CS269682B1 - A method of cooling a belt of heavy duty steel - Google Patents

Abstract

Method of cooling a strip 1.8 | to .0 mm thick after hot rolling from deep-1 drawn steel containing 0.005 to 0.10 wt. % carbon, at least 0.10 £ wt. silicon, 0.10 to 0.60 wt. % manganese, 0.005; to 0.030 wt. phosphorus, 0.001 to 0.025 ¿ wt. sulfur and 0.010 to 0.08 > wt. aluminum from a rolling temperature in the range of 830 to 900 °C to a winding temperature in the range of 500 to 600 °C, which consists in cooling the strip first with water at a rate of 30 to 80 °C.s- for 0.3 to 2.5 s, then with air for 2 to 10 « and finally with water at a rate of 40 to 7C °C.s- for 1 to 8 3. The advantage of this procedure is that this steel with a defined chemical composition ensures reduced microhardness and hardness of the structure, and thus also reduced strength properties and improved cold formability. The possibility of using sheets produced in this way for cold pressing for more demanding stampings of body parts and other stampings is expanded.

Description

The invention relates to a process for cooling a strip after hot rolling of deep-drawn steel, which is used for further processing in cold rolling mills.

It is now known that deep-drawn steel with a maximum carbon content of 0.10 wt.% Is uniformly cooled in the run-off section of the hot broadband line at a rate of 30 to 60 ^% Cs 1, depending on the strip thickness. The resulting strength properties, i.e. after processing in a cold rolling mill, reach values depending mainly on the carbon content in the melt analysis, while the morphology of the structure can be practically the same. As a rule, a rolling temperature in the range of 830 to 900 ° C and a winding temperature in the range of 500 to 600 ° C are used.

The disadvantage of this method of cooling is that the substructure of the substructure is not optimally achieved in terms of obtaining minimum strength properties, in particular the yield strength after cold rolling.

This disadvantage is eliminated by the method of cooling the 1.8 to 4.0 mm thick strip after hot rolling from deep-drawn steel with a content of 0.005 to 0.10 wt.%, Carbon, maximum 0.10 wt.%, Silicon, 0.10 to 0.60%. of manganese, 0.005 to 0.030% by weight of phosphorus, 0.001 to 0.025% by weight of sulfur and 0.010 to 0.08% by weight of aluminum, the essence of which consists in that such steel is rolled into a strip of thickness up to 4.0 mm at Finishing rolling temperature of 830-900 ° C and the run-out cooling section of the hot wide-route cooled in three stages according to the hírúbky the strip, so that, in the first stage is cooled dou at 30 to 80 ° C ^- ^ for 0, 3 to 2,5 s, ▼ second stage ea is cooled by air for 2 to 10 s and in the third stage it is cooled by water at a rate of 40 to 70 ° Cs ^-1 for 1 to 8 s, reaching a winding temperature of maximum 600 ° C.

The strip thus cooled is used for further processing in a cold rolling mill. The advantage of the invention is that this steel with a defined chemical composition ensures a destroyed, microhardness and hardness of the structure, and thus reduced strength properties and improved cold formability. Improved formability expands the possibility of using cold-formed sheets produced in this way for more demanding moldings of body parts and other moldings. It makes it possible to achieve guaranteed mechanical properties with such production certainty that there is practically no reclassification of sheets at a qualitatively lower quality level. The economic advantage of the new method of cooling the strip after hot rolling according to the invention is therefore that the occurrence of unsatisfactory mechanical properties in the produced deep-drawn steel is substantially reduced, and thus the need for reclassification to lower quality after final cold rolling is reduced. This will reduce the loss due to the lower price of reclassified quality sheets.

The following are two examples of a method of cooling a deep-drawn steel strip according to the invention.

Example 1

Steel containing 0,05% by weight of carbon, 0,28% by weight of manganese, 0,012% by weight of phosphorus, 0,014% by weight, sulfur and 0,032% by weight of aluminum, rolled to a thickness of 2,2 mm at a rolling temperature of 854 ° It was cooled in a three-stage manner, first with water at a rate of 80 ^° C for 1 hour for 0.8 b, then with air for 5 seconds and finally with water at a rate of 45 ° C for 3.3 s, whereby a winding winding was achieved. temperature 560 ° C. After cold rolling to a depth of 0.7 nm, recrystallization annealing and strip smoothing, the following mechanical properties were achieved: yield strength 189 MPa, strength 321 MPa and ductility Aqq. 36.4%.

Example 2

Steel containing 0.01% by weight of carbon, 0.25% by weight of manganese, 0.013% by weight of phosphorus, 0.007% by weight of sulfur and 0.027% by weight of aluminum, rolled to a thickness of 3 mm at a rolling temperature of 861 ° C , was cooled in a three-stage process, first with water at a rate of 65 ° Cs -1 for 1.2 s, then with air for 6 s and finally with water at a rate of 40 ° Cs ^-1 for 4.0 s, reaching a winding temperature of 556 ° C. After cold rolling to a depth of 1.5 mm, recrystallization annealing and strip smoothing, the following mechanical properties were achieved: slip limit 171 MPa, strength * 308 MPa and elongation Α $ θ 42.5

Claims (1)

OBJECT OF THE INVENTION A method of cooling a strip 1.8 to 4.0 mm thick after hot rolling from deep-drawn steel b containing 0.005 to 0.10% by weight, carbon, maximum 0.10% by weight, silicon, 0.10 to 0.60% by weight, manganese, 0.005 to 0.030 wt.%, phosphorus, 0.001 to 0.025 wt.%, sulfur and 0.010 to 0.08 wt.%, aluminum from a rolling temperature in the range of 8.30 to 900 ° C to a winding temperature in the range of 500 to 600 ° C, characterized in that that the strip is cooled first with water rýchloetou 30-80 θΟ.β "· ¹ is approximately 0.3 to 2.5 seconds, then air drying for 2 to 10, the water passes at a rate of 40 to 70 ⁰ C ^- ^ for 1 to 8 3.