Method of production of a sheet steel

FIELD: metallurgy, production of rolled steel.

SUBSTANCE: the invention is pertaining to the field of metallurgy, production of rolled steel, in particular, to methods of production of cold rolled steel sheets with the high drawing properties for a cold forming of details of cars bodies. The technical problem being solved by the invention consists in improvement of the quality of a cold rolled sheet steel. The method provides for hot rolling of continuously-cast low-carbon steel slabs, etching treatment, multirun cold rolling with total relative reduction of no less than 75 %, a recrystallization annealing in the following mode: a heating at an average speed of 70-80°C/h up to temperature of 490-510°C, a repeated heating at an average speed of 3-4 °C/h up to the intermediate temperatures of 540-560 °C/h and the final heating at an average speed of 50 - 55°C/h up to the annealing temperature of 700-720 °C, at which the steel rolls are kept for 12-18 h. Upon termination of keeping the rolls at the annealing temperature they are cooled at the rate of 19-21 °C/h up to the temperatures not exceeding 690 °C. At that the continuously cast low-carbon steel slabs have the following chemical composition (in mass %): 0.025-0.050 - carbon, 0.003-0.010 - silicon, 0.12-0.19 - manganese, 0.02-0.05 - aluminum, no more than 0,011 - nitrogen, the rest - iron and impurities.

EFFECT: the invention ensures improvement of the quality of a cold rolled sheet steel.

3 cl, 5 ex, 3 tbl

 

The invention relates to metallurgy, and more specifically to a technology of manufacturing cold-rolled steel sheet with high exhaust properties for cold forming parts of passenger cars.

Technological properties of the finished cold-rolled sheet, i.e. the ability to take the desired shape in the drawing, without losing stability in stamps, as well as the surface condition of the facial details depend on the extent of segregation and segregation of chemical elements, gas saturation, the content of non-metallic inclusions and captivity. Therefore, in the automotive industry use cold-rolled sheet steel with mechanical properties matching category VOSV (GOST 9045) and 1-th surface finish group. In addition to the strength and plastic properties of cold rolled sheet steel should have high values of normal plastic anisotropy R and the rate of strain hardening n.

A method of producing a cold-rolled sheet steel, stabilized aluminum. The method includes continuous casting in the steel slabs the following chemical composition, wt.%:

Carbon is not more than 0.10

Manganese is not more than 0.60

Nitrogen 0,0030-0,0100

Phosphorus not more than 0,008

Sulfur is not more than 0,008

Iron rest

The slab is heated to a temperature of 950-1200°, laminates when temperature is round above point AG 3and bind the strips into rolls at a temperature not exceeding 600° C. the hot-Rolled strip is subjected to etching and rolled on the cold rolling mill with reduction of 70-80%. The cold rolled strip is heated with an average speed of not more than 100° C/h to a temperature of 800° in bell-type furnaces and produce their annealing. Annealed strip trained [1].

The disadvantages of this method are low stanoevska cold rolled sheets, in the presence on their surface of small captive. This degrades the quality of cold rolled sheet steel.

There is also known a method of manufacturing cold-rolled steel sheet, in which a steel slab with a carbon content 0,008% by weight is heated and rolled in continuous wide-strip hot rolling mill in the band. Hot rolled strip after etching is subjected to cold rolling to a thickness of 0.7-0.8 mm, and Then cold-rolled strip is annealed in the passing of the furnace at a temperature of 700-900° C for 3-5 min [2].

The disadvantages of this method are that because of non-optimal parameters of the microstructure and of the presence of non-metallic inclusions ready-rolled sheets are of low quality.

The closest in technical essence and the achieved results of the present invention is a method of production of steel sheet for cold forming (the ar list), including smelting and continuous casting into slabs brand 08U the following chemical composition, wt.%:

Carbon is not more than 0.07

Manganese 0,25-0,35

Silicon 0,01

Phosphorus not more than 0,020

Sulfur does not exceed 0.025

Nickel is not more than 0,06

Copper not more than 0,06

Chromium not more than 0,03

Iron rest

Continuously cast slab is subjected to hot rolling in the band. Hot-rolled strip is subjected to etching and multi-pass cold rolling to the desired thickness. Then, the cold rolled strip in coils annealed at a temperature of 680-690° C for 30-40 h and trained with compression 1.0 to 1.5% [3] is a prototype.

