JP3627684B2 - Partial repair method for blast furnace core - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention cuts and removes the damaged part during the rest period in which the air blowing is suspended for several hours to several tens of hours in order to repair the damaged part of the iron skin where cracks, melting damage, etc. occur. The present invention relates to a partial repair method for a blast furnace furnace core skin that welds and repairs a new skin to a notch.
[0002]
[Prior art]
In general, the blast furnace iron skin is made of materials such as carbon steel and low alloy steel, but during the operation period of the blast furnace for a long time, the heat load from inside the furnace increases due to the wear of the refractory inside the iron skin, The iron skin may be damaged, such as cracking or melting, under the influence of the furnace pressure in the high-pressure operation of the blast furnace. When such damage to the blast furnace iron shell has progressed to the whole, the operation of the blast furnace will be stopped and repairs will be made, but if the damaged part is in a localized state, this damaged part will be cut out. The operation is continued by performing partial repairs that remove and replace the part with a new iron skin.
[0003]
Such partial repair of the iron skin is performed by performing a resting wind for temporarily stopping the operation of the blast furnace for several hours to several tens of hours, and performing partial replacement of the iron skin during the resting wind. When welding is performed when a new iron skin is joined to the damaged part and partial replacement of the iron skin is performed, generally as a welding material for the welding rod, a 50 kg class high strength steel having a tensile strength equivalent to that of the iron skin material. Welding materials are used.
[0004]
[Problems to be solved by the invention]
However, the thickness of the furnace shell is about 25 to 90 mm, and because it is a partial repair, it is frame welded with a new core being fitted and welded. become. For this reason, there exists a tendency for the welding residual stress after a welding repair to become high, and there is a concern about the situation of destruction by welding residual stress.
[0005]
Therefore, conventionally, for the purpose of preventing brittle fracture due to the above-mentioned welding residual stress and extending the fatigue fracture life, plastic working is performed by peening for each pass of the weld bead, or after welding as defined in JISZ3700. A method of performing a post heat treatment at around 600 ° C. is recommended.
However, each method has a problem that there is unevenness in the effect of reducing the residual stress while requiring a large welding repair time. Moreover, since the temperature inside the furnace decreases while the blast furnace is closed, it may interfere with the operation of the blast furnace by performing a long break. As described above, there is a problem in that the range of repairs that can be repaired at a time is limited because the time during which the wind is not working is greatly limited.
[0006]
The present invention has been made paying attention to the above points, and even with a welded joint having a high degree of restraint such as partial repair of the blast furnace iron skin, the residual stress of the welded portion is reduced by a simple operation, and It is an object of the present invention to provide a method for partially repairing a blast furnace core body by an efficient welding method capable of preventing delayed fracture.
[0007]
[Means for Solving the Problems]
The present inventors conducted various experiments and analyzes on the relationship between the temperature of the blast furnace iron skin to be welded, the properties of various welding materials, and the welding residual stress depending on the presence or absence of peening.
As a result, since the blast furnace iron skin is at a temperature of 50 to 100 ° C. even during a rest period, it is only necessary to preheat the new iron skin (the fitting material to be fitted), and the temperature of the repaired part is increased in a short time, and In the welding of low-alloy high-strength steel, it has been found that when a ferritic stainless steel welding material is applied, the residual stress of the weld is low even under conditions of no peening and no post-heating.
[0008]
That is, based on such a viewpoint, in order to solve the above-described problems, the present invention removes a repaired portion of the blast furnace iron skin when the blast furnace is closed, and joins the new iron skin to the repaired portion by welding. in the Hare unit content repair methods row repair Te, it is an feature the use of ferritic stainless welding material as welding material during the welding.
[0009]
As the ferritic stainless welding materials according to the present invention can be exemplified by D430 system such as defined in JISZ3221.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments according to the present invention will be described with reference to the drawings.
As shown in FIG. 1, when the blast furnace operation is temporarily stopped, as shown in FIG. 1, the repaired portion in which the blast furnace iron skin 1 is deteriorated or damaged is opened in a frame shape. In addition, although the case where the opening part 2 is a rectangular shape is illustrated in FIG. 1, the outline of the opening part 2 may be any shape other than a hexagonal shape.
[0011]
Next, a new iron skin 3 having a shape that can be engaged with the opening 2 is fitted into the opening 2. At this time, the distance between the outer peripheral end face of the new iron skin 3 and the opening 2 is set so as to have a route interval as shown in the enlarged view of FIG. 2 over the entire circumference. In FIG. 2, only the outer peripheral end face side of the new iron skin 3 is cut out to form a one-side groove.
