JPH06158163A - Production of bend pipe excellent in wear resistance - Google Patents

Abstract

PURPOSE:To provide the method for producing a bend steel pipe combining high workability and excellent weldability and furthermore excellent in wear resistance. CONSTITUTION:A low carbon steel pipe is heated to a temp. in the two phase regions of austenite and ferrite and is subjected to bend forming in the same temp. range, or a low carbon steel pipe is subjected to cold bend forming and is heated to a temp. in the two phase regions of austenite and ferrite, and after that, cooling is executed at >=5 deg.C/sec cooling rate to obtain the objective bend steel pipe excellent in wear resistance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bend excellent in wear resistance, which is used for transportation of an air transportation system such as a garbage transportation system, or a transportation of a slurry-like substance such as an ore slurry and a calcareous slurry, or a hard substance having high wear resistance. The present invention relates to a method for manufacturing a steel pipe.

[0002]

2. Description of the Related Art Generally, the wear resistance of a steel sheet is improved by increasing its surface hardness. For this reason, the conventional wear-resistant steel plate is often manufactured by quenching steel containing C and a large amount of alloying elements. However, such wear-resistant steel has drawbacks such as poor workability due to its high hardness and inferior weldability due to inevitably high carbon equivalent.

In order to solve these problems, there has been proposed a method for producing wear-resistant steel by rolling and quenching steel having a relatively low carbon equivalent (Japanese Patent Publication No. 56-1412).
No. 7, JP-A-57-89426, JP-A-61.
-76615 publication).

Further, a steel sheet has been developed in which only the surface hardness is increased by using a composite steel sheet, the workability and weldability of the steel are secured inside a soft interior, and the wear resistance is secured at the hardened portion of the surface layer ( JP-A-3-227223).

Furthermore, a method for producing a wear-resistant steel pipe using austenite or duplex stainless steel which is excellent in weldability and workability (JP-A-51-13361) and a method for producing a wear-resistant clad steel pipe (JP-A-51) JP-A-63-290616) is also proposed.

As described above, various methods for producing wear-resistant steel and wear-resistant steel pipe have been proposed, but methods for producing bend steel pipes excellent in wear resistance using these techniques have not been proposed yet. . On the other hand, a bend pipe manufactured by casting is used for an air transportation system and the like.

[0007]

As described above, it is possible in principle to manufacture a bend steel pipe by using the above-mentioned technique, but the steel pipe manufactured by the above-mentioned technique has poor workability, In the case of a steel pipe manufactured by internal quenching, there are problems that the hardened layer is thin and that when a high alloy is used, it is expensive. Therefore, although wear-resistant steel pipes with excellent workability and weldability are required in the fields of pneumatic transportation and slurry transportation, wear-resistant steel pipes are required, but bendable steel pipes that can be processed and welded locally and have excellent wear resistance. Is currently not manufactured. Moreover, the bend pipe made of cast iron, which is currently used for an air transportation system or the like, is insufficient in workability and weldability, and is expensive.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a method for manufacturing a bend steel pipe having both high workability and excellent weldability and excellent wear resistance. To do.

[0009]

[Means and Actions for Solving the Problems] First, the present invention relates to a low carbon steel pipe containing austenite and ferrite.
After heating to the temperature of the phase range and bend molding in that temperature range,
Provided is a method for producing a bent steel pipe having excellent wear resistance, which is characterized by cooling at a cooling rate of 5 ° C./second or more.

Secondly, the wear resistance is characterized in that the low carbon steel pipe is cold bend-formed, heated to a temperature in the two-phase region of austenite and ferrite, and then cooled at a cooling rate of 5 ° C./sec or more. Provided is a method for manufacturing a bent steel pipe having excellent properties.

The inventors of the present invention have variously manufactured in order to produce a bent steel pipe having both high workability and excellent weldability, that is, having relatively low hardness and low carbon equivalent, and having excellent wear resistance. As a result of repeated studies, steel in which martensite is dispersed in the ground structure such as ferrite and bainite has relatively low hardness, so that it has excellent workability, good weldability, and excellent resistance. It was found to have abrasion resistance. Further, they have found that it is not necessary to add a large amount of alloying elements as in the case of conventional steels in order to obtain such a structure, and ordinary low alloy steels may be subjected to a specific heat treatment.

