RU2152444C1 - Method of manufacture of steel strips - Google Patents

Abstract

FIELD: plastic metal workings; manufacture of thin steel strips used as semi-finished rolled stock for zinc-plating. SUBSTANCE: method may be used for steels containing carbon within 0.004 to 0.05 mass-% and aluminium no more than 0.05 %. Method includes hot rolling at final temperature t₁=760-810 C, reeling at t₂=680-720 C, cold rolling, pickling, recristallization annealing in shielding atmosphere in bell-type furnace in the mode stipulated for low-carbon steel, secondary cold rolling (temper rolling) at light reduction within 3.2 to 29.6% and completing annealing for further zinc-plating. EFFECT: improved mechanical properties of steel sheets pressworkability).

Description

 The invention relates to rolling production and can be used in the manufacture of thin steel strips (rolled) for galvanizing.

 Strip low-carbon steel with a thickness of 0.5 ... 1.5 mm for applying zinc coating is usually made using a technology similar to the production of cold-rolled steel strips: after hot rolling on broadband mills with predetermined modes (values of reduction, temperature of the beginning and end of rolling and winding) the rolled strips enter the cold rolling workshop, where they are preliminarily subjected to sulfuric or hydrochloric acid etching on continuous units, and then cold rolling also with predetermined modes (compression and Pulling). The technology for producing thin steel strips that can be used as a tack for galvanizing is described in sufficient detail, for example, in the reference book edited by V.I. Zyuzin and A.V. Tretyakova "Technology of rolling production", Prince. 2, M., "Metallurgy", 1991, p. 556-595 and 632-664.

 According to modern technology, before the task of strip steel in the hot continuous galvanizing unit (AGNC), it is preliminarily annealed (more precisely, it is subjected to low-temperature tempering) with constant movement through the continuous annealing unit (ANO).

 A known method of producing sheets in which a strip steel of optimal composition is subjected to hot rolling with a total compression of 70%, and then annealed in a reducing or neutral atmosphere (see US Pat. ODA N 3642468, class C 22 C 39/26, C 22 C 39 / 50 dated 02.15.72.) As a result, a product is obtained, although it has a deep drawing, but its quality makes it impossible to use it for galvanizing.

 The closest analogue to the claimed method is a method for the production of strips according to A.S. USSR N 1388122, MKI B 21 B 1/22 dated 10.30.86, publ. in B.I. N 14, 1988.

 This method includes hot rolling, winding, etching of strips, edge trimming, cold rolling and is characterized by the fact that before trimming edges determine the non-flatness of the strip and the degree of its distribution along the width.

 The disadvantage of this method is that the resulting metal has low punchability, as a result of which mechanical properties are unsuitable for further galvanizing.

 The technical task of the invention is to improve the consumer qualities of the metal, namely mechanical properties and stampability. Such requirements apply to the metal sent for galvanizing.

где C - содержание углерода в стали, равное 0,004 - 0,05%.вес.To solve this problem, in a method for the production of steel strips, including hot and cold rolling, winding and etching in the presence of aluminum in the steel no more than 0.05%, hot rolling is carried out at a final temperature t ₁ = 760 ^o C - 810 ^o C, winding strips - at t ₂ = 680 ^o C - 720 ^o C, and after cold rolling, the metal is subjected to recrystallization annealing, and then cold rolling is repeated with the total relative compression determined from the expression:

where C is the carbon content in steel equal to 0.004 - 0.05%. weight.

 Below and above the stated temperature limits, the stated technical task was not achieved, namely, the quality of the steel did not meet the requirements that are necessary for its further galvanization. This also follows from the essence of the solution, which consists, firstly, in optimizing the modes of hot rolling of steel with the specified carbon and aluminum contents (the purpose of the latter is to reduce the tendency of the metal to age, as a result of which on strip steel subjected to deep and complex drawing under stamping, there may be irreparable defects on the surface (the so-called Chernov-Luders lines) and, secondly, in the secondary cold rolling after recrystallization annealing in a limited range of total compression. As a result, "triggered" aging low carbon steel strip immediately before the low-temperature tempering preceding galvanizing operation.

 The mathematical dependence given in the description and in the claims is obtained as a result of processing the experimental data and is empirical.

