SE411770B - SET TO MANUFACTURE STEEL PRODUCTS - Google Patents

Description

¿* Mzszn-v 5 10 h f- 15 20 25 F f- 30 35 40 2 greater induction significantly the technical parameters of these motors.

It is an important requirement that the unalloyed iron is magnetically isotropic, ie. that its magnetic behavior is almost the same in all directions. Another requirement is that the iron does not age magnetically, ie. that the magnetic properties (coercive force, magnetic induction, etc.) are not reduced when the motor is used for a long time.

The manufacturing processes for unalloyed, electrotechnical iron strips and plates for further processing into stator and rotor cores in electric motors are still subject to significant technical difficulties. Namely, favorable magnetic properties of unalloyed electrotechnical steels can be obtained only if the amount of impurities, especially carbon and oxygen, is very small in the steel used for the production and in addition a special rolling and heat treatment process is required to obtain high induction. and acceptably low iron loss. " In the production of the steel used as a starting material for further processing into known unalloyed electrotechnical steel strips requires special care, because the oxygen and carbon content of the ingot should be kept at the lowest possible level, but - due to the equilibrium conditions, too low carbon content requires higher oxygen content.

To reduce the amount of inclusions, such steels are usually produced by a converter process, and to improve their mechanical properties, a small amount of phosphorus, and / or manganese is generally added to the steel as an alloying component. The steel ingot with the correct composition is preheated and hot rolled to a thickness of about 1.8-2.5 mm, then it is pickled and rolled to the final thickness (generally about 0.5-1.0 mm) required for its use. . This last step is usually carried out in the following way: the sheet is cold-rolled to a thickness which is about 4-12% larger than the final one, whereupon the steel is annealed and rolled to a final thickness by so-called "critical cold working". g To achieve the required magnetic properties, the steel must be annealed at the final dimensions. The unalloyed iron strip, which has been subjected to known heat treatment, for example kid 750-780 ° C for 2 hours under a protective atmosphere or in a vacuum, is too soft and its consistency causes many problems when punching iron cores with complicated shape. the cut edges get degrees and consequently a number of difficulties arise during assembly and winding of the cores. At the same time, the magnetic properties of the cores greatly deteriorate due to the deformation.

In order to eliminate the above-mentioned disadvantages, the unalloyed electrotechnical steel strips are marketed by the manufacturers in cold-rolled, hard condition such as so-called semi-finished product. In the factory in which the motors are manufactured, stators and rotors for electric motors are punched out of these semi-finished products, ie. strips, which have been rolled to final thickness but not subjected to heat treatment, and the cores are usually subjected to heat treatment after assembly.

In order to achieve the desired magnetic properties, care is taken that scale formation is avoided, which is why the heat treatment at high temperatures is carried out under a protective atmosphere.

The main disadvantage of this process is that the production of the starting material with extremely high purity entails much higher costs than the production of unalloyed steel strips of ordinary quality. Most difficulties occur when insuring low carbon content, ie. maximum 0.02-0.03%. For many manufacturers, additional difficulties can arise due to the fact that in order to ensure the desired magnetic properties, the products already punched in certain dimensions must be subjected to a final heat treatment and factories for the manufacture of electric motors generally do not have a heat treatment furnace operating at the temperature suitable for this purpose and is equipped with a device for providing a protective atmosphere.

It is also known that the undesired carbon content of the steel can be reduced not only while the steel is in the form of a melt during the steel production but also where the steel is in the solid state. Thus, many methods are known for reducing the carbon content of solid state steels and these are referred to as carbonization.

The simplest of these procedures is the so-called the black annealing, which is a very special heat treatment, in which the hot-rolled, uncoated (striped) steel strip is subjected to a heat treatment in the air at a temperature above 700 ° C, preferably at 800 ° Cr, before the cold rolling. the carbon contained in the steel by the oxide content of the superficial oxide layer (the roll skin) in a manner not yet clarified.

A disadvantage of this process is that the decarburization is time consuming. Under industrial conditions, you need about 24-96 hours for this purpose. In addition, during this long heat treatment, the metallic iron in the surface layer absorbs oxides, which are trapped in the surface layer at different depths due to internal oxidation.

According to another known decarburization process, in which mainly cold-rolled electrotechnical steel-silicon alloys are produced for further treatment into transformer and generator strips, the entire surface of the cold-rolled strip is exposed to a final or suitable intermediate thickness at 750-960 ° C for a decarburizing / shielding gas. for example a moist mixture of hydrogen and nitrogen, which does not oxidize the steel. Under these conditions, the thin strips are rapidly charred. A disadvantage of this method, however, is that in order to ensure efficient decarburization, the entire surface of the belt must be exposed to the gas mixture, which means that for the process one must have access to expensive so-called pull-over ovens and continuously operating systems, which entails relatively high operating costs.

