JPS5852697B2 - catalyst - Google Patents

Description

[Detailed description of the invention] The present invention relates to a catalyst for heat treatment of steel materials.

Generally, a hydrogen atmosphere or an ammonia decomposition gas atmosphere is used for bright heat treatment of steel sheets.

Heat treatment in a hydrogen atmosphere is best, but ammonia decomposition gas is generally used since it is inexpensive.

The mixed gas of hydrogen gas and nitrogen gas produced by thermally decomposing ammonia gas using nickel as a catalyst is generally called ammonia decomposition gas.

Several hundred to several thousand ppm of undecomposed ammonia remains in this ammonia decomposition gas, and this undecomposed ammonia reacts with the surface of the steel to be heat treated, producing harmful nitrogen compounds near the surface of the steel to be heat treated. This impairs the processability of

It is particularly harmful to the heat treatment of aluminized steel.

In other words, when undecomposed ammonia gas comes into contact with the steel material, Fe becomes a catalyst at the heat treatment temperature, and the undecomposed ammonia decomposes to generate nitrogen, a highly active generator, which reacts with the trace amount of Ae present in the steel material. As a result, fine particles of AeN precipitate near the surface of the steel material, deteriorating the drawability of the steel material.

This is especially bad for steel materials that are deep drawn, such as those used in automobile bodies.

The present invention relies on a trace amount of undecomposed ammonia as described above.

This invention relates to a catalyst for preventing an adverse effect on the drawability of heat-treated steel materials.

That is, elements with high affinity for nitrogen gas, Ae, Ti, B
Fe alloy powder containing at least one of , Si, and Zr is applied to the surface of the skeleton 2, which has a three-dimensional irregular network skeleton structure having communicating pores 1 made of metal as shown in FIG. This relates to a catalyst that is integrated by coating and baking.

When ammonia decomposition gas containing undecomposed ammonia comes into contact with the catalyst having the above structure at high temperature (500°C to 1400°C),
Due to the catalytic action of Fe, undecomposed ammonia is decomposed,
The nitrogen gas generated by the generator at that time combines with the elements Aes Ti-B, Si, and Zr, which have a high affinity for nitrogen and are contained in at least one kind of the Fe alloy powder. , A8, TiN, BN, Si 3 N, , Z
It is possible to generate a nitrogen compound of rN and supply a stable ammonia decomposition gas that does not contain undecomposed ammonia and highly active generator nitrogen.

The elements A e, T i q B, S 1 , and Z r were selected here because of their affinity with nitrogen.

The free energy of nitride formation is -80 kcae in Ae.
/mole, Ti -100kcae/mol
e, -60 kcaff in B, - in 'molaSi
40kcal/mole, 120kc in Zr
The reason is that al/mole has a much greater affinity with nitrogen than with other elements.

Therefore, Ae, Ti, B,
It is possible to prevent the nitrogen gas from reacting with additive elements such as Si and Zr, and to obtain a heat-treated steel material with good deep drawing workability.

In the catalyst of the present invention, an atomic metal element having a high affinity for nitrogen dissolved in Fe reacts with nitrogen as an atomic generator, so that the reaction proceeds even at a relatively low temperature.

According to thermobalance measurement, the effect is recognized when the temperature is 520°C or higher.

However, in reality, γFe has a high solid solubility of nitrogen in Fe.
Approximately 900℃, which is the region where (austenite) exists
A range of 1400°C is good for the reaction.

The element contained in iron alloy powder is A, which has a high affinity for nitrogen.
Considering e, T t , B-S i, and Z r, Ae is better from an economic point of view.

The amount of Ae added in the Fe-Ae gold alloy powder depends on the amount of undecomposed ammonia in the ammonia cracked gas, the life of the catalyst (the amount of added A
The amount of Ae added is optimally 50 atoms or less.

If it exceeds 50 atoms, a complex intermetallic compound of Fe and Ae will be formed, the melting point will be lowered, and an oxide film of Ae will be formed, which is not suitable.

This is because when the number is 50 atoms or less, it is in the range of α phase in which Fe-Ae is dissolved in solid solution, and the catalytic action is high.

Industrially, alloy powder particles such as Fe-Ae are filled into a reaction tower, and when ammonia decomposition gas containing undecomposed ammonia flows through the reaction tower, the undecomposed ammonia is decomposed and the generated nitrogen gas from the generator is Stable AeN by reacting with Ae etc.
A reaction is carried out to form a compound such as

Therefore, catalyst packed beds of various shapes are used in order to satisfy conditions such as improving gas flow, that is, reducing pressure loss, and ensuring close contact with the catalyst layer.

Another condition of the present invention is heat resistance.

For example, by forming a metal foam with Ni as shown in Figure 1, which has a three-dimensional irregular network skeleton structure with continuous pores,
This is used as a catalyst carrier, and the above-mentioned Fe alloy powder is thinly applied and coated on the surface of the skeleton forming the three-dimensional structure of this carrier foam, and the catalyst is then firmly baked.

Although such a metal foam catalyst has a porosity of 95 to 98 pores and is bulky, it is extremely lightweight and has a small pressure loss.

Furthermore, because the three-dimensional structure is connected in a network, it also has strong characteristics.

The foam is manufactured by subjecting polyurethane foam to conductive treatment, electroplating, and then roasting and removing the polyurethane foam.The average pore diameter of the continuous pores can be changed arbitrarily, and the specific surface area is 15,000TrLV77L.
3 is also possible.

The extremely high specific surface area increases the contact area between the gas and the catalyst, improving the efficiency of the catalytic reaction.

Also, due to its high porosity, pressure loss is small.

The effect of the catalyst of the present invention was that undecomposed ammonia gas, which remained at several hundred ppm, was reduced to 10 ppm or less.

The effects of the present invention will be explained below in detail with reference to Examples.

The catalyst layer of the present invention (diameter 5Q mmφ, thickness 50 m
The results of measuring the amount of undecomposed ammonia in the passing gas and the results of measuring the amount of undecomposed ammonia in the gas passing through the catalyst layer of the present invention and the results of heat-treating general aluminum killed steel materials at 1100 ° C. for 2 hours using the ammonia decomposition gas after passing through the catalyst layer of the present invention. The results of analyzing the increased nitrogen gas are shown in the table below.

As shown in this example, the reduction of undecomposed ammonia in the ammonia decomposition gas and the increased amount of nitrogen gas in the heat-treated steel material are extremely reduced by using the catalyst of the present invention, and the effect of the present invention is high. I understand.

Incidentally, one method is to bake Fe alloy powder onto the surface of the skeleton of a foam made of Ni, but the method is not limited to this, and it is also possible to use a foam made of a skeleton of Fe alloy. .

The catalyst may be used, for example, by installing it at the outlet of an ammonium decomposition furnace, installing it in a steel heat treatment furnace, or coating a material to be heat treated with the catalyst of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a conceptual diagram of a three-dimensional irregular network metal foam having continuous pores used in the catalyst, where 1 indicates the pores and 2 indicates the skeleton.

Claims (1)

[Claims] 1 A e 4T, an element with high affinity for nitrogen gas
1. Iron alloy powder containing at least one element among B, Si, and Zr is placed on the skeletal surface of a metal foam having a three-dimensional irregular network skeletal structure with continuous pores. A catalyst for heat treatment of steel materials using ammonia decomposition gas, which is coated and baked.