 As a result of the implementation of the claimed method, the authors obtained steel with high mechanical properties, suitable both for complex hoods, and in full for a very deep (CB and VG categories according to GOST 9045) hoods without the appearance of the aforementioned yield lines (Chernov-Luders), which allows you to use it, for example, for car body parts.

 Experimental verification of the proposed method was performed at OJSC "Magnitogorsk Iron and Steel Works".

 To this end, 08ps low-carbon steel (with a content of C = 0.004-0.05% and Al ≤ 0.05%) was first rolled on a broadband hot rolling mill 1450, after which it was subjected to recrystallization annealing in rolls and secondary cold rolling; the resulting rolled products were sent to ANO and AGNTS (annealing and galvanizing units). In the experiments, the modes of hot rolling (the temperature of its end and winding), as well as the amount of compression during secondary cold rolling, were varied depending on the carbon content in the steel. The test results were evaluated by stampability and mechanical properties of finished galvanized steel.

 The best results (100% of steel withstood a very deep, and about 30% - complex drawing without the appearance of yield lines, and during tensile tests there was practically no yield area on the tensile diagram) were obtained for metal manufactured by the proposed technology. It was noted that the required degree of total reduction during secondary cold rolling should be the greater, the less carbon in the steel, and it is invariant to the aluminum content in the steel.

 A change (compared with the recommended values) of the hot rolling temperatures, as well as the reduction values during secondary cold rolling, led to a deterioration in the properties of galvanized steel (with the same parameters of the metal coating process), which manifested itself in the appearance of the yield area on the tensile diagrams and, ultimately , - to the occurrence of yield lines, as a result of which the yield of steel not only of the CB category (according to GOST 9045), but also of the high-temperature steel, decreased.

 A number of steel strips were also produced for subsequent galvanizing according to the method chosen as the closest analogue (see above). Only 12% of galvanized steel corresponding to the properties of the VG category was managed to be made from the rolled product (the rest is category G according to GOST 9045). Thus, the pilot test confirmed the acceptability of the claimed technical solution for the task and its advantage over the known technology.

 According to the central control laboratory of OJSC Magnitogorsk Iron and Steel Works, the use of the proposed method in the production of rolled steel for galvanizing allows for a 100% yield of galvanized steel of the VG category and obtain up to 30% of sheets of the SV category, which will accordingly increase the profit from the sale of this type of rolled metal.

 Examples of specific performance.

 Example 1

 From steel 08ps with a content of 0.004% carbon and 0.04% aluminum, roll strips 2.6 mm thick were produced on a hot rolling mill.

The temperature of the end of hot rolling t ₁ = 760 ^o C, the temperature of the winding t ₂ = 680 ^o C.

 After cold rolling, the strips etched and wound into coils are subjected to recrystallization annealing in a protective atmosphere in bell furnaces according to the regime for low carbon steel.

до толщины h = 0,9 (1- ε) = 0,9(1- 0,296) = 0,63 мм,
а затем передают на агрегат непрерывного отжига для дальнейшего цинкования.0.9 mm thick annealed strips are cold rolled again with total compression

to a thickness h = 0.9 (1- ε) = 0.9 (1- 0.296) = 0.63 mm,
and then transferred to a continuous annealing unit for further galvanizing.

 Example 2

h=0,9(1-0,19)=0,73 мм.The same with t ₁ = 790 ^o C, t ₂ = 700 ^o C

h = 0.9 (1-0.19) = 0.73 mm.

 Example 3

h=0,9(1-0,032)=0,87 мм.The same at t ₁ = 810 ^o C, t ₂ = 720 ^o C,

h = 0.9 (1-0.032) = 0.87 mm.

Claims (1)

Method for the production of steel strips, including hot and cold rolling, winding and etching, characterized in that when the aluminum content in the steel is not more than 0.05%, hot rolling is carried out at a temperature of rolling end t ₁ = 760 - 810 ^o C, the strip winding is at t ₂ = 680 - 720 ^o C, and after cold rolling, the metal is subjected to recrystallization annealing, and then cold rolling is repeated with the total relative compression determined from the expression:

where C is the carbon content in steel equal to 0.004 - 0.05 wt.%.