RU2521921C1 - Production method of ultra low carbon cold-rolled isotropic electrical steel - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: method involves combined metal blowing in a converter, decarburisation of metal in vacuum, steel alloying by ferrosilicon refined from carbon, continuous pouring of liquid metal into slabs from a lined steel pouring ladle through an intermediate ladle to a continuous-casting machine (CCM) crystalliser using a slag-forming mixture in the latter, which contains not more than 1.5% of carbon, hot rolling, normalising annealing, etching, cold rolling till final size and final annealing. During the alloying process there added is ferrosilicon with carbon content of not more than 0.02% in the quantity providing silicon content in the melt within 0.5÷3.2%; pouring of liquid metal into slabs is performed with addition to the intermediate ladle of a heat insulating mixture with carbon content of not more than 2%. With that, a steel pouring ladle with the main lining, in which carbon content is not more than 2%, is used.

EFFECT: invention allows obtaining low content of carbon in finished isotropic steel and providing uniformity of mechanical and electromagnetic properties of a strip along and across the rolling direction.

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Description

The invention relates to the field of ferrous metallurgy, in particular to the production of especially low-carbon cold-rolled isotropic electrical steel used for the manufacture of electric machines, magnetic circuits, relays, chokes, generators, energy converters.

Known methods for the manufacture of sheets of electrical steel according to US patent No. 3130091, class. 148-111, 1964, in which non-textured material is obtained by primary or collective recrystallization of a cold-rolled metal. This provides for sequential smelting, casting, hot rolling, pickling, heat treatment of metal and one or more cold rolling with intermediate or final annealing for decarburization of steel.

The disadvantages of the known methods is the relatively low level of magnetic properties of the finished metal, large differences in properties along and across the direction of rolling, a complex and expensive technology for producing non-textured steel.

The closest to the proposed technical solution for the technical nature and the achieved result (prototype), according to the authors, is a method of manufacturing cold-rolled non-textured electrical steel based on the article by I. Zaydman, V. Borisenko “Simplified technology for the production of cold-rolled low-textured electrical steel”, “Steel”, 1963, No. 1, pp. 76-80, which provides for the smelting, casting of steel, hot rolling, pickling, cold rolling and vacuum annealing.

The disadvantage of this method is the low level of magnetic properties in the finished material, a large difference in the values of the magnetic characteristics along and across the direction of rolling, which is associated with a partial course of the secondary recrystallization during final annealing, and a large difference in thickness of the finished sheet.

The task to which the technical solution is directed is to obtain a carbon content of not more than 0.005% in the finished isotropic steel. At the same time, obtaining such a technical result as reducing production costs and obtaining additional profit from the sale of isotropic steel of 0 ÷ 4 alloying groups by increasing the productivity of continuous annealing units (eliminating decarburizing annealing from the technological cycle) is achieved.

The aforementioned disadvantages are eliminated by the fact that in the production method of a particularly low-carbon cold-rolled isotropic electrical steel, including combined metal blowing in a converter, metal decarburization in vacuum, carbon alloyed with carbon-refined ferrosilicon, continuous casting of molten metal into slabs from a lined steel casting mill using in the last slag-forming mixture containing not more than 1.5% carbon, hot rolling y, normalization annealing (if necessary), etching, cold rolling to the final size and final annealing; when alloyed, ferrosilicon with a carbon content of not more than 0.02% in an amount providing the silicon content in the melt in the range of 0.5 + 3.2 %, liquid metal is poured into slabs with an additive in the intermediate ladle of an insulating mixture with a carbon content of not more than 2%, while the lining of the steel casting ladle is made basic, with a content of not more than 2% carbon.

A comparative analysis of the proposed technical solution with the prototype shows that the claimed method differs from the known one in that ferrosilicon with carbon content of not more than 0.02% in an amount providing the silicon content in the melt in the range of 0.5–3.2% is added during alloying liquid metal is poured into slabs with an additive in the intermediate ladle of a heat-insulating mixture with a carbon content of not more than 2%, while the lining of the steel casting ladle is made basic, with a content of not more than 2% carbon. Thus, the claimed method meets the criteria of the invention of "Novelty."

Since the present invention can be used in industry, in particular, in the production of especially low carbon cold rolled isotropic electrical steel, and testing of the proposed method has already shown positive results, therefore, this technical solution meets the criteria of the invention "Industrial Applicability".

A comparative analysis of the proposed solution, not only with the prototype, but also with other technical solutions, did not reveal the essential features inherent in the claimed solution. It follows that the claimed combination of significant differences provides the above-mentioned technical result, which, according to the authors, meets the criteria of the invention "Inventive step".

The proposed technical solution will be clear from the following description.

A method of manufacturing a particularly low-carbon cold-rolled isotropic electrical steel is as follows.

First, they conduct a combined purge of metal in the converter, decarburization of the metal in vacuum, alloying of steel with carbon-refined ferrosilicon, continuous casting of liquid metal into slabs from a lined steel-pouring ladle through an intermediate ladle into a continuous casting mold using a slag-forming mixture containing no more than 1.5% carbon. Then hot rolling is carried out to an intermediate size, normalization annealing (if necessary), etching, cold rolling to the final size and final annealing. When alloying steel, ferrosilicon is added with a carbon content of not more than 0.02% in an amount providing a silicon content in the melt in the range of 0.5–3.2%, liquid metal is cast into slabs with an insulating mixture containing no carbon in the intermediate ladle more than 2%, while the lining of the steel pouring ladle is made basic, with a content of not more than 2% carbon.

