DE2456268A1 - METHOD OF ANNEALING OF ROLLED STEEL PRODUCTS - Google Patents

Description

ITALSIDEK S.p.A., Italy

Process for annealing rolled steel products

The invention relates to a method for producing an annealed or quenched and tempered steel (annealed steel) with a predetermined mechanical Hardness. In particular, a solution to the technical problem is to be found according to the invention, continuously a rolled steel product with a predetermined and uniform mechanical hardness to be determined independently of local changes in the carbon content.

The invention is based on the principle that is rolled Subject steel product to double measurement of magnetic property; one upon entry into the Annealing furnace to determine the actual carbon content and thus to select the appropriate annealing

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cycle to the desired hardness after treatment obtain; the other when exiting the annealing furnace to measure the hardness according to a procedure, which the influence of the carbon content, which can vary from case to pail, on the magnetic Property itself taken into account. To determine the mechanical hardness of steel, apart from direct measurements indirect techniques already known which have the undeniable advantages have with respect to the preceding that they ensure a continuous and non-destructive measurement. All indirect measurements are carried out by means of devices in which the determination the mechanical hardness value is carried out by measuring a magnetic property of the steel, which is indicated by a transducer suitably arranged at the exit from the annealing furnace thanks to a correlation between this magnetic property and the mechanical one Hardness.

So the working principle of these facilities is based on the measurement of the hardship and the exploitation of the relationship, which relates this property to one of the following magnetic properties puts:

a) residual induction B;

b) permeability / α

c) coercive field H;

These correlations, however, are determined by the chemical composition of the rolled strip and by temperatures during finished hot rolling and due to the hot winding temperature influenced. For steels, however, that are normally on

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continuous annealing lines "are treated the predominant importance in the chemical composition and thus in practice in the carbon content . It is also known that the carbon content with regard to the nominal value or nominal value from bundle to bundle and over the same bundle between head, Middle and end part varies, although the variations in the transverse direction have to be mentioned all the more. The influence of these changes in chemical composition is such that to determine the mechanical hardness within permissible [tolerances a continuous measurement of the carbon content along the belt in addition to the magnetic measurements due to the known devices should. To overcome this difficulty, were the materials treated so far in classes with a limited field of variation of the nominal carbon salary divided. Considerable limitations are encountered here as a result of the number of Classes that become necessary; on every pail will not the problem of changing the carbon content The determination of is still resolved via the tape Steels with properties outside the tolerance before annealing are possible. It has now turned out that by the measure according to the invention it is possible will solve the above difficulties, providing a method for indirect magnetic, continuous and non-destructive measurement of the value of the mechanical hardness of a rolled steel product at the exit from the annealing furnace independently any change in carbon content becomes possible. A way has actually been found into the correlation formula between the values of a magnetic parameter found at the exit from the furnace and the values of mechanical hardness

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To incorporate a correction element that takes into account the carbon content in front of the annealing line, which
continuously by measuring the value of the
same magnetic property at entry into
the furnace is determined; (a measurement taken from
For this reason, taking place after the furnace would lead to unreliable values as a result of the influence, apart from the carbon content, of the degree of recrystallization that occurs during annealing). This coupling of the mechanical measurement in front of the furnace with that behind the furnace is equivalent to the determination of the carbon content and thus allows an interpretation of the magnetic measurement made behind the furnace.

The above-mentioned correction element is derived from the correlation, which is determined by the statistical Analysis of an accumulation of puncture data j

C = K (M _0R ) ^ + K ₀ (1)

- C is the carbon content in ppm;

- Mqtj is the value of the magnetic property before Annealing furnace}

- K and K constants;

- «t is an exponent whose value is between 2 and 3» 5 lies.

Thus, the new system of magnetic measurement to which the invention relates is based on the following

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linear regression equation generated by computer using statistical analysis of an accumulation of functional data according to the least squares method is determined:

DV a;.% + B M ₀₀ + c M _CR 'S ₊ d M _Q0 , S + A _£

where <o (.

