JPS5815525B2 - Improvements in electrical steel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the production of steel for electromagnetic equipment, ie for forming magnetic circuits in electrical machines.

The invention particularly relates to electrical steels that are not intentionally inoculated with silicon to reduce conductivity and impart other desirable properties to the steel, thereby preventing losses due to eddy currents and the like that occur when the steel is energized. .

Such silicon-free steel usually has a silicon content of 0.5 to 3.25%.
It has a silicon concentration of less than 0.05% by weight compared to a silicon concentration of less than 0.05% by weight.

Generally, electromagnetic steels are produced from conventional utility steels, which are refined by any basic oxygen, open hearth or other steelmaking process, and which typically have carbon concentrations of 0.05
%, up to 0.025% phosphorus, the balance being iron, exclusive of other incidental impurities.

After flattening and hot rolling such steel, the strip thus produced is cold rolled and then decarburized annealed to reduce the carbon to an acceptable level.

After this decarburization annealing, the strip is cold thinned to approximately final gauge.

Performing a decarburizing anneal to reduce carbon in the strip emerging from a one-break thickness reduction considerably increases the cost of the strip or sheet thus produced.

This cost disadvantage is due in part to the high price of the reducing gas that must be fed to the annealing furnace, and in part to the high cost of furnaces that can be safely adapted to the reducing gas atmosphere.

One object of the present invention is to produce an electrical steel with suitable hardness and magnetic properties, yet without the drawbacks resulting from the need for decarburization during annealing.

According to its broadest aspect, the present invention provides a method for producing silicon-free steel for electromagnetic equipment, which involves vacuum degassing of steel derived from conventional refining processes to reduce the carbon concentration to 0. 0.02% and adjust the phosphorus concentration before, during or after degassing to 0.05-0.15%
The steel thus produced is hot and cold rolled to intermediate gauge, the cold rolled steel is annealed without decarburization, and the annealed steel is then cold rolled to its final gauge. It includes doing.

The steel to be vacuum degassed is derived from any basic oxygen, open hearth refining or other steelmaking process and preferably contains manganese in the range 0.35 to 0.9% by weight.

If the manganese concentration is outside this range, it is adjusted to within the preferred range by appropriate inoculation before, during or after vacuum degassing.

Typical steels according to the invention, after degassing, range from 0.004 to 0.
．． 02% carbon, 0.04% oxygen, 0.35-0.9
% manganese, and 0.07-0.15% phosphorus, the balance containing iron excluding incidental impurities.

The oxidation content of the steel can be further reduced to less than 0.02% by the addition of suitable chemical deoxidizers, such as silicon or aluminum, in which case the amount of deoxidizer added is equal to that in the steel. The concentration should not increase by more than 0.01% and preferably not more than 0.005%.

Phosphorus in steel, which is known to be effective in compensating for hardness deterioration caused by subsequent static annealing, is a ferrophosphorus compound that has relatively low evaporation properties at the temperature at which it is introduced into the melt. It is suitably introduced into the steel by inoculation with or.

The steel after cold thinning into strip has a temperature of 660-70
Static non-decarburizing annealing is performed in the 5°C (1220-1300'F) range, although higher or lower temperatures may be used.

The annealing process is operated to leave a bright finish on the cold rolled strip, and the process is carried out in an atmosphere containing a small amount of a reducing gas such as hydrogen.

A suitable gas for bright non-decarburizing annealing is, for example, nitrogen containing about 4% by volume hydrogen.

The hot and cold rolling parameters used in the present invention are those conventionally used in silicon-free electrical steel manufacturing technology.

Typically, steel has a finishing temperature of 843-1010°C (1,55°C).
0-1850 below) and then one-break rolling to within 5-15% of final gauge before non-decarburizing annealing.

In one embodiment of the invention, the steel derived from the basic oxygen refining process is poured into a converter mustard in an unkilled state.

At this stage the steel typically has 0.02 to 0.0 carbon
7% by weight and 0.04-0.14% oxygen, the balance being iron excluding other impurities associated with the individual purification steps.

While in the ladle, the steel is inoculated with phosphorus in the form of ferrophosphorus, and the amount reduces the phosphorus concentration of the melt to about 0.
．． 10%.

The steel is then introduced into a vacuum degasser to reduce the carbon concentration to less than 0.02% under reduced pressure.

During vacuum degassing the oxygen concentration of the melt (which is reduced) is further reduced by the addition of a chemical deoxidizer such as aluminum, and this amount is equal to the final aluminum concentration, i.e. 0.01%.
It is effective in providing a concentration that does not exceed 0.005%, particularly 0.005%.

During chemical deoxidation, which is also preferably carried out in a vacuum F, residual free oxygen is converted to alumina, which is removed from the melt by flotation using turbulence in the melt induced by the vacuum process itself. be done.

Typical final oxygen concentration after chemical deoxidation is 0002-0.0
It is 3%.

If required, manganese may be added to the steel melt at this stage, especially still under vacuum, to raise the manganese concentration to about 0.65%, but manganese can be added to the steel together with phosphorus at any other suitable stage of the process. May be added.

The steel produced as described above can be cast into ingots in batch mode or continuously into plates in a suitable manner.

After reheating for a minimum of 3 hours in the 1210-1330°C (2200-2400"F) range, the plate is hot rolled into strips, which
Finish rolling is performed at ``F''.

= The hot rolled strip, generally having a thickness of 19 to 2.1 mm, is then cold rolled to a finish gauge of about 6 to 8 mm.
% (preferably 7% when measured stretched).

Cold rolled intermediate strip temperature 660~705℃
Non-decarburizing annealing is performed in a box annealing furnace maintained at (1220-1300'F).

The strip is held at this temperature for about 4 hours in a gas atmosphere called HNX, which contains 4% hydrogen and 96
% nitrogen, which is effective in preserving the shiny surface finish of the coil.

After cooling, the coil is cold thickened to final gauge and ready for use.

In use, the coils are punched, cut or otherwise mechanically formed into thin sheets which are stacked to form the magnetic core of the electrical machine.

At this stage, the sheet or other shaped piece is decarburized and annealed by any procedure known in the art to improve its magnetic properties.

The steel produced in accordance with the present invention can be manufactured by a process route that involves either hot rolling prior to cold thinning, decarburization of the IJ tube, or decarburization annealing in a continuous furnace following cold thinning. It was found to have physical properties equivalent to those obtained.

Furthermore, despite the lack of silicon additives, these steels
It has superior magnetic properties to silicon steels that have undergone these process routes (those with silicon levels of 2% or more and 1.5%).

The following table compares typical steels of two different gauges treated according to the present invention with silicon-free steels treated by conventional methods, i.e. by the route mentioned at the beginning of this specification. .

Typical values for the magnetism and hardness of the steels that are the subject of the present invention and typical values for the magnetism and hardness of conventional steels are as follows.

Claims (1)

[Claims] 1 Steel derived from conventional refining processes is vacuum decased to reduce the carbon concentration to less than 0.02% by weight and the phosphorus concentration is adjusted to 0.05% before, during or after degassing.
~0.15%, the steel thus produced is hot and cold rolled to intermediate gauge, the cold rolled steel is non-decarburized annealed, and the annealed steel is then subjected to its final A method of manufacturing silicon-free steel for electromagnetic equipment, comprising cold rolling into a gauge.