JPH02263920A - Production of nonoriented silicon steel for low temperature use having high magnetic flux density - Google Patents

Abstract

PURPOSE:To produce a steel stock having high magnetic properties and toughness at low temp. by subjecting a steel containing specific weight percentages of C, Cr, Mo, Cu, N, Al, O, and B to casting, solidification, and cooling at specific velocity and then subjecting the resulting cast slab to heating at specific temp., to rolling, and to annealing at specific temp. CONSTITUTION:A molten steel has a composition containing, by weight, <=0.005% C, <=0.5% Si, <=0.015% P, <=0.005% S, <=0.05% Cr, <=0.01% Mo, <=0.01% Cu, <=0.004% N, and <=0.005% Al. This molten steel is cast after the concentration of dissolved oxygen in the molten steel is limited to <=0.0050% and B is incorporated by 0.0005-0.0030% to the molten steel. After solidification, the resulting cast slab is cooled through the temp. region from 1300 to 900 deg.C at 0.05-0.5 deg.C/S cooling rate. Then, the cast slab is heated up to 1150-1300 deg.C, rolled at 900 deg.C finishing temp., and annealed at 750-910 deg.C. By this method, the steel stock utilizing magnetic phenomena due to D.C. magnetization and applicable to large-sized structure can be provided.

Description

[Detailed Description of the Invention] (Industrial Application Field) Steel materials with excellent magnetic properties are required for magnetic shielding of giant magnet synchrotron radiation (SOR) for particle accelerators, electromagnets for medical accelerators, or medical equipment (MHI), etc. It is being

The present invention provides a method for producing steel that has excellent low-temperature toughness properties necessary for structural steel, in addition to high magnetic flux density properties used for the iron core of electromagnets used under these DC magnetization conditions or for shielding magnetic fields. It is related to.

(Prior Art) As is well known, in the field of thin plates, there are many types of electromagnetic steels with high magnetic flux densities, including silicon steel plates and electromagnetic soft iron plates.

However, when used as a structural member, there were problems with assembly and strength, necessitating the use of thick steel plates. Until now, electromagnetic plates have been manufactured using pure iron-based components. For example, Japanese Patent Application Laid-open No. ShofiO-96749 is known.

However, as devices have become larger and their performance has improved in recent years, devices with even better magnetic properties, especially in low magnetic fields, such as 80A/
There is a strong demand for the development of steel materials with high magnetic flux density at m. In the above-mentioned patents and the like, a high magnetic flux density in a low magnetic field of 80 A/m cannot be stably obtained.

Furthermore, the desired low-temperature toughness cannot be obtained by simply increasing the purity.

(Problems to be Solved by the Invention) The purpose of the present invention was made in view of the above points, and is to provide a non-oriented electrical steel that has a high magnetic flux density in a low magnetic field and also has low-temperature toughness. .

(Means for Solving the Problems) The present invention includes C: 0.005% or less and Si: 0.005% or less by weight.
5% or more, Mn: 0.2% or less, P: 0.015% or less, S: 0,005% or less, Cr: 0.05% or less, M
o: 0, 0.01% or less, Cu: 0.01% or less,
Deoxidizes molten steel with a composition of N: 0.0040% or less and AIl: 0.005% or less to reduce the dissolved oxygen concentration of the molten steel to 0,0.
B is limited to 0.050% or less, and B is further limited to 0.0005 to 0.050%.
0030% and the remainder consists of Fe and unavoidable impurities. After solidification, the cooling rate at 1300 to 900°C is controlled to 0.05 to 0.5°C/s to produce a slab. Heating to 1300℃, rolling under conditions where the finishing temperature is 900℃ or higher, 750 to 910℃
This is a method for producing a non-oriented high magnetic flux density electrical steel with excellent low-temperature toughness, which is characterized by annealing at a temperature of 910 to 1000°C or skewering at a temperature of 910 to 1000°C.

(Function) In order to increase the magnetic flux density of steel in a low magnetic field, it is necessary to reduce as much as possible the precipitates and inclusions of C and N, which hinder the movement of domain walls. However, extreme reduction in C reduces the toughness of the steel. In order to develop a steel that combines high magnetic flux density and excellent low-temperature toughness, the present inventors conducted a detailed study on the cause of the decrease in toughness.

