JPH08277435A - Mo-si alloy excellent in heat resistance - Google Patents

Abstract

PURPOSE: To produce an Mo-Si alloy excellent in castability and toughness as well as heat resistance and usable even at an ultrahigh temp. of 1500 deg.C. CONSTITUTION: This Mo-Si alloy excellent in heat resistance is the one having a compsn. contg., by weight, 35 to 45% Si and total >5% of one or >= two kinds among <=25% Co, <=5% Ni and <=10% Fe, and the balance Mo with inevitable impurities, or is the one in which the same alloy furthermore contains one or two kinds among A group elements and B group elements by the following quantity: A group elements (Ca, Mg, B and rare earth elements): one or more kinds by 0.01 to 0.3wt.% in total and B group elements (Cr, W, V, Zr, Ti, Nb, Ta, Al, Mn and Cu): one or more kinds by 0.1 to 5.0wt.% in total.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Mo-Si alloy which has excellent heat resistance and can be used even at an extremely high temperature of 1500 ° C.

[0002]

2. Description of the Related Art A bright annealing furnace is known as a furnace for heating and heat-treating a material to be heated such as a steel material without generating an oxide scale. This furnace indirectly heats the inside of the furnace by flowing a combustion gas into a heating furnace tube called a radiant tube, and creates a furnace atmosphere in which a reducing gas is introduced into the furnace, thereby heating the material to be heated. It is a type of furnace that prevents oxidation. At present, the heat-resistant temperature of materials such as radiant tubes used in bright heat treatment furnaces is at most about 1150 ° C, so that the heating temperature of the material to be heated can be raised to at most 1000 ° C.

As a material that can be used even at an extremely high temperature exceeding 1300 ° C., a silicide of refractory metal such as Mo is known. For example, JP-B-53-35889 discloses a coating alloy composed of three heavy transition metals selected from Co or Ni, Mo and Cr and Si, and the total amount of two heavy transition metals being 60. At least more than atomic%, the Laves phase in it is 30 ~
Alloys have been proposed which are present in a proportion of 85% by volume and have outstanding resistance to wear and corrosion.

Further, in Japanese Patent Application Laid-Open No. 53-40612, Mo is added to 40
%, A SiC fiber-reinforced Mo-based composite material has been proposed in which 2 to 80% by volume of SiC fiber containing 0.01 to 20% of free carbon is compounded in a Mo-based metal matrix containing at least 0.1%.

Further, conventionally known alloys such as MoSi ₂ are
Although it has extremely good high temperature oxidation resistance in an ultrahigh temperature oxidizing gas atmosphere exceeding 1300 ° C, it is a material that is extremely brittle in the low temperature range, and such brittle intermetallic compounds are heated in a heating furnace such as a radiant tube. It is difficult to mold it into a shape such as a pipe. Further, in an actual furnace, a heating furnace is heated and cooled so that a thermal shock is applied to the heating furnace tube. Therefore, the heating furnace material is required to have toughness that is not damaged by the thermal shock. Specifically, at room temperature, a Charpy impact value of about 5 J / cm ² or more is required, but MoSi ₂ alloy is brittle like glass, and of course it can be formed into a heating furnace tube, etc. It has a problem that it can not stand at all.

Therefore, if a heating furnace material such as a radiant tube having excellent heat resistance that can be used at an ultrahigh temperature of about 1500 ° C. is obtained, a bright furnace can be applied to heating a slab, a billet or the like. By completely preventing the scale generated during heating or heat treatment of the material to be heated, the yield and quality of the material to be heated can be improved and the production process can be omitted.

[0007]

SUMMARY OF THE INVENTION The object of the present invention is 1500
Not only heat resistance that can be used even at ultra high temperature of ℃, castability,
An object of the present invention is to provide a Mo-Si alloy which is excellent in toughness and is particularly useful as a material for a heating furnace such as a radiant tube.

[0008]

Means for Solving the Problems The present inventors have found that MoSi ₂ which has extremely good high temperature oxidation resistance in an ultrahigh temperature oxidizing gas atmosphere exceeding 1300 ° C., but is extremely brittle in a low temperature range. As a result of repeated studies from the aspect of structure and chemical composition in order to improve castability and toughness,
The following findings were obtained and the present invention was completed.

