DD275415A1 - METHOD FOR THE PRODUCTION OF SEAMLESS PIPES OF HIGH-WELD, WELDABLE, COLD-COATING MODELS - Google Patents

Abstract

The invention relates to a method for the production of seamless tubes made of high-strength, weldable, cold-chewed construction steel. It concerns the technical field of producing seamless steel tubes on a boulevard. By specifying a specific temperature and forming regime, which takes into account the conversion behavior of microalloyed steels, it is possible to obtain from the rolling heat without additional heat treatment or rendering steps seamless tubes with structures and associated mechanical properties which significantly improve the mass performance. Guarantee the quality of constructions or components.

Description

Field of application of the invention

The invention relates to a method for the production of seamless steel tubes made of high-strength, weldable, cold-strength structural steel, which are used for construction and construction elements of steel pipes.

Characteristic of the known state of the art

As is well known, seamless tubes of high strength, weldable, cold-worked structural steels obtain their mechanical properties for use by analysis, by the application of thermomechanical treatment processes in hot rolling or by heat treatment processes. Tempering plays a dominant role among heat treatment processes. However, it is an additional processing method, which is time consuming and energy consuming and therefore associated with considerable costs. Although the tempering from the rolling heat is also known, but requires special equipment that must be classified in the rolling mill. To classify such plants retroactively in an existing rolling mill and to adjust their performance requires considerable costs.

Thermomechenische treatment require in addition to a narrow temperature, transformation and time regime to ensure relatively narrow Anaiysentoleranzen. Even small deviations of the contents of some elements can change the temperature-time regime of a steel significantly, so that the guarantee of the desired mechanical properties is no longer possible and lead to committee or possibly subsequent heat treatments. To extend the temperature and time regime in the thermomechanical treatment micro-alloying with some elements is known.

So z. For example, DE-PS 3313755 proposes to maintain a carbon-to-vanadium ratio in the steel of 0.4 to 1.5, to preform above 1 200T with at least 40% degree of deformation, finish in several forming stages with a total of at least 50% decrease, wherein a final rolling temperature of 800 to 1000 ⁰ C is observed. This method is not possible in boot roads, in which a large part of the tube assortments is finally reduced only in diameter. This resulted in Endumformgrade of 2 to 20%.

DE-PS 3127373 proposes for a microalloyed with nitrogen and vanadium steel to perform after punching (pre-forming) a heating to 50 to 130K on AC3 and finish rolling. Then cool down quickly to 100K under AC1 and continue in air. This process is especially suitable for N80 oilfield pipes with increased carbon content (at least 0.25%) and additionally requires systems for rapid cooling after final forming with water or a water-air mixture.

DE-PS 3311629 proposes for a niobium, titanium, nitrogen and boron microalloyed steel to draw the pipe precursor at 1150 to 122O ⁰ C, then to punch and roll at least 40% longitudinal, then about 5 to 20 minutes at a temperature to keep 700-850 ⁰ C, fertigzuwalzen at this temperature for at least 6% strain, then with - at least 6 K / s to 600 to 45O ⁰ C and continue to cool to room temperature to cool. Subsequent tempering is required if the water is cooled. The relatively long compensation is very energy and costly. Subsequent tempering or tempering requires additional technical and economical applications.

Object of the invention

Object of the invention It is seamless steel tubes with the following mechanical properties

Yield strength Rpo,} at least 600 MPa

Tensile strength Rm 760-950 MPa

Elongation at break A 5 at least 16% (12.6% for strip samples)

Notched impact strength KCV

boi-40 ° C mind.34J / cm ²

Produce on a boot street with the least possible technical and energy expenditure.

Explanation of the essence of the invention

The invention has for its object to develop a temperature and Umformregime for producing seamless tubes made of high-strength, weldable, cold-strength structural steels, with which the necessary properties of the finished products from the rolling heat can be ensured without additional heat treatment.

