JPH04136120A - Production of steel plate for structure purpose having high young's modulus - Google Patents

Abstract

PURPOSE:To smoothly, stably and economically produce the steel plate for structure purposes which is improved in the Young's modulus in a direction C without impairing its toughness by restrictively combining rolling conditions of the unrecrystallization regions of the steel products for structure purposes and rolling conditions of a two-phase area. CONSTITUTION:The steel slab for structure purposes with which solidification is completed is heated at >=900 deg.C and <=1250 deg.C and is then subjected to hot rolling at >=20% draft in the temp. region below the recrystallization end temp. and above the Ar3 point. The steel plate is then subjected to two-phase area rolling at >=50% draft in the temp. region below the Ar3 point. The steel plate is thereafter preferably subjected to controlled cooling down to <=600 deg.C at >=5 deg.C/sec cooling rate. The steel products for structure purposes improved in the Young's modulus in the direction C by >=10% is produced.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention is directed to the production of structural steel sheets that have excellent toughness and dramatically improve Young's modulus in the direction perpendicular to the rolling direction (hereinafter referred to as the C direction). It is about the method.

<Prior Art> Generally, the rigidity of a steel plate is proportional to Young's modulus if the shape is constant.

In conventional steel, the Young's modulus is approximately 21,000 kgf/as, excluding special cases such as single crystal and magnetic steel sheets.
was considered to be a constant value, so it was not considered to be a material property of particular interest.

However, in recent years, there has been a demand for improved rigidity in a specific direction during use, and application of the C direction with a high Young's modulus tm+i in the C direction has been considered for this purpose.

This is because according to this method, it is possible to increase the rigidity of the structure without increasing the plate thickness or changing the shape.

On the other hand, there are various proposals regarding the manufacturing method of high Young's modulus steel, and for example, the manufacturing method is disclosed in Japanese Patent Publication No. 5B-14849.

This manufacturing method involves rolling sea bream with defined chemical components in a two-phase region, controlling the cooling rate to 300°C after finishing the rolling, and then tempering at a temperature of 700°C or less.
It has been shown that the Young's modulus in the C direction can be increased by about 10%.

In addition, Japanese Patent Publication No. 62-4448 specifies the rolling reduction rate in the temperature range of 600°C or higher below the Art point for a steel containing less than 0.03% by weight, and after rolling, the rolling reduction rate is 450°C or higher.
We have proposed a manufacturing method that increases the Young's modulus in the C direction to a maximum of 24,300 kgf/■-2 by winding at a temperature of 20° C. or lower.

In other words, these methods are characterized by developing a rolling texture by rolling in a two-phase region or a ferrite region to improve the Young's modulus in the C direction of the wire material.

<Problems to be Solved by the Invention> However, all of the above-mentioned proposals have inherent problems described below, and improvements are awaited in each of them.

In other words, the proposal in Japanese Patent Publication No. 5B-14849 guarantees toughness at only 0°C, and in recent years has been required for important members of structural steel plates, especially from the viewpoint of ensuring safety during use. This does not meet the requirements for guaranteeing toughness below ℃.

This is because a significant amount of processed ferrite is generated by rolling in the two-phase region, and this processed ferrite deteriorates the toughness.

Furthermore, this method requires heating to a temperature of 700° C. or lower to perform a tempering treatment after hot rolling, which requires a large amount of thermal energy and inevitably increases manufacturing costs.

In addition, the proposal in Japanese Patent Publication No. 62-4448 is C50.0
This is a manufacturing method for extremely mild steel that requires a steel content of 3%, which does not meet the required strength for structural steel.

The present invention has a structure that has excellent low-temperature toughness, does not require tempering treatment, solves the problems of the conventional technology described above, and improves Young's modulus by 10% or more by manufacturing with high productivity and low cost. The objective of this research is to understand the manufacturing method of steel sheets for industrial use.

<Means for Solving the Problems> In order to achieve the above problems, the present invention has the following objectives: (1) After heating four pieces of structural steel that have completed #J hardening to a temperature of 900°C or higher and 1250°C or lower, the recrystallization end temperature is Below, A
Hot rolling is carried out at a rolling reduction of 20% or more in the temperature range above the RZ point, and 2 at a rolling reduction of 50% or more in the temperature range below the Ar3 point.
The first method is to produce a high Young's modulus structural steel plate, which is characterized by phase region rolling.
After heating to 250°C or less, hot rolling is performed at a reduction rate of 20% or more in a temperature range below the recrystallization end temperature and above the Ar□ point,
After performing two-phase rolling at a reduction rate of 50% or more in a temperature range below Ar3 point, 600°C at a cooling rate of 5°C/sec or more.
The second method is a method for producing a high Young's modulus structural steel sheet, which is characterized by controlled cooling to a temperature of .degree. C. or lower.

