ISSN 0967�0912, Steel in Translation, 2012, Vol. 42, No. 3, pp. 255–256. © Allerton Press, Inc., 2012.Original Russian Text © T.P. Poletskova, S.G. Andreev, Yu.P. Demidchenko, T.M. Kochneva, P.P. Poletskov, 2012, published in “Stal’,” 2012, No. 3, pp. 35–36.

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In 2010, specialists at OAO Magnitogorskii Metal�lurgicheskii Kombinat (MMK) corrected the produc�tion technology for increased�strength 08ГCЮT steelsheet used in the auto industry (thickness 0.7–2.8 mm;width 1000–1500 mm) in accordance with TechnicalSpecifications TU 14�1�3764–84. The problem was theunsatisfactory plasticity of the sheet produced: in somecases, the relative elongation was as low as 20–22%(whereas the TU 14�1�3764–84 requirement is ≥28%).

Research regarding the influence of annealing ofthe cold�rolled sheet on the physicomechanical prop�erties indicated the need for comprehensive correctionof the production technology. The following modifica�tions were introduced.

(1) Adjustment of the chemical composition of08ГCЮT steel, by reducing the permissible carbon andmanganese content and limiting the content of residualelements (Cr, Ni, Cu) and impurities (S, P). Table 1 pre�sents the new requirements on the chemical composition.

(2) Adjustment of hot rolling on the 2000 mill, with30°C increase in the final rolling temperature and thestrip coiling temperature.

The annealing of the cold�rolled strip was markedlychanged. The core temperature of the coil at the endof heating was increased from 650 to 660°C. As aresult, the difference between the specified tempera�ture according to the built�in thermocouple (680°C)and the theoretical core temperature of the coil at theend of heating (660°C) is 10°C smaller. At the sametime, the heating time must be increased correspond�ingly—by ~5 h. These annealing parameters are com�pletely confirmed by experimental data. Two melts arechosen for the experiment. Each of the experimental

melts is divided into two portions, one of which under�goes the existing heat treatment, while the otherundergoes the proposed treatment. Table 2 comparesthe mechanical properties of 08ГCЮT steel after theexisting and proposed heat treatments.

However, the elevated temperatures and extendedheating times in recrystallizational annealing increasethe welding of the turns in the coil and hence pose therisk of fracture in subsequent temper rolling. There�fore, we must consider the production of flatter stripafter cold rolling. To this end, the profile of rollers forthe 2500 cold�rolling mill has been redesigned. Thecorresponding data for a four�cell mill are as follows:

Cell 1 2 3 4

Supporting rollers, mm

0.00 with bevels (250 ×

1.5 mm)

+1.80 +1.80 +1.80

Working rollers (total for pair), mm (base�line profile; strip width <1450 mm)

+0.8 –0.5 –0.5 –0.5

Corrections to base�line profile, mm

for wear of sup�porting rollers

0.1 for 30000 t of strip

– – 0.1 for 35000 t of strip

for maximum width of rolled strip, mm

1451–1550 – – – 0.21551–1700 0.2–0.3 0.0–0.2 0.0–0.2 0.2–0.31701–1800 0.4–0.5 0.3–0.4 0.3–0.4 0.4–0.5>1850 0.5–0.6 0.4–0.5 0.4–0.5 0.5–0.6

Improving the Production of Steel Sheet for the Auto Industry

T. P. Poletskova, S. G. Andreev, Yu. P. Demidchenko, T. M. Kochneva, and P. P. PoletskovOAO Magnitogorskii Metallurgicheskii Kombinat, Magnitogorsk, Russia

Abstract—A production technology has been developed for increased�strength steel sheet used inthe auto industry. The sheet produced is characterized by a good combination of strength and plasticity.

DOI: 10.3103/S0967091212030102

08ГСЮТ

08ГСЮТ

Table 1. New chemical composition of 08ГCЮT steel

Standard documentContent, wt %

C Si Mn S P Cr Ni Cu Al Ti

Technical Specifications TU 14�1�3764–84

≤0.09 0.3–0.6 0.7–1.1 ≤0.030 ≤0.030 0.30 0.30 0.03 0.02–0.07 0.02–0.08

New requirements 0.04–0.07 0.3–0.6 0.7–0.9 ≤0.015 ≤0.015 ≤0.10 ≤0.10 ≤0.10 0.02–0.05 0.02–0.04

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POLETSKOVA et al.

Note that the correction to the baseline profileconsists of reducing the convexity and increasing theconcavity at the diameter.

In cell 1, the profiling of the working rollers is con�vex, with corresponding cylindrical profiling of the

supporting rollers. In cell 2–4, the profiling of theworking rollers is concave, with correspondingincrease in the convex profile of the supporting rollers.The new production technology for 08ГCЮT steelsheet in accordance with Technical SpecificationsTU 14�1�3764–84 yields the required mechanicalproperties. Table 3 presents the characteristics of sheetproduced by the new technology. Table 4 summarizesthe mechanical properties of 08ГCЮT steel sheetproduced by the existing technology.

CONCLUSIONS

By correcting the production technology so as toimprove the plasticity of 08ГCЮT steel sheet inaccordance with Technical Specifications TU 14�1�3764–84, OAO Magnitogorskii MetallurgicheskiiKombinat has been able to meet the auto industry’squality requirements and also to ensure timely orderfulfillment.

Table 2. Comparison of the mechanical properties ofbatches of 08ГCЮT steel annealed in different conditions

Number ofσy,

N/mm2σB,

N/mm2 δ4, %melt sample

3** 1/2 335/335 435/440 28/29

4 1/2 365/370 470/465 23/27

Technical Specifications TU 14�1�3764–84

≥294 ≥392 ≥28

Notes: * Existing/proposed conditions;** Ti content: 0.027% in melt 3 and 0.034% in melt 4.

Table 3. Mechanical properties of 08ГCЮT steel sheetproduced by the new technology

Sample σy, N/mm2

σB, N/mm2 δ4, %

1 335 445 29.0

2 300 95 30.0

3 310 425 31.0

4 310 420 29.0

5 295 415 29.0

6 310 430 28.0

Technical Specifications TU 14�1�3764–84

≥294 ≥392 ≥28.0

Table 4. Mechanical properties of 08ГCЮT steel sheetproduced by the existing technology

Number ofσy,

N/mm2σB,

N/mm2 δ4, %melt sample

1 1 380 480 22.5

1 2 355 465 21.5

1 3 370 465 20.0

2 1 365 485 22.0

2 2 380 480 22.0

Technical Specifications TU 14�1�3764–84

≥294 ≥392 ≥28