DE2056313B2 - Continuous tempering process for cold-rolled, deep-drawable strip - Google Patents

Description

The present invention relates to a continuous tempering process for cold-rolled, deep-drawable strip from a non-killed cast steel, which contains less than 0.08% carbon and less than 0.003% nitrogen in dissolved form, was cold-rolled in the usual way, then to a temperature of 710 to heated 800 ⁰ C and was maintained at this temperature, cooled to a temperature of less than 500 ° C and for at least 10 second: is maintained at a temperature of 300 to 500 ⁰ C, and a '· application of this method.

It is generally known that ks't rolled. deep-drawable strip material has to be produced by batch-wise tempering or tempering in an unrolled state, despite the fact that the productivity in this case is poor. Therefore, much research has been made into producing cold-rolled drawable steel by a continuous tempering process. Such a method is described in German Offenlegungsschrift 1483 017. In this process, the cold-rolled steel strip is first heated above the recrystallization point up to a maximum temperature which is above 600 ° C., preferably around 700 ^° C. This heating takes place as quickly as possible, preferably in less than 20 seconds Edge is then held at this temperature for a period of time which is preferably 20 seconds, in order then to be cooled to an overaging temperature which is lower than 400 ° C. and is kept at this temperature for a period of 10 to 30 minutes. A cooling rate is maintained so that the total cooling phase lasts longer than 20 seconds. The result is a cold-rolled steel strip that is suitable for use and whose carbon content is between 0.05 and 0.07% and the nitrogen content between 0.0015 and 0. (102 "").

The goal of HiTmdung lic.ni is to improve of the continuous system process for cold weather / -tes. ticl / iehfahiyes band / ugrunde.

This means that the crimdunusgemiilV process is verified / calibrated. dal released the assumption of 1'achwell, that the treated steel becomes softer, the lower the speed limit is. the • \ bkühlungsgesch \\ indigkeH flour "aK ^ O μι J -, cc heirägl.

On the basis of the daruestcliicn in the / eichnimuen preferred embodiments, the invention is explained in more detail below, for example.

F i g. Fig. 1 shows a continuous tempering cycle A. compared to box annealing B;

Fig. 2 shows a diagram for a relationship

between the aging index (left abscissa) or the yield point (right abscissa) and the annealing temperature;

F i g. 3 shows a relationship between the aging index and the cooling rate;

F ~ i g. 4 shows a diagram showing the relationship between the aging index (left abscissa) or the yield point (right abscissa) and the post-annealing temperature represents;

F i g. 5 shows a diagram showing the relationship

between the aging index (left abscissa) or the yield point (right abscissa) and the post-annealing time made clear.

The in F i g. Relationships shown in FIGS. 2 through 5 were established using the following Example 1 obtained as steel designated steel 1.

In investigations by the applicant it was found that the lower limit of the annealing temperature is higher than the transformation point A _x and at least 710 in order to increase the carbon content to a value that is necessary to increase the number of crystallization nuclei for dissolved carbon during cooling Should be ^{0 C.} Because the more the amount of saturated carbon increases, the more the precipitation of dissolved carbon is accelerated. The upper limit of the annealing temperature is lower than about 800 ° C because of the aging index, since this aging index is an important property for the press forming of the steel and this property increases rapidly when the steel is heated to a temperature of more than 800 ° C. These relationships are shown in FIG. 2 shown. From Fig. 2 it can be seen that the Allerungsiiulex 1 of steel decreases rapidly at a temperature above about 710 C and

ho quickly at a temperature greater than about SOO C increases, whereas the yield point decreases 2 mil increasing temperature a! '.

It goes without saying that the housing must be limited in some elements in the steel.

f \ s so that you get the desired results using the above (ilühheliaiullung can achieve. The carbon content should be less than or equal to Ο.ΟΝ'Ί, be, gleieh-Luiltiü. what kind of steel it is.

When the content of carbon is more than 0.08%, the yield strength and the aging index of the steel become higher, and accordingly the steel is not suitable for compression molding. The dissolved nitrogen content in boiled steel is off limited to an amount less than or equal to 0.003% for the same reason. For the others in the steel no restriction is required. The process follows a normal ω from the manufacture of the steel to the cold rolling stage

When using the method on a killed steel that contains less than 0.08% carbon and 0.01 to 0.06% dissolved aluminum, the steel is hot-hashed after hot forming at a temperature of more than 630 ^° C. and then cold-rolled. The Haspelung at a temperature of more than 630 ⁰ C is necessary to act to the precipitation of AlN in such a large scale as possible to be ". If a usual low coiling temperature is used, it is impossible to recoverable excellent press formability of the steel · :: "; even if the method according to the invention is used.

