JPH03223424A - Production of semiprocessed nonoriented silicon steel sheet excellent in magnetic property - Google Patents

Abstract

PURPOSE:To improve the iron loss and magnetic flux density of the silicon steel sheet by carrying out hot rolling, coiling, heating after cold rolling, and continuous annealing under respectively specified conditions at the time of producing a semiprocessed nonoriented silicon steel sheet with a specific composition. CONSTITUTION:A slab which has a composition consisting of, by weight, <=0.005% C, 0.1-1.0% Si, at least 0.25% Mn, at least 0.03% P, 0.004-0.080% SolAl, 0.001-0.005% N, and the balance Fe with inevitable impurities and satisfying 2<=[SolAl(atomic%)/N(atomic%)]<=20 is heated to >=1150 deg.C and hot rolled. Subsequently, the resulting steel strip is coiled at a coiling temp. CT represented by 450<=CT<=-7.5 [Al(atomic%)/N(atomic%)]+650( deg.C), pickled, cold-rolled, heated at a heating rate HR satisfying 5<=HR<=40( deg.C), and continuously annealed at >=720 deg.C soaking temp. By this method, the semiprocessed nonoriented silicon steel sheet excellent in iron loss and magnetic flux density can be obtained with high production efficiency.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing semi-processed non-oriented electrical steel sheets that are subjected to strain relief annealing at the customer's end. The present invention provides a method for manufacturing steel plates at low cost.

[Conventional technology]

So-called low-grade non-oriented electrical steel sheets with a Si content of 1% or less are
Although the iron loss value is high, the magnetic flux density is high.

Also, because it is inexpensive, it is used in large quantities, mainly in small motors for home appliances. These electromagnetic steel sheets are fully processed materials that are made to have predetermined magnetic properties by the steel manufacturer, then assembled into products after being punched by the consumer, and are subjected to strain relief annealing after being punched by the consumer to achieve the final magnetic properties. It is broadly classified into semi-processed materials.

Two main magnetic properties are required for electrical steel sheets: core loss and magnetic flux density.The metallurgical factors that determine these magnetic properties include steel composition, ferrite grain size,
It is known that there are many kinds of collective tissues. In order to reduce iron loss, it is effective to increase the amount of Si and increase the specific resistance, but in order to reduce the iron loss value at a certain Si level, increasing the ferrite grain size is most effective. . Furthermore, in order to improve the magnetic flux density, it is necessary to develop a texture that is favorable in terms of magnetic properties. Based on these,
In order to improve the magnetic properties of semi-processed materials,
The following technologies have been disclosed.

■Technique of annealing a hot-rolled sheet after hot rolling (for example, JP-A No. 57-203718) ■Technology of self-annealing by hot-rolling and high-temperature coiling (for example, JP-A-54-76422) ■Two-cold rolling , a technique of performing two-time annealing ■ a technique of performing temper rolling after annealing ■ a technique of coarsening the grain size using precipitation of AiN (Japanese Patent Publication No. 50-8976, Japanese Patent Application Laid-Open No. 1-139720) Among them, method (2) aims to reduce iron loss by increasing the ferrite grain size after cold pressing and annealing by annealing at the hot-rolled sheet stage, and also aims to improve magnetic flux density by improving the texture. However, since a new annealing process is added, a significant increase in cost cannot be avoided.

Method (2) performs self-annealing using the heat possessed by the hot-rolled sheet after rolling, and is more advantageous than method (2) in terms of cost. However, if this method is to be effective, it is necessary to raise the winding temperature extremely high, which makes stable operation difficult and also makes it difficult to obtain uniform characteristics over the entire length of the coil. Furthermore, there is also the problem that the surface quality deteriorates due to internal oxidation during winding.

Method (2) requires more steps than method (2), resulting in a significant increase in cost, and is a manufacturing method that conflicts with the mission of low-grade electrical steel sheets to reduce costs.

Method (2) involves annealing (hereinafter referred to as "finish annealing") at the steel manufacturer, followed by skin pass rolling, which induces strain to improve grain growth during strain relief annealing at the customer, thereby reducing iron loss. It is something that we try to do. However, even in this method, the step of temper rolling is added, leading to an increase in cost. In addition, since the temper rolling rate is high, there is a problem in that shape defects such as ear waves and mid-elongation occur.

