JPS61253192A - Production of composite cast steel pipe - Google Patents

Abstract

PURPOSE:To obtain a composite cast steel pipe which has the fine structure on the surface and has good wear resistance by melting an electrode by electroslag welding while adding a high-carbon high alloy thereto. CONSTITUTION:The steel pipe 8 which is a base metal is perpendicularly set onto a mold 13 for a start tab and thereafter a water cooled mold 14 is set at a start position, i.e., bottom end to build up a build-up metal 15 to be formed as the inside layer of the composite cast steel pipe. A welding wire 9 is continuously fed into the groove of the mold 14 and the mold 13 added preliminarily with a flux and molten slag 16 is formed. Building up is executed upon lapse of the specified time while a specified amt. of a molten metal 11 melted in another melting furnace is introduced into the mold from a tundish 12. The slag line rises on progressing of the building up and therefore the mold 13 and the steel pipe 8 are continuously or intermittently lowered to prevent the molten metal from overflowing from the mold 14.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a composite cast steel pipe used for transporting earth and sand or slurry, etc. The inner surface of the pipe is made of a high carbon high alloy material with excellent wear resistance and corrosion resistance. The present invention relates to a method of manufacturing a composite cast steel pipe made of cast steel.

(Prior Art) Composite cast steel pipes whose inner surface is made of high-carbon, high-alloy cast steel are used for mud pump liners and the like.

The small sizes used for mud pump liners are manufactured by centrifugal casting. In the centrifugal casting method, a mold (mold) is rotated at high speed as shown in Figure 3.
The molten metal that has been pre-melted in a melting furnace to form the outer layer 3 is injected into the mold 2 to a certain thickness, and after a certain period of time has passed and the outer layer 3 has completely solidified, it is poured into another melting furnace. A composite cast steel pipe is manufactured by injecting the molten metal 5 which melts into the inner layer 4.

(Problems to be Solved by the Invention) However, the composite cast steel pipe manufactured by this method has a coarse structure because the inner surface of the pipe for transporting slurry etc. becomes the final solidification zone, and is subject to severe wear and short life.

In addition, the inner surface of the tube has large irregularities due to the final solidification zone, and machining requires time t, and an improvement is desired.

Further, when forming a composite by centrifugal casting, there is a limit to the thickness of the inner layer I-, which limits the amount of heat required for welding, and it is not possible to reduce the thickness of the expensive inner layer. Further, there are other problems such as non-bonding when the inner surface of the outer layer is contaminated with slag or slack or oxidized, and it is difficult to control the thickness of the fusion at the boundary.

The present invention relates to a method for manufacturing this composite cast steel pipe.

(Means and effects for solving the problems) The present invention advantageously solves the above-mentioned problems. That is, the gist of the present invention is to apply electroslag welding to a heat source that controls joining. In order to control the composition and improve welding speed, the molten metal or high chromium cast iron powder is melted in slag, making it possible to freely control the inner layer thickness, and not only has excellent bonding properties at the boundary, but also improves the inner surface of the tube. Improves wear resistance by improving surface roughness and solidification structure.

A feature of the present invention is that electroslag welding is applied as a heat source.

For the purpose of wear resistance, the material has a high carbon content, and moreover, alloying elements such as Or are increased to crystallize or precipitate carbides to increase hardness. When you overlay such materials,
TAP○0 welding with a small amount of heat that cools quickly after overlaying, TIG
During welding, cracks occur in the overlay metal. Fig. 4 shows the relationship between the cracking rate and the occurrence of cracks in overlay metals, and shows that electroslag welding is the only method available for overlaying components such as the inner layer of composite cast steel pipes.

The composite cast steel pipe is manufactured as shown in FIG. 1 as follows.

After the steel pipe 8, which will become the outer base material of the composite cast steel pipe, is vertically set on the start tab mold 13.

The water-cooled mold 14 for overlaying the overlay metal [15 that will become the inner layer of the composite cast steel pipe] is set at the starting position, that is, at the lower end. Then, the welding wire 9 is continuously fed into the groove of the water-cooled mold 14 to which 7 lux has been added and the start tab mold 13 to form a molten slag 16.

