EP0850701B1 - Method and installation for producing bars with a refined and/or compressed structure by roll forging - Google Patents

Abstract

The method involves use of continuously cast products (20) of forgeable steel quality and an approximately square cross section, with inclined corner regions (21), in the role of the initial material. At a forging heat above the transformation temperature, by continuous twist-free forming alternatingly in at least one two-roll stand and/or at least one four-roll stand, these products are subjected to a multistage reshaping process with a relatively small elongation and comparatively very high rolling forces to produce a rolled product with a compacted core. Also claimed is a corresponding rolling installation. Such an installation includes a preliminary rolling section consisting of at least some of the following forming facilities: (a) at least a two-stand block for preliminary sizing of the cast product; (b) at least one duo horizontal stand or duo vertical stand for smoothing the billet surface; (c) least one four-roll stand and (d) means for (preferably inductive) intermediate h eating of the rolled material.

Description

The invention relates to a method for producing bar steel with refined and / or compacted structure. The invention also relates to a rolling mill system to carry out the procedure.

Improving the mechanical properties of steel by forging is known from ancient times. Through intensive press and forging blows with heavy hammers break up coarser crystal structures in the material and refined the grain structure of the workpiece treated in this way, the Material is compacted, porosity reduced and toughness significantly increased. When forging, grain compaction occurs when the material is extended achieved in the order of a factor of 2 to 3.

"Theoretische und experimentelle Untersuchungen zum Formänderungsverlauf und zu Spannungszustand an einer Schmiedewalzanlage (GFM/Krupp) zur Herstellung von Stabmaterial"

des Dipl. Ing. Tuke aus Dortmund, vorgelegt bei der Rheinisch-Westfälischen Technischen Hochschule Aachen im Oktober 1979, ist ein Schmiedevefahren an einer Durchlaufschmiedeanlage bekannt, bei der als Umformwerkzeug verwendete Hämmer konzentrisch auf ein Schmiedestück einwirken und dieses dabei stark verdichten. Die hierbei verwendeten Knüppel erhalten beim Schmieden in diagonal unter 45° hochgestellter Lage die ersten Press- und Schmiedeschläge. Es wird jedoch kein Walzgerüst verwendet und somit auch keine erhöhte Produktivität erreicht.From the dissertation entitled

"Theoretical and experimental investigations on the course of deformation and the state of stress in a forging mill (GFM / Krupp) for the production of rod material"

by Dipl. Ing. Tuke from Dortmund, submitted to the Rheinisch-Westfälische Technische Hochschule Aachen in October 1979, a forging process on a continuous forging plant is known in which hammers used as forming tools act concentrically on a forging and thereby densify it. The billets used here receive the first pressing and forging blows when they are forged in a diagonally raised position at 45 °. However, no roll stand is used and therefore no increased productivity is achieved.

In the journal Stahl and Eisen 110 (1990) No. 6, pages 59 to 64 that is High precision rolls of steel bars on the fine steel and wire mill of von Moosstahl AG (Lucerne / Switzerland). This publication is concerned with with a rolling process under high pressure in a horizontal stand and a Vertical scaffold. The known method is aimed at an economical one Setting very tight tolerances for diameter and roundness in fine steel and wire to avoid or save expensive rework. A Core compression of the material does not take place and is also not intended.

From the technical report on rolling mill systems No. 2000.09.92 LD from SMS Schloemann-Siemag AG, Düsseldorf, published in September 1992, in particular Figures 3 and 4 do connect a continuous caster to a Rolling mill for fine steel from billets addressed. The aim is to save costs as much as possible Connection of the continuous casting plant to fine steel or wire rolling mills, especially for optimal use of the heat capacity contained in the cast strand.

JP-A-5-337510 discloses the closest prior art a process for the production of steel bars with refined and / or compacted Structure. However, no continuously cast long goods are used, and nor are billets with an approximately square cross-section and beveled Corner areas.

The invention is based on the object of specifying a method and a system, with which the production of a core-compacted product is compared for forging much higher productivity and consequently greatly reduced Costs succeed, while the overall benefits of rolling in quality improvement from steel through forging to an economical-technical one Unite overall success.

