JP2007332414A - High strength wide steel sheet pile and its production method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high strength wide steel sheet pile having an effective width of ≥500 nm and a yield point of ≥390 N/mm<SP>2</SP>which can be produced without degrading a productivity. <P>SOLUTION: A steel stock having a componential composition comprising, by mass, 0.01 to 0.20% C, 0.05 to 1.0% Si, 0.1 to 2.0% Mn, ≤0.030% P, ≤0.030% S and 0.3 to 2.0% Al, and the balance Fe with inevitable impurities, and in which C and Al satisfy inequality (1) of Al≥1.3×C+0.3; wherein, C and Al satisfy the composition (mass%) of each element is heated at 1,200 to 1,350°C, is thereafter hot-rolled at ≥850°C, is further subjected to joint forming/rolling at 600 to 800°C, and is allowed to cool, so as to obtain the high strength wide steel sheet pile. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to a steel sheet pile for use in use mainly in the fields of civil engineering and construction, in particular, the effective width of 500mm or more, yield point 390 N / mm ² or more, a tensile strength of 540N / mm ² or more, at 0 ℃ The present invention relates to a high-strength wide steel sheet pile with Charpy absorbed energy of 43 J or more and a method for producing the same.

  The steel sheet pile is an indispensable member in harbors, rivers, road revetments, earth retaining works, architectural foundation works, and the like. This steel sheet pile is usually manufactured by hot rolling. JIS A 5528 defines “hot rolled steel sheet pile” and JIS A 5523 defines “hot rolled steel sheet pile for welding”. .

  Such steel sheet piles tend to be expanded from 400 mm to 500 mm and 600 mm in order from the viewpoint of improving the efficiency of construction. In recent years, ultra-wide steel sheet piles having an effective width of 900 mm have been developed. Yes.

However, the widening of the steel sheet pile as described above necessarily involves an increase in the rolling width, so that the hot rolling load (rolling load) increases and the formability of the joint portion (claw portion) decreases and the steel This leads to a decrease in productivity, such as an increase in the off-line correction rate due to a decrease in the dimensional accuracy of the sheet pile. In particular, at yield as SY390 and SYW390 in JIS standards 390 N / mm ² or more, the tensile strength of 540N / mm ² or more sheet pile, normally, Nb and V, microalloying such as Ti is added For this reason (for example, see Patent Document 1), as compared with low strength SY295 and SYW295, an increase in rolling load due to an increase in hot deformation resistance becomes remarkable, and a reduction in productivity becomes remarkable.
Japanese Patent Laid-Open No. 10-001721

Accordingly, an object of the present invention is to propose a high-strength wide steel sheet pile having an effective width of 500 mm or more and a yield point of 390 N / mm ² or more, which can be manufactured without impairing productivity, and an advantageous manufacturing method thereof. There is to do.

The inventors produce a high-strength and wide steel sheet pile without impairing productivity. Specifically, while suppressing an increase in deformation resistance in hot rolling and reducing the rolling load, The production of a high strength wide steel sheet pile with a yield point of 390 N / mm ² or more and an effective width of 500 mm or more was repeated. As a result, by adding an appropriate amount of Al to the steel material, a ferrite phase is generated in a part of the steel structure in a high temperature range where hot rolling is performed, and the deformation resistance is increased at 1000 ° C. or less, and hence the rolling load. As a result, it was found that the target strength (yield point) of 390 N / mm ² or more can be secured by the solid solution strengthening of Al, and the present invention was completed.

That is, the present invention is C: 0.01-0.20 mass%, Si: 0.05-1.0 mass%, Mn: 0.1-2.0 mass%, P: 0.030 mass% or less, S: 0 0.030 mass% or less, Al: 0.3 to 2.0 mass%, the balance is made of Fe and inevitable impurities, and C and Al are represented by the following formula (1);
Al ≧ 1.3 × C + 0.3 (1)
However, C and Al content of each element (mass%)
It is a high-strength wide steel sheet pile having a composition that satisfies the above.

The present invention is characterized in that the effective width is 500 mm or more and the yield point is 390 N / mm ² or more.

