JPS62253721A - Production of thin-walled h-shape steel having excellent toughness and strength - Google Patents

Abstract

PURPOSE:To obtain the title H-shape steels having a uniform quality and a high flange/web thickness ratio by differentiating the roll finishing temps. of the web and flange of the billet having a specified composition, rolling the billet at a specified total draft of the web, and cooling the flange forcibly and naturally. CONSTITUTION:The thin-walled H-shape steels wherein the thickness of the web is controlled to <=20mm and the thickness ratio of flange/web is adjusted to >=1.5 are produced by the following method. Namely, the billet contg., by weight, 0.01-0.13% C, 0.05-0.90% Si, 0.05-0.50% Mn, <=0.030% P, <=0.03% S, and 0.005-0.500% Sol Al is prepared. The billet is rolled under conditions where the roll finishing temp. of the web is made lower than the 730 deg.C transformation point, the roll finishing temp. of the flange is made >=130 deg.C higher than the transformation temp., and the total draft of the web at <=800 deg.C is controlled to >=30%. The flange is then forcibly cooled at the rate of 5-35 deg.C/sec, cooling is stopped at 400-650 deg.C, the flange is then naturally cooled, and the thin-walled H-shape steels having desired toughness and strength are obtained.

Description

[Detailed description of the invention] [Technical field of invention] This invention relates to a method for manufacturing H-shaped steel.

[Prior art and its problems]

In recent years, there has been a growing trend in the construction industry to use H-beam steel with a small web thickness. The reason for this is that the benefits of weight reduction are enormous.

There are no design problems in using such H-beam steel with a small web thickness. Therefore, recently there has been a demand for H-beam steel with a ratio of flange thickness (tr) to web thickness (tw), that is, tF/1w, of 2.0 to 4.5 or more and a thin web thickness (tw). It's increasing.

However, when manufacturing H-shaped steel by rolling, the ratio of the flange thickness (tF) to the web thickness (tw), that is, the value of tF/1w, is large, and the web (t
If the thickness of w) is small, there is a problem that distortion called 'web waves' occurs in the web. If this distortion is large, it is impossible to use it as a product. The mechanism by which the web waves are generated is as follows. That is,
When the thickness of the flange and the web are different, the rolling temperature of the flange and the web during hot rolling and the cooling rate after rolling are different. This difference creates tensile residual stresses in the flange and compressive residual stresses in the web. The residual stress increases as the ratio between the flange thickness (tF) and the web thickness (tw), ie, tF/1w, increases. This is because there is a large difference in rolling temperature and cooling rate between the flange and the web. For this reason, when the web thickness is small, the overall strength of the web is
Web waves occur when the generated stress cannot be withstood. Generally, the generation of web waves is determined by the thickness of the flange (tF)
is 1.5 times or more the thickness of the web (tw), and
H with a web thickness (tw) of 151!1 or less
It often occurs in shaped steel.

Traditionally, the thickness of the flange (tF) is the thickness of the web (t
w) 1.5 times or more, and the thickness of the web (tw
) is 15 or less, various measures are taken to prevent the occurrence of web waves, one of which is water cooling of the flange. However, even in the case of this method, there is a problem that the materials of the flange and the web are non-uniform. That is, the required strength (40K'i/mn?).

Alternatively, if an H-type steel is rolled using a conventional steel type having a chemical composition that gives a strength of 50 Ky/mm" and the flange is water-cooled to prevent web waves from forming, the strength of the flange is significantly increased. Therefore, there are problems such as differences in material properties between the flange and the web, and the formation of a hardened structure in the surface layer of the flange.

[Purpose of the invention]

Therefore, the object of the present invention is to provide a web having a thickness of 20 mm or less, a flange thickness of 1.5 times or more of the web thickness, excellent toughness and strength, and both the flange and the web being homogeneous. An object of the present invention is to provide a method for manufacturing thin-walled H-shaped steel.

