RU2414973C1 - Method of producing cold-rolled automobile sheet - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention aims at increasing quality of sheets intended for producing automotive face parts. Proposed method comprises cold rolling at reversing or continuous mills, strip coil annealing and temper rolling. Cold rolling of strips with thickness h-0.5…2.0 mm and width of 1.0…1.65 m at reversing mill is carried out at grain-oriented rolls with microrelief of the final stand: Ra=3.2…3.7 mcm and Pc=70…80 units/cm for first 70 km of strip length after roll changing. Note here that, at h=0.5…0.7 mm, specific rolling tension T_sp is taken to equal 55…46 N/mm², while at h=0.8…1.0 mm, T_sp =46…37 N/mm², and, at h=1.1…2.0 mm, T_sp =35…29 N/mm², while additional T_sp for h=0.5 mm is set to equal 70 N/mm², for h=0.6…0.8 mm T_sp = 60 N/mm², for rest h, T_sp = 50 N/mm². Cold rolling at continuous mill is carried out in grain-oriented rolls of final stand with microrelief: Ra=3.2…3.7 mcm and Pc=70...80 units/cm in first 1000 t after roll changing, tension T at downcoilers of this mill at h=0.5… 1.3 mm is 1.2…1.6 times higher with increase in h, while for h= 1.4…2.0 mm, T increases with increase in h equal to 1.2…1.8 times for all widths of the strip. Note here that, after annealing, wet temper rolling is carried out at oriented rolls with Ra=2.9…3.5 mcm and Pc = 70…90 units/cm with consumption of temper rolling fluid varying from 40% to 60%, at concentration of said fluid of 3-5% and temperature of 40…55°C.

EFFECT: production of required sheet micro geometry.

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Description

The invention relates to the processing of metals by pressure and can be used in the technology for the production of cold rolled sheet steel, mainly for the front parts of a car.

The production technology of such steel is described in sufficient detail, for example, in the book by P.I. Polukhina et al. “Rolling production”. M .: Metallurgy, 1982, p. 511-535. The rolling parameters of such steel depend on the required category of steel drawing, as well as on its range (in particular, on the thickness of the strips).

A known method of cold rolling sheet steel, including transshipment of mill working rolls for wear, rolling and tempering of strips with rollers with a given microgeometry of their barrels, in which, when producing strip steel with a glossy surface, its rolling starts after 300 ... 310 tons of metal with non-gloss surface on new rolls with the height of the microroughness of their barrels Ra = 3.0 ... 3.5 μm, and the training of rolled metal is carried out on polished rolls with Ra≤1 μm. However, this method does not provide the specified microgeometry of cold-rolled sheets (RF Patent No. 2334569, B21B 1/28).

The closest analogue to the claimed object is a method for the production of sheet steel for flat enameled products, including cold rolling a strip billet of a given thickness, annealing roll strips and tempering annealed steel (RF Patent No. 2340414, B21B 1/28).

However, this method does not provide high-quality cold-rolled automotive sheet.

An object of the present invention is to provide a cold rolled automotive sheet with a high quality surface.

To solve this problem, in the proposed method for the production of cold-rolled automotive sheet, which includes cold rolling on reversible or continuous mills, annealing of rolled strips and their training, in contrast to the closest analogue, cold rolling on a reversing mill of strips with a thickness of h = 0.5 ... 2.0 mm with a width of 1.0 ... 1.65 m is carried out on textured rolls of the last stand with a microrelief: Ra = 3.2 ... 3.7 μm and Pc = 70 ... 80 units / cm for the first 70 km of strip length after transshipment, while when h = 0.5 ... 0.7 mm, the specific tension T _beats during rolling is taken equal to 55 ... 46 N / mm ² , with h = 0.8 ... 1.0 mm - T _beats = 46 ... 37 N / mm ² and with h = 1.1 ... 2.0 mm - T _beats = 35 ... 29 N / mm ² , and additional T _beats for h = 0.5 mm are set to 70 N / mm ² , for h = 0.6 ... 0.8 mm - 60 N / mm ² , for the rest h - 50 N / mm ² , and cold rolling in a continuous mill is carried out on textured rolls of the last stand with a microrelief: Ra = 3.2 ... 3.7 μm and Pc = 70 ... 80 units / cm in the first 1000 tons after transshipment, the tension T on the winder of this mill at h = 0 , 5 ... 1.3 mm increase 1.2 ... 1.6 times with increasing h, and for h = 1.4 ... 2.0 mm - T increase with increasing h 1.2 ... 1.8 times for all bandwidths, in addition, “wet” training after annealing performed on a textured rolls with Ra = 2.9 ... 3.5 m, and Pc = 70 ... 90 pcs. / cm at a flow rate of liquid to a skinpass 40 ... 60% its concentration of 3-5% and a temperature of 40 ... 55 ° C.