The disadvantages of this method are as follows. Nitrogen and oxygen to metal from the atmosphere and from the tuyeres steel form in her nonmetallic inclusions type: FeO, SiO2, MnO, 2FeO· SiO2, 2MnO· SiO2, F· Al2About3, IGO· Al2About3, 3l2About3·2SiO2, MPO· Al2O3·2SiO2and other Nonmetallic inclusions are the cause of education captivity, tears, delamination, tears, holes and other defects of cold-rolled metal. In addition, they reduce its stampability. All this leads to lower quality cold-rolled steel sheet.

The technical problem solved by the invention is to improve the quality of the hole is Nakatani sheet steel.

The specified technical task is solved in that in the known method of manufacturing cold-rolled steel sheet for deep drawing, including hot rolling continuously cast slab of low carbon steel, etching, multi-pass cold rolling, recrystallization annealing of coils in the cover furnace with heating for several stages, aging, cooling and training, according to the proposed invention multi-pass cold rolling is conducted with total relative compression of not less than 75%, and recrystallization annealing is performed in the mode: heating at an average speed of 70-80° C/h to a temperature of 490-510° With repeated heating at an average speed of 3-4° C/h to the intermediate temperature 540-560° and a final heating at an average speed of 50-55°/h before annealing temperature 700-720° in which the rolls are incubated for 12-18 h after exposure at a temperature of annealing the coils are cooled with speed 19-21° C/h to a temperature of not higher than 690° C. in Addition, the continuously cast slab of low carbon steel has the following chemical composition, wt.%:

Carbon 0,025-0,050

Silicon 0.003 to 0.01 to

Manganese 0,12-0,19

Aluminum 0,02-0,05

Nitrogen not more than 0,011

Iron and impurities Else

The invention consists in the following. The presence of non-metallic inclusions and high witin the properties of cold-rolled steel sheet for forming complex-shaped products are laid on the stages of smelting and casting. In the process of continuous casting of steel the proposed structure is formed cast slab with a minimum porosity of the carbon, and the lack of segregation of non-metallic inclusions in the axial portion of the ingot. This allows to form in the hot process, cold rolling and recrystallization annealing uniform microstructure, in which the ferritic matrix cleared of carbides and inclusions dispersed throughout the volume of the metal.

During cold rolling of hot-rolled strips with a compression of not less than 75% achieved the desired thickness of the strips and the degree of comminution of the deformed ferrite grains, as well as non-metallic inclusions in steel. In the recrystallization annealing of cold rolled strips with a degree of hardening of not less than 75% mode: heating at an average speed of 70-80° C/h to a temperature of 490-510° With repeated heating at an average speed of 3-4° C/h to the intermediate temperature 540-560° and a final heating at an average speed of 50-55°/h before annealing temperature 700-720° in which the rolls are incubated for 12-18 h, formed a homogeneous microstructure of ferrite with a score of grain 6-7 and a minimum allocation of structurally free cementite.

For the first two stages of heating initially with a speed of 70-80°/h to 490-510° and then, with a speed of 3-4°/h to 540-560° is provided in Surat steel her microstruture prepared for recrystallization, roll evenly heated throughout the section. Therefore, when the final heating stage with an average speed of 50-55° C/h up to 700-720° and exposure within 12-18 h complete and uniform recrystallization of deformed metal, grain microstructure acquire radiovideo form. Particles A1N and fine non-metallic inclusions exert an inhibitory effect on the recrystallization grains after annealing. The structure of the steel after annealing predominant crystallographic orientation (111), the most favorable for cold forming. Slow cooling speed 19-21°/h from the annealing temperature to a temperature not higher than 690° stabilizes the microstructure of the steel of the proposed structure, prevents further aging cold rolled sheets and degradation of their mechanical properties.

