KR100927470B1 - Grate alloys for waste incinerators - Google Patents

Abstract

The waste incinerator grate alloy according to the present invention is, by weight, C: 0.35% to 1.2%, Si: 8.0% or less, Mn: 2.0% or less, Ni: 2% to 8%, Cr: 22% to 32% , Mo: 0.5% or less, N: 0.05% or less, Co: 10% or less, and the balance consists of Fe and unavoidable impurities. According to the present invention, in order to solve the cost and operation problems of the conventional grate alloy containing a large amount of Ni, an expensive component element, while reducing the content of Ni and at the same time to improve the stability of the oxide film on the grate surface By selecting the appropriate chemical composition to improve, the service life of the grate can be extended. In addition, after casting the alloy of the composition as described above according to the invention, it is also possible to further extend the service life of the grate by increasing the hardness and ductility by heat treatment at a temperature range of 850 ℃ 1100 ℃.

Grate, Incinerator, Wear Resistance, Corrosion Resistance, Heat Resistance

Description

Alloy for Grate of Waste Incinerator {ALLOY FOR GRATE OF INCINERATOR}

The present invention relates to a heat-resistant alloy for waste incineration facilities, and more particularly, to a grate alloy for waste incinerators, which exhibits excellent wear resistance / corrosion resistance and crack resistance even in high temperature corrosion and frictional environments in waste incinerators, thereby greatly extending their lifespan. will be.

In a stalker type waste incinerator which is generally adopted in Korea, a series of grate rows constituted by alternately arranging a moving end and a fixed end in a staircase or zigzag form are provided in the incineration chamber. When the grate is driven for incineration by the steps of drying, combustion, and post-combustion while moving the waste loaded in the incineration chamber and loaded on the grate, abrasion occurs due to friction between the grate and the waste.

In addition, the combustion load fluctuates every time the waste is sequentially introduced onto the grate, resulting in uneven combustion, and in the case of an incinerator in which the grate is arranged in a stepped manner, abrasion occurs between the grates vertically positioned at the movable stage. As a result, there is a problem that the oxide protective film formed on the grate surface is broken or peeled off.

In particular, the upper surface of the grate of the movable end exposed to high temperature is likely to be worn by frictional contact with the lower surface of the grate positioned thereon. In the case of conventional heat-resistant cast steels of SCH13, SCH22, and SCH23, an oxide protective film formed on the surface thereof is used. There was a problem that the resistance to frictional contact is low and easily peeled off.

Meanwhile, the types of wastes to be incinerated include not only general household waste but also medical wastes, construction wastes, and industrial wastes generated by industries.In such wastes, hard materials such as metal or glass fragments, earth and sand are often mixed. As a result, damage to the grate due to wear is further accelerated. Therefore, as some of the characteristics to be provided by the grate, hardness or strength at high temperatures, abrasion resistance, stability of the oxide protective film, and the like are required.

In addition, the grate is suitable for corrosive components such as combustion gases such as O ₂ , CO ₂ , CO, HCl, Cl ₂ , H ₂ S, SO ₂ , SO, and incineration and melting materials including alkali sulfates. Since it is directly exposed, acid resistance, corrosion resistance, etc. are also required as a heat resistant alloy.

Conventionally, heat-resistant cast steels such as SCH13, SCH22, and SCH23 containing Ni and Cr as main alloy components are mainly used as grate materials. In general, when a grate of such a material is placed in a high temperature corrosion environment in an incinerator, Cr mainly forms a protective film (dynamic film) on the surface of the grate to prevent the grate from being lost due to corrosion. Silver is known to play a role of enhancing the effect of increasing the oxidation resistance and high temperature strength and suppressing the fall of the Cr oxide film.

However, in the case of a conventional heat-resistant cast steel containing Ni, the Ni component reacts with sulfur to form a binary compound having a low melting point, and when the ambient temperature in the incinerator rises above the melting point of the compound (about 400 ° C to 500 ° C) Sudden corrosion will occur.

To prevent this, the temperature of the grate is controlled not to exceed 400 ℃ as much as possible during the operation of the incinerator, but in the case of incineration of industrial waste containing a large amount of plastic material, or household waste in which a large amount of plastic or paper is mixed In case of incineration, the calorific value increases, so the surface temperature of the grate often exceeds about 500 ℃ .In the case of industrial wastes, the incinerator is operated under overheating conditions to prevent excessive clinker formation. The temperature of the grate at this time may reach 900 ° C.

