JPH0483821A - Production of wide flange shape excellent in refractoriness and toughness in weld zone - Google Patents

Abstract

PURPOSE:To improve base material characteristics, refractoriness, and toughness in weld zone by controlling the amount of dissolved oxygen in a molten steel and carrying out hot rolling while specifying finishing temp. CONSTITUTION:A liquid iron is refined so that the amount of dissolved oxygen is regulated, by weight, to 0.003-0.015% by means of vacuum degassing treatment and preliminary deoxidizing treatment by indepent addition of pure metal, such as Al, Si, Ca, and Mg as deoxidizing elements, or combined addition of alloys thereof or by means of vacuum degassing treatment alone. By means of alloy addition, the liquid iron is regulated into a molten steel having a composition consisting of, by weight, 0.05-0.20% C, 0.05-0.50% Si, 0.4-2.0% Mn, 0.3-0.7% Mo, 0.05-0.20% V, 0.0070-0.0150% N, <0.005% Al, and the balance Fe with inevitable impurities, and further, by means of final deoxidation, this molten steel is regulated into a molten steel containing Ti by the amount, by weight percentage, satisfying the relation in -0.006<=[Ti%]-2[0%]<=0.008 based on the amount of dissolved oxygen [0%] in the molten steel. A steel slab prepared from this molten steel is reheated to 1100-1300 deg.C and hot-rolled, and finishing temp. is regulated to 750-1050 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for manufacturing H-beam steel having excellent fire resistance and weld zone toughness and used as a structural member of buildings.

(Conventional technology) Due to the rise in the height of buildings and the sophistication of architectural design technology, a review of fire resistance design was carried out under a comprehensive project by the Ministry of Construction.
In March 1988, the "New Fireproof Design Law" was enacted. According to this regulation, the temperature of the rope should be reduced to 350 in the event of a fire under the old law.
The restriction that fireproof coatings must be applied to temperatures below ℃ has been lifted, and it is now possible to determine the appropriate fireproof coating method based on the balance between the high-temperature strength of the steel and the actual load of the building.

That is, if the design high temperature strength at 600°C can be secured, the fireproof coating can be reduced accordingly.

In response to these trends, we first filed a patent application No. 14374 (1983).
No. 0 proposes a low-strength ratio steel for construction with excellent fire resistance, a steel material, and a method for producing the same. The gist of this prior invention is to improve high-temperature strength by adding Mo and Nb so that the yield point at 600° C. is 70% or more of that at room temperature. The design high-temperature strength of the steel material was set at 600''C based on the knowledge that it is the most economical option considering the increase in steel material cost due to alloying elements and the resulting fireproof coating construction cost.

(Problems to be Solved by the Invention) The present inventors have used the steel manufactured by the above-mentioned prior art technology to produce various shapes, especially H-beams with complicated shapes and severe rolling forming restrictions. As a result of trying to apply
Differences occur in rolling finishing temperature, rolling reduction rate, and cooling rate at each part of the web, flange, and fillet, resulting in differences in room temperature and high temperature strength,
The ductility and toughness varied, and some parts did not meet the standards.

Furthermore, as buildings become taller and more intelligent, steel materials for building materials are required to have higher reliability and improved welding performance for higher efficiency.

The purpose of the present invention is to solve the above-mentioned problems by improving the rolling finishing temperature for high temperature strength properties and material properties.

A low-cost, economical H-beam steel with excellent fire resistance and weld toughness that has low dependence on rolling reduction ratio and steel sheet thickness (cooling rate), excellent base metal properties, and excellent weld toughness. The purpose is to provide a manufacturing method.

(Means for Solving the Problems) The present invention has been made to solve the above-mentioned problems, and the gist thereof is as follows.