It is found experimentally that when the total relative compression in the process of cold rolling is less than 75% not achieved the necessary degree of grinding of non-metallic inclusions in steel, which degrades the quality of the finished sheets.

The heating in the first stage with a speed of at least 70° C/h to a temperature below 490° inappropriate, since it does not improve the quality of sheet steel, but only prolongs the process of annealing. Increase the speed of heating is more than 80° C and temperatures above 510° increases the unevenness of the temperature field of the coil, increasing the weight load on the external coils and their deformation, which degrades the quality of the finished product.

Re-heating with a rate of less than 3° C/h to a temperature below 540° lengthens the annealing process and degrades the uniformity of heating of the roll when it is heated to the annealing temperature. The increasing heating rate of more than 4° and With temperatures above 560° disturbs the uniformity of crystallization of the individual turns of the coil and quality sheet steel.

The decrease in the heating rate in the third stage, less than 50°/h unnecessarily lengthens the cycle annealing. Increase this speed over 55°/h contributes to the formation of non-uniform microstructure and properties along the length of the strip.

Decrease annealing temperature below 700° as reducing the dwell time at this temperature for less than 12 hours does not provide the maximum allowable stanoevska for steel of this composition. Increasing the annealing temperature above 720° and the exposure time of more than 18 h unreasonably prolong annealing and provoke welding of coils turns.

Slow cooling at speeds below 19° S/h does not improve the quality of cold rolled steel, and only lengthens the process. Increasing the cooling rate in excess of 21° C/h, as well as increasing the temperature so it ends above 690° To promote the formation of non-uniform microstructure and properties along the length of cold rolled strips, which is unacceptable.

Carbon steel is the principal hardening element. When the carbon content is less than 0.025% strength properties of steel sheet below an acceptable level. The increase in the concentration of carbon in excess 0,050% reduces stampability sheet steel, which is unacceptable.

Silicon rascism and hardens steel. The reduction in silicon content less than 0,003% increases the oxidation of steel, deteriorate its mechanical properties. The increase in the content of this element more than 0,010% leads to a loss of plasticity, increasing the number of nonmetallic inclusions.

Manganese has a strengthening, rascislau and desulphurise action. When the manganese content less than 0.12% strength properties below an acceptable level, and the increase of its contents exceed 0.19% deteriorates the ductility ratio of plastic anisotropy and stampability steel.

Aluminum is introduced to modify steels and fix nitrogen in the nitride. The nitrides of aluminum reinforce cold rolled steel and are instrumental in obtaining the structure Radevich grains of ferrite and favorable for extraction operations crystallographic orientation. By reducing the aluminum content less than 0.02%, the steel becomes prone to the degradation of its mechanical the TV (aging). Increasing the aluminum content exceeds 0.05% promotes graphitization of steel, the deterioration of its mechanical properties below an acceptable level.

Nitrogen as an impurity element hardens steel, but if the number exceeds 0,011%, the steel becomes prone to deformation, aging, deteriorating exhaust properties and quality of cold rolled sheets.

Examples of implementation of the method

In a basic oxygen furnace with a capacity of 350 tons smelted low-carbon steel of the following composition, wt.%:

SiMnAlNFe+impurities
0,0380,0070,160,040,006rest

Melted steel is poured on the machine continuous casting into slabs section 250× 1280 mm weight 28 tons Casting lead with a speed of 0.5 m/min at a temperature of cast metal 1535° C.

Cast slabs after cooling load in a gas oven with a walking beam furnace, heated to a temperature of austenitization 1200° C.

The slabs successively issued on an oven conveyor continuous broadband mill 2000 and compresses in the burst section h mm. Then the roll set in a continuous 7-stand group and rolled to the final thickness 3, mm. Temperature strips on the output from the last stand finishing mill support equal 860° C. the hot-Rolled strip on the delivery table cool water to a temperature of 630° and wound into rolls.

Chilled rolls is subjected to acid etching in a continuous pickling line.

