JPS58161722A - Production of hot rolled steel plate of blank material for electric resistance welded pipe having excellent bending workability of pipe - Google Patents

Abstract

PURPOSE:To produce a titled hot rolled steel pipe having excellent workability after making of pipes easily and economically, by hot-rolling the low carbon aluminum kelled steel which is limited in the chemical compsn. of C, Si, Mn, Al, B, N, etc. under specific conditions. CONSTITUTION:The aluminum killed steel contg. 0.025-0.06% or 0.001-0.009% C, <=0.03% Si, 0.10-0.25% Mn, 0.005-0.08% SolAl, 0.0010-0.0040% B, <= 0.0030% N, and if necessary, consisting further of 0.005-0.030% 1 or 2 kinds Ti or V and the balance Fe and unavoidable impurities is hot rolled at Ar3+ 40 deg.C finishing temp. of hot strips and further >=650 deg.C coiling temp. down to a prescribed thickness, whereby the hot steel plate which yields intended products easily and economically without requiring any special heat treatments after pipe making for the rupture or shape defects during working to pipes is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a hot-rolled steel sheet material for electric resistance welded pipes (hereinafter simply referred to as ERW) having excellent pipe bending workability.

The purpose of the present invention is to solve the problem of breakage or shape defects during round tube processing, which cannot be solved with conventional hot-rolled steel sheets for GW, without requiring special heat treatment of the pipe ridge. The object of the present invention is to provide a method for manufacturing hot rolled steel sheets that can avoid a decrease in efficiency and economic disadvantage.

Regarding the hot-rolled steel sheets used for ERW, it is difficult to process the subsequent bending or expansion of steel pipes that have been plated (e.g., zinc immersion plating or zinc grain blast plating) or painted by some method for rust prevention after pipe manufacture. However, in general, KW materials that have been plated or painted and baked as described above have a high high temperature strain aging and have low elongation as pipe materials, so it is difficult to bend the pipe. Alternatively, the pipe expandability tends to decrease (the pipe breaks), and the workability level is also quite low. Therefore, a method that requires special workability (simple or annealing) is adopted, but it is common to perform processing while adjusting the core metal during pipe processing.

That is, the former has the disadvantage of unavoidably increasing manufacturing costs due to heat treatment costs, etc., and the latter tends to have an unstable shape (flattening of the curved pipe section and partial buckling), which has a negative impact on product quality. It has some undesirable drawbacks.

The present invention provides a method for solving the four problems of the conventional method as described above, and the target hot-rolled steel sheet for i-painting is a hot-rolled steel sheet with a tensile strength of 28 kl/D" or more. The present invention is characterized by the following two points.

The first is the chemical composition of the starting material of the present invention, which is defined as follows.

That is, the starting material of the present invention has a C content of 9.001 or more and 0.
．． 009s or less, tiO, 025 or more and 0.061 or less, and sto, oso* or less, Mn 0.10-
0.25%5o4jLt 0.005-0.0801.
Bo, 0010-0.0040%.

NO,003G- or less, the remainder consisting of iron and unavoidable impurities, and if necessary, lf' of 1 #v
It is possible to contain 0.005 to 0.03011 of 1 or 2 types.

The second is to increase the finishing temperature to Ays point +4 during hot rolling.
Make the winding temperature as high as possible above 0℃, and further increase the winding temperature to 650℃.
This is the point at which hot arcing occurs up to a predetermined thickness at temperatures above ℃. The microscopic structure of the hot-rolled copper plate obtained by K is comprised of ferrite/pearlite with a large ferrite grain size and has high ductility. Furthermore, there is significantly less deterioration due to high-temperature aging of the metal plating and coating after pipe making, and it has good pipe workability.

To explain the composition range of each component in the present invention as described above, it is desirable that C is as low as possible, but 0.009-
If it is less than 0.025, it is difficult for C to precipitate, and in many cases it is solid solution.) In this state, it is difficult for Fi/Mirrite to precipitate, and the ductility is good at room temperature and in the state of a steel plate. , the ductility is greatly deteriorated due to high temperature strain aging based on solid solution C, such as forming, welding, and then metal plating or painting at medium temperature heat treatment of the cape at 100 to 450°C.
0911 super ~ 0.0! ! Less than $- is undesirable, and the C content must be at least 0, ozB, or C is 0.06%.
Super-temperature pipe manufacturing at room temperature! i! Further inclusion of ore is not desirable because the ductility after surface finishing, drilling, and painting (that is, as a steel pipe material) deteriorates.

For the above-mentioned nine reasons, in the present invention, the C content o, oos
Excluding oq less than 0.025 Is, 0.0011
1 to 0.009% or C0.025% to 0.06 *
o 2 - limited to O range. Then CO,001-0
,009* rU 4 After hot rolling - no light is produced, the solid solute C content is low, and the high temperature strain aging property after pipe making is also low. In this case, more preferable results can be obtained when the amount of C is less than Fio, oosl. That is, C0,
025 to 0.06) Although the cost is slightly higher, the pipe processing characteristics are much better as shown in the table and figure below.