■The method is. A technology that utilizes the precipitation of AlN. When finished annealing, the AIN pinning effect produces fine grains, and by releasing the AIN pinning during strain relief annealing, coarse ferrite grains appear, reducing core loss. It is. Among these, Special Publication No. 50-8976 has a C content of 0.0.
05 wt% or more to smooth AiN precipitation during final annealing, but in order to avoid magnetic aging due to C, annealing must be performed in a decarburizing atmosphere, which greatly reduces production efficiency. In addition, by using a high C material, although the effect of smoothing the precipitation of AIN during finish annealing is utilized, on the other hand, the manufacturing process attempts to achieve the contradictory phenomenon of lowering C through decarburization at the same time. Law and therefore. It is difficult to stabilize the precipitation state of AlN, and it is also difficult to stabilize the coarsening of AlN. Furthermore, since the aim is simply to reduce core loss by coarsening the ferrite grains, the magnetic flux density, which is another index of magnetic properties, tends to be the same or to decrease even after strain relief annealing. Also, JP-A-1-1397
Similar to the above technology, No. 20 simply coarsens the ferrite grains and aims at lower core loss. For this reason, the finish annealing temperature is also low-temperature annealing of 700° C. or less simply from the viewpoint of punchability, but at this annealing temperature, the effect of improving the magnetic flux density as described later is not observed, and the magnetic flux density is at a low level.

[Problem to be solved by the invention]

The above-described technology for coarsening ferrite grains using precipitation of AIN achieves a certain level of reduction in core loss without causing a significant increase in cost, and is an effective technology for improving core loss. However, the magnetic flux density is by no means at a satisfactory level. In particular, in the field of small motors that the present invention targets, low magnetic flux density materials cannot achieve further miniaturization of the motor and also lead to an increase in current during use. If you do so, you will not receive a high evaluation. For this reason, the development of an electrical steel sheet with excellent iron loss and magnetic flux density while taking advantage of low cost has been awaited.

In view of the problems of the conventional method described above, the present invention provides a method for manufacturing a semi-processed non-oriented electrical steel sheet with a significantly high magnetic flux density, which enables further reduction in core loss after strain relief annealing using a low-cost manufacturing method. We aim to provide the following.

[Means to solve the problem]

The present inventors have repeatedly conducted experiments and research in order to achieve both low iron loss and high magnetic flux density without increasing cost in semi-processed non-oriented electrical steel sheets that are intended for strain relief annealing at customers. It's here. As a result, the solid solution state of AIN before final annealing was optimized by specifying both the steel composition and hot rolling coiling temperature,
In the subsequent final annealing, continuous annealing is performed by optimizing the heating rate and temperature for the steel components.
The present invention has been completed based on the new discovery that it is possible to appropriately match the progress of precipitation and recrystallization to improve the magnetic properties, especially the magnetic flux density, after strain relief annealing.

That is, the feature of the present invention is that C: 0.005%it%
Below, Si: 0.1 to 1.0 wt%, Mn: 0
．． 25wt% or more, P: 0.0:ht% or more, Sol,
Al: 0.004-0.080wt%, N: 0.0
01 to 0.005 wt%, the balance consisting of Fe and inevitable impurities, and Sol. The atomic weight ratio of Al content and N content is {2≦(Sol, Al(at%)/N(at%))}≦20
Heating a slab with a composition that satisfies the above to 1150℃ or higher,
After hot rolling, the steel plate is 450≦CT≦-7,5(^1(at%)/N(at%
)) Coiling at a coiling temperature CT in the range of +650 ('C), pickling the steel strip, cold rolling, and heating at a heating rate HR in the range of 5≦HR≦40 ('C/s). , continuous annealing is performed at a soaking temperature of 720° C. or higher.

[For production]

Hereinafter, the configuration of the present invention and the reasons for its limitations will be explained in detail.

First, the reasons for limiting the composition of steel will be explained.

C: When a large amount of C is contained, it becomes necessary to perform decarburization annealing during finish annealing or strain relief annealing, resulting in a decrease in productivity. At the same time, the state of AIN precipitation is affected by the degree of progress of decarburization and becomes unstable. In order to eliminate the need for such decarburization annealing, stabilize AiN precipitation, and prevent magnetic aging, C:
Ultra-low carbon steel with a carbon content of 0.005 wt% or less.