The essence of the proposed technical solution lies in the development of an integrated technology for the production of high-quality cold-rolled automotive sheet. Indeed, one of the most important requirements for this type of rolling products is the cleanliness of the surface of the sheets, more precisely, the state of its microgeometry, determined by the indicator Ra.

The necessary microgeometry of the sheet surface is provided, first of all, by a certain microrelief of the rolls of the last mill stand and a given value of specific tension during rolling (on a reversing mill) or by tension on a drum of a continuous mill winder. In addition, the rolling of a certain amount of metal in both mills is carried out on the reloaded rolls of the last stand. Since sheet steel training is the final operation of its production, the surface condition of the roll barrels of the temper mill should correspond to the required microgeometry of the sheet surface.

This technology can be implemented both on a two-stand reversing mill and on a continuous (for example, 4-stand) broadband mill.

An experimental verification of the proposed technical solution was carried out on the respective cold rolling mills of OJSC Magnitogorsk Iron and Steel Works. The results of the experiments were evaluated by microgeometry of sheet steel after its training in accordance with the requirements of consumers of a sheet (AvtoVAZ requirements Ra = 0.8 ... 1.2 μm, the number of Ps peaks> 50 per 1 cm of length).

For this purpose, when rolling on both mills, rolls of the last stands with different microreliefs of the surface of their barrels were used, a certain amount of metal was rolled only after transshipment of the last stands, different values of specific tension were used, both “dry” and “wet” training were used, the latter varied the parameters of the training fluid.

The best results (yield of a high-quality automotive sheet with regulated roughness of up to 98.7%, including 60.5% with group I of the surface finish) were obtained using the inventive technology. Deviations from its recommended parameters worsened the achieved indicators.

So, the use of rolls of the last stand with another microrelief (Ra ≠ 3.2 ... 3.7 μm and Pc ≠ 70 ... 80 units / cm) did not allow to obtain an autolist of the required microgeometry. A similar result was the increase in the total length of the strips rolled after transshipment of the last mill stands. The decrease in T _beats during rolling on a reversing mill (less than 46, 37 and 29 N / mm ² for strips of corresponding thicknesses - see above) leads to loose winding and, as a result, to defects “scratch”, “telescope”; an increase in specific tensions leads to the formation of a “strip-slip line” defect, i.e. reduced quality of the surface of the sheets.

Also reduced the yield of the required microgeometry and training in rolls with Ra ≠ 2.9 ... 3.5 microns and Pc ≠ 70 ... 90 units / cm. During “dry” training, “imprints from dirt” appeared on the strip surface, and the use of “wet” training with training fluid parameters different from the recommended ones led to other surface defects, for example, “corrosion”, which negatively affects the surface quality of the sheets.

The known technology, chosen as the closest analogue (see above), was not used in experiments due to its obviously unsuitability for solving the task. Thus, a pilot test confirmed the acceptability of the technical solution found to achieve the goal and its advantage over the known technology.

Feasibility studies have shown that the implementation of the present invention in OJSC MMK will increase the output of a car sheet from 0.5 to 2.0 mm thick with regulated microgeometry by at least 10%, and the output of an autosheet of the 1st surface finishing group by almost 7 % with a corresponding increase in profits from the sale of cold-rolled automotive sheet with a high-quality surface.

Case Studies

1. A cold-rolled sheet with h = 1.2 mm and B = 1.3 m is rolled on a two-stand reversing mill. The rolls of the last rolling mill stand are textured with a microrelief: Ra (average microroughness height) = 3.4 microns; Pc (the number of peaks of the relief projections) = 75 per 1 cm.

Rolling is carried out for the first 70 km of strip length after transshipment (after transshipment of the work rolls of the last rolling stand before operating time of 70 km along the total length of the strip on the rolls).

The value of the specific tension is 32 N / mm ² , the additional specific tension is 50 N / mm ² .

The annealed metal is trained on textured rolls with Ra = 3.3 μm and Pc = 85 units / cm using a training fluid up to 50% at a concentration of 4% and a temperature of 50 ° C.

Microgeometry of sheets after training: Ra = 1.0 ... 1.1 μm at Ps = 70 per 1 cm.

