JPS63309393A - Roll cladded by welding for hot rolling - Google Patents

Abstract

PURPOSE:To improve ductility and wear resistance for protecting a roll from accident by forming cladded layer having the specific composition on outer periphery of barrel part of the roll made of steel having ductility by plasma powder welding. CONSTITUTION:The composition of the cladded layer is made to 1.5-3.0wt.% C, 0.1-1.5% Si, 0.1-1.0% Mn, 0.1-1.5 Ni, 1.0-5.0% Cr, 1.0-5.0% Mo, 5.0-15.0% Co, 5.0-15.0% W, 2.0-5.0% V, 1.0-8.0% Nb and the balance substantially Fe. On the barrel part 1 of the roll as base material, positive voltage is impressed to electrode 5, and the plasma arc is generated at gap between the surface of the barrel part 1 for the base material and the electrode 5, and also the powder for cladding by welding is supplied from powder supplying passage 9 to weld, and rapid cooling for solidifying on the surface of the barrel part 1 to form the cladded layer 3. The special element of Nb is contained in the high carbon high-speed steed and the structure is made to fine, the coarsening of crystal grain at high temp. is prevented, and the wear resistance and ductility are improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a weld build-up roll for hot rolling that has a hard build-up layer as a rolling layer.

(Prior art) Hot rolling rolls generally have good wear resistance and crank resistance (
Materials that have good toughness and are resistant to rough skin and heat cracks are required, and conventional rolls include single rolls such as chilled alloy rolls, high alloy grain rolls, and Adamite rolls, as well as high chromium cast iron, high base metal grain rolls, and Adamite rolls. Composite rolls with an outer layer of

(Problems to be Solved by the Invention) Various components are blended into the above-mentioned roll material in order to make it have all the necessary properties as a hot rolling roll, but it is difficult to make it have all the necessary properties. Generally, materials with excellent wear resistance have poor toughness and are prone to heat crank. Another problem is that when used alone, expensive materials are used for the entire roll.

On the other hand, in composite rolls, the outer layer and core member used can be made of materials that emphasize the necessary characteristics, respectively.
Moreover, although it has the advantage that only the outer layer is usually made of an expensive material, it still has the problem of having to rely on expensive centrifugal casting.

In addition, whether it is a single substance or a composite, it is necessary to ensure toughness from the standpoint of accident resistance, and therefore there are inherent restrictions on the composition.
No dramatic improvement in wear resistance could be expected.

(Means for Solving the Problems) The present invention solves the above problems, ensures sufficient toughness in terms of accident resistance, has excellent wear resistance, and can be manufactured at low cost. This was done with the purpose of providing rolls, and in order to achieve the same purpose, a built-up layer was formed as a rolling layer by plasma powder welding on the outer periphery of the roll body made of tough steel material. The overlay layer has a composition in weight percentage: C: 1.5-3.0%, Si: 0.1-1.5%, M
n: 0.1-1.0%, Ni: 0.1-1
．． 5%, Cr: 1.0-5.0%, Mo:
1.0-5.0%, Co: 5.0-15
．． 0%, W: 5.0-15.0%, V: 2.0-5
．． 0%, Nb: 1.0 to 8.0%, and the balance substantially comprised of Fe.

(Example) Examples will be described below with reference to the drawings.

Figures 1 and 2 are views showing an embodiment of the present invention in which a build-up layer 3 having the above-mentioned specific composition is formed on the outer periphery of the roll body l as a base material by plasma powder welding, and 2 is a shaft. 1 shows a case where the roll body 1 and the shaft 2 have different diameters, and FIG. 2 shows a case where the roll body 1 and the shaft 2 have the same diameter.

3 to 5 show roll examples in which a built-up layer 3 is formed on the outer periphery of the roll body 1 via a sleeve 1a fixed to the roll body 1. In other words, the overlay layer 3 is the sleeve 1a.
is used as the base material and is overlaid by welding.

For the roll body 1 and the shaft portion 2 which are integrally made, it is possible to use a steel material having toughness, for example, an inexpensive steel material such as forged SCM440 material, or cast steel. It is possible to use ordinary inexpensive steel pipes. Shrink fitting is generally used to secure the sleeve 1a, but forging is also possible, and if the roll body is formed by casting, it is also possible to integrate them at the time of casting.

