RU2483121C1 - Method of producing work-hardened low-carbon sheet steel - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: proposed method comprises sheet hot rolling from steel of the following chemical composition in wt %, i.e. carbon - 0.010.11, manganese - 0.20-0.65, silicon - 0.01-0.17, aluminium - not over 0.10, iron and impurities making the rest, and multipass cold rolling to preset thickness. Note also that hot rolling is carried out to thickness defined by the following relationship

where H is hot-rolled strip thickness and final thickness of cold-rolled sheet,

σ_hr is hot-rolled sheet yield point; σ_cr is preset temporary tear resistance of cold-rolled strip.

EFFECT: higher metal yield thanks to reaching preset yield point.

1 tbl, 2 ex

Description

The invention relates to rolling production and can be used to produce cold rolled strips and tapes delivered to consumers in a cured state, for example, for packaging goods.

A known method of producing sheet steel with a given yield strength, including hot rolling of strips, according to which the specific consumption of water supplied to cool the strips, is established by empirical regression depending on the chemical composition of the steel, temperatures of the end of rolling and winding, strip thickness [1].

However, this method is not suitable for the production of cured low-carbon sheet steel with a predetermined yield strength.

There is also known a method for the production of low-carbon sheet steel with a given yield strength, including hot rolling of strips to an intermediate thickness of 2.0-3.5 mm at regulated temperature conditions, etching of scale, cold rolling to a final thickness, recrystallization annealing and tempering. In this case, low-carbon steel contains carbon, manganese, silicon, aluminum (or without it), iron and impurities [2].

The disadvantages of this method are that in the production of sheet steel in a cured (riveted) state immediately after cold rolling, it does not provide a predetermined yield strength. This is the reason for the rejection of metal.

The closest analogue to the present invention is a method for the production of cold rolled strips of steel containing carbon, manganese, silicon, aluminum, alloying elements, impurities and iron.

The steel slab is subjected to hot strip rolling, pickling and cold rolling to a final thickness. Hot rolling is carried out with regulated temperatures of the end of rolling and winding, and the thickness of the hot-rolled strip h _{gk is} determined by the following experimental dependence:

where h _xk is the final thickness of the cold-rolled strip [3].

The disadvantage of this method is that it does not allow to determine the thickness of the hot-rolled strip of mild steel, from which cold rolling to the final thickness will guarantee the production of cured sheet steel with a predetermined yield strength. This leads to a decrease in yield.

The technical problem solved by the invention is to increase the yield by obtaining a predetermined yield strength of sheet steel.

To solve the technical problem in the known method for the production of cured low-carbon sheet steel containing carbon, manganese, silicon, aluminum (or without it), iron and impurities, including hot rolling of strips and their subsequent multi-pass cold rolling to a final thickness, according to the invention, hot rolling strips lead to a thickness determined by the formula:

,

,

where H, h is the thickness of the hot rolled strip and the final thickness of the cold rolled sheet steel;

;

;

σ _gk is the yield strength of the hot-rolled strip;

σ _hk - the specified value of the yield strength of the cold-rolled strip.

In addition, mild steel has the following chemical composition, wt.%:

Carbon 0.02-0.11 Manganese 0.20-0.65 Silicon 0.01-0.17 Aluminum no more than 0.10 Iron and impurities rest.

The invention consists in the following. In the production of cold-rolled steel, it is necessary to simultaneously solve two problems by choosing the compression mode: to obtain a cold-rolled strip of finite thickness and, at the same time, due to strain hardening (hardening), to provide the specified yield strength specified by the consumer. The instability of the chemical composition of mild steel, the deformation and temperature conditions of hot rolling, the change in the thickness of the hot-rolled strips - all this leads to a spread of the actually obtained values of the yield strength of the hardened mild steel sheet and a decrease in the yield.