After the MoSi ₂ is melted in an arc melting furnace or an induction heating furnace, the very early stage (2000 ° C.
At 00 ℃), the solidification structure first separates into two phases with different chemical components, and then these two phases react with each other in the lower temperature range (1900 ℃ and below) to form the final single-phase solidification structure. Become. At this time, the interfacial energies of the two types of solidified texture phases are remarkably high, and in this temperature range, the dissimilar two-phase interfaces are easily separated from each other, so that a large number of voids (voids) are generated and the toughness is lowered.

In order to prevent the separation between the two phases, which is the main cause of void formation during the solidification process, the solidification stress generated during solidification is relaxed by precipitating a ductile third phase during the solidification / cooling process. Separation between phases is prevented. This suppresses the formation of pores and improves toughness.

Co, Ni and Fe not only improve the high temperature strength but also promote the precipitation of a ductile third phase such as CoSi ₂ , NiSi ₂ and FeSi ₂ to relieve the stress generated during solidification and reduce defects. It is an element effective in reducing solidification cracking and preventing shrinkage cavities.

The gist of the present invention is one or more of Si: 35 to 45%, Co: 25% or less, Ni: 25% or less, Fe: 10% or less, in weight%. Is a Mo-Si alloy excellent in heat resistance, characterized by containing more than 5% and 25% or less in total, and the balance being Mo and inevitable impurities.

The above alloy is a Mo--Si alloy having excellent heat resistance, which further contains one or two of the following amounts of Group A elements and Group B elements.

Group A elements (Ca, Mg, B, rare earth elements): 1
0.01 to 0.3% by weight in total of more than one species B group element (Cr, W, V, Zr, Ti, Nb, Ta, Al, Mn, C
u): 0.1 to 5.0% by weight in total of 1 or more

[0015]

[Action]

Si: 35-45% MoSi ₂ alloy was used as a basic component from the viewpoint of heat resistance such as high temperature strength and oxidation resistance at an ultrahigh temperature of about 1500 ℃. Therefore, the Si content is set to 35 to 45%. When the Si content is less than 35%, the oxidation resistance at high temperature decreases, and it is not possible to obtain a sufficient amount of tetragonal MoSi ₂ that serves as a matrix, and the high temperature strength decreases. On the other hand, if the Si content exceeds 45%, the toughness decreases. Therefore, the Si content is set to 35 to 45%.

Co, Ni, Fe: Co, Ni and Fe are effective elements for improving high temperature strength. In addition, ductile CoSi ₂ and NiS
i _2, to promote a third phase of deposition of FeSi _2, etc., to relieve stress MoSi ₂ is generated to separate into two phases during solidification. As a result, the occurrence of defects such as solidification cracking and shrinkage cavities can be prevented, and toughness can also be improved. To achieve this effect, one or more of Co, Ni, and Fe should be 5% in total.
It is necessary to contain more than. When the content is 5% or less, the precipitation of the third phase having excellent ductility is insufficient, solidification cracking and shrinkage cavities occur, and the toughness also decreases.

On the other hand, when Co and Ni are contained in excess of 25% and Fe in excess of 10%, the volume fraction of the low melting point compound is increased and the toughness is lowered. Further, even if two or more kinds are contained at the same time, the toughness tends to decrease if the content is large, so the upper limit of the total amount of Co, Ni, and Fe is set to 25%. Note that Fe
As for the above, even if it is contained in a complex form with Co or Ni, the Fe content in that is up to 10%.

Group A elements (Ca, Mg, B, rare earth elements): 1
0.01 to 0.3% in total of at least one kind In order to improve workability, one or more kinds of Ca, Mg, B, and rare earth elements are contained as necessary. These alloying elements react with O (oxygen) in the alloy, reduce the amount of oxygen that forms a solid solution in the alloy, and contribute to improving workability. The effect is that the content is
It is recognized in 0.01% or more, and even if it exceeds 0.3%, the effect is saturated, so the content of group A elements is 0.
It was set to 01 to 0.3%.