After a certain period of time has elapsed, he pours a certain amount of the molten metal 11, which was melted in another melting furnace, through the tundish 12, and performs a flesh feeling process. The mold 13 for the start tab and the steel pipe 8 serving as the base material are placed continuously or intermittently so that they do not flow. At this time, the inner water cooling mold 14 and the welding nozzle lO are fixed -fi:
, Ma\ is. Moreover, powder can also be used instead of the molten metal 11.

(Example) Next, an example will be given and explained.

[Example 1] The base material used was a carbon steel pipe SGP 300A with a length of 500 threads. Overlaying was carried out under the conditions shown in Table 1.

The electrical conditions at this time were such that appropriate penetration could be obtained from past experiments.

As a result, the penetration of the base material was approximately 1 m, and was uniform over the entire length. Also, the electrode oscillates within the groove in the circumferential direction.

The melting was uniform. Therefore, the ingredients are almost as expected, 2.8-3.0%○, 0.9-1.
1%si, 0.8~L, O%Mrl, 29~31%
Or.

It was in the range of 1.5-1.7% Mn.

On the other hand, the inner surface is also cooled with a water-cooled mold.

The overlay on the inside was beautiful, and the black skin could be removed by shaving 1 meter off of one piece of meat. Since the inner surface was forcedly cooled, the solidified structure was also fine.

[Example 2] This is an example in which powdered powder was added instead of molten metal.

The base material used was a carbon steel pipe SGP 200A with a length of 300 mm. Overlaying was carried out under the conditions shown in Table 2. The electrical conditions at this time were slightly thicker than those when adding the molten metal.

As a result, the penetration of the base material was approximately 0 to 2 mm, which was approximately uniform over the entire length. Also, for one circumferential direction [
Same as Example 1], it is almost uniform and the actual components are 2.
6~2.8%0,0.9~l-INS's 1
0.7-0.9%Mns 28-30 XO'bl-
The value of 2 to 5%V was close to the target value, and the inner surface was as beautiful as [Example 1].
It was found that the black skin was completely removed by scraping with ms "! 3.
A (Effect of the invention) From the above, the composite cast steel F pipe manufactured by the method of the present invention has a finer surface structure, better wear resistance, and lower wear resistance than conventional continuously cast composite steel pipes. As shown in Fig. 2, it has been significantly reduced, and even when applied to an actual machine, a significant extension of life can be expected. In addition, because the overlay surface has significantly smaller irregularities than conventional continuously cast composite steel pipes, the processing time for the inner surface is significantly shortened to about 100 to 300 volts on average, and depending on the product, it can be used as is without processing the inner surface. Monokaashi and processing costs can be significantly reduced.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram for explaining the method of the present invention, Fig. 2 is a diagram showing the results of a wear test on a conventional centrifugally cast composite steel pipe manufactured by the method of the present invention, and Fig. 3 is a diagram showing the results of a conventional centrifugal cast composite steel pipe. A schematic diagram illustrating the production of a composite cast steel pipe using the centrifugal casting method. FIG. 4 is a diagram showing eight results of overlay metal cracking tests using various welding methods. l... Mold (mold), 2... Coating mold, 3... Outer layer,
4... 1st layer, 5... Molten metal that becomes the inner layer, 6... Tanditshu. r...Rotating roller, 8...Steel pipe serving as base material, 9...
・Bath welding gloss, 10... Welding nozzle, 11-... Molten metal, 12... Tan tissue, 13... Mold for start tab, L4... Water cooling mold, 15... Overlay to become inner layer Gold g&, [6... Molten slag. Agent: Patent attorney Masamitsu Akizawa and 2 others - amount of wear and tear (9)

Claims (1)

[Claims] (1) A method for manufacturing a composite cast steel pipe, characterized in that high carbon high alloy steel is overlaid on the inner surface of the steel pipe by melting an electrode by electroslag welding while adding high carbon high alloy. manufacturing method.