The problem is solved with a method for producing steel bars with a refined and / or condensed structure by combining them coordinated work steps according to claim 1.

Thanks to multi-stage forming, especially in a two-roll stand sequence and four-roll stand or in a stand sequence of four-roll stands the structure is refined in the manner of a deep kneading process and compacted, and thus the mechanical properties of the so treated Stahls significantly improved. The method according to the invention before forming, also known as forging rolling, by rolling down of corner areas of the billets in at least one four-roll stand with so high rolling force ensures that the resulting and recognizable, for example, in the micrograph Compression compressive stresses are effective down to the core zone. The The method further provides that after the cast strand has solidified, the billets Temperature compensation and heating to a designated forging roll temperature pre-calibrated and the flanks of the billets are deformed concavely. The the resulting cross-sectional shape of the billets guarantees that that the compression pressures generate compressive stresses down to the core and create a relatively even structure across the entire cross-section.

It is essential for forging rolls to adhere to a specified and forging temperature conforming to material. As a result, it is under construction the invention advantageous, depending on the rolling temperature on the inlet side of a scaffolding, an increase in temperature, preferably by induction heating to make.

In an embodiment of the method it is provided that for a rolling stock with a maximum of 480 cm ² , corresponding for example a square cross section with an edge length of approx. 22 cm, and for an unalloyed or weakly alloyed tempering steel with a C content of 0.1 to 0.3% is carried out. This ensures that effective compression and compressive stresses come into effect right into the core zone.

An advantageous embodiment of the invention provides that the pre-calibrated Billets are preferred in a combination of horizontal roll stand and vertical roll stand smoothed and then immediately into the four-roll stands introduced and deformed therein by forging rollers.

The invention enables that according to the degree to be achieved Structural compaction Forming of the rolling stock by immediately following one another Stitches in a sequence of two-roll stands and four-roll stands be made. The determination of whether a wire with sufficient structural compaction up to the core zone can be reached by a series of tests on rolled specimens, especially after they have cooled down by micrographs determine and reproduce safely with the experience gained.

In continuation of the inventive concept, it is used to achieve extremely high rolling pressures required that the forging rolls be used comparatively very rigid roll stands with preferably cylindrical rolls from comparatively small diameter is carried out.

At least one four-roll stand with four can be used for forging rolls driven rollers are used. With corresponding requirements other rolling parameters may also suffice for forging at least one four-roll stand with two driven rolls used is, for example. With two driven horizontal rollers and two non-driven Vertical rolling.

For a particularly deep penetration of the compressive stress during forging down to the core of the material to be formed is advantageous in that the billet at least for the first stitch for rolling down the corner areas in one Two-roll stand or in a four-roll stand in a diagonal position below 45 ° are brought. The advantage here is that a maximum amount of deformation work realized with a relatively small elongation of the rolled product becomes. This advantage can still be used to a greater extent by the fact that Sticks are turned 45 ° for each subsequent stitch. The smoothing stitch in the two-roll horizontal stand or in the two-roll vertical stand is approximately 10%, whereas the forging rolling in the four-roll stand with one pass reduction from 30 - 60%.

Finally, the method according to the invention provides with great advantage that Continuous casting billets in the roughing train of a rolling mill to produce steel bars processed by forged rollers and / or compacted structure and that the hot rolled steel bar immediately afterwards in an intermediate or finishing train of the rolling mill system to a calibrated or profiled Finished product is rolled.

• zumindest einen zweigerüstigen Block zum Vorkalibrieren von Stranggusslangprodukten, wie gegossene Knüppel,
• wenigstens ein Duo-Horizontal- oder Duo-Vertikal-Gerüst zum Glätten der zu verformenden Knüppeloberfläche,
• wenigstens ein Vierwalzengerüst mit Mitteln zum Führen und Wenden der Knüppel,
• Mittel zum bevorzugt induktiven Zwischenerwärmen der Knüppel.

To carry out the method according to the invention, a rolling mill plant for the production of steel bars with a refined and / or compacted structure is proposed, which is characterized in that the plant part for the production of forged-rolled steel bars is a roughing mill which has the following or at least some of the following forming means :

• at least one two-stand block for the pre-calibration of long cast products, such as cast billets,
• at least one duo-horizontal or duo-vertical framework for smoothing the billet surface to be deformed,
• at least one four-roll stand with means for guiding and turning the billets,
• Means for preferably inductive intermediate heating of the billets.