[Summary of the invention]

In this invention, the thickness of the web is 201EI or less, and
H where the thickness of the flange is 1.5 times or more the thickness of the web
In the manufacturing method of thin-walled H-shaped steel, in which the shaped steel is manufactured by rolling, C: 0.01 to O@13wt, %, Si: 0.05 to 0.90 wt, %, Mh:
0.05-0.50 wt, %, P: 0.030
wt. S or less, S: 0.030wt, 1 or less, 5olAl: 0.005-0.500wt, %, Fe
and unavoidable impurities: remainder, or in addition to the above components, Nb: 0.005 to 0.100 wt.%, or in addition to the above components, V: 0.100 wt. Below, Cu: 0.25wt. S or less, Cr: 0.25wt, S or less, Ni: 0.25wt, S or less, Mo: 0.25wt, S or less, or in addition to the above components, Nb: 0 .05 to 0.100 wt.], and V: 0.100wt. S or less, Cu: 0.25wt, S or less, Cr: 0.25wt, S or less, Ni: 0.25Wt-S or less, Mo: 0.25wt, 1 or less, at least one member of the group consisting of: The rolling finishing temperature of the web of the steel billet is 730°C or more, the rolling finishing temperature of the flange is 130°C or more higher than the rolling finishing temperature of the web, and the total rolling reduction of the web is 800°C or less. The steel billet is rolled at a temperature of 30°C or more, then the flange is immediately forcedly cooled at a cooling rate of 5°C to 35°C/sec, and the cooling is stopped at 400°C to 650°C, and then , which is characterized by natural cooling.

[Structure of the invention]

Next, the method of this invention will be explained in detail.

The present inventors have determined that the thickness of the web is 2011B or less, and
H where the thickness of the flange is 1.5 times or more the thickness of the web
In order to manufacture shape steel, we have conducted extensive research on a method to obtain H-shape steel that has excellent toughness and strength, and has a homogeneous flange and web. As a result, we obtained the following knowledge. That is,
A difference is made between the rolling finishing temperatures of the flange and the web, the rolling finishing temperature of the flange is set above the transformation point, the rolling finishing temperature of the web is set below the transformation point, and the transformation temperature of the steel is set from 800°C to 860°C. If the rolling finish temperature difference between the flange and the web is 130°C or more, and only the flange is forcedly cooled at a prescribed cooling rate after rolling, it will have excellent strength and toughness, and both the flange and the web will be homogeneous. H-shaped steel can be manufactured.

In this invention, the reason why the chemical composition of the steel is limited as described above will be described below.

C: C has the effect of improving the strength of steel. However, if C is 0.01wt or less than 1, yield strength (YS)≧
32 Niri/mtr? and tensile strength (TS)≧40Kq
/mrr? is not obtained. On the other hand, when C exceeds 0.13 wt%, the transformation temperature is too low and the transformation temperature (T)2
The problem arises that the temperature of 800° C. cannot be satisfied and that the hardness of the flange surface layer increases. Therefore, the content of C is 01~
It should be 0.13wt%.

Mn: Like C, M and n have the effect of improving the strength of steel. However, if Mn is less than Q, Q5wt%, yield strength (ys) ≧32 Ky/mrr? and tensile strength (
TS) ≧40 Kq/mtf? is not obtained. on the other hand,
If M exceeds 0.50 wt%, the problem arises that the transformation temperature is too low and the transformation temperature (T) of 2800°C cannot be satisfied. Therefore, the Mn content is 0.05 to 0.50
It should be wt%.

Si: Si is an element effective as a deoxidizing agent. however,
When the Si content is less than 0.05wt%, the desired effect cannot be obtained in the above action, while on the other hand, when the Si content is less than 0.90w
If it exceeds t%, a problem arises in that the cleanliness of the steel deteriorates.

Therefore, the Si content should be between 0.05 and 0.9 wt%.

BOl,)dl: 5o11. Like Si, M is an effective element as a deoxidizing agent and has the function of fixing ON in the steel and ensuring the transformation temperature (T) of the steel of 2800°C. However, if the content of Sol and M is less than 0.005 wt, the desired effects described above cannot be obtained;
If it exceeds 0.500 wt%, there is a problem in that the cleanliness of the steel deteriorates and there is a risk that surface flaws will occur in the steel. Therefore, the content of BOl, M is 0.005wt%
It should be ~0.500 wt%.

P: If the P content exceeds 0.030 wt%, segregation may occur. Therefore, the content of P is 0.030w
It should be less than t%.

S: If the S content exceeds 0.030 wt%, segregation may occur. Therefore, the S content is 0.030
It should be less than wt%.