The structural steel to which the present invention is directed is described, for example, in the above-mentioned Japanese Patent Publication No. 5B-14849, and as described below,
In order to obtain the required material properties of ordinary welded structural steel, the types and amounts of additive elements that have been determined based on the relationship between action and effect that has been confirmed through use in five industrial fields are used in the same way. The same effect and effect can be obtained.

Therefore, the present invention targets all steels containing these.

Each of these component elements, the reason for their addition, and their amounts are shown below.

C is added as an effective component to improve the strength of the steel, but if the content exceeds 0.20%, the deformation resistance during rolling in the two-phase region increases, making rolling difficult, and also causing damage to the welded joint. Since it precipitates island-like martensite and significantly deteriorates the toughness of steel, it is restricted to 0.20% or less.

Si is an element that deoxidizes molten steel and is also an element that increases strength. If less than 0.01% is added, the deoxidizing effect will be insufficient, and if more than 1.0% is added, the workability of the steel will be reduced and the toughness of the welded part will be deteriorated, so the amount added is between 0.01 and 1%. It is regulated at .0%.

Mn is a deoxidizing component element, and if it is less than 0.3%, the cleanliness of the steel decreases and impairs workability. On the other hand, to improve the strength of steel materials, it is necessary to add 0.3% or more. However, Mn
The addition of J! Ii temperature is lowered, and excessive addition lowers the two-phase region rolling temperature and causes an increase in deformation resistance, so the upper limit is 2.
It is set at 0%.

A1 and N are added to make the steel finer with AI nitrides, as well as to have an effective function in matching the crystal orientation and recrystallization of the steel through solid solution and precipitation during the rolling process, but it is difficult to maintain the effect. and AI: 0.00 to prevent toughness deterioration, respectively.
1 to 0.20%, N: limited to 0.020% or less.

The basic components of the steel targeted by the present invention are as mentioned above, but in addition, Ni, Cr, No5Cu, WSCo, V.

Nb, Ti, Zr, τa, Hf, rare earth elements, Y
, Ca, Mg.

One or more of Te, Se, and B are added.

Since this addition lowers the transformation temperature, increases deformation resistance in the two-phase region, and makes rolling in the two-phase region difficult, the total amount of these additions is regulated to 4.5% or less.

The heating temperature of the steel slab obtained from the above steel is set at the lower limit of 900°C, which is the limit temperature at which rolling can be continued even if there is a temperature drop during rolling, under the normal heating conditions for this type of steel slab. The upper limit is set at 1250° C., which is the temperature at which the chemical reaction can be prevented.

Further, when rolling is performed in a temperature range below the recrystallization end temperature and above the Ar2 point, if the rolling reduction is less than 20%, good low-temperature toughness cannot be obtained, so the rolling reduction is set to be 20% or more.

Furthermore, if the rolling reduction in the temperature range below Ar3 points is less than 50%, the improvement in Young's modulus will not reach 10% or more, so the rolling reduction is set to be 50% or more.

Furthermore, in order to accelerate the cooling of this steel plate and improve its strength, no matter which coolant is used, such as water, steam, or air/water temperature combination,
It is sufficient to cool to a temperature of 600°C or less at a cooling rate of ℃/sec or more, and when the cooling rate is less than 5" (:/sec or the cooling stop temperature is 600°C), no improvement in strength by accelerated cooling is observed in sardines. .

<Function> In order to solve the problems of the prior art and achieve the objects of the present invention, the present inventors have repeatedly conducted various experimental studies using general structural steel having the following chemical components. . The results are shown in FIGS. 1 and 2.

C: 0. lO ~ 0.15% Si: 0°150.2
5%Mn: 0.8-1.6% Al: 0.
01~0.05%N: 0.0020~0.0050
Figure 1 shows the relationship between Young's modulus divided by angle from the rolling direction (hereinafter referred to as the backward direction) and the rolling reduction in the two-phase region.

