JPH01148405A - Guide shoe for hot diagonal rolling mill for seamless tube - Google Patents

Abstract

PURPOSE:To impart both stable seizing and high wear resistances against rolling of high Cr stainless steel, etc., by forming a build-up layer layer consisting of dispersed particles having a specific composition of Cr steel and a specific amount of niobium carbide particles on the sliding face of a guide shoe. CONSTITUTION:A guide shoe 20 consists of a guide shoe base material 21 and a composite build-up layer 22 formed on the sliding face. The layer 22 has a composite structure containing a metal matrix of 5-20% Cr, <=5% Ni as an impurity, remaining part of Fe, and mixedly existing 50-80% NbC particles as a dispersed phase. The guide shoe has the stable seizing and high wear resistances against a rolled stock as high Cr steel, etc., owing to a stable self- lubrication capability. Further, the layer 22 is also formed by use of a mixture of metal powders as a matrix and NbC powders and by a transfer arc type plasma arc welding method.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a guide shoe for a seamless pipe hot tilt rolling mill.

[Conventional technology]

Seamless Pipe As a pipe material made by hot tilt rolling, it is used not only for low alloy steels such as carbon steel and eCr steel, but also for applications in severe corrosive environments such as heat exchangers (for seawater) etc. As a high-grade pipe material, various stainless steels such as 22%Cr-5%Ni-3%Mo-Fe duplex stainless steel or 5uS304 (18~20%Cr-
8-10.5%N1-Fe) and 5US32017-19
%Cr-9 to 13%N1-Ti-Fe) and other high Cr-high Nl stainless steels are now being subjected to piercing rolling.

This seamless pipe hot inclined rolling is carried out using barrel-shaped inclined rolls (10, 10) arranged on the left and right as shown in Fig. 4.
In between is a rolled material (red-hot billet) that is a raw pipe material) (W)
The red-hot billet is plug-pierced under high-speed rotation to form a blank tube with a predetermined diameter and wall thickness.・
Guide shoes (20, 20) are arranged to adjust the wall thickness.

The guide shoe needs to have excellent high-temperature abrasion resistance and seizure resistance because it comes into sliding contact with the red-hot billet under high surface pressure (roll reduction blade: about 80 tons). Conventionally, this guide shoe has been made of 23% Cr-3.
Iron-based alloys such as %Ni-Fe system, 26%Cr-2%Ni-Fe system, or 15%Cr-5%Mo-1%C-Ni
30% Cr-30 is currently used as a nickel-based alloy with improved wear resistance and seizure resistance.
A guide shoe made of high Cr-high N1-Fe alloy steel such as %Ni-Fe has also been proposed (Japanese Patent Publication No. 61-4
No. 5695, No. 62-5979, No. 62-6630, No. 62-8507).

[Problem that the invention seeks to solve]

The above-mentioned conventional guide shoe exhibits stable wear resistance and does not suffer from seizure when the rolled billet that slides on it is made of low-alloy steel such as carbon steel or QCrC steel. On the other hand, if the billet is made of 13Cr stainless steel or higher-grade duplex stainless steel, seizure is likely to occur (and wear on the sliding contact surface is also significant).
This is because when the billet is made of carbon steel or QCr steel, the billet surface is covered with thick oxide scale, and the guide shoe surface is protected by the lubricating action of the oxide scale, whereas when the billet is made of 13Cr stainless steel or Billets such as duplex stainless steel have a thin surface oxidation scale,
Moreover, the sliding surface with the guide shoe is 1250 to 1300℃.
It turns out that this is because the oxide scale is easily destroyed by sliding contact under high surface pressure because the temperature is close to the melting temperature. Seizure on the guide shoe impairs the surface quality of the subsequent billet and thus of the product obtained by rolling. For example, 30% C, r −30
%Ni-Fe based casting alloy guide shoes, surface flaws due to seizure occur when 2 to 4 billets are rolled. Further, the wear of the sliding surfaces progresses rapidly. Therefore, early replacement of the guide shoe and frequent repair work are required, which inevitably increases maintenance costs.

The object of the present invention is to provide an improved guide shoe to solve the above problems.