In the case of shrink-fitting, a sleeve that has been overlaid and welded is shrink-fitted.

FIG. 3 shows an embodiment in which a sleeve 1a provided with a built-up layer 3 is fixed over the entire length of the roll body 1, and FIG. FIG. 5 shows an embodiment in which the split sleeves la are fixed to the roll body 1 in abutting relation to each other, and FIG. 5 shows an embodiment in which the split sleeves 1a are fixed to the roll body at intervals.

Although the figure shows a case where there are three split sleeves 1a, it goes without saying that the number should not be limited to three.

FIG. 6 is a schematic explanatory diagram of plasma overlay welding. In the figure, 4 is a welding torch, a plasma gas flow path 7 is provided between the electrode 5 and the inner cylinder 6, and a plasma gas flow path 7 is provided between the inner cylinder 6 and the intermediate cylinder 8. A powder supply path 9 is provided between the intermediate cylinder 8 and the outer cylinder 10, and a shield gas flow path 1) is provided between the intermediate cylinder 8 and the outer cylinder 10.

A positive voltage is applied to the electrode 5 of the roll body 1 of the base material, and a plasma arc is generated between the surface of the base material body 1 and the electrode 5, and the overlay powder is injected into this arc. It is supplied from the powder supply path 9 and melted, and is rapidly solidified to form the build-up layer 3 on the surface of the body 1.

By the way, the build-up layer in the present invention has a fine structure by containing the special element Nb in a high-carbon high-speed steel material, prevents coarsening of crystal grains at high temperatures, and improves wear resistance and toughness. It also has excellent surface roughness resistance, which is necessary for finishing rolls, and contains Nb, which is difficult to contain in large amounts in conventional ingot-produced high-speed steel.
It is possible to contain a large amount of this material by overlaying by plasma powder welding.Next, the reasons for limiting the components will be described.

C: 1.5-3.0% C is a carbide-forming element, but if it is less than 1.5%, the amount of carbide is small and wear resistance is insufficient, while if it exceeds 3.0%, the carbide formed becomes coarse. , thermal shock resistance deteriorates.

Si: 0.1 to 1.5% Si is effective as a deoxidizing agent, but increasing the amount makes the base brittle, so if it is less than 0.1%, the deoxidizing effect is insufficient; If this is the case, the required toughness cannot be maintained.

Mn: 0.1-1.0% Mn combines with S and eliminates the harmful effects of S, but if it is less than 0.1%, the effect is small, while if it exceeds 0.1%, it deteriorates the toughness of the material. do.

Ni: 0.1"1.5% Ni increases the base hardness, but on the other hand reduces the high-temperature stability of the structure. Therefore, the range of 0.1 to 1.5% is set to provide good hardness and high-temperature stability.

Cr: 1.0-5.0% Cr stabilizes the carbide and improves the wear resistance of the base, but if it is less than 1%, the effect is small (on the other hand, if it exceeds 5%, it will crystallize the brittle eutectic carbide. Decreases ejection toughness.

Mo: 1.0-5.0% Mo increases base hardness, but if it is less than 1.0%, the effect is not sufficient, and if it exceeds 5%, there is no corresponding effect.
Therefore, from an economical point of view, the content was set at 1.0 to 5.0%.

Go: 5.0 to 15.0% Co is mostly dissolved in the base and improves heat resistance, but
If it is less than 15%, the effect will be small, and if it exceeds 15%, the toughness will deteriorate.

W:5. Q~15.0% W combines with C to form dungesten carbide and contributes to wear resistance, but since it has low thermal conductivity, if it is contained in a large amount, crank resistance due to thermal distortion will deteriorate.

Therefore, the content is limited to 5.0 to 15.0% as a range that provides good wear resistance and crank resistance.

V: 2.0-5.0% V combines with C to form vanadium carbide.

Vanadium carbide has high hardness, and also precipitates in a spherical shape to provide good toughness, so it is limited to 2.0 to 5.0% in consideration of the balance with other carbide-forming elements.

Nb: 1.0-8.0% Nb combines with carbon to form niobium carbide.

On the other hand, as mentioned above, it refines the structure and prevents coarsening of crystal grains at high temperatures, improving wear resistance, toughness, and roughness resistance. However, if it is less than 1.0%, there is no effect, and if it exceeds 8.0%, the hardenability decreases.

