JP2000080414A - Manufacture of hot-dip galvanized refractory steel product for structural - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a refractory steel product for structural having excellent fire resisting strength even if fireproofing coating is omitted and usable as a hot-dip galvanized steel product. SOLUTION: A steel bloom having a steel composition which consists of 0.06-0.15% C, 0.10-0.25% Si, 0.50-1.40% Mn, 0.20-0.60% Mo, 0.02-0.06% V, 0.0010-0.0060% N, 0.01-0.08% Al and the balance Fe with inevitable impurities and in which the value of G stipulated by an equation mentioned below is 0.7-1.2, is heated at 1,050 to 1,200 deg.C and then, hot rolled at 760 to 880 deg.C of a rolling finishing temperature. After the completion of hot rolling, hot-dip galvanizing is performed as secondary working.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a refractory steel material for a hot-dip galvanized structure, and more particularly to a method for reducing a refractory coating used in the production of various structures in the fields of construction, civil engineering and marine structures. The present invention relates to a method for manufacturing a hot-dip galvanized structural fire-resistant steel material having excellent corrosion resistance in consideration of being used as an external structural member without coating, while maintaining sufficient safety in a fire even if omitted.

[0002]

2. Description of the Related Art Materials that can exhibit sufficient fire resistance even without a fire-resistant coating have been developed, and some proposals have already been made as follows.

[0003] Japanese Patent Application Laid-Open No. HEI 3-100118 is a steel excellent in fire resistance in which steel satisfying the following formula is hot-rolled, and then water-cooled or water-cooled and tempered after hot rolling.

[0004]

(Equation 2)

[0005] However, the regulation of the E value and the Ceq value are independent, and the mutual relationship between the room temperature strength and the high temperature strength is not clearly expressed. There is room for improvement, such as the necessity of extra processes such as water cooling, water cooling and tempering.

JP-A-3-173715 C: 0.05 to 0.15%, Si: 0.05 to 0.60%, Mn: 0.50 to 1.50
%, Cr: 0.10 to 0.60%, Mo: 0.10 to 0.60%, Nb: 0.005
This is a method for producing a refractory steel in which hot rolling is carried out on a steel which satisfies the following formula, comprising -0.060%, balance Fe and inevitable impurities.

[0007]

(Equation 3)

[0008] However, there is no mention of hot dip galvanization. Although Pcm is widely recognized as an index for evaluating weldability, it cannot evaluate hot-dip galvanization.

[0009] finishing temperature 900 while restricting the steel composition as JP-A-3-107420 following
A method for producing a structural steel material excellent in fire resistance by performing hot rolling at -750 ° C is disclosed.

[0010]

(Equation 4)

Certainly, Mo is an element effective for obtaining high-temperature strength, and Ceq is an index for evaluating weldability and has a strong correlation with the strength at room temperature. Therefore, it is not possible to achieve a proper balance between the room temperature strength and the high temperature strength.

[0012]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for producing a hot-dip galvanized structural fire-resistant steel material having excellent fire resistance and excellent corrosion resistance even if a fire-resistant coating is omitted. is there.

More specifically, high temperature proof strength at 600 ° C. is 2/3 or more of normal temperature proof strength, TS490N / mm ² or more, yield ratio is 80% or less, and excellent corrosion resistance is used for refractory steel for hot-dip galvanized structure. Is to provide a method of manufacturing the same.

[0014]

In order to secure a high yield strength at 600 ° C, which cannot be obtained with conventional structural steel, 0.20 to 0.60
% Mo + 0.02-0.06% V compound addition is extremely effective,
Furthermore, it has been found that by adding 0.10 to 0.25% of Si, the hot-dip galvanizing property is also improved.