[Means and effects for solving the problems] The guide shoe for a seamless pipe hot inclined rolling mill of the present invention is made of Cr.
Ni: 5% to 20%, impurity Ni: 5% or less, the balance essentially consisting of a metal matrix consisting of Fe, and 50 to 80% by weight of niobium carbide (N b C) mixed as a dispersed phase in the matrix. It is characterized in that the sliding surface is formed of a build-up layer (hereinafter referred to as a "composite build-up layer") having a composite structure consisting of particles.

The sliding surface of the guide shoe of the present invention is self-lubricating and has wear resistance and high temperature strength. That is, the composite build-up layer forming the sliding surface of the guide shoe of the present invention is coated with an oxide film having a sufficient layer thickness to function as a lubricating film, and the oxide film prevents contact with the red-hot billet. Direct metal-to-metal contact between them is interrupted. This stable surface oxide film is closely related to the presence of niobium carbide particles in the metal matrix. In the case of a sliding surface made of a single phase matrix metal without niobium carbide particles, the oxide film formed on the surface is thin and easily destroyed, so it cannot be expected to function stably as a lubricating film. In the composite cladding layer of the present invention in which niobium carbide is mixed as a dispersed phase, the niobium carbide particles act as a catalyst for the formation of an oxide film, forming a stable oxide film as a lubricating film on the surface of the cladding layer. Moreover, the niobium carbide particles exist as an extremely hard and chemically stable dispersed phase, and their dispersion-strengthening action provides the build-up layer with high wear resistance and high-temperature strength.

The lower limit of the amount (mixing ratio) of niobium carbide particles in the composite overlay layer forming the sliding surface of the guide shoe is 50% by weight. From the viewpoint of promoting the formation of an oxide film by the niobium carbide particles, the amount may be smaller than that, but the dispersion strengthening effect will be insufficient. By setting the lower limit to 50% by weight, in addition to the seizure resistance due to the oxide film,
Wear resistance and high temperature strength are ensured by dispersion strengthening effect.

The effect improves as the amount of niobium carbide particles increases.

On the other hand, the reason for setting the upper limit at 80% by weight is that if it exceeds 80% by weight, weldability is poor when forming a composite overlay by welding, and the bonding strength at the interface between the guide shoe base material and the composite overlay is poor. In addition, the toughness of the built-up layer itself becomes insufficient, resulting in peeling and peeling due to thermal and mechanical shock during actual machine use.
This is because cracks are likely to occur. Note that the particle size of the niobium carbide particles is not particularly limited, but is approximately 50 to 200μ from the viewpoint of both oxide film formation promotion effect and dispersion elasticity effect.
A value of about m is appropriate.

On the other hand, the matrix metal of the composite overlay layer is Cr5-20%.
The reason why the alloy is limited to an iron-based alloy consisting of 5% or less Ni and the balance substantially Fe is to ensure a sufficient composite effect with the niobium carbide particles, and the reason for limiting the components is as follows.

Cr: 5-20% Cr forms a dense oxide film at high temperatures and coats the surface of the metal matrix, thereby imparting oxidation resistance and seizure resistance to the overlay layer. This requires at least 5%. The above characteristics improve as the amount of Cr increases, but if it exceeds 20%, the seizure resistance tends to decrease, so 20% is set as the upper limit.

Ni: 5% or less Although Ni is not a particularly necessary element, it may be mixed in during the manufacturing process of overlay materials, and if the amount of the mixed metal does not exceed 5%, no harmful effects will appear. Therefore, the upper limit is set at 5%.

Fe: The remainder Fe is an element with a very high diffusion rate, and contributes to improving seizure resistance by forming an oxide film on the matrix surface together with chromium oxide.

FIG. 1 shows an example of the guide shoe of the present invention. (2
1) is a guide shoe base material, and (22) is a composite overlay layer formed on its sliding surface. The composite overlay (22) can be formed as a weld overlay by transferred arc plasma welding (PTA) using a mixture of metal powder as a matrix and niobium carbide powder as a dispersed phase as an overlay material. . Alternatively, the sintering material may be formed by using the mixed powder as a sintering raw material and using a known sintering method such as a hot press method or a hot isostatic pressure sintering method. The thickness of the built-up layer may be, for example, 3 to 20 m. Note that the guide shoe base material (21) itself does not require seizure resistance or wear resistance, and its material may be, for example, carbon steel, low alloy steel, or the like.