That is, by heating the low-carbon steel pipe to a temperature in the two-phase region to form a two-phase structure of ferrite and austenite, carbon and other elements are concentrated in the austenite by diffusion, and the subsequent emergency treatment is carried out. As a result, austenite is transformed into martensite, so that a two-phase structure of ferrite with good workability and martensite with good wear resistance can be obtained. To make the entire structure martensitic, it is necessary to add a large amount of carbon and other alloying elements that deteriorate weldability, but in order to make part of the structure martensitic, addition of these elements is necessary. Only a small amount is required and there is little deterioration in weldability. The present invention having the above-described configuration was made based on the findings of the present inventors. Hereinafter, the present invention will be described in detail.

The method of manufacturing the low carbon steel pipe used in the present invention is not particularly limited. For example, seamless steel pipes, electric resistance welded steel pipes, UO steel pipes, spiral steel pipes and the like are all acceptable. Further, the method for manufacturing a steel plate used for manufacturing a steel pipe is not limited to a special method.

The low carbon steel pipe is a low carbon iron-based low alloy structural steel (for example, JIS G3101, 310).
6,3115, etc.), and the composition is not limited as long as it is within this range, but it is preferable that C, Si, and Mn are contained as basic components in the following ranges. C: 0.05 to 0.30 wt% Si: 0.50 to 2.00 wt% Mn: 0.50 to 2.50 wt% The reason why the preferable range is limited in this way is as follows. C: 0.05 to 0.30% by weight

C is an important element in order to secure a sufficient area ratio of martensite, but its addition amount is 0.0
If it is less than 5% by weight, the effect is small, and conversely 0.3% by weight.
If it exceeds 1.0, weldability is deteriorated. Therefore, the C content is 0.1.
The range of 0 to 0.30% by weight is preferable. Si: 0.50 to 2.00% by weight

When the amount of Si is reduced, a pearlite structure is easily formed, the amount of martensite is reduced, and good wear resistance cannot be obtained. Further, if added excessively, the hot ductility of the steel sheet and the weldability are deteriorated. From these viewpoints, the Si amount is preferably in the range of 0.50 to 2.00% by weight. Mn: 0.50 to 2.50% by weight

Mn is an element that increases the hardenability of austenite during heating and is an element effective for securing the amount of martensite and stably obtaining martensite after cooling. If it is less than 2.5%, the effect is small, and if it exceeds 2.50% by weight, the weldability is deteriorated. Therefore, the Mn content is preferably 0.50 to 2.50% by weight. In addition, from the viewpoint of corrosion resistance, etc., the above basic components are
You may add at least 1 sort (s) of u, Ni, and Cr in the following ranges. Cu: 0.005-1.00 wt% Ni: 0.005-2.00 wt% Cr: 0.005-0.50 wt%

These elements increase the amount of martensite,
It is added to improve the corrosion resistance, and to improve the wear resistance performance of the ground structure due to the increase in hardness, the lower limit of any element is the minimum necessary amount to obtain these effects, The upper limit is the upper limit at which the effect can be obtained without deteriorating the weldability. Furthermore, in order to increase the hardness of the ground structure part and obtain more excellent wear resistance performance, Nb,
You may add at least 1 sort (s) of Ti in the following ranges. Nb: 0.005 to 0.10% by weight Ti: 0.005 to 0.10% by weight These lower limits are the minimum amounts effective in increasing hardness,
The upper limit is an upper limit value at which the above effect can be obtained without deteriorating the weldability and workability.

The heating of the low carbon steel pipe is carried out at a temperature in the two-phase region of austenite and ferrite in order to obtain an appropriate amount of the two-phase structure of ferrite and austenite. The heating temperature is from Ac ₁ to Ac ₁ +100. It is preferably in the range of ° C. If the heating temperature is less than Ac ₁ , transformation from ferrite to austenite does not occur, and a two-phase structure cannot be obtained during heating. On the other hand, when the temperature exceeds Ac ₁ + 100 ° C., the amount of austenite during heating is too large and the increase in the concentration of carbon and the like is small, and it is difficult to obtain a preferable two-phase structure of ferrite and martensite even if a sudden treatment is performed.

The cooling rate after the heat treatment is specified to be 5 ° C./second or more. This is because austenite at the time of heating transforms to martensite by cooling at a rate higher than this, and at a cooling rate lower than this, a two-phase structure of ferrite and martensite cannot be stably obtained. The upper limit of the cooling rate is not particularly limited.

The bend forming process may be performed cold before the above heating, or may be performed in that temperature range after heating. In any case, a bend steel pipe having a desired structure can be obtained. However, the bend forming process in the heating temperature range has an advantage that the forming is easier than the cold forming process. For the bend forming process at this time, a commonly used method is adopted.