In the configuration of the rolling mill system, it is provided that the roughing road for the production of steel bars with forged rolls an intermediate or finishing train in a refined and compacted structure is immediately subordinate.

Figur 1

im Querschnitt einen als Ausgangsmaterial vorgesehenen Stranggussknüppel;

Figur 2

im Querschnitt den Knüppel um 45° gedreht zwischen einem Paar Horizontalwalzen;

Figur 3

einen Stammbaum einer Walzwerksanlage zum Durchführen des erfindungsgemäßen Verfahrens.

Further details, features and advantages of the invention result from the following explanation of an exemplary embodiment shown schematically in the drawings. Show it:

Figure 1

in cross section a continuous casting billet provided as the starting material;

Figure 2

in cross section the stick rotated 45 ° between a pair of horizontal rollers;

Figure 3

a family tree of a rolling mill system for performing the method according to the invention.

Figure 1 shows the cross section of a as a starting material for manufacturing of steel bars with and refined by forging rolls compacted structure of continuously cast billet 20. It has one approximately square cross section with the vertical plane y-y and the horizontal plane x-x. At an angle of 45 ° between them Layers shows the cross-sectional shape of strongly sloping corner areas and initially even flanks 22. After solidification of the as starting material initially continuously cast strand 10 is in this first a temperature compensation, for example, in a conventional manner Equalization furnace (not shown) and the strand with a pair of scissors 11 cut into individual billets. Before or after there is heating to the forging temperature, after which the Sticks pre-calibrated, smoothed and their flanks 22 accordingly the representation in Fig. 2 are deformed concavely. Hereby there are optimal conditions for the subsequent Microstructure compaction during forging rolling. According to Fig. 2 the Stick 20 rotated by 45 ° and, for example, in a first stitch another sequence of steps between a pair of horizontal rollers 4 Rolling down the corner regions 21 in a first compression step subjected. The resulting compression zones in the structure are indicated by the reference number 30 in FIG. This illustration also clearly shows the concave shape 23 of the prepared for the billet cross sections.

Figure 2 shows the preparation of the next forming stitch in a universal scaffold 5, 7 of FIG Vertical rolls 14.

With this stitch in one or both of the universal frameworks 5, 7 the major part of the forging work carried out, where at less elongation of the multi-stage forming process with comparative extremely high rolling forces that can be seen in the micrograph Compression compressive stresses 30 are effective in the core zone.

FIG. 3 shows an example of a family tree Carrying out the process suitable rolling mill system. she owns an upstream system unit 1 in the form of a continuous casting system for the production of continuous cast and for forging rolling thermally prepared billet 20 made from the endless cast strand 10 can be cut to length with scissors 11. The facility also shows in a preparatory part a roughing stand 2 for pre-calibration and then for smoothing a duo-horizontal frame 3 with subordinate Vertical smoothing scaffold 4. Essential elements for that Forging rolls are the following two universal stands 5 and 7 preferably with smooth cylindrical rollers, between which there are a device 6 for preferably inductively heating the billets 20 is located. This can be followed by a duo frame 8 for smoothing his.

As FIG. 3 further shows, there is one in the system of the Vorstrasse 15 Finishing line 9, not specifically identified, with, for example, five finishing stands subordinate. The core is compacted into these by forging rolls Steel bars introduced hot and rolled in a heat.

The aforementioned process steps and the corresponding plant are only to be understood as examples. You can use the usual procedure by the specialist provided for Work programs and according to material-dependent process parameters be modified.

