JPS61296962A - Surface hardening method for hot tool - Google Patents

Abstract

PURPOSE:To prolong the life of a tool by forming a surface hardened part by controlling the feeding ratio of an alloy powder and hard granular body and by buildup-welding with plasma arc. CONSTITUTION:A plasma arc is generated between an electrode 2 and elongator plug 21 by connecting the cathode side of a power source to a bar electrode 2 and by connecting the anode side to the plug 21 as well. The alloy powder having heat resistance and wear resistance and the hard granular body of more than one kind selected among a carbide, nitride and oxide are simultaneously melted by feeding into the plasma arc with controlling the respective feeding ratio and/or feeding quantity. The built up surface hardened part 22 is then formed by depositing on the surface of the necessary part of the plug 21.

Description

[Detailed description of the invention] [Object of the invention] (Industrial field of application) The present invention is used for hot working, and in particular for obtaining a hot working tool that achieves an improvement in tool life by improving surface properties. The present invention relates to a surface hardening method for hot tools used.

(Prior Art) Examples of hot tools of this type include perforation plugs, elongator plugs, and guide shoes used for manufacturing seamless steel pipes. Among these, the perforation plug and the elongator plug consist of a tip, a body, and a relief, and the tip usually has an arc shape. In the case of a perforated plug, this tip has a relatively small heat capacity compared to other parts and is subjected to strong pressure.
It is easily damaged by melting during drilling, so it is required to have excellent resistance to melting and wear, especially at this tip portion.

Furthermore, in the case of an elongator plug, the body and relief portions are subjected to strong pressure, so these portions are required to have excellent wear resistance.

On the other hand, guide shoes come into contact with the steel pipe material between the rolls and directly regulate the ellipticity and outer diameter of the steel pipe material during the drilling, rolling or rolling process. , it is required to have excellent abrasion resistance.

Conventionally, in hot tools for making pipes, Cr is generally used as the material for the perforation plug and elongator plug.
-Ni-based cast steel is used, and in order to increase high-temperature strength, materials to which Mo, Co, W, etc. are added are also used. In addition, the material for the guide shoe is generally high Cr-N.
I-series cast steel is used.

(Problems to be Solved by the Invention) In such conventional hot work tools, for example, when excellent heat resistance and wear resistance are required as described above, high Cr-Ni cast steel is used. It is used as a raw material, but when the whole is molded from the same material by casting,
The problem was that they were quite expensive and their lifespans varied widely.

This invention was made by focusing on the above-mentioned conventional problems, and has extremely excellent heat resistance and abrasion resistance on the surface, has a long service life, and therefore reduces processing costs and crystal manufacturing costs. It is an object of the present invention to provide a method for surface hardening a hot tool that can obtain a hot tool that can be heated.

[Structure of the Invention] (Means for Solving the Problems) The method for surface hardening a hot work tool according to the present invention includes, for example, a hardening process between a rod-shaped electrode and a torch inner cylinder disposed around the rod-shaped electrode. A plasma working gas is supplied, and in the plasma arc where the plasma working gas decomposes and becomes plasma, an alloy powder having heat resistance and wear resistance, and one or more hard materials selected from carbides, nitrides, and oxides are added. The method is characterized in that a hardened build-up surface portion is formed on the surface of a desired part of the tool by plasma arc build-up welding in which the powder material is supplied while controlling the feed ratio and/or amount of each feed. and,
- In the fourth embodiment, the surface hardening part is formed only in the part of the tool that contacts the workpiece and/or only in the worn part after use, thereby realizing further cost reduction. It is characterized by

In the hot tool surface hardening method according to the present invention, carbon tool steel (S
K), alloy tool steel (SKS, SKD, SKT,
5KH) etc. are used.

Further, as the alloy powder for overlay welding having heat resistance and wear resistance that is overlayed on the surface of the tool by plasma arc overlay welding, high Cr.

High Cr-W, high Cr-Mo, high Cr-Ni.

117) Co-based alloys such as high Cr-N1-W and high Cr.