The heating method may be either high-frequency heating or a heating furnace, but it is most preferable to bend-form while heating using a high-frequency heating coil equipped with a water cooling device and immediately cool with water. This is the preferred method.

[0023]

Embodiments of the present invention will be described below.

Table 1 shows the composition and carbon equivalent Ceq of the steel pipe used in this example. All of A to M are compositions of general structural steel, and therefore Ceq is also equivalent to that of general structural molten steel.
However, A to J are within the above-mentioned preferable composition range, while K to M are out of the composition range. In addition, Table 1
The values of Ac ₁ and Ac ₃ of each composition are also shown in Table ₁ .

[0025]

[Table 1]

Using the steels having the compositions shown in Table 1, Tables 2 and 3
A bend steel pipe was manufactured under the conditions shown in. Tables 2 and 3 show steel pipe manufacturing methods, bending methods, and heat treatment conditions. The high frequency bend in the column of “bending method” in these tables means a process of performing bend forming together with heating using a high frequency heating coil, and the cold bend means a process of performing cold bend forming. The heat treatment after cold bending was performed using a heating furnace.

In Tables 2 and 3, the steel pipe No. 1 of each steel was manufactured under the conditions within the scope of the present invention and at a heating temperature in the range of Ac ₁ to Ac ₁ + 100 ° C. In addition, the heating temperature of No. 2 of each steel except Steel B is Ac
It is less than ₁ and is outside the scope of the present invention. The number 3 of each steel except the steel B is within the scope of the present invention, but the heating temperature exceeds Ac ₁ + 100 ° C. Furthermore, steel B
No. 4 of each of the steels except for the heating temperature is within the range of the present invention, but the cooling rate is out of the range of the present invention.

Steel B Nos. 2 and 3 are those whose heating temperature and cooling rate are out of the range of the present invention, No. 4 are those which were not heat-treated, and No. 5 are those whose cooling rate is out of the range of the present invention. .

A wear test was conducted on these bent steel pipes. The wear test was carried out by a test piece rotation type wear test apparatus in an environment in which water and silica sand were mixed as shown in FIG.
1A shows a test apparatus, and FIG. 1B shows an enlarged test piece used in this apparatus. In the abrasion test, silica sand and water are charged into a container 1, a disk 2 is embedded horizontally in them, and a test piece 3 having a shape shown in FIG. It is performed by rotating the disk 2 around the axis 4. The wear characteristics are evaluated by a value obtained by simultaneously testing the test piece of the test material and the SS400 test piece to measure the wear loss of these and dividing the wear loss of the SS400 test piece by the wear loss of the test piece of the test material. did. The larger the value, the better the abrasion resistance.
The wear characteristics thus obtained are also shown in Tables 2 and 3.

[0030]

[Table 2]

[0031]

[Table 3]

As is clear from these tables, all the bent steel pipes manufactured under the conditions within the scope of the present invention have 1.5
The above wear characteristics were obtained. In particular, those having a heating temperature in the range of Ac ₁ to Ac ₁ + 100 ° C. showed good wear characteristics. Further, A-1 to M-1 are all within the scope of the present invention, but A-1 having a preferable composition
.About.J-1 showed better wear characteristics than K-1 to M-1 outside the range.

On the other hand, all the heat treatment conditions A-2 to J-2, A-4 to J-4, B-3, and B-4 which were not heat-treated were 1.5. Wear characteristics of less than. From this result, it was confirmed that the present invention can provide a bent steel pipe having good wear resistance. In addition,
All of the bend steel pipes obtained by the method of the present invention had good workability and excellent weldability.

[0034]

According to the present invention, a low-alloy steel is used as a base and a two-phase structure of ferrite and martensite is formed, so that it has both high workability and excellent weldability, and has excellent wear resistance. An excellent bend steel pipe can be manufactured.

[Brief description of drawings]

FIG. 1 is a diagram for explaining a wear test.

[Explanation of symbols]

 1; container, 2; disk, 3; test piece, 4; rotating shaft.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazou Ume 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd.

Claims (2)

[Claims] 1. A wear resistance characterized in that a low carbon steel pipe is heated to a temperature in a two-phase region of austenite and ferrite, bend-formed in the temperature range, and then cooled at a cooling rate of 5 ° C./sec or more. Excellent bend steel pipe manufacturing method. 2. A low-carbon steel pipe is cold bend-formed, heated to a temperature in the two-phase region of austenite and ferrite, and then cooled at a cooling rate of 5 ° C./sec or more to provide wear resistance. Excellent bend steel pipe manufacturing method.