Moreover, in addition to the said component composition, this invention contains the component of at least 1 group from the following A group to C group further.
Group A; Cu: 1.0 mass% or less, Ni: 2.0 mass% or less, Cr: 1.0 mass% or less and Mo: 0.5 mass% or less, Group B: V or more : 0.2 mass% or less, Nb: 0.2 mass% or less and Ti: 0.03 mass% or less selected from one or more C group; B: 0.0030 mass% or less, Ca: 0.0050 mass% Hereinafter, one or more selected from REM: 0.020 mass% or less, Zr: 0.010 mass% or less, and Mg: 0.010 mass% or less

In the present invention, C: 0.01-0.20 mass%, Si: 0.05-1.0 mass%, Mn: 0.1-2.0 mass%, P: 0.030 mass% or less, S: 0 0.030 mass% or less, Al: 0.3 to 2.0 mass%, the balance is made of Fe and inevitable impurities, and C and Al are represented by the following formula (1);
Al ≧ 1.3 × C + 0.3 (1)
However, C and Al are the composition of each element (mass%)
Of a high-strength wide steel sheet pile that is heated to 1200 to 1350 ° C., hot-rolled at a temperature of 850 ° C. or higher, then joint-rolled at a temperature of 600 to 800 ° C., and left to cool. A manufacturing method is proposed.

The manufacturing method of the present invention is characterized in that after the joint forming and rolling, accelerated cooling is performed to a temperature of Ar ₃ transformation point to 500 ° C. at a cooling rate of not less than 10 ° C./s and not more than cooling.

Further, the high-strength wide steel sheet pile in the production method of the present invention is characterized in that the effective width is 500 mm or more and the yield point is 390 N / mm ² or more.

In addition to the above component composition, the production method of the present invention further includes at least one component of the following groups A to C.
Group A; Cu: 1.0 mass% or less, Ni: 2.0 mass% or less, Cr: 1.0 mass% or less and Mo: 0.5 mass% or less, Group B: V or more : 0.2 mass% or less, Nb: 0.2 mass% or less and Ti: 0.03 mass% or less selected from one or more C group; B: 0.0030 mass% or less, Ca: 0.0050 mass% Hereinafter, one or more selected from REM: 0.020 mass% or less, Zr: 0.010 mass% or less, and Mg: 0.010 mass% or less

According to the present invention, a high-strength, wide-strength steel sheet pile having an effective width of 500 mm or more and a yield point at room temperature of 390 N / mm ² or more can be produced without impairing productivity.

An experiment that triggered the development of the present invention will be described.
FIG. 1 shows a C: 0.15 mass% Si—Mn steel used for manufacturing JIS standard SYW295 (YP ≧ 295 N / mm ² , TS ≧ 490 N / mm ² ), and Nb for this steel. 0.015 mass% added to ^{SYW390 (YP ≧ 390N / mm 2} , TS ≧ 540N / mm 2) is used in manufacturing C: about 0.15 mass% of Si-Mn-Nb steel, 900 ° C. and 1000 ° C. The deformation resistance at the time of hot rolling in is measured, and the result of obtaining the increasing rate of the deformation resistance by adding Nb is shown. Deformation resistance was measured by heating a cylindrical test piece of 8 mmφ x 12 mm height to 1300 ° C, cooling to a predetermined temperature at 1 ° C / s, and compressing 30% at a strain rate of 1 / s. It was derived by doing. From these results, microalloys such as Nb, V, Ti and the like have the effect of remarkably increasing the normal temperature strength even when added in a small amount, but they have increased the deformation resistance in hot rolling by about 10%. It was found that the rolling load was increased.

Therefore, the inventors have achieved a high strength at room temperature while suppressing an increase in deformation resistance in hot rolling, specifically, considering the productivity and suppressing it to less than 5%. A detailed study was conducted. As a result, by adding an appropriate amount of Al to the steel material, a ferrite phase is generated in a part of the steel structure in the hot rolling temperature range, and an increase in rolling load in a temperature range of 1000 ° C. or lower can be suppressed, It has been newly found that the room temperature strength is increased by the solid solution strengthening of Al, and the base material strength can be set to a target YP390N / mm ² or more.

