JP2001271148A - HIGH Al STEEL SHEET EXCELLENT IN HIGH TEMPERATURE OXIDATION RESISTANCE - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain inexpensively a steel sheet with improved in high temperature oxidation resistance by adding 5 to 10% Al thereto, compared to stainless steel. SOLUTION: This high Al steel sheet has a fundamental composition containing <=0.01% C, 0.01 to 2.0% Si, 0.05 to 2.5% Mn, <=0.02% P, 5 to 10% Al, <=0.010% S and <=0.010% N and exhibits high temperature oxidation resistance and high temperature strength so as to be sufficiently used in a high temperature atmosphere of >=850 deg.C. Moreover, in the case one or more kinds of metals selected from Ti, Nb, Mo and V are added by 0.01 to 0.3% in total, its high temperature strength is further improved, and in the case one or more kinds of rare earths selected from La, Ce, Nd and Y are added by 0.01 to 0.2% in total or in the case 1 to 8% Cr is added, its high temperature oxidation resistance is further improved. Secondary working cracks at the time of press working can be prevented by the addition of 0.0002 to 0.002% B.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used as a solid structural material capable of withstanding a high-temperature atmosphere of 850 ° C. or higher, and is a high Al steel sheet having excellent resistance to high-temperature oxidation and high-temperature and good workability at room temperature. About.

[0002]

2. Description of the Related Art Various stainless steels containing about 10% by mass or more of Cr have been used as materials exhibiting excellent high-temperature oxidation resistance in a high-temperature atmosphere of 800 ° C. or more. Stainless steel exhibits excellent high-temperature oxidation resistance due to the protective action of a Cr-based oxide film (passive film) formed on the surface layer, but has a disadvantage in that steel material costs are high. Therefore, a hot-dip aluminum-plated steel sheet having improved high-temperature oxidation resistance by applying hot-dip aluminum plating to the surface of a steel sheet using ordinary steel as a base material has been put to practical use. For example,
Japanese Patent Application Laid-Open No. 56-102523 discloses a method for producing a hot-dip aluminum-coated steel sheet having a low-carbon Ti-added steel as a base and being subjected to hot-dip aluminum plating to improve the high-temperature oxidation resistance at relatively high temperatures. Is introduced. JP-A-56-102556 introduces a plated steel sheet having improved heat resistance by applying hot-dip aluminum plating based on an ultra-low carbon Ti-added steel containing up to 5 mass% of Cr. In addition to stainless steel, as a solid material, a material exhibiting excellent high-temperature oxidation resistance in a high-temperature atmosphere exceeding 850 ° C. is Fe.
Al-containing Fe-Al alloys have been known for a long time.

[0003]

The usable temperature of a normal hot-dip aluminized steel sheet using ordinary steel as a base material is as follows:
At most it is only about 830 ° C. A hot-dip aluminized steel sheet based on a steel sheet to which Cr has been added to about 5% by mass has a slightly improved high-temperature oxidation resistance,
In a high-temperature atmosphere exceeding 50 ° C., abnormal oxidation occurs in a short period of time, and cannot withstand normal use. On the other hand,
Although the Fe-Al alloy is excellent in high-temperature oxidation resistance, a simple Fe-Al binary system cannot provide sufficient high-temperature strength as a structural material. Increase the Al content of Fe-Al alloy to increase F
Although it is possible to improve the high-temperature strength by producing ordered alloys such as e ₃ Al and FeAl, it is very difficult to produce thin sheet materials because these ordered alloys have poor toughness at room temperature.

[0004]

DISCLOSURE OF THE INVENTION The present invention has been devised to solve such a problem, and has excellent resistance to ordinary use as a solid structural material in a high-temperature atmosphere exceeding 850 ° C. An object of the present invention is to obtain a steel plate which has high-temperature oxidation properties and high-temperature strength, is excellent in workability at room temperature, and is less expensive than stainless steel. The present inventors have conducted various investigations and studies on a steel sheet having excellent high-temperature oxidation resistance as a solid material. As a result, C: 0.01% by mass or less, Si: 0.01 to 2.
0% by mass, Mn: 0.05 to 2.5% by mass, P: 0.0
2% by mass or less, Al: 5 to 10% by mass, S: 0.010
Mass% or less, N: 0.010 mass% or less, and when the balance is substantially the same as the basic composition of Fe, high-temperature oxidation resistance and high-temperature strength enough to withstand use in a high-temperature atmosphere of 850 ° C. or more are obtained. And workability at room temperature is also ensured.

