JP2007270249A - Special steel for sinter cake supporting stand - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To elongate the service life of a sinter cake supporting stand installed at a sintering pellet in a lower suction type sintering machine. <P>SOLUTION: The special steel used as the material for a sinter cake supporting stand 1 has a composition comprising, by weight, 0.4 to 0.8% C, 0.2 to 2.0% Si, 0.1 to 1.5% Mn, 25 to 29% Cr and 0.2 to 2.0% Ni, and the balance Fe with inevitable impurities. Namely, by making the contents of C and Cr higher than those in the conventional steel, its hardness and corrosion resistance are increased, and its wear resistance is improved, thus the progression of wear is suppressed. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a special steel suitable for use as a material for a sinter cake support stand installed on a sintering pallet of a downward suction type sintering machine.

  In iron making processes such as blast furnaces, sintered ore obtained by sintering powder iron ore into a lump with a sintering machine is often used as a raw material. FIG. 3 shows a sinter production process by a general sintering machine. In this sintered ore production process, firstly, the main raw material powdered iron ore, the auxiliary raw material limestone, and the fuel coke are cut out from the hoppers 11, 12, and 13, respectively, and the returned ore cut out from the return hopper 14 together with the mixer 15. Condition and granulate to make a sintered raw material. The sintered raw material is transported to the surge hopper 16 and temporarily stored, then cut out from the drum feeder 17 and supplied to the supply portion of the sintered pallet 19 via the chute 18 so that the sintered raw material is placed on the sintered pallet 19. Layer 20 is formed. Then, the coke on the surface layer of the sintering raw material layer 20 conveyed by the sintering pallet 19 is ignited by an ignition furnace 21, and the coke is burned while sucking air below the sintering raw material layer 20. The sintering raw material layer 20 is sequentially sintered from the upper layer to the lower layer. This sintering method is called “downward suction type”. The raw material thus sintered is discharged from the discharge part of the sintering pallet 19 as sintered ore.

  In a sintering machine that employs the downward suction type sintering method as described above, the upper layer portion of the sintering raw material layer is sintered before the lower layer portion, and is sintered (hereinafter referred to as “sinter cake”). Therefore, as the sintering progresses, the lower layer portion of the raw material layer receives the weight of the sinter cake and is compressed to become high density. When the sintered raw material layer is densified, the air permeability is lowered, resulting in a reduction in the combustion rate of coke and uneven combustion. As a result, the sintering speed is slowed, the quality of the sintered ore discharged from the sintering pallet is highly varied, and the productivity tends to be lowered. Therefore, a support member (hereinafter referred to as “sinter cake support stand” or simply “stand”) that receives the weight of the sinter cake is usually installed on the sintering pallet so as to be buried in the sintering material layer. Therefore, the lowering of the air permeability due to the higher density of the lower layer of the raw material layer is prevented, and the productivity of the sintered ore is improved.

By the way, the sinter cake support stand has a large temperature difference in the height direction on the way from the supply part of the sintering pallet to the discharge part, and the whole is cooled when returning from the discharge part of the sintering pallet to the supply part. Due to repeated thermal stress. Moreover, the use environment becomes a hot corrosive atmosphere. Therefore, it is desirable that the material for forming the stand has sufficient heat fatigue resistance and high temperature strength and is excellent in corrosion resistance. As a material having such characteristics, it has been proposed to use a special steel containing about 0.2 wt% C and about 13 wt% Cr (for example, see Patent Document 1).
Japanese Patent No. 3151653

  However, in addition to the above properties, the material for the sinter cake support stand is also required to have wear resistance. That is, this stand wears by rubbing against the raw material when the sintering raw material is supplied to the supply part of the sintering pallet or when the raw material after completion of sintering is discharged as sintered ore at the pallet discharging part. . And since it is not possible to support the weight of the sinter cake due to thinning and it is not possible to prevent a decrease in air permeability of the sintered raw material layer, it is necessary to replace it. Therefore, wear resistance is one of the factors determining the length of life. It has become. On the other hand, the stand formed of the special steel described in Patent Document 1 cannot always be said to have sufficient wear resistance, and may have a short life due to early wear.

  An object of the present invention is to extend the life of a sinter cake support stand installed on a sintering pallet of a downward suction type sintering machine.

  In order to solve the above-mentioned problems, the present invention has a composition of a special steel used as a material for a sinter cake support stand, C: 0.4 to 0.8 wt%, Si: 0.2 to 2.0 wt%, It contained Mn: 0.1 to 1.5 wt%, Cr: 25 to 29 wt%, Ni: 0.2 to 2.0 wt%, and the balance was made of Fe and inevitable impurities.