Ni-based alloys such as high Cr-Ni Cr-B, high Cr,
Fe-based alloys such as high Cr-Ni and high Cr-Ni-Mo are used.

Furthermore, the hard powder particles supplied together with the above-mentioned alloy powder for overlay welding include WC and NbC.

Carbides such as Tic, nitrides such as TiN, BN, 5i3Na, molten metals such as Al2O3, 5i02, ZrO2, etc.
Physical strength) 1 liter of powdered material is used.

Alloy powder with such heat resistance and wear resistance,
Using plasma arc overlay welding, which supplies hard powder and granules while controlling the feed ratio and/or amount of each alloy powder and hard powder, weld overlay and overlay on the surface of the desired part of the tool. As a welding plasma torch of a plasma arc build-up welding apparatus used when forming a hardened build-up surface part, for example, one having a structure shown in FIG. 2 is used. That is, the plasma torch 1 shown in the figure has a rod-shaped electrode 2 at its center connected to the cathode side of a power source (not shown), and a torch inner cylinder 3 is arranged concentrically with and spaced apart from the rod-shaped electrode 2. .

In the illustrated example, this torch inner cylinder 3 has a tip 4 at its lower end.
Although it is equipped with screws and is screwed, it is also possible to integrate them. A cooling water passage 5 is provided in the torch inner cylinder 3 and the tip 4, and a plasma working gas flow passage 6 is provided between the rod-shaped electrode 2 and the torch inner cylinder 3.
is formed, and a plasma actuating gas body 8 having a plurality of plasma actuating gas passage holes 7 is disposed between the rod-shaped electrode 2 and the torch inner cylinder 3.

Furthermore, a torch outer cylinder 11 is arranged at intervals on the outer circumference of the torch inner cylinder 3, and a nozzle hole 12 is formed at the lower end of the torch outer cylinder 11. The alloy powder and powder supply path 1 is connected to the torch outer cylinder 11.
3 is formed, and a mixed powder 14 of heat-resistant and wear-resistant alloy powder for overlay welding and hard granular material can be supplied at an appropriate feed ratio and/or feed rate. There is. In this case, as shown in the illustrated example, the supply paths for each gold powder and the granular material may be the same or may be formed separately. A passage 15 is formed.

Further, a gas lens 16 is provided at the lower end of the torch outer cylinder 11 concentrically with the nozzle hole 12, so that the shielding gas supplied from the shielding gas supply path 17 uniformly shields the periphery of the plasma arc. It's Nishide.

Then, using such a plasma torch 1, a mixed powder 1 is prepared by mixing a powder for overlay welding having heat resistance and wear resistance and a hard granular material in a desired ratio in a plasma arc.
4 is supplied and plasma arc build-up welding is performed on the surface of a desired portion of the tool, thereby forming a hard build-up surface portion.

In this case, when the plug has a rotationally symmetrical shape, such as a perforation plug or elongator plug of a pipe making machine, the plasma torch 1 is fixed and the plug is rotated.
Further, in the case of an asymmetrical shape such as a guide shoe of a pipe making machine, it is desirable to select an appropriate means depending on the shape of the hot tool, such as fixing the guide shoe and moving the plasma torch 1.

In such hot-working tools, hardfacing parts made of alloys and hard particles with excellent heat resistance and wear resistance are formed on the required parts of the surface, so they come into contact with the workpiece and generate heat. It has excellent heat resistance and extremely good abrasion resistance, so it has a long life.

In addition, by re-forming the worn parts of hot tools after use, we re-form hardfacing parts made of alloys and hard particles that have excellent heat resistance and wear resistance. #It can be made to have extremely excellent abrasion resistance, increasing the number of times of repeated use.

Since the hardfacing part is formed by plasma arc build-up welding, the plasma arc heat melts an appropriate amount of the surface of the hot tool, and the weld build-up alloy and hot tool melt together. Since the amount of penetration is adjusted to obtain a healthier alloy phase, it is possible to effectively prevent the hardfacing part from peeling off during use.

