CS195091B1 - Steel for producing oriented transformer strips - Google Patents

Description

BACKGROUND OF THE INVENTION The present invention relates to steel for the production of cold rolled silicon steel transformer strips.

So far, the starting steel generally contains 2.0 to 4.0 wt. silicon, the remainder being iron and the necessary impurities. Some of these impurities have a very special function in the texture-forming and recrystallization processes during the processing of steel into a oriented strip, especially in the final high-temperature annealing above 1000 ° C, acting as a Goss-oriented preferred texture growth inhibitor expressed by Miller indices. (110 // 001), These are mostly non-metallic phases, very finely dispersed in the base ferritic mass, which, during high temperature annealing, inhibit normal grain growth until the onset of secondary recrystallization, when grain growth with orientation (110 // 001) begins. During the development of the technology of the production of oriented transformer belts, several different technological variants were gradually patented and introduced into production.

The starting steel is cast into molds and rolls; hot rolled or continuously cast, then hot rolled, strip annealed and pickled and cold rolled to a final thickness of 0.1 to 0.5 mm in one or two stages with annealing, annealing for decarburization and finally anneals high temperature above 1000 ° C for orientation development (110 // 001).

For example, U.S. Pat. No. 3,802,937 discloses a manufacturing process wherein the starting steel has a composition of 0.015-0.035% carbon, 0.03-0.08% manganese, 0.015-0.030% sulfur. max. 0.007% nitrogen, max.

0.045% oxygen, max. 0.008% aluminum, and the remainder essentially consists of iron, considered in weight%.

Inhibition phase in this case consists of Mn and Fe sulfides, which is the most common case in industrial practice. Another technological variant is, for example, U.S. Pat. Nos. 3,159,511 * 3,287,183 or 3,642,456. This technical variant uses simultaneously Mn sulfides and Al nitrides as inhibition phase. The starting steel generally contains 2.0 to 4.0% of silicon, less than 0.085% of carbon, 0.003 to 0.100 of sulfur and 0.010 to 0.065 of acid-soluble aluminum, a low manganese content and the remainder consisting of the necessary impurities and iron. Similarly, according to French Patent No. 2,238,770, the starting steel has a mass composition of 2.5 to 3.5 Z silicon, 0.010 to 0.050 Z aluminum and a carbon content of less than or equal to 0.060%; the sulfur content is not indicated. The treatment of the steel of this variant, based on the effect of: aluminum nitrides or aluminum nitrides and manganese sulphides, differs substantially from that of the steel with the sulphide-inhibiting phase variant only.

Yet another variation is shown in U.S. Pat. No. 3 575 739. The starting steel has a composition by weight of 1.5 to 5.0 7 silicon .0,010 to 0.030 nitrogen, Z _t Z less than 0.005 sulfur less than 0.05 of carbon, the remainder being essentially consisting of a small amount of manganese and iron. This technological variant

95091 uses silicon nitride Si ₃ N _é as the inhibition phase.

The present invention relates to a completely different production, wherein the starting steel generally contains in weight percent 2.5 to 3.5% silicon, to 0.06 Z carbon, 0.04 to 0.20% manganese, 0.004 to 0.010% nitrogen, less than 0.010% aluminum and less than 0.015% sulfur.

In this technological variant, silicon nitride Si? N? Is used as the inhibition phase. The starting steel is poured into the ingot mold or is continuously cast, hot rolled into a strip, the strip is annealed and pickled, then cold rolled in a second stage to a final thickness of 0.2 to 0.5 mm. Further, the strip is decarburized in moist hydrogen or split ammonia, covered with a stripping agent to prevent the coil from welding during subsequent annealing, and finally the strip in the coil is annealed to 1100 to 1200 ° C in hydrogen for the time required to refine nitrogen and sulfur.