There is no limit to the glow time after heating the S'ahl. A glow period. like them at a conventional continuous tempering process used as a horizontal or vertical process is sufficient. There is no limitation on the heating speed. In the inventive Processes have no influence either on the heating rate or the annealing time on the draw or press deformability.

According to the invention, a high cooling rate is used. The faster the cooling off of the The high temperature in the range from 710 to 800 C is carried out to a temperature of less than 500 C, the more the saturated carbon content increases. This relationship is shown in FIG. 3. It can be seen from it that the aging index 1 of the steel increases considerably at a cooling rate of increases more than 50 degrees / sec.

The steel is then kept at a temperature of 300 to 500 ° C. for at least 10 seconds held. In this stage the saturated carbon is precipitated as carbide. It's easy to see that the more the amount of saturated carbon increases with the rapid cooling, the precipitation of the carbide is accelerated all the more. Such a precipitation of carbide has a large one Influence on the mechanical properties of the steel belt. This relationship is shown in FIG. 4 and 5 shown.

From Fig. 4 shows that the holding temperature, ie the post-treatment temperature. has a great influence on allergy index 1 and yield point 2. While the yield strength 2 decreases, the more the annealing post-treatment temperature s> is set, /.eigl the Allenmgsiiulex I a desired value. ie about 4 kg nmr at a temperature between 300 and 5 (K) (. and increases rapidly. For this reason the (iliihnachheliandlunüslemperalur a jf 300 to 500 (') results from I i <·. 5, i -If the age is stable for 10 seconds after a C iKihnachlungshMiiperaliir and then hardly changes. On Sundays, a typical Mitimiiei prefers to be compared to an a / wise aclis. as in dei! ■ 1 >. '. 1 üc / hurries.

After the above post-annealing treatment, the steel is cooled to room temperature and then wound up.

The following examples are intended to explain the invention further.

Example 1 Steel production: LD converter

Table I.

Chemical composition of C. Mn F ' S. Steel blocks (%) Solved A Steels 0.04
0.08 0.31
0.34 0.013
0.013 0.018
0.016 Solved N. traces
traces 1 0. (X "3
0.0015

30th

35

40

45

5 °

Hot rolling conditions

Final rolling temperature 86O ⁰ C

Winding temperature 575 "C

Thickness after deformation 2.8 mm

Thickness, cold rolled 0.8mm

Event conditions

A. Continuous tempering cycle according to the invention

Annealing temperature 75O ⁰ C

Cooling rate 100 degrees / sec

Tempering temperature 400 ° C

Tempering time about 20 seconds

B. usual continuous starting cycle.

C. Standard box annealing, i.e. 700 ° C 6 hours.

Table II
Mechanical properties

I. cycle Stretch train Deh Allergy Steels "'' border strength tion index Λ (kg / mnr) (kgmnr) <%) (kg nmr) B. 22.6 33.1 46.2 4.3 1 C. 26.9 35.2 40.1 6.9 A. 23.3 33.7 46.0 4.9 B. 23.5 34.1 46.2 4.8 C. 29.0 36.9 39.1 7.5 24.1 34.1 45.0 5.3

7-Wcrl

.31 .28, 30 .29 .29, 23

do. From animal table

It is found that all of the materials examined were unsettled steel. , From tier table Il can be seen that the mechanical properties the steels which are treated with the A- / ykltis according to the method according to the invention, are superior to the materials that resound by either the B cycle according to the usual continuous starting times or the ('cycle according to a usual box heating.

Ii cis ρ ι c I 2
Sin h I manufactu im: 1.1) -Kon vert er M eis ρ ic 1 3 Steel manufacture: LI) -K (inverlor

Chemical Mn Ta at k III S. Solved N. Loosened ^{ΛΙ l0} chairs Chemical Mn Table V S. Solved ΛΙ N C. 0.31 0.018 0.0013 Tracks | C. 0.26 0.015 0.012 0.034 lahl 0.04 0.34 Composition ("·») 0.016 0.0015 Lanes 2 0.04 0.31 Composition ('O) 0.017 0.035 0.037 I. 0.08 0.32 P. 0.019 0.0015 Tracks' 5 3 0.05 0.29 P. 0.017 0.048 0.051 2 0.10 0.33 0.013 0.016 0.0033 traces 0.05 0.011 3 0.05 0.29 0.013 0.017 traces 0.048 0.012 4th 0.05 0.011 0.016 5 0.011 0.016

