JPH0770647A - Production of hot dip galvanized steel sheet for corrosion resisting refractory structure - Google Patents

Abstract

PURPOSE:To produce a hot dip galvanized steel sheet for a corrosion resisting refractory structure excellent in high temp. properties, corrosion resistance and formability by using a steel compsn. close to that of common steel. CONSTITUTION:Steel contg. 0.03 to 0.2% C, <=0.1% Si, 0.3 to 2.0% Mn, 0.03 to 0.15% P, <=0.02% S, 0.005 to 0.1% Al, 0.05 to 1.0% Mo, 0.6 to 2.0% Cu and 0.3 to 2.0% Ni is subjected to not rolling and is pickled. After that, the surface of the steel is activated by reduction under heating to 450 to 750 deg.C reduction heating temp. by continuous hot dip galvanizing equipment, and then, hot dip galvanizing is applied. The steel to be used may contain one or >= two kinds among 0.05 to 1.0% Cr, 0.005 to 0.2% V, 0.01 to 1.0%W, 0.005 to 0.2% Ti, 0.005 to 0.2% Nb and 0.0003 to 0.003% B as well.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention provides a hot-dip galvanized steel sheet which is used as a structure in the field of construction, etc., enables the structure to have high strength, and has sufficient corrosion resistance to maintain sufficient strength even in the event of a fire. It relates to a method of manufacturing.

[0002]

2. Description of the Related Art JIS standard steel materials used for steel structures include general structural rolled steel sheets (JIS G3101), welded structural rolled steel sheets (G3106), and welded structural weather resistant hot rolled steel materials (G3114). . In addition, hot-rolled soft steel plate (G3132), hot-dip galvanized steel plate (G3302), and the like are widely used as materials for structural lightweight structural steel, structural steel pipe, and the like. In order to ensure safety in the event of a fire, steel materials used as structures are required to be provided with a fireproof coating so that the steel material temperature does not exceed 350 ° C. However, if sufficient high temperature strength is secured, it is possible to use steel without coating. Therefore, various studies have been conducted on the use of steel materials that exhibit high yield strength even at high temperatures.

The high temperature strength of steel has been investigated and studied for a long time, and has been standardized for steel sheets for boilers, pressure vessels and the like. This type of steel material has high strength when used at high temperatures for a long time such as tens of thousands of hours as a boiler, a pressure vessel, or the like, that is, a high creep strength. On the other hand, the strength at issue in the present invention is the strength within a few hours of a fire. In this respect, the conventional steel sheet for high temperature use has too high strength at room temperature, and is significantly inferior in cold workability and weldability to the structural steel sheet. Therefore, steel plates for boilers, steel plates for pressure vessels, etc. are not suitable as structural steel plates. Structural steel sheets are required to have the necessary structural strength when a structure is exposed to a high temperature atmosphere for several hours during a fire. As a steel plate for construction having high-temperature strength, there are disclosed in Japanese Patent Laid-Open Nos. 4-136118 and 4-102.
In Japanese Patent No. 802, etc., Mo and V are added. Mo
And V precipitate as fine carbides in the process of exposing the steel material to a high temperature during a fire, and give the steel material the necessary high temperature proof stress. However, since expensive Mo is used as an alloy element, the manufacturing cost increases. Moreover, the corrosion resistance is insufficient for extending the life of the steel sheet.

[0004]

SUMMARY OF THE INVENTION The object of the present invention is to provide excellent high-temperature characteristics, workability for forming lightweight steel frames, etc., and corrosion resistance of the base material, and to use no special means in the steelmaking process to hot rolling process. The present invention provides a method for producing a galvanized steel sheet for a corrosion resistant refractory structure, which has a steel composition similar to that of ordinary steel and is economically excellent. Specifically, the corrosion resistance is improved by adding P and Cu as a basic component. Also, Cu is ε-C at high temperature.
Since it also has the effect of precipitating u and increasing the high temperature strength, the amount of Mo added can be reduced, and the manufacturing cost becomes low.

