RU2433199C1 - Autoplate cold-rolled steel for deep forming - Google Patents

Abstract

FIELD: metallurgy. ^ SUBSTANCE: steel contains carbon, manganese, silicon, sulphur, phosphorus, chrome, nickel, copper, nitrogen, aluminium, titanium, niobium and iron at the following component ratio, wt %: carbon of more than 0.007 - 0.009, manganese 0.10 0.14, silicon ëñ 0.02, sulphur ëñ 0.013, phosphorus ëñ 0.012, chrome ëñ 0.02, nickel ëñ 0.03, copper ëñ 0.04, nitrogen ëñ 0.006, aluminium 0.030.06, titanium (2.4S+3.43N) (2.4S+3.43N)+0.03, niobium 7.75C7.75C+0.02, iron is the rest, where (S), (N), (C) - content of sulphur, nitrogen and carbon in steel. It has ultimate strength âu=270350 N/mm2, yield strength äëñ180 N/mm2, relative elongation â4ëÑ38 %, plastic anisotropy factor r90ëÑ1.8, strain strengthening parameter n90ëÑ0.22. ^ EFFECT: improving steel application properties. ^ 1 ex

Description

The invention relates to ferrous metallurgy and can be used in the production of cold rolled sheet steel for the manufacture of stamped front parts of the car body.

Such steel contains a relatively small amount of carbon and other elements, including aluminum. This steel should have certain mechanical properties (temporary resistance - σ _in , yield strength - σ _t and elongation δ ₄ ), providing its ability to complex and very particularly complex drawing during cold stamping. The classification of sheet steel (08Yu, 08kp, ps) is given, for example, in the reference book of V.N. Zhuravlev and O.I. Nikolayeva "Engineering Steel". M .: Engineering, 1981, p. 170 ... 171.

Known steel of increased wear resistance during impact-abrasive wear, containing carbon, silicon, manganese, chromium, titanium, vanadium, nitrogen and iron, moreover, the carbon content in it is 0.8 ... 1.0 wt.%. (see AS of the USSR No. 969779, class C22C 38/38, published in BI No. 40, 1982) However, this steel is unsuitable for the production of a sheet due to its insufficient formability.

The closest analogue to the inventive steel sheet is cold rolled steel for deep drawing (RF Patent No. 2034088, C22C 38/50).

This steel with specified mechanical properties contains carbon, manganese, sulfur, phosphorus, silicon, chromium, nickel, copper, nitrogen, aluminum, titanium, niobium and iron.

The disadvantage of this steel is its relatively low consumer properties, especially when stamping automotive body parts.

An object of the present invention is to improve the consumer properties of steel sheets.

To solve this problem, the proposed cold-rolled autogap steel for deep stamping, containing carbon, manganese, silicon, sulfur, phosphorus, chromium, nickel, copper, nitrogen, aluminum, titanium, niobium and iron, is characterized in that it contains these components in the following ratio , wt.%:

carbon from more than 0.007 to 0.009 manganese 0.10 ... 0.14 silicon ≤0.02 sulfur ≤0.013 phosphorus ≤0.012 chromium ≤0.02 nickel ≤0.03 copper ≤0.04 nitrogen ≤0.006 aluminum 0.03 ... 0.06 titanium (2,4S + 3,43N) ... (2,4S + 3,43N) +0,03 niobium 7.75С ... 07.75С + 0.02 iron rest,

where (S), (N), ( C) - the content in the steel of sulfur, nitrogen and carbon, and has a tensile strength σ _B = 270 ... 350 N / mm ^2, yield stress σ _m ≤180 N / mm ^2, elongation δ ₄ ≥38%, and the coefficient of plastic anisotropy r ₉₀ ≥1.8 and the strain hardening index n ₉₀ ≥0.22.

The definition of r ₉₀ and n ₉₀ is given, for example, in the overview information “Analysis of modern methods for assessing the stampability of low-carbon sheet steel”, TsNIITI bulletin, “Rolling production” series, issue 3. M., 1989, pp. 11 and 13: r ₉₀ is the ratio of deformation by the cross-sectional area of the sample to deformation by its thickness; n ₉₀ is the hardening coefficient: the smaller it is, the earlier plastic deformation occurs.

The essence of the proposed technical solution is to optimize the chemical composition and mechanical characteristics of super low carbon cold rolled steel (C from more than 0.007 to 0.009), as a result of which high consumer properties of the sheet are provided. This is due to the presence of nitrogen, titanium and niobium in the steel, the presence of which compensates for the very low carbon content in it and favorably affects its microstructure. Regulability indicators r ₉₀ and n ₉₀ guarantees the possibility of obtaining a very particularly complex hood with deep stamping.