(Example) In this example, welding plasma torch 1 shown in FIG.
, argon was used as the plasma working gas, two types of compositions shown in Table 1 were selected as alloy powders for overlay welding, and carbides, nitrides, An oxide was selected, and argon was used as a feed gas for the mixed powder 14 of the overlay welding powder and the hard powder.

Furthermore, as a hot work tool, an elongator plug 21 having the shape shown in FIG. 1 and made of hot work tool steel (SKD61) is used.
was used.

Therefore, when forming the built-up surface hardened portion 22 at the required part of the elongator plug 21, the cathode side of a power source (not shown) is connected to the rod-shaped electrode 2, and the anode side of the power source is shown in FIG. Connect to Elongator plug 21,
At the same time that a plasma arc is generated between the rod-shaped electrode 2 and the plug 21, a mixed powder 14 in which alloy powder for overlay welding and hard powder particles are mixed in the ratio shown in Table 1 is supplied into the plasma arc. The plug 21 is in a molten state.
By welding it to the surface of a desired portion of the cladding surface, a hardened build-up surface portion 22 having the build-up thickness shown in Table 1 was formed.

At this time, since a plasma working gas rectifier 8 is provided between the rod-shaped electrode 2 and the torch inner cylinder 3, the plasma working gas is uniform with no density in the horizontal section, and the concentration of the plasma gas is reduced. , and the supply of the mixed powder 14 of the alloy powder for overlay welding and the hard granular material was made uniform in the horizontal cross section, and good overlay welding could be performed.

Next, the elongator plug 21 with the hardfacing surface hardened portion 22 of each of the above compositions was prepared, and for comparison, a two-longator plug made of an integrally cast product with the composition (No. 11) shown in Table 1 was prepared. When a 13cr stainless steel seamless pipe was subjected to an actual machine test at a rolling temperature of 1190°C and an outer diameter of 120mmΦ, comparative examples as shown in Table 1 (No.
A life comparison result was obtained in which 11) was set as 1.

As shown in Table 1, in the case according to this invention (No.
1 to 10), it is clear that the life index of the elongator plug 21 is considerably improved compared to the comparison case (No. 11), and there was no peeling of the fleshy surface hardened portion 22 during the actual machine test. I was not able to admit.

[Effects of the Invention] As explained above, in the surface hardening method for hot tools according to the present invention, heat resistance and
Plasma arc overlay welding in which abrasive alloy powder and one or more hard powder particles selected from carbides, nitrides, and oxides are supplied while controlling the feed ratio and/or amount of each. By applying weld overlay to the surface of the required part of the tool to form a hardened overlay surface, the heat resistance and abrasion resistance of the surface are extremely excellent, making it suitable for hot-working tools used for example in the production of seamless steel pipes. Even when used in applications that are subject to severe frictional heat and pressure, such as pipe-making tools, the tool has a long service life, and therefore it is possible to reduce processing costs and product costs. This provides a very excellent effect of providing a hot tool.

[Brief explanation of the drawing]

FIG. 1 is an explanatory view of an elongator plug as a hot tool according to an embodiment of the present invention, and FIG. 2 is an explanatory cross-sectional view showing an example of the structure of a welding plasma torch used for plasma arc overlay welding. 1... Plasma torch for welding, 13... Powder supply path, 14... Mixed powder of alloy powder and hard powder for overlay welding, 21... Elongator plug (hot tool) 22 ...
Hardened overlay surface area.

Claims (2)

[Claims] (1) During the plasma arc, alloy powder having heat resistance and wear resistance and one or more hard powder particles selected from carbides, nitrides, and oxides are fed at respective feeding ratios and/or feeding rates. A method for hardening the surface of a hot tool, characterized by forming a hardened build-up part on the surface of a desired part of the tool by applying plasma arc build-up welding while controlling the amount. (2) The heat build-up surface hardened portion is formed only on the part of the tool that contacts the workpiece and/or only on the worn part after use. Surface hardening method for intermediate tools.