Nb: Nb improves the strength of steel and adds 36Kfmr to steel.
r? Yield strength of more than 50 to 97 mrr? It has the effect of imparting the above tensile strength. However, Nb is o, o
If the content is less than 0.100 wt%, the desired effect cannot be obtained. On the other hand, if it exceeds 0.100 wt%, no further effect can be obtained, and the cost increases. Therefore, the Nb content should be between o, oos and 0.109 wt%.

■, (: u, Cr, Ni, Mo: V, Cu, Cr, Ni, Mo each has the effect of improving the steel O strength. However, ■
Even if the content exceeds 0.100 wt%, no better effect can be obtained, and on the contrary, the problem of too high hardness occurs. If the content of each of Cu, Cr, Ni, and Mo exceeds 0.25 wt%, as in ■,
No better effect can be obtained, and on the contrary, the problem arises that the hardness is too high. Therefore, ■ is 0.100wt%
Below, Cu is 0.25wt% or less, Cr is 0.25wt%
% or less, Ni is less than 25wt%, MO is 0.25w
It should be less than t%.

Moreover, two or more types of V p Cu + Cr r Nl + Mo can be contained. however,
When the total content exceeds 0.50 wt%,
A problem arises in that the transformation temperature of the steel becomes low. Therefore, V, C
u, Cr, Ni.

When at least two or more types of MO are contained, the total amount is preferably 0.50 wt% or less.

Next, the reason for limiting the rolling and cooling conditions will be described below.

In order to produce H-beam steel with a web thickness of 20 mm or less and a flange thickness of 1.5 times or more than the web thickness by the method of the present invention, the finishing temperature of the web must be adjusted from 730°C to below the transformation point. at a temperature between Rolling must be carried out under conditions of 30% or more.

The reason why the rolling finishing temperature of the web was set from 730° C. to a temperature below the transformation point is as follows. That is, by setting the rolling finishing temperature of the web to a temperature below the transformation point, the web is rolled down after transformation. Therefore, in the steel having the above-mentioned basic composition, or in the above-mentioned basic composition, V is o,ioowt% or less, Cu is 0.25wt% or less,
In steel containing at least one of the group consisting of Cr of 0.25 wt% or less, Ni of 0.25 wt% or less, and MO of QJ5 wt% or less, ferrite recrystallization progresses, forming a fine structure and weighing 40 kg. A tensile strength of /m or more and good toughness can be obtained. In addition, the basic component composition described above contains 0.005 to 0.100 wt% of Nb, or in addition, ■ is 0.100 wt% or less, Cu
is 0.25wt% or less, Cr is 0.25wt% or less, N
In steel containing at least one member of the group consisting of i = 25 W't% or less and MO = 0.25 wt% or less, by being rolled in a state of unrecrystallized austenite and ferrite composition, 50Ky/mrr? It is possible to obtain higher tensile and tensile strength and better toughness. If the temperature is less than 730°C, the rolling mill will be burdened and efficient rolling will not be possible.

The reason why the finishing rolling temperature of the flange was set to be 130° C. or more higher than the finishing temperature of the web and a temperature higher than the transformation point is as follows. In other words, by setting the flange finishing temperature to 130°C or more higher than the web finishing temperature, the flange finishing temperature becomes a temperature higher than the transformation point, and the rolling of the flange is completed before the start of transformation. finish. Therefore, in the steel having the above-mentioned basic composition, or in the above-mentioned basic composition, ■ is 0.100 wt% or less,
Cu is Q, 25 wt% or less, ('r is 0.25 wt% or less, Ni is 0.25 wt% or less, MO is 0.25 wt%
Group Aa consisting of the following: 1-J1 Polar Δ Female 2 Bilateral W 711 Eight Coarseening of recrystallized austenite grains during rolling is suppressed, and carbides are uniformly dispersed. As a result, it is possible to provide the flange with strength equal to or higher than that of the web and good toughness. In addition, the basic component composition described above contains Nb of 005 to 0.100 wt%, or in addition, ■ is 0.100 wt% or less and Cu is 0.
．． 25 wt% or less, Cr is 25 wt% or less, Ni
In steel containing at least one member of the group consisting of 0.25 wt% or less and MO of 25 wt% or less, coarsening of recrystallized austenite grains during rolling is similarly suppressed, and υ , 50 Kq/mtr?
The above tensile strength and good toughness can be obtained.