In particular, since the plastic in the waste is mainly vinyl chloride-based, a large amount of chlorine gas is generated during incineration, and the Cr oxide formed on the surface of the grate lacks stability in a high temperature atmosphere containing chlorine.

Therefore, in order to prolong the life of the incinerator grate, it is necessary to ensure that the passivation film formed on the surface of the surface prior to the selection of the high quality material can be effectively maintained in a high temperature and harsh working environment, and its wear characteristics and corrosion characteristics are improved.

An object of the present invention devised to solve the problems of the prior art as described above is to provide a heat resistant alloy for grate incinerator having excellent wear resistance and corrosion resistance at high temperature.

Another object of the present invention is to reduce the content of Ni and appropriate chemistry to solve this problem in order to solve the problems of costs and operational problems of conventional grate alloys containing a large amount of Ni, an expensive component element. By selecting the ingredients, it is possible to produce grate at low cost.

Still another object of the present invention is to reduce the damage rate of the grate by improving the strength and adhesion of the oxide film and suppressing the peeling of the oxide film.

Still another object of the present invention is to further extend the service life of the grate by uniformizing the structure of the heat-resistant alloy for grate through heat treatment, removing segregation or residual stress, and increasing hardness and ductility to further improve crack resistance. will be.

MEANS TO SOLVE THE PROBLEM In order to solve the subject of this invention mentioned above, the present inventors earnestly examined the cause and damage mechanism of grate wear.

First, considering the process of gratings exposed to high temperatures in the movable stage by sliding the upper surface of the grate and the end of the grate, if the high temperature is exposed to the surface of the grate, however, high temperature corrosion occurs, this layer of corrosion is The material forms a dense passivation film that prevents further corrosion, but sliding friction makes it difficult to maintain the film during operation, and the process of peeling off the film, which maintains the film and promotes it, occurs periodically during operation. It has been noted that the process of exposing the surface of the new metal material is repeated.

If the passivation film is not effective, the result is that even high-quality materials cannot be more resistant to wear at high temperatures. Therefore, in the case of incinerators, it is often the case that high-quality materials do not necessarily yield better results for the same reasons as they undergo material-based friction. As a result, considering the life characteristics of the grate should be able to solve the damage characteristics together rather than a high-quality material, the study for this has been achieved to achieve the present invention.

The alloy for the grate of the waste incinerator according to the present invention is, by weight, C: 0.35% to 1.2%, Si: 8.0% or less, Mn: 2.0% or less, Ni: 2% to 8%, Cr: 22% to 32 %, Mo: 0.5% or less, N: 0.05% or less, and remainder consists of Fe and an unavoidable impurity.

According to a preferred embodiment of the present invention, the grate alloy further contains one or more of Al: 0.5% to 5%, Nb: 0.1% to 0.5%, and Co: 10% or less by weight.

According to another embodiment of the invention, the step of casting a grate of the alloy composition as described above, and the cast grate in the temperature range of 850 ℃ to 1100 ℃ 0.2 hours / cm ~ 1 hour / cm depending on the thickness of the grate It provides a method for producing a grate alloy of the waste incinerator comprising a heat treatment under the conditions of.

According to the present invention, even if the content of Ni, which has been added in a large amount to a conventional heat-resistant alloy for grate, is greatly reduced, the grate alloy can be provided at low cost since the alloy for grate of incinerator having excellent abrasion resistance and corrosion resistance can be provided. Can produce.

In particular, as the atmosphere in the incinerator gradually increases in temperature due to the polymer material contained in a large amount of waste, the temperature of the grate itself also tends to increase over 500 ° C. The grate alloy according to the present invention It is possible to cope with these recent trends and can be used universally for a variety of wastes, from household waste to industrial waste.

Further, the life of the grate in the operation of the incinerator can be further extended by an additional element for improving the stability, adhesion and the like of the oxide film on the surface of the grate, or by heat treatment for improving the strength and toughness simultaneously.

