DD149943A1 - PROCESS FOR PRODUCING HIGH-WELD WELDABLE CONCRETE STEELS - Google Patents

Abstract

The process for the production of high-strength weldable concrete braces in the form of bar steel or wire rod is particularly suitable for the production of wire rod in ring coils on high-performance Kontidrahtstraszen. The disadvantages associated with thermal consolidation or thermomechanical rolling must be eliminated and concrete floors with yield strengths above 390 N / mm & exp2! which, in addition to high strength, also have universal weldability and good cold workability at the same time. This is accomplished by cooling the wire rod for a new time-temperature regime settable on a high-performance continuous wire strands, the chemical composition of the steel being specifically tailored to this treatment. The wire rod is cooled very quickly to preferably below 750 degrees C immediately after hot working. D. further Abkuehlung to a temperature above about 550 degrees C is so on d. Alloy contents of Si and Mn tuned that the conversion is practically complete in d. Perlite step expires. Below 550 degrees C, it can be cooled down to 350 degrees C with a minimum of 2 degrees C / s.

Description

-A-

Title of the invention

Process for the production of high-strength weldable reinforcing steel

Field of application of the invention

The invention relates to a method for producing high-strength weldable reinforcing bars in the form of bar steel or wire rod in rod or ring form. The method is particularly suitable for the production of Y / alzdraht in annular collars on high performance Kontidrahtstraßen in which the Y / alzdraht by a rotating Legearm is fanned out in turns on a conveyor belt.

Characteristic of the known technical solutions

In order to reduce the specific use of steel and thus to improve the material economy, the construction industry is interested in constantly increasing the use of high-strength reinforcing steel with yield strengths above 390 U / mm. However, an economical use of these steels is only given if they are available in the entire range of dimensions required and, in addition to the high strength, have universal weldability and good cold-sealability on the same side. The latter requirements are of the so-called. Natural hard steels, the relatively high

1 1 - <- / - η π π. O Γ; '>;'*,'"''

C, Si, Mn and / or, have Cr contents and the kaltv.erformte reinforcing bars, due to the solidification, which occurs in the cold deformation after hot rolling, not met.

It is known to eliminate the present in these steels Kachteile in a steel with G, Si and LIn contents, which ensure a universal weldability, to increase the strength to perform a partial compensation directly from the rolling heat, the near-surface areas through an intensive water cooling is quenched below the martensite point and then tempered by the heat remaining in the core in the course of the subsequent temperature compensation. This so-called thermal hardening is preferably suitable for the production of rod material on chip mill mills. It is not suitable for the production of wire rod on modern high-performance wire lines, in which the wire rod is fanned by a rotating laying arm in turns on a conveyor belt. "Winding and adjusting the thermally bonded wire presents extraordinary difficulties and leads to disasters and disruptions in the production process.

It is w? Eiterhin known that rolled steel with high strength and toughness and excellent weldability and cold formability by so-called. Controlled or thermomechanical rolling can be produced "The essence of controlled rolling is that the rolling process, which is usually between 1100 and 13OO ⁰ G begins and is terminated between 950 and 1100 ⁰ G, is divided into a pre-rolling and finish rolling. After pre-rolling, a rolling break of a few seconds to several minutes is allowed, during which the Yifalzgut cools down to a temperature in the lower Austenitge 'area (below 950 ⁰ G). Only then is the finish rolling with a predetermined degree of deformation, which can be applied in one or more rolling passes * In this way, we obtain a very fine Sekuiidärgefüge ₅ which gives the steel high strength at the same time very good toughness. This procedure can be used at low

carbonized ferritic-berlite Si-Mn structural steels which are additionally micro-alloyed with a few hundredths to tenths of a percent Hb, V, Ti or a combination of these elements, with very good weldability and cold workability

Yield limit values up to about 450 N / mm. However, the method has the disadvantage that an unacceptably high production loss occurs due to the pause for intermediate cooling of the pre-rolled material, unless special locations, eg. B. Parallel roller tables for work roll in heavy plate rolling mills, are present, which allow to take the pre-rolled material for intermediate cooling from the production flow.

Furthermore, it is also known to thermomechanically roll micro-alloyed reinforcing bars. However, because of the associated technical and technological problems, the process has not gained any significance for continuous gauge and wire lines.

Object of the invention

The object of the invention is to eliminate the drawbacks associated with the production of high-strength reinforcing steel in annular coils on high-performance continuous-wire lines, which are associated with thermal consolidation or thermomechanical rolling, and to develop a high-strength reinforcing steel which can be used without derating and high production security on a modern high performance wire line.

.Development of the essence of the invention

The invention has for its object to develop a method that allows high-strength reinforcing steels with yield strengths on a high-performance Kontidrahtstraße with high productivity and high production reliability

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390 H / mm, which, in addition to its high strength, sees at the same time a universal sweat

fitness and good cold workability.

According to the invention this object is achieved in that the wire rod is cooled to a new adjustable on a high-power Kontidrahtstraße time-temperature regime, the chemical composition of the steel is tailored to this treatment, It has been shown that by this treatment a similar effect on the secondary Fige, especially the ferrite grain size and thus the mechanical properties can be achieved, as it sets in the thermomechanical rolling, so as to obtain a steel with high strength and good toughness at the same time.