(1) Vacuum degassing treatment of molten iron and deoxidizing element A/, 5iC
a. Perform preliminary deoxidation treatment by adding pure metal Mg alone or a combination of these alloys, or by vacuum degassing treatment alone to reduce the dissolved oxygen to 0.003 to 0.015% by weight, and then prepare the alloy. By addition, C in weight %: 0.05-0.
20% Si: 0.05-0.50% Mn: 0.4
~2.0%, Mo: 0.3~0.7%, V: 0.0
5-0.20% N: 0.0070-0.0150
%, , AI<O, OO 5%, the remainder is Fe and unavoidable impurities, and final deoxidation is performed to obtain -0,006≦[Ti
%]-2[O%]≦0.008, and after reheating the slab obtained from the molten steel to a temperature range of 1100 to 1300°C, A method for producing an H-section steel having excellent fire resistance and weld toughness, characterized by performing intermediate rolling and setting the finishing temperature in the range of 750 to 1050°C.

(2) Vacuum degassing treatment of molten iron and deoxidizing element A/, Si.

After performing preliminary deoxidation treatment by adding pure metals such as Ca and Mg alone or in combination with their alloys, or by vacuum degassing treatment alone, dissolved oxygen is reduced to 0.003 to 0.015% by weight, and then the alloy is prepared. By addition, C in weight%: 0.05-0
．． 20%, Si: 0.05-0.50%.

Gate n: 0. 4-2. 0%, Mo
: 0.3 to 0.7%, v:o, os to 0.2
0%, N: 0.0070-0.0150%, A4
<0.005% plus Cr≦0.7%, Ni≦1.
0%, Nb≦0.05%, Cu≦1.0%, and the remainder is Fe and unavoidable impurities. %] -0,006≦(Ti%)-2[O%
] ≦o, oos
A method for manufacturing an H-beam steel with excellent fire resistance and weld toughness, characterized by reheating to a temperature range of 0 to 1300"C, followed by hot rolling to a finishing rolling temperature of 750 to 1050"C. .

(for production) The present invention will be explained in detail below.

The high temperature strength of steel is 700, which is approximately 1/2 the melting point of iron.
At temperatures below ℃, the strengthening mechanism is almost the same as that at room temperature, and is dominated by (1) refinement of ferrite crystal grain size, (2) solid solution strengthening by alloying elements, (2) dispersion strengthening by hardening phases, and (2) precipitation strengthening by fine precipitates. In general, to increase high temperature strength, M
This is achieved by increasing the softening resistance at high temperatures by adding precipitation strengthening and reducing the disappearance of dislocations by adding o, Cr.

However, the addition of Mo and Cr significantly increases the hardenability, and the ferrite+pearlite structure of the base material becomes easier to form into a bainite structure. When a component that easily generates a bainitic structure is applied to an H-beam steel, the rolling finish temperature, rolling reduction rate, and cooling rate will vary depending on the shape of the web, flange, and fillet. The bainite structure ratio changes significantly. As a result, room temperature and high temperature strength, ductility, and toughness vary, and some parts do not meet the standards. In addition, the addition of these elements significantly hardens the weld and reduces toughness.

The present invention is characterized by two points: improvement in the material properties of the base material and improvement in the toughness of the weld zone during welding. Regarding the base material, by controlling the amount of dissolved oxygen in molten steel and selecting the procedure for adding deoxidizing elements, VN can be precipitated with oxide particles such as Ti oxide or Si-Mn oxide dispersed in the steel as nuclei. Utilizing the effect of promoting intragranular ferrite transformation from within the austenite grains, changes in the microstructure ratio of bainite and ferrite in each part of the H-beam steel were reduced, and the mechanical properties of the base metal were made uniform. The high temperature strength is improved by precipitation strengthening of VN.

The weld heat affected zone (hereinafter referred to as HAZ) is heated to a temperature just below the melting point of iron, causing significant coarsening of austenite grains, resulting in coarsening of the structure and significantly lowering toughness. Ti oxide dispersed in steel according to the invention, 5
Oxide particles such as 1-Mn oxide have an excellent ability to generate acicular intragranular ferrite, which generates an intragranular ferrite structure using this as a nucleus, which significantly refines the structure and improves toughness. .

