RU2228374C2 - Method of production of cold-rolled electrical isotropic steel - Google Patents

Abstract

FIELD: ferrous metallurgy; methods of production of cold-rolled electrical isotropic steels. SUBSTANCE: proposed method includes melting, hot rolling, pickling, cold rolling and decarburizing recrystallization annealing. Chemical composition of steel is as follows, mass-%: silicon, 0.9-2.6; phosphorus, 0.08-0.25; aluminum, no more than 1.0; carbon, no more than 0.04; manganese, no more than 1.0; sulfur, no more than 0.01; the remainder being iron. Unavoidable admixtures are not higher than AC₃, depending on content of silicon and phosphorus. EFFECT: enhanced strength characteristics and degree of isotropy by specific magnetic losses of cold-rolled electrical isotropic steel. 2 tbl, 2 ex

Description

The invention relates to ferrous metallurgy, and specifically to methods for producing cold-rolled electrical isotropic steel used for the manufacture of magnetic circuits of electrical machines.

In the known method for the production of electrotechnical isotropic steel, given in the USSR author's certificate SU 1786134 A1 of 04/23/1990, in order to improve the quality characteristics of silicon steel, it is additionally alloyed with phosphorus.

The method involves smelting, after-furnace treatment, continuous casting, hot rolling, normalization, pickling, cold rolling and final heat treatment of steel containing, wt.%: Carbon 0.02-0.05; manganese 0.1-0.4; silicon 1.5-3.3; aluminum 0.3-0.6; phosphorus 0.02-0.10; iron the rest.

In order to reduce specific magnetic losses, out-of-furnace treatment is carried out by evacuation, and to increase the manufacturability of processing, normalization of hot-rolled strips is used at a temperature of (810-830) ± 10 ° С.

However, the processing of steel by this method with the normalization of hot-rolled steel complicates the production technology and significantly increases the cost of finished products. Normalization treatment also leads to additional oxidation of the surface of the hot-rolled strips, which causes certain difficulties in its removal during subsequent etching.

Closest to the technical nature of the present invention is a method for producing electrical isotropic steel described in Russian patent RU 2155234 C1 dated 06/28/1999, which also uses alloying of silicon steel with phosphorus.

The method involves steelmaking, hot and cold rolling, decarburization-recrystallization annealing. The temperature of the final recrystallization annealing after cold rolling is determined taking into account the content of silicon and phosphorus from the ratio:

when changing the silicon content in the range 1.4 ÷ 2.6% and phosphorus 0.05 ÷ 015%.

But in this method, when conducting the final recrystallization annealing at a temperature above the critical point AC ₃ (911 ° C), the optimum level of electromagnetic and mechanical properties is not achieved. On the one hand, there is an increase in the anisotropy of specific magnetic losses ΔP _{1.5 / 50} (%), on the other hand, the ratio of the yield strength to tensile strength Gt / Gv decreases, which worsens the felling of magnetic circuit products on high-speed dies among consumers.

The technical result of the invention is to reduce the temperature of recrystallization annealing of cold rolled steel with an increase in the level of alloying of steel with phosphorus, which improves the structural and texture state of the finished steel. In this case, the recrystallization process occurs below the critical point of AC ₃ , which ensures, firstly, an increase in the degree of isotropy of the finished steel with a decrease in the anisotropy of specific magnetic losses ΔР _{1.5 / 50} , and secondly, the ratio Gt / Gv increases, which improves stampability steel.

The problem is achieved in that the temperature of recrystallization during decarburization-recrystallization annealing of cold-rolled steel with a silicon content of 0.9-2.6%; phosphorus 0.08-0.25%; aluminum no more than 1.0%; carbon not more than 0.04%; manganese not more than 1.0%, sulfur not more than 0.01%; the rest of the iron and the inevitable impurities and past smelting, hot rolling, etching and cold rolling set no higher than the critical point AC ₃ , depending on the content of silicon and phosphorus in accordance with the ratio:

where tр is the temperature of recrystallization, ° C,

911 - the temperature of the phase transformation of perlite to austenite in pure iron, ° C;

K is an experimentally determined coefficient;

K = 44.3 [° C · (%)];

Si — silicon content in steel, wt.%;

P is the phosphorus content in steel, wt.%.