Claims (15)

1. Method of producing steel rod with a refined and/or condensed structure, comprising the following working steps

   a) continuously cast elongate products in the form of billets (10) of forgeable steel quality with approximately square cross-section and chamfered corner regions (21) are used as starting material,

   b) the billets (20) after hardening of the cast strip (10), temperature compensation and heating to forging temperature are initially subjected to a roughing pass and the billet flanks (21) in that case concavely deformed (23), wherein

   c) in dependence on the roll stock temperature at the inlet side of a stand (7) a requisite increase in the roll temperature is preferably undertaken by means (6) for induction heating, and

   d) the preshaped billets heated to forging temperature above the conversion temperature are subjected to a multi-stage reshaping process, by continuous twist-free reshaping by means of directly successive passes in each case in a series of two-high roll stands and four-high roll stands (3, 4, 5, 7, 8), with small elongation by way of forging rolling at such high rolling force into a condensed-core rolled product that the thus-arising condensing compressive stresses (30), which are recognisable for example in the ground finish, are effective into the core zone.
2. Method according to claim 1, characterised in that the billet (20) is turned through 45° for each succeeding pass.
3. Method according to claim 1 or 2, characterised in that it is carried out with a roll stock with a cross-section, which corresponds to at most 480 cm² and is, for example, square, with about 22 cm edge length and with an unalloyed or lightly alloyed tempering steel with a carbon content of 0.1 to 0.3%.
4. Method according to one or more of claims 1 to 3, characterised in that the preshaped billet (20) is smoothed preferably in a combination of horizontal roll stand (13) and/or vertical roll stand (4) and is subsequently introduced directly into the four-high roll stand or stands (5, 7) and deformed therein by forging rolling.
5. Method according to one or more of claims 1 to 4, characterised in that deformations of the roll stock are carried out by directly successive passes respectively in a series of two-high roll stands and four-high roll stands (3, 4, 5, 6, 8) in dependence on the degree of structure condensing to be achieved.
6. Method according to one or more of claims 1 to 5, characterised in that the forging rolling is carried out with use of roll stands (5, 7), which are comparatively very stiff in bending, with preferably cylindrical rolls (4, 14) of comparatively small diameter.
7. Method according to one or more of claims 1 to 6, characterised in that at least one four-high roll stand (5, 7) with four driven rolls (4, 14) is used for the forging pass.
8. Method according to one or more of claims 1 to 7, characterised in that at least one four-high roll stand (5, 7) with two driven rolls (4 or 14) or with, for example, two driven horizontal rolls and two non-driven vertical rolls is used for the forging rolling.
9. Method according to one or more of claims 1 to 8, characterised in that the billet (20) is brought into a two-high roll stand (3, 4) or four-high roll stand (5, 7) in a diagonal setting for the first pass for rolling down the corner regions (21).
10. Method according to one or more of claims 1 to 9, characterised in that the smoothing pass in the two-high horizontal rolling stand or in the two-high vertical rolling stand amounts to about 10% and that the forging rolling is carried out in the four-high roll stand with a pass reduction of 30 to 60%.
11. Method according to one or more of claims 1 to 10, characterised in that the continuously cast billet (20) is processed in the preliminary train (15) of a rolling mill into steel rod with a structure (30) refined and/or condensed by forging rolling and that the hot-rolled steel rod is subsequently finished-rolled in an intermediate or finishing train (9) of the rolling mill into a sized or profiled end product.
12. Rolling mill with a mill part for production of steel rod with a refined and/or condensed structure (30), for carrying out the method according to claims 1 to 11, characterised in that the mill part for production of forge-rolled steel rod is a preliminary train (15) which comprises the following reshaping means:

    at least one two-high block (2) for rough passing of continuously cast elongate products such as cast billets,

    at least one tandem horizontal stand (4) or tandem vertical stand (3) for the smoothing of the billet surface to be deformed, and/or

    at least one four-high roll stand (5, 7) with means for guiding and turning the billets (20), and

    means for intermediate heating of the billets (20) preferably inductively.
13. Rolling mill according to claim 12, characterised in that an intermediate or a finishing train (9) is arranged directly downstream of the preliminary train (15).
14. Rolling mill according to claim 12 or 13, characterised in that a foundry for production of continuously cast elongate products, which are thermally prepared for forging rolling, such as for example billets, is arranged upstream of the preliminary train (15).
15. Rolling mill according to claim 13 or 14, characterised in that the two-high roll stand (3, 4) is a conventional tandem horizontal stand or tandem vertical stand and the four-high roll stand is a universal stand, in each case equipped with smooth rollers.

Images