для расчета необходимой оптимальной величины относительного обжатия ε исходя из предела текучести σ_гк горячекатаной полосы и заданного значения предела текучести σ_хк холоднокатаной полосы. Использование в предложенной формуле значения σ_гк позволяет учесть влияние нестабильности химического состава малоуглеродистой стали и температурно-деформационных режимов горячей прокатки полос на свойства наклепанной холоднокатаной стали, что повышает точность расчета относительного обжатия ε.The results of experimental studies and their mathematical processing using step-by-step regression analysis made it possible to establish in analytical form the proposed formula

to calculate the necessary optimal value of the relative compression ε based on the yield strength σ _{g of the} hot rolled strip and the specified value of the yield stress σ _{h of the} cold rolled strip. The use of the σ _gk value in the proposed formula allows one to take into account the influence of the instability of the chemical composition of mild steel and the temperature-deformation regimes of hot strip rolling on the properties of cold-rolled steel, which increases the accuracy of calculating the relative compression ε.

определяют точное значение толщины горячекатаной полосы Н, из которой после обжатия с относительной величиной ε будет получена холоднокатаная полоса конечной толщины h.Subsequently, using the value of ε, by the relation

determine the exact value of the thickness of the hot-rolled strip H, from which, after crimping with a relative value of ε, a cold-rolled strip of finite thickness h will be obtained.

были получены по экспериментальным данным. Применительно к малоуглеродистым сталям, соответствующим предложенному химическому составу, мас.%:It should be noted that the numerical values of the regression coefficients are 0.01, 2.5 · 10 ^-4 and 0.018 in the formula

were obtained from experimental data. In relation to mild steels corresponding to the proposed chemical composition, wt.%:

Carbon 0.02-0.11 Manganese 0.20-0.65 Silicon 0.01-0.17 Aluminum no more than 0.10 Iron and impurities rest,

the scatter of σ _hk values of the crated sheet steel from the nominal value, as shown by experiments, does not exceed ± 5%. Due to this, the yield is close to 100%. This is especially important when the consumer regulates the tolerance σ _xk in a narrower range of values.

For transcendental values of the concentrations of chemical elements in steel, the spread of σ _xk values increases. But in cases where the consumer regulates the deviation of σ _hk from the nominal value in the range of ± 10% or more, it is permissible to use mild steel with a different content of these chemical elements.

Carbon and manganese are the main reinforcing elements in fretted steel. With a decrease in carbon content of less than 0.02% or manganese less than 0.20%, the yield strength σ _{hk of} sheet hardened mild steel decreases relative to the set value, and when the carbon content is more than 0.11% or manganese more than 0.65%, the yield strength σ _xk increases . And in fact, and in another case, this leads to a decrease in yield.

Silicon increases the rate of increase of the yield strength σ _xk with increasing ε. When the silicon concentration is more than 0.17%, the longitudinal thickness difference of the hot-rolled strips leads to an increase in the dispersion σ _xk and a decrease in the yield. A decrease in the silicon concentration of less than 0.01% requires an increase in the relative compression ε, which causes cracking of the edges of the cold-rolled strips and reduces the yield.

Aluminum is a stabilizing element, due to which the cured mild steel for a long time maintains a stable value of σ _хк . If further processing of cured mild steel is carried out immediately, then aluminum can not be introduced into its composition. However, when the aluminum content is more than 0.10%, uneven properties are formed due to the segregation in the cold-rolled strip of mild steel, which reduces the yield.

Method implementation examples

Example 1. According to consumer requirements, for the manufacture of fuel filters of diesel internal combustion engines, a cured strip with a thickness of h = 0.6 mm from mild steel with a nominal yield strength σ _hk = 90 kg / mm ² ± 10% is required. That is, the yield strength should be in the range: σ _хк = 81 ... 99 kg / mm ² . For the production of tape using continuously cast slabs of mild steel of the following composition, wt.%:

FROM Mn Si Al Fe + impurities 0.08 0.70 0.20 0.10 Rest.

Reference data determine the yield strength of hot-rolled steel of a given composition: σ _hk = 30.8 kg / mm ² . Using the proposed regression dependence, the parameter ε of cold deformation is calculated:

.

.

After that, the thickness of the hot-rolled strip N is calculated:

.

.

Continuously cast slabs are rolled on a continuous broadband mill 2000 into strips of thickness H = 2.07 mm at a temperature of the end of rolling of 890 ° C, cooled by water on an outlet roller table to a temperature of 560 ° C and wound into rolls.

