DE2105218B2 - Manufacture of hot-dip galvanized deep-drawing steel - Google Patents

Description

Lately the use of galvanized sheet steel for vehicle construction has increased. d. H. for the body and the chassis, to prevent corrosion due to the atmospheric Conditions of using salt on the roads to remove ice and the like are severe elevated. This development is based on the corrosion resistance of this galvanized steel is significantly better than that of conventional low-carbon steel. However, it is known that the press molds galvanized this Are there limits to steel? d. Some parts are therefore not producible by compression molding.

Studies of the invention have shown that the limits of the deformability on the continuous Electroplating processes that require rapid cooling after hot dipping power. So in the well-known Armco-Sendzimir process leads with its fast Cooling of the running strip with a temperature of about 460 ^ C on the hot-dip galvanizing stage a quench hardness generally due to supersaturated carbon in the steel, and this Quench hardening leads to a reduction in the mechanical properties of the steel, in particular its deep-drawability. to be worsened.

The invention is therefore based on the object in the production of a hot-dip galvanized steel, the is subjected to severe compression deformation to avoid quench hardening.

The invention is based on a known process (US Pat. No. 3,248,270) for the production of hot-dip galvanized deep-drawing steel, in which the steel, after hot rolling and pickling, is decarburized to less than 0.01% carbon at a temperature of less than 750 ° C. then cold-rolled and annealed at a temperature between the recrystallization temperature and the A ₃ point and finally skin-pass, and it consists in this process on a steel with a carbon content between 0.03 and 0.06 ° η and an oxygen content between more than 0.06 and 0.1% apply.

In the following, the invention will be explained using an example.

Decarburization before cold reduction

Steel making furnace: LD converter.

Chemical composition: unkilled steel.

C 0 04 P 0.010, N 0.0018 «

Mn 0.33. S 0.017, O 0.058 "".

Hot rolling conditions after slab formation:

Final temperature 850 ^J C

Wrapping temperature 595 ° C

Thickness of the band 2.3 mm

Decarburization conditions after pickling:

Heat treatment furnace used Bund annealing furnace

Atmosphere of wet water stagnation

Treatment temperature ... 730 ° C / 18 hours

Carbon content of

Stahls .Γ. 0.002 »..

Cold deformation conditions:

Reduction ratio ... 65.2%
Final thickness. Γ C, S mm

Continuous hot-dip galvanizing process:

Process type used Armco Scndzim
Heat treatment temperature 850 ^ C 1 min.

Hot dip temperature 460 "C

Passage 1.5%

The mechanical properties of the above :;■
th steel are summarized in Table II.

Table II

Final carbon content .... 0.002%

Yield strength 17.3 kg'mm-

Yield point elongation .... 0%

Tensile strength 28.7 kg / miiv-

Total elongation 52.3 "Ό

Hardness. HR-30T 41.8

Mean Lankford value r 1.67

The reason for limiting the carbon content to values between 0.03 and 0.06% for the The method used in the present invention is as follows.

A carbon content of up to 0.03% cannot be achieved with conventional steelmaking processes can be achieved, and steels with a carbon content of 0.06% or more are difficult to achieve can be effectively decarburized. The reason for limiting the oxygen content to values between 0.06 and Ö.1% is due to the fact that an oxygen content of up to 0.06% makes the ferrite grain coarser and that 0.1% or more oxygen is detrimental to the purity of the steel. the There is a correlation between the above-mentioned oxygen content and the decarburization temperature the most important feature of this invention. The drawing shows the results of the above correlation, which was obtained through many experiments. It shows the relationship between the decarburization temperature and the amount of oxygen in the steel which directly affects the ferrite grain. It is it can be seen that the area of uniform grain with an oxygen content of more than 0.06% and a decarburization temperature of less

<f

is lower than 750 ° C. The area of less than 0.05% oxygen and more than 780 ° C is hardly usable, since in this case the grain becomes coarser comes.

A method for producing cold-rolled steel, wherein the steel after hot rolling and pickling bd a temperature of less than 75O ⁰ C to less than 0.01 ^o / o carbon decarburization-annealed and then cold-rolled at a temperature between the recrystallization temperature and the A ₃ point annealed and finally skin-pass is applied to a steel with a carbon content between 0.03 and 0.06% and an oxygen content between more than 0.06 and 0.1%, has already been proposed and is the subject of the Patent application P 21 04 824.8-24, but the steel produced afterwards is not galvanized.

The technical progress associated with the invention lies not only in the information given in the description, achievable mechanical properties, the known method from which the invention is based, is subject to restrictive conditions. Before the glow or the one preceding the glow Cold rolling must not allow the strip to be deformed

ίο subject to the formation of coarse grains, and one is also not free with regard to temperature. The inventive method is free from such temperature restrictions. End temperatures of 850 ° C are permissible and winding temperatures from 595 ° C.

For this ! Sheet drawings

Claims (1)

Table I. Claim: Application of the process for the production of hot-dip galvanized deep-drawing steel, in which the steel 5 after hot rolling and pickling at a temperature of less than 750 ° C to less Decarburization annealed as 0.01% carbon, then cold rolled and at a temperature between the recrystallization temperature and the A _, point is annealed and finally conditioned, on a steel with a carbon content between 0.03 and 0.06% and an oxygen content between greater than 0.06 and 0.1%. 15th