JPS5836652B2 - Overaging treatment method in continuous annealing - Google Patents

Description

[Detailed Description of the Invention] This invention takes into consideration the design of hearth rolls based on the amount of strain (hereinafter referred to as plastic strain amount unless otherwise specified) that the steel strip receives in the overaging treatment zone in a continuous annealing furnace. To efficiently and quickly produce a cold-rolled steel strip of excellent quality without imparting excessive strain (hereinafter referred to as plastic strain unless otherwise specified) to a copper strip in an over-aging treatment zone. The present invention relates to an overaging treatment method in continuous annealing for the purpose of

In the production of cold-rolled steel sheets, it is common practice to adjust the elongation and hardness of the steel sheet by annealing it after the rolling process.

Conventionally, the heat treatment described above has been carried out by box annealing a cold rolled steel strip.

Box annealing is performed by winding a copper strip into a coil and annealing it as it is, a so-called batch annealing type tight annealing method, and by winding the coil loosely and annealing it, a so-called method.
There is an open coil annealing method.

However, even in the above-mentioned collapsed annealing method, it takes 2 to 30 minutes to complete the annealing.
Production efficiency is low because it takes a long time of 4 days, and
There have been problems in that the quality of the coils tends to vary due to differences in temperature when the coils are stacked, resulting in defects in material quality.

Therefore, in recent years, a so-called continuous annealing method that can process cold rolled copper strips in a short time has been developed and put into practice.

When overaging treatment is performed during continuous annealing, the copper strip is folded back to create a loop structure, and the folding of the copper strip is performed via a hearth roll. If the diameter is not appropriate, excessive bending strain will be applied to the passing steel strip, resulting in finer particles precipitated during overaging treatment, hardening the steel strip material, and deteriorating the quality of the copper strip. have a negative impact on

The inventors of the present application have conducted various studies to prevent the hardening of the copper strip material caused by excessive bending strain in hearth rolls as described above. Since the yield stress, Young's modulus, and tension of the copper strip change depending on the conditions, we obtained the knowledge that the above problem can be solved by taking these into account and appropriately setting the amount of strain in the copper strip that is suitable for the diameter of the hearth roll. Ta.

The present invention has been made based on the above findings, and provides the following methods for controlling the amount of strain that a copper strip undergoes by no-throttle in an overaging treatment zone in a continuous annealing facility.

The feature is that the overaging treatment is performed in such a way that the following formula is satisfied.

The equation giving the above amount of distortion was determined as follows.

The stress and strain conditions that occur in the copper strip during swirling are shown schematically in FIG.

Here, ε is the total strain (elastic strain ε) entering the steel strip 2 of the hearth roll 1.

10 plastic strain εp), σ is the stress.

The relationship between the stress and strain of the copper strip is ε and εYP (yield strain) is σ
=Yε, and in the case of ε≧εYP, we assume σ=σYP (yield stress) and x + c, and furthermore, as compatible conditions, ε1Di11−c22T (bending center C= ), force balance condition Toshi2σY
At P it72, σdx=T must be satisfied, t/
Note that the details of the stress and strain conditions at the time the turn is initiated are shown in Figures 2a and b.

From FIGS. 2a and 2b, the average amount of strain (average in the plate thickness direction) introduced into the copper strip per turn is (the same amount of strain is introduced at the end of the turn as at the start of the turn).

[Di σyp T ε=-((---)2+( )2) given p
t DY DσYP.

Therefore, the total bending strain (Ep
) is ND t σ when the number of rolls is N.
yp T BP=Nε=-((---)2+( )2]p
t DY DσYP.

The above X indicates the distance in the plate thickness direction (see Figure 1).

Note that the above εp (average strain amount) is obtained as follows.

The value obtained by averaging the amount of strain introduced into the steel strip at the start of turning in the thickness direction, that is, the average amount of strain, is expressed by:

ε is the elastic strain ε rather than the strain ε.

is subtracted by p becomes.

