DE19736509A1 - Titanium-alloyed, isotropic, earing-free, cold rolled strip steel is produced - Google Patents

Abstract

Cold rolled Ti-If strip is produced from a steel in which the C and N are completely combined with Ti by continuously rolling rough rolled strip or thin slab to hot strip at below the Ac3 temperature to 750 deg C and coiling at 750-650 deg C, followed by cold rolling and recrystallization annealing. Cold rolled Ti-If steel strip, with excellent formability and isotropic properties, is produced from a steel of composition (by wt.) \}0.02 % C, \}1.0 % Si, \}1.0 % Mn, \}0.1 % P, \}0.02 % S, \}0.1 % Al, \}0.01 % N, \}0.2 % Ti and balance Fe, in which the C and N contents are completely combined with Ti, by casting to slabs, continuously rolling the rough rolled strip or thin slab to hot strip in a finishing train at below the Ac3 temperature to 750 deg C, followed by coiling at 750-650 deg C, cold rolling with 40-80 % reduction and then recrystallization annealing.

Description

The invention relates to a method for producing a cold-rolled Ti-If Steel strip, such steels and their composition to the state of the Technology belongs.

Cold rolled steel strip is widely used for the production of cold formed products nits used. Depending on the type of forming process, they are different properties (characteristic values) required.

The increasing demands regarding the application and usage s at low production costs increasingly require better me Chanic, especially forming properties. Good formability is ge characterized by the highest possible r-values, which characterize the deep-drawability low Δr-value, high n-values characterizing the stretchability and high, elongation values characterizing the plane strain properties.

It has proven to be advantageous if the forming properties in the different which directions, in particular in the longitudinal, transverse and diagonal directions, are as equal as possible, d. H. are largely isotropic. If this condition for the If the r value applies, this also means that the so-called Δr value is very small, and after the pressing of rotationally symmetrical parts largely freedom from corners is achieved. The advantages of isotropic properties are essentially expressed a uniformity of the material flow and a reduction of the sheet waste out.  

There have also been successful efforts to achieve isotropic egg for a long time properties. Examples of this are steels deformed without tails, drawn drinks kedose (KHS) or "B-factor" from Brockhaus "Der Spiegel", No. 19/1966, p. 125. However, this production route requires a very high degree of cold rolling or even a normalizing glow to set the tip clearance.

In recent times, examples of high strength sheet steel have been used to achieve Tip freedom from DE-PS 38 03 064 and DE 195 47 181 C1 become known. Also The positive effect of the alloy was already mentioned in previous publications elemental niobium (Satoh, S. et al .: Kawasaki, Techn. Rep. 8 (1983) S. 1, steel and egg sen 110 (1990), No. 9, pp. 65-68) and a niobium-titanium alloy (EP 0 108 268) in the case of If steels with regard to a reduction in the Δr value.

However, there was a lack of a concept for cold strip production of an isotropic If steel only alloyed with titanium, which has the following advantages over an alloy with Nb alloy steel.

• - Low alloy costs
• - Low recrystallization temperature

Here, the present invention uses the features specified in claim 1 len. According to the present invention, a low rolling temperature below half A _{r3 is combined} with a certain reel temperature range. Surprisingly, this resulted in properties and features that were previously unknown for Ti-If steel.

The process according to the invention not only allows the production of isotropic steel strips after the hood, but also according to the continuous process as well as the Vered development in the hot-dip process.  

Some examples are intended to illustrate the result of the method according to the invention chen.

Table 1 shows the chemical composition of the steel.

Table 2 shows the manufacturing conditions of the steel strips. You show the inventions combination of properties according to the invention low rolling temperature in combination with a certain reel temperature range.

Table 3 shows the mechanical quality values and the grain size of the steels of 70% cold rolled strip.

In Fig. 1 the tip height is plotted against the degree of cold rolling for the continuously annealed steels and in Fig. 2 that for the annealed steels. The records show that in the case of the continuous annealed as well as the annealed annealed steels at cold rolling grades between approx. 40 and 80% low-strip cold strips were produced. The usual degree of cold rolling of approx. 70% the tip height of all examples

It can also be seen from FIGS. 1 and 2 that a reel temperature which is too high (No. 1) or too low (No. 5 and 6), in deviation from the invention, results in a high degree of trickle. This underlines the requirement of the combination of rolling and coiling temperature according to the invention.

Claims (1)

Process for producing a cold-rolled Ti-If steel strip with excellent formability and isotropic properties from steel with the following composition in percent by weight:
max .: 0.02% C max .: 0.02% S max .: 1.0% Si max .: 0.1% Al max .: 1.0% Mn max .: 0.01% N max .: 0.1% P max .: 0.2% Ti Remainder iron, by hot rolling, cold rolling, and recrystallizing annealing, in which the content of C and N is completely set in Ti, and in which the steel is poured into slabs, which are then rolled out as hot rolled steel strip or as a thin slab in a finishing series be, the rolling temperature in the finished batch below A _r3 to 750 ° C and the reel temperature between 750 to 650 ° C and the steel is cold rolled after hot rolling with a rolling degree of 40 to 80% and then annealed to recrystallize.