EP1218559A2

EP1218559A2 - Use of a steel alloy for producing high-tensile seamless steel tubes

Info

Publication number: EP1218559A2
Application number: EP00965759A
Authority: EP
Inventors: Ingo Von Hagen; Kurt Niederhoff; Bernhard Koschlig; Markus Pardun
Original assignee: V&M Deutschland GmbH
Current assignee: Vallourec Deutschland GmbH
Priority date: 1999-08-30
Filing date: 2000-08-14
Publication date: 2002-07-03
Anticipated expiration: 2020-08-14
Also published as: ES2199865T3; WO2001016391A2; MXPA02001916A; DE19942641A1; EP1218559B1; DE50002289D1; US20020150497A1; WO2001016391A3

Abstract

The invention relates to the use of a steel alloy that contains (in % by weight):C 0.12-0.25 %; Si </= 0.40 %; Mn 1.20-1.80 %; P </= 0.025 %; S </= 0.010 %; Al 0.01-0.06 %; Cr 0.20-0.50 %; Mo 0.20-0.50 %; V 0.03-0.10 %; Cu </= 0.20 %; N </= 0.02 %, remainder iron and usual impurities, for producing high-tensile, weldable seamless steel tubes to be used as constructional tubes. The steel tubes are hot-rolled and are then quenched and tempered. The invention is especially characterized in that the steel alloy additionally contains 0.30-1.00 % W and that the Ni content possibly present in the alloy does not exceed 0.20 %.

Description

Use a steel alloy to make high-strength seamless

steel pipes

description

The invention relates to the use of a steel alloy for the production of high-strength, weldable seamless steel tubes, which are to be used as construction tubes.

Material sheet 290 R from Mannesmannröhren-Werke AG (October 1994 edition) is a weldable fine-grain structural steel e.g. known as FGS 70 V, which has the following composition (% by weight):

C <0.20%

Si 0.15 - 0.50%

Mn <1.70%

P <0.025%

S <0.015%

Cr <1.0%

Ni 0.30 - 0.70%

Mo 0.30 - 0.45%

B <0.005%

Nb <0.05%

V <0.12%

This steel is used for the production of pipes, in particular profile pipes (ie pipes with a cross-section deviating from a circular shape) and pipe products, these products being subjected to a final tempering treatment. The products are particularly suitable for heavy-duty use welded components such as constructions of steel construction (e.g. in bridge, ship, hoist and truck construction) In this context, a high-strength, weldable seamless steel pipe is to be understood as a construction pipe, the tensile strength R _m and the yield strength R _p02 depending on the wall thickness At least the values specified in table 1 are achieved

Table 1

Construction pipes have an elongation at break A that is at least for long samples

16% and at least 14% for transverse samples. Furthermore, such high-strength steel pipes must also have a toughness that corresponds at least to the values for the impact energy specified in Table 2

Table 2

In the manufacture of high-strength structural pipes from steel such as those listed here by conventional hot rolling and subsequent tempering, problems regularly arise with regard to the nature of the surface of the pipes produced.

Rolling process or also according to the pilgrim rolling process The surface problems are particularly pronounced with the so-called warm mushrooms. It arises here through the long-term heating of the insert blocks Rolling temperature on the block surfaces a thick scale layer, the formation of which is at the same time characterized by the presence of non-scaled nickel in a sponge-like form Machining reworking is necessary In continuous rolling, however, due to the significantly shorter lay time of the blocks in the rotary hearth furnace, scaling scars are only more or less pronounced, since the construction tubes produced in this way are often used in machines and systems in which they are visible from the outside Appearance, such a surface is often not accepted by the manufacturers of the respective machines and systems

From W098 / 31843 is a process for the production of seamless conduits in the range X52 -X90 by hot rolling a pipe pre-material from one

Steel alloy known which has the following composition (% by weight)

C 0.06 - 0.18%

Si <0.40%

Mn 0.80 -1.40%

P <0.025%

S <0.010%

AI 0 01 - 0.06%

Mo <0.50%

V <0.10%

Nb <0.10%

N <0.015%

W> 0.30 - 1.0%

Balance iron and usual impurities

These tubes are tempered after hot rolling. The addition of tungsten, which is unusual for line tubes, ensures that the tubes produced have a stable yield strength up to an operating temperature of 200 ° C. and essentially constant stress, strain characteristics The object of the present invention is to propose high-strength weldable seamless steel tubes which can be used as construction tubes and which meet the minimum requirements mentioned above in terms of tensile strength, yield strength, elongation at break and notched impact strength, the production of which should be possible with as little effort as possible and lead to optically perfect tube surface areas

This object is achieved according to the invention by the use of a steel alloy according to claim 1. A steel tube according to the invention as a construction tube, in particular as a profile tube, has the features of independent claim 5. Advantageous further developments of the invention result from the dependent subclaims

The investigations carried out in the course of the present invention led to the surprising result that without the steel according to material sheet 290 R to achieve its strength and

Toughness properties of essential nickel a suitable steel alloy can be found, which results from a specific modification of the alloy known from W098 / 31843 for seamless conduits. The steel alloy to be used according to the invention differs from the latter in particular by the mandatory addition of 0.2%. 0.5% Cr

In addition, the predetermined ranges for the contents of C and Mn are shifted towards higher values and a minimum vanadium content of 0.03% is required in any case. According to the invention, a steel alloy is therefore proposed for the production of high-strength, weldable seamless steel tubes for this purpose unusual addition of tungsten in the range of 0.3%

- 1.0% stipulates that the W content is at least 0.5%. To the extent that Ni is present as an impurity in the steel, for example if it is generated from scrap in an electric furnace, its content must not exceed 0.20% The Ni content is preferably limited to a maximum of 0.15%, in particular a maximum of 0 10%. In order to achieve particularly appealing strength values with at the same time still excellent values with regard to toughness, the content of C is preferably limited to 0 14% to 0.20%

