JP2527581B2 - Seamless pipe Guide shoe for hot tilt rolling mill - Google Patents

Description

The present invention relates to a guide shoe for a seamless pipe hot tilt rolling mill.

[Conventional technology]

Seamless pipe As a pipe material produced by hot tilt rolling, it can be used for low-alloy steel such as carbon steel and 9Cr steel, and recently for heat exchangers (for seawater) and other severe corrosive environments. As a high-grade pipe material, various stainless steels such as
22% Cr-5% Ni-3% Mo-Fe Duplex stainless steel or S
US304 (18-20% Cr-8-10.5% Ni-Fe) and SUS321 (17-19
% Cr-9 to 13% Ni-Ti-Fe) and other high Cr-high Ni stainless steels are used for piercing and rolling.

In this seamless pipe hot tilt rolling, as shown in FIG. 4, a rolled material (red hot billet) (W) which is a raw pipe material is supplied between barrel-shaped tilt rolls (10, 10) arranged on the left and right. The plug is used to perforate a glowing billet under high speed to form a shell with a predetermined diameter and wall thickness. The outside diameter and wall thickness of the shell are above and below the billet (W) to be plug-punched. Guide shoes (20, 20) for adjusting the are arranged.

Since the guide shoe is in sliding contact with the red hot billet at a high surface pressure (roll rolling force: about 80 tons), it must have excellent high temperature wear resistance and seizure resistance.
Conventionally, as this guide shoe, 23% Cr-3% Ni-Fe
System, 26% Cr-2% Ni-Fe type iron-based alloy, or 15% Cr-
A 5% Mo-1% C-Ni-based nickel-based alloy is used, and recently, as a product with improved wear resistance and seizure resistance,
A guide shoe made of high Cr-high Ni-Fe alloy steel such as% Cr-30% Ni-Fe has also been proposed (Japanese Patent Publication No. 61-45695,
62-5979, 62-6630, 62-8507).

[Problems to be solved by the invention]

The above-mentioned conventional guide shoe, when the billet that is the material to be rolled in sliding contact with it is low-alloy steel such as carbon steel or 9Cr steel or the like, shows stable wear resistance, and seizure is not a problem. On the other hand, when the billet is 13Cr stainless steel or duplex stainless steel which is a higher grade material, seizure is likely to occur and the sliding contact surface is significantly worn. This is because when the billet is carbon steel, 9Cr steel, etc., the billet surface is covered with a thick oxide scale, and the lubricating effect of the oxide scale protects the guide shoe surface, whereas the 13Cr stainless steel and Since the surface oxidation scale of billets such as duplex stainless steel is thin and the sliding surface with the guide shoe has a high temperature of 1250 to 1300 ° C, which is close to the melting temperature, oxidation occurs due to sliding contact under high surface pressure. It turned out that the scale was easily destroyed. The seizure of the guide shoe impairs the surface quality of the subsequent billet and thus the surface quality of the product obtained by rolling. For example, even when a guide shoe made of a 30% Cr-30% Ni-Fe-based casting alloy is used, when 2 to 4 billets are rolled, surface defects due to seizure occur. Further, the wear of the sliding surface progresses quickly. Therefore, it is necessary to replace the guide shoes at an early stage and frequently perform repair work, which inevitably increases maintenance costs.

The present invention seeks to provide an improved guide shoe for solving the above problems.

[Means and Actions for Solving Problems]

The guide shoe for the seamless pipe hot-rolling mill of the present invention comprises Cr: 5 to 20%, Ni as an impure component: 5% or less, and a metal matrix consisting of the balance substantially Fe, and mixed as a dispersed phase in the matrix. The sliding surface is formed by a built-up layer having a composite structure composed of 50 to 80% by weight of niobium carbide (NbC) particles.

The sliding surface of the guide shoe of the present invention has a self-lubricating action, and has abrasion resistance and high temperature strength. That is, the composite buildup layer forming the sliding surface of the guide shoe of the present invention is covered with an oxide film having a sufficient layer thickness to function as a lubricating film, and the oxide film forms a red hot billet. Direct metal-to-metal contact is interrupted. This stable surface oxide film is closely associated with the presence of niobium carbide particles in the metal matrix. In the case of a matrix metal single-phase sliding surface in which niobium carbide particles are not mixed, the oxide film formed on the surface is thin and easily broken, so a stable function as a lubricating film cannot be expected.
In the composite facing layer of the present invention in which niobium carbide particles are mixed as a dispersed phase, the niobium carbide particles act as a catalyst for forming an oxide film and form a stable oxide film as a lubricating film on the surface of the overlaying layer. is there. In addition, the niobium carbide particles exist as a dispersed phase that is extremely hard and chemically stable, and imparts high wear resistance and high temperature strength to the overlay layer by its dispersion strengthening action.

The lower limit of the amount (mixing ratio) of the niobium carbide particles in the composite facing layer forming the sliding surface of the guide shoe is 50% by weight. The amount may be smaller than that from the viewpoint of accelerating the formation of an oxide film by the niobium carbide particles, but this does not provide sufficient dispersion strengthening action. By setting the lower limit to 50% by weight, the abrasion resistance due to the dispersion strengthening effect and the high temperature strength are secured together with the seizure resistance due to the oxide film. The effect improves with an increase in the amount of niobium carbide particles. On the other hand, the upper limit of 80% by weight is that if it exceeds 80% by weight,
Weldability is poor when the composite overlay is formed by the welding method, the bond strength at the interface between the guide shoe base material and the composite overlay becomes insufficient, and the overlay itself has poor toughness,
This is because peeling and cracking due to thermal / mechanical shocks that occur when used in an actual machine are likely to occur. The particle size of the niobium carbide particles is not particularly limited, but from the viewpoints of both the oxide film formation promoting action and the dispersion strengthening action, it is generally about 50 to 200 μm.