Note that the remainder is substantially Fe.

The raw material powder for forming a built-up layer having the above composition is composed of high carbon high speed steel material powder and N
Although a mixed powder of bC powder is used, the combination is not necessarily limited to this, and it is also possible to use a combination of other powders that collectively fall within the above-mentioned specific composition.

Next, specific examples of the present invention will be shown.

a) Roll size φ350 X5001 (n)
b) Roll material (base material) SCM440 C) Overlay layer 5fl d) Powder used Mixed powder of Fe-based alloy powder and NbC powder 1) Fe-based alloy powder...Particle size 60-250 mesh, blending amount 90w t% Composition (T%) C: 1.45%, Si: 0.37%, Mn: 0
．． 40%, Ni: 0.72%, Cr: 4.50
%, Mo: 2.72%, Co: 10.5%
, W: 1). 2%, V: 3.21%, remainder substantially Fe.

1i) NbC powder...particle size 60-250 mesh,
Compounding amount 10-t% e) Overlay conditions Preheating temperature 400°C Current 145 A Voltage 33 V f) Overlay layer composition (wt%) (Analytical value) C: 2.32%
, Si: 0.35%, Mn: 0.35%, Ni:
0.60%, Cr: 4.30%, Mo: 2
．． 52%, Co: 9.8%, W: 10.
5%, V: 3.07%, Nb: 5.04%,
The remainder is essentially Fe.

g) Heat treatment FIG. 7 shows a metallographic micrograph (x 400) of the build-up layer of the example roll obtained by tempering at 540° C. three times or more after weld build-up.

FIG. 8 is a graph showing the high-temperature hardness of the build-up layer, with Hv 880 at room temperature and Hv 61 at 600°C.
It shows an excellent value like 0.

Figure 9 is a graph of the hardness at each depth from the surface of the built-up layer, and the built-up area from the surface to 5mm is H B C6.
It shows excellent hardness of 3-66.

(Effects of the Invention) As described above, the present invention forms a built-up layer of a composition of high carbon high speed steel containing Nb on the outer periphery of the roll body made of tough steel material by plasma powder welding. Therefore, it has superior wear resistance, toughness, and roughness resistance compared to conventional casting rolls as well as build-up rolls, and uses ordinary inexpensive steel materials for the roll body and inexpensive steel pipes for the sleeve as well. It is possible to do so and is economically superior, and the industrial value of the present invention is significant.

[Brief explanation of drawings]

1 to 5 are sectional views of essential parts of a roll according to an embodiment of the present invention. Figures 1 and 2 show examples of rolls with a build-up layer formed by plasma powder welding using the roll body as a base material. is the case where the roll body and the shaft have the same diameter. 3 to 5 show examples of rolls having a built-up layer formed by plasma powder welding using a sleeve fixed to the roll body as a base material. FIG. 6 is a schematic explanatory diagram of plasma powder welding, and FIG. 7 is a metal microscopic photograph (×400) of the build-up layer of the example. FIG. 8 is a graph showing the temperature characteristics of the surface hardness of the build-up layer of the example roll, and FIG. 9 is a graph showing the relationship between the distance from the build-up layer surface and the hardness of the example roll. DESCRIPTION OF SYMBOLS 1... Roll body part, 1a... Sleeve, 2... Shaft part, 3... Overlay layer, 4... Plasma powder welding torch, 5... Electrode, 6... Inside Cylinder, 7... Plasma gas flow path, 8... Intermediate cylinder, 9... Powder supply path, 10...
・Outer cylinder, 1)...shielding gas flow path.

Claims (2)

[Claims] (1) A build-up layer is formed as a rolling layer on the outer periphery of a roll body made of tough steel material by plasma powder welding, and the build-up layer has a composition in weight percentage, C: 1.5 ~ 3.0%, Si: 0.1-1.5%, Mn
:0.1~1.0%, Ni:0.1~1.5%, Cr:
1.0-5.0%, Mo: 1.0-5.0%, Co: 5
．． 0-15.0%, W: 5.0-15.0%, V: 2.
0 to 5.0%, Nb: 1.0 to 8.0%, and the balance substantially consisting of Fe. (2) Weld overlay for hot rolling according to claim 1, characterized in that the overlay layer is formed on the outer periphery of the roll body via a sleeve fixed to the roll body. roll.