The alloy for grate according to the present invention, in weight percent, C: 0.35% to 1.2%, Si: 8.0% or less, Mn: 2.0% or less, Ni: 2% to 8%, Cr: 22% to 32%, Mo : 0.5% or less, N: 0.05% or less, and remainder consists of Fe and an unavoidable impurity. The reason for limiting the components of the alloy is as follows, and% indicating the content of the component means weight%.

C is an element that gives strength to the alloy and stabilizes austenite, and Cr carbide is crystallized in the casting step to secure wear resistance at high temperatures. If the C content is less than 0.3%, such an effect is not exerted, and if the Cr content is more than 1.2%, toughness or thermal shock resistance is lowered.

Si has the effect of improving the flowability of the molten metal as a ferrite forming element to improve the castability, and contributes to the corrosion resistance by forming a protective film of SiO ₂ on the alloy surface in combination with oxygen. In particular, unlike the Cr oxide film, the Si oxide film does not break even in a high temperature environment containing Cl ⁻ , and can be formed and maintained as a stable protective film. When the Si content is increased, the ferrite content is increased, the wear resistance is lowered, and the toughness is also reduced, so it is preferable to manage it in the range of 8% or less, and more preferably in the range of 0.5% to 5%.

Mn is added to improve the deoxidation, desulfurization and castability of the molten metal and is also an austenite forming element. If the Mn content exceeds 2%, embrittlement of the alloy occurs, which is not preferable.

Ni is an austenite forming element, which enables material change by causing ferrite / austenite transformation to occur in the ferritic C-Cr-Si alloy. In addition, Ni reduces the embrittlement of the alloy caused by the elements added to improve the corrosion resistance, thereby improving the toughness of the material and suppressing the occurrence of cracks during use of the grate. If the Ni content is less than 2%, the application to the grate is restricted due to the problems described above. In addition, when the content of Ni exceeds 8%, since the high temperature corrosion resistance of the alloy is degraded under the severe corrosion condition by S, it is preferable to manage the Ni content in the range of 2% to 8%.

Cr combines with oxygen to form a Cr ₂ O ₃ protective film on the surface of the alloy to improve oxidation and corrosion resistance. In addition, Cr forms carbides or forms austenite phases with Fe to improve strength at high temperatures. To this end, more than 22% Cr is added, and when the content of Cr exceeds 32%, the effect is saturated.

Mo improves the high temperature strength of the alloy and improves the corrosion resistance, especially in the presence of large amounts of chloride. Although the strength and corrosion resistance of the alloy are improved up to an increase of Mo content of about 2%, Mo is also an element that embrittles the alloy. In particular, when used for a long time at a high temperature such as a grate promotes embrittlement of the alloy, it is preferable to make the upper limit of the Mo content to 0.5% in order to effectively prevent this.

N, like C, is an austenite stabilizing element and forms nitrides or carbonitrides together with Cr to improve high temperature strength and creep strength. However, when the content of N exceeds 0.05%, defects such as blow holes are easily generated when the nitride or carbonitride is coarsened or cast.

According to a more preferred embodiment of the present invention, the grate alloy of the waste incinerator further contains at least one of Al: 0.5% or more and 5% or less, Nb: 0.1% or more and 0.5% or less, and Co: 10% or less.

Al forms a dense oxide film on interaction with Cr or Si and imparts corrosion resistance in a corrosive environment such as chloride. If the Al content is 0.5% or less, the effect is not sufficient. If the Al content is 5% or more, a decrease in strength and toughness is caused, and a large amount of Al oxide is generated in the molten metal to lower castability.

Since both Al and Si lower the strength and toughness of the grate alloy, when coexisting, it is preferable to control the content of Al and Si to 8% or less, more preferably in the range of 0.5% to 5%. .

Nb is an element that tends to form very strong carbides, especially by controlling the shape of Cr carbide at grain boundaries to delay grain boundary corrosion and increase resistance to cracking due to creep deformation at high temperatures. In addition, the present invention improves the adhesion between the oxide film and the alloy base to alleviate the phenomenon that the oxide film is peeled off due to thermal shock or mechanical impact, and the oxide film can be more stably maintained on the alloy surface. In order to obtain such an effect, Nb is required to be 0.1% or more, and when the Nb content exceeds 0.5%, the toughness of the alloy is lowered.