According to the present invention, based on this knowledge, the range of industrially most effective chemical components is limited to simultaneously realize the high-temperature proof stress and hot-dip galvanizing property. (1) C: 0.06 to 0.15%, Si: 0.08 ~ 0.25%, Mn: 0.50 ~
1.40%, Mo: 0.20 to 0.60%, V: 0.02 to 0.06%, N: 0.
010 to 0.0060% and

[0016]

(Equation 5)

After the slab having a ratio of 0.7 to 1.2 is heated in a temperature range of 1050 to 1200 ° C., hot rolling is completed in a temperature range of 760 to 880 ° C., and the 0.2% proof stress at 600 ° C. A steel material having a proof stress of 2/3 or more, characterized in that the steel material is subjected to hot-dip galvanizing as a secondary process, a method for manufacturing a 400-500 N / mm class ² refractory steel material for hot-dip galvanized structure, (2) The steel composition further comprises Cu: 0.10 to 0.40
%, Ni: 0.10 to 0.40%, Cr: 0.10 to 0.40%, Ca: 0.0005
The production method according to the above (1), which contains one or more of 0.0040% to 0.0040% and Ti: 0.008% to 0.030%.

[0018]

Next, the reason why the steel composition and the production conditions are limited as described above in the present invention will be described together with the operation thereof.

C: C is an element that contributes to an increase in strength, but if it is less than 0.06%, it is difficult to secure strength.
When added in a large amount exceeding 0.15%, the weldability and toughness are deteriorated. Therefore, its addition range is from 0.06 to 0.15
%. Preferably, it is 0.08 to 0.12%.

Si: Si is an element effective for deoxidation, but 0.0
In the range of 5% or more and less than 0.08% or more than 0.25%, the amount of zinc applied during hot-dip galvanizing is remarkably increased, causing so-called galling. On the other hand, if it is less than 0.05%, the deoxidizing effect cannot be obtained. Therefore, the addition range is 0.
08 to 0.25%. Preferably it is 0.10-0.25%, More preferably, it is 0.10-0.12%.

Mn: Mn is an important element in securing the strength and toughness of steel. However, if it is less than 0.50%, its effect is low, and in order to obtain the strength required in the present invention, 1.40%.
There is no industrial merit even if it is added in a large amount exceeding the above, and the cost will increase unnecessarily. Therefore, the addition amount is set in the range of 0.50 to 1.40%. Preferably, 1.00-1.30
%.

Mo: Mo is the most effective element in suppressing strength deterioration at high temperatures. However, 0.20%
If it is less than the above, it is insufficient to secure the target proof stress at 600 ° C. If added in excess of 0.60%, the weldability is impaired and the industrial value is lost due to increased costs. Therefore,
The added amount is 0.20 to 0.60%. Preferably, 0.45-
0.55%.

V: V is an element effective for increasing the strength.
If it is less than 0.02%, the effect corresponding to the added amount cannot be obtained,
If added over 0.06%, the weldability is impaired.
Therefore, the addition amount is set to 0.02 to 0.06%. Preferably, it is 0.04 to 0.05%.

N: N is an element effective for increasing the strength, but if it is less than 0.0010%, the effect is small, and if it exceeds 0.0060%, the disadvantage of deterioration in weldability is great. Therefore, its addition range is set to 0.0010 to 0.0060%. Preferably, 0.0010 to
0.0040%.

Al: Al is an element indispensable for deoxidation.
The deoxidizing effect can also be obtained by i. Further, since addition of more than 0.080% is unnecessary, the content is set to 0.01 to 0.08%. Preferably, it is 0.02 to 0.05%.

In the present invention, if necessary, C
At least one of u, Ni, Cr, Ca, and Ti is added. Each of these elements is an element that improves toughness, and so long as it is equivalent, may be appropriately selected and added according to the purpose of improving toughness.

Cu: Cu is an element that improves the hardenability of steel and contributes to improvement of toughness, but also improves corrosion resistance.
If it is less than 0.10% for this purpose, it is not sufficient, and if it exceeds 0.40%, hot workability is impaired. Therefore, it is set to 0.10 to 0.40%. Preferably, it is 0.15 to 0.35%.

Ni: Ni is an element for improving toughness,
At 0.05% or more, the effect is exhibited, but at less than 0.10%, an effect commensurate with the addition cannot be obtained. Further, if it is added in excess of 0.40%, the cost rises remarkably, and is not suitable for the intended use of the present invention. Therefore, the added amount is set to 0.10 to 0.40%. Preferably, it is 0.20 to 0.35%.

Cr: Cr is an element for improving the toughness by increasing the hardenability, but at the same time, precipitates carbide by tempering to improve the fire resistance. However, if the addition is less than 0.10%, an effect commensurate with the addition cannot be obtained, and if the addition exceeds 0.40%, it is unnecessary as a structural steel material targeted by the present invention. I do. Preferably,
It is 0.15 to 0.30%.

