Comparative Examples 17 to 28, the component composition is outside the range of the present invention and the bar steel finish rolling temperature is It is a test material within the scope of the present invention.

  Table 3 shows the tensile test results and impact test results. In the tensile test, 0.2% yield strength, tensile strength, elongation, and drawing were determined. In the impact test, a 2 mm U notched impact test piece was used, and the impact value at a test temperature of 20 ° C. and −100 ° C. was obtained. Three tests were performed at each test temperature, and the average value was listed in the table.

In Examples 1 to 80 of the present invention, the tensile strength (TS) is 802 (Example 73) to 988 N / mm ² (Example 4), and the impact value at 20 ° C. is 200 (Example 13) to 278 J / cm. ² (Example 68), impact values at −100 ° C. of 100 (Example 3) to 193 J / cm ² (Example 42) were obtained.

On the other hand, in Comparative Examples 1 to 28, with respect to the target properties of 800 N / mm ² class tensile strength and room temperature toughness of _2U E ₂₀ : 200 J / cm ² or more and low temperature toughness of _2U E _-100 : 100 J / cm ² or more. Comparative Examples 1 and 3 have low tensile strength, room temperature toughness, and low temperature toughness, Comparative Examples 17 and 21 have low tensile strength, and other comparative examples have low room temperature toughness and low temperature toughness.

In the examples of the present invention, the reheating water quenching temperature was set to Ac ₃ +50 to Ac ₃ + 100 ° C. (Examples 1 to 80 to Examples 3, 4, 13, 14, 23, 24, 27) , 34, 41, 48, 60, 67, 73, and 74), it was confirmed that the toughness at −100 ° C. was particularly excellent.

From the above test results, when the steel bar having the component composition of claims 1 and 2 and rolled with a steel bar at a finish rolling temperature of 900 to 1100 ° C. is cold-formed into a stabilizer shape and then reheated with water quenching, High strength and excellent low temperature toughness were obtained, and it was confirmed that particularly excellent low temperature toughness was obtained when the reheating quenching temperature was set to Ac ₃ +50 to Ac ₃ + 100 ° C.

The stabilizer obtained in the present invention, the tensile strength of 800N / mm ² class of clear evaluation criteria 100,000 times as a stabilizer in the endurance test of the stress amplitude ± 397N / mm ² to be used in the normal test, defects such as cracks or damage It was confirmed that no fatigue occurred and the tire had good fatigue characteristics.

The impact value at −100 ° C. of the stabilizer using the current steel S48C was 16 J / cm ² , which was significantly inferior to the examples of the present invention.

Claims (3)

In mass% C: 0.05 to 0.20%,
Si: 0.60% or less,
Mn: 0.30 to 1.50%,
Cr: 0.05 to 0.80%,
Al: 0.005 to 0.065%,
The balance Fe and inevitable impurities,
Steel for high-strength stabilizers that can be rolled with steel at a finish rolling temperature of 900 to 1100 ° C. to obtain excellent toughness after quenching in a reheated water after cold forming into a stabilizer shape. In mass% C: 0.05 to 0.20%,
Si: 0.60% or less,
Mn: 0.30 to 1.50%,
Cr: 0.05 to 0.80%,
B: 0.0005 to 0.0050%,
Al: 0.005 to 0.065%,
Furthermore, Ti: 0.005 to 0.050%,
V: 0.005 to 0.050%,
Nb: 0.005 to 0.050% of one or more,
The balance Fe and inevitable impurities,
Steel for high-strength stabilizers that can be rolled with steel at a finish rolling temperature of 900 to 1100 ° C. to obtain excellent toughness after quenching in a reheated water after cold forming into a stabilizer shape. A steel having a composition according to claim 1 or 2 is rolled at a finish rolling temperature of 900 to 1100 ° C, cold-formed into a stabilizer shape, reheated to Ac ₃ +50 to Ac ₃ + 100 ° C, and then water-quenched. A method for producing a high strength stabilizer with excellent toughness.