JPS6043412B2 - Method for manufacturing H-beam steel with excellent low-temperature toughness at the base of the web - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention has the effect of forced cooling of the intersection between the flange and the web (hereinafter referred to as the web root) of an H-beam steel after hot rolling and self-tempering through recuperation. The present invention relates to a method for producing an H-beam steel with excellent low-temperature toughness at the root.

H-shaped steel has a more complicated shape than steel plates, and the web root has a fillet, so the web root has a H-shape.
The largest thickness in the cross section of the section steel.

In the conventional manufacturing method of H-section steel, the finish rolling temperature of the thick web root is higher than other parts, and the cooling rate after finish rolling is slower than other cross-sectional parts. , the crystal grain size of the transformed structure becomes coarse. The grain size has a correlation with the fracture surface transition temperature of the impact test characteristic value.

The higher the finish rolling temperature and the slower the cooling rate, the higher the fracture surface transition temperature and the worse the low temperature toughness.
In addition, in the conventional production method, after hot-rolled H-beam steel is air-cooled, the bends that occur during cooling are made into a straight product using a roller straightening machine or a press straightening machine. In such cases, the root portion of the web is subjected to distortion accompanied by a decrease in thickness of around several percent by the roller straightening machine, which increases the fracture surface transition temperature and deteriorates the low-temperature toughness of the web root portion. An object of the present invention is to provide a method for manufacturing an H-beam steel having excellent low-temperature toughness at the base of the web, which solves these problems.

That is, the present invention has the following features: (1) CO. O3~0.20%, Sil. 0% or less, M
nO. 5-2.2%, N≦0.020%, AlO. OO
3 to 0.10%, with the remainder consisting of iron and unavoidable elements, is hot rolled to form an H-beam steel, and the web root of the hot-rolled H-shape steel is heated to Arl + 30°C or higher. Cooling fluid is sprayed from inside the flange of the H-section steel or from the inside and outside of the flange so that the recuperation temperature at the web root after cooling in the temperature range from 500°C to 500°C is higher than 500°C and below 700°C. A method for manufacturing an H-beam steel having excellent low-temperature toughness at the base of the web, characterized in that the web is cooled at a cooling rate of 20 to 200° C./S, and air-cooled after the recuperation.

(2) CO. O3~0.20%, Sil. 0% or less, M
nO. 5-2.2%, N≦0.020%, AlO. OO
Steel containing 3 to 0.01% Ni, . CrNCu.
．． A steel containing 1.5% or less of one or more types of MO in a total of 1.5% or less, with the remainder consisting of iron and unavoidable elements, is hot rolled to form an H-beam steel, and after the hot rolling. The recuperation temperature of the web root after cooling the web root of H-section steel in the temperature range from Arl + 30℃ or higher to 500℃ is 5.
Cooling fluid is sprayed from the inside of the flange of the H-section steel or from the inside and outside of the flange so that the temperature is higher than 00°C and below 700°C, and cooled at a cooling rate of 20 to 200°C/S, and after the above recuperation, air cooling is performed. A method for producing an H-beam steel having excellent low-temperature toughness at the base of a web, the method comprising:

3) CO. O3~0.20%, Sil. 0% or less, Mn
O. 5-2.2%, N≦0.020%, AlO. OO3
~0.01%, in addition to Nbl■, Ti. ．． A steel containing one or more types of Zr in a total of 0.3% or less and the balance consisting of iron and unavoidable elements is hot rolled to form an H-beam steel,
The web root of the H-shaped steel after hot rolling was heated to Arl + 30°C.
From the inside of the flange of the H-section steel or from the inside and outside of the flange so that the recuperation temperature at the web root after cooling is higher than 500°C and lower than 700°C in the temperature range from the above temperature to 500'C. Spray cooling fluid for 20 to 20 minutes.
A method for manufacturing an H-beam steel having excellent low-temperature toughness at the base of the web, characterized by cooling at a cooling rate of 0° C./S and air cooling after the above-mentioned recuperation.