As a result, it was found that the reduction in C promotes grain boundary segregation of S and N, resulting in a decrease in grain boundary strength and grain boundary cracking. In order to reduce the grain boundary segregation of these elements, it is sufficient to extremely reduce the content of the elements, but this reduction is not practical because it causes a significant increase in steel manufacturing cost.

Therefore, a method was implemented to reduce the grain boundary segregation of elements such as S, N, and P that cause grain boundary embrittlement by other means. That is,
Since the amount of grain boundary segregation increases or decreases in proportion to the amount of solid solution elements, the amount of grain boundary segregation can be reduced by fixing the solid solution elements as precipitates or inclusions.

To achieve this objective, to reduce solid solution S, a known deoxidizing agent such as Ca-51 alloy was added to form calcium sulfur oxide, and to reduce solid solution N, B was added to form boron nitride. .

Furthermore, this steel is characterized by the deoxidation of CaSi alloy instead of Al1, which achieves the above objectives and reduces the AJ712 content. This is because Ap forms AgN, has the effect of making crystal grains finer, and deteriorates magnetic properties.

Next, the reason for limiting the basic component range of the steel of the present invention will be described.

First, C is an element that increases the internal stress in steel and reduces the magnetic properties, particularly the magnetic flux density in a low magnetic field, the most, and therefore needs to be reduced as much as possible. Furthermore, from the viewpoint of magnetic aging, the smaller the amount, the more it is possible to prevent deterioration of the magnetic properties over time, and the better the magnetic properties can be permanently maintained. From this point of view, the content was set to 0.005% or less.

Si and Mn form oxide and sulfide inclusions that lower the magnetic flux density in low magnetic fields, so they must be reduced.
was 0.5% or less, and Mn was 0.2% or less.

P is set to 0.015% or less because it segregates at grain boundaries, causes grain boundary embrittlement, lowers toughness, and further increases internal stress through solid solution strengthening, which lowers magnetic properties.

S segregates at grain boundaries, causes grain boundary embrittlement, lowers toughness, and further forms sulfides, which impedes movement of domain walls and lowers magnetic flux density, so S is set to 0.005% or less.

Cr, Mo, and Cu increase the unrestricted magnetic properties and reduce the magnetic flux density in low magnetic fields due to segregation, etc.
It is necessary to reduce as much as possible, Cr is 0.05% or less, Mo
was 0.01% or less, and Cu was 0.0196 or less.

N increases internal stress and reduces magnetic flux density in low magnetic fields, and also causes grain boundary segregation and reduces low-temperature toughness, so the upper limit should be set to 0.
．． 0040%.

Since 0 forms non-metallic inclusions in the steel, resulting in poor magnetic properties and toughness, it is deoxidized to 0.005% or less using a known deoxidizing agent such as Ca-51 alloy.

Al is a strong deoxidizing element, and addition of 0.005% or more increases inclusions and promotes precipitation of AflN, leading to deterioration of magnetic properties, so the content was set to 0.005% or less.

B was added to convert solid solution N into BN and fix it.

If B is less than 0.0005%, BN cannot be sufficiently formed and it does not have the effect of improving toughness, and if it exceeds 0.0030%, excessive solid solution B causes deterioration of magnetic properties, so 0.0005 to 0.
．． 00 (limited to 0%).

Next, the manufacturing method will be described.

Cooling rate of 1300-900℃ after solidification of slab is 0.0
The purpose of controlling the temperature at 5 to 0.5°C/s was to slowly cool the precipitation temperature range of boron nitride to cause sufficient precipitation, and to make it coarse and loosely dispersed. This is to prevent deterioration of magnetic properties due to fine precipitation of boron nitride. In other words, rapid cooling at a cooling rate of 0.5°C/s or more precipitates fine boron nitrides and deteriorates magnetic properties, while slow cooling at a cooling rate of 0.05'C/s or more is effective but impractical. limited to a range.

Regarding the rolling conditions, the heating temperature before rolling was set to 1150° C. or higher in order to coarsen heated austenite grains and improve magnetic properties. For heating above 1300℃, the upper limit has been set to 13 to prevent scale loss and to save energy.
The temperature was 00°C.