Then the pickled strip in coils rolled in 5-stand mill four-high cold rolling with a thickness of 3.2 mm to a thickness of 0.7 mm with a total relative compression ε ∑ equal

The cold rolled strip in coils loaded into a bell-type gas odnostolpnoy furnace with hydrogen protective atmosphere and heated in the first stage with an average speed of V1=75° C/h to a temperature T1=500° C. Upon reaching this temperature reheat coils at an average speed of V2=3,5° C/h to the intermediate temperature T2=550° C. Final heating of the coils are at an average speed of V3=53°/h before annealing temperature Tabout=710° C. When the annealing temperature Tabout=710° rolls survive for the time τ =15 o'clock after a specified time the gas to reduce and produce slow cooling coils with velocity Vthe OHL=20° C/h to a temperature Tthe OHL=680° C. then rolls on laidout using a cooling cap to a temperature of unpacking 80° C. Annealed strips are trained on a single-stand mill quarto. Training lead by compression of 1.0%. After that make testing of mechanical properties of cold rolled sheet steel and assess the quality of the surface.

Table 1
The compositions of low-carbon steels
No. of trainsThe content of chemical elements, wt.%
 SiMnAlNFe+impurities
10,0240,0020,110,010,007Rest
20,0250,0030,120,020,008--
30,0380,0070,160,040,009--
40,0500,0100,190,050,011--
5to 0.0600,0120,200,060,012--
6 steel (08U)0,0700,0100,300,06the e DHL. --

From table 1-3, it follows that in case of realization of the proposed method (options No. 2-4) achieves the improvement of the qualitative characteristics and increasing the yield of the sheet steel of the highest quality. With exorbitant values of the declared options (options 1 and 5) and using the prototype method (option 6) qualitative characteristics and the output sheet steel of the highest quality are reduced.

Technical appraisal and economic benefits of the proposed method consist in the fact that when its implementation is achieved by the simultaneous formation of the microstructure, providing high stampability cold-rolled sheets, and minimize the negative impact of non-metallic inclusions in steel.

As the base object when determining the technical and economic advantages of the proposed method is adopted prototype method. The use of the proposed method will improve the profitability of production of steel sheet with high exhaust properties for cold forming by 10-15%.

Table 3
The quality and output sheets from the 1st surface finish group
№ p/pσtN/mm2 σinN/mm2δ10, %RnThe output of the 1st group surface finish, %
1210-250370-38028-321,70,2068,7
2155-162270-27545-482,80,2985,8
3162-175305-31048-542,90,3087,5
4165-180325-33744-492,80,3286,9
5186 to 190320-36036-391,90,2276,6
6180-220260-33032-371,80,2065,3

Sources of information

1. Application 59-13030 (Japan), IPC 21 D 9/48, 21 D 8/04, 1984

2. U.S. patent No. 4368084, IPC C 21 D 8/06, 1983

3. USA and other Continuous thermal processing of autopistol steel. M, metallurgy, 1979, p.9-25 prototype.

1. Method of manufacturing cold-rolled steel sheet for deep drawing, including hot rolling continuously cast slab of low carbon steel, etching, multi-pass cold is rogatko, recrystallization annealing of coils in the cover furnace with heating for several stages, aging, cooling and tempering, wherein the multi-pass cold rolling is conducted with total relative compression of not less than 75%, and recrystallization annealing is performed in the mode: heating at an average speed of 70-80°C/h to a temperature of 490-510°With repeated heating at an average speed of 3-4°C/h to the intermediate temperature 540-560°and a final heating at an average speed of 50-55°/h to annealing temperature 700-720°in which the rolls are incubated for 12-18 hours

2. The method according to claim 1, characterized in that after heating at a temperature of annealing the coils are cooled with speed 19-21°C/h to a temperature of not higher than 690°C.

3. The method according to any one of claims 1 and 2, characterized in that the continuously-cast slab of low carbon steel has the following chemical composition, wt.%:

Carbon 0,025-0,050

Silicon 0.003 to 0.01 to

Manganese 0,12-0,19

Aluminum 0,02-0,05

Nitrogen Not more than 0,011

Iron and impurities Else



 

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FIELD: metallurgy, production of rolled steel.