[0005] The basic composition of Ti, Nb, Mo, V
When a seed or two or more kinds are added in a total amount of 0.01 to 0.3% by mass, the high-temperature strength is further improved without greatly deteriorating the workability at room temperature. High temperature oxidation resistance is La, C
e, Nd, Y or one or more of them in total of 0.01 to
It is further improved when 0.2% by mass or 1 to 8% by mass of Cr is added. The secondary work cracking resistance during press working as a structural material is B: 0.0002 to 0.002.
It is improved by adding% by mass.

[0006]

The alloy components and contents contained in the high Al steel sheet of the present invention will be described below. C: 0.01% by mass or less C is an alloy component that has an adverse effect on high-temperature oxidation resistance and workability at room temperature, and it is preferable to reduce the C content as much as possible. However, excessive decarburization causes an increase in the production cost. Therefore, in the present invention, the upper limit is set to 0.01% by mass, at which no adverse effect of C appears. Si: 0.01 to 2.0% by mass An alloy component effective for improving high-temperature oxidation resistance and high-temperature strength. At 0.01% by mass or more, the effect of Si becomes remarkable. However, when an excessive amount of Si exceeding 2.0% by mass is included, the workability at room temperature and the resistance to secondary working cracking are deteriorated.

Mn: 0.05 to 2.5% by mass An alloy component effective for improving high-temperature strength. At 0.05% by mass or more, the effect of Mn becomes remarkable. However, when an excessive amount of Mn exceeding 2.5% by mass is included, the workability at room temperature and the resistance to secondary working cracking are deteriorated. P: 0.02% by mass or less P is an alloy component effective for improving high-temperature strength, but segregates at grain boundaries and adversely affects toughness at room and low temperatures. The effect of P on toughness becomes significant in a component system in which the C content is reduced. In this regard, the P content is preferably as low as possible, and in the present invention, the upper limit was set to 0.02% by mass.

[0008] Al: 5 to 10% by mass is an alloy component essential for improving high-temperature oxidation resistance.
In order to obtain high-temperature oxidation resistance that can withstand use in a high-temperature atmosphere, an Al content of 5% by mass or more is required. From the viewpoint of high-temperature oxidation resistance, the higher the Al content, the better,
When an excessive amount of Al exceeding 10% by mass is contained, a very hard and brittle Fe ₃ Al ordered alloy is formed, and the workability at room temperature is largely deteriorated. S: 0.010% by mass or less S is a harmful component that has an adverse effect on high-temperature oxidation resistance and workability at room temperature. It is preferable to reduce the S content as much as possible. 0.010% by mass. N: 0.010% by mass or less N is a harmful component that has an adverse effect on high-temperature oxidation resistance and workability at room temperature, and it is preferable to reduce the N content as much as possible. 0.010% by mass.

One or more of Ti, Nb, Mo and V
Upper: 0.01 to 0.3% by mass in total as an alloy component added as required, and exhibits an effect of improving high-temperature strength. The mechanism by which the high-temperature strength is improved by the addition of Ti, Nb, Mo, V, etc. is not always clear, but Ti, Nb, Mo, V, etc., may cause S, C, N
Precipitates such as sulfides, carbides and carbonitrides formed by bonding with Ti and Nb, Mo, and V dissolved in the matrix
It is presumed that these are due to the solution drag effect that regulates the movement of dislocations. The effect of adding Ti, Nb, Mo, V, etc. becomes remarkable at 0.01% by mass or more. However, even if it exceeds 0.3% by mass, the effect of improving the high-temperature strength is saturated, Workability at room temperature and high-temperature oxidation resistance deteriorate.