Next, the reason for limiting the basic component range of the steel subject to the present invention will be described.

First, C is added as an effective component to improve the strength of steel; if it is less than 0.05%, the strength required for structural steel cannot be obtained, and if it is added in excess of 0.20%, , the upper limit was set at 0.20% because it significantly deteriorates base metal toughness, weld cracking resistance, HAZ toughness, etc.

Next, Si is necessary to ensure the strength of the base material and to generate Si-based oxides, but if it exceeds 0.50%, a high carbon mantenside, which is a hardened structure, will be generated in the heat-treated structure, significantly reducing toughness. let In addition, if the Si content is less than 0.05%, the necessary Si-based oxide cannot be generated, so the Si content should be reduced from 0.05 to 0.
．． Limited to 50%.

Mn needs to be added in an amount of 0.4% or more to ensure strength and toughness of the base metal, but the upper limit was set to 2.0% within an allowable range such as weld toughness and cracking resistance.

At is a strong deoxidizing element, and its content of 0.005% or more promotes intragranular ferrite transformation.
Because Mn oxides etc. are not formed, resulting in a decrease in toughness, and excessive solid solution^l combines with N to form AIN, reducing the amount of VN precipitation, which is a characteristic of the steel subject to the present invention. It was limited to less than 0.005%.

N is an extremely important element for the precipitation of VN, and 0.00
If it is less than 70%, the amount of VN precipitated is insufficient, a sufficient amount of ferrite structure cannot be obtained, and high temperature strength at 600° C. cannot be ensured, so it is set to 0.0070% or more. If the content exceeds 0.0150%, it will reduce the toughness of the base material and cause surface cracking of the steel billet during continuous casting.
% or less.

Mo is an effective element for ensuring base metal strength and high temperature strength. If it is less than 0.3%, sufficient high-temperature strength cannot be secured due to the combined effect of VN precipitation strengthening, and if it exceeds 0.7%, the hardenability increases too much and the base material toughness (HAZ toughness) deteriorates. It was limited to 3-0.7%.

■ is extremely important as VN for the generation of intragranular ferrite structure, its refinement, and ensuring high temperature strength, and is 0.05
If it is less than 0.2%, the amount of VN precipitated is insufficient, and if it exceeds 0.20%, the amount of VN precipitated becomes excessive and the base metal toughness and weld zone toughness deteriorate, so it was limited to 0.05 to 0.20%.

The amounts of P and S contained as unavoidable impurities are not particularly limited, but they should be reduced as much as possible because they cause weld cracking due to solidification segregation and a decrease in toughness.
The amount of S is 0.02% or less.

The above are the basic components of the steel subject to the present invention, but for the purpose of increasing the strength of the base metal and improving the toughness of the base metal, Cr, Ni, Nb
, Cu or more.

First, Ni is an extremely effective element for increasing the toughness of the base material, but addition of more than 1.0% increases alloy cost and is not economical, so the upper limit was set at 1.0%.

Cr is effective in strengthening the base material and strengthening it at high temperatures by improving hardenability and precipitation hardening. However, excessive addition exceeding the upper limit is harmful from the viewpoint of toughness and hardenability, so the upper limit was set at 0.7%.

Nb is effective in toughening the base material, but excessive addition exceeding the upper limit is harmful from the viewpoint of toughness and hardenability, so it is
．． 05% or less.

Cu is an effective element for strengthening and weathering the base material, but the upper limit was set at 1.0% in consideration of temper brittleness due to stress relief annealing, weld cracking, hot work cracking, etc.

Vacuum degassing treatment of molten iron and deoxidizing elements Al, Si, C
a.