1) CO. O3~0.20%, Sil. 0% or less, Mn
O. 5-2.2%, AlO. Contains OO3~0.10%, N 0.02% or less, and 0.15% rare earth elements.
A steel containing the following, with the remainder consisting of iron and unavoidable elements, is hot rolled to form an H-beam steel, and the web root of the hot-rolled H-shape steel is heated from a temperature of Arl + 30°C or higher to 500°C. The recuperation temperature at the base of the web after cooling the temperature range is 500
Cooling fluid is sprayed from the inside of the flange of the H-section steel or from the inside and outside of the flange to cool the steel at a cooling rate of 20 to 200°C/S so that the temperature is higher than 700°C and below 700°C.
A method for producing an H-beam steel having excellent low-temperature toughness at the base of the web, the method comprising air cooling after the reheating.

(5) CO. O3~0.20%, Sll. 0% or less, M
nO. 5-2.2%, N≦0.020%, AlO. OO
The steel containing 3 to 0.01% of Ni. ．． CrlCu,
．． It contains one or more types of MO, singly or in combination, in a total amount of 1.5% or less, and NblV. Tl. A steel containing one or more types of Zr in a total of 0.3% or less and the balance consisting of iron and unavoidable elements is hot-rolled to form an H-beam steel, and the hot-rolled H-beam steel is attached with a web. The inside of the flange of the H-beam steel or the inside of the flange and A method for manufacturing an H-beam steel having excellent low-temperature toughness at the base of a web, characterized in that cooling is carried out at a cooling rate of 20 to 200'C/S by spraying a cooling fluid from the outside, and air cooling is performed after the above-mentioned recuperation.

It is. Next, the present invention will be explained in detail.

First, the chemical composition of the steel used in the present invention will be explained.

C is a fundamental factor for strength and toughness, and the lower limit was set at 0.03% from the viewpoint of hardenability and strength, and the upper limit was set at 0.20% from the viewpoints of weldability and low-temperature toughness.

S1 has a deoxidizing effect and is necessary for producing homogeneous steel; If it exceeds 0%, the low temperature toughness decreases, so the content was set to 1.0% or less. Mn is an element that improves hot workability, and is also an essential element for improving the ductility and toughness of steel.The lower limit of Mn is 0.5 from the viewpoint of hardenability, hot workability, and low-temperature toughness. %
The upper limit is 2.2, which is the limit at which the effect of low-temperature toughness is saturated.
%.

In addition to having a strong deoxidizing effect, A1 is an element that fixes N in steel, has a remarkable effect on refining austenite grains, and is useful for improving low-temperature toughness, and its lower limit of 0.003% is an element that This is the minimum value at which grain size can be refined, and the upper limit was regulated to 0.10% in view of inclusions.

Nb. ．． V. ．． Tl. ．． Zr is an element added to form precipitate particles to refine the crystal grains of the steel material during rolling, and its upper limit of 0.3% is the limit at which the toughness deteriorates. Ni. ．． Cr. ．． CuNMO increases hardenability and also
, Ar3 has the effect of improving the balance of strength and toughness in addition to adjusting the transformation point, and its upper limit was set at 1.5% in terms of weldability and economic efficiency.

Rare earth elements are elements that are added as necessary to eliminate the harmful effects of S, but if their content exceeds 0.15%, oxides will increase and cleanliness will decrease. .15
% or less.

N is A1, Nbl■, Ti. ．． Forms nitride with Zr,
There are elements useful for refining crystal grains.