  FIG. 2 shows a C—Mn—Al steel having C: 0.15 mass%, Mn: 1.45 mass%, and Al: 0.03 mass% as a base steel, and Al in the range of 0.1 to 2 mass%. The added steel was melted in the laboratory, 100 kg of ingot was roughly rolled to 100 mm × 200 mm × 650 mm, and the deformation resistance at 900 ° C. when these coarsely pressed materials were hot-rolled to a thickness of 12 mm, The tensile strength at normal temperature of the steel after the hot rolling is measured, and the influence of the Al addition amount on them is shown. The deformation resistance was calculated from this value by measuring the rolling load during hot rolling. For comparison, the same investigation was performed on the steel obtained by adding 0.018 mass% of Nb to the above base steel and shown in the figure. From FIG. 2, Nb greatly increased not only the normal temperature strength but also the deformation resistance at 900 ° C. even when added in a small amount, whereas Al suppressed the increase in hot deformation resistance while maintaining the normal temperature strength. It turns out that there is an effect which raises. The present invention is based on the above findings.

Next, the reason for limiting the component composition of the steel sheet pile according to the present invention will be described.
C: 0.01-0.20 mass%
C is a component useful for increasing the strength of steel. However, if its content is less than 0.01 mass%, the above effect is poor. On the other hand, if it exceeds 0.20 mass%, weldability is impaired. The range is 0.01 to 0.20 mass%.

Si: 0.05 to 1.0 mass%
Si is an effective component for increasing the strength of steel, and it is necessary to add 0.05 mass% or more. However, excessive addition of Si leads to deterioration of the toughness of the base material, so the upper limit is made 1.0 mass%. Preferably, it is the range of 0.10 to 0.6 mass%.

Mn: 0.1 to 2.0 mass%
Mn is a useful component for ensuring the strength of the steel, and requires addition of 0.1 mass% or more. However, if added over 2.0 mass%, as with C, the weldability is lowered, so the upper limit is made 2.0 mass%. Preferably, it is in the range of 0.5 to 1.5 mass%.

P: 0.030 mass% or less P is a harmful element that promotes embrittlement of steel, and is desirably as small as possible. In the present invention, P is 0.030 mass% or less.

S: 0.030 mass% or less S, like P, is a harmful element that promotes embrittlement of steel, and is desirably as small as possible. In the present invention, it is 0.030 mass% or less.

Al: 0.3 to 2.0 mass%
As described above, Al is a component that generates a ferrite phase in a part of the steel structure in the hot rolling temperature region to suppress an increase in hot deformation resistance and contributes to an improvement in strength at room temperature (see FIG. 2), the most important element in the present invention. However, in order to obtain the effect, addition of 0.3 mass% or more is necessary. On the other hand, since addition exceeding 2.0 mass% causes an increase in cost, the upper limit is set to 2.0 mass%.

Al ≧ 1.3 × C + 0.3
In the present invention, in the temperature range of 800 ° C. to 1000 ° C. in the latter half of the hot rolling in which the rolling load increases, in order to ensure that the steel structure has a two-phase structure of ferrite + austenite and to suppress an increase in deformation resistance, Al Is added in the following formula (1):
Al ≧ 1.3 × C + 0.3 (1)
(Here, Al and C are the contents of each element (mass%))
It is necessary to satisfy.

The steel sheet pile of this invention can add the following component according to a required characteristic other than the said basic component.
One or more selected from Cu: 1.0 mass% or less, Ni: 2.0 mass% or less, Cr: 1.0 mass% or less, and Mo: 0.5 mass% or less Cu, Ni, Cr and Mo are Both are effective elements for improving the strength of steel. However, when excessively added, Cu causes hot brittleness, Ni is expensive, and thus the economical efficiency is impaired, and Cr and Mo deteriorate weldability. Therefore, it is preferable to add Cu up to 1.0 mass%, Ni up to 2.0 mass%, Cr up to 1.0 mass%, and Mo up to 0.5 mass%.

V: 0.2 mass% or less, Nb: 0.2 mass% or less and Ti: 0.03 mass% or less selected from one or more types V, Nb and Ti all form carbonitrides, It is a useful component that precipitates finely in the steel structure and increases the strength of the steel. However, if V and Nb are 0.20 mass% and Ti exceeds 0.03 mass%, both lead to a decrease in the toughness of the base material, so V is 0.2 mass% or less, Nb is 0.2 mass% or less, Ti is preferably 0.03 mass% or less.