/ ^on the basis of (1) equals l / Ο

represents the component that is introduced into the correlation to make the magnetic measurement called Correct function of carbon content;

- K and K are constants whose value is given by the statistical analysis of an accumulation of functional data can be determined;

- Mq _{0 is} the magnetic measurement behind the furnace;

- S is the nominal thickness of the tape; and

the coefficients a, b, c, d and the constant A _{Q are} determined by statistical analysis of an accumulation of function data; For example, for carbon steel sheet (steel with a nominal C content between 600 and 1000 ppm) with a thickness between 0.17 and 0.35 mm, the following values were determined:

a = 0.261

b = 0.215

c = 0.0104

d = 0.0215

A ₀ = 38.874

More precisely, there is the method for producing a

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annealed steel rolled product with predetermined mechanical hardness therein, the rolled product, its carbon content is only roughly known to suspend the following operations or processes:

- magnetization;

- Determination of any magnetic ear characteristics M before entry into the annealing furnace (Mqjj), which is a function of the carbon content, based on the following relationship isti

0 = K (M _0R f + K ₀

where G is the carbon content in ppm, ^M GR ^ ^er ^ ^er ^ ^ ^er selected magnetic property, K and K are constants whose value can be determined statistically from the experimental data, and oi is an exponent whose value between 2 and 3, 5 lies;

- Choice of the indicated glow cycle as it is most suitable with respect to the desired hardness taking into account the value C;

- Determination of the value of the magnetic property. M at the exit from the annealing furnace (Mq ₀ ) and at the same point where the measurement of Mqtj was carried out;

- Determination of the range of mechanical hardness by means of the following relationship

^{D = a M} 0R + b M ₀₀ + c M _0B .S + d M ₀₀ -S + A _Q (2)

The yor-

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part, which regarding the state of the art in the The fact to look for is that if the same area of steel enters and exits the Annealing furnace is checked, only equation (2) is needed; otherwise expressed is not necessary, the device for the magnetic measurement of each. Times to calibrate as their displays are independent of the changes in the carbon content of the steel from Sample to sample and for one and the same sample are from place to place.

The following example explains the invention without limiting it.

Example:

A cold rolled steel strip having the following properties must be annealed j

. Thickness 0.17 mm

Carbon content (nominal value or nominal value?) 600 ppm width 800 mm

Since the hardness required at the end of the continuous annealing line is between 56 and 59 Rockwell (B.30T), the tape is subjected to the following process according to the invention:

a) magnetization to saturation;

b) determining the coercive field at the entry of the strip into the annealing furnace, M _0R = 300 mY (the measurement of the field is converted into mV ");

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c) Calculation of the carbon content in ppm the formula:

G = 22.36 * ΙΟ " ^5. (M _CR ) ³ + 151.7 = 907;

d) Choice, based on the Grlühstrasse workflow and taking into account the value of G and the desired hardness, the following

- heating to 62O ⁰ G in 30 seconds;

- Equalization or soaking at 620 ^° C. for 27 seconds;

Slow cooling down to 10 ^° C. in 32 seconds;

- rapid cooling to 50 ⁰ C in 27 seconds;

e) determining the coercive field at the exit from the annealing furnace M ₀₀ = 120 mV;

f) Calculation and verification of the value R3QI the basis of the relationship given under (2)

R3OT = 0.261 M _0R - 0.215 M ₀₀ - 0.0104 M _0R S + 0.0215 M _Q0 S + 38.874

Substituting the known values of M _QR , M ₀₀ and S results in the value 58 for R30T. It should be pointed out that if the annealing cycle had been applied with regard to the nominal carbon content, the value 63 would have been obtained for R30T that would have been outside the tolerance limits.

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Claims (2)

PATENT CLAIMS 1. Process for the continuous production of an annealed rolled steel product with a predetermined Uniform mechanical hardness, independent of local fluctuations in the carbon content, thereby characterized in that the rolled steel product is subjected to the following gates: - magnetize; , - Determine any magnetic property M before entering the annealing furnace (M _0R ), which is a union of the carbon content on the basis of the relationship G = K (M _0R f> K _o (1) is, where C is the carbon content in ppm; Mq _{R is} the value of the chosen magnetic property; K and K are constants whose value can be derived statistically from experimental data and ii is an exponent whose value is between 2 and 3.5; - Selecting the appropriate annealing cycle as a function of desired hardness and the specified carbon content; - Determination of the value of the magnetic property M at the exit from the annealing furnace (M ₀₀ ) and at the same point at which the measurement M _{0R was} carried out; - Determining the value of the mechanical hardness by means of the following relationship; D = a M _{CR +} b M ₀₀ + c M _0R .S + d M ₀₀ -S + A _Q (2) - 10 50 9 8 43/0557 - ίο - where D is the mechanical hardness, S is the thickness at the point where the determinations of M ₀₀ and M _GR were made; and a, b, c, d and A _{Q are} coefficients, the values of which are determined by analyzing an accumulation of functional data according to known statistical methods. 2. Process for the continuous production of annealed rolled steel products with predetermined uniform mechanical hardness, independent of local fluctuations in the carbon content, im essentially as described, set forth and claimed in the examples. 509843/0557