JP2587012B2 - Manufacturing method of hardened overlay - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for producing a hardfacing roll having excellent abrasion resistance and excellent heat resistance and durability.

[Conventional technology]

Rolls used in severe environments such as hot rolls are required to have particularly excellent wear resistance, durability and heat resistance. Conventionally, such rolls are made of a roll body made mainly of toughness, and then overlaid with a hardfacing welding rod that ensures high hardness (for example, 750 HV) on the outer peripheral surface. The manufactured hardfacing roll excellent in toughness and hardness is used.

As the heat treatment of the overlay roll, tempering is performed after the overlay, or quenching and tempering after the overlay welding is performed for the purpose of uniformizing the structure of the overlay to prevent peeling and pitting.

[Problems to be solved by the invention]

However, in order to increase the hardness of conventionally used hardfacing materials, the carbon content (all "contents" in this specification are indicated by weight%) exceeds 0.4%. High carbon content carbon steel or alloy steel is used.
In addition, alloy steels not only have a high carbon content but also have a large amount of alloying components are used, so that the weldability is poor, causing cracks and internal defects, peeling, pitting, etc. Is the cause of the failure. In addition, there is also a problem that an increase in the amount of alloy components inevitably increases the cost.

The present invention has been made in view of such a conventional problem, and it is possible to easily and inexpensively produce a hardfacing roll having excellent abrasion resistance and excellent heat resistance and durability. The aim is to provide a method.

[Means for solving the problem]

In order to solve the above problems, the method for manufacturing a hardfacing roll according to the present invention has a low hardness but a good weldability and a low carbon content on the outer peripheral surface of the roll body as compared with a conventionally used welding rod. Carbide welding is performed using a welding rod of carbon steel with a low carbon content of 0.4% or less or alloy steel with a low carbon content of 0.4% or less, and the surface of the formed overlay is carburized. After that, the surface hardness is increased by quenching, and the required hardness is secured.

The material of the roll body used in the present invention is not particularly limited, and a material having toughness, heat resistance and the like according to the intended use of the roll is used.

[Action]

The welding rod used for overlay welding in the present invention is a welding rod made of carbon steel or alloy steel having a low carbon content,
Further, when alloy steel is used, the amount of alloy components can be made lower than before, so that weldability is good and the price is low.
Therefore, overlay welding is easy and the cost can be reduced.

Here, the carbon content (hereinafter referred to as C content) of carbon steel or alloy steel used for the welding rod is usually selected to be 0.4% or less. When the C content exceeds 0.4%,
The weldability deteriorates, which is not preferable. When alloy steels are used, for example, small amounts of Cr, Mo, V,
Those containing Co are used. Of course, materials containing other alloy components can also be used, and the material is selected in consideration of the properties required for the roll surface, such as hardness, heat resistance, weldability, and carburization. Also, the content of the components is selected so as to provide good weldability and not increase the cost.
The thickness of the build-up layer formed by build-up welding is preferably selected to be about 3 to 10 mm. If the thickness is less than 3mm,
Peeling easily occurs, and the life is shortened. Conversely, if the thickness is more than 10 mm, unnecessary thickness increases, and the price increases, which is not preferable.

As described above, in the present invention, first, a build-up layer is formed on the outer peripheral surface of the roll body by performing build-up welding using a welding rod of carbon steel or alloy steel having good weldability and a low carbon content.
For this reason, the resulting overlay has almost no cracks or internal defects, and has a good structure with little segregation that may cause bead marks. However, the surface hardness is lower than the final target hardness.

Next, in the present invention, a carburizing treatment is applied to the build-up layer formed by the build-up welding, whereby the vicinity of the outer surface can be made high carbon. For this reason, the hardenability of the surface can be improved, and after that, the hardening layer can be formed with an extremely high surface hardness.

Here, the carburizing treatment may be performed by a known method and conditions.
Carburization depth is about 2-3mm, carbon content near outer surface is
It is preferably at least 0.8%. 0.8% carbon content
At lower values, the quench hardness increases as the carbon content increases, but becomes almost constant above 0.8%. Therefore, by setting it to 0.8% or more, uniform high hardness can be obtained.

Quenching may be performed by a known method and conditions. Also, quenching and tempering are performed as necessary.

As described above, in the present invention, a build-up layer having almost no defects can be obtained by build-up welding using a welding rod made of carbon steel having a low carbon content or alloy steel having a low carbon content and having good weldability. Then, by carburizing the surface of the build-up layer, a surface layer with good hardenability can be obtained, and the build-up layer can be hardened or quenched and tempered to obtain a uniform high hardness. So that there are almost no defects,
In addition, a high-hardness (for example, Hs85 or more) hardfacing layer having a good structure in which bead marks are not easily generated and having a uniform hardness is obtained.

 Hereinafter, the effects of the present invention will be described with reference to examples.