2. A cold-rolled sheet with h = 0.8 mm and B = 1.4 m is rolled on a two-stand reversing mill. The rolls of the last rolling mill stand are textured with a microrelief: Ra (average microroughness height) = 3.5 microns; Pc (the number of peaks of the relief projections) = 72 per 1 cm.

Rolling is carried out after transshipment of the work rolls of the last rolling stand to an operating time of 50 km along the total length of the strips on the rolls.

The specific tension is -40 N / mm ² , the additional specific tension is 60 N / mm ² .

Annealed metal is trained on textured rolls with Ra = 2.9 μm and Pc = 80 units / cm using a training fluid up to 50% at a concentration of 4% and a temperature of 50 ° C.

Microgeometry of sheets after training: Ra = 0.9 ... 1.1 μm at Ps = 60 per 1 cm.

3. A strip with a thickness of h = 1.4-1.6 mm and a width of 1400 mm is rolled on a continuous broadband mill. The rolls of the last rolling mill stand are textured with a microrelief: Ra (average height of microroughness) = 3.5 microns; Pc (the number of peaks of the relief projections) = 75 per 1 cm.

Rolling is carried out in the first 1000 tons after transshipment (after transshipment of the work rolls of the last rolling roll to a total operating time of 1000 tons on rolls). The tension on the winder of this mill for the assortment of 1.4 × 1400 mm is T = 4.7 tf, and for the assortment of 1.6 × 1400 mm - T = 5.9 tf, i.e. increases 5.9: 4.7≅1.3 times. The annealed metal is trained on textured rolls with Ra = 2.9 μm and Pc = 60 units / cm using a training fluid up to 50% at a concentration of 4% and a temperature of 47 ° C.

Microgeometry of sheets after training: Ra = 0.8-0.9 μm at Ps = 60 per 1 cm.

4. On a continuous broadband mill, a strip is rolled with a thickness of h = 0.7-1.2 mm and a width of 1400 mm. The rolls of the last rolling mill stand are textured with a microrelief: Ra (average microroughness height) = 3.6 microns; Pc (the number of peaks of the relief projections) = 70 per 1 cm. Rolling is carried out after transshipment of the work rolls of the last rolling roll to a total operating time of 500 tons on the rolls.

The tension on the winder of this mill for the assortment of 0.7 × 1400 mm is T = 3.0 tf, and for the assortment of 1.2 × 1400 mm - T = 4.1 tf, i.e. increases by 4.1: 3.0-1.4 times. The annealed metal is trained on textured rolls with Ra 3.2 μm and Pc = 80 units / cm using training fluid up to 50% at a concentration of 4% and a temperature of 47 ° C.

Microgeometry of sheets after training: Ra = 0.9-1.2 μm at Ps = 65 per 1 cm.

Claims (1)

A method of manufacturing a cold-rolled automotive sheet, including cold rolling on a reversible or continuous mill, annealing roll strips and their training, characterized in that rolling on a reversing mill strips with a thickness of h = 0.5 ... 2.0 mm, a width of 1.0 ... 1, 65 m is carried out on textured rolls of the last stand with a microrelief Ra = 3.2 ... 3.7 μm and Pc = 70 ... 80 units / cm for the first 70 km of strip length after transshipment, with a specific tension of T _beats during rolling, for strips of thickness h = 0.5 ... 0.7 mm component 55 ... 46 N / mm ² , thickness h = 0,8 ... 1,0 mm T _beats - 46 ... 37 N / mm ² and thickness h = 1,1 ... 2.0 mm T _beats - 35 ... 29 N / mm ² , and additional specific tension for winding strips with a thickness h = 0.5 mm, equal to 70 N / mm ² , with a thickness h = 0.6 ... 0.8 mm - 60 N / mm ² , for the remaining strips - 50 N / mm ² , and rolling in a continuous mill of 1000 tons of metal after transshipment is carried out on textured rolls of the last stand with a microrelief Ra = 3.2 ... 3.7 μm and Pc = 70 ... 80 u / cm, with an increase in tension T on the winder of this mill with increasing thickness for strips with a thickness h = 0.5 ... 1.3 mm 1.2, ... 1.6 times, for strips with a thickness h = 1.4 ... 2, 0 mm 1.2 ... 1.8 times for all strip widths, and after annealing, wet dressing is carried out textured rolls with Ra = 2.9 ... 3.5 microns and Pc = 70 ... 90 units / cm at a flow rate of training fluid up to 40 ... 60%, its concentration of 3-5% and a temperature of 40 ... 55 ° C.