SUBSTANCE: the invention is pertaining to the field of metallurgy, production of rolled steel, in particular, to methods of production of cold rolled steel sheets with the high drawing properties for a cold forming of details of cars bodies. The technical problem being solved by the invention consists in improvement of the quality of a cold rolled sheet steel. The method provides for hot rolling of continuously-cast low-carbon steel slabs, etching treatment, multirun cold rolling with total relative reduction of no less than 75 %, a recrystallization annealing in the following mode: a heating at an average speed of 70-80°C/h up to temperature of 490-510°C, a repeated heating at an average speed of 3-4 °C/h up to the intermediate temperatures of 540-560 °C/h and the final heating at an average speed of 50 - 55°C/h up to the annealing temperature of 700-720 °C, at which the steel rolls are kept for 12-18 h. Upon termination of keeping the rolls at the annealing temperature they are cooled at the rate of 19-21 °C/h up to the temperatures not exceeding 690 °C. At that the continuously cast low-carbon steel slabs have the following chemical composition (in mass %): 0.025-0.050 - carbon, 0.003-0.010 - silicon, 0.12-0.19 - manganese, 0.02-0.05 - aluminum, no more than 0,011 - nitrogen, the rest - iron and impurities.

EFFECT: the invention ensures improvement of the quality of a cold rolled sheet steel.

3 cl, 5 ex, 3 tbl

FIELD: ferrous metallurgy; motor-car industry; production of steels intended for manufacture of items of a complex configuration with the help of cold sheet stamping.

SUBSTANCE: the invention is pertaining to the field of ferrous metallurgy and motor-car industry, in particular, to methods of production of steels intended for manufacture by cold sheet stamping of items of a complex configuration, predominantly details for motor cars. The technical problem is to boost steel stamping, to improve the quality of a surface of a steel strip and hence to improve adhesion of a protective cover. The method includes a steel smelting, casting, hot rolling, strips reeling in rolls, a cold rolling, a recrystallization annealing and a temper rolling. The steel contains components in the following ratio (in mass %): Carbon - 0.002 - 0.008, silicon - 0.005-0.025, manganese - 0.05-0,20, phosphorus - 0.005-0.025, sulfur - 0.003-0.012, aluminum - 0.02-0.07, titanium - 0.02-0.05, niobium - 0.001 0.080, iron and imminent impurities - the rest. The hot rolling is completed at the temperature determined from the ratio: Tf.r≥ 7300 / (3.0-Ig [Nb] [C]) - 253, where Tf.r - temperature of the end of the rolling, °C; [Nb] and [C] - the shares of niobium and carbon in the steel accordingly in mass %, and the recrystallization annealing is carried out in a pusher-type furnace at the temperature assigned depending on the contents of niobium in steel according to the equation: Tan= (750+ 1850 [Nb]) ± 20, where Tan - a temperature of the thermal treatment, °C; [Nb] - the contents of niobium in the steel, in mass %.

EFFECT: the invention allows to boost the steel stamping, to improve the quality of the steel strip surface and adhesion of a protective cover.

4 ex, 1 tbl

FIELD: metallurgy; methods of production of thin-sheet hot-rolled steel.

SUBSTANCE: the invention is pertaining to the field of rolling, in particular, to methods of production of thin-sheet hot-rolled steel. The technical result of the invention is production of hot-rolled steel of no more than 3.9 mm thick with the properties similar to the properties of the cold- rolled sheet steel, and having a tarnish or a rough surface, that increases commercial profits of the rolled steel. The offered method provides for hot rolling of bands, their refrigerating to the temperature of a reeling - tc by the sectional water quenching, a reeling, etching treatment with HCI solution and a temper rolling. For the bands of steel with a carbon share of up to 0.1 mass % the temperature of the end of rolling is kept equal to 860... 890°C. The water quenching of the bands begin in 7...9 seconds after the end of rolling, and tc is taken within the temperatures range of 640... 700°С. At that the bands temper rolling for production of their tarnish surface realize in the rollers with a height of micro-asperities of the barrels Ra = 2.2... 2.7 microns and for production of the rough surface - with = 2.9... 4.0 microns.