[0005]

In order to achieve the object, the method for producing a hot-dip galvanized steel sheet for corrosion resistant refractory structure of the present invention is C: 0.03 to 0.20% by weight, Si: 0.1
% Or less, Mn: 0.3 to 2.0% by weight, P: 0.0
3 to 0.15% by weight, S: 0.02% by weight or less, Al:
0.005-0.1 wt%, Mo: 0.05-1.0 wt%, Cu: 0.6-2.0 wt% and Ni: 0.3-
After hot rolling and pickling a steel containing 2.0% by weight,
It is characterized in that it is heat-reduced in a temperature range of 450 to 750 ° C. in a continuous hot-dip galvanizing facility and then hot-dip galvanized. The steel used is Cr: 0.05-1.0 wt%, V: 0.005-0.2 wt%, W: 0.01-
1.0 wt%, Ti: 0.005-0.2 wt%, N
b: 0.005-0.2 wt% and B: 0.0003-
It may contain one or more of 0.003% by weight.

[0006]

The present inventors conducted various investigations and studies on the chemical composition, production conditions, etc., which affect the steel plate strength at 600 ° C. and the corrosion resistance of the base metal. As a result, they have found that when a specified amount of Mo, Cu and P is added to a composition system close to that of ordinary steel, a hot-dip galvanized steel sheet for corrosion resistant refractory structures excellent in high temperature strength and base material corrosion resistance can be obtained. The obtained steel sheet has a ratio of the yield strength at 600 ° C. to the yield strength at room temperature of 0.6 or more, and the high temperature strength is not significantly reduced even when exposed to a high temperature atmosphere. Especially, C whose content is strictly regulated
u is not only effective in improving the corrosion resistance, but also precipitates as ε-Cu in the steel at high temperatures, increasing the high temperature strength. As a result, the amount of Mo added can be reduced, and the manufacturing cost can be reduced. High temperature strength and base material corrosion resistance are Cr,
It is further improved by adding one or more of V, W, Ti, Nb and B.

The alloying elements of the steel materials used in the present invention and their contents will be described below. C: 0.03 to 0.20% by weight It is an alloying element effective in imparting the required strength to the steel material, and the content of 0.03% by weight or more is required. However, when a large amount of C exceeding 0.20% by weight is contained,
Workability, weldability, toughness, etc. deteriorate. Si: 0.1 wt% or less Si is effective as a strength improving element, but since the effect of improving the high temperature strength and corrosion resistance, which is the object of the present invention, is relatively small, it is limited to 0.10 wt% or less. Mn: 0.3 to 2.0% by weight It is an alloying element effective for increasing the strength of steel materials, and exhibits an effect at 0.30% by weight or more. However, a large amount of Mn content exceeding 2.0% by weight deteriorates workability.

P: 0.03 to 0.15% by weight It is an alloying element effective for improving the strength of steel materials. Further, when added in combination with Cu, it contributes to the improvement of corrosion resistance. In order to obtain such an effect, it is necessary to contain 0.03% by weight or more of P. However, 0.15% by weight
If a large amount of P is contained in excess of 1.0, embrittlement is promoted. S: 0.02% by weight or less It is an element that is essentially harmful to the base steel, and the lower the better, the more preferable. The S content is 0.02 in the steel of the present invention.
Up to wt% is acceptable. Al: 0.005 to 0.1% by weight An element added as a deoxidizer, but N in steel is Al
It also has the effect of fixing as N. For this, 0.0
05 wt% or more is required. However, when the Al content exceeds 0.1% by weight, inclusions increase and workability and surface quality deteriorate.

Mo: 0.05 to 1.0% by weight It is an important alloying element in the steel of the present invention, and improves the high temperature strength of the steel material by forming a solid solution or precipitating carbide in the steel. Such an effect becomes remarkable when the Mo content is 0.05% by weight or more. However, even if a large amount of Mo exceeding 1.0% by weight is contained, the effect commensurate with the increase in the expensive Mo content cannot be obtained, and rather the workability deteriorates due to the higher strength. Cu: 0.6 to 2.0% by weight It is an important alloying element in the steel of the present invention, and forms a solid solution in the steel or finely precipitates as ε-Cu to improve the high temperature strength of the steel material. In addition, the interaction with P forms a fine corrosion product, and the corrosion resistance is also improved. The effect of improving the high temperature strength becomes remarkable when the Cu content is 0.6% by weight or more, and is saturated when the Cu content is 2.0% by weight. Further, if a large amount of Cu is contained in excess of 2.0% by weight, embrittlement easily occurs during hot rolling, which causes hot cracking and the like.