Group B elements (Cr, W, V, Zr, Ti, Nb, Ta,
Al, Mn, Cu): 0.1% to 5.0% in total of 1 or more: Cr, W, V, Zr, Ti, Nb, Ta, Al, if necessary, for the purpose of improving high temperature strength at ultrahigh temperature. One of Mn and Cu
A total of 0.1% to 5.0% can be contained. These alloy elements form a solid solution in the base material and contribute to the high temperature strength of the alloy. The effect is recognized when the content is 0.1% or more. On the other hand, when the content exceeds 5.0%, a phase having poor heat resistance and ductility such as CrSi ₂ and Ti ₅ Si ₃ is precipitated in the matrix of the solidified structure, resulting in deterioration of heat resistance and toughness.

Further, in addition to the above elements, C and N have a function of forming a solid solution in the base material to improve the high temperature strength. Therefore, in order to positively obtain this effect, it is preferable to contain one or two of C and N in a total amount of 0.01% or more. On the other hand, if the total amount exceeds 0.5%, carbides and nitrides of Mo will be excessively precipitated and the toughness will decrease, so the upper limit for inclusion is 0.5%.

The alloy of the present invention is capable of relaxing the solidification stress generated during solidification by precipitating the second phase having excellent ductility, improving the toughness of the steel ingot, and reducing defects during solidification. Can be molded and processed by a known method.

However, voids in the solidified tissue are remarkably formed by applying some force from the outside, for example, centrifugal force, in the temperature range of solidification and cooling processes in which two-phase tissues having different temperatures of 2000 to 1800 ° C. coexist. It can be reduced and the toughness is significantly improved.
Therefore, it is preferable to use the centrifugal casting method when forming and processing into a tubular shape such as a radiant tube.

Further, it is preferable that the centrifugal casting is performed at a rotational speed N satisfying the following formula (1). For example, outer diameter 2
If you want to manufacture a tube with a thickness of 10 mm, a thickness of 10 mm, and a length of 3000 mm, 85
By manufacturing at a rotation speed of 0 rpm, there is no particular problem with dimensional tolerance, and a tube without casting cracks or shrinkage cavities can be manufactured.

Rotational speed N (rpm) ≧ (10000 × D ^−1/2 ) ... (1) where D is the inner diameter (mm) of the casting pipe

[0025]

EXAMPLES Inventive alloys having chemical compositions shown in Tables 1 to 3 and comparative alloys shown in Table 4 were produced using a vacuum centrifugal casting machine. Metallic powders of Mo, Si, Co, Ni, Fe, etc. were used as melting raw materials, and a well-mixed material was put into a crucible and melted in an amount of 2 kg each in a vacuum induction heating furnace.

The molten metal was poured into an inner surface of a steel mold having an inner diameter of 60 mm and rotating at a high speed in an Ar stream for about 2 minutes to produce a tube having an outer diameter of 60 mm, an inner diameter of 40 mm and a length of 200 mm. The mold rotation speed during casting was adjusted to 2000 rpm.

The castability was evaluated by visually observing the presence or absence of solidification cracks in the ingot produced by the centrifugal casting method.

The shrinkage cavity is evaluated by dividing the tube in half and measuring the thickness in the thickness direction of the shrinkage cavity. When the thickness of the shrinkage cavity exceeds 50% of the total thickness, x is calculated. The case of 25 to 50% was evaluated as △, and the case of less than 25% of the total thickness was evaluated as ○.

Further, from the center of the wall thickness of the created pipe, JI
An impact test piece (width 2.5 mm) corresponding to 1/4 the size of the No. 4 impact test piece specified in SZ 2202 was cut out by machining and subjected to an impact test based on JIS Z 2242 at room temperature. Similarly, in order to investigate the high temperature tensile properties of alloys, JIS Z 22
Cut out the No. 14A test piece (6 mm diameter) described in 01,
It was subjected to a tensile test at 00 ° C.