Consequently, the process costs become high and the price of the unalloyed electrotechnical bands becomes too high.

According to the invention, this means a process which enables the reduction of the carbon content of unalloyed, semi-finished steel products (intermediates) in a plant with conventional devices, thereby enabling the production of non-alloyed electro-technical steel strips and sheets of good quality and favorable magnetic characteristics.

The invention is based on the discovery that the time required for decarburizing heat treatment (black annealing) of steel intermediates coated with incandescent chips can be significantly reduced and that at the same time the formation of oxide inclusions due to internal oxidation can be avoided if the intermediate products are pre-heat treated. a coating of certain metal hydroxides and / or carbonates.

Furthermore, the invention is based on the discovery that the time required for the above-mentioned decarburizing heat treatment can be further reduced and the quality of the obtained intermediate product can be further improved by introducing air or an inert gas with a high dew point into the furnace during the heat treatment. .

Finally, the invention is based on the discovery that the mechanical and magnetic properties of the product can be favorably affected by carrying out the final heat treatment of the product, which is cold-rolled to a final thickness, in two steps, the temperature in the second stage is higher than in the first.

Under these conditions, high-quality non-alloy steel alloys and sheets can also be made from non-alloy steels suitable for general use only.

Thus, the invention relates to a process for the production of steel products, preferably strips and sheet metal with improved magnetic and mechanical properties, in which the thermoformed product is pickled, transferred to its final dimensions in the cold state, subjected to a final heat treatment and the the product provided with scale before the pickling is subjected to heat treatment at a temperature between 700 and 950 ° C, which procedure is characterized in that, before the heat treatment carried out at 700-950 ° C, a layer of one or more of the following compounds, namely alkali metal hydroxide, alkaline earth metal hydroxide, alkali metal carbonate, alkaline earth metal carbonate and aluminum hydroxide, and optionally carrying out the final heat treatment in two steps, one at 550 -600 ° C, preferably at 460-490 ° C and the other at 600-780 ° C, preferably at 680-760 ° C.

According to a preferred embodiment of the invention, air or a shielding gas with a dew point above + 20 ° C, preferably above 50 ° C, is introduced into the furnace during the heat treatment of the product provided with a scale.

The hydroxide or carbonate layer is conveniently applied by dipping the product, which is provided with a scale, in a solution or dispersion containing the appropriate hydroxide and / or the appropriate carbonate. According to another embodiment, the solution or dispersion is sprayed on the surface of the product to be treated. When treating rolled strip, the solution or dispersion is suitably deposited on the surface of the strip by spraying it while the strip is being flushed.

The main advantages of the method according to the invention are the following: a) The decarburization rate and efficiency can be significantly increased. Thus, the carbon content of a steel strip can be reduced to 0.01% or even less from an initial value of 0.08-0.40% without overloading the heat treatment capacity. Accordingly, as a starting material for the production of high-quality non-alloyed electrotechnical steel strips, unalloyed, hot-rolled steel strips having a conventional composition and the like can be used. which are produced in the usual way for the production of steel for general purposes, for example structural steel.

I b) The process according to the invention makes it possible to use as starting material for the production of electrotechnical steel strips unalloyed, hot-rolled steel strips produced for general purposes and containing the usual impurities. c) The method according to the invention does not require any special equipment and can be carried out without additional costs in heat treatment furnaces, for example in bell furnaces, ie. furnaces found in virtually all rolling mills. d) In the method according to the invention, conventionally produced steels of ordinary purity can be used as the starting material for the production of unalloyed electrotechnical steel strips.

In addition, according to the invention, if steel is processed, which has a higher degree of purity and which is produced by means of a more carefully controlled method, end products with significantly improved magnetic properties can be obtained. e) Due to the excellent mechanical properties of the product prepared according to the present invention, it is possible to punch out core plates with complicated shape and the magnetic properties of the product hardly undergo any deterioration by the punching, so that the subsequent treatment under a protective atmosphere can generally be eliminated. i.e. the treatment which is generally difficult to carry out in the factory in which the engines are manufactured. The invention is illustrated in more detail in the following examples.

Example 1: A 2 mm thick, hot-rolled steel strip, the surface of which was provided with hot-rolled skin and which was made of steel for general construction purposes containing 0.08% C; 0.36% Mn; 0.02% si; 0.027% s ooh o, o1o m P as impurities, was dissolved with Ca (OH) 2 by dipping in lime milk. After the coating dried, the strip was heated at 800 ° C for 4 hours in a muffle furnace (laboratory scale) with electrical resistance heating. During the heat treatment, the carbon content of the belt dropped to 0.007%.