〔Example〕

CI) Formation of built-up layer Carbon steel disk (φ50 x 10t, am) is used as a base material,
A composite build-up layer consisting of a metal matrix and niobium carbide particles (average particle size: 100 μm) was formed on one side by PTA welding, and the surface of the build-up layer was machined and polished. (Invention example) was obtained.

Its matrix metal composition is Cr: 12%, Ni: 2
%, balance Fe, niobium carbide particles (average particle size: approx. 1
00 μm) is 55% by weight.

On the other hand, as a comparative example, the conventional guide shoe material 3
A disk having the same shape as above was cut out from a 0%Cr-30%Ni-Fe alloy cast material, and one side (test surface) of the disk was machined and polished to obtain sample B.

(II) High-temperature sliding test and test results A high-temperature sliding test shown in FIG. 3 was conducted for each sample material A and B. In the figure, (1) is a heating furnace, (2) is a rotating shaft for mounting a test piece, and (3) is a fixed shaft for mounting a mating material.

The mating member (4) attached to the lower end of the fixed shaft (3) is a ring having an annular projection (4.1) on the periphery of the lower surface, and its material is 5tlS 304 stainless steel. Rotating axis (2
) The test material A or B is attached to the top of the test material (4) with its test surface facing upward, and the annular protrusion (
4.1) is pressed.

In the above test apparatus, a mating material (4) and a specimen material A (
B) is heated and maintained at 1000°C, and the rotating shaft ( 2) Measure the torque and determine whether seizure has occurred based on the torque fluctuation.

The measurement results are shown in Figure 2. Curve (a) is sample material A (invention example), and curve (b) is sample material B (comparative example). In sample material B, which is a conventional material and is made of a 30% Cr-30% Ni--Fe cast alloy, an abnormal increase in torque occurs from around a load of 20 kg f. This indicates that significant seizure has occurred on the sliding surface. On the other hand, in sample material A (invention example), there was no abnormal torque fluctuation at all, the torque curve showed a smooth increase, and the torque value was stable at a nearly constant value at a load of about 50 kgf or more. A good self-lubricating effect of the layer can be observed.

(III) Hardness measurement The hardness (Hv, 10 kg) of the above sample material A (invention example) and sample material B (comparative example) was measured, and the hardness (Hv, 10 kg) of sample material A was Hv500. For sample material B, a result of Hv300 was obtained. The hardness of the composite build-up layer of the invention example improves as the amount of niobium carbide particles increases, and when the blending amount is 80% by weight, the hardness becomes Hv700 or more.

This increased hardness ensures stable wear resistance that exceeds that of conventional guide shoes.

The guide shoe base material (3
45C carbon steel) surface formed, stainless steel seamless pipe (SOS 304.5IJS 321) (7)
Actual machine use in hot inclined rolling (temperature of rolled material: 12
50~1300°C), the results showed that the conventional guide system (30%Cr-30%Ni-
(made of Fe-based cast alloy) has a service life of only 2 to 3 rolls, whereas the number of rolls that can be rolled using the guide shoe of the invention example is 9 to 10, which is about 5 times longer. Ta.

〔Effect of the invention〕

The guide shoe of the present invention has excellent and stable seizure resistance even on rolled materials such as high Cr stainless steel due to the stable self-lubricating effect of the composite overlay layer formed on the sliding surface. , and has a high degree of wear resistance. Therefore, by using the guide shoe of the present invention, the effects of significantly reducing maintenance, improving the productivity of the inclined rolling line, and stabilizing and improving the surface quality of rolled products can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of the present invention ([■] is a front view, (
II) is its I-1 sectional view), Figure 2 is a graph showing the torque curve obtained from the high temperature sliding test, Figure 3 is an explanatory diagram of the high temperature sliding test, and Figure 4 is a seamless pipe inclined rolling mill. It is a figure shown typically. 10: Barrel-shaped inclined roll, 20 Ni guide shoe, 21 Ni guide shoe base material, 22: Composite overlay layer, W: Rolled material (red-hot billet).

Claims (1)

[Claims] (1) Meat with a composite structure in which 50-80% of niobium carbide particles are mixed as dispersed phase particles in a metal matrix consisting of Cr: 5-20%, impurity Ni: 5% or less, and the remainder substantially Fe. A guide shoe for a seamless pipe hot inclined rolling mill that has excellent seizure resistance and wear resistance, and is characterized by a built-up layer formed on the sliding surface.