20th

Hot rolling conditions after flat rolling

Deformation temperature ... 870 ^{0 C}

Coiling temperature steels 1, 2, 3

and 4: 58o ° C Steel 5: 68O ⁰ C thickness, cold-rolled 0.8 mm

Continuous tempering conditions 30

according to the inventive method

Annealing temperature 760 "C

Cooling speed 100 degrees / see

Tempering temperature 450 ° C 35

Tempering time about 20 seconds

Hot rolling conditions after flat rolling

Deformation temperature 870 "C

Winding temperature ^{700 ° C}

Thickness after deformation 2.8 mm

Thickness, cold rolled 0.8 mm

Continuous tempering conditions in the process according to the invention

Annealing temperature 75O ⁰ C

Cooling rate 120 degrees / sec

Tempering temperature 470 "C

Tempering time about 20 seconds

Table VI Mechanical properties (thickness 0.8 mm)

Table IV

Mechanical properties of the materials studied

Stretch train Deh Aging awl border strength tion indcx (kg / mm ² ) (kg / mm ² ) (4) (kg mm ² l i 22.9 33.1 46.3 4.1 2 23.6 33.9 46.0 4.5 3 25.6 35.6 44.1 6.9 4th 24.8 35.0 43.5 6.7 5 21.2 34.3 45.5 3.0

40

45

F-Wcrt

1.33 1.31 1.34 1.26 1.31

Stretch train Deh Aging border strength tion index (kgmm ² ) (kg / mm ² ) f%) (kg / mm ² ) 1 24.4 34.7 43.0 4.4 2 22.3 33.5 44.8 3.4 3 21.2 33.1 45.5 3.0

7-Wcrt

1.24 1.37 1.31

From Tables V and VI it can be seen that the mechanical properties of these steels by increasing Solute Al content can be improved.

55

Steels 1 and 2 of Table III are steels which have been used 60 according to the method according to the invention : should be. Steels 3 and 4 are outside: this range. The steel 5 is an Al-killed ihl, who acted according to the method according to the invention.

From Table IV it can be seen that the 65 moderate procedure is very effective for Al-pacified ahl who at the above-mentioned higher temperar was wound up.

Example 4 Steel production: LD converter

Table VII Chemical Composition (%)

stole C. Mn P. S. Solved Al N 4th 0.04 0.26 0.011 0.016 0.037 0.0034

2697

Hot rolling conditions after rolling

Winding temperature

Steels

temper .1 (111 SW) C. SSO C. 875 " C. 845 " C.

\ D ^8th

label le VIII Mechanical properties

760 C 700 C 630 C 560'C

Thickness after deformation 2.6 mm

Thickness, cold rolled 0.8mm

Continuous tempering conditions * according to the method according to the invention

Annealing temperature 760 ⁰ C

Cooling rate 100 degrees / sec

Annealing temperature 450 ⁰ C.

Starting time 20 seconds

Chairs

4-1
4-2
4-3
4-4

SlI ¹ CLk- / UL'- Deh Allci'iinjr-, ureii / e l'cstigkcil tion in <lc \ (ku Trim I Iku iniir'i ("ill lkμ mni'l 23.8 35.4 42.6 4.9 21.6 33.6 45.2 3.3 22.8 33.9 45.8 3.4 27.6 36.9 37.3 6.5

In this example, the influence of the hot rolling conditions, especially the winding temperature, on the mechanical properties of the products examined. From Table VIII it can be seen that the mechanical properties of the * Steel 4-1 worsen that at a low one Temperature than was wound up in the method according to the invention.

1 sheet of drawings

209 546 '!

2697

Claims (2)

Patent claims: 1. Continuous tempering process for cold-rolled, Deep-drawable strip made of a non-calmed cast steel that contains up to 0.08% carbon and up to 0.003% nitrogen in dissolved Contains form, has been cold-rolled in the usual way, then to a temperature of 710 to 800 ° C and held at that temperature to a temperature of less cooled than 500 ° C and for at least 10 seconds at a temperature of 300 to 500 ° C is held, characterized in that the Aufühlgeschwindigkeii is more than 50 degrees / sec. 2. Application of the method according to claim 1 to a killed steel which contains less than 0.0d ° / ₍ carbon and 0.01 to 0.06% dissolved aluminum and which after hot forming at a temperature of more than al <63O ° C was hot-coiled and then cold-rolled.