RU1788026C - Modifying mixture - Google Patents

Abstract

Usage: production of castings of high-strength cast iron with increased durability. SUMMARY OF THE INVENTION: The modifying mixture contains (wt.%) Boric acid 18-25; copper oxide 10-17; silicobarium 15-23; zirconium nitrides 12-17; cobalt powder 11-15; lithium 6-13; magnesium 6-12. 2 tab.

Description

The invention relates to metallurgy, in particular to liquid cast iron modifiers used in the manufacture of castings from ductile iron with increased cyclic durability.

Known modifying mixture containing, wt.%:

Silicocalcium 30-40 Graphite 5-10 Cryolite. 5-10 Aluminum 2-6 Calcium carbide Rest. This mixture provides desulfurization, deoxidation and carburization, but has a low assimilation of components and does not provide a significant increase in the mechanical properties of modified cast iron in castings.

Known powder modifying mixture DG processing of molten iron, containing, wt.%:

Magnesium powder. 10-40 Sodium Fluoride Powder. о 5-32 Iron Powder Else However, when using this modifying additive, a lot of fumes are noted and it is not always possible to obtain a homogeneous structure in cast iron castings and high mechanical and operational properties.

The closest in technical essence and the achieved result is a modifying mixture for cast iron, containing boric acid and copper oxide as carbide forming component, and silicobarb as graphitizing component. in the following ratio of components, wt.%:

Copper oxide 20-30 Boric acid 50-60 Silicobarium 10-30

AND

When modifying pre-eutectic cast iron, containing, wt.%: Carbon 2,4; silicon 1.1; manganese 0.4; chrome 0.06; sulfur 0.06, phosphorus 0.07 and the rest iron, after graphitizing annealing in the SNOL-1.6 furnace, the following mechanical properties are achieved; hardness is 137-144 HB, tensile strength is 480-495 MPa, elongation is 12-15%, shear modulus .-. 72000-73500 MPa1, cyclic durability - 7600-12500 cycles up to times-1 destruction.; H; : -; l: n:; x ;; 7-Vv ;: .. .-. ;:.

The disadvantages of the modifying mixture are the low strength and cyclic durability characteristics of the modified cast iron.

The purpose of the invention is to increase the cyclic durability of cast iron. - v

The goal is achieved in that the modifying mixture containing boric acid, copper oxide and silicobarium additionally contains zirconium nitrides, cobalt powder, lithium and magnesium in the following ratio of components, wt.%: -: i. , Boric acid 18-25 Copper oxide 10-17 Silicobarium 15-23 Zirconium nitrides 12-17. Cobalt powder 11-15 Lithium. 6-13 Magnesium 6-12 The additional introduction of zirconium nitrides provides an increase in the graphitizing effect of the mixture, grinds the structure, increases crack resistance, shear modulus, impact strength and cyclic durability.

At a concentration of zirconium nitrides up to 1.2 wt.%, The structure and characteristics of the shear modulus, toughness and cyclic durability are insufficient, and with an increase in zirconium nitrides more than 17 wt.%, The concentrations of nonmetallic inclusions in cast iron increase, and scrap reject increases. which leads to a decrease in the plastic and operational properties of cast iron, cyclic durability and shear modulus.

Magnesium refines and modifies the iron-carbon melt, increasing the plastic properties, crack resistance, and cyclic durability. At a magnesium concentration of up to 6 wt.%, The plastic properties and cyclic durability of cast iron are low, and at a concentration in a magnesium mixture of more than 12 wt.%, The perlite content in cast iron is increased and crack resistance, yield strength, shear modulus, service life and cyclic durability of modified cast iron are reduced.

Lithium is introduced as a strong deoxidizer and spheroidizer of graphite, which increases the dispersion of the structure in the molten state, strengthens the structure and increases the cyclic crack resistance, shear modulus, mechanical and operational properties. Its content is accepted

0 from 6 wt.%, From which its spheroidizing and hardening effect begins to manifest and is limited by a concentration of 13 wt.%, Above which fumes and instability of mechanical properties are increased, impact resistance and cyclic durability are reduced.