Co is an element that stabilizes the austenite structure to increase the high temperature strength, and especially when coexists with Ni, further stabilizes the austenite structure. In addition, Co has an effect of improving the toughness by preventing the precipitation and coarsening of the fine carbide. When the content of Co exceeds 10%, the further strength improving effect is slowed down. On the other hand, since Co is an expensive metal, it is more preferable to add it in the content of 5% or less from a viewpoint of cost.

In addition, when the temperature of the grate increases above 500 ° C. in the incinerator atmosphere in which S is present, Ni forms a low melting sulfide, so the content of Ni within the range of the content of Ni and Co defined in the present invention is increased. It is desirable to lower the content of Co to 1% or more. Therefore, according to a more preferred embodiment of the present invention, the grate alloy contains Ni: 2% to 4% and Co: 1% to 5%.

The alloy for grate according to the present invention can be manufactured by a conventional casting method, and can be used for grate use as a material in a cast state, but also removes segregation and residual stress in the alloy through heat treatment and makes the structure more uniform, The distribution of precipitates in alloys such as carbides and nitrides may be improved to further improve strength and toughness. It is preferable to set the heat treatment temperature in the range of 850 ° C to 1100 ° C. If the heat treatment temperature is 850 ° C or lower, the effect of improving strength and toughness is not expressed, and at 1100 ° C or higher, the grain coarsening of the alloy becomes remarkable. not.

The heat treatment time is preferably set according to the thickness of the grate, and can be appropriately selected within the range of 0.2 hour / cm to 1 hour / cm according to the thickness of the grate expressed in units of cm.

<Example>

Through a series of processes such as melting, melt treatment, and casting, grate for incinerator made of alloy composition shown in Table 1 was prepared. The grate included a top plate (230 mm wide, 600 mm long, 25 mm thick) extending in the horizontal direction and sidewalls (65 mm high) integrally extending in the vertical direction from the front, rear, left and right edges of the top plate.

In Table 1, Inventive Example 1 is a alloy containing the essential essential components of the present invention, Inventive Example 2 is an alloy in which Al is further added and Al and Si content is 5% or less for stabilization of the oxide film, Inventive Example 3 is an alloy to which Nb is additionally added, Inventive Example 4 is an alloy to which Al and Nb are added together, and Inventive Example 5 is an alloy with Co added as a value near the lower limit.

In order to compare with the grate alloy according to the present invention, gratings were prepared by casting conventional SCH13 and SCH23 alloys according to a conventional casting method, and the composition of this alloy is shown in Table 1 in Comparative Example 1 and Comparative Example. 2 is indicated.

division Alloy composition (% by weight) C Si Mn Ni Cr Mo N Etc Inventive Example 1 0.78 3.82 1.14 5.25 24.3 0.30 0.02 - Inventive Example 2 0.62 2.12 0.89 4.36 23.7 0.33 0.02 Al: 2.47 Inventive Example 3 0.74 4.88 1.26 6.11 24.9 0.29 0.03 Nb: 0.33 Inventive Example 4 0.71 0.93 1.37 4.59 22.6 0.30 0.02 Al: 3.45, Nb: 0.25 Inventive Example 5 0.52 3.93 1.12 2.85 23.6 0.35 0.02 Co: 4.43 Comparative Example 1 (SCH13) 0.32 1.15 1.06 13.6 26.8 - - - Comparative Example 2 (SCH23) 0.42 1.05 0.94 20.3 29.2 - - -

Samples were taken from the top plate of the grate, and the thermal shock resistance test of the oxide film was carried out in addition to the tensile test, the hardness and the corrosion test, and the results are shown in Table 2.

In addition, in the alloy according to the present invention, Example 1 and Example 4 were air-cooled after heat treatment at 900 ℃ for 2 hours, which is shown in Table 2 as Example 11 and Example 14.

In the corrosion test for evaluating the corrosion resistance, test pieces prepared in a width of 50 mm, a length of 50 mm, and a thickness of 10 mm were embedded in a synthetic incinerator composed of 60% by weight of Na ₂ SO ₄ and 40% by weight of NaCl for 7 days at 600 ° C. (168 hours) After heating, the corrosion loss was measured.