B: 0.0030 mass% or less, Ca: 0.0050 mass% or less, REM: 0.020 mass% or less, Zr: 0.010 mass% or less, Mg: 0.010 mass% or less B is an effective component for increasing the strength of steel with a small amount of addition, but if added in excess of 0.0030 mass%, the toughness decreases, so the upper limit is preferably made 0.0030 mass%. Ca is a component useful for improving S toughness by fixing S, but even if added over 0.0050 mass%, the effect is not only saturated, but also the cleanliness of the steel is reduced. Therefore, it is preferable to set it as 0.0050 mass% or less. REM, Zr, and Mg are effective elements for refining crystal grains and improving toughness. However, even if REM is added in an amount of 0.020 mass%, Zr is added in an amount exceeding 0.010 mass%, and Mg is added in an amount exceeding 0.010 mass%, the effect is saturated.

Next, the manufacturing method of the high intensity | strength wide steel sheet pile concerning this invention is demonstrated. In the present invention, the wide width means that the effective width is 500 mm or more, and the high strength means that the yield point is 390 N / mm ² or more.
Heating temperature of steel material: 1200-1350 ° C
Prior to hot rolling, the steel material whose component composition is adjusted to the above appropriate range needs to be charged into a heating furnace and heated to a temperature of 1200 to 1350 ° C. The hot deformation resistance is related to the rolling temperature and usually decreases as the rolling is performed at a higher temperature. Therefore, in the present invention, the heating temperature is set to 1200 ° C. or more in order to sufficiently reduce the deformation resistance. On the other hand, if the heating temperature becomes too high, the oxidation loss of the steel material will increase, damage to the furnace body of the heating furnace will progress, and it will be disadvantageous in terms of thermal energy, so 1350 ° C will be the upper limit. There is a need to.

  The steel material heated to the above temperature is subjected to rough hot rolling at a temperature of 850 ° C. or higher by reverse rolling in the same manner as in the ordinary process, and then formed and rolled into a joint at a temperature of 600 to 800 ° C. to obtain a desired shape and size. It is a steel sheet pile. Steel sheet piles are required to have high dimensional accuracy at the joints because fitting is important. However, when the joint is formed and rolled at a temperature of 600 ° C. or lower, the formability is insufficient, and it becomes difficult to ensure desired dimensional accuracy. On the other hand, when trying to form and roll the joint at 800 ° C. or higher, considering the temperature drop during hot rolling, the heating temperature of the material needs to be 1350 ° C. or higher, which is not preferable.

The steel sheet pile of the present invention can obtain a high strength with a yield point of 390 N / mm ² or more simply by allowing a steel material having a composition suitable for the present invention to be hot-rolled under the above conditions and then allowing to cool. However, when it is desired to secure high strength stably even when the effective width portion is thick or when it is desired to obtain higher strength, the cooling after hot rolling is performed at a cooling rate of not less than 10 ° C./s. Thus, accelerated cooling is preferably performed to a temperature of Ar ₃ transformation point to 500 ° C. When the cooling rate exceeds 10 ° C./s or the cooling stop temperature is less than 500 ° C., in the steel sheet pile having an irregular shape, shape defects such as bending and warping due to residual stress due to uneven cooling occur. Because. A more preferable cooling stop temperature is a temperature range of Ar ₃ transformation point to 600 ° C.

  Steel having the composition shown in Table 1 is melted in a laboratory in a vacuum melting furnace to make a 100 kg ingot into a 100 mm × 200 mm × 650 mm slab by rough rolling, and then this ingot is installed in a heating furnace. Then, after heating to 1300 ° C., which is the same as the manufacturing conditions for the wide steel sheet pile, hot rolling was performed to a finishing temperature of 900 ° C. to obtain a hot-rolled sheet having a thickness of 12 mm, and then allowed to cool or accelerate. In the hot rolling, the rolling temperature and rolling load of each pass were measured, and deformation resistance at 1000 ° C. and 900 ° C. was obtained. Further, as a conventional example, the same measurement was performed for a conventional material of JIS standard SYW295 class (steel A) and a conventional material of JIS standard 390 class (steel B), and deformation resistance was obtained.

In addition, from the hot-rolled sheet obtained as described above, a No. 1A tensile test piece defined in JIS Z 2201 was sampled along the rolling direction, subjected to a tensile test in accordance with JIS Z 2241, and yield point ( YP) and tensile strength (TS) were determined. Furthermore, a V-notch impact test piece defined in JIS Z 2202 was taken from the hot rolled sheet along the rolling direction, and a Charpy impact test was performed in accordance with JIS Z 2242. The impact test was performed in the temperature range of −80 to 20 ° C., and the absorbed energy (vE ₀ ) at 0 ° C. and the fracture surface transition temperature (vTr _s ) with a ductile fracture surface ratio of 50% were determined.