According to the invention the object is achieved in that continuously cast or rolled round billet of a steel, the conversion behavior of the special conditions of boot roads (long secondary and transport times) corresponds to max. 0.08% C, max. 1.6% Mn, max. 0.5% Si, max. 0.02% P or S, max. 0.08% Al, at least 1.3% Cr, at least 0.3% Mo, at least 0.4% Ni, max. 0.07% Nb and heated with conventional impurities to 1120 ° C and held for a maximum of 10min. This is followed by the production of the billet on a Schrägftalzwerk, wherein the degree of deformation is at least 55%. This is followed by air cooling of the billet to 900 ° C, the longitudinal rolls in the plug stand with at least 25% degree of deformation and smoothing. The final Endumformen is carried out with at least 2% in the sizing mill at temperatures between ⁰ and 850 C or at least 38% stretch at temperatures between 900 and 1000 ⁰ C, to which an intermediate heating performed wirJ. The cooling of the finished rolled tubes takes place in still air to room temperature.

embodiment

The invention will be explained below with reference to two exemplary embodiments:

1st embodiment

A steel melted in an electric arc furnace and post-metallurgically treated in the following composition

0.06% C 0.41% Mo 1.32% Mn 0.05% Nb 0.33% Si 0.078% Al 0.015% P 0.12% Cu 0.006% S 0.0084% N 1.34% Cr and common impurities to V and Ti 0.49% Ni and Ti

was treated as follows:

- AustenitisierungdesAusgangsmaterials (rund120mm): 1100 ⁰ C - · Forming the billet 125 χ 9.0 mm:

Total conversion: 71%

Lupine temperature: 117O ⁰ C

- Air cooling to 900 ⁰ C.

- longitudinal rolls to the pipe in 3 stitches with total forming 41%

- Smoothing of the tubes, while slightly widening

- Reheating to temperatures around 800 ⁰ C

- finish rolling to tube 102 χ 6.0 mm:

Forming temperature: 800-700 ⁰ C

Forming: 14%

2nd embodiment

A likewise in the electric arc furnace melted and Pfannenmetallurgisch aftertreated steel of the following chemical composition

0.08% C 1.44% Cr 114O ⁰ C 1.38% Mn 0.47% Ni 0.32% Si 0.44% Mo 77% 0.010% P 0.06% Nb 1200 ⁰ C 0.008% S 0.038% Al 900 ⁰ C 0.092% N was treated as follows: 40% - Austenitizing the starting material (around 140 mm) at - Forming to the billet 146 x 8.0 mm: 760-860 ⁰ C. Total deformation: Luppentemperatur: 760-700 ⁰ C - Air cooling on 8th% - Long rolls to the pipe in 3 stitches with total deformation - Smoothing of the tubes, while slightly widening - Reheat to temperatures around - finish rolling to tube133x7.0mm: forming temperature transformation

Advantages:

With this procedure is achieved, üaZ

- Does not have to be austenitized above 1200 ° C.

- Due to the relatively high pre-deformation due to dynamic recrystallization a fine-grained structure is formed

- Saved by the lowered Endwalztemperaturen energy

- Can be dispensed with expensive equipment for targeted or accelerated cooling from the rolling heat.

Claims (1)

1. A process for producing seamless steel tubes from high-strength, weldable, cold-strength structural steels, which are used as main components Max. 0.08% C Max. 1.6% Mn Max. 0.5% Si Max. 0.02% P or S Max. 0.08% Al at least 1.3% Cr at least 0.3% mo at least 0.4% Ni Max. 0.07% Nb
contained on a boot road, characterized in that the starting material is austenitized in the rotary hearth furnace at temperatures of at most 1120 ° C / for about 10 minutes, - the pre-forming to a billet in the cross rolling mill with at least 55% acceptance takes place - then an air cooling to temperatures around 900 ⁰ C is performed, - the slats are subsequently subjected to at least 25% reduction of longitudinal rolling via an internal tool, - The final forming without internal tool with decreases between 2 and 25% in sizing rolls boi temperatures between 700 and 850 ⁰ C takes place or with decreases between 40 and 70% in the stretch reduction at temperatures between 900 and 1000 ° C. - The cooling takes place after the final deformation of static air