JP2000102866A - Overlaying method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an overlaying method which can decrease possibility that crack generated at a hard overlaying part reaches base metal fracture and can reduce progress of cracks to the base metal. SOLUTION: In this method, a high hardness metal (high carbon, high chromium) is overlaid on the surface of a base metal 3 composed of a high cracking sensitive material (high chrome cast iron). For forming a first layer covering the surface of the base metal 3, welding beads 12-15 are parallely formed on the base metal 3 surface in a manner that the adjacent beads are separated, and then welding beads 16-17 are formed between the adjacent beads in a manner to overlap both sides of the welding beads, using a welding condition which generates fine cracks to a welding bead of each pass by restraining heat input of each pass at lower than a given value. Thereby, fine and irregular cracks occur at the overlaying part, and a welding residual stress is released immediately after welding so as to prevent cracks from proceeding deeply inside the base metal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for forming a weld on a surface of a material which is highly susceptible to cracking, which is liable to cause a weld crack in the weld when welding is performed. The present invention relates to a technique for multi-layer overlay welding of high hardness metals.

[0002]

2. Description of the Related Art Parts that are required to have abrasion resistance, such as roller tires of vertical mills, table segments, hoppers, and other parts whose surface is severely worn by raw materials to be ground, such as roller tires of vertical mills, table segments, and hoppers as parts used for coal grinding in boilers for thermal power generation. A member having high wear resistance, such as a high-hardness metal formed by multi-layer overlay welding of a high-chromium cast iron, a mild steel, or a cast steel base material surface, is used. These may be used by multi-layer build-up welding of a high hardness metal to a wear portion after use or to a portion where wear is expected before use. Generally, high hardness metals have low cracking resistance, and it is difficult to avoid the occurrence of cracks when welding with high hardness metals regardless of the base metal and welding material. May cause. Therefore, a method has been proposed to reduce the heat input during build-up welding and to intentionally generate fine cracks in the build-up weld using a rapid heating / cooling process to release residual stress and reduce the progress of cracks in the base metal. The used multi-layer build-up welding is performed.

[0003]

In the conventional method described above, when the heat input of the overlay welding is suppressed low and the crack is intentionally generated, as shown in FIG. In the case of overlay welding, cracks generated in the first weld bead propagate to the adjacent weld bead one after another, resulting in a relatively regular shape in which the cracks are fine but are connected vertically and horizontally. When multilayer overlay welding is performed by this method, cracks generated in the first layer extend to the second and third layers, and the shape of the crack in the initial layer is reproduced on the surface of the weld overlay. In such a regular cracked shape, the possibility of peeling of the weld metal and breakage of the base material increases, and for example, when applied to a portion where severe vibration occurs, such as a roller tire of the above-mentioned vertical mill, a table segment, and a problem. Become.

Further, in the conventional method, fine cracks are generated by continuously suppressing the heat input during the overlay welding,
The amount of weld metal is small and inefficient work.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems in the conventional method and to secure a build-up welded portion which has a low possibility of peeling of a weld metal and breakage of a base material and minimizes the growth of cracks in the base material. An object of the present invention is to provide an overlay welding method.

[0006] Another object of the present invention is as described above,
To provide a build-up welding method that secures a build-up welded portion that minimizes the possibility of peeling of the weld metal and breakage of the base material and minimizes the progress of cracks in the base material, and further improves the welding efficiency. is there.

[0007]

In order to achieve the above object, a method of overlay welding of the present invention comprises a method of overlay welding a high-hardness metal to a surface of a base material made of a material having high crack sensitivity in multiple passes. In order to form the first layer covering the base material surface, first, welding is performed on the base material surface using welding conditions that limit the heat input of each pass to a predetermined value or less and generate a fine crack in the weld bead of each pass. The method is characterized in that the beads are formed in parallel and with the adjacent weld beads separated, and then the weld beads are formed so as to overlap between the adjacent weld beads with the two weld beads.

[0008] By the above method, the weld residual stress is released immediately after the build-up welding by generating fine and irregular cracks in the build-up welded portion, and the base material is broken without deep cracks developing inside the base material. Can be prevented.

Another object of the present invention is to provide a method of overlay welding a multi-pass, multi-layer, high-hardness metal on a surface of a base material made of a material having high crack susceptibility. In the fill welding method, using welding conditions that limit the heat input of each pass to a predetermined value or less and generate fine cracks in the weld bead of each pass, (1) first place a weld bead on the base metal surface in parallel and next to Forming a first layer covering the base material surface by forming a welding bead so as to be spaced apart, and then forming a welding bead between adjacent welding beads so as to overlap with both welding beads, (2) and In the same manner as the first layer, the heat input of each pass is limited to a predetermined value or less to form a weld bead in parallel and by separating adjacent weld beads, and then, the adjacent weld beads overlap with the two weld beads. The second layer by forming a weld bead as shown Formed, (3) further initial layer of heat input, and higher second layer, and performing overlay welding of the third and subsequent layers.