The measurement results are shown in Table 2. In addition, the deformation resistance increase rate in Table 2 is an increase rate with respect to the deformation resistance of steel A (SYW295 grade). From the results of Table 2, the steel having the composition suitable for the present invention has a deformation resistance increase rate of 5% or less in hot rolling compared to the conventional material (steel A), and after rolling. The yield point YP of the steel sheet at room temperature is 390 N / mm ² or more, which is excellent in impact characteristics. On the other hand, both the conventional material (steel B) with a small Al content and microalloy (Nb, Ti) added and the comparative example (steel D) not satisfying the formula (1) of the present invention are hot. It can be seen that the rate of increase in deformation resistance in rolling exceeds 10%, and the impact characteristics are inferior to the steel of the present invention.

  The high-strength wide steel sheet pile of the present invention can be applied not only to the civil engineering field but also to structural uses such as architecture and bridges.

It is the graph which compared the 900 degreeC and 1000 degreeC high temperature deformation resistance of SYW295 grade Si-Mn steel and SYW390 grade Si-Mn-Nb steel. It is a graph which shows the addition effect of Al or Nb which acts on the 900 degreeC deformation resistance of C-Mn-Al steel.

Claims (9)

C: 0.01-0.20 mass%, Si: 0.05-1.0 mass%, Mn: 0.1-2.0 mass%, P: 0.030 mass% or less, S: 0.030 mass% or less, Al : A high-strength wide steel sheet pile containing 0.3 to 2.0 mass%, the balance being Fe and inevitable impurities, and C and Al satisfying the following formula (1).
Al ≧ 1.3 × C + 0.3 (1)
However, C and Al are content (mass%) of each element. The high-strength wide steel sheet pile according to claim 1, wherein the effective width is 500 mm or more and the yield point is 390 N / mm ² or more. In addition to the above component composition, Cu: 1.0 mass% or less, Ni: 2.0 mass% or less, Cr: 1.0 mass% or less, and Mo: 0.5 mass% or less The high-strength wide steel sheet pile according to claim 1 or 2, characterized by comprising: In addition to the above component composition, it further comprises one or more selected from V: 0.2 mass% or less, Nb: 0.2 mass% or less, and Ti: 0.03 mass% or less. The high-strength wide steel sheet pile according to any one of claims 1 to 3. In addition to the above component composition, B: 0.0030 mass% or less, Ca: 0.0050 mass% or less, REM: 0.020 mass% or less, Zr: 0.010 mass% or less, and Mg: 0.010 mass% or less The high-strength wide steel sheet pile according to any one of claims 1 to 4, comprising one or more selected. C: 0.01-0.20 mass%, Si: 0.05-1.0 mass%, Mn: 0.1-2.0 mass%, P: 0.030 mass% or less, S: 0.030 mass% or less, Al : A steel material containing 0.3 to 2.0 mass%, the balance being Fe and inevitable impurities, and C and Al satisfying the following formula (1) is heated to 1200 to 1350 ° C., and then 850 A method for producing a high-strength wide steel sheet pile, which is hot-rolled at a temperature equal to or higher than ° C., then joint-rolled at a temperature of 600 to 800 ° C., and allowed to cool.
Al ≧ 1.3 × C + 0.3 (1)
However, C and Al show the composition (mass%) of each element. The manufacturing method according to claim 6, wherein after the joint forming and rolling, accelerated cooling is performed to a temperature of Ar ₃ transformation point to 500 ° C. at a cooling rate of not lower than 10 ° C./s. The manufacturing method according to claim 6 or 7, wherein the high-strength wide steel sheet pile has an effective width of 500 mm or more and a yield point of 390 N / mm ² or more. The manufacturing method according to any one of claims 6 to 8, further comprising at least one component of the following group A to group C in addition to the above component composition.
Group A; Cu: 1.0 mass% or less, Ni: 2.0 mass% or less, Cr: 1.0 mass% or less and Mo: 0.5 mass% or less, Group B: V or more : 0.2 mass% or less, Nb: 0.2 mass% or less and Ti: 0.03 mass% or less selected from one or more C group; B: 0.0030 mass% or less, Ca: 0.0050 mass% Hereinafter, one or more selected from REM: 0.020 mass% or less, Zr: 0.010 mass% or less, and Mg: 0.010 mass% or less

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