When manufacturing alden-killed steel, around 0.014 is unavoidably mixed in from steelmaking raw materials and additive alloys, but 0.03
- Since there is a problem of plating burnout occurring during plating, the upper limit is set at 0.03%.

MEI is also 8 in order to ensure tensile strength and in hot rolling process.
In order to avoid the hot embrittlement caused by this, the lower limit was set at 0.10-, but in order to ensure as much ductility as possible, it is desirable to have as low a level of intuition as possible, and the upper limit was set at 0.25-.

If moL, kL B is less than 0.005 To, in continuous casting materials, unless other deoxidizing elements are added, and unless special casting conditions are used, deoxidation will be insufficient and defects will occur on the surface of the copper plate.
It is also necessary to improve the immobilization of the amount of N2 contained. Also, if the content exceeds o, oso-, the crystal grain size will become coarse due to the relationship with the winding temperature, thereby realizing the effects of the present invention. Since it is difficult to do so, the upper limit is set at 0.080-.
Desired effects can be obtained in the range of 005 to o, oso-.

Also, when a small amount of B is added, it fixes N2 as BN before rubbing, reducing solid solution N and making it harmless! It is well known that it is effective for softening as it scavenges birds and sours, and that workability is significantly improved.

However, the optimum range of the amount of B added is determined depending on the relationship with N in the steel, and a B/N depth Q of 8 to 1.2 degrees is desirable.

It is necessary to suppress it to 0.003011 or less, and the lower the lower limit of l, the better, but considering the economic effect, it is desirable that the lower limit is 0.001011 and the upper limit is 0.00401.

Now, as the N content increases, the workability, toughness, etc. decrease during room temperature processing and strain aging, and the required B and At amounts increase, so it is preferable to have a lower N content. Then, the upper limit of N content is t-0,003091
Good results were obtained.

Furthermore, in order to improve workability, coarsening of grain size caused by ultra-high temperature finishing rolling and high-temperature winding and rise in transition temperature due to NK are prevented, and to improve toughness, either or both of 〒i or V is omitted. , oos~o, o;to- is more effective.

Next, in the present invention, the finishing temperature is Ar, the transformation point temperature +40
The reason for setting the temperature to be higher than ℃ is because the finishing temperature is Ar, and the temperature is higher than ℃
This is because if the temperature range is less than 40° C., the crystal grains of the rolled steel sheet become fine, making it impossible to obtain good elongation properties necessary for pipe bending. Finishing temperature Ars + 40
If the temperature is higher than 0.degree. C., the crystal grains of the rolled steel sheet will be sufficiently large and the elongation properties will be good.

Here, the transformation point varies depending on the composition of the rolled steel sheet (C, 111°Mn nat) and the cooling rate, but it means the temperature at which the austenite phase changes to the ferrite + pearlite phase, and it cannot be simply determined by the composition alone. If the final rolling is carried out at a temperature higher than this temperature, it can be said that this is the minimum finishing temperature for rounding at which the crystal grains become uniform and a good material with small in-plane anisotropy is obtained. Rolling at a temperature of (
When processing strain) is carried out, the so-called cold-rolled round shape and 1
k] Depending on the component, the grains become coarse or a cold-rolled fiber structure is formed. Specifically, for example, a low carbon HT killed steel plate (CO,03%-Mu0.
23%, P 0.0121G) 0Ile850℃
Teal.

Reasons why the winding temperature was set at 650°C or higher: If the rolling temperature is lower than 650°C, the rolled steel sheet will not be sufficiently softened, but if it is higher than 650°C, the softening will occur due to the fixation of N by U and IK and the growth of crystal grains. This is so that you can be saved. Although there is no particular upper limit for the coiling temperature, for the purpose of the present invention, the higher the coiling temperature is, the better, as long as the equipment conditions and rolling conditions permit. However, the upper limit of the winding temperature that can be realized is determined by the performance of the hot rolling mill, such as the finished plate thickness, etc., and there are also restrictions such as preventing descaling and the formation of ultra-coarse grains during pickling of the steel plate, making it extremely difficult. Of course, it is not something that can be made very high. The highest winding temperature in the example shown in Table 1 was 720°C, but
It can be considered that about 0 is almost the upper limit.

Next, specific examples of the present invention will be described.

The following 11th example shows the specific composition of the hot rolled steel sheet material for IRW according to the present invention, the hot rolling conditions, and those of comparative materials.
! As shown below. That is, symbols A to G indicate the steel according to the present invention, and symbols H to L indicate the chemical composition and hot rolling conditions of the comparative material.

Table 2 shows tensile test pieces in the rolling direction of hot-rolled steel plates (thickness: 3.3 mm) manufactured under these conditions, and their electrical resistance.
The tensile test values of test pieces cut from the longitudinal direction of galvanized steel pipes after pipe manufacturing with an outer diameter of 43 cm are shown below. The bending formability column in Table 2 also shows the results of bending tests on steel pipes, which were conducted using a draw bending method using a normal metal core to achieve a bending radius of 65.
■ Shows the condition of the bent part of the steel pipe when bent to (1,5D),
``Fracture'' indicates the occurrence of cracks at the bent part, ``Poor shape 1'' indicates the occurrence of wrinkles due to large flattening or buckling of the bent part, and ``Good'' indicates that the bending was good without any breakage or defective shape. show.