Si: Since an increase in Si has a large effect of increasing specific resistance and reducing iron loss, the lower limit is set to 0.1 wt%.

However, if it exceeds 1 wt%, the saturation magnetic flux density will decrease and the cost will increase, so the upper limit is set at lwt%.

Mn: In the present invention, Mn is an important component for improving texture. As described later, the amount of Mn is 0.25w
If it is less than t%, a low iron loading can be achieved by coarsening the ferrite grains, but even if the heating rate is optimized, the texture will not be improved and the magnetic flux density will not be improved.Therefore, the lower limit is set to 0.
It is set to 25wt%. However, unnecessarily increasing the amount of Mn will only lead to an increase in cost, so it is preferable to add Mn at an upper limit of 2%.

P: Normally, P is often added to improve punchability, but in the present invention, P is added to promote the precipitation of AjN during final annealing.
It is defined as an essential component as a stabilizing element. If P is less than 0.03 wt%, sufficient precipitation of AIN will not be obtained even if the solid solution state of AIN before final annealing is optimized, and coarsening of ferrite grains will not be achieved.Therefore, the lower limit is set to 0.03 wt%.
03wt%. However, from the viewpoint of preventing deterioration of rollability and punchability due to embrittlement, it is desirable to keep P at 0.5 wt% or less, and furthermore, since adding P strengthens the effect of suppressing grain growth, Taking this point into consideration, it is preferable to set the upper limit to 0°3 wt%.

Sol. Al: Sol, consideration is the most important element in the present invention. The present invention utilizes the grain boundary pinning effect and texture improving effect due to the precipitation of fine AIN during final annealing. For this reason, Sol. Al
The amount is 0.004 to 0.080, which is suitable for the precipitation of fine AtN.
Limited to wt%. If it is less than 0.004 wt%, the required amount of AjN precipitation cannot be obtained.

On the other hand, if it exceeds 0.080 wj%, the pinning effect cannot be utilized because the precipitated AIN aggregates and becomes coarse.

N: N is also an element that affects the precipitation of AIN.

If it is less than 0.001 i+t%, sufficient AiN precipitation cannot be obtained, while if it exceeds 0.005 ist%, the magnetic properties will deteriorate.

Sol. Al (at%)/N (at%): As mentioned above, the amount of At and the amount of N influence the precipitation of AIN, but the precipitation of AIN is not uniquely determined by the individual contents; The amount, size, and distribution form of lunar N precipitation are determined by the amount and the existence ratio of N amount. Sol. A
Atomic weight ratio of l and N [Sol.

Al(at%)/N(at%)] (hereinafter simply [Aj/
If [Ai/N] is less than 2, the amount of precipitated AIN necessary for pinning cannot be obtained, and if [Ai/N] exceeds 20, the AtN that has precipitated will aggregate and become coarse.
Fine AIN, which is an important element in the present invention, cannot be produced.

Next, the component conditions and processing and treatment conditions of the present invention are
This will be explained from the perspective of optimizing solid solution and increasing magnetic flux density.

{Optimization of AlN solid solution) In the present invention, steel having the above-mentioned composition is subjected to hot rolling. Regarding the heating temperature during hot rolling, heating at a temperature of 1150° C. or higher is essential in order to sufficiently promote solid solution of AIN.

In the present invention, it is essential to have sufficient solid solution of AiN before final annealing, and it is intended to achieve solid solution of AI at low cost without solution annealing at the hot rolled sheet stage. It is. For this purpose, it is important to control the coiling temperature after hot rolling within an appropriate range and to suppress precipitation of AIN during coiling. In order to clarify this point, the following test was conducted.

Steel A1 with different At and N contents as shown in Table 1
After heating the A8 slab to 1250°C and hot rolling, 4
Winding was carried out at temperatures between 50 and 700°C. After being pickled and cold rolled to a thickness of 0.5m, the plate was heated at 10°C.
Finish annealing was performed by continuous annealing at 820° C. for 1.5 minutes at a heating rate of /S. Figure 1 shows these steel plates.
Effect on iron loss (W□, /,.) after strain relief annealing under the conditions of heating rate 5°C/min and soaking at 750°C for 2 hours [^1
7N] and the influence of the coiling temperature, and the photograph in FIG. 2 shows the ferrite structures of steels Al, A4, and A8 coiled at 500° C. after strain relief annealing.