If the rolling finish temperature difference between the flange and the web is less than 130°C, the rolling finish temperature of the flange will be below the transformation point,
There is a risk that the flange will be forcedly cooled after the transformation begins. Therefore, the desired strength and toughness cannot be imparted to the flange.

Based on the above, the lower limit of the rolling finish temperature of the flange is -8
60°C, L4 Lee This temperature is the upper limit of the transformation temperature.

If the upper limit of the transformation temperature exceeds 860° C., the temperature at which cooling of the flange starts may occur after the start of transformation, making it impossible to ensure sufficient strength of the flange. The lower limit of the transformation temperature is 8oo°C. If the lower limit is less than 800° C., it is necessary to further lower the finishing temperature in order to ensure the strength and toughness of the web, which poses a problem of placing a burden on the rolling mill. The total reduction rate of the web is 800℃
It must be 30% or more at the above temperature. The total rolling reduction of the web is 30% at temperatures of 800°C or higher.
If the thickness is less than 201B, the thickness of the web is 201B or less, and
H-shaped steel whose flange thickness is 185 times the web thickness cannot be efficiently rolled.

Next, the cooling conditions will be described.

In this invention, steps 5 to b are applied to the 7 lunges immediately after the rolling is completed. When the cooling rate is 5 to b, it is not possible to impart the same strength and toughness to the flange as the web. On the other hand, the cooling rate is 35℃/Se
If C is exceeded, the strength will be too high, the toughness will deteriorate, the hardness will increase significantly at the surface layer of the flange, and further problems will occur such that the materials of the web and the flange become non-uniform. Therefore, the cooling rate of the flange is 5℃/8ec~35℃/see
Should be.

The cooling stop temperature should be 400-650°C. If the cooling stop temperature exceeds 650°C, no improvement in strength and toughness will be obtained, while if the cooling stop temperature is less than 400°C, a problem arises in that the hardness of the flange surface layer increases significantly.

[Embodiments of the invention]

Next, the present invention will be further explained using examples.

Steel slabs 1 to 7 having compositions within the range of the present invention shown in Table 1 were prepared. Next, each of the steel billet points 1 to 7 was
After heating to 0°C, it is rolled in the usual manner and the thickness of the flange (t
F) is 20 mm, web thickness (tw) is 12 states, (tF
/1w=1.67).

The rolling finishing temperature was 900°C for the flange (TF) and 760°C for the web (TW). Immediately after rolling was completed, the flange was forcibly cooled by water cooling. Cooling start temperature is 880℃
, the cooling stop temperature is 600'C, and the cooling rate during this time is 20'C/sea, or 10'C/sea.
And so. As a result, as shown in Table 1,
In both cases, the desired metamorphosis point was obtained.

Next, tensile test specimens (cross section 9φ, goose length (GL) 32 cm) and impact test specimens (V-cut Notch 2, cross section 10111'
x10 parrots), and for each of these test pieces,
Tensile and impact tests were conducted. Table 2 shows the test results. As shown in Table 2, both the flange and the web were substantially uniform, and good strength and toughness were obtained, while at the same time the generation of web waves and residual stress was completely prevented. Next, the thickness (tF
) is 17m5. H with dimensions of web thickness (tw) of 11 m, web height of 600 m, and flange width of 200 m.
Type steel and conventional mechanical structural carbon steel (S24C) with the chemical composition shown in Table 3 are shown in Table 2 YS: Yield strength EL: Elongation vTs: Fracture transition temperature T
S: Tensile strength RA: Reduction of area WEB: Shelf energy was used to compare the hardness distribution of the flange with H-shaped steel manufactured by conventional technology. FIG. 1 is a diagram showing the comparison results. As shown in FIG. 1, the steel grave 1 of the present invention exhibits a uniform hardness distribution. In contrast, the hardness distribution of conventional steels was extremely uneven.

Table 3 [Effects of the Invention] As described above, according to the method of the present invention, even though the web thickness is small and the thickness ratio to the flange is large, the material is uniform and the web waves are Since it is possible to manufacture high-quality H-beam steel that does not generate heat, it has excellent industrial effects and is expected to be used in many industrial fields, including the construction industry.

In the drawing, the flange thickness is 17 mm, the web thickness is 11 mm,
In the case where an H-shaped steel with a web height of 600mm and a flange width of 20018mm was manufactured using the method of the present invention, and when it was manufactured using the conventional method using carbon steel for machine structures (824C). , is a diagram showing a comparison of the hardness distribution of flanges.