An experimental verification of the proposed steel was carried out at OJSC Magnitogorsk Iron and Steel Works. For this purpose, its chemical composition was varied during steel smelting, and hot and cold deformation (rolling) was carried out with the same modes, evaluating the results (when testing the samples) on the output of the autobench with the recommended indicators that affect its ability to stretch during stamping.

The best results (the yield of sheets of VOSV category - 99.8%, the rest - WWS) were obtained using the inventive steel. Deviations from the proposed chemical composition, mechanical properties and plastic characteristics worsened the achieved indicators.

The most important impurities that determine the strength, plastic and technological properties are carbon, nitrogen, silicon, manganese, phosphorus and sulfur. By increasing the content of C, Si, P, S and Cr in the steel increased _in magnitude σ and σ _m, with simultaneous reduction value δ _4, which reduced the magnitude of r and _90, whereby the output category SRES sheets did not exceed 98.0%. Ni - provides an anisotropy index, an increase in its content of more than 0.03% and a Cu content of more than 0.04% led to an increase in the amount of dispersed perlite, which worsened the plastic properties of steel. An increase in the Mn content, which is introduced to bind sulfur, increased by 0.1% the strength by ~ 5.0 N / mm ² with a deterioration in plastic properties, when the ratio Mn / S≤10, hot rolling conditions worsened due to the formation of cracks on the lateral edges .

Increasing the content of chromium and titanium box led to an increase _in the quantities σ _m and σ, as well as to improve the relationship σ _r / σ _in, and to a decrease of ₉₀ r (<1,8), n ₉₀ (<0.22) . This worsened the stampability of steel and gave an output of VOSV category sheets of not more than 98.2%. An increase in nitrogen content of more than 0.006% increased the tendency to aging, thereby increasing the tensile strength and yield strength.

A decrease in the content in the steel of elements, especially C, Si, Ni, Ti, and Nb, led to an increase in δ ₄ , a decrease in σ _in and σ _t , which caused the appearance of slip lines (Luders) during stamping. A decrease in the Mn content of less than 0.1% worsens the hot rolling conditions due to the formation of cracks on the lateral edges.

Thus, an experimental verification confirmed the acceptability of the technical solution found to achieve the goal and its advantage over a known object.

The feasibility study showed that the use of the proposed cold-rolled steel sheet with improved consumer properties will increase the profit from the sale of sheet steel by at least 7%, and the yield of high-quality steel sheet by at least 5%.

Concrete example

A 1.8-mm low-carbon cold-rolled sheet steel containing components in the following ratio:

C = 0.008 wt.%, Mn = 0.14%, Si = 0.015%, S = 0.01%, P = 0.01%, Cr = 0.02%, Ni = 0.02%, Cu = 0.035 %, N = 0.006%, Al = 0.045%;

Ti = 2.4S + 3.43N + 0.015% = 2.4 * 0.01 + 3.43 * 0.006 + 0.015 = 0.245%, a

Nb = 7.75C + 0.01% = 7.75 * 0.05 + 0.01 = 0.4% the rest is iron.

smelted in a converter way, rolled on a broadband hot rolling mill at Tk.p = 860-850 ° C, Tcm = 640-660 ° C. Cold rolling was carried out on a 4-stand mill 2500 with a 3.8 mm roll (compression - 52.6%), annealed in bell-type furnaces with a nitrogen-hydrogen protective atmosphere, and trained with compression 0.8 ± 0.1%.

Mehsvoystva become: σ _in = 310 N / mm ^2, σ _m = 165 N / mm ^2, δ ₄ = 40%. The value of r ₉₀ = 2.0, the indicator n ₉₀ = 0.25.

Claims (1)

Cold-rolled autodized steel for deep stamping, containing carbon, manganese, silicon, sulfur, phosphorus, chromium, nickel, copper, nitrogen, aluminum, titanium, niobium and iron, characterized in that it contains these components in the following ratio, wt.%:
carbon from more than 0.007 to 0.009 manganese 0.10-0.14 silicon ≤0.02 sulfur ≤0.013 phosphorus ≤0.012 chromium ≤0.02 nickel ≤0.03 copper ≤0.04 nitrogen ≤0.006 aluminum 0.03-0.06 titanium (2.4S + 3.43N) - (2.4S + 3.43N) +0.03 niobium 7.75C-7.75C + 0.02 iron rest,
where S, N, C - content of the steel of sulfur, nitrogen and carbon, and has a tensile strength σ _B = 270 ÷ 350 N / mm ^2, yield stress σ _m ≤180 N / mm ^2, elongation δ ₄ ≥38%, plastic anisotropy coefficient r ₉₀ ≥1.8 and strain hardening index n ₉₀ ≥0.22.