Alloying the steel by sitting ferrosilicon with a carbon content of more than 0.02% in an amount providing a silicon content of less than 0.5% does not provide the required (less than 0.005%) carbon content in the finished steel, which is unacceptable.

Alloying steel with ferrosilicon sitting with a carbon content of more than 0.02% in an amount providing a silicon content of more than 3.2% leads to brittle fracture of steel during cold rolling and, as a consequence, loss of marketable products, which is unacceptable.

The casting of liquid metal into slabs with an additive in the intermediate ladle of a heat insulating mixture with a carbon content of more than 2% does not provide the required (less than 0.005%) carbon content in the finished steel, which is undesirable.

The lining of the steel pouring ladle is minor and with a carbon content of more than 2% leads to uncontrolled saturation of the steel with silicon and does not provide the required (less than 0.005%) carbon content in the finished steel, which is unacceptable.

Example

NLMK OJSC conducted pilot production of cold-rolled isotropic electrical steel according to the proposed method. In converter shop No. 1 in a converter with a capacity of 160 tons, a combined metal purge was carried out, in which oxygen was supplied to the liquid metal melt, and inert gas (argon) was supplied to the melt within 50 s no later than 3 minutes before the end of purging ) with a flow rate of 0.15 Nm ³ / min. Then, the obtained melt was poured into a pre-prepared steel pouring ladle, the outlet of which was pre-filled with a low-carbon backfill to open a glass such as staurolite. The lining of the steel pouring ladle was made of refractory material with a carbon content of 1.3-1.8%. The decarburization of the liquid metal was carried out in vacuum using a vacuum cleaner for a predetermined time, after which ferrosilicon with a carbon content of not more than 0.02% in an amount of 20 kg / t, providing a specified silicon content in the melt, was seated in the melt in the steel pouring ladle, moreover ferrosilicon was planted in portions uniformly until the end of the vacuum treatment process. Then, continuous casting of liquid metal was carried out at the continuous casting machine through an intermediate ladle with a capacity of 50 t and a mold into slabs measuring 250 × 900 × 1300 mm. A heat insulating mixture with a carbon content of 1.3-1.8% was planted in an intermediate bucket, and a slag-forming mixture containing 1.5% carbon was used in the mold. Then, in the sheet rolling hot rolling shop, the hot slabs were hot rolled. The slabs were heated to a temperature of 1210-1220 ° C, the heating time of 3.5-4.0 hours. Rolling was performed at a thickness of 2.0 mm, the temperature of the end of rough rolling was 940–960 ° С, the temperature of the end of finish rolling was 770–790 ° С. Laminated strips were wound into a roll with a winding temperature of 620-640 ° C. After that, in the dynamo steel production workshop, further processing of the obtained coils was carried out. Normalization annealing was performed in the normalization unit at a temperature of 800 ° C. Etching of normalized rolls was carried out on NTA in hydrochloric acid. Cold rolling was carried out on a 4-stand mill 1400 to a thickness of 0.5 mm. After cold rolling, the final (recrystallization) annealing was carried out in a nitrogen-hydrogen protective atmosphere with a hydrogen content of 30-40% at a temperature of 1050 ° C.

The properties of isotropic electrical steel obtained as a result of the experimental use of the proposed technical solution are presented in the table.

Properties of isotropic electrical steel Technology Electromagnetic properties The output of the 1st class of flatness,% P _{l, 5/50} , W / kg AP _{l, 5/50} . % B ₂₅₀₀ , T existing 2.92 ÷ 3.13 7-11 1.54 ÷ 1.55 twenty proposed 2.61 ÷ 2.78 7-9 1.55 ÷ 1.57 80

From the analysis of the table data, it can be concluded that the complex of electromagnetic and mechanical properties (specific magnetic losses P _{1.5 / 50} , magnetic induction B ₂₅₀₀ and flatness) of the obtained steel using the proposed method is higher than steel obtained by the previously known method.

The use of evacuated rolled products with a carbon content of less than 0.005% allows to increase the performance of continuous annealing aggregates (eliminating decarburization annealing from the technological cycle), increase the level of electromagnetic properties (the absence of an internal oxidation zone on the surface of strips), increase the yield of a flatness class 1 (decrease in the strip cooling rate when eliminating decarburizing annealing from the technological cycle).

Thus, the use of the proposed method in the production of especially low-carbon cold-rolled isotropic electrical steel allows not only to obtain a carbon content of not more than 0.005% in the finished product with an improvement in its electromagnetic properties and flatness, but also to reduce production costs (on average by 20%) and obtain additional profits from the sale of isotropic steel 0 ÷ 4 alloying groups.

Therefore, the task to which the technical solution is directed is fulfilled, while achieving the above technical result is achieved.

Claims (1)

Method for the production of especially low-carbon cold-rolled isotropic electrical steel, including combined metal blowing in a converter, decarburization of metal in a vacuum, alloying of steel with carbon-refined ferrosilicon, continuous casting of steel into slabs from a lined steel-pouring ladle through an intermediate ladle in a mold containing MNL3 containing no more than 1.5% carbon, hot rolling, normalization annealing if necessary, pickling, cold bottom rolling to the final size and final annealing, characterized in that ferrosilicon with a carbon content of not more than 0.02% in an amount providing a silicon content in the melt in the range of 0.5–3.2% is poured into the slab during casting, steel casting into slabs lead with an additive to the intermediate ladle of a heat insulating mixture with a carbon content of not more than 2%, while using a steel pouring ladle with a main lining in which the carbon content is not more than 2%.