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

Cr: 5 to 20% Cr forms a dense oxide film at high temperature and coats the surface of the metal matrix to impart oxidation resistance and seizure resistance to the overlay layer. This requires at least 5%. Although the above properties improve as the Cr content increases, if it exceeds 20%, the seizure resistance tends to decrease, so the upper limit is 20%.

Ni: 5% or less Ni is not a particularly required element, but Ni may be mixed in the manufacturing process of the overlay material, and if the mixing amount does not exceed 5%, no harmful effect will appear. Therefore, the upper limit is 5%.

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

FIG. 1 shows an example of the guide shoe of the present invention.
(21) is a guide shoe base material, and (22) is a composite buildup layer formed on the sliding surface thereof. The composite overlay (22) is
A mixture of a metal powder that serves as a matrix and a niobium carbide powder that serves as a dispersed phase can be used as a build-up material and can be formed as a build-up weld layer by a transfer arc plasma welding method (PTA). Alternatively, the above mixed powder may be used as a sintering raw material and formed by a known sintering method such as a hot pressing method or a hot isostatic pressing method. The buildup layer may have a layer thickness of, for example, 3 to 20 mm. The guide shoe base material (21) itself does not need seizure resistance or wear resistance, and its material may be, for example, carbon steel, low alloy steel or the like.

〔Example〕

[I] Formation of build-up layer A carbon steel disc (φ50 × 10 ^t , mm) is used as a base material, and on one side surface thereof, a composite consisting of a metal matrix and niobium carbide particles (average particle size: 100 μm) is formed by PTA welding. A build-up layer was formed, and machining and polishing were applied to the surface of the build-up layer to obtain a test material A (Invention Example). The matrix metal composition was Cr: 12%, Ni: 2%, balance Fe, and the mixing ratio of niobium carbide particles (average particle diameter: about 100 μm) was 55% by weight.

On the other hand, as a comparative example, a conventional guide shoe material is used.
From the 30% Cr-30% Ni-Fe alloy cast material, a disk having the same shape as above was cut out, and one side surface (test surface) was subjected to machining and polishing to obtain a test material B.

[II] High Temperature Sliding Test and Test Results The high temperature sliding test shown in FIG. 3 was performed on each of the test materials A and B. In the figure, (1) is a heating furnace, (2) is a test piece mounting rotary shaft, and (3) is a mating member mounting fixed shaft. The mating material (4) attached to the lower end of the fixed shaft (3) is a ring having an annular projection (4.1) on the lower surface periphery, and the material is SU.
S304 stainless steel. The test material A or B is attached to the top of the rotary shaft (2) with its test surface facing upward, and the annular projection (4.1) of the mating material (4) is pressed against the test surface.

In the above test equipment, the mating material (4) and the test material A
(B) is heated and held at 1000 ° C., the test material A (B) is rotated at 600 RPM with respect to the mating material (4), and the pressing load on the sliding contact surface is gradually increased from 0 to 100 kgf while the rotating shaft ( The torque in 2) is measured, and the presence or absence of seizure is determined from the torque fluctuation.

The measurement results are shown in FIG. The curve (a) is the test material A (invention example), and the curve (b) is the test material B (comparative example). In the case of Specimen B, which is a conventional 30% Cr-30% Ni-Fe casting alloy,
An abnormal increase in torque occurs at a load of around 20 kgf.
This indicates that significant seizure has occurred on the sliding surface. On the other hand, in the test material A (invention example), there was no abnormal fluctuation of the torque at all, the torque curve showed a smooth increase, and it was stable at a substantially constant torque value at a load of about 50 kgf or more. A good self-lubricating action of the layer can be seen.

[III] Hardness Measurement The hardness (Hv, 10 kg) of the above-mentioned test material A (invention example) and test material B (comparative example) was measured.
For the test material B, the result of Hv300 was obtained. The hardness of the composite facing layer of the invention example is improved with an increase in the amount of niobium carbide particles, and the hardness is Hv 700 or more when the compounding amount is 80% by weight. This increased hardness ensures a stable wear resistance over conventional guide shoes.

The same composite build-up layer as the sample material A was formed on the surface of the guide shoe base material (S45C carbon steel), and the actual machine was used in hot tilt rolling of stainless steel seamless pipes (SUS304, SUS321) (rolled material temperature: 1250 As a result of being subjected to ~ 1300 ° C), conventional guide shoes (30% Cr-30% N) under the same operating conditions
The service life of (i-Fe-based casting alloy) is only 2 to 3 in terms of the number of rollings, 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 as long as the life. Was obtained.

〔The invention's effect〕

INDUSTRIAL APPLICABILITY The guide shoe of the present invention has excellent and stable seizure resistance even to rolled materials such as high Cr stainless steel due to the stable self-lubricating action of the composite facing layer formed on its sliding surface. It also has a high degree of abrasion resistance. Therefore, by using the guide shoe of the present invention, it is possible to significantly reduce the maintenance, improve the productivity of the inclined rolling line, and stabilize and improve the surface quality of the rolled product.

[Brief description of drawings]

FIG. 1 is a view showing an embodiment of the present invention ([I] is a front view,
[II] is a cross-sectional view of II), FIG. 2 is a graph showing a torque curve obtained by a high temperature sliding test, FIG. 3 is an explanatory diagram of a high temperature sliding test, and FIG. 4 is a seamless pipe inclined rolling mill. FIG. 10: barrel type inclined roll, 20: guide shoe, 21: guide shoe base material, 22: composite overlay, W: rolled material (red hot billet).

Claims (1)

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