A necessary condition for increasing the degree of isotropy of magnetic properties and a high level of mechanical characteristics of finished steel is an increase in the pole density of {200} cubic density in the metal and the formation of an optimal micrograin size. When carrying out recrystallization annealing of cold rolled steel at a temperature not higher than the critical point of AC ₃ , in order to increase the strength properties of rolled products, the improvement of structural and textural characteristics is achieved by increasing the degree of alloying of the metal with phosphorus to 0.25%.

Being a strong ferrite-forming element that sharply narrows the γ-region, phosphorus promotes rapid growth and an increase in the average grain size, which ensures, under conditions of lowering the temperature of steel recrystallization, obtaining an equiaxial homogeneous microstructure over the entire thickness of the annealed strips.

This leads to an increase in the degree of isotropy of the microstructure and contributes to an increase in the pole density of the {200} cubic orientation in the surface and middle layers of the strip.

An increase in the phosphorus content in the steel also leads to additional hardening of the solid solution. This is due to the smaller diameter of phosphorus atoms compared to iron and silicon atoms, and alloying steel with phosphorus increases the packing density of the metal matrix, which leads to an increase in the Gt / Gv ratio of the finished metal. This provides improved stampability of electrical isotropic steel among consumers.

The range of values of the degree of alloying of steel with phosphorus, based on laboratory and industrial experiments, was chosen equal to 0.08-0.25%. The lower limit is due to the insignificant effect on the structure and Gt / Gv ratio of the finished phosphorus steel at a content of less than 0.08%, and the upper one is due to a decrease in the processability of rolled metal processing due to an increase in the hardness of the metal with a phosphorus content of more than 0.25%.

The recrystallization of steel below the critical point AC ₃ is due to the fact that during the heat treatment of cold-rolled steel above the point AC _{3 the} metal microstructure becomes different-grained, which leads to an increase in the anisotropy of specific magnetic losses ΔP _{1.5 / 50} and a decrease in the ratio Gt / Gv, which worsens the stampability of steel .

The content of phosphorus and silicon affects the grain size of steel and the formation of a crystallographic texture; therefore, when assigning the recrystallization temperature of cold rolled steel to no higher than the critical point AC ₃ , experiments show that the content of these elements must be taken into account.

The application of the invention allows to improve the electromagnetic and mechanical properties of cold-rolled electrical isotropic steel, including reducing the anisotropy of specific magnetic losses ΔР _{1.5 / 50} by 5-8% and increasing the ratio of yield strength to tensile strength by 0.04-0.07 units.

A method for the production of cold-rolled electrical isotropic steel is as follows.

Example 1. Smelted steel with a silicon content of 1.78%; phosphorus 0.11%; aluminum 0.35%; carbon 0.020%; manganese 0.25%; sulfur of 0.008% was hot rolled to a thickness of 2.2 mm; pickling and cold rolling to a thickness of 0.50 mm.

Recrystallization of cold rolled steel during decarburization-recrystallization metal annealing was performed at a temperature of 820 ° C.

Example 2

Smelted steel with a silicon content of 2.45%; phosphorus 0.16%, aluminum 0.40%; carbon 0.03%; Manganese 0.20%; sulfur 0.010% then it was subjected to hot rolling to a thickness of 2.2 mm; etching and cold rolling to a thickness of 0.65 mm.

Cold rolled steel was subjected to recrystallization during decarburization-recrystallization annealing at a temperature of 855 ° C.

Table 1, 2 shows the qualitative characteristics (ΔР _{1,5 / 50} , Gt / Gв) of electrotechnical isotropic steel in the thickness of 0.50 and 0.65 mm according to the known and proposed method.

Claims (1)

Method for the production of cold rolled electrical isotropic steel, including smelting, hot rolling, pickling, cold rolling and decarburization-recrystallization annealing, characterized in that the recrystallization temperature during decarburization-recrystallization annealing of cold rolled steel with a content, wt.%, Silicon of 0.9-2, 6, phosphorus 0.08-0.25, aluminum no more than 1.0, carbon no more than 0.04, manganese no more than 1.0, sulfur no more than 0.01, the rest of the iron and inevitable impurities set no higher than the critical point of the AS _3, depending on the soda Zhaniya silicon and phosphorus in accordance with the relation

where t _p is the temperature of recrystallization, ° C; 911 - the temperature of the phase transformation of perlite to austenite in pure iron, ° C; K is an experimentally determined coefficient equal to K = 44.3 [° C · (%)]; Si — silicon content in steel, wt.%; P is the phosphorus content in steel, wt.%.