According to Tables 1 and 2, the bending workability of steel pipes produced by electric resistance welding and galvanized from steel sheets A to G manufactured according to the present invention is good, whereas comparative steel sheets 111 It is clear that the bending workability of the steel pipe made from -L is poor.

This is because steel plates A to G manufactured according to the present invention are made into pipes by electric resistance welding, and the tensile test value after galvanizing is shown to be larger than that of the comparative material. This is because the material according to the present invention is smaller than H-LK and exhibits excellent workability even after high-temperature strain aging.

In particular, Ni material has a low C content of 0.014 and 0.0159II compared to other materials, so the elongation value when hot-rolled steel is good, but the pipe is made by electric resistance welding, and after galvanizing, the second As shown in the table, the elongation value becomes low. This is because the C content is 0.
．． In the range of 0.01 to 0.0241, high temperature strain aging due to C is large, indicating that the elongation as a pipe material has deteriorated.

Comparative material H was rolled at a temperature of 5 points + 40°C or more within the range of the composition of the present invention, but the index temperature was as low as 600°C, so the crystal grains were not sufficiently large. The steel did not achieve ductility and was inferior to the steel of the present invention.

Figure 1 shows the relationship between the tensile strength, T, and Et of sandals cut from the longitudinal direction of the skeleton steel pipes of steel pipes made of the present invention steel and a comparison material (thickness 3.3 M) after electrical resistance welding and galvanization. However, it is clear that the steel of the present invention has lower tensile strength and significantly larger T and Et than the comparative materials even after high temperature strain aging. That is, as mentioned above, the present inventors
o, oi super~0.02! I
In the state of hot-rolled steel sheet as a material for R%V, T and Et are increased, and further tube forming and plating are performed.

Ultra-high-temperature finishing of B-added aluminum killed steel to minimize high-temperature aging deterioration during paint baking processing.

This invention is a method of high-temperature winding, and has made it possible to manufacture steel sheets that exhibit the excellent functions and effects described above.According to the invention described above, special post-tube heat treatment is not required. The present invention makes it possible to manufacture metal-plated or paint-baked ERW steel pipes with excellent pipe workability and excellent pipe workability (by a manufacturing process that is easy and does not result in an increase in manufacturing costs). The industrial benefits are extremely large.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between the tensile strength and T and W of samples cut from the longitudinal direction of steel pipes made of the steel of the present invention and a comparative material (thickness: 33 mm) which were galvanized after electrical resistance welding. Rod / 354° tension 5! Sa-1 (

Claims (4)

[Claims] (1) CO,025~0.069&, l111
0.03 S or less. Mn 0.1 (1~0.25 To, aoj-ju
o, 005~0.080111IB 0.0010~0
．． 0040%, NO, 0030% or less, balance iron and unavoidable impurities, aluminum killed steel is finished at a temperature of Ats + 40°C or higher and then hot-rolled to a predetermined thickness at a winding temperature of 650°C or higher. A method for producing a hot-rolled steel sheet material for electric resistance welded pipes, which is characterized by rolling, and has excellent pipe bending workability after pipe forming. (2) CO, 025-0.06%, lit
0.03% or less, duty 0.10-0.25 To,
sol, A70.005~0.0801G, 10.00
10-0.0040%, NO, 00301 or less eTlt
7tijV 1s or 2 types 0.005-0.0301
After pipe making, the aluminum (killed steel) consisting of the remaining iron and unavoidable impurities is hot-stretched and hot-rolled to a predetermined thickness at a finishing temperature of +40°C or higher and a winding temperature of 650°C or higher. A method for manufacturing hot-rolled steel sheets for electrical pile welded pipes with excellent bending workability. (3) CO,OOl ~0.00991,810.
0311i and below, MnO, 10~01! h%
* msj, juO, 005-0.080 arrogant, B
Aluminum killed steel consisting of O,0010~0.00401G, NO,0030% or less, the balance iron and unavoidable impurities is hot-striped and finished at a temperature r5 + 40℃ or higher, and then rolled to a predetermined thickness at a winding temperature of 650℃ or higher. The method for producing hot-rolled steel pipes, which is a material for electrical resistance S* pipes and has excellent workability, is characterized by hot rolling. (4) CO,001~0.00911,810.0
3- Below, -0,10P-025111,sam AtO
,005~0.0801 Bo,0010~0.004
05G, NO, 003011 and below, TI or VOI seeding is 2 types 0.005-0.030 Is, the balance is iron and aluminum killed steel consisting of unavoidable impurities is hot strip finished as temperature difference r i + 40℃ or more. A method for producing a hot-rolled steel sheet material for electric resistance welded pipes having excellent bending workability after pipe forming, characterized by hot rolling the steel sheet to a predetermined thickness at a winding temperature of 6 sO<0>C or higher.