[0010] One or more of La, Ce, Nd, and Y
Above: 0.01 to 0.2% by mass in total as an alloying component that is added as required, and functions to densify a protective Al-based oxide film formed in a high-temperature region and further improve high-temperature oxidation resistance. Present. La, Ce, Nd, Y
And the like effect becomes remarkable at 0.01% by mass or more,
Even if it is added in excess of 0.2% by mass, the effect of improving high-temperature oxidation resistance is saturated, which causes an increase in steel material cost. Cr: 1 to 8% by mass An alloy component added as necessary, forms a protective oxide film like Al, and effectively acts to improve high-temperature oxidation resistance. The effect of adding Cr is manifested by adding 1% by mass or more of Cr in a system in which 5% by mass or more of Al is added in combination. However, an excessive addition of Cr exceeding 8% by mass causes an increase in steel material cost.

B: 0.0002 to 0.002% by mass An alloy component added as necessary. Generally speaking, in ultra-low carbon steels, the amount of C segregated at the grain boundaries is small, so that sufficient grain boundary strength cannot be obtained. Intergranular cracking may occur. In this regard, the addition of B, which tends to segregate at the grain boundaries, improves the grain boundary strength and improves the secondary work cracking resistance. The improvement in the secondary work cracking resistance becomes remarkable when B is added in an amount of 0.0002% by mass or more. However, when an excessive amount of B exceeding 0.002% by mass is added, the workability at room temperature is rather deteriorated.

[0012] The steel material whose composition is adjusted as described above can be manufactured by a normal thin steel sheet manufacturing process. The resulting high Al steel sheet is basically a thin steel sheet excellent in high temperature oxidation resistance,
When used as a material for an electric resistance welded steel pipe, an electric resistance welded steel pipe excellent in high-temperature oxidation resistance can also be obtained. In order to improve corrosion resistance, it can be used as an original plate for plating.

[0013]

Example 1 Molten steel having the composition shown in Table 1 was melted in a high-frequency vacuum melting furnace and cast into a 30 kg steel ingot. The obtained steel ingot was hot forged to a thickness of 30 mm, heated to 1250 ° C., and hot rolled at a finishing temperature of 910 ° C. to a thickness of 3.2 m.
m hot-rolled steel strip.

[0014]

After the hot-rolled steel strip was pickled to remove scale on the surface, it was cold-rolled to a thickness of 1.0 mm. Then 8
Short-time annealing of 50 ° C. × soaking for 60 seconds was performed. Test pieces were cut out from the annealed material and subjected to a tensile test, a high-temperature oxidation resistance test, a high-temperature strength test, and a secondary work cracking resistance test.

In the tensile test, JIS No. 5 tensile test pieces cut out in parallel with the rolling direction were used to investigate the tensile properties at room temperature. In the high-temperature oxidation resistance test, a test piece punched into a shape having a diameter of 45 mm was placed in a muffle furnace heated to 900 ° C., and the amount of oxidation increase was measured after holding for 100 hours in an air atmosphere. Oxidation was evaluated. In the high-temperature strength test, a high-temperature tensile test piece having a parallel portion of 10 mm and a gauge length of 50 mm was used, and the high-temperature strength was evaluated based on the yield strength at 800 ° C. measured according to JIS G0567. In the secondary work cracking resistance test, a test piece was cup-shaped so as to have a drawing ratio of 2.5, then kept in a refrigerant cooled with dry ice, liquid nitrogen, etc. for 15 minutes, and pressed with a 60 ° conical punch. An expansion test was performed, and the lowest temperature at which grain boundary cracking did not occur was evaluated as the limit temperature of secondary work cracking resistance.

As can be seen from Table 2 and the investigation results in FIG. 1, in Test Nos. 1 and 2 in which the Al content was less than 5% by mass, the oxidation increase exceeded 100 g / m ² , whereas the Al content increased. Is 5% by mass or more, the oxidation weight gain is 20 g / m ² or less, and very excellent high-temperature oxidation resistance is obtained. As shown in FIG. 1, the high-temperature oxidation resistance sharply changes at an Al content of 5% by mass and increases with an increase in the Al content. When Cr and a rare earth element (REM) coexist, the resistance to high temperature oxidation increases. It can be seen that the high-temperature oxidation property is further improved.

