Method of manufacturing cold-rolled strips of steel sverhskorostey

 

(57) Abstract:

The invention relates to the technology of production of cold-rolled strips of sverkhnizkochastotnye steels for the automotive industry, with a hardening effect during drying of the paint coating (EXT-effect). The proposed method includes a steel containing, in wt.%: carbon 0,006-0,10; manganese 0,01-0,15; phosphorus 0,07; nitrogen 0,0025; aluminum 0,04; niobium 0,031-0,06; sulfur 0,008; iron and inevitable impurities else, casting, heating the slab to a temperature of 1150-1200oWith, hot rolling temperature of the end of hot rolling, equal 910-920oWith the winding at a temperature of 740-750oWith, cold rolling with a total reduction of at least 70%, heating the obtained cold-rolled strip to the annealing temperature with a speed of 10-20oC/s and continuous annealing, the temperature of which is determined depending on the relationship Nb/C by the formulas: when 3,1 Nb/C 4,65 TOTG=7,52(Nb/C)2+ 45,55 Nb/C + 791,oWith 4,65 < Nb/C 10 TOTG=1,75(Nb/C)2+ 33,81 Nb/C + 730,oFrom where Nb and C contents of niobium and carbon in steel, wt.%, the shutter speed when the annealing temperature for 50-60 C and strip cooling speeds of 15-25oC/C to a temperature of 340-360oC. the Method provides stabiliser obtaining a hardening effect not less than 40 MPa.

The invention relates to rolling production, in particular to the production technology of cold rolled strips of sverkhnizkochastotnye steels for the automotive industry, with ProCredit effect drying of the paint coating (EXT-effect).

A method of producing low carbon cold rolled steel for stamping and subsequent enameling, namely, that after melting the steel containing the following components, wt.%: carbon 0.04 to 0.08, silicon, 0.01 to 0.05, manganese 0.1 to 0.3, to 0.025 sulfur, phosphorus, up to 0.03, chrome to 0.06, boron up to 0.005, Nickel up to 0.06, copper to 0.06, aluminum 0.01 to 0.04, iron and inevitable impurities rest is subjected to hot rolling ending temperature range Ac1+90oS-AU3-20oWith, wound into a roll at a temperature of not more than 30oWith lower temperature Ac1conduct cold rolling with deformation rate of 50-70% and provide heating to the annealing temperature after cold rolling with a velocity in the range of 10-50oWith/h (RF patent 2159820, CL 21 D 8/04, s 21 D 9/46, publ. 27.11.2000).

The known method does not provide a high output cold rolled strips category very very difficult extraction of WONCA, due to the low stability of svojstva automotive sheet of ultramicroporous steels, including steel containing, %: carbon 0,0025; silicon 0,0030; manganese 0,125; sulphur and phosphorus on 0,007; aluminum 0,038; nitrogen 0,002; titanium 0,012; niobium from 0.01 to 0.022; iron and inevitable impurities - the rest, casting, heating the slab to a temperature of 1250oWith, hot rolling temperature end of the rolling 900oWith the winding sheets at temperatures of 650oC and 770oWith, cold rolling the steel at a compression of about 70%, heat treatment comprising heating to 550oWith, exposure for 10 min with subsequent cooling in water, the continuous annealing at temperatures in the range from 790 to 890oWith aged 60 and then cooled at a rate of about 10oWith/s (Liters M Storozheva, K. Escher, R., Bode, K. Hulka, D. A. Burko, "Metallography and heat treatment of metals", 3, 2002, S. 6-12).

Signs nearest analogue, coinciding with the essential features of the claimed invention: steel smelting, casting, heating of the slab, hot rolling, winding at a temperature of 740-750oWith, cold rolling and continuous annealing of the obtained cold-rolled strip with subsequent cooling.

The known method cannot provide the required technical result for the following reasons.

In izvestnova steel on the annealing temperature. As a result, when there is insufficient temperature annealing NR-effect will be low or absent, and at elevated temperature annealing the steel is heated to an unnecessarily high temperature. Higher heating during the annealing leads to a transition in solid solution more carbon that along with increasing NR effect will lead to changes in the mechanical properties of the strip (tensile strength, yield strength and coefficient of normal plastic anisotropy) and could cause the natural aging that will not provide the required performance for the category VOSV. Even minor fluctuations in the chemical composition cause the temperature of the strip required for a given NR-effect, varies greatly.

For getting into narrow interval of contents microeconomic supplements while using the technique of increasing the number of iterati, i.e., a constant approximation to a given chemical composition of steel by entering small amounts of alloying elements, mixing, sampling, expectations analysis, and so on, These operations are repeated to obtain the given chemical composition of steel, which entails resulting voltage with casting nature performance and increase in the cost of steel.

The basis of the invention the task is improving the method of production of cold-rolled strips of sverhskorostey steel by optimizing process parameters and regulation of annealing temperature depending on the specific chemical composition of steel. The expected technical result is stabilization of the complex mechanical properties while providing a category very very difficult extraction with simultaneous achievement of hardening effect is not less than 40 MPa.

