RU2302478C2 - Low-carbon steel - Google Patents

Abstract

FIELD: production of special-purpose steels, for welding electrodes in particular.

SUBSTANCE: proposed steel contains the following components at the following ratio, mass-%: carbon, up to 0.10; silicon, up to 0.03; manganese, 0.35-0.60; chromium, up to 0.12; nickel, up to 0.25; sulfur, up to 0.02; phosphorus, up to 0.02; aluminum, up to 0.01; calcium, up to 0.009; the remainder being iron. Proposed composition and ratio of components of calcium and aluminum in steel of 0.2 to 0.9 makes it possible to obtain steel at ratio of yield point to ultimate strength equal to 0.5-0.75, thus improving operating conditions for continuous casting machines and cold drawing of wire from this steel.

EFFECT: enhanced efficiency.

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Description

The invention relates to metallurgy and can be used in the production of steel for special purposes, mainly steel for welding electrodes.

Cold drawn welding wire can be made of low carbon and alloy steel, grades and chemical composition of which are given in GOST 2246. Low carbon steel (according to GOST 2246 - Sv-08, Sv-08A and Sv-08AA grades) contains up to 0.01 wt.% Aluminum. During the continuous casting of these steels, certain difficulties are observed associated with the "overgrowing" of casting glasses by non-metallic inclusions based on aluminum oxides.

Known alloy steel containing carbon, silicon, manganese, chromium, titanium, vanadium, nitrogen and iron, which additionally contains aluminum in an amount of 0.2 ... 0.5 wt.%, Which increases the wear resistance of products from this steel under impact -abrasive wear (see AS USSR No. 969779, class C22C 38/38, publ. in BI No. 40, 1982). However, this steel is unacceptable for cold drawing due to its insufficient ductility.

The closest analogue to the claimed object is steel Sv-08AA, described in GOST 2246.

This steel contains carbon, silicon, manganese, chromium, nickel, sulfur, phosphorus and aluminum and is characterized by a relatively low content of carbon (up to 0.1 wt.%) And aluminum (up to 0.01%). The disadvantage of this steel are:

- in the process of casting steel at the continuous casting machine, there are numerous cases of “overgrowing” of refractory glasses by non-metallic inclusions based on aluminum oxides, leading to an emergency stop of the continuous casting machine and downtime of the equipment;

- gusts of metal when drawing on high-quality mills and low yield.

An object of the invention is to improve the spillability of steel at the continuous casting machine and increase yield by drawing steel.

To solve this problem, the specified steel containing carbon, silicon, manganese, chromium, nickel, sulfur, phosphorus, aluminum and iron, in contrast to the closest analogue, additionally contains calcium in the following ratio of components (wt.%):

Carbon up to 0.10 Silicon up to 0.03 Manganese 0.35 ... 0.60 Chromium up to 0.12 Nickel up to 0.25 Sulfur up to 0.02 Phosphorus up to 0.02 Aluminum up to 0.01, Calcium up to 0,009 Iron Rest

Moreover, the ratio [Ca] / [Al] = 0.2 ... 0.9, where [Ca] and [Al] in wt.%.

The magnitude of the mechanical characteristics of the steel ratio in the range σ _r / σ _s = 0,50-0,75 where σ _m and σ _in - respectively, the values of yield strength and tensile strength.

The essence of the technical solution found is to add calcium to the steel at the optimum ratio of its content and aluminum, as well as to optimize the ratio σ _t / σ _c . As a result of this, the operation of the continuous steel casting machine (the absence of "overgrowing" of the walls of the casting cups) and the conditions for cold drawing of wire from this steel (reducing gusts during drawing to a minimum) are improved.

An experimental verification of the proposed technical solution was carried out in the production of the above steel in the open-hearth shop of OJSC Magnitogorsk Iron and Steel Works and during its cold drawing in OJSC Magnitogorsk Hardware and Metallurgical Plant with the production of wire for welding electrodes.

The best results (no downtime of the continuous casting plant, yield when drawing up to 99.5%) were obtained using the proposed steel. Deviations from the recommended values (see above) of the ratios [Ca] / [Al] and σ _t / σ _in led to the deterioration of the experimental results.

All of the above limits of the content of components in the proposed steel, as well as the magnitude of the ratio σ _t / σ _in obtained as a result of processing of experimental data and are empirical.

So the downtime of the continuous casting plant associated with the emergency stop of the continuous casting machine due to the “overgrowing” of the casting nozzles was observed at [Ca] / [Al] <0.2 and> 0.9.

At values of [Ca] / [Al] <0.2, complex solid complexes are formed in liquid steel based on aluminum oxides of the type Al ₂ O ₃ , 6Al ₂ O ₃ · CaO, 2Al ₂ O ₃ · CaO having a melting point above 1550 ° C, which is significantly higher than the crystallization temperature of steel. These solid inclusions in the process of continuous casting adhere to the inner walls of the steel pouring cup, while the inner diameter of the steel pouring cups decreases, which leads to a decrease in the casting speed and emergency stop of the continuous casting machine.

At a ratio of 0.2 <[Ca] / [Al] <0.9, a complex compound 7Al ₂ O ₃ · 12CaO is formed in liquid steel, having a melting point of about 1420 ° C, which is lower than the crystallization temperature of steel. With this ratio of "overgrowing" the walls of the refractory glasses are absent.

At a ratio of [Ca] / [Al]> 0.9, non-metallic inclusions in the form of CaO are also formed in the metal, leading to steel contamination.

In the ratio of σ _r / σ _in> 0.75 were breakages wire cases (if drawing) due to rapid hardening of the metal. At σ _t / σ _at <0.50, the yield decreased to 92 ... 95% due to the receipt of a wire with a reduced (against the required value by order) diameter, which is explained by its increased ductility.

Tests of Sv-08AA steel led to a reduction in cases of stopping continuous casting (up to 2% of machine time), and the yield during wire drawing did not exceed 96.5%.

Thus, the pilot test confirmed the acceptability of the claimed technical solution to achieve the goal and its advantages over the object selected as the closest analogue.

According to technical and economic studies conducted at the Central Control Laboratory of OJSC MMK, the use of the proposed low-carbon steel for the production of welding electrodes will reduce the downtime of the continuous casting plant associated with the replacement of casting glasses by at least 2% and the yield of suitable electrode increase the average wire by 3% with a corresponding increase in profits from the sale of products.

Concrete example

Mild steel for welding electrodes contains, wt.%:

C = 0.09; Si = 0.027; Mn = 0.5; Cr = 0.10; Ni = 0.23; S = 0.018; P = 0.015; Al = 0.009; Ca = 0.0036 (i.e., the value of [Ca] / [Al] = 0.4); the rest is iron.

Mechanical characteristics of steel produced for drawing:

σ _T = 226 MPa, σ _in = 375 MPa, σ _r / σ _s = 0.60.

Claims (1)

Low-carbon steel, mainly for welding electrodes, containing carbon, silicon, manganese, chromium, nickel, sulfur, phosphorus, aluminum and iron, characterized in that it additionally contains calcium in the following ratio, wt.%: Carbon up to 0.10 Silicon up to 0.03 Manganese 0.35 ... 0.60 Chromium up to 0.12 Nickel up to 0.25 Sulfur up to 0.02 Phosphorus up to 0.02 Aluminum up to 0.01 Calcium up to 0,009 Iron Rest the ratio of [Ca] / [Al] = 0.2 ... 0.9.