DD160457A1 - METHOD FOR THE THERMOMECHANICAL TREATMENT OF ROLLING STEEL - Google Patents

Abstract

1. A method for the thermomechanical treatment of continuously hot rolled steel, especially wire rods and small sections, in which the rolled stock subsequent to preceding passes is cooled on the surface thereof and during the subsequent establishment of thermal equilibrium between its surface zone and the core is subjected to a further hot forming operation, wherein the surface of the rolled stock, starting from the temperature of the last-preceding pass, is cooled at a cooling rate of 1 800 degrees C/s by at least 600 degrees C, and wherein during the subsequent forming operation a reduction of at least 10% is observed.

Description

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Inventor :. PA 132

Dipl.-Ing. Franz Tamm Dipl.-Ing. Bernhard Earicke

Τ- r ~ Tr., "J- iff η J. jj. g,. ii.U- u «Oj

Representative ; DPE: C '21 D, 1/02

.Ernst-Karl Vollbreciit IPC:

YEB Steel and Rolling Mill "Wilhelm Florin" TSB Quality and Stainless Steel Combine Office for Property Rights- 1422 Hennigsdorf Veltenar Straße

Title of the invention

Process for the thermomechanical treatment of rolled steel

Field of application of the invention

The invention relates to the hot rolling of fine and medium bar steel and wire in fine steel rolling mills, especially in continuous fine steel rolling mills. It relates to a method for the treatment of steel in connection with the hot forming j whereby the structural and material properties of the steel in various directions according to the requirements of further processing influenced.

Characteristic of the known technical solutions The development of rolling mill technology has led to high rolling speeds, which are still being constantly increased. In connection with this, preference is given to using high ITmform temperatures which, although they are favorable in terms of deformation resistance, frequently have negative effects on the microstructure and the material properties

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to have. Reducing the molding temperatures brings improved material properties, but disadvantages due to increased power requirements for the forming, increased wear of the rolls or - eictur ⁱ - ^cr ' ^c ' back ' ^{: r} ' ^o ' ^ncr ' of the streets in Sauf take.

In several developed industrialized countries, various thermomechanical treatment processes are already being used for production purposes or prepared for use. It is known in this context that can be usefully influenced by Umformt empe rat ur en, degrees of deformation, forming speeds, forming times and the residence time after the conversion and the subsequent cooling, microstructure and properties. So z. B. in the controlled rolling perlitarmer aikrolegierter steels increased strength properties at good plastic values and good weldability achieved. The controlled rolling, d. H. The transformation of the steel at reduced temperatures, but still in the range of stable austenite requires sn-frzzwzzws Walzwerksausrüstungen with sufficient drive power and mechanical stability. The requirements for rolling mill equipment are even higher if austenite form hardening , ie the transformation of the metastable austenite, is to be used to improve the properties of the material. In this case, the rolling mills are already designed to withstand the high stresses or the process is not applicable in the usual rolling mills.

In the known method of thermal solidification from the rolling heat, in which the rolling stock is subjected to intensive cooling after completion of the transformation, a certain heat removal is necessary to achieve the required surface area compensation structure in the edge zones of the rolling stock. The higher the rolling end temperature is, the more difficult it is to accomplish this task, and as a result the method can only be used up to certain dimensions.

Both in the usual hot forming on VVT and in the application of modern thermo-mechanical processes, it is assumed that the rolling stock has a more or less uniform temperature over the cross section in order to achieve correspondingly homogeneous material properties. A uniform temperature across the rolling stock cross-section is adjusted by either cooling with slow temperature changes, such as air cooling or intense quenching z. 3, with pressurized water, connected to a temperature compensation applied. In both cases, the continuity of the rolling process is interrupted, and the transformation can be continued only after a certain period of time, reductions in the performance of the rolling mill are often unavoidable.

Object of the invention

The object of the invention is to provide a thermomechanical treatment of rolled steel in which the continuity of the rolling process is not interrupted, which ensures the operation of the mill with high performance, which leads to improved material properties for the further processing of the steel and that facilitates the application of additional thermo-mechanical treatment of the rolled steel.

Explanation of the essence of the invention

The invention has the object zügrunde, set during continuous hot rolling necessary to achieve certain material properties, compared to the previous rolling process reduced forming temperature immediately before the finishing stitch or the finishing stitches. This object is achieved in that the rolling stock during the rolling process of a 'temperature of about 11CO ⁰ C on its surface to a temperature above M "abge-

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cools and Sin forming is subjected during the temperature equalization between peripheral zone and core of a "with a Unrformgrad of at least IO%. Another feature of the invention is that after the completion of Warmum_ modeling optionally additionally a thermomechanically ^ treatment is carried out.

The invention will be explained below with reference to a Ausführungsbeispieis «

embodiment

FIG. 1 shows the method according to the invention in a ZTU diagram.

Starting from the forming temperature of, for example, 1100 ⁰ C of the previous rolling passes intensive cooling of the rolling stock on its surface to a temperature above M by means of pressurized water in the area a. Subsequently, in the phase of temperature compensation between the surface and the core, further hot forming takes place. In this phase, the core is even warmer than the hand zone and can preferably be shaped. In the colder edge zone, the recrystallization is slowed down, and as a result of the treatment is in this edge zone, which occupies a relatively large area fraction of the cross-section, a finer grain structure, as it adjusts itself without cooling a Due to the temperature compensation during molding, the core temperature drops rapidly A refinement of the G-efuge is the result. In the final result, the edge zone and the core have only small structural differences. The example shown in Fig. 1 shows a further cooling stage c following the treatment according to the invention, which contributes to the adjustment of certain strength properties in a known manner, however, is carried out by the previous cooling stage with significantly reduced cooling technology effort.

The Eühlstufe a thus has a positive effect on the result of any subsequent thermomechanical treatment.

By experiencing the invention, it is possible, despite high rolling speeds and temperatures, to achieve the optimum material properties which are possible in a given steel analysis,

Claims (2)

/ 14 U PA would indunssansOruch steel, in particular in the continuous rolling of wire and fine steel, wherein the rolling stock during the rolling process of a temperature of about * 1100 ⁰ G on its surface to a temperature above M is cooled, characterized in that the rolling stock is subjected to a deformation with a ümformgrad of at least 10% during the üJemperaturausgleichs between edge zone and core, 2 ,. Method according to item 1, characterized in that optionally another additional thermomechanical treatment is carried out after completion of the hot forming. this 1 page drawings,