After cooling, the hot rolled strips are subjected to hydrochloric acid etching. Etched strips are rolled on a continuous 5-stand mill quarto 1700 into strips of final thickness h = 0.6 mm, after which samples are taken and yield strength is measured: σ _хк = 88.0 ... 95.0 kg / mm ² . Due to the fact that the measured values of the yield strength of cold-rolled cold-rolled strips are within the range of permissible values σ _xk = 85 kg / mm ² ± 10%, the yield is W = 98.6%.

Example 2. According to the requirements of consumers, for automated packaging of long products a cold-rolled cured strip of mild steel with a thickness of h = 1.5 mm with a nominal yield strength of σ _hk = 60 kg / mm ² ± 5% = 57 ... 63 kg / mm ^{2 is} required. Since the permissible range of change in yield strength is already twice as narrow as in Example 1, continuously cast slabs of mild steel of the proposed chemical composition, wt.%:

FROM Mn Si Al Fe + impurities 0.06 0.40 0.09 0.05 Rest.

By reference data, the yield strength of hot-rolled steel of a given composition is determined: σ _hk = 28 kg / mm ² , and the parameter ε of cold deformation is calculated:

.

.

Then calculate the thickness of the hot-rolled strip H:

.

.

Continuously cast slabs are heated to a temperature of 1250 ° C, rolled on a continuous broadband mill 2000 into strips 1.67 mm thick and wound into rolls. Then the hot rolled strips are subjected to hydrochloric acid etching and cold rolling on a continuous 4-stand mill 1400 to a final thickness h = 1.5 mm. As a result of cold rolling, hardened strips have a yield strength σ _hk = 60 ... 61 kg / mm ² . Due to this, the yield is W = 99.9%.

The options for implementing the method of example 2 for mild steels with different chemical composition are shown in the table.

Table Yield strength of cold rolled packaging tapes and yield No. p / p The content of chemical elements, wt.% σ _hk, kg / mm ² W% FROM Mn Si Al Fe + impurities one 0.01 0.19 0.009 0,03 Rest 53-63 75.6 2 0.02 0.20 0.01 - -: - 58-60 99.8 3 0.06 0.40 0.09 0.05 -: - 60-61 99.9 four 0.11 0.65 0.17 0.10 -: - 61-63 99.8 5 0.12 0.67 0.18 0.11 -: - 58-66 74,2

From the data given in the table, it follows that in the case of the implementation of the proposed method using mild steel of the proposed composition (options No. 2-4), an increase in the yield is achieved by obtaining a predetermined yield strength of the caked tape: the spread of σ _xk does not exceed 2 kg / mm ² . This is important for the stable operation of the automated packaging unit.

With prohibitive values of the declared chemical composition (options 1 and 5), the spread in the values of the yield strength increases, which leads to a decrease in yield.

The technical and economic advantages of the proposed method consist in the fact that rolling of hot-rolled strips with a thickness determined by the proposed experimentally determined dependencies makes it possible to carry out strain hardening (hardening) of cold-rolled strips of low-carbon steels to a predetermined yield strength during subsequent cold rolling. The result is an increase in yield. In addition, the use of mild steel of the proposed composition can further reduce the variation in yield strength values, which is important for a number of consumers of cold-rolled cold-rolled sheet metal.

As a basic object in assessing the technical and economic efficiency of the proposed method, the closest analogue was adopted [3]. Using the proposed method allows to increase the profitability of the production of cured low-carbon sheet steel by 10-15%.

Literature

1. Auth. testimonial. RF №1493339, IPC В21В 1/26, 1989

2. M. A. Benyakovsky and others. Production of automobile sheet. M .: Metallurgy, 1979, pp. 30-31, 98, 146-147.

3. RF patent No. 2432404, IPC C21D 8/04, C21D 9/48, C22C 38/16, 2011

Claims (1)

A method for the production of cured low-carbon sheet steel, including hot rolling continuously cast slabs from steel having the following chemical composition, wt.%:
carbon 0.02-0.11 manganese 0.20-0.65 silicon 0.01-0.17 aluminum no more than 0.10 iron and impurities rest,
subsequent multi-pass cold rolling of the strip to a final thickness h, while hot rolling of the strips is carried out to a thickness H, determined by the formula:

where ε is the relative compression ratio of cold rolling,%;

σ _gk - yield strength of the hot-rolled strip, kg / mm ² ;
σ _hk - the set value of the yield strength of the cold-rolled strip, kg / mm ² .