Ca: Ca is an element that contributes to improvement in toughness by controlling the morphology of inclusions, and is an element that improves the properties in the thickness direction by a small amount. However, if less than 0.0005%, this effect cannot be obtained, and 0.0040% When added in excess of the above, large inclusions are generated and ultrasonic defects are likely to occur. Therefore, the addition amount is 0.00
05 to 0.0040%. Preferably, it is 0.0010 to 0.0035%.

Ti: Ti is an element that suppresses coarsening of austenite grains and also contributes to improvement of toughness by forming fine ferrite, and is an element that is particularly effective in suppressing toughness deterioration of a welded joint. It is. But 0.008%
If the content is less than 0.030%, the effect is not sufficient, and if added over 0.030%, on the contrary, the toughness of the welded joint is deteriorated. Therefore, the added amount is made 0.008 to 0.030%. Preferably, it is 0.010 to 0.025%.

Further, the range of addition of each element is regulated by the G value represented by the following formula.
It is an index that represents the proper balance with the high-temperature strength at a time.

[0033]

(Equation 6)

When the G value is regulated in the range of 0.7 to 1.2, the high temperature characteristics aimed at by the present invention can be exhibited most industrially effectively.

The properties to be provided as structural steel materials include not only fire resistance but also good weldability and
It is important that the workability and the secondary workability, for example, the hot-dip galvanizing property, are good. That is, when these properties are poor, even if the properties of the steel material itself are good, an increase in the processing cost is unavoidable, and the industrial value is completely lost.

From these viewpoints, in the present invention, the high temperature proof stress is maintained at 2/3 or more of the standard normal temperature proof stress in order to secure the fire resistance performance, and the normal temperature strength is suppressed relatively low from the viewpoint of workability.
Furthermore, in order to improve the weldability, an index that remarkably indicates the relationship between the added amounts of the respective chemical components and the appropriate amounts of the respective chemical components is introduced to obtain a structural steel material having excellent performance.

In the manufacturing method according to the present invention, the reason why the heating temperature is limited to 1050 ° C. or higher is to sufficiently dissolve each of the added elements, while the upper limit is set to 1200 ° C. The purpose is to prevent coarsening of grains and to achieve finer grains and higher toughness by rolling.

The reason why the rolling end temperature is set to 760 ° C. or higher is that at a rolling end temperature lower than this temperature, the yield ratio exceeds 80% due to work hardening of ferrite, and the performance required for structural steel, especially for building use, is obtained. If the temperature at the end of rolling exceeds 880 ° C., austenite becomes coarse grains and the toughness is deteriorated, and normal temperature strength is obtained, but shortage of high temperature proof stress occurs. Next, the operation and effect of the present invention will be described more specifically with reference to examples.

[0039]

EXAMPLES Forty-five steels according to the present invention shown in Table 1 and comparative steels shown in Table 3 were subjected to hot rolling under the conditions shown in Tables 2 and 3, and the respective test materials obtained at that time were subjected to hot rolling. Various mechanical properties were evaluated. The results are also shown in Tables 2 and 3.

As is clear from Table 2, the present invention examples No. 1 to No. 1
No.45 has a tensile property at room temperature of 490 N /
mm ² grade JIS G 3106 is a steel, sufficiently satisfies its SM490A, and yield ratio also becomes 80% or less which is required for the construction steel.

The high-temperature proof stress at 600 ° C. required for fire-resistant steel is about 2/3 of the standard value of the proof stress at normal temperature.
It is a value of 7 N / mm ² or more. Further, the fracture surface transition temperature in the Charpy impact test is as good as −35 ° C. or less.

Further, in hot-dip galvanizing at a plating temperature of 440 ° C. and an immersion time of 3 minutes, no galling occurred and good characteristics were exhibited. On the other hand, as shown in Table 3, the comparative example
In No. 1, the yield ratio at room temperature is unsuitable as a steel for construction because the rolling end temperature is slightly lower than the limited range of the present invention.