In addition to the evaluation of castability and shrinkage cavity, the impact value in the impact test and the tensile strength in the high temperature tensile test are shown in Tables 1 to 4.

[0031]

[Table 1]

[0032]

[Table 2]

[0033]

[Table 3]

[0034]

[Table 4]

From Tables 1 to 3, in the alloy of the present invention, solidification cracking and shrinkage cavities are suppressed by further adding Co, Ni and Fe to Mo and Si. Further, the alloy of the present invention has an impact value of 9 J / cm ² or more, and the alloy of the present invention has a toughness at a level that poses no problem in practical use. In particular, Group A elements (Ca, Mg, B, rare earth elements) ) Is added, the impact value is higher. Furthermore, it has high tensile strength even at an extremely high temperature of 1500 ° C, and in particular, it contains B group elements (Cr, W, Fe, V, Zr, Ti, Nb,
When Ta, Al, Ni, Co, Mn, Cu) is added, the strength is higher.

On the other hand, among the comparative alloys in Table 4, the conventional Mo-Si
Nozomi alloy has solidification cracking and shrinkage cavities, and both impact value and high temperature strength are low. When the Si content is out of the lower limit, the high temperature strength is remarkably reduced, and when it is out of the upper limit, the toughness is deteriorated. Further, when the content of Co, Ni, Fe is less than the lower limit, solidification cracking and shrinkage cavities occur, and the impact value also decreases.
On the other hand, when the value exceeds the upper limit, the impact value is lowered. Furthermore, the impact value is lowered when the group B element is excessively added.

Further, some of the alloys of the present invention were subjected to a room temperature tensile test using the above-mentioned No. 14A test piece (6 mm diameter), and the workability of the alloy was evaluated by the drawing value of the fractured part. The results are also shown in Tables 1 and 2. The aperture is the value obtained by dividing the amount of diameter reduction after the test by the original diameter (6 mm). From these results, the aperture value of the alloys added with the group A elements (Ca, Mg, B, rare earth elements) is improved as compared with the alloys not added with these elements. It can be seen that it has the effect of improving sex.

[0038]

The alloy of the present invention has extremely high temperature oxidation resistance in an ultrahigh temperature oxidizing gas atmosphere exceeding 1300 ° C. and has sufficient resistance to thermal shock during use. .

Accordingly, the alloy of the present invention was added to a radiant tube.
By using it for heating, it is possible to raise the temperature of the bright furnace where the heating temperature of the material to be heated reaches about 1300 ° C, and it is possible to solve various scale problems including scale loss all at once. .

[0040]

Claims (4)

[Claims] 1. Si: 35-45%, and Co: 25% in weight%.
The heat resistance is characterized by containing one or two or more of Ni: 25% or less and Fe: 10% or less in total of more than 5% and 25% or less, with the balance being Mo and inevitable impurities. Excellent Mo-Si alloy. 2. Si: 35-45%, and Co: 25% in weight%.
In the following, Ni: 25% or less, Fe: 10% or less, or a total of more than 5% and 25% or less, and Ca, M
A Mo-Si alloy having excellent heat resistance, which comprises 0.01 to 0.3% by weight in total of one or more of g, B, and rare earth elements, and the balance being Mo and inevitable impurities. 3. Si: 35-45% and Co: 25% in weight%.
In the following, Ni: 25% or less, Fe: 10% or less, or a total of more than 5% and 25% or less, and Cr,
Excellent heat resistance characterized by containing 0.1 to 5.0% by weight in total of one or more of W, V, Zr, Ti, Nb, Ta, Al, Mn, and Cu, with the balance being Mo and inevitable impurities. Mo-Si alloy. 4. Si: 35-45% and Co: 25% in weight%.
In the following, Ni: 25% or less, Fe: 10% or less, or a total of more than 5% and 25% or less, and Ca, M
0.01 to 0.3% by weight of one or more of g, B and rare earth elements, and 0.1 to 5.0% by weight of one or more of Cr, W, V, Zr, Ti, Nb, Ta, Al, Mn and Cu in total. %, And the balance is Mo and inevitable impurities, and is a Mo-Si alloy with excellent heat resistance.