  That is, focusing on the fact that cracks due to insufficient ductility are relatively unlikely to occur in this application, the C content is increased in a range where cracks do not occur compared to the special steel described in Patent Document 1 described above (conventional steel). Thus, the hardness is increased, and the Cr content is increased to further enhance the corrosion resistance, thereby improving the wear resistance and extending the stand replacement cycle.

Next, the reason why the content of each alloy element is limited to the above range will be described.
(1) C is an element effective for increasing the high-temperature strength and hardness by forming a carbide in addition to strengthening the base material by partly dissolving in the base material. In addition to ensuring the necessary high temperature strength, at least 0.4 wt% is included in order to improve wear resistance. The higher the content, the higher the high-temperature strength and hardness. However, the precipitation amount of secondary carbide due to aging at the time of high-temperature use becomes excessive, leading to a decrease in ductility. The upper limit of the content was set to 0.8 wt% so as not to occur.

(2) Si is a deoxidizing element when the alloy is melted, and has the effect of increasing the fluidity of the molten metal in the casting process. It also improves the corrosion resistance at high temperatures. These effects are improved in proportion to the content, but if contained excessively, the ductility is lowered, so the content is set to 2.0 wt% or less. On the other hand, if the content is extremely small, baking is likely to occur after being subjected to a thermal cycle, leading to a reduction in ductility. Therefore, it is necessary to contain 0.2 wt% or more.

(3) Mn is an element having a deoxidizing action and detoxifying by fixing S, and it is necessary to contain 0.1 wt% or more. On the other hand, even if the amount is increased to 1.5 wt% or more, the increase in the effect is small, so the upper limit of the content was set to 1.5 wt%.

(4) Cr is an element that improves high-temperature strength and corrosion resistance. In order to improve the corrosion resistance so as to contribute to the improvement of the wear resistance, the lower limit of the content was set to 25 wt%. However, if contained excessively, the ductility is lowered, so the upper limit was made 29 wt% so that cracking would not occur in this application.

(5) Ni is contained in an amount of 0.2 wt% or more in order to increase the high temperature strength. However, since an austenite phase will increase and a linear expansion coefficient will become large and thermal deformation will become large if it contains excessively, the upper limit was 2.0 wt%.

  As described above, the special steel for the sinter cake support stand of the present invention increases hardness and corrosion resistance by increasing the content of C and Cr in a range where cracking does not occur in this application compared to conventional steel. Abrasion is improved. Therefore, if this special steel is used as the material of the stand, the stand replacement cycle becomes longer than before, and the maintenance cost can be reduced by reducing the production cost of the new stand and the labor cost of the stand replacement work. Further, since the time for stopping the entire sintering machine for the stand replacement operation is shortened, the productivity of the sintered ore can be improved.

  Embodiments of the present invention will be described below. Table 1 shows the composition of the special steel of the embodiment (Examples 1 to 3) and the conventional steel equivalent (comparative example) and the hardness measurement result at room temperature (5-point average value). As can be seen from Table 1, the hardness of each example increased almost in proportion to the C content, and even in the examples (Example 1) having the smallest C content, the hardness was 15% compared to the comparative example. High hardness is obtained.

  Next, the sinter cake support stand 1 shown in FIG. 1 was formed using the special steels of the examples in Table 1. The stand 1 includes a trapezoidal plate-like main body 2 and a mounting portion 3 continuous therebelow, and as shown in FIG. 2, a stand for a sintering machine in a general sintered ore manufacturing process (see FIG. 3). Two to four rows are arranged on the sintering pallet 19 (FIG. 2 shows an example of two rows). The height of the main body 2 is 300 mm, and the main body 2 is formed on the sintering pallet 19 and buried in the sintering raw material layer 20 having a height of about 600 mm. It is designed to support the sinter cake produced by ligation.

  As a result of conducting an experiment in which the stand 1 is continuously used in the installation state shown in FIG. 2, the progress of wear is slower than that of a stand made of conventional steel, and the replacement cycle can be extended significantly. It was also confirmed that there were no cracks during the replacement.

The perspective view of the stand formed with the special steel of the embodiment The perspective view which shows the installation state of the stand of FIG. Illustration of general sinter manufacturing process

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Stand 2 Main-body part 3 Attachment part 11, 12, 13, 14 Hopper 15 Mixer 16 Surge hopper 17 Drum feeder 18 Chute 19 Sintering pallet 20 Sintering raw material layer 21 Ignition furnace

Claims (1)

  Used as a material for a sinter cake support stand installed on a sintering pallet of a lower suction type sintering machine, C: 0.4 to 0.8 wt%, Si: 0.2 to 2.0 wt%, Mn: 0. A special steel for a sinter cake support stand containing 1 to 1.5 wt%, Cr: 25 to 29 wt%, Ni: 0.2 to 2.0 wt%, the balance being Fe and inevitable impurities.

Images