EP0130173A1 - Process for the production of a microkilled steel for cold-working on a continuous caster without stoppage - Google Patents

Abstract

For the production of a micro-calming steel which can be cast in freewheel mode on continuous casting machines for subsequent cold forming, it is proposed that the C content be <= 0.05%, preferably <= 0.03%, the Si content to <= 0.05%, preferably 0.02 to 0.04%, and adjust the Al content to <= 0.006%. A value <= 0.14%, preferably 0.10-0.12%, is set for the equivalent carbon content, the relationship Ceq =% C + 1/7% Si + 1/5% Mn + 1/7% Cr + 1 / 20% Ni + 1/9% Cu + 1/2% Mo + 1/2% V is used to determine the equivalent carbon content. Advantageously, the steel is freshly blown in a bottom-blowing or flushing converter and, after the Si and / or Mn content has been set, the oxygen activity a [o] is measured and the oxygen content is adjusted to 60 by adding a corresponding amount of a further deoxidizer, in particular Al -150 ppm set.

Description

The invention relates to a method for producing a micro-calmed steel castable on free-running continuous casting machines for subsequent cold working, in particular for drawing wires.

In order to achieve good cold formability, low-carbon, unsettled steel is usually selected as the primary material. Such low-carbon unsteady steels allow a ductility of up to 99% deformation and such a unsteady steel is clearly superior in its cold-forming properties to one that has been calmed with aluminum or with silicon, as well as to the various types of semi-calmed steels. Depending on the choice of deoxidizing agent, calmed steels either have the tendency to be too hard from the start or show a stronger strain hardening after being pulled. In order to achieve good casting properties and good drawing behavior, it was previously only possible to carry out a vacuum treatment which is extremely complex and expensive in terms of apparatus. With such a vacuum calming, a large part of the oxygen could be removed and the disadvantages of unrestored steels during casting could be largely eliminated with these measures.

Calmed steels, which would in themselves be better suited for subsequent cold working, have the disadvantage during casting that large non-metallic inclusions can occur and segregation peaks occur in the block head which impair the usability of such a steel. The use of manganese as a sedative is due to the increase in hardness associated with this measure Although suitable for improving the casting behavior, it brings about a deterioration in the drawing behavior.

The invention now aims to provide a process for the production of a steel, in which the advantages of calmed steels during casting are obtained in a continuous casting process without the need for complex vacuum calming processes, while at the same time good drawing properties or cold forming properties are to be achieved. To achieve this object, the invention essentially consists in that the C content is ≤ 0.05%, preferably ≤ 0.03%, the Si content is ≤ 0.05%, preferably ≤ 0.02 to 0.04 %, and the Al content is set to ≤ 0.006%, with an equivalent carbon content according to the relationship C _eq =% C + 1/7% Si + 1/5% Mn + 1/7% Cr + 1/20% Ni + 1/9% Cu + 1/2% Mo + 1/2% V ≤ 0.14% and preferably 0.10 - 0.12%. In this way, wire drawing grades are achieved, which can be expected to have the same properties as the unsteady soft steel, without the castability being impaired on continuous casting systems in free-running mode. The demands placed on these wire drawing grades with regard to low levels of carbon, silicon, aluminum, nitrogen and impurities that cause strength increases, such as chromium, nickel and copper, as well as the lowest possible pearlite contents and large ferrite grains, ensure low deformation resistance, high ductility and low Strain hardening so that good ductility and cold compressibility can be achieved. By setting a carbon content of less than 0.05%, preferably less than 0.03%, the tendency to form bubbles and bubble channels during casting in the strand is reduced, and less work hardening is achieved. Likewise, the setting of a silicon content of less than 0.05%, preferably 0.02 to 0.04%, is responsible for the tendency to work hardening as well as the Initial strength is reduced. The setting of the aluminum content of less than 0.006% aims to exclude precipitations of aluminum nitride, which would reduce the grain size. Low phosphorus, nitrogen, chromium, nickel and copper contents reduce the tendency to work hardening and the wire rod strength per se is reduced. By maintaining a carbon _{equivalent of} C _eq =% C + 1/7% Si + 1/5% Mn + 1/7% Cr + 1/20% Ni + 1/9% Cu + 1/2% Mo + 1/2 % V of max. 0.14 and preferably 0.10 to 0.12%, a grain size of 15 to 20 μm and a pearlite content of ≤ 0.007% are achieved. Such steel can easily be cast in the strand without requiring special protective measures and, with diameters from 5.5 to 13 mm, initial strengths of ≤ 360 N / mm ² , a yield strength 6280 N / mm ² , an elongation ≥ 20 % and a constriction ≥ 80%. The maximum inclusion size present in the wire was determined to be ≤ 4 according to Stahleisen test sheet 1570, which was plastic manganese silicates with a maximum length of 20 µm.

