JPS59182920A - Manufacture of seamless steel pipe - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is characterized in that the yield point is at least 60 ON/mm in longitudinal test pieces.
Notch impact test value at 2.0℃ is at least 210J
In particular, the present invention relates to a method for manufacturing seamless steel pipes for the petroleum industry.

Seamless steel pipes with the above-mentioned strength are manufactured from steel containing approximately 0.4% carbon and optionally other alloying elements that increase hardness, and are quenched and tempered to form finished pipes. Since this method uses alloying elements and requires quenching and tempering, it is expensive to manufacture and consumes a lot of heat.

Yet another proposal is to normalize a steel with the same carbon base and manganese content as above between rough forming and finishing forming, and then rapidly cool it by about 100°C to a temperature below Arl after finishing forming. There is a way to do it. Although this method is inexpensive, it does not allow the production of tubes with the high viscosity that is sought to be obtained with the method of the present invention.

An object of the present invention is to simplify the production of seamless steel pipes and further improve their quality, particularly by refining the structure.

The method according to the invention can be carried out in all relevant installations for producing seamless steel pipes. Perforation of the steel bar can be carried out in a perforation mill or perforation press at the above-mentioned drawing temperatures. The drawing of the perforated strips is carried out at the same temperature in a continuous rolling mill or a piercing mill. Stretching can also be carried out in a pilger mill. Stretching to reduce the wall thickness to 4, with the inner diameter of the tube remaining approximately unchanged, results in very long hollow bodies. In this case, it is necessary to obtain a deformation of 40 units. In the subsequent longitudinal rolling, the diameter is usually reduced while the wall thickness remains largely unchanged.

If the obtained rough tube is further longitudinally rolled, a drawing machine is also suitable for this method.

Observation of temperature and component content ranges is an absolute prerequisite for the method of the invention, and even relatively minor deviations in these can lead to large deviations in the quality of the product. The holding time must be selected depending on the thickness of the steel bar.

The carbon in the retained austenite, which does not sufficiently influence pearlite formation after rough forming and does not dissolve into ferrite,
The aim is to equalize during reheating, thereby preparing the stage for ultrafine structure formation during cooling after vertical rolling.

Further, the reheating temperature makes a further contribution to the formation of a fine structure after longitudinal rolling, and is a forming temperature suitable for longitudinal rolling.

Cooling after finish rolling, which is carried out at temperatures of 700 to 850° C., is therefore also particularly important. Cooling is done at a very low rate. Of course, this cooling speed is not so fast that it necessarily requires quenching with water. Cooling with still air only provides properties at the lower end of the desired range. Observing the prescribed component values guarantees that extremely fine bainite will be produced.

Cooling from a temperature of 600 to 450° C. can be carried out optionally. Due to the low carbon content of the alloy, there is no risk of martensite formation when cooling to room temperature, but air cooling is chosen to save costs.

By tempering the tube in the manner described in the subordinate frame after cooling to room temperature, the method of the present invention is further improved and the strength of the seamless steel tube is further improved.

The properties of tubes produced by the method of the invention are illustrated by examples.

The following composition of outer diameter t7smx, that is, 0.032°C
;1.924■;0.0024chiS, 0.043
%At-.

0.021 Ti; 0.27%Mo; 0.00
23chiB, 0.051chiNb1O, 0056%N
; A continuous casting billet with normal impurities and residual iron is charged into a rotary heating furnace at room temperature, heated sufficiently at 1150°C, and then taken out. This is perforated using a piercing rolling mill, and stretched using a so-called continuous rolling mill to have an outer diameter of 1521 W and a wall thickness of 14 mm. This is a 75-degree rough forming process, and the forming process must be carried out all at once so that the hollow body is not cooled below P<Arl, but instead is charged into the soaking furnace at a slightly higher temperature. The hollow body is normalized at 780° C. for 12 minutes. Also, at this temperature, the outer diameter was 110.6 m with a reduction mill.

It is finish rolled to a finished size of wall thickness 16 mm. This is the final molding of 30 inches.

The following examples were air cooled and then tempered at 550° C. for 30 minutes.

In Example B, the sample was cooled to 500°C with water at a rate of about 15°C/sec, and then cooled with air to room temperature.

Implementing individual Example B Yield point N7mg2605 693 Tensile strength
N/Drinking 2749 828 Stretching Chi
2220 Notch impact test value JO°C 230 272 The structure of each example was completely a bainite structure.

105

Claims (1)

[Claims] 1) A rolled or continuously cast steel bar is heated, and in one or more processing steps, it is roughly formed into a hollow body having approximately the wall thickness of the finished pipe, and then reheated and processed into a finished pipe. Longitudinal specimens with a yield point of at least 60 ON/
Notch impact test value of vrm2.0℃ is at least 210J
In particular, in the manufacturing method of seamless steel pipes for the petroleum industry,
Steel is carbon 0.02 - 0.12
Related manganese 1.3 - 2.2
%Sulfur 0.001-0.01TiTitanium 0.01-0.04TiNiobium 0.02-0.06Nitrogen
0.003 - 0.008% aluminum 0.03 - 0.05 residual amount of normal impurities and molybdenum 0.3% or less nickel
0.5 or less boron 0. OQl -0,003 alone or in any combination with iron, the product is sent to rough forming at a drawing temperature of 1150 to 1220°C, then lowered and segmented at a temperature of 700 to 850'C for 5-20 minutes. , a method characterized by sending it to final molding, and then cooling it. 2) Immediately after finish rolling, the finished tube is heated to a temperature of 600 to 450.
1°C, e.g. water and then air at least 6°C/
Claim 1 characterized in that the cooling is performed in sec.
The method described in section. 3) Immediately after finish rolling, the finished pipe is brought to room temperature with air%/%
2- Method according to claim 1, characterized in that it is cooled. 4) After cooling the product to room temperature, the temperature is 400 to 65
A method according to claim 2 or 3, characterized in that it is tempered to 0° C. and held in the above temperature range for 4 minutes.