The elongation in the room temperature tensile test was Al, Si, M
The tendency was found to decrease as the content of n increased. Test No. 7 in which Al exceeds 10% by mass;
Test number 10 and Mn exceeding 0% by mass are 2.5% by mass
In Test No. 13 exceeding, the elongation was less than 20% and the ductility was poor. Test No. 14, which contained an excess amount of C exceeding 0.01% by mass, was also inferior in ductility. T
In Test Nos. 15 to 21, 23, and 24 including one or more of i, Nb, Mo, and V, although high temperature strength of 30 N / mm ² or more was shown, the total amount was 0.3% by mass. In Test No. 19 exceeding, ductility at room temperature and secondary work cracking resistance were inferior. In addition, when the test number 24 containing B was compared with the test number 15 having almost the same composition except that B was not added, the limit temperature of the secondary work cracking resistance was -7 in the test number 15.
In contrast to 0 ° C., Test No. 24 showed a good value of −110 ° C.

[0019]

[0020]

Example 2 A steel ingot obtained by continuously casting molten steel adjusted to the components shown in Table 3 was heated at a temperature of 1250 ° C. and a finishing temperature of 9%.
Hot rolling was performed under the conditions of 00 ° C and a winding temperature of 550 ° C to produce a hot-rolled steel strip having a thickness of 3.0 mm. After pickling the obtained hot-rolled steel strip, it was cold-rolled to a thickness of 1.0 mm, passed through a continuous annealing line, and annealed at 850 ° C. × soaking for 60 seconds.

[0021]

The tensile properties, high-temperature oxidation resistance, high-temperature strength and secondary work crack resistance of the obtained cold-rolled steel strip were examined in the same manner as in Example 1. As can be seen from the investigation results in Table 4, in Comparative Steel A having a small Al content, the oxidation weight increase at 900 ° C. was 10%.
It showed a very large value exceeding 0 g / m ² . On the other hand, the steels of the present invention B and C having the compositions specified in the present invention are:
The amount of oxidation increase at 900 ° C. was small, and good values were also exhibited for other characteristics.

[0023]

[0024]

As described above, according to the present invention, the high Al
The steel sheet is excellent in high-temperature oxidation resistance as a solid material, has good high-temperature strength and workability at room temperature, and is less expensive than stainless steel. Utilizing such high-temperature properties and workability, steel sheets used in a wide range of fields, such as automobiles and members of various types of combustion equipment, are provided.

[Brief description of the drawings]

FIG. 1 is a graph showing the effect of Al content on high-temperature oxidation resistance.

Claims (5)

[Claims] 1. C: 0.01 mass% or less, Si: 0.0
1 to 2.0% by mass, Mn: 0.05 to 2.5% by mass,
P: 0.02% by mass or less, Al: 5 to 10% by mass, S:
A high Al steel sheet having excellent high-temperature oxidation resistance, comprising 0.010% by mass or less and N: 0.010% by mass or less, and the balance substantially consisting of Fe. 2. C: 0.01 mass% or less, Si: 0.0
1 to 2.0% by mass, Mn: 0.05 to 2.5% by mass,
P: 0.02% by mass or less, Al: 5 to 10% by mass, S:
0.010% by mass or less, N: 0.010% by mass or less, further contains one or more of Ti, Nb, Mo and V in a total amount of 0.01 to 0.3% by mass, and the balance is substantially A high Al steel sheet excellent in high-temperature oxidation resistance characterized by being made of Fe. 3. One or more of La, Ce, Nd, and Y
The high Al steel sheet according to claim 1, comprising a total of 0.01% to 0.2% by mass of at least one kind. 4. The method according to claim 1, further comprising 1 to 8% by mass of Cr.
4. A high-Al steel sheet according to any one of claims 1 to 3. 5. The high Al steel sheet according to claim 1, further comprising B: 0.0002 to 0.002% by mass.