However, if the amount is too large, solid solution N increases and the toughness of the steel decreases, so the upper limit was set at 0.02%.
The method of the present invention involves heating the steel having the above-specified composition to an appropriate temperature in the austenitic region, and then hot rolling it into an H-beam of a predetermined size and shape in the austenitic region. The recuperation temperature of the web root 4 after cooling from the temperature of Arl + 30°C to 500°C is higher than 500°C 7
For example, as shown in Fig. 1, the temperature is below 00°C.
Cooling water, which is a cooling fluid, is sprayed onto the web root portion 4 from the inside of the flange 2 of the H-section steel or the inside and outside of the flange 2, and the web root portion 4 is cooled at a cooling rate of 20 to 2000 C/Sec. After reheating to a temperature higher than 500°C and lower than 700'C, air cooling is performed. When cooling the web base 4 by spraying cooling water, intermittent cooling is preferably performed in this case to reduce tissue unevenness in the thickness direction when the web base 4 becomes thick.

As shown in FIG. 1, the web root portion 4 can be cooled by spraying cooling water from a cooling nozzle 5 provided at the lower inside of the flange 2, or by spraying cooling water onto the nozzle 5 and the center outside of the flange 2. Cooling is performed by spraying cooling water from both nozzles of the provided cooling nozzle 6, or cooling water is sprayed from both nozzles of the cooling nozzle 6 provided at the center outside of the nozzle 5 and flange 2. Depending on the arrangement, the cooling nozzle 7 may be provided above the inside of the flange 2, and cooling may be performed by combining the cooling nozzle 7 with the cooling nozzle 5 and the cooling nozzle 6, respectively. Cooling from the web is not very preferable because cooling water tends to accumulate on the upper surface of the web, resulting in overcooling of the web.

In the method of the present invention, the temperature range of the cooling fluid (cooling water) is set from Arl + 30°C or higher to 500°C, because in order to sufficiently harden the web root, the cooling start temperature must be from the austenite region. and Ar
The temperature l+30°C was determined experimentally.

The lower limit of cooling temperature was set to 500℃ for Arl+30~5
Slow cooling to 00°C produces ferrite and pearlite transformed structures. The aim of the present invention is to obtain a hardened structure, and it is necessary to rapidly cool the steel to 5000C to prevent ferrite and pearlite transformation. Therefore 50
The lower limit was 0°C. Also, the cooling rate is 20 to 2000
It is necessary to cool with C/S. In addition, this cooling temperature range Ar''1+30℃ or more ~ 500℃, cooling rate 20~
The cooling condition of 200° C./S is also necessary for air cooling the web root portion after cooling and reheating it to 500 to 700° C. The reason why the above cooling rate was set to 20 to 200°C/S is because the structural critical cooling rate of steel to which the above-mentioned hardenability improving elements are added close to the upper limit is 20°C/S, and the hardenability gradient is contains the elements and C. ．． This is because the structural critical cooling rate of steel with a lower Mn content is 200° C./S.
Further, the reason why the reheating temperature is set higher than 500°C and lower than 700°C is that this is within a range where sufficient self-tempering can be achieved in a short time. There is a good correlation between the recuperation temperature and time and the fracture surface transition temperature of impact properties.
) is expressed by the tempering parameter defined by the formula.

Note 1, Note 2 The recuperation temperature is the peak value of the recuperation temperature shown in Figure 3, and the recuperation time is (peak value - 20
)℃ or higher temperature.

There is a correlation between the tempering parameters and the fracture surface transition temperature as shown in Figure 4, and the value of P is 14,000 to 1,850.
If it is 0, the fracture surface transition temperature is good.

The degree of influence of recuperation temperature and reheating time in self-tempering is large. The relationship between the recuperation temperature and the fracture surface transition temperature (VTrS), which indicates low-temperature toughness, is as shown in FIG. 5, and the fracture surface transition temperature exhibits a good value when the recuperation temperature is in the range of 500 to 700°C. Next, examples of the method of the present invention will be described.

The chemical composition of the test steel is shown in Table 1.

