Carburization resistant metal material

Abstract

There is provided a metal material having excellent workability and metal dusting resistance, which is suitable as a raw material for cracking furnaces, reforming furnaces, heating furnaces, heat exchangers, etc. in petroleum refining, petrochemical plants, and the like.The metal material is characterized by consisting of, by mass %, C: 0.08 to 0.4%, Si: 0.6 to 2.0%, Mn: 0.05 to 2.5%, P: 0.04% or less, S: 0.015% or less, Cr: 18 to 30%, Ni: 20% or higher and less than 30%, Cu: 0.5 to 10.0%, Al: 0.01 to 1%, Ti: 0.01 to 1%, N: 0.15% or less, and O (oxygen): 0.02% or less, the balance being Fe and impurities, and satisfying Expression (1).C≧0.062×Si+0.033×Cu−0.004×Cr+0.043  (1)in which the symbol of element in Expression (1) represents the content of that element in mass %.

Description

TECHNICAL FIELD[0001]The present invention relates to a metal material that has excellent high-temperature strength and superior corrosion resistance, and in particular is used in a carburizing gas atmosphere containing hydrocarbon gas and CO gas. More particularly, it relates to a metal material having excellent weldability and metal dusting resistance, which is suitable as a raw material for cracking furnaces, reforming furnaces, heating furnaces, heat exchangers, etc. in petroleum refining, petrochemical plants, and the like.BACKGROUND ART[0002]Demand for clean energy fuels such as hydrogen, methanol, liquid fuels (GTL: Gas to Liquids), and dimethyl ether (DME) is expected to significantly increase in the future. Therefore, a reforming apparatus for producing such a synthetic gas tends to be large in size, and an apparatus that achieves higher thermal efficiency and is suitable for mass production is demanded. Also, heat exchange for recovering exhaust is often used to enhance en...

AI Technical Summary

Benefits of technology

[0043]The metal material in accordance with the present invention has an effect of restraining reaction between carburizing gas and the metal surface, and has excellent metal dusting resistance, carburization resistance, and coking resistance. Further, since the weldability is improved, the metal material can be used for welded structure members of cracking furnaces, reforming furnaces, heating furnaces, heat exchangers, etc. in petroleum refining, petrochemical plants, and the like, and can significantly improve the durability and operation efficiency of apparatus.

[0044]In particular, the metal material in accordance with the present invention is suitable as a metal material used for reaction tubes and heat exchangers used for heat exchange in a temperature range (400 to 800° C.) lower than the conventional temperature range, so that metal dusting, which poses a problem in this temperature range, can be restrained effectively.

Problems solved by technology

To effectively use the heat of such a high-temperature gas, heat exchange in a temperature range of 400 to 800° C., which is relatively low, has become important, and corrosion caused by carburization of a high Cr— high Ni—Fe alloy based metal material used for reaction tubes, heat exchangers, and the like in this temperature range poses a problem.

In a portion such as a heat exchange part in which the temperature is relatively low, however, the diffusion of element from the inside to the surface of metal material is insufficient.

Therefore, the formation of oxide film, which achieves a corrosion restraining effect, delays, and additionally, such a gas having a composition containing hydrocarbon comes to have carburizing properties, so that carbon intrudes into the metal material through the surface thereof, and carburization occurs.

As a result, fine cracks are liable to develop, and in the worst case, the tube in use is broken.

Also, if the metal surface is exposed, carbon precipitation (coking) in which metal serves as a catalyst occurs on the surface, so that the flow path area of the tube decreases and the heat-transfer characteristics degrade.

Therefore, a base material metal is exfoliated away and the thickness of base material decreases, that is, corrosion loss called metal dusting proceeds.

If the cracks, loss, and in-tube closure increase, an apparatus failure or the like occurs.

As a result, operation may be suspended.

However, even if a Cr or Ni content in the Fe-based alloy or the Ni-based alloy is merely increased, a sufficient carburization restraining effect cannot be achieved, so that a metal material having higher metal dusting resistance has been demanded.

Although effective at the early stage, this method may lose effectiveness in that the thin layer is exfoliated in long-term use.

However, the increase of Si, Al and the like sometimes leads to the decrease in hot workability and weldability.

Unfortunately, all of these prior arts require special heat treatment or surface treatment, and therefore they are inferior in economy.

Also, since scale restoration (scale recycling) after the pre-oxidized scale or the surface treatment layer has exfoliated away is not considered, if the material surface is damaged once, the subsequent effect cannot be anticipated.

In this patent document, however, the improvement of weldability, which is an issue of the Cu-containing steel, has not been studied.

However, the application of this method is restricted because H2S may remarkably decrease the activity of a catalyst used for reforming.

However, since these elements segregate not only on the metal surface but also at the grain boundary of metal grainy, a problem associated with hot workability and weldability remains to be solved.

Therefore, the solid-solution strengthening of C cannot be anticipated, and a sufficient high-temperature strength cannot be obtained.

For this reason, these techniques are unsuitable for a metal material used at high temperatures.