Preliminary deoxidation using FIIg pure metal or alloy, either alone or in combination, can highly purify the molten iron and at the same time reduce dissolved oxygen by 0.003 to 0.015% by weight.
This is an extremely important process in order to control the Further, if the [O] concentration of the molten iron before deoxidation is less than 3% O, OO, intragranular ferrite generation nuclei such as Ti oxide and 51-Mn oxide that promote intragranular ferrite transformation are reduced, and toughness cannot be improved. - On the other hand, if it exceeds 0.015%, even if other conditions are met, the oxide becomes coarse grained and becomes the starting point of brittle fracture, reducing toughness. It was limited to 0.003 to 0.015%.

Ti is added during the final deoxidation of molten steel, and the molten forging thus obtained has -0,006≦(Ti%)-2[O%]≦0.008 with respect to dissolved oxygen [O%] of molten steel. The reason why the adjustment is limited to the content of T1 in the weight% that satisfies the relationship is that in this relational expression, Ti is [O
] If it is in excess of the [O] concentration, the excess Ti will generate more TiN than necessary, reducing the amount of VN precipitation, which is a feature of the steel subject to the present invention, and if Ti is too small in terms of [O] concentration in terms of weight percent. In some cases, Ti oxide and Si become intragranular ferrite nuclei.
- This is because the total number of Mn oxides no longer satisfies the required number.

The reason why the reheating temperature was limited to the temperature range of 1100 to 1300°C is that heating to 1100°C or higher is necessary to facilitate plastic deformation in the production of section steel by hot working, and V,
In order to increase the yield point of Mo at high temperatures, it is necessary to sufficiently dissolve these elements in solid solution, so the lower limit of the reheating temperature was set at 1100°C. The upper limit was set at 1300° C. in view of the performance and economic efficiency of the heating furnace.

The reason for setting the finishing temperature of hot rolling to 750 to 105° is that although cold rolling improves the toughness,
This is because processing at temperatures below 0°C is difficult, and processing at temperatures above 1050°C produces a coarse grain structure and reduces toughness.

The effects of the present invention will be further illustrated by Examples below.

(Example) The test steel was melted in a converter furnace, and after degassing treatment, it was continuously cast into 2
After casting into slabs with a diameter of 50 to 300 mm, H-beams having various shapes shown in Table 1 were manufactured for each flange thickness by rolling. A test piece for the mechanical properties of the base metal was taken in the rolling direction at the 174F section of the H-beam cross section shown in FIG. The welded joint Charpy test specimen was measured at the center of the plate thickness of the flange (Fig. 2).
1/2t2) and was collected from 1/4 width (1/4B) of the total width. The reason why the flange 174F section was selected and its properties were determined was because it was thought that this location exhibited approximately average mechanical properties of H-section steel and could represent the mechanical test characteristics of H-section steel.

The toughness of the weld zone was evaluated by a 2 an V non-chiralpy test using multi-layer submerged arc welding using a ladder groove and a groove groove. Welding current is 700A and voltage is 32cm.

This is one-electrode latent arc welding with a welding speed of 30 cm/min and a heat input of 45 kJ/cm.

Table 2 shows the chemical composition of the test steel, and Table 3 shows the rolling conditions and mechanical test characteristics. The rolling heating temperature was set at 1280°C because it is well known that lowering the heating temperature improves mechanical properties, and it is assumed that high-temperature heating conditions show the lowest value of mechanical properties. This is because the value was determined to be representative of the characteristics at heating temperatures below that value.

As shown in Table 3, ml-13 according to the present invention has a change in rolling finishing temperature and flange plate thickness (cooling rate).
It fully satisfies the target base material mechanical properties of room temperature strength, high temperature strength at 6D O'C, and Charpy value of 3.5 kgf-m or more at OoC. Furthermore, the OoC Charpy value of the welded joint/HAZ portion is 3.5 kgf-m or more. On the other hand, steel 14, which is a comparison steel, cannot secure high-temperature yield strength because it does not have any additives, and steel 15 has insufficient high-temperature strength due to no addition of MO, and has 0.21% C, which exceeds the claimed range, resulting in poor HAZ toughness. Unable to meet required values.

