RU2387729C1 - Corrosion-resistant cast iron with spherical graphite - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: cast iron can be used for manufacture of working elements of sludge and sand pumps and hydraulic machines, which pump abrasive pulps, mixtures and suspensions. Corrosion-resistant cast iron with spherical graphite contains the following, wt %: carbon 3.2-4.0; silica 1.5-3.0; manganese 0.8-3.5; chrome 7.0-10.0; nickel 2.0-4.0; boron 0.2-0.4; vanadium 0.4-1.0; molybdenum 0.1-0.5; titanium 0.1-0.4; aluminium 0.05-0.2; cerium 0.03-0.2; magnesium 0.02-0.1; calcium 0.05-0.2; iron- the rest.

EFFECT: cast iron has increased resistance to impact of corrosion abrasive media.

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Description

The invention relates to foundry, and in particular, to the search for corrosion-resistant nodular cast iron for the production of parts intended for work in conditions of waterjet wear, in particular for the manufacture of working bodies of soil and sand pumps and hydraulic machines, pumping abrasive slurries, suspensions and mixtures.

Known wear-resistant cast iron, containing, wt.%: Carbon 3.0-3.7; silicon 0.5-3.0; manganese 0.2-1.5; chrome 4.0-15.0; nickel 4.0-8.0; phosphorus up to 0.4; sulfur up to 0.15; iron is the rest (see US patent No. 2662011, CL 75-128, 1953). The disadvantage of this cast iron is the low concentration of dissolved chromium (up to 6%) in its metal base. In this regard, on the surface of products from it does not form a corrosion-resistant passivating film. As a result, it has a low resistance to corrosive abrasive media.

Known chrome-nickel cast iron with spherical graphite (see, for example, the description of the patent of the Russian Federation No. 2234553, C1, 7 C22C 37110, 2004), selected as a prototype for the content of incoming components and having the following composition, wt.%: Carbon 3,2 -4.0; silicon 1.4-2.5; manganese 0.4-1.2; chrome 7.0-10.0; nickel 2.5-5.5; boron 0.2-0.4; vanadium 0.6-1.0; aluminum 0.05-0.15; cerium 0.05-0.20; magnesium 0.3-0.12; calcium 0.05-0.20; iron the rest.

In the metal base of the specified spheroidal graphite iron, the concentration of dissolved chromium reaches 11.8%. Thanks to this, he acquires the first boundary of a stable passive state. However, the maximum corrosion resistance of Fe – C alloys is ensured when their base contains more than 12% chromium [1].

The objective of the invention is to increase the concentration of dissolved chromium (more than 12%) in the metal base of chrome nickel iron with spherical graphite in order to increase the resistance of products from it to the effects of corrosive abrasive media.

The technical result achieved by the implementation of the proposed technical solution consists in increasing the corrosion resistance of cast iron while reducing its cost, intended for the manufacture of castings of complex configuration, for example, wheels of working pumps for pumping abrasive mixtures, pulps and suspensions.

The specified technical result is ensured by the fact that in the proposed chromium-nickel iron with spherical graphite containing: carbon, silicon, manganese, chromium, nickel, boron, vanadium, aluminum, cerium, magnesium, calcium, iron, molybdenum and titanium are additionally introduced in the following ratio of components , wt.%: carbon 3.2-4.0; silicon 1.5-3.0; manganese 0.8-3.5; chrome 7.0-10.0; nickel 2.0-4.0; boron 0.2-0.4; vanadium 0.4-1.0; molybdenum 0.1-0.5; titanium 0.1-0.4; aluminum 0.05-0.2; cerium 0.03-0.2; magnesium 0.02-0.1; calcium 0.05-0.2; iron the rest.

The introduction of molybdenum into the composition of the proposed cast iron makes it possible to increase the concentration of dissolved chromium in its metal base due to the partial substitution of chromium atoms in the carbide phase by molybdenum.

The introduction of molybdenum of less than 0.1% does not provide an increase in the concentration of dissolved chromium in the metal base; an increase in the molybdenum content of more than 0.4% causes the release of molybdenum carbides of the type Mo ₂ C, which does not provide an increase in the concentration of chromium in the metal base of cast iron and, accordingly, its corrosion resistance.

The addition of titanium to the composition of the proposed cast iron contributes to an increase in the concentration of dissolved chromium in its metal base due to the partial replacement of chromium atoms by titanium in the carbide phase.

The introduction of titanium of less than 0.1% does not provide an increase in the concentration of dissolved chromium in the metal base; an increase in titanium content in excess of 0.4% causes the precipitation of titanium carbides TiC, which does not provide an increase in the concentration of chromium in the metal base of cast iron and, accordingly, its corrosion resistance.

An increase in the content of manganese in cast iron makes it possible to increase its concentration in austenite.

The introduction of manganese in an amount of less than 0.8% does not provide an increase in a sufficient concentration of manganese in austenite, which contributes to the partial decomposition of austenite upon cooling into troostite, which has low corrosion resistance. This entails a sharp decrease in the resistance of chromium-nickel cast iron with spherical graphite to the effects of corrosion-abrasive media, as a result of which the service life of articles made of it is reduced. An increase in manganese content of over 3.5% causes the release of manganese carbides of the type Mn ₃ C, which increases the brittleness of cast iron and affects the processing of castings by cutting.

Reducing the nickel content in cast iron allows to reduce the cost of manufacturing castings.

The introduction of Nickel in an amount of less than 2.0% does not ensure the achievement of a sufficient concentration of nickel in austenite, which contributes to the partial decomposition of austenite upon cooling into a corrosion-unstable troostite. An increase in nickel content in excess of 4.0% contributes to an increase in the fraction of residual austenite in the metal base of cast iron, resulting in a decrease in its hardness.

Iron is smelted in induction or electric arc furnaces using standard charge materials. Alloying elements such as nickel, molybdenum, chromium and vanadium are introduced into the metal plant. After the charge is melted and the cast iron is overheated to 1450-1500 ° С, silicon and manganese are introduced into the melt mirror in the form of 75% ferrosilicon and 60% ferromanganese. Then aluminum and calcium are added (in the form of 20% silicocalcium). Magnesium in the composition of the spheroidizing additive, as well as cerium, boron and titanium in the form of ferrocerium, ferroboron and ferrotitanium, is introduced to the bottom of the casting ladle before the liquid metal is discharged from the furnace.

Table 1 shows the chemical composition of the known and proposed cast irons. Table 2 shows their mechanical properties and resistance in aggressive abrasive media.

The technical result is, as can be seen from the data in table 2, a higher concentration of chromium in the metal base and, accordingly, a higher corrosion resistance and wear resistance of the proposed cast iron in comparison with the prototype.

Temporary iron flexural resistance (σ _mfd) were determined on cylindrical specimens (⌀30 × 340 mm) at a distance between centers of bearings 300 mm (GOST 27208-87).

Rockwell hardness was determined on a TK-2M instrument according to GOST 9013-59.

The microdistribution of chromium in a metal base of cast iron was studied on an MS-46 Cameca microanalyzer.

Corrosion resistance in a sulfuric acid medium was determined by the weight loss of the samples after testing for a duration of 75 hours according to GOST 5272-50.

The concentration of sulfuric acid was 0.02%, and the pH of the medium was 4.5.

Wear resistance under conditions of hydroabrasive wear was determined by cup grinding at the stand of the TsNIITMASH design. During the test, samples (