EFFECT: higher efficiency.

1 ex

FIELD: metallurgy; methods of production of steels with homogeneous properties.

SUBSTANCE: the invention is pertaining to the field of metallurgy, in particular, to production of deep-drawing steels used for production of items of the complex configuration, predominantly - he details of motor-cars. The technical result of the invention is increased homogeneity of mechanical properties of the steel and reduction of cost of its production. This technical result is achieved due to the fact, that they conduct a continuous casting of the steel containing of no more than 0.007 mass % of carbon and 0.006 mass % of nitrogen in slabs, heating and hot rolling in bands, refrigeration, a reeling in rollers, etching, cold rolling with compaction of no less than 70 %, annealing and temper rolling. The annealing of cold-rolled steel conduct in the pusher-type furnace at temperatures of 750 ÷ 900°C during 5 ÷ 18 minutes.

EFFECT: the invention ensures increased homogeneity of mechanical properties of the steel and reduction of cost of its production.

2 tbl 1 ex

FIELD: ferrous metallurgy; methods of a steel production.

SUBSTANCE: the invention is pertaining to ferrous metallurgy, in particular, to the methods of production of steel for a deep drawing applied at production of items of a complex configuration, predominantly details of cars. The technical result of the invention is an increase of homogeneity of its mechanical properties and reduction of expenditure for its production. The technical result is reached by conducting a continuous casting of the steel containing of no more than 0.007 mass % of carbon and 0.006 mass % of nitrogen in slabs, their heating at the temperatures of 1000÷1160°C and their hot rolling in bands with the temperature of the end of rolling equal to 620 ÷ 720°C, chilling of bands by a still air and their reeling in rolls at temperatures of 600 ÷ 680°C, etching treatment, cold rolling with cold reduction by not less than 70 %, an annealing at temperatures of 650 ÷ 900°C and temper rolling. Aging of the cold-rolled steel at annealing conduct during 5÷18 minutes at temperatures of 750÷ 900°C in pusher-type furnaces, and aging for 11÷34 hours - at temperatures of 650÷ 750°C in the bell-type furnaces.

EFFECT: the invention ensures increased homogeneity of the steel mechanical properties and reduction of expenditure for its production.

2 cl, 1 dwg, 2 tbl, 1 ex

FIELD: black metallurgy.

SUBSTANCE: method includes hot rolling, cooling down to winding temperature, winding of bar in a roll, heating bar up to zinc-plating temperature and applying of zinc plating, cooling of bar is performed after black group of cages with speed 0,3-0,6°C/c, and after white - with speed 20-30°C/c with point of start of process in 2,5-3,0 after exit of bar from last cage of white group.

EFFECT: higher efficiency.

1 tbl, 5 ex

FIELD: ferrous metallurgy; methods of production of the steel strips.

SUBSTANCE: the invention is pertaining to the field of ferrous metallurgy, in particular, to the method of production of the steel strips from the low-carbon automobile-body sheet steel. The technical result of the invention is the increased output the steel strips: the rather special complex ironing (RSCI), the special complex ironing (SCI), the complex ironing (CI) and ensuring achievement of the required level of the physical-mechanical properties of the steel strips. The technical problem has been solved in three versions. The steel strip is produced by the hot rolling, the subsequent cold rolling, the reeling of the cold-rolled strips in the rolls and their annealing in the bell-type furnaces with the heating up to the temperatures of the recrystallization annealing belowACl : 650-720°C. The RSCI rolls heating exercise in four stages: on the first stage - up to 320-600°C with the rate of 60-270°C/h, on the second stage - up to 360-630°C with the rate of 10-30°C/h, on the third stage - up to 400-649°C with the rate of 5-7°C/h, on the fourth stage - up to 650-720°C with rate of 8-70°C/h. In the second version SCI rolls are heated up in three stages: on the first stage - up to 320-600°C with the rate of 60-270°C/h, on the second stage - up to 360-649°C with the rate of 10-30°C/h, on the third stage - up to 650-720°C with the rate of 8-70°C/h. In the third version the CI rolls are heated up to 650-720°C in two stages: on the first stage - up to 320-649°C with the rate of 60-270°C/h, on the second stage - up to 650-720°C with the rate of 8-70°C/h.