In order to evaluate the thermal shock resistance of the oxide film, the test piece was heated at 900 ° C. for 1 day (24 hours), and then air cooled 10 times, and the weight of the oxide film dropped from the surface was measured and added.

Tensile strength, MPa Elongation,% Hardness, HS Corrosion loss, mg / ㎠ Anodized weight, mg / ㎠ Inventive Example 1 681 3.6 37.3 9.5 3.5 Inventive Example 2 617 1.9 33.3 7.3 2.2 Inventive Example 3 653 2.2 34.5 9.5 1.1 Inventive Example 4 682 3.2 35.0 6.8 1.2 Inventive Example 5 704 5.5 38.7 8.1 3.6 Inventive Example 11 874 6.3 43.9 8.2 3.2 Inventive Example 14 862 5.3 45.0 7.1 1.5 Comparative Example 1 613 23.3 26.3 24.3 8.5 Comparative Example 2 596 29.1 27.6 33.8 6.3

Compared with the alloy of the comparative example, the alloy according to the present invention has improved strength and hardness, and the weight loss of the oxide film due to repeated heating and heating in the incineration material containing Na ₂ SO ₄ and NaCl is 1/2 to 1 /. 6 decreased.

Inventive Examples 2 to 4 in which Al and Nb were added improved the corrosion resistance and / or the stability of the oxide film. Particularly, Inventive Example 3 containing Nb had no significant change in corrosion loss compared to Inventive Example 1, but the oxide film peeling weight was reduced to 1/3 level, and Inventive Example 4 in which Nb and Al were added at the same time. Also in comparison with the invention example 1, the oxide film peeling weight was significantly reduced.

The corrosion loss and the oxide film peeling weight of Inventive Example 5 to which Co was added were almost the same as those of Inventive Example 1, but the strength and ductility were improved. In particular, the invention example 5 is suitable for the use of the grate for incinerators of the atmosphere in which the amount of heat is large and containing a large amount of S by the reduction of Ni.

In the case of Inventive Example 11 and Inventive Example 14, the increase in strength and ductility was remarkable compared to Inventive Example 1 and Inventive Example 4 before heat treatment. It contributes greatly to the wear resistance of the grate.

The prototypes shipped after the above-mentioned evaluation of the laboratory scale were applied to an incinerator operated 24 hours a day, and the field test was conducted. In the same incinerator which has been using heat-resistant cast steel of SCH13 and SCH23 materials, It was possible to extend the service life of the grate by more than 50% under the same incinerator operating conditions.

More specifically, in the case of conventional alloys of SCH13 and SCH23, the replacement cycle of the grate is 4 months to 6 months when used for industrial / construction waste, 9 to 12 months when used for household waste, and for medical waste When it was 3 months to 4 months, according to the type of waste according to the present invention applied to the grate alloy according to the present invention was able to guarantee the grate life of 1 to 2 years or more.

In particular, in medical wastes containing a large amount of glass and metal, the grate material according to the present invention does not show such a problem because the grate according to the present invention has a short period of replacement of the grate due to early cracking. Grate life could be improved. That is, the alloy according to the present invention was found to be superior to the conventional SCH13 alloy thermal shock resistance and toughness of the alloy matrix at high temperatures through field tests.

In addition, in the case of the grate supplied by heat treatment according to the present invention, it was possible to further extend the service life of the grate by about 20% to 30%.

As mentioned above, although preferred embodiment of this invention was described, the scope of the present invention is not limited to the said embodiment, Of course, various modification forms are possible without deviating from the essential and essential characteristic structure of this invention. The foregoing embodiments are, therefore, to be considered in all respects only as illustrative and not restrictive, and the scope of the present invention is to be understood to include the matters set forth in the appended claims and all modifications that may be understood therefrom. do.

Claims (8)

delete delete delete delete By weight, C: 0.35% to 1.2%, Si: 0.5% to 8.0%, Mn: 2.0% or less (excluding 0%), Ni: 2% to 8%, Cr: 22% to 32%, Mo: Alloy for waste incinerator grate containing 0.5% or less (excluding 0%), N: 0.05% or less (excluding 0%), Co: 10% or less (excluding 0%). The method of claim 5, A waste incinerator grate alloy containing, in weight percent, 2% to 4% Ni and 1% to 5% Co. delete delete