In Comparative Example No. 2, the toughness was significantly reduced because the heating temperature was out of the upper limit from the limited range of the present invention. In Comparative Example No. 3, the proof stress at 600 ° C. did not reach the target value because the rolling end temperature was out of the upper limit from the limited range of the present invention. Also, the toughness is low.

In Comparative Examples No. 4, No. 8, and No. 11, since Si was out of the upper limit from the limited range of the present invention, an excessive amount of coating was applied during hot-dip galvanizing, which caused so-called plating burn. ing.

In Comparative Examples No. 5 to No. 9, the proof stress at 600 ° C. did not reach the target value because the G value which is the fire resistance performance index introduced in the present invention was outside the lower limit of the limited range. This is also due to the fact that the proof stress at 600 ° C does not reach the target value in No. 6 to No. 9 in which the rolling end temperature is lowered, despite the fact that the room temperature strength is improved, and the G index is also effective. Sex is shown.

In Comparative Example No. 10, Mo was added in excess of the limited range of the present invention, so that the properties at 600 ° C. were obtained but exceeded the standard strength at room temperature. Furthermore, they do not satisfy the low yield ratio YR ≦ 80% required for building steel materials.

[0047]

[Table 1]

[0048]

[Table 2]

[0049]

[Table 3]

Next, based on the composition of steel No. 2 above, when various amounts of Mo and V were added to the steel No. 2 to the normal temperature YS of 600%
The change in the ratio of ° C YS was examined, and the results are shown in the graph of FIG. When Mo is 0.10% or more, more specifically 0.20% or more, V
It can be seen that the ratio exceeds 0.3 in both cases of addition and no addition.

FIG. 2 is a graph showing the change in the coating weight when hot-dip galvanizing was performed for each of the comparative steel No. 4 and the inventive steels Nos. 1 and 6 while changing the plating temperature and the immersion time. is there. Under any conditions, the steel produced by the present invention has good plating adhesion.

FIG. 3 is a graph showing the amount of coating in the case of hot-dip galvanizing under the conditions of a plating temperature of 440 ° C. and an immersion time of 3 minutes for the inventive steels Nos. 1 to 25 in Table 1. It can be seen that in the range of Si: 0.10 to 0.30%, there is no occurrence of plating burn and good plating is performed.

[0053]

The refractory steel according to the method of the present invention is a steel having excellent tensile strength at room temperature and high toughness as a structural steel and having a high yield strength at 600 ° C. At the time of manufacture, the refractory coating required for conventional steel can be significantly reduced or omitted. Furthermore, when used without coating, it is excellent in secondary processing performance such as hot-dip galvanizing, and has great industrial value. Further, in the embodiment of the present invention, a thick steel plate is taken as an example, but it goes without saying that the present invention can be applied to a strip steel, a section steel and the like.

[Brief description of the drawings]

FIG. 1 is a graph showing the effect on the proof stress ratio between normal temperature and 600 ° C. when the V content and the Mo content are changed in a steel based on the composition of steel No. 2 in Examples of the present invention. is there.

FIG. 2 is a graph showing a relationship between a plating temperature, an immersion time, and a plating adhesion amount.

FIG. 3 is a graph showing a relationship between a Si amount and a plating adhesion amount.

Claims (2)

[Claims] C. 0.06 to 0.15%, Si: 0.08 to 0.25%, Mn: 0.50 to 1.40% by weight.
%, Mo: 0.20 to 0.60%, V: 0.020 to 0.060%, N: 0.0010
~ 0.0060%, Al: 0.010 ~ 0.080%, with the balance being a steel composition consisting of Fe and unavoidable impurities,
After heating a steel slab having a G value of 0.7 to 1.2 defined by the following formula (1) in a temperature range of 1050 to 1200 ° C, hot rolling is performed at a rolling end temperature of 760 to 880 ° C, and 600 ° C. 0.2% in
A method for producing a refractory steel material for a hot-dip galvanized structure, wherein a steel material having a proof strength of not less than 2/3 of a standard proof strength at room temperature is subjected to hot-dip galvanizing as secondary processing. (Equation 1) 2. The steel composition, in weight%, further contains: Cu: 0.10 to 0.40%, Ni: 0.10 to 0.40%, Cr: 0.10 to 0.40%.
%, Ca: 0.0005 to 0.0040%, and Ti: 0.008 to 0.030%.