As is clear from Figure 1, the iron loss after strain relief annealing is 5 W.
The good range of less than /kg depends on both [AIc] and the winding temperature. In the region where [AI/N] is less than 2, the iron loss is 5°OW/k at any winding temperature.
On the contrary, when looking at the same winding temperature, even if AI/Nl is above a certain level, the iron loss is 5. OW/
kg or more, and it can be seen that there is an optimal [AI/N] region. This optimum range of [AI/N] is expanding as the winding temperature decreases. In other words, [AI/
[-7,5({Al)/(N))+650]
If it is wound at a temperature below 'C, the iron loss is 5.0W/kg.
It has become clear that less than This is A
This is caused by the precipitation state of IN and coarsening of ferrite grains. As shown in the photograph of FIG. 2, in the region where [AAc] is less than 2, even if the material is rolled at a low temperature, precipitation of AIN is small, so that coarsening of ferrite grains does not occur. On the other hand [AI/N]
If the temperature is high or the winding temperature is high. Although precipitation of AlN occurs, since AjN aggregates and becomes coarse, the ferrite grains do not become coarse. On the other hand, [AI/
N] and the winding temperature are within the range specified by the present invention, the ferrite grains become coarse due to the grain growth driving force when the fine J18AjN pinning is released, and low core loss is achieved.

In the present invention, based on these results, [AI/Nl is 2 to 2]
20, and the winding temperature is [-7,5((A
)/(N)) +6501 'C These are the following.

Regarding the control of AIN precipitation during winding, lowering the winding temperature is effective, but if the winding temperature is extremely low, stable operation becomes difficult, and the plate The lower limit is set to 4 to avoid shape defects such as thickness fluctuations.
Limited to 50°C.

In order to stably control AIN precipitation during continuous annealing as in the present invention. In addition to optimizing the solid solution state of Al, it is necessary to take measures to further promote the precipitation of AIN. As a result of examining various methods for this purpose, it became clear that the addition of P was the most effective. Slabs of steel B1 to B6 with varying amounts of P as shown in Table 1 were prepared at 1
After heating to 200°C and hot rolling, it was wound up at 500°C, followed by pickling and cold pressing to give a plate thickness of 0.5mm. Thereafter, continuous annealing was performed at 800°C for 2 minutes at a heating rate of 10°C/S, and strain relief annealing was performed at a heating rate of 5°C/min and soaking at 750°C for 2 hours. FIG. 3 shows the iron loss CWxs/s of the steel plate thus obtained. ) shows the influence of P on

As shown in the figure, when P is 0.03 wt% or more, the ferrite grains become coarse during strain relief annealing, resulting in an iron loss of 5 and OW.
/kg or less, which is a good value. On the other hand, P is 0.03wt
When the P content is less than 0.03 wt%, the grain size only increases due to normal grain growth, and coarse grains do not occur.A similar investigation was conducted on other [AI/N] steels, but in all cases, when the P content is less than 0.03 wt%, the ferrite grain size increases. No coarsening occurred.

(Higher magnetic flux density) As mentioned above, by regulating the steel composition and coiling temperature, the solid solution state of AIN before final annealing is optimized, and by promoting the precipitation of fine IN, coarse ferrite Although it is possible to achieve low iron loss through coarsening, it is not possible to achieve high magnetic flux density by this alone.As a result, the inventors have repeatedly studied ways to improve magnetic flux density while retaining the advantages of coarsening. It has been newly discovered that a high magnetic flux density can be achieved after strain relief annealing by containing Nn at a certain level or more and optimizing the final annealing conditions, especially by appropriately selecting the heating rate. The final annealing conditions, which are the most important requirements of the present invention, will be explained below.

