JPH0336214A - Method for continuously annealing non-oriented electrical steel sheet - Google Patents

Abstract

PURPOSE:To execute the finish continuous annealing to a non-oriented electrical steel sheet without developing pickup by running the steel sheet containing a specific quantity of Si and Al under weak reducing or reducing atmosphere at the specific sheet temp. in the specific dew point of the range in the furnace. CONSTITUTION:In the finish continuous annealing for the non-oriented electrical steel sheet containing <=2wt.% [Si+Al], the temp. of steel sheet running in the range in the furnace under a weak reducing or reducing atmosphere of the first half part in the furnace and in -15 deg.C<DP<+5 deg.C of high dew point(DP), is controlled at <=900 deg.C. By this method, the development of oxide of Fe-Si series on the surface of the steel sheet is restrained and the sintering reaction to roll in the furnace caused by lowering m.p. of oxide is prevented. Therefore, the development of pickup based on the sintered material can be suitably prevented.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a continuous annealing method for non-oriented electrical steel sheets.

[Conventional technology]

In the production of non-oriented electrical steel sheets, especially electrical steel sheets with [Si+A Q ] of 20% or more, in-furnace pick-up that occurs during final annealing poses a major problem in terms of product quality. In other words, this type of pressing method is a cause of deterioration of magnetic properties due to a decrease in space factor and the like.

Conventionally, in such pressing methods, prevention of this occurrence has been studied in relation to hot rolling conditions, pickling conditions, and annealing conditions.

[Problem to be solved by the invention]

Among these conditions, regarding the final annealing conditions, attempts have been made to prevent pick-up by changing the material of the furnace roll, for example, using carbon rolls, various thermal spray rolls, or ceramic rolls as the furnace roll. Many proposals have been made.

However, rolls made of these materials not only have various problems in terms of strength, workability, manufacturing cost, etc., but also cannot be expected to be reliably effective in preventing pick-up, making their practicality problematic. .

[Means to solve the problem]

As mentioned above, conventionally, pickup occurrence and finish annealing conditions have mostly been studied from the viewpoint of the material of the furnace roll, and there have been few cases in which other factors have been studied.

In response to this, the present inventors investigated the relationship between the atmosphere in the furnace, the heating pattern, and the occurrence of pickup.
We have discovered that by adjusting the temperature of the steel sheet being passed to a specific condition in relation to the dew point in the furnace, it is possible to effectively prevent the occurrence of pickup without using rolls made of special material.

The present invention was made based on such knowledge, and its characteristics are that in continuous finish annealing of non-oriented electrical steel sheets with (Si+AQ)≧2tmt%, the dew point DP is -15℃< DP
The plate temperature of the steel plate passing through the furnace area of <+5℃ is 900℃.
The reason is that it is controlled as follows.

The present invention will be explained in detail below.

When considering the heating and soaking zone during final continuous annealing of non-oriented electrical steel sheets, in the first half of the furnace, scale etc. of the steel sheet undergoes the following reaction in a reducing or weakly reducing atmosphere, resulting in 3-FeO+)l. , −+ I(□O+ FeF
e3O4+4H2→4H20+3Fe Therefore, the atmosphere has a higher dew point than the latter half of the furnace. Generally, the dew point DP inside the furnace is -15°C<DP<+5°C in the first half of the furnace.
In the second half of one furnace, the value of DP<-15°C is taken.

In the case of a high Sj electrical steel sheet with (Si + A Q )≧2tyt%, the sheet temperature is 90% in a high dew point atmosphere such as the first half of the above furnace.
When the temperature exceeds 0°C, (12) Fe-Si-based oxides are generated even under a 10% reducing atmosphere, and a sintering reaction occurs on the furnace roll due to the lowering of the melting point of the oxides. Then, the sintered material on this roll hits the back side of the steel plate being passed and, in some cases, adheres to the plate, causing pickup.

This is why when inspecting the rolls during continuous furnace repair, sintering reactions are more often seen in the rolls in the first half of the heating and soaking zone than in the second half.

Therefore, in the present invention, the angle at which pickup is likely to occur is 15°.
In the furnace area (mainly the front half area of the furnace) with an atmosphere of C < DP < +5℃, the temperature of the steel plate to be threaded is set to 9.
The temperature is controlled to below 00°C. On the other hand, the dew point DP is
In the furnace area (mainly the rear half of the furnace) where DP≦-15℃,
The plate temperature may be set to 900° C. or higher, and may be metallurgically determined depending on each grade of the non-oriented electrical steel sheet.

Figure 1 shows a non-oriented electrical steel sheet with 21wt% Si.
The limit of occurrence of pickup was investigated based on the relationship between the steel plate temperature and the dew point inside the furnace.In contrast, when the dew point DP is in the DP>-15℃ region and the plate temperature exceeds 900℃, pickup occurs. It can be seen that by setting the plate temperature to 900° C. or less, the occurrence of pickup can be effectively suppressed.

Note that the atmosphere inside the finishing continuous annealing furnace is weakly reducing or reducing, and is usually maintained at an atmosphere where H2>10%.

In order to more reliably prevent pickup, which is the objective of the present invention, while ensuring magnetic properties, (Si+A Q
) It is preferable to adopt a specific hot rolling coiling temperature and final annealing temperature depending on the amount. In other words, the steel plate (Si+A
Q) It is preferable to carry out hot rolling and 4-finish annealing at the hot rolling coiling temperature and final annealing temperature under the following conditions.

Finish annealing temperature: 940°C or less Finish annealing temperature: 1000°C or less Finish annealing temperature: 1060°C or less If the hot rolling coiling temperature exceeds each of the above upper limit temperatures, pick-up is likely to occur, while if it falls below the lower limit temperature, the iron loss value deteriorates. Moreover, when the final annealing temperature exceeds the above-mentioned upper limit temperature, the magnetic properties, especially the magnetic flux density, deteriorates, while when it falls below the lower limit temperature, problems occur in ensuring grain growth, that is, in iron loss value.

In this way, by adjusting the hot rolling coiling temperature and final annealing temperature according to the amount of (Si + A Q ), pickup can be more reliably prevented and the magnetic properties shown in the figure below can be ensured. can.

〔Example〕

After heating a slab having the composition shown in Table 1 to 1140°C, 2. Hot rolled to Ommt, then hot rolled sheet annealed depending on the component group, cold rolled or warm rolled to 0,50mmt, then finish annealed by continuous annealing (furnace atmosphere H: 25 %) was carried out.

The magnetic properties and occurrence of pickup of the obtained non-oriented electrical steel sheet are shown in Table 2 together with the hot rolling and winding conditions and finish annealing conditions.

Table 1 7 - [Effects of the Invention] According to the present invention described above, the occurrence of pickup can be appropriately prevented by controlling the plate temperature according to the dew point in the annealing furnace.

[Brief explanation of drawings]

FIG. 1 shows the limit of occurrence of pickup in terms of the relationship between steel plate temperature and furnace dew point. Figure 2 (a), (0 indicates the annealing heat cycle adopted in the example. =9--15 Furnace dew point

Claims (1)

[Claims] In continuous finish annealing of a non-oriented electrical steel sheet with [Si+Al]≧2wt%, an area in the furnace where the dew point DP is -15°C<DP<+5°C in a weakly reducing or reducing atmosphere is A continuous annealing method for a non-oriented electrical steel sheet, characterized by controlling the temperature of the steel sheet being passed to 900°C or less.