Furthermore, Table 2 shows the mechanical properties of H-beam steels manufactured by the method of the present invention and the conventional method using the steels shown in Table 1. Second
As is clear from the table, all of the A-M steels to which the method of the present invention is applied have a significant improvement effect on the fracture surface transition temperature (VTrS), which indicates the low-temperature toughness of the web root, compared to the conventional method. Next, using A steel as an example, the fracture surface transition temperature at the web root is the worst value in the cross section after straightening of H section steel by the conventional manufacturing method. By applying this, the fracture surface transition temperature at the web root can be significantly improved.

In addition, the web root of the H-beam steel to which the method of the present invention is applied has less deterioration in impact properties due to straightening.

This tendency is the same for all types of B-M steel. Test No. in A steel. A-2, A-3 and B-M steel were water cooled using only the cooling nozzle 5 shown in Figure 1, and air cooling was performed after recuperation. .

Test No. FIG. 3 shows the cooling curves of the web bases of A-1, A-2, and A-3.

A-1 is an example of production using the conventional method, in which hot-rolled H-beam steel is air-cooled (the base of the web is also air-cooled).
2, A-3 is a hot-rolled H-beam whose web root temperature is 860°C, and the web root is water-cooled using a cooling nozzle 5, and the amount of cooling water is on one side of the H-beam. The cooling rate is 5e and 15e per meter at the base, and the cooling rate from the cooling start temperature (860℃) to the temperature of 5000C is 70℃/Sec18O for A-2 and A-3, respectively.
°C/Sec, and the reheating temperature after cooling was 700 °C and 640 °C.

The fracture surface transition temperature at the root of the H-section steel web in A-1 before straightening is -15°C, while that in A-2 and A-3 is -35C1-55°C after straightening, respectively. The fracture surface transition temperature also shows good values.

Furthermore, the amount of increase in fracture surface transition temperature before and after straightening is 15°C for A-1, while it is 5°C for A-2 and A-3, respectively.
It can be seen that the amount of increase in fracture surface transition temperature is also smaller in the case where the method of the present invention is applied, which is 10°C and 10°C. A-4 was cooled by using cooling nozzle 5 and cooling nozzle 7 shown in Figure 1 in combination, and spraying cooling water of 7.5e/M (7.5e per meter of base on one side) from each nozzle. Something,
The cooling rate from the cooling start temperature of 86 (range) to a temperature of 500°C is slightly faster than that of A-3, and the cooling after the recuperation temperature of 510'C is performed by water cooling from 500°C. For this reason, the structure of the web root portion is more uniform in the thickness direction than in A-2 and A-3.

A-5 uses both the cooling nozzle 5 and the cooling nozzle 6 shown in FIG. 1, and cools by spraying cooling water of 7.5e/M from each nozzle. This product has a smaller amount of water at the base of the web than A-3 and has a slightly less quenching effect, but the recuperation temperature is in a good temperature range. As described above, according to the method of the present invention, among the impact characteristics within the cross section of H-beam steel produced by the conventional method, the fracture surface transition temperature, particularly at the web root portion, can be improved at a low cost and in a simple manner.

Furthermore, if the heat treatment method according to the present invention is used to control and cool the central part of the flange of an H-shaped steel from the outside of the flange, it is possible to improve the impact characteristics of the central part of the flange. Arl+3 only on thick parts
By rapidly cooling from a temperature of 0°C or higher to a temperature of 500°C, and then reheating through heat conduction from other parts to create a tempering effect, we manufacture a section steel with an excellent balance of toughness within the cross section. It is also possible to do so.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an example of the nozzle arrangement for water cooling the web base of an H-beam according to the method of the present invention, Fig. 2 is a diagram showing the parts in the H-beam from which impact test pieces were taken, and Fig. 3 The figure shows an example of the cooling curve at the base of the web, Figure 4 shows the influence of the fracture surface transition temperature on tempering of 7 meters, and Figure 5
The figure shows the influence of recuperation temperature on fracture surface transition temperature. 1...H-shaped steel, 2...flange, 3...
... Web, 4 ... Web base, 5, 6
, 7... Cooling nozzle.