In contrast, the production of wires from ingot material is associated with greater inhomogeneities and the inclusion sizes for wires made from ingot material are significantly higher. Inclusion sizes of 50 to 100 μm have been found in particular in the case of wires which are drawn from the material of the base zone of the block, and the deformation behavior of these non-metallic inclusions, which arise when the block casting is unoccupied, is considerably less favorable. The hardening when pulling the primary material produced in the manner according to the invention practically corresponds to the values which result for material made of unsteady steel.

A steel with the composition according to the invention has so far only been able to achieve the desired drawing behavior using a vacuum treatment to adjust low carbon contents and with vacuum calming. In contrast, according to the invention, the low C content can be achieved in a particularly preferred manner by refining the steel in a floor-blowing or floor-washing converter.

Subsequent to tapping, the steel is subjected to a conditioning treatment according to the invention, the silicon and manganese contents being set as a function of the final carbon content achieved. In a particularly advantageous manner, the procedure is such that the steel is subjected to a conditioning treatment after the refining, in which the Si content and the Mn content as a function of the C eg content at values of C _eq ≥ 0.025%, in particular by adding Si to a sum of% Si + 0.1% Mn = 1.53% C + 0.012.

The remaining oxygen content can be determined by measuring the oxygen activity and, depending on the carbon and silicon content, can be corrected by metered addition in the pan. For this, the procedure is advantageously such that, after the Si and / or Mn content has been set, the oxygen activity a _{[o] is} measured and adjusted to 60-150 ppm by adding an appropriate amount of a further deoxidizer, in particular Al. This procedure avoids smearing in the freewheel casting and it is possible to achieve steel which can be cast without bubbles in the strand.

In the drawing, the inventive method is explained in more detail. The conditions to be maintained within the scope of the method according to the invention, in particular the critical silicon contents for achieving the desired properties, can be clearly seen from the drawing figure. For equivalent carbon contents of> 0.025, the curves drawn change into straight-line areas parallel to one another, each curve being valid for the respectively stated manganese content. For the carbon content obtained in each case after refining, a steel must now be obtained by adding silicon, the composition of which in the drawing lies to the right of the curve applicable to the manganese content, so that no bubbles occur during casting. If these conditions are met, the steel can be cast without bubbles and good drawing properties are guaranteed compared to vacuum-reduced steels.

Claims (4)

1. A process for producing a free-cast, micro-calming steel castable on continuous casting plants for a subsequent cold working, in particular for the drawing of wires, characterized in that the C content to ≤ 0.05%, preferably 6 0.03%, of the Si Content is ≤ 0.05%, preferably 0.02 to 0.04%, and the Al content is set to ≤ 0.006%, an equivalent carbon content corresponding to the relationship C =% C + 1/7% Si + 1 / 5% Mn + 1/7% Cr + 1/20% Ni + 1/9% Cu + 1/2% Mo + 1/2% V ≤ 0.14% and preferably 0.10 - 0.12% . 2. The method according to claim 1, characterized in that the steel is refreshed in a floor-blowing or floor-washing converter. 3. The method according to claim 1 or 2, 'characterized in that the steel is subjected to a conditioning treatment after the refining, in which the Si content and the Mn content depending on the C _eq content at values of C _eq ≥ 0.025%, in particular by adding Si to a sum of% Si + 0.1% Mn = 1.53% C + 0.012. 4. The method according to claim 3, characterized in that after the adjustment of the Si and / or Mn content, the oxygen activity a _{[o] is} measured and adjusted to 60-150 ppm by adding a corresponding amount of a further deoxidizer, in particular Al.

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