A sample of the same strip, also provided with a hot-rolled skin coating, was heat-treated under the above conditions but without a calcium hydroxide coating. During this heat treatment, the carbon content dropped to only 0.039%.

Example 2: A sample of the belt 10 mentioned in Example 1 was surface-coated with hot-rolled skin dipped in a solution containing 120 g / l NaOH and 100 g / l Al. When the coating dried, the strip was subjected to heat treatment under the conditions set forth in Example 1. As a result, the carbon content in the belt dropped to 0.009%.

Example 3: A 2 mm thick strip of steel having the composition given in Example 1 and provided with hot rolled skin having a thickness of at least 20 mp was provided with a calcium hydroxide coating in the manner set forth in Example 1. After the coating was dried, heat treated. the band for 4 hours at 80,000 in a vacuum of 10.1 mmHg.

Through the heat treatment, the carbon content of the steel strip was reduced to 0.002%.

Example 4: A coil of a 2 mm thick strip of steel with the composition set forth in Example 1 was surface coated with Ca (OH) 2 without removing the hot roll skin by loosening the coil; were made apart, after which the coil was dipped several times in a lime milk solution.

After drying, the coil was heat treated at 800 ° C in a clock oven, ensuring that all parts of the coil were kept at 800 ° C for at least 3 hours. During this treatment air was blown under the clock with an egg point of + 50 ° C. after the heat treatment, the clock was removed and the coil was cooled rapidly. The cooling rate is admittedly not critical, but with regard to the subsequent, special and final heat treatment, it is advantageous to have relatively fast cooling.

Then the coil was pickled in a 15-20% sulfuric acid solution in a conventional manner and the strip was cold rolled in several sticks to a final thickness of 0.70 mm in the usual manner. (If a strip with a different final thickness is required, the product can be rolled to a suitable dimension, for example a thickness of 0.5 mm, 0.65 mm, 0.85 mm or 1.00 mm.) The strip rolled to its final thickness is heat was traded in an exothermic shielding gas of ordinary composition (for example 16% az, 10% coz, 10% co and the residue NZ) at 47 ° C.

(All parts of the tape should be kept at the said temperature for 2 hours.) Thereafter, the tape 1111 e90 ° C was kept at this temperature until each part of the coil was exposed to 690 ° C for 0.5 hours. By this heat treatment a strip was obtained which was easy to cut and which had a thickness of 0.70 mm. The iron loss (V10) amounted to 4.3 W / kg. The B25 induction value of the band (induction determined at a field strength of 25 Oe) was 1.67 tesla. 7213524-7 10 15 20 8, §§gm2elv5: As a starting material, a hot-rolled strip of a steel with the composition specified in Example 1 was used.

This belt was treated essentially as indicated in Example 4, but the heat treatment was carried out in two steps. Thus, the 2 mm thick strip was first subjected to cold rolling in several sticks to a thickness of 0.77 mm, after which the strip was annealed in the usual manner at 720 ° C. The annealed strip was cold rolled in a single stick to the final thickness of 0.70 mm. The strip thus obtained was subjected to heat treatment in two steps in the manner set forth in Example 4. The heat-treated strip had an iron loss (V10) of 3.7 W / kg and an induction (B25) of 1.68 tesla.

The belt thus treated had slightly worse punching properties than the belt treated according to Example 4.

Example 6: A hot-rolled strip with a thickness of 2 mm and containing 0.31% Si; 0.52% Mn; 0.06% C; 0.007% S and 0.011% P as impurities were treated in the manner set forth in Example 4. The thus treated strip with a final thickness of 0.70 mm had good punching properties after heat treatment.

The iron loss (V10) was 3.3 W / kg and the induction (B25) 1.64 tesla.

Claims (2)

72 15 7213524-7 Patent claims Methods of producing steel products, in particular strip and sheet metal, with improved magnetic and mechanical properties, wherein the thermoformed product is pickled, transferred to its final dimensions in the cold state, subjected to a final heat treatment and subjected to the annealed product before pickling. heat treatment at a temperature between 700 and 950 ° C for cooling, in the heat treatment carried out by w: man, fen-eden at 70 DEG-95 DEG C., a layer of one or more several of the following compounds, namely hydroxide of alkali metal, hydroxide of alkaline earth metal, carbon of alkali metal, carbonate or alkaline earth metal and aluminum hydroxide, and optionally carry out the final heat treatment in two steps, one at 550-600 ° C, preferably at 460-490 ° C and it dries at 600 ~ 780 ° C, preferably at 680-760 ° C. 2. A method according to claim 4, characterized in that in the oven during the heat treatment of the product, which is coated fi with a glow plug, air or a shielding gas with a dew point above + 20 ° C, preferably above + 50 ° C, is introduced. k ä n n e t e c k n'a t STATED PUBLICATIONS: US 935 274 (179-185)