Therefore, the above integration need only be performed for ε>σyp/Y.

This integral corresponds to the shaded area in FIG. 2b.

The area of the shaded area in FIG. 2b is as follows.

During roll turning, the above distortion is introduced twice: at the start of the turn and at the end.

Therefore, the average strain amount ε, is obtained by averaging the above value by t and doubling it.

This invention will be explained in further detail by way of examples.

A copper strip consisting of a certain portion was hot rolled at a winding temperature of 680° C., then cold rolled at a rolling reduction of 60 to 75 degrees, and then continuously annealed.

The continuous annealing conditions at this time were as follows.

That is, the copper strip after cold rolling is heated to a temperature of 850°C for 1 time.
The sample was heated and held for a minute, then cooled to 600°C, rapidly cooled from this temperature with jet water for 1 minute, then reheated, and over-aged at a temperature of 400°C for 1 minute.

Table 1 shows the results of the total bending strain when the number of hearth rolls, yield stress and Young's modulus of the copper strip are kept constant, and the steel strip thickness, hearth roll diameter and line tension are varied to various values. has been done.

Example 2 A certain amount of steel used in Example 1 was hot rolled under the same conditions as Example 1, then cold rolled, and continuously annealed under the following conditions.

That is, the steel strip after cold rolling was heated and held at 850° C. for 1 minute, cooled from this temperature by a gas jet, and then overaged for 5 minutes at a temperature of 350° C. according to the method of the present invention.

Table 2 shows the results of the total bending strain when the number of hearth rolls, the yield stress and Young's modulus of the copper strip are kept constant, and the steel strip thickness, hearth roll diameter and line tension are varied to various values. has been done.

Example 3 The same amount of steel as that used in Example 1 was hot-rolled and then cold-rolled under the same conditions as Example 1, except that the continuous annealing and overaging treatment conditions were 450°C. It was carried out under the same conditions as in Example 1.

The results of the total bending strain when the steel strip thickness, hearth roll diameter, and line tension are varied to various values while keeping the number of rolls, yield stress, and Young's modulus of the copper strip constant are the third results. shown in the table.

FIG. 3 shows the relationship between the total bending strain, elongation, and yield point in Examples 1 to 3 described above.

As is clear from the figure, when the amount of distortion is small, that is, 0
．． At 0.01% or less, the elongation of the copper strip increases due to the overaging treatment, and the yield point of the steel strip becomes low, indicating that the effect of the overaging treatment is sufficiently obtained.

On the other hand, the amount of strain is o. It can be seen that when o1% is exceeded, both elongation and yield point deteriorate.

Therefore, in this invention, the amount of distortion is limited to 0.01% or less.

As explained above, according to the present invention, excessive bending strain is not applied to the copper strip passing through the hearth roll in the overaging treatment zone of continuous annealing, and as a result, the steel strip is not adversely affected by the strain, and therefore, The useful effect is that a steel strip of stable quality can be obtained without deteriorating the steel strip material.

[Brief explanation of drawings]

Figure 1 is a schematic diagram of stress and strain states, Figures 2a and b are explanatory diagrams of stress and strain states at the time when turning starts, and Figure 3 is a diagram showing the relationship between strain amount, elongation, and yield point. It is a figure showing a relationship. In the drawings, 1... hearth roll, 2...
...Steel belt.

Claims (1)

[Claims] 1. In order to control the amount of strain applied to the copper strip by the hearth rolls in the over-aging treatment zone of continuous annealing equipment, however, in the above formula, N: number of hearth rolls, D: hearth roll diameter ( mm), t: steel strip thickness (g), T: line tension per unit steel strip (kg/yta),
Y: Young's modulus of the steel strip at the overaging temperature (kg/myi), σYP: Yield stress of the steel strip at the overaging temperature (kg/x
i) and are shown respectively. An overaging treatment method in continuous annealing, characterized in that the overaging treatment is carried out such that the following formula is satisfied.