In each of the above-mentioned overlay welding methods, it is preferable that the overlay welding is performed using open arc welding. In each overlay welding method, when the material having high crack sensitivity is high chromium cast iron and the high hardness metal contains 5.4 wt% or less of carbon, the welding heat input of each pass forming the first layer. Is preferably less than 2,000 J / cm. In another overlay welding method, a high-efficiency overlay welding can be performed by setting the heat input after the third layer to 2,000 J / cm or more, for example, 7000 J / cm or more.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a view showing a build-up welding method according to the present invention. In multi-layer build-up welding of a hard metal on a material surface having high crack susceptibility, as shown in FIG. 1 (a), the first layer is welded so that the weld beads 12, 13, 14, 15 do not overlap each other. After performing build-up welding and generating an independent crack in each weld bead, as shown in FIG. 1 (b), weld beads 16, 17, and 18 are formed between the weld beads and overlay-welded. Fine and irregular cracks occur on the surface of the first layer overlay weld. In the figure, a horizontal crack in a direction crossing the longitudinal direction of the weld bead is shown.

FIG. 2 shows an example of an automatic arc welding apparatus for performing multi-layer build-up welding of a hard metal on a material surface having high crack sensitivity according to the present invention. The automatic arc welding apparatus includes a welding control device 1, a welding power source 2, a welding torch 4,
And a welding wire 5 to be fed to the welding torch 4, a welding wire 5 to be fed to the welding torch 4, and a self-loading unit having the welding torch 4, the left and right moving unit 6, the up and down moving unit 7, and the like. It comprises a traveling vehicle 8, a rail 9 mounted on the material to be welded (base material) 3 and guiding the self-propelled vehicle 8, and the like. Reference numerals 10 and 11 denote a power cable and an earth cable for arc current. Welding by this device is performed by open arc. for that reason,
The position and state of the arc and the molten pool can be easily checked from the surroundings.

[0013] In the case of overlay welding by the method of the present invention, a special device or technique is not required, and the advantage is that a conventional gas shield arc device can be used as it is.

A high chromium cast iron (C:
3 wt%, Cr: 20 wt%) and high hardness metal (C: 5.
(2 wt%, Cr: 25.3 wt%).

Table 1 and FIG. 3 show the results of measurement of the average crack pitch and the base metal extension crack depth on the surface of the overlay when two-layer overlay welding is performed while changing the welding conditions. Test piece No. 1 to
The test piece No. 3 is one obtained by overlay welding by the conventional half lap method. Nos. 4 to 7 are overlay-welded by the method of the present invention (referred to as the jump pass method). Welding heat input 1200, 1500, 1 by conventional half-lap method
When welding was performed under various conditions of 800 J / cm, the average crack pitch was 8, 10, and 11 mm, and the base material extension crack depth was 4, 4.5, and 4.5 mm. When the welding is performed under the same conditions of 1200, 1500 and 1800 J / cm by the jump pass method of the present invention, the average crack pitch is 6, 7, 9
mm, and the maximum base metal extension crack depth was 3, 3, 3.5 mm. Thus, compared with the conventional method, the welded material welded by the method of the present invention has a smaller average crack pitch and a shallower base material propagation crack depth, so that the welding residual stress is released to the maximum and the influence on the base material is reduced. It can be seen that it is extremely small. In addition,
In No. 7, which was overlay-welded by the jump pass method of the present invention, since the heat input was as large as 2000 J / cm, the average crack pitch was 11 mm.
mm and the base metal extension crack depth was as large as 4.5 mm.

[0016]

[Table 1]

Here, the average crack pitch is a value obtained by averaging the intervals between the horizontal cracks intersecting in the longitudinal direction of the weld bead, and a square of 30 mm square was used for the measurement. Heat input J (J / cm)
Is expressed as follows, where I: welding current (A), E: welding voltage (V), v: welding speed (cm / min).

[0018]

(Equation 1)

Next, the first and second layers of the overlay welding are welded at a low heat input by setting the heat input to 1800 J / cm by using the jump pass method of the present invention. Various heat input conditions (1800, 4032, 6000, 7980 J / c
m) to perform multi-layer build-up welding (about 20 mm). Table 2 shows the test pieces Nos. 8 to 11, which were welded, the welding conditions, and the measurement results of the base metal propagation crack depth. Even when the heat input in the overlay welding of the third and subsequent layers is increased, the maximum value of the base material extension crack depth is constant at 3.5 mm, which indicates that it has not increased. This is because the fine and irregular cracks formed in the first layer propagate one after another to the second and subsequent layers, so that the welding residual stress can be released without keeping the heat input in the overlay welding low. It is shown that.

[0020]

[Table 2]

FIG. 4 shows the state of cracking in one section of the test piece cut in a direction perpendicular to the surface of the base material, and FIG. 5 shows one section of the test piece cut in parallel with the surface of the base material (about 20 m of the multilayer overlay).
(surface position corresponding to almost half of the thickness m).