Claims (1)

[Claims] 1 C0.03 to 0.20%, Si 1.0% or less, Mn
0.5-2.2%, N≦0.020%, Al≦0.00
3 to 0.10%, with the remainder consisting of iron and unavoidable elements, is hot-rolled to form an H-beam steel, and the web root of the hot-rolled H-shape steel is heated to a temperature of Mr_1+30°C or higher. H so that the recuperation temperature at the base of the web after cooling in the temperature range from 500°C to 500°C is higher than 500°C and below 700°C.
The low-temperature toughness of the web root is improved by spraying a cooling fluid from the inside of the flange of the section steel or from the inside and outside of the flange to cool it at a cooling rate of 20 to 200°C/S, and air cooling after the recuperation. Excellent method for manufacturing H-beam steel. 2 C0.03-0.20%, Si1.0% or less, Mn
0.5-2.2%, N≦0.020°C, Al0.003
~0.10% Ni, Cr, Cu, Mo
A steel containing 1.5% or less of one or more of The inner side of the flange of the H-beam steel or the flange so that the recuperation temperature at the web root after cooling the steel web root in the temperature range from Ar_1+30℃ to 500℃ is higher than 500℃ and lower than 700℃. A method for producing an H-beam steel with excellent low-temperature toughness at the base of the web, characterized in that cooling is performed at a cooling temperature of 20 to 200°C/S by spraying a cooling fluid from the inside and outside of the web, and air cooling is performed after the recuperation. . 3 C0.03-0.20%, Si1.0% or less, Mn
0.5-2.2%, N≦0.020%, Al0.003
~0.10%, plus 1 of Nb, V, Ti, and Zr
A steel containing 0.3% or less in total of 0.3% or more and the balance consisting of iron and unavoidable elements is hot-rolled to form an H-beam steel, and the web root of the hot-rolled H-shape steel is Ar_1+30. ℃
Cooling fluid is supplied from inside the flange of the H-section steel or from the inside and outside of the flange so that the recuperation temperature at the web root after cooling is higher than 500°C and lower than 700°C in the temperature range from above to 500°C. Spray at 20-200℃/
A method for producing an H-beam steel having excellent low-temperature toughness at the web root, the method comprising cooling at a cooling rate of S, and air cooling after the recuperation. 4 C0.03~0.20%, Si1.0% or less, Mn
Contains 0.5-2.2%, Al 0.003-0.10%, N 0.02% or less, and 0.15% rare earth elements.
A steel containing the following, with the remainder consisting of iron and unavoidable elements, is hot rolled to form an H-beam steel, and the web root of the hot-rolled H-shape steel is heated from a temperature of Ar_1+30°C or higher to 500°C.
The recuperation temperature at the base of the web after cooling the temperature range up to 50
Cooling is performed at a cooling rate of 20 to 200 °C/S by spraying cooling fluid from the inside of the flange of the H-section steel or from the inside and outside of the flange so that the temperature is higher than 0 °C and lower than 700 °C,
A method for producing an H-beam steel having excellent low-temperature toughness at the base of the web, the method comprising air cooling after the reheating. 5 C0.03-0.20%, Si1.0% or less, Mn
0.5-2.2%, N≦0.020%, Al0.003
~0.10% Ni, Cr, Cu, Mo
Contains 1.5% or less of one or more of the following in total, singly or in combination, contains 0.3% or less of one or more of Nb, V, Ti, Zi, and Zr in total, and the balance is iron. A steel consisting of unavoidable elements is hot-rolled to form an H-beam, and the web root of the hot-rolled H-beam is cooled in a temperature range from Ar_1+30°C to 500°C. Cooling fluid is sprayed from inside the flange of the H-section steel or from the inside and outside of the flange to cool it at a cooling rate of 20 to 200°C/S so that the recuperation temperature at the root is higher than 500°C and lower than 700°C. . A method for manufacturing an H-beam steel having excellent low-temperature toughness at the base of the web, characterized by air cooling after the reheating.