Claims (4)

[Claims] (1) In a method for manufacturing a thin H-shaped steel by rolling an H-shaped steel whose web thickness is 20 mm or less and whose flange thickness is 1.5 times or more the web thickness, C: 0.01 to 0. .13wt. %, Si: 0.05-0.90wt. %, Mn: 0.05-0.50wt. %, P: 0.030wt. % or less, S: 0.030wt. % or less, solAl: 0.005 to 0.500wt. %, Fe and unavoidable impurities: the balance, the rolling finish temperature of the web is set to 730 ° C. or higher, and the rolling finish temperature of the flange is set to a temperature higher than the rolling finish temperature of the web by 130 ° C. or more, and The steel billet is rolled under the condition that the total rolling reduction of the web is 30% or more at a temperature of 800°C or less, and then the flange is immediately forcedly cooled at a cooling rate of 5°C to 35°C/sec, and A method for manufacturing a thin-walled H-shaped steel with excellent toughness and strength, characterized by stopping cooling at 650°C and then cooling naturally. (2) In a method for producing a thin H-shaped steel by rolling an H-shaped steel whose web thickness is 20 mm or less and whose flange thickness is 1.5 times or more the web thickness, C: 0.01 to 0. .13wt. %, Si: 0.05-0.90wt. %, Mn: 0.05-0.50wt. %, P: 0.030wt. % or less, S: 0.030wt. % or less, solAl: 0.005 to 0.500wt. %, and further contains V: 0.100wt. % or less, Cu: 0.25wt. % or less, Cr: 0.25wt. % or less, Ni: 0.25wt. % or less, Mo: 0.25wt. % or less, containing at least one member of the group consisting of Fe and unavoidable impurities. The steel billet is rolled at a temperature 130°C or more higher than the finishing temperature and the total rolling reduction of the web is 30% or more at a temperature of 800°C or less, and then the flange is immediately rolled at 5°C to 35°C/ Forced cooling at a cooling rate of sec, and stopping cooling at 400°C to 650°C,
Next, a method for producing a thin-walled H-shaped steel with excellent toughness and strength, which is characterized by natural cooling. (3) In a method for producing a thin H-shaped steel by rolling an H-shaped steel whose web thickness is 20 mm or less and whose flange thickness is 1.5 times or more the web thickness, C: 0.01 to 0. .13wt. %, Si: 0.05-0.90wt. %, Mn: 0.05-0.50wt. %, P: 0.030wt. % or less, S: 0.030wt. % or less, solAl: 0.005 to 0.500wt. %, Nb:
0.005-0.100wt. %, Fe and unavoidable impurities: the balance, the rolling finish temperature of the web is set to 730 ° C. or more, and the rolling finish temperature of the flange is set to a temperature higher than the rolling finish temperature of the web by 130 ° C. or more, and The steel billet is rolled under the condition that the total rolling reduction of the web is 30% or more at a temperature of 800°C or less, and then the flange is immediately forcedly cooled at a cooling rate of 5°C to 35°C/sec, and A method for manufacturing a thin-walled H-shaped steel with excellent toughness and strength, characterized by stopping cooling at 650°C and then cooling naturally. (4) In a method for manufacturing a thin H-type steel by rolling an H-type steel whose web thickness is 20 mm or less and whose flange thickness is 1.5 times or more the web thickness, C: 0.01 to 0. .13wt. %, Si: 0.05-0.90wt. %, Mn: 0.05-0.50wt. %, P: 0.030wt. % or less, S: 0.030wt. % or less, solAl: 0.005 to 0.500wt. %, Nb:
0.005-0.100wt. %, and further contains V: 0.100wt. % or less, Cu: 0.25wt. % or less, Cr: 0.25wt. % or less, Ni: 0.25wt. % or less, Mo: 0.25wt. % or less, containing at least one member of the group consisting of Fe and unavoidable impurities. The steel billet is rolled at a temperature 130°C or more higher than the finishing temperature and the total rolling reduction of the web is 30% or more at a temperature of 800°C or less, and then the flange is immediately rolled at 5°C to 35°C/ Forced cooling at a cooling rate of sec, and stopping cooling at 400°C to 650°C,
Next, a method for producing a thin-walled H-shaped steel with excellent toughness and strength, which is characterized by natural cooling.