In order to confirm that sufficient wear resistance was secured in the welded portion by the overlay welding of the high hardness metal, an abrasion test was performed on the overlay welded portion. As shown in FIG. 6, the abrasion test was performed by applying a load to the test piece 19 by the weight 22, supplying silica sand between the test piece 19 and the rubber lining wheel, and rotating and causing friction. The test materials are test pieces Nos. 8 to 11 shown in Table 2.
Table 3 shows the conditions of the wear test, and Table 4 and FIG. 7 show the results of the wear test.

[0023]

[Table 3]

When the abrasion resistance is represented by a numerical value (ratio) obtained by dividing the abrasion amount of the base material (high chromium cast iron) by the abrasion amount of each test piece, test piece Nos. 8 to 11 correspond to 1 of the base material. Is 1.69, 2.
45, 2.75. From this test result, it can be seen that the overlay welding portion of the high hardness metal has better wear resistance than the base material 1, and the wear resistance increases with an increase in the heat input during overlay welding. This is because the increase in the heat input promotes the crystal growth of carbides in the weld metal. However, there is an upper limit to the increase in wear resistance, that is, the crystal growth of carbides in the weld metal, and even if the heat input during build-up welding is increased unnecessarily, an increase in wear resistance beyond a certain level cannot be expected. Conversely, if the heat input during the overlay welding is excessively increased, the residual stress is not sufficiently released, and as a result, the base material may be broken. Therefore, it is considered that the upper limit of the heat input during the overlay welding of the high hardness metal is about 10,000 J / cm.

[0025]

According to the present invention, the overlay welding method of overlaying a hard metal on the surface of a base material made of a material having high crack susceptibility can be performed by using a low build-in heat input during the formation of the first layer. First, the weld bead is formed in parallel and the adjacent weld bead is separated, and then the weld bead is formed so that the adjacent weld bead overlaps with both weld beads. Irregular cracks are generated, the welding residual stress is released immediately after welding, and there is an effect that peeling of the weld metal and propagation of cracks deep inside the base metal can be prevented.

According to the present invention, another overlay welding method is to form a first layer and a second layer in the same manner as the above-mentioned overlay welding method, and to form a weld bead with a larger heat input after the third layer. Since it is formed, there is an effect that, as described above, the propagation of cracks is prevented, and a high-efficiency overlay welding can be performed.

[Brief description of the drawings]

FIG. 1 is a diagram showing a forming order of a weld bead by a welding overlay method of the present invention and a crack shape on a surface of a weld overlay.

FIG. 2 is a diagram showing an example of a welding device for implementing the present invention.

FIG. 3 is a diagram comparing the average crack pitch and the base metal extension crack depth on the surface of the second layer weld formed by the method of the present invention and the conventional method, respectively.

FIG. 4 is a diagram showing cracks in a cross section obtained by cutting a weld overlay formed by the welding overlay method of the present invention perpendicularly to a base material surface.

FIG. 5 is a view showing cracks in a cross section obtained by cutting a weld overlay formed by the welding overlay method of the present invention in parallel with a base material surface.

FIG. 6 is a view showing an experimental apparatus for performing a wear test on a hardfacing welded portion.

FIG. 7 is a view showing a wear test result of a weld overlay formed by the weld overlay method of the present invention.

FIG. 8 is a view showing a forming order of a weld bead by a conventional half lap method and a crack shape on a surface of a weld overlay.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Welding control device 2 Welding power source 3 Base material 4 Welding torch 5 Welding wire 8 Self-propelled trolley 12-18 Weld bead 23 Overlay weld 24 Crack

Claims (6)

[Claims] In a build-up welding method in which a high-hardness metal is multi-pass welded to a base material surface made of a material having high crack susceptibility, a first layer covering the base material surface is formed in each pass. Using welding conditions that limit the heat input to a predetermined value or less and generate a fine crack in the weld bead of each pass, first form a weld bead on the surface of the base material by separating the adjacent weld beads in parallel and adjacently, Then, a weld bead is formed so as to overlap the adjacent weld beads with the two weld beads. 2. A build-up welding method in which a high-hardness metal is multi-pass welded to a surface of a base material made of a material having high crack susceptibility by limiting the heat input of each pass to a predetermined value or less. First, a welding bead is formed on the surface of the base material in parallel and by separating adjacent welding beads, using the welding conditions for generating fine cracks in the welding bead, and then the adjacent welding beads are formed with the two welding beads. An initial layer covering the base material surface is formed by forming a welding bead so as to overlap, and the heat input of each pass is limited to a predetermined value or less on the initial layer in the same manner as the initial layer, and the welding bead is formed in parallel. The second layer is formed by forming a weld bead so as to overlap the adjacent weld beads, and then forming a weld bead between the adjacent weld beads so as to overlap the two weld beads. , Make the second layer higher, and An overlay welding method characterized by performing descending overlay welding. 3. The overlay welding method according to claim 1, wherein the overlay welding is performed using open arc welding. 4. The overlay welding method according to claim 1, wherein the material having high crack susceptibility is high chromium cast iron. 5. The overlay welding method according to claim 4, wherein said high hardness metal contains 5.4 wt% or less of carbon. 6. The multilayer overlay welding method according to claim 5, wherein the welding heat input of each pass forming the first layer is less than 2,000 J / cm.