〔Example〕

0.3% C, 7% Cr, M on the surface of roll body (material: S35C)
o Welding was performed using a welding rod made of a low carbon content alloy steel containing 3.5%, V 1.0%, and Co 1.5% to obtain a 4mm thick overlay. The fault hardness distribution of the overlay was measured and the first
The results shown in the figure were obtained.

Next, the overlay was carburized under the following conditions, and then induction hardened and tempered under the following conditions. The cross-sectional hardness distribution of the resulting overlay was measured to obtain the results shown in FIG.

(1) Carburizing conditions Carburizing material: gas carburizing (propane) Carburizing temperature: 950 to 1000 ° C Carburizing time: 10 hours (2) Quenching and tempering conditions Quenching temperature: 950 to 1000 ° C Tempering temperature: 250 ° C Tempering time : 2 hours As can be clearly seen from Figs. 1 and 2, the hardness of the build-up layer immediately after the build-up is about 700HV, but as a result of carburizing and quenching and tempering, the hardness exceeds 800HV. Could be obtained.

As a comparative example, a conventional high-carbon alloy steel with a high carbon content and a large amount of alloy components that guarantees a high build-up hardness of 750 to 800 HV on the surface of a roll body (material: S35C) similar to that used in the examples (C 0.9%, Cr 7%, Mo 5%, V 3.5%, Co 5%) Welding was performed using a welding rod to obtain a 4 mm thick overlay.
The sectional hardness distribution of the overlay was measured to obtain the results shown in FIG.

Next, induction hardening was performed on this overlay under the following conditions.
The cross-sectional hardness distribution of the resulting overlay was measured to obtain the results shown in FIG.

Quenching conditions Quenching temperature: 1150-1180 ° C In the case of the alloy overlay with a high carbon content shown in Fig. 3, the hardness of the overlay immediately after the overlay shows a high value close to 800HV. Even after quenching, the hardness increases only slightly, as shown in FIG. This is because in the case of a high carbon content alloy cladding material, the alloy component is inserted in the form of ferroalloy carbide to prevent cracking during welding, and there is little free C, that is, pearlite necessary for hardenability, on the ground. Therefore, the effect of quenching is small. Therefore, quenching after welding only slightly improves the structure and slightly increases the hardness.

On the other hand, in the case of the embodiment of the present invention, the build-up layer after the build-up has a low carbon content, so that the hardness is low as shown in FIG. 1, but the pearlite increases in the ground by carburization. As shown in Fig. 2, the hardness of the surface is improved by the quenching, and the hardness of the surface is improved. Hardness comparable to the one was obtained.

The hardened build-up roll manufactured in the above example and the hardened build-up roll manufactured in the comparative example were used as a work roll for a scale breaker in an actual machine. After using the hardfacing roll of the example for one month, the wear amount was measured.
The outer diameter was only 0.4 mm, and no so-called bead mark was generated. In contrast, the hardfacing roll of the comparative example
After a week of use, so-called bead marks and spalling occurred. This is presumably because the welding rod used in the comparative example had poor weldability due to a high carbon content and a high alloying component, and had a defect in the overlay. On the other hand, since the welding rod used in the examples had good weldability, there was no defect in the build-up layer and it could be used stably.

〔The invention's effect〕

As described above, the present invention relates to welding of a carbon steel having a low carbon content of 0.4% or less or an alloy steel having a low carbon content of 0.4% or less to a roll body. Since overlay welding is performed using a rod and then carburizing and quenching are performed, the overlay welding is easy and a hard-facing layer with almost no defects can be formed. An embossed layer is obtained, which is quenched and hardened to obtain a bead-mark-free structure and a high-hardness overlay having uniform hardness and almost no defects and surface hardness. This makes it possible to easily and inexpensively manufacture rolls having a high roll size.

[Brief description of the drawings]

FIG. 1 is a graph showing the hardness distribution of a build-up layer formed by a welding rod of a low carbon content alloy steel in an embodiment of the present invention, and FIG. 2 is a view showing a case where the build-up layer is carburized and induction hardened. FIG. 3 is a graph showing the hardness distribution of the cladding layer after the reversion, and FIG. 3 is a graph showing the hardness distribution of the cladding layer formed by a conventional welding rod of alloy steel having a high carbon content and a high alloy component. FIG. 4 is a graph showing the hardness distribution of the overlay after induction hardening.

Claims (2)

(57) [Claims] 1. A welding rod of a carbon steel having a low carbon content of 0.4% or less by weight or an alloy steel having a low carbon content of 0.4% or less is provided on the outer peripheral surface of a roll body. A method for producing a hardfacing roll, comprising: performing overlay welding using the same, performing carburizing on the surface of the formed overlay, and then quenching. 2. The welding rod according to claim 1, wherein said welding rod is 7% by weight,
2. The method for producing a hardfacing roll according to claim 1, which is a low carbon content alloy steel containing 1.0%, 1.0% V and 1.5% Co.