DE19856265A1 - Process for the production of fire-resistant steel sheets - Google Patents

Abstract

Constructional sheet is manufactured from a nickel-free low alloy steel having a low yield strength ratio by hot rolling cast slab to strip and air cooling to the coiling temperature. Production of an up to 15 mm thick sheet from a steel having a yield strength (Re) greater than 235 N/mm<2>, yield strength ratio (Re/Rm) 0.4-0.65, and composition of (by weight) 0.01-0.14% C, 0.20-1.20% Mn, 0.020-0.045% soluble Al, 0.70-0.90% Cr, 0.10-0.25% Mo, 0.01-0.05% V, balance Fe and impurities, comprises hot rolling cast slabs or thin slabs to strip using a starting temperature of 1000-1350 degrees C and a finishing temperature of above 850 degrees C, air cooling to a coiling temperature of 720-780 degrees C, and then cutting up the coiled strip into sheets.

Description

The invention relates to a method for producing fire-resistant steel sheets with a yield strength Re <235 N / mm ² and a yield strength ratio Re / Rm (yield strength R _e : tensile strength R _m ) between 0.4 and 0.6 for use in steel construction .

Fire resistant steels must have high heat resistance have, so in steel construction a reduction of expensive Fire protection measures is made possible. At the same time a fire resistant steel to achieve a good one Deformation behavior a very low yield strength have ratio Re / Rm. This increases the security of the Construction against mechanical failure Burden. The steels to be created according to the invention also have the construction steel for steel design requirements with regard to To meet toughness and processing behavior and increased resistance to atmospheric corrosion To have (weather resistance).

For fire protection of steel structures Steel parts currently z. B. by spray plaster or plates covered. The aim is to extend the duration in the event of a fire Reaching a critical temperature for as long as possible maintain or not reach this temperature at all.  

The critical temperature is reached when the at this temperature measured yield point below 2/3 of the yield point measured at room temperature has sunk. Conventional structural steels have about 350 ° C their critical temperature. Because of the need expensive fire protection measures for conventional structural steels Having to undertake to a considerable extent is one Inexpensive construction work is not guaranteed and a optimal use of space is often difficult.

In order to reduce the fire protection measures to reduce costs in steel structures, a number of suitable fire-resistant steels with yield strengths of at least 270 to 450 N / mm ² and increased heat resistance are known. B. from EP 0 470 055 A2. The critical temperature could be up to max. 600 ° C can be raised. This has already improved fire protection. The improvement in the deformation behavior is very small, however, because the yield ratio of these steels is only 10% lower than that of conventional structural steels with the same yield strength.

The object of the present invention is now based on an inexpensive method of manufacture to propose steels with which fire protection measures by a critical over the state of the art Temperature can be further reduced and the improved ductility due to a low stretch limit ratio of 0.4 to 0.6. Hereby is supposed to be an inexpensive and modern building design high security against mechanical and thermal Construction failure enabled and in parallel increased resistance to atmospheric corrosion be created.  

This object is achieved by a method with the measures of claim 1. A nickel-free steel with the following chemical composition (in mass%) is processed using this process:

0.01 to 0.12% C,
0.20 to 1.00% Mn,
0.020 to 0.045% Al _solvent ,
0.7 to 0.9% Cr,
0.10 to 0.30% Mo,
0.01 to 0.05% V,

Remainder iron with impurities due to melting.

Optionally, one or more of the following elements can also be added to this steel in the stated amounts (in% by mass):

up to 0.30% Si
up to 0.008% N,
up to 0.50% Cu,
up to 0.0040% B,
up to 0.0030% Ca,
up to 0.02% Nb,
up to 0.02% Ti

This steel becomes slabs in free-standing or continuous casting or shed thin slabs. The slabs are made with a Starting temperature in the range from 1000 to 1350 ° C Hot rolled strips. In the case of slab production these are at the hot rolling start temperature heated up. On the other hand, if thin slabs are poured, these can be removed from the pouring heat after cooling to the Hot rolling start temperature immediately afterwards the casting process can be further processed by  Strips are rolled out. The final hot rolling temperature is above 850 ° C, preferably not higher than 900 ° C. The hot-rolled strips with thicknesses up to max. 15 mm are at at a temperature in the range of 700 to 760 ° C. After that, sheets are removed from the strips.

The sheets produced in this way are preferred in Temperature range from 880 to 950 ° C, preferably at 920 ° C, normalized for a maximum of 30 min. The sheets can then also in the temperature range of 400 to 700 ° C.

The inventive method is in the Sheet steel creates a multi-phase structure that predominantly made of ferrite with embedded bainitic / martensitic islands and above also has finely divided carbide deposits. On this structure is based on the high heat resistance and that low yield ratio as a prerequisite for good ductility of the sheets.

In Table 1, the chemical compositions are three inventive fire resistant nickel free steels in Form of 5 and 10 mm thick sheet listed.

The steels were cast into slabs, which were then were heated to 1200 ° C and hot rolled into strip. The Final rolling temperature was 890 ° C, the reel temperature at 740 ° C. After rolling were off the tapes Sheet metal that has been normalized at 920 ° C have been subjected to a holding time of less than 30 minutes.  

Table 2 contains the mechanical properties measured on samples of the sheets from the fire-resistant nickel-free steels of the composition according to Table 1. Characteristic is in particular the significantly higher heat resistance, which is characterized here by the yield strength Re at 600 ° C, which is between 180 and 188 N / mm ² . This corresponds to a yield point reduction compared to room temperature of more than 3/5. This can raise the critical temperature to over 600 ° C and thus significantly reduce the effort required for additional insulation to prevent the steel from heating up in the event of a fire.

It also improves the ductility of the sheets produced according to the invention fire-resistant steels compared to conventional ones Steels clearly. So generated according to the invention Approx. 0.48 to 0.54 sheets. 15 to 20% lower Yield ratio on conventional steels, which have the same high yield strength values.  

Table 1

Table 2

Claims (5)

1. Process for the production of sheet metal with thicknesses up to 15 mm from one of the steel with a yield strength Re <235 N / mm ² and a yield strength ratio Re / Rm between 0.4 and 0.6 for the steel construction, consisting of (in mass %):
0.01 to 0.12% C,
0.20 to 1.00% Mn,
0.020 to 0.045% Al _solvent ,
0.70 to 0.90% Cr,
0.10 to 0.30% Mo,
0.01 to 0.05% V,
Remainder iron and unavoidable impurities, characterized in that the steel cast into slabs or thin slabs is hot-rolled into strips with an initial temperature in the range from 1000 to 1350 ° C at final rolling temperatures above 850 ° C, that the strips are then reeled to a temperature in the range from 700 to Cooled 760 ° C and that the coiled strip is then cut into sheets. 2. The method according to any one of claims 1, characterized in that the steel is additionally alloyed with at least one of the following elements in the specified amounts (in% by mass):
up to 0.30% Si
up to 0.008% N,
up to 0.50% Cu,
up to 0.0040% B,
up to 0.0030% Ca,
up to 0.02% Nb,
up to 0.02% Ti. 3. The method according to claim 1 or 2, characterized in that the sheets at a temperature in the range of 880 ° C normalized up to 950 ° C. 4. The method according to any one of claims 1 to 3, characterized in that the sheets at temperatures in the range of 400 to 700 ° C. 5. The method according to any one of claims 1 to 3, characterized in that the finish rolling temperature in the range of 850 to 900 ° C lies.