Steel 16 cannot secure high-temperature strength due to insufficient precipitation strengthening of VN due to excess AI, and steel 17 cannot secure base metal and HAZ toughness due to an increase in zero concentration due to insufficient deoxidation.

In addition, in fill B, since the amount of Ti is insufficient relative to the dissolved [O] concentration, the generation of intragranular ferrite in the HAZ portion is insufficient, and the HAZ toughness is significantly reduced, making it impossible to achieve the target value. Because the wire 19 contains excess Si and the wire 20 contains excess N, the base material and HA
Z toughness cannot be ensured.

That is, when all the requirements of the manufacturing method of the present invention are satisfied, even the flange 174F section, which is representative of the mechanical test characteristics of H-beam steel, can be heated to a sufficient temperature at room temperature, as shown in Steels 1 to 13 shown in Table 3. It becomes possible to manufacture H-beam steel that has high temperature strength, excellent toughness, fire resistance, and excellent weld zone toughness.

Table (mm) (Effects of the Invention) The H-beam steel produced according to the present invention has excellent high-temperature properties and weldability, and can achieve fireproofing purposes with a refractory coating thickness of 20 to 50% of the conventional thickness, and construction costs are low. Significant cost reductions can be achieved by reducing costs and shortening the construction period.

In addition, flange 174, which represents the mechanical test characteristics of H-beam steel,
Excellent HA with sufficient room temperature and high temperature strength in the F section
It has become possible to manufacture H-beam steel with Z toughness, and the industrial effects such as improving the reliability of large buildings, ensuring safety, and economic effects are extremely significant.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the cross-sectional shape of the H-section steel and showing the sampling positions of mechanical test pieces. FIG. 2 is a schematic explanatory diagram of the groove shape and weld shape of the weld joint half.

Claims (2)

[Claims] (1) Vacuum degassing treatment of molten iron and deoxidizing elements Al, Si,
After performing preliminary deoxidation treatment by adding pure metals such as Ca and Mg alone or in combination with their alloys, or by vacuum degassing treatment alone, dissolved oxygen is reduced to 0.003 to 0.015% by weight, and then the alloy is prepared. By addition, C: 0.05-0.
20%, Si: 0.05~0.50%, Mn: 0.4~
2.0%, Mo: 0.3-0.7%, V: 0.05-0
．． 20%, N: 0.0070-0.0150%, Al<
0.005%, with the remainder consisting of Fe and unavoidable impurities, and further deoxidized to -0.006≦[Ti%]-2[O%] relative to the dissolved oxygen [O%] of the molten steel.
] ≦0.008, and the steel pieces obtained from the molten steel were adjusted to have a Ti content of 1100 to 1% by weight.
A method for producing an H-beam steel having excellent fire resistance and weld zone toughness, which comprises reheating to a temperature range of 300°C, followed by hot rolling to a rolling finishing temperature in the range of 750 to 1050°C. (2) Vacuum degassing treatment of molten iron and deoxidizing elements Al, Si,
After performing preliminary deoxidation treatment by adding pure metals such as Ca and Mg alone or in combination with their alloys, or by vacuum degassing treatment alone, dissolved oxygen is reduced to 0.003 to 0.015% by weight, and then the alloy is prepared. By addition, C: 0.05-0.
20%, Si: 0.05~0.50%, Mn: 0.4~
2.0%, Mo: 0.3-0.7%, V: 0.05-0
．． 20%, N: 0.0070-0.0150%, Al<
In addition to 0.005%, Cr≦0.7%, Ni≦1.0%
, Nb≦0.05%, Cu≦1.0%, and the remainder is Fe and unavoidable impurities.
] -0.006≦[Ti%]-2[O%]≦0.
The molten steel containing Ti by weight% satisfying the relationship 008 was prepared, and the steel pieces obtained from the molten steel were heated at 1100 to 1300°C.
A method for producing an H-section steel having excellent fire resistance and weld zone toughness, the method comprising: reheating the steel to a temperature range of 750 to 1050°C, and then hot rolling to a finishing temperature of 750 to 1050°C.