Next, along the boundary (joint part) between the old iron skin 1 and the new iron skin 3 of the blast furnace, welding is performed by a welding method such as arc welding, and both 1 and 3 are joined together to form a welded joint, thereby partially repairing. Is done. In FIG. 2, reference numeral 4 indicates a weld metal.
[0012]
In this embodiment, a welding rod made of ferritic stainless steel is used as a welding material used in the above welding.
Here, the iron skins 1 and 2 are made of thick carbon steel or alloy steel, and since the furnace iron skin itself has high rigidity and is frame welded, it is difficult to deform the shape of the welded portion. The degree of restraint of the welded joint is high. In particular, in the case of a welded joint having a weld thickness of 25 mm or more, the welding amount increases, so that the welding residual stress increases and the binding force increases.
[0013]
Thus, part repaired portion of the blast furnace steel shell is a high degree of restraint weld joint, in this embodiment, the ferritic stainless welding materials of the welding materials as specified in JISZ3221 as welding material Therefore, the residual stress can be reduced. The reason is that the ferritic stainless welding materials, while having a high tensile stress is due to the property that a 0.2% yield strength is relatively low.
[0014]
In addition, in low alloy steels such as blast furnace iron skin, there is a possibility of diffusible hydrogen cracking at the welded part, so preheating is usually required at the time of welding. Since it is maintained at a relatively high temperature of 100 ° C., the welding operation can be started simply by preheating the new iron skin 3 in the welding repair, and the operation can be simplified.
[0015]
【Example】
In order to confirm the effect of the present invention, as shown in FIG. 1 above, the center of the test material 1 having a length of 3 m × width of 3 m × thickness of 50 mm is rectangular in length 0.5 m × width 0. A 5 m opening was opened, and a repair member 3 (corresponding to a new iron skin) having a length of 0.492 m × 0.492 m × thickness 50 mm was fitted into the opening 2 and frame welding was performed.
[0016]
As the test material 1 and the repair member 3, SM490 (tensile strength of 490 to 610 MPa) steel material defined in JIS G3106 was used.
And as an Example based on this invention, it welded by the one side groove | channel of 4 mm of root space | intervals using D430-16 (tensile strength 522MPa, 0.2% yield strength 310MPa) prescribed | regulated to JISG3221 as a welding material.
[0017]
In addition, for comparison, as a comparative example, welding was performed with a one-side groove having a root gap of 4 mm using D5016 (tensile strength 560 MPa, 0.2% yield strength 490 MPa) defined in JIS G3212 as a welding material. That is, the conditions were the same as in the examples except for the welding material.
Using these two types of specimens, the welding residual stress of the constrained welded joint was measured. The result is shown in FIG.
[0018]
In this test, as shown in FIG. 2, the strain gauges 5 are attached to both sides of the welded joint, welding is performed, and the stress generated by welding is measured by measuring the strain after welding. In FIG. 3, the stress value generated in each part is indicated by a width.
In addition, in the test body of a comparative example, the test was performed about what was peened after welding, and three types of test bodies which performed the post-heat treatment after performing peening, respectively. The post-heat treatment was performed by holding at 600 ° C. for 4 hours from one side using a panel heater, assuming partial repair work of the blast furnace iron skin during blast furnace quiescence.
[0019]
As can be seen from FIG. 3, the comparative example without peening or post heat treatment shows high welding residual stress, whereas in this example, the peening or post heat treatment in the comparative example was performed without performing peening or post heat treatment. The welding residual stress level is the same as that of the post-heat treatment.
That is, it can be seen that, in the welding work in the partial repair based on the present invention, the level of welding residual stress can be kept low without performing peening or post-heating before and after welding.
[0020]
【The invention's effect】
As described above, according to the present invention, by applying the ferritic stainless welding materials for welding high welded joint of degree of restraint, such as parts repair of blast furnace steel shell of the blast furnace rest in air, post heat treatment Since it is not necessary to perform a process such as peening, it is possible to avoid a decrease in welding repair efficiency.
[0021]
Further, since the residual stress in the repaired portion can be reduced, brittle fracture and fatigue life due to the residual stress can be prevented.
[Brief description of the drawings]
FIG. 1 is a diagram for explaining partial repair according to an embodiment of the present invention.
FIG. 2 is a diagram of a portion A in FIG. 1 for explaining a welded joint according to an embodiment of the present invention.
FIG. 3 is a diagram for explaining a relationship between each weld joint and welding residual stress in an example.
[Explanation of symbols]
1 Iron skin 2 Opening 3 New iron skin 4 Weld metal 5 Strain gauge

Claims (1)

Ferritic stainless steel welding material as a welding material at the time of welding in the partial repairing method in which the repaired part is removed by repairing the repaired part by welding a new iron skin to the repaired part when the blast furnace is closed. portion repairing method of the blast furnace body furnace shell to feature the use of.

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