The reason why the rolling finishing temperature is set at 900° C. or higher is that a lower finishing temperature lower than this temperature causes grain refinement and deteriorates the magnetic properties.

Annealing is performed to coarsen crystal grains and remove internal strain.
If the temperature is lower than 50°C, sufficient coarsening of crystal grains will not occur, and 910°C.
At temperatures above ℃, the homogeneity of the grains in the thick plate direction cannot be maintained.
The annealing temperature was limited to 750 to 910°C.

The standard temperature is set to adjust the crystal grains in the direction of the thick plate and remove internal strain, but if the temperature is below 910℃ and above 1000"C, the homogeneity of the crystal grains in the direction of the thick plate cannot be maintained, so the standard temperature is set to 9
The temperature was 10°C to 1000°C.

(Example) Table 1 shows the relationship between the chemical composition of the prototype steel, the cooling rate of the slab after solidification, the toughness, and the magnetic flux density in a low magnetic field.

The test steel was a 250mm thick slab heated to 1250°C for 2 hours and rolled to a thickness of 50mm. 750℃
The product was annealed for 2 hours. The toughness is measured at 2 m from the test steel.
It was processed into a V-notch Charpy shape, and the impact fracture transition temperature (hereinafter referred to as vTrs) was determined and evaluated. Note that all steels except Steel 9 were manufactured by deoxidizing Ca-51 alloy.

Steels 1 to 6 are steels of the present invention with reduced Ag, deoxidized with Ca5t alloy, and 0.0
It was produced by cooling at a rate of 5 to 0.5°C/s. In the steel of the present invention, the solid solution N is sufficiently reduced by the BH precipitation treatment, and the rolling finishing temperature is 950'C or higher and the annealing temperature is 750°C, satisfying the claimed conditions, so the magnetic flux density in a low magnetic field is 1. It exhibits high magnetic properties of over 0 tesla. Furthermore, Ca-
51 alloy has excellent low-temperature toughness due to the reduction of solid solution S by deoxidation, and exhibits high toughness at vTrs of -30°C or less.

Steels 7 to 12 are comparative steels, in which steel 7 has a cooling rate exceeding the upper limit after solidification, steel 11 has an annealing temperature of 700 °C, and steel 1
In No. 2, the rolling finishing temperature is 850° C., which is a low temperature outside the claimed range, so the magnetic flux density decreases to 1.0 Tesla or less. Since steel 8 (BEi), steel 9 has an Ag content, and steel IO has an O content that exceeds the upper limit, vTrs increases and the magnetic flux density also decreases to 1.0 Tesla or less.

(Effects of the invention) Through the appropriate ingredient limitation and manufacturing method of the present invention, we have succeeded in manufacturing steel materials with high magnetic properties and low-temperature toughness, and we have succeeded in manufacturing steel materials with high magnetic properties and low-temperature toughness. This is what I did.

In particular, improved low-temperature toughness makes it possible to adapt this type of material in cold regions where the toughness is improved, and its economic and other industrial effects are extremely remarkable.

Claims (1)

[Claims] 1. In weight%, C: 0.005% or less, Si: 0.5% or less, Mn: 0.2% or less, P: 0.015% or less, S: 0.005% or less, Deoxidizes molten steel with a composition of Cr: 0.05% or less, Mo: 0.01% or less, Cu: 0.01% or less, N: 0.0040% or less, Al: 0.005% or less to dissolve the molten steel. Oxygen concentration 0.005
Limit B to 0% or less, and further reduce B to 0.0005 to 0.00.
After casting steel with a composition containing 30% and the remainder consisting of Fc and unavoidable impurities, and controlling the cooling rate at 1300 to 900 °C after solidification to 0.05 to 0.5 °C / s to produce a slab, 1150 °C Heat to ~1300℃ and finish temperature at 90℃
A method for producing a non-oriented high magnetic flux density electrical steel having excellent low-temperature toughness, which comprises rolling under conditions of 0°C or higher and annealing at 750 to 910°C. 2. The method for producing a non-oriented high magnetic flux density electrical steel with excellent low-temperature toughness according to claim 1, which comprises normalizing at 910 to 1000°C after rolling.