The problem is solved in that in the method of manufacturing of cold rolled strips of sverkhnizkochastotnye steel, including steel smelting, casting, heating of the slab, hot rolling, winding at a temperature of 740-750oWith, cold rolling and continuous annealing of the obtained cold-rolled strip with subsequent cooling, according to the invention smelted steel containing, %: carbon 0,006-0,01; manganese 0,01-0,15; phosphorus 0,07; nitrogen 0,0025; aluminum 0,04; niobium 0,031-0,06; sulfur 0,008; iron and inevitable impurities rest, heated slabs are up to temperature 1150-1200oWith the temperature of the end of hot rolling is equal to 910-920oWith, cold rolling is conducted with a total compression of at least 70%, heating the strip to a temperature of annealing the>/BR>when 3,1 Nb/C 4,65 TOTG=7,52(Nb/C)2+45,55 Nb/C+791,oWITH,

when 4,65 Nb/C 10 TOTG=1,75(Nb/C)2+33,81 Nb/C+730, oWITH,

where Nb and C contents of niobium and carbon in steel weight. % and after aging at the temperature of annealing for about 50-60 with a cool band with a speed of 15-25oC/C to a temperature of 340-360oC.

Hardening cold-rolled strip occurring during drying stamped and colored products, is due to the presence of the solid solution of carbon atoms. During the drying of paint, the metal is heated to a temperature of 150-200oWith the mobility of carbon atoms increases significantly and they fix dislocations introduced during training and stamping.

In the proposed method, the optimal temperature annealing is determined by empirical formulas, taking into account the influence of the relationship Nb/C on the annealing temperature required for dissolution of carbides of niobium in an amount sufficient to obtain a reinforcing effect NR240 MPa, at a speed of over 50-60 C. the ratio Nb/C is limited in the range of 3.1-10, as at a lower or higher ratio, the required temperature annealing exceeds 900oWith and cannot be achieved in potable the annealing temperature is determined by the formula:

TOTG=7,52(Nb/C)2+45,55 Nb/C+791; oWITH,

when 4,65 <Nb/C 10 the annealing temperature is determined by the formula:

TOTG=1,75(Nb/C)2+33,81 Nb/C+730;oWITH,

where Nb and C contents of niobium and carbon in steel, wt.%.

Cooling after annealing carried out with the speed of 15-25oC/C to a temperature of 340-360oC. High cooling rate necessary to keep the carbon in the solid solution and to provide a high reinforcing effect.

Using the proposed method allows to obtain holodnokatanuju, including a galvanized steel strip with a yield strength0.2<185 MPa, tensile strengthin= 280-350 MPa, elongation = 38% and the ratio of the normal plastic anisotropy rm= 2,0, enough to supply category hoods VOSV.

Example 1

In the oxygen Converter smelted steel of the following chemical composition, wt. %: 0,006 C; 0.1 MT; 0,07 P; 0,0025 N; 0,04 Al; 0,06 Nb; 0,007 S. After casting machine continuous casting the resulting slabs were heated to a temperature of 1150-1200oWith, were subjected to hot rolling (TCP=910-920oS, Tcm= 740-750oC) etching and cold rolling with a reduction of at least 70%.

D)2+33,810,06/0,006+730=893oC.

After holding at the annealing temperature for 50-60 with strip was cooled with a rate of 15-25oC/C to a temperature of 350oC. Then the strip was applied to the continuous hot dip galvanizing line and subjected to training with a compression of less than 0.8%.

The resulting strip has a yield strength0.2= 170 MPa, tensile strengthin= 325 MPa, elongation =41%, the coefficient of the normal plastic anisotropy rm=2.1 and has BH-effect NR2=41 MPa.

Example 2

In the oxygen Converter smelted steel of the following chemical composition, wt. %: steel With 0,01; 0,1 MP; 0,07 P; 0,0025 N; 0,04 Al; 0,031 Nb; 0,007 S. After casting machine continuous casting the resulting slabs were heated to a temperature of 1150-1200oWith, were subjected to hot rolling (TCP= 910-920oS, Tcm= 740-750oC) etching and cold rolling with a total reduction of at least 70%.

Next, the steel was subjected to continuous annealing in ANO. Heating to the annealing temperature was performed with a speed of 10-20oC. the annealing Temperature was defined as:

TOTG=7,52(0,031/0,01)2+ 45,550,031/0,01+791=859oC.

After holding at the annealing temperature for 50-60 is th speed and subjected to training with a compression of less than 0.8%.

The resulting strip has a yield strength0.2= 182 MPa, tensile strengthin= 345 MPa, elongation =40%, the coefficient of the normal plastic anisotropy rm=2.0 and has BH-effect NR2=48 MPa.

Method of manufacturing cold rolled strips from low-carbon steel, including steel smelting, casting, heating of the slab, hot rolling, winding at a temperature of 740-750oWith, cold rolling, continuous annealing of the obtained cold-rolled strip up to temperature, which is determined depending on the relationship Nb/C, patience and cooling, characterized in that the smelted steel containing, by weight. %: carbon 0,006-0,10, manganese 0,01-0,15, phosphorus 0,07, nitrogen 0,0025, aluminum 0.04; the niobium 0,031-0,06, sulfur 0,008, iron and inevitable impurities rest, heated slabs are up to temperature 1150-1200oWith the temperature of the end of hot rolling is equal to 910-920oWith, cold rolling is conducted with a total compression of at least 70%, heating the strip to the annealing temperature lead with a speed of 10-20oC/C, the annealing temperature is determined depending on the relationship Nb/C formula

when 3,1 Nb/C 4,65

TOTG= 7,52(Nb/C)2+ 45,55 Nb/C + 791,oWITH,

when 4,65 < Nb/C 10

TOTG= 1,75(Nb/C)2oC/C to a temperature of 340-360oC.

 

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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

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