The disadvantage of this production was until recently very different achieved magnetic properties of steel from different melts. Magnetic properties are here in particular meant specific wattage losses and magnetic induction, which are important quality indicators for consumer-oriented transformer bands. For example, the specific losses at 1.5 T induction varied from 0.95 to 1.20 W / kg at different heats, with an average oriented strip thickness of 0.34 mm.

These disadvantages are overcome by the steel for the production of oriented transformer belts according to the invention, containing in addition to iron and carbon 2.0 to λ, Ο 7 wt. % silicon, 0.02 to 0.20 wt. % manganese, 0.004 to 0.010 wt. nitrogen, traces up to 0.015-wt. % and traces up to 0.010 wt. Aluminum, processed by hot rolling to strip, pickling, cold rolling two-stage with annealing, decarburization and finally high temperature annealing at 1000 to 1200 ° C. The present invention is characterized in that the steel contains from 0.025 to 0.035% by weight. carbon;

The steels according to the invention achieve a significant improvement in the average level of specific losses as well as a narrowing of the variance of the magnetic properties. The statistical evaluation of the effect of the chemical composition of the melt on the achieved magnetic properties revealed that the carbon content of the melt has the greatest influence.

The function of the carbon C content in the melt can be explained by the influence of the carbon content on the structure, and thus also on the texturizing and recrystallization processes in the steel processing of the oriented formator belt. It has been found that at a high carbon C content, the web structure * is uneven and, besides ferrite, there is more or less perlite in the structure, which at higher contents causes an uneven course of recrystallization in the sheet cross-section. Conversely, at a very low carbon content of C, for example 0.020 wt. In the hot rolling, the carbon content of C is further reduced by about 0.005 wt. , the structure of the hot-rolled strip is too coarse-grained, and it is difficult to achieve a fine-grained structure during processing, which is a precondition for achieving a perfect texture (110 // 001) in the final high-temperature annealing.

The control of the carbon content of the invention within a very narrow range is accomplished by any of the known methods, for example by controlling the oxidation process of the oxygenation of steel. This method consists in the fact that, according to carbon content and temperature of the steel before kyslíkováním kyslíkování govern the conditions at each one t ^- 'Live melt, for example by controlling the time kyslíkování, quantity and pressure of oxygen, the height of the nozzle above the surface and the like. However, the control of the carbon C content may also be carried out in another way without prejudice to the spirit of the invention, i.e. maintaining the carbon C content of the steel in the range of 0.025 to 0.035% by weight.

Example

In an electric arc furnace, melts having a composition of 7% by weight of silicon are produced; 0,10 7 «manganese; 0.028 Z carbon;

0.004 7 aluminum; 0.007 7 nitrogen; 0.0035 7 oxygen; 0.010 7 Sulfur.

The steel is cast into ingots, rolled to slabs and after reheating is rolled to a strip of thickness. 2.5 mm. The hot-rolled strip is annealed at 970 ° C with a holding time of 0.5 min., The strip is pickled and cold rolled to a thickness of 0.7 mm.

The strip is then calcined in a neutral atmosphere. 850 ° C for 2 min. It is then cold rolled again to a final thickness of 0.34 mm.

After decarburization annealing 800 ° C with holding time 2 min. in damp hydrogen, the strip is coated with a MgO slurry and annealed to 1150 ° C with high temperature for 20 hours in a hydrogen atmosphere. The transformer band produced has specific losses at a magnetic induction of 1.5 Τ about 1.0 W / kg and a magnetic induction ‘B at an intensity of 800 A / m of about 1.76 T.

Claims (1)

Steel for the manufacture of oriented transformer belts, containing in addition to iron and carbon 2,0 to 4,0% by weight % silicon, 0.02 to 0.20 7c wt. % manganese, 0.004 to 0.010 wt. nitrogen, traces up to 0.015 7 wt. sulfur and traces up to 0.010 7 wt. Aluminum, processed by rolling. heat per strip, pickling and cold rolling, two-stage annealing, decarburizing, and finally high temperature annealing at 100.0 to 1200 ° C, characterized in that it contains 0.025 to 0.035 7 wt. carbon.