According to a further aspect of the present invention, a weldable seamless construction tube which is high-strength and weldable in the sense of the values described at the beginning is provided, which is designed in particular as a profile tube and is produced by hot rolling and subsequent tempering. It consists of a steel alloy with the following composition

C 0.12 - 0.25%

Si <0.40%

Mn 1, 20 - 1, 80%

P <0.025%

S <0.010%

AI 0.01 - 0.06%

Cr 0.20 - 0.50%

Mo 0.20 - 0.50%

V 0.03 - 0.10%

W 0.30 - 1.00%

Ni 0.00 - 0.20%

N <0.02%

Cu ≤ 0.20% balance iron and usual impurities

In particular, the contents of C, W and Ni can advantageously be modified as has already been described above for the alloy to be used according to the invention. The steel tubes according to the invention have excellent values with regard to their strength and toughness properties, as can be seen in detail from the following exemplary embodiments

A steel alloy with the following composition was melted and cast into a tubular cross-section

C 0.17%

Si 0.32%

Mn 1.50%

P 0.01%

S 0.001%

AI 0.031%

Cr 0.32%

Mo 0.27%

Cu 0.16%

Ni 0.12%

V 0.07%

W 0.56%

N 0.006%

Cu 0.02%

Balance iron and usual impurities

Some of the measured values determined in the exemplary embodiments have been graphically represented in the figures. Show it:

1 shows the _{proof stress} R _p0 , ₂ as a function of the wall thickness,

2 shows the tensile strength R _m as a function of the wall thickness,

Fig. 3 shows the elongation at break A ₅ depending on the wall thickness.

This tube raw material was then rolled in a manner known per se on a pilgrim route into tubes of different dimensions. After cooling to room temperature, the tubes produced in this way were also known per se

Undergone remuneration treatment. Compared to corresponding steel pipes made from the known steel FGS 70 V, the construction pipes made from the steel used according to the invention had a smooth surface without the usual, distinctive shells, so that these pipes could already be used as construction pipes without additional finishing. The technological properties of the pipes were determined by testing cross samples taken from the pipes produced. Samples were used which were taken from pipes with a diameter of 457 mm and a wall thickness of 20 mm or 404 mm diameter and a wall thickness of 41 mm and a diameter of 410 mm and a wall thickness of 60 mm. The measured values for the _{proof stress} R _p0 , ₂ have been shown graphically in FIG. 1 as a function of the wall thickness. The minimum yield strength for the known material FGS 70 V mentioned as an example has also been entered in the form of a stair line. It can be seen that even the lowest measured values are still far above the required minimum values. The result of the determination of the tensile strength was correspondingly shown in FIG

R _{m is shown} graphically, whereby the minimum values for the material FGS 70 V were drawn in as a stair line. Here, too, the lowest determined values are significantly above the required minimum values. 3 also shows the result of the measurement of the elongation at break A ₅ on transverse samples for different wall thicknesses. Again, the lowest values are significantly higher than the required minimum of 14%.

The toughness properties were examined by means of cross-specimens by impact test, since these give the values which are more critical for the assessment of this property. The results are shown numerically in Tables 3 and 4. The samples were taken from tubes measuring 457 x 20 mm and 404 x 41 mm.

Table 4

A comparison of the measured values with the prescribed minimum values from Table 2 for the test temperature - 40 ° C shows that the mean values are several times higher than the required minimum values and that even the smallest individual values determined are still approximately twice as high or more than 50% above the required minimum value.

Overall, this means that the construction pipes produced had very good strength properties, which were combined with excellent toughness properties. At the same time, these pipes had very good weldability and surfaces that were free of defects even when rolled. This was achieved by using a steel alloyed with tungsten, in which the nickel content was reduced at least to below a critical limit.

Claims

claims:

1. Use of a steel alloy containing (% by weight)

C 0.12 - 0.25%

Si <0.40%

Mn 1, 20 - 1, 80%

P <0.025%

S <0.010%

AI 0.01 - 0.06%

Cr 0.20 - 0.50%

Mo 0.20 - 0.50%

V 0.03 - 0.10%

Cu <0.20%

N <0.02% balance iron and common impurities

as a material for the production of high-strength, weldable seamless steel tubes as construction tubes by hot rolling and subsequent tempering with the proviso that the steel alloy additionally contains 0.30-1.00% W and an existing Ni content of no more than 0.20%.

2. Use according to claim 1, characterized in that the steel alloy contains at least 0.50% W.

3. Use according to one of claims 1 to 2, characterized in that the steel alloy contains less than 0.15%, in particular at most 0.10% Ni.

4. Use according to one of claims 1 to 3, characterized in that the C content is in the range from 0.14 to 0.20%.

5.High strength, weldable seamless construction tube, in particular profile tube, produced by hot rolling and subsequent tempering, consisting of a steel alloy with the following composition:

C 0.12-0.25%

Si <0.40%

Mn 1.20-1.80%

P ≤ 0.025% s ≤ 0.010%

AI 0.01 -0.06%

Cr 0.20-0.50%

Mo 0.20-0.50%

V 0.03-0.10%

W 0.30-1.00%

Ni 0.00-0.20%

Cu <0.20%

N ≤ 0.02%

Balance iron and usual impurities

6. Construction pipe according to claim 5, characterized in that the steel alloy contains at least 0.50% W.

7. Construction pipe according to one of claims 5 to 6, characterized in that the steel alloy contains less than 0.15%, in particular at most 0.10% Ni.

8. Construction pipe according to one of claims 5 to 7, characterized in that the content of C is in the range of 0.14 to 0.20%.