Slabs of steel C4 shown in Table 2 were heated to 1250°C and hot rolled, then wound up at 500°C, followed by pickling and cold rolling to give a thickness of 0.5cm. This steel plate was subjected to finish annealing. Figure 4 shows the iron loss (W1s/s) and magnetic flux density (Bs,) of these steel plates after final annealing and strain relief annealing at a heating rate of 10°C/min and soaking at 750°C for 2 hours.
As shown in Figure 0, which examines the influence of heating rate on the magnetic flux density, both iron loss and magnetic flux density are dependent on the heating rate.

The behavior of iron loss is divided into three regions with heating rates of 5°C/S and around 50°C/S.6 In the low heating rate region of less than 3°C/S, iron loss is low if finish annealing is performed. It is the lowest, and the change due to strain relief annealing is also small. This is because the pinning of AIN weakens during final annealing, secondary recrystallization already occurs during the final annealing stage, and the ferrite grains become coarse.

Therefore, changes due to strain relief annealing are small.Conversely, in the high heating rate region of 60°C/S or more, the iron loss is lower than the intermediate region when finished annealing, but after strain relief annealing, the iron loss is lower than the intermediate region. -Highest of all, this is because recrystallization and grain growth precede AIN precipitation in the final annealing stage, so the grain growth suppressing effect of AIN weakens and grain growth occurs to some extent, but in strain relief annealing, AIN inhibits grain growth. This is thought to be because although it is suppressed, only normal grain growth occurs, so the reduction in iron loss is small.

On the other hand, in the intermediate region of the heating rate of 5 to 40° C./S, although fine AIN is precipitated during final annealing, secondary recrystallization does not occur, resulting in a small grain size and a high iron loss value.

However, the effect of coarsening of ferrite grains due to the release of pinning of fine AiN during strain relief annealing.

Coupled with the texture improvement effect described later, iron loss is significantly reduced.

Regarding the magnetic flux density, first, in the low heating rate region of less than 5° C./S, the ferrite grains are already coarsened and the magnetic flux density is low in the finish annealing.

Even after strain relief annealing, the change is small, and the characteristics are the same as after rough finish annealing. A heating rate region where the heating rate is 5° C./S or more shows a higher magnetic flux density than a low heating rate when finish annealing is performed, but particularly after strain relief annealing, a remarkable heating rate dependence is observed. In other words, in the region where the heating rate is 50°C/S or higher, no coarsening occurs during strain relief annealing, and the change in magnetic flux density is small.On the other hand, when the heating rate is 5~B, the magnetic flux density improves significantly and exhibits excellent properties. ing.

Although the details of this phenomenon are not necessarily clear, in the intermediate heating rate region, fine AIN precipitates at appropriate times during the recovery during final annealing and the early stage of recrystallization, resulting in selective growth of recrystallized grains. (100), which affects the texture formation and is advantageous for the magnetic properties.
110) Increased surface strength, disadvantageous for magnetic properties (111)
This is thought to be due to the suppression of the increase in the number of surfaces. On the other hand, in the case of a low heating rate, precipitation of AIN takes precedence, and conversely, in the high heating rate region, recrystallization and grain growth take precedence, so such texture improvement is not achieved. In the case of coarsening by normal secondary recrystallization (111
) The surface strength tends to be strong, but as in the present invention, the surface strength becomes fine and (100) at the final annealing stage.

When the (110) plane component is large, the frequency of occurrence of (100) and (110) plane crystal grains increases even in secondary recrystallization during strain relief annealing, and even though they are coarse grains, after strain relief annealing, This is expected to improve the magnetic flux density.

Next, we investigated in more detail the effects of these heating rates on the texture, and found that it was not possible to achieve a stable high magnetic flux density simply by optimizing the heating rate. It became clear that there was a need to optimize the 6 with different amounts of Mn as shown in Table 2
The steels C1 to C6 were made into steel plates with a thickness of 0.5 mm by the same process as the steel C4 described above. These steel plates were subjected to finish annealing at various heating rates for 2 minutes at a temperature of 700 to 850°C, and then further annealed at a heating rate of 10°C/min and 750°C.
Strain relief annealing was performed under the condition of soaking for 2 hours. Figure S shows the magnetic flux density (Bs.) after strain relief annealing when finish annealing is performed at a heating rate of 10''C/s, classified by 1.80.As shown in the figure, the annealing temperature is When the temperature is as low as 700° C. or when the amount of Mn is less than 0.25 wt%, high magnetic flux density cannot be achieved even though the heating rate is optimal.