As a result of this investigation, it was found that by increasing the rolling reduction in two-phase region rolling to 50% or more, the Young's modulus in the C direction could be improved by 10% or more.

Figure 2 shows the relationship between toughness and rolling reduction in the uncrystallized region and the two-phase region.

As is clear from the figure, toughness decreases as the rolling reduction in the two-phase region increases, but if the rolling reduction in the non-recrystallized region is maintained at 20% or more, the toughness improves and reaches a level below -40°C. I found out.

This is considered to be because the coarsening of the fracture surface unit is maintained even after rolling in the two-phase region due to the refinement of ferrite grains achieved by applying a reduction in the non-recrystallized region at a reduction rate of 20% or more.

Furthermore, if the rolling reduction in the non-recrystallized region is set to 20% or more and the two-phase region rolling reduction is ensured to be 50% or more, then the C-direction will be reduced.The present invention was made based on the above-mentioned findings.

<Example> (1) Test steel The steel of the present invention may be made of any combination of the elements and additive amounts of the general structural steels mentioned above, but the steels have different strength levels in the field of structural steels. Chemical components of typical examples are shown in Table 1 along with comparative examples.

(2) Rolling conditions and material Hot rolling conditions, cooling conditions, and the resulting material are shown in Table 2.

Regarding the test steels shown in Table 1, Perfume 1.2 is 40 kg class steel, Perfume Nos. 3 to 6 are 50 kg class steel, and Perfume No. 7 is 60 kg class steel.

In addition, the sample steel may contain V, Nb, Ni, Ti, or
Cu.

Alloying elements such as Ni, Cr, and No are added.

Inventive examples No. and A1 to A7 were all manufactured with good productivity without any heat treatment after rolling.

The Young's modulus in the C direction was improved by 10% to 16%, and a structural steel plate was obtained that fully satisfied the target and had excellent low-temperature toughness.

On the other hand, Comparative Examples No. and Old to B7 each had their own problems, and structural steel plates satisfying the above requirements could not be obtained.

That is, in Comparative Example No. B1 in which Ar and the intended two-phase region reduction rate were less than 50%, the improvement in Young's modulus did not reach the required range.

Moreover, comparative example No. B2. has a high heating temperature of 1300°C. B
3. Furthermore, comparative example No. where the reduction rate in the non-recrystallized region is less than 20%,
B4°5 lacked toughness at -20°C and -23°C, and could not be used for the intended purpose.

Comparative example No. B6. B7 is a comparative example of the accelerated coolant of the second claim, and is the invention example No. 86. A7, No. B6 of the comparative example. Both TS and vTrs of B7 were lower.

<Effects of the Invention> The manufacturing method of the present invention described above is based on the knowledge of the present inventors, and is a limited combination of rolling conditions in the non-recrystallized region and rolling conditions in the two-phase region of structural steel materials. As a result, structural steel plates with stiffness in the C direction, that is, Young's modulus in the C direction, have been improved by 10% or more, without compromising toughness and with high productivity by omitting post-rolling tempering. , which has made it possible to produce it stably and economically, and has an extremely large industrial effect.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between the Young's modulus divided by angle from the rolling direction and the rolling reduction in the two-phase region. FIG. 2 is a diagram showing the relationship between the rolling reduction in the non-recrystallized region and toughness. Patent applicant Nippon Steel Corporation

Claims (2)

[Claims] (1) Structural steel pieces that have been solidified are heated to 900°C or higher for 1
After heating to 250℃ or less, below recrystallization completion temperature, Ar_2
A high Young's modulus structural steel plate characterized by hot rolling at a reduction rate of 20% or more in a temperature range of Ar_2 or higher, and rolling in a two-phase region at a reduction of 50% or more in a temperature range of less than Ar_2. manufacturing method. (2) Structural steel pieces that have been solidified are heated to 900°C or higher for 1
After heating to 250℃ or less, below recrystallization completion temperature, Ar_3
Hot rolling is carried out at a rolling reduction of 20% or more in a temperature range of Ar_3 or above, and two-phase rolling is carried out at a rolling reduction of 50% or more in a temperature range of less than Ar_3, followed by a cooling rate of 5°C/sec or more. So 6
A method for producing a high Young's modulus structural steel plate characterized by controlled cooling to a temperature of 00°C or less.