EFFECT: the invention ensures the achievement of the required level of the physical-mechanical properties of the steel strips.

3 cl, 3 tbl, 5 ex

FIELD: metallurgy, namely processes for cold rolling steel sheets with high drawing properties, possibly used for cold forming of body parts of passenger cars.

SUBSTANCE: method is realized at keeping temperature values of rolling termination and coiling in ranges 850 - 910°C and 540 - 730°C respectively. Cold rolling is performed at total reduction 65 - 88%. Annealing stage is performed at heating up to temperature 700 -750°C and soaking at such temperature for 10 - 25 h. Steel for making cold rolled sheets contains next ingredients, mass %: carbon, 0.001 - 0.006; silicon, 0.005 - 0.04; manganese, O.05 - 0.25; aluminum, 0.01 - 0.08; titanium, 0.01 - 0.09; niobium, no more than 0.05; boron, no more than 0.001; chrome, no more than 0.06; nickel, no more than 0.06; copper, no more than 0.06; sulfur, no more than 0.012; phosphorus, no more than 0.10; nitrogen, no more than 0.006; iron, the balance. If niobium is absent and relation Ti/(4C + 3.43N + 1.5S)≥ 1 is satisfied, reduction degree at skin pass rolling is set in range 0.20 - 0.60% and if given relation is less than 1 it is set in range 0.61 - 1.2%. If niobium is present and next relations of chemical elements content in steel Ti/3.43N ≥ 1 and Nb/7.75C ≥ 1 are satisfied, reduction degree at skin pass rolling is set in range 0.20 - 0.60% and if given relations are less than 1 it is set in range 0.61 - 1.2%.

EFFECT: less loss of yield, improved drawing capability of steel sheets.

7 cl, 3 tbl, 1 ex

FIELD: metallurgy; heat treatment of materials.

SUBSTANCE: proposed method consists in heating the roll at temperature interval of 200-570°C at rate of 80-90°C/h followed by heating to temperature of 640-660°C at rate of 20-30°C and heating at rate of 20-25°C/h to annealing point. Besides that, holding at annealing temperature is set according to the following relationship: τ=(0.8-0.9)M, where τ is holding time, h; M is mass of lower roll in stack, t.

EFFECT: reduced duration of annealing at high mechanical properties and improved quality of cold-strip surfaces.

2 cl, 3 tbl, 1 ex

FIELD: ferrous metallurgy, namely cold sheet forming, particularly motor vehicle parts.

SUBSTANCE: method comprises steps of melting steel, casting it, hot rolling in rough and finish stand group of continuous wide rolling mill, coiling strip, cold rolling, subjecting it to recrystallization annealing in hood furnace at temperature no less than 690°C and skin pass rolling of strip. Melt steel contains, mass %: carbon, 0.01 -0.06; silicon, 0.003 - 0.030; manganese, 0.05 - 0.25; phosphorus, 0.003 - 0.020; sulfur, 0.002 - 0.023; acid soluble aluminum, 0.01 - 0.06; nitrogen, 0.002 -0.007; iron and inevitable impurities, the balance while satisfying next relations: [Mn]x{S]≤ 0.045 and 5 ≤ [Al}/[N]≤ 20. Hot rolling in rough stand group is ended when thickness of rolled piece is 35 mm and more at temperature Tp ≥ 1050 + 8000[Mn][S]. Heating at recrystallization annealing is realized at first up to 450 - 500°C for time period no more than 10 h. After temperature 450 - 500°C is achieved heating is realized at rate no more than 20°C/h at least till 550 - 600°C and then at rate no more than 50°C/h till annealing temperature.

EFFECT: improved formability of steel at keeping its surface quality.

1 tbl, 5 ex

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