Ni: 0.3 to 2.0% by weight It is also effective for preventing the reduction of hot brittleness due to the addition of Cu. In this respect, the Ni content is set to be approximately the same as the Cu content, that is, in the range of 0.30 to 2.0% by weight. Cr: 0.05 to 1.0% by weight It is an alloying element added as necessary to improve the corrosion resistance of the base material and improves the high temperature strength. Such an effect becomes remarkable when 0.05 wt% or more of Cr is contained. However, even if a large amount of Cr exceeding 1.0% by weight is contained, the effect corresponding to the increase of Cr is not improved. V, Ti, Nb: 0.005 to 0.2% by weight It is an alloying element effective in improving the room temperature strength and the high temperature strength, and when the content is 0.005% by weight or more, a remarkable effect is obtained. However, even if the content exceeds 0.2% by weight, the effect commensurate with the increase in amount cannot be obtained. Therefore,
When V, Ti, Nb, etc. are added, the respective contents are set within the range of 0.005 to 0.2% by weight.

W: 0.01 to 1.0% by weight It is an alloying element that is added as required, and has the effect of improving the high temperature strength of steel by forming a solid solution or precipitating carbide in steel. The effect of the addition of W remarkably appears at 0.01% by weight or more and saturates at 1.0% by weight. B: 0.0003 to 0.003% by weight Since it improves hardenability and strengthens grain boundaries,
It is an alloying element added as necessary. The effect of the addition of B becomes remarkable at 0.0003% by weight or more,
Saturate at wt%.

Steel having the above-mentioned components and compositions is made into a slab by a usual process and then hot-rolled into a steel plate having a predetermined thickness. Hot rolling is performed at a heating temperature of 1050 to 1250 ° C, a finishing temperature of 800 to 950 ° C, and a winding temperature of 500 to 700.
It is preferably carried out under the condition of ° C. The hot-rolled steel sheet, after pickling,
Introduced to continuous hot dip coating equipment. In the continuous hot dip coating facility, the hot rolled steel sheet is heated to a surface temperature of 450 to 750 ° C. in a reducing atmosphere to remove foreign matters, oxide film and the like on the surface of the steel sheet. The heating temperature increases the activity of the surface of the steel sheet and improves the wettability with respect to the plating metal.
It is set to 0 to 750 ° C. If the heating temperature is lower than 450 ° C, the activation becomes insufficient and the adhesion of the hot-dip galvanized layer deteriorates. On the contrary, at a heating temperature of higher than 750 ° C., the effect of contributing to the improvement of the plating property is saturated and, on the contrary, an excessive amount of heat energy is required, thus impairing the production efficiency.

[0013]

EXAMPLE Steels having the compositions shown in Table 1 were melted, made into slabs by a conventional method, and hot-rolled to obtain hot-rolled steel sheets having a thickness of 3.2 mm. Group A in Table 1 indicates a steel according to the invention. Group B shows comparative steels that do not contain Cu. After the hot-rolled steel sheet was pickled, hot-dip galvanizing with a basis weight of 45 g / m ² was performed in a continuous hot-dip galvanizing facility. Table 2 shows the conditions of hot rolling and hot dip galvanizing.