In other words, if the annealing temperature is low. Even if the timing of AlN precipitation is optimized, the texture is not improved because the progress of grain growth is insufficient. Furthermore, when the amount of Mn is low, the selection phenomenon of recrystallized grains due to interaction between AIN and Mn does not occur in the early stage of recrystallization, so even if grain growth is sufficient, the texture is not improved.

As described above, the heating rate and annealing temperature were optimized by containing more than a certain amount of lupus. It has become clear that by appropriately matching the timing of AlN precipitation and the progress of recrystallization, it is possible to achieve both low iron loss and high magnetic flux density. Therefore, in the present invention, the annealing temperature is 720°C within the heating rate range of 5 to 40°C/S, which has the greatest effect.
The above is defined as the optimum finish annealing conditions.

〔Example〕

A 220m5 thick slab of steel with the six types of composition shown in Table 3 was hot-rolled under the hot-rolling conditions shown in Table 4, followed by pickling and cold rolling, resulting in a plate thickness of 0.5 ■The steel plate was used. These steel plates were subjected to finish annealing and strain relief annealing under the annealing conditions shown in Table 4. Note that the soaking time during final annealing is constant at 2 minutes under all conditions.

The right column of Table 4 shows the iron loss (Wl,...) and magnetic flux density (Bso) of these steel plates as finished annealed and after strain relief annealing. As is clear from the table, the steel sheets manufactured using the composition, coiling temperature, and heating rate according to the conditions of the present invention have good magnetic properties after strain relief annealing, and a very excellent iron loss and magnetic flux density balance. . In particular, regarding the magnetic flux density, 0.22%Si material (steel type G) has a magnetic flux density of 1.81 or more, and 0.78Si material (steel type H)
) 1-1.79 or higher. On the other hand, in the case of components outside the conditions of the present invention (Execution NQ2.3.21.22) and the case of the coiling temperature outside the conditions (Execution &4.12.13), even low core loss was not achieved. In the case of a heating rate outside the conditions of the present invention (implementation N111.6.11.14.
15.20) has a somewhat low core loss, but the magnetic flux density is low.

〔Effect of the invention〕

As described above, according to the method of the present invention, in the production of semi-processed non-oriented electrical steel sheets, there is no need to use means that increase costs such as hot-rolled sheet annealing or additional steps of skin-pass rolling, and there is no need for deterioration of surface properties. It is possible to provide electrical steel sheets with excellent iron loss and magnetic flux density with high production efficiency without deteriorating product characteristics such as deterioration of flatness due to heat rolling or deterioration of flatness due to temper rolling, and its industrial effects are extremely large.

[Brief explanation of drawings]

Figure 1 shows the effect of S on iron loss (W15/S.) after stress relief annealing.
ol, atomic weight ratio of Al amount and N amount [Al (at%)
This is a graph showing the influence of /N(at%) and winding temperature, and FIG. 2 is an optical microscope enlarged photograph of the ferrite metal structure of a typical sample at that time. FIG. 3 is a graph showing the influence of P on iron loss after stress relief annealing. Figure 4 is a graph showing the relationship between magnetic properties and heating rate during final annealing.
The figure is a graph showing the influence of the amount of Mn and the annealing temperature on the magnetic flux density (B, .) after strain relief annealing. 14/15150 Winding temperature (C)

Claims (1)

[Claims] C: 0.005wt% or less, Si: 0.1 to 1.0wt
%, Mn: 0.25wt% or more, P: 0.03% or more,
Sol. Al: 0.004-0.080wt%, N: 0
．． 001 to 0.005 wt%, the remainder consisting of Fe and inevitable impurities, and Sol. The atomic weight ratio between Al content and N content is 2≦[Sol. Al(at%)/N(at%)]≦20
A slab having a composition satisfying 450≦CT≦-7.5{Al (at%)/N (at%
)}+650 (℃) The steel strip is coiled at a coiling temperature CT in the range of +650 (℃), and after pickling and cold rolling, the steel strip is heated at a heating rate HR in the range of 5≦HR≦40 (℃/s). A method for producing a semi-processed non-oriented electrical steel sheet with excellent magnetic properties characterized by continuous annealing at a soaking temperature of ℃ or higher.