The most essential features of the invention consist in the following;

The wire rod is cooled very quickly immediately after the hot forming, ie at a cooling rate of at least 200 ° C / s down to a temperature in the range of perlite, preferably below 750 ° 0 ». The further cooling to a temperature above about 550 ⁰ C is tuned to the alloy contents of Si and in particular Mn that the conversion takes place almost completely in the perlite and the formation of bainite and / or martensite is avoided. This is achieved by setting the condition for the cooling rate ν in this temperature range

log ν ^ 0.97 - 1.02 exp - 1 * | 2 - 1.95 exp - ^ Φ- (1)

Si ^d MnT

is complied with. Equation (1) gives ν in ° C / s when the contents of the steel of these elements in mass% are used for Si and Mn. Below 550 ⁰ G, the wire rod is cooled to at least 2 ° C / s down to ca =, 350 G and then arbitrarily up to room temperature. The cooling of the whale wire immediately after hot rolling

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tion into the Bereieh the pearlite can also be performed in 2 stages, so that the cooling immediately after the Warmumforraung at least 200 ° C / s initially only up to a temperature of = 850 ⁰ C, at which the Windungsiegen takes place, carried out is and immediately thereafter with maximum cooling capacity of the system, but at least 5 ° C / s, to a temperature in the range of perlite, preferably below 750 ⁰ C, further cooled. The cooling after the last roll pass up to the temperature of Windungsiegens z. B in one or more stages with pressurized water or another suitable cooling medium, so that the required cooling rate of more than 200 ° C / s is achieved. The further cooling from the temperature of Y / indungslegens into the range of Perlitstufe can, for. B _{0 be carried out} by intensive cooling with forced air, water or an air-water mixture.

The steel to be treated according to the invention has the following alloy contents and combinations:

C: Max. O 30 Si: Max. 1 , 0 Mn: Max. 2 , 0

Rest iron with the usual impurities and may as well be with

max · 0.2 % V and / or max 0.1 % Nb and / or max. 0.2 % Ti

be microalloyed.

To ensure good weldability and cold workability during further processing in construction, the following ranges are preferably selected for the chemical composition:

0.20 - 0.60% Si. "0.50-1.00 % Mn, in the case of a micro-alloy, preferably the following

Alloy contents are used;

0.05-0.12% V or 0.02-0.06 % Nb or 0.05-0.12 % Ti

or a combination of V and Nb within the specified limits,

embodiment

The invention will be explained in more detail using an example. ·

From 4 different microalloyed steels, the chemical composition of which is given in Table 1, 10 mm diameter wire rod was produced.

Table 1: Chemical composition of the investigated steels

0 Dry Si Mn composition S in mass% Ti stole 0.21 0.49 0.84 P 0,020 other V No. 0.21 0.45 0.81 0,015 0.019 0.13 Nb; 0.09 V 1 0.20 0.46 0.77 0,014 0,018 0.09 Nb 2 0.22 0.41 0.92 0,014 0,025 0.04 3 0.016 0.06 4

For the cooling of the 4 steels after the last rolling pass, two different variants were chosen.

Variant 1: uncontrolled cooling in air

Variant 2: (inventive method): accelerated cooling of the wire after the last rolling pass at a rate of 260 ° C / s to 710-740 ⁰ C.

Then controlled cooling at a rate of 3 ° C / s up to 550 ⁰ C and then further cooling at 6 ° C / s up to

300 ⁰ C.

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During the testing of the wire rod, the values compiled in Table 2 were determined.

Table 2: Mechanical properties of the wire rod

Cooling variant 1 ⁰ B 26.5 Cooling variant 2 ⁰ B 28 8th N / mm ² 28.6 ⁶ p N / mm ² 29 0 stole N / mm ² 647 27.2 N / mm ² 682 29 7 No. 4-33 633 29.6 566 682 30 3 1 442 632 559 688 2 4-50 605 594 662 3 4-22 , 558 4

From Table 2 it is apparent that by the treatment according to the invention a wire rod with very high strength

> 550 N / mm '). with good plastic properties

> 28 %) was generated.

Claims (2)

· - 8 Claim for success 1, Method of making high strength weldable reinforcing steels with a yield strength of at least 390 N / n on high-performance Eontidrahtstraßen, characterized in that the wire rod immediately after the. - Hot forming with at least 200 ° C / s to a temperature in the range of perlite, preferably below 750 ⁰ G is cooled, in the subsequent cooling to a temperature = 500 ⁰ C, the velocity ν in ° C / s of the relationship log ν έ 0.97 - 1.02 exp. - 1 * S2 -1.95 exp "- Si Mn and below 550 C with at least 2 ° C / s is cooled to about 35Ο ⁰ C and that the thus treated wire rod consists of a steel, the maximum alloying proportions of 0.30% C, 1.0% Si, 2, 0 % Mh, 0.2 % V, 0.1% Nb and 0.2 % Ti, but preferably 0.18 to 0.26 % C, 0.20 to 0.60% Si, 0.50 to 1 , 00 % Mn and additional microalloy levels of 0.05 to 0.12 % Y or 0.02 to 0.06 % Nb or 0.05 to 0.12 % Ti or a combination of V and Nb within the specified limits can have. 2, Method nach.-point 1, characterized in that the cooling immediately after the hot forming with at least 200 ° C / s initially only up to a temperature of = 85Ο ⁰ C, at which the Windungsiegen occurs, is performed and immediately afterwards with maximum cooling capacity of the plant, but at least at 5 ° C / s, down to a temperature in the range of perlite, preferably below 750 ⁰ G, is cooled *