Cobalt powder stabilizes the modification process and increases crack resistance, shear modulus, impact

0 viscosity and cyclic durability. An increase in toughness and cyclic durability is noted with a content of 11. wt%, and with an increase in cobalt powder of more than 15 wt%, the modifying ability of the mixture decreases, the hardness of cast iron increases, and the impact strength, cyclic crack resistance and shear modulus decrease.

The introduction of 10-17 wt.% Copper oxide reduces and evens out the hardness of cast iron, increases the graphitizing ability, casting properties, dispersion and uniformity of the structure, which leads to an increase in impact strength,

5 yield strength, cyclic durability of cast iron in castings after heat treatment. When its concentration is less than 10 wt.%, An increase in hardness and a decrease in plastic properties and cyclic

0 durability, and with an increase in the concentration of more than 17 wt.%, The liquations, sinter, heterogeneity of the structure of cast iron in the castings increase, which leads to a decrease in toughness, cyclic durability and stability of mechanical properties,

Boronic acid in an amount of 18-25 wt.% Provides additional modification of cast iron with boron, increasing the graphitizing ability of cast iron, lowering hardness, increasing yield strength and cyclic crack resistance. The upper limit of the concentration of boric acid in the mixture is limited by the content of 25 wt.%, Above which the heterogeneity of the structure and the cyclic crack resistance of cast iron in castings are increased and the operational properties and shear modulus and yield strength are reduced. With a decrease in the concentration of boric acid below 18 wt.%, Low characteristics of mechanical properties and the degree of graphitization of cast iron are noted.

Silicobarium is introduced as an effective deoxidizing, modifying, and graphitizing additive that increases impact strength and cyclic crack resistance. When it is contained more than May 23%, the mixture burns up, the heterogeneity of the structure, and the cyclic crack resistance and mechanical properties decrease. When the concentration of silicobar is up to 15 wt.%, The graphitizing ability of the mixture decreases, the perlite content in the structure increases, which reduces the plastic properties and performance, cyclic durability. . Example. Cast iron melts are carried out by a duplex-process cupola-induction mixer. For processing, cast irons of the following composition are used, wt.%: Carbon 2.8–2.85, silicon 1.6–1.7, manganese 0.5–0.6, chromium 0.03–0.04, sulfur 0, 03-0.04, phosphorus 0.05-0.06 and iron - the rest. For the modification of cast iron, 5 compositions of the proposed modifying mixture and the known modifying mixture in the amount of 0.2% by weight of the melt are used.

Modifying mixtures are made by mechanical mixing of boric acid powders (GOST 18704-78), copper oxide (TU 78-21-355-85), zirconium nitrides (TU 6-09-4050-75), cobalt powder (GOST 9721- 79),. Grinded to a fraction of 0.5-2 mm silicobar SBZO (TU 14-5-116-79), lithium L E-1 (GOST 8774-78) and Mg1 magnesium (GOST 804-72) ...: ......

The compositions of the modifying mixtures are presented in table 1. Technological samples are cast from modified cast iron; samples for mechanical tests are cast

ni fl 10-45 mm and tube blanks. The technological properties of the modified cast irons are determined on standard cast samples, and the mechanical properties on samples with a diameter of 10 mm. Cyclic durability tests are determined on tube blanks with a diameter of 30-35 mm. Operational durability is determined by testing cylindrical specimens under conditions of impact tests.

Table 2 shows the mechanical and technological properties of the modified cast irons. As can be seen from table 2, cast irons modified with the proposed mixture of compositions 2, 3 and 4 have higher mechanical properties, cyclic durability and operational stability than when modifying them with a known mixture of optimal composition (experience

1). ..

The use of the proposed modifying mixture will improve the operational stability and mechanical properties.

Claims (1)

The claims A modifying mixture containing boric acid, copper oxide and silicobarium, characterized in that, in order to increase the cyclic durability of cast iron, it additionally contains zirconium nitrides, cobalt powder, lithium and magnesium in the following ratio, wt.%: Boric acid 18-25; Copper oxide 10-17; Silikobariya. 15-23; Zirconium nitrides 12-17; . Cobalt Powder 11-15; Lithium 6-13; Magnesium. 6-12, Table 1 table 2