[0014]

[Table 1]

[0015]

[Table 2]

From hot dip galvanized steel sheet to JIS Z220
A No. 5 test piece specified in 1 was cut out and subjected to a tensile test at room temperature. Further, a high-temperature tensile test piece based on JIS G0567 was prepared, and the test piece was held at 600 ° C for 15 minutes, and then the tensile strength and the yield strength were measured. As an index of high temperature strength, 600 against yield strength at room temperature
The yield strength ratio in ° C was adopted. The corrosion resistance was evaluated by the maximum erosion depth after the corrosion test. That is, a 70 mm × 150 mm test piece cut out from a hot-dip galvanized steel sheet was subjected to a combined cycle corrosion test of salt spray, dry and wet (3 cycles / day) under the conditions shown in FIG. This corrosion test was repeated for 240 cycles (80 days) to remove the corrosion product, and then the maximum erosion depth was measured. As is clear from Table 3 showing the investigation results, the test piece of test number B1 shows excellent strength and ductility at room temperature, but at 600 ° C.
Yield strength was significantly reduced and the yield strength ratio was 0.6.
It is less than. That is, the material is inferior in high temperature strength. Further, the maximum erosion depth is as deep as 1.04 mm, and the corrosion resistance is poor.

[0017]

[Table 3]

The test pieces of test Nos. B2 and B3 showed no decrease in ductility at room temperature, satisfied the requirement of a yield strength ratio of 0.6 or more, and had a small decrease in yield strength at 600 ° C. It can be said that it is an excellent material. But,
Maximum erosion depth is 0.88 mm for B2 and 0.8 for B3
It is as deep as 2 mm and has poor corrosion resistance. On the other hand, the test pieces of Group A according to the present invention did not show a large decrease in ductility at room temperature, and exhibited excellent properties in yield strength at 600 ° C. Further, it can be seen that the maximum erosion depth is shallower than that of B1 to B3, and the corrosion resistance is excellent. In particular, the test piece A8 containing Cr, V, and W added together and the test piece A13 containing Nb and B added together had yield strength ratios of 0.70 and 0.74, respectively, and maximum erosion depths of 0.53 mm and 0, respectively. As shown by 0.48 mm, it has excellent characteristics in both high temperature characteristics and corrosion resistance.

[0019]

As described above, according to the present invention, there is no need for special means in the steel making process or the hot rolling process, and the composition is similar to that of ordinary steel and is economically excellent in corrosion resistance and refractory structure. A galvanized steel sheet is manufactured. The obtained plated steel sheet is excellent in high-temperature characteristics, corrosion resistance, formability, etc., and is therefore used as a fireproof structural material in a wide range of fields.

[Brief description of drawings]

FIG. 1 is a combined cycle corrosion test adopted in an example of the present invention.

Claims (2)

[Claims] 1. C: 0.03 to 0.20% by weight, Si:
0.1% by weight or less, Mn: 0.3 to 2.0% by weight, P:
0.03 to 0.15% by weight, S: 0.02% by weight or less,
Al: 0.005-0.1% by weight, Mo: 0.05-
1.0 wt%, Cu: 0.6-2.0 wt% and Ni:
Steel containing 0.3 to 2.0% by weight is subjected to hot rolling and pickling, followed by heat reduction in a temperature range of 450 to 750 ° C. in a continuous hot dip galvanizing facility, and then hot dip galvanizing. A method for producing a hot-dip galvanized steel sheet for a corrosion resistant refractory structure, which is characterized. 2. C: 0.03 to 0.20% by weight, Si:
0.1% by weight or less, Mn: 0.3 to 2.0% by weight, P:
0.03 to 0.15% by weight, S: 0.02% by weight or less,
Al: 0.005-0.1% by weight, Mo: 0.05-
1.0 wt%, Cu: 0.6-2.0 wt% and Ni:
0.3 to 2.0% by weight, further Cr: 0.05 to
1.0% by weight, V: 0.005-0.2% by weight, W:
0.01-1.0% by weight, Ti: 0.005-0.2% by weight, Nb: 0.005-0.2% by weight and B: 0.0
Steel containing 003 to 0.003% by weight of one kind or two kinds or more is subjected to hot rolling and pickling, and then subjected to heat reduction in a temperature range of 450 to 750 ° C. in a continuous hot dip galvanizing facility, and then hot dip zinc A method for producing a hot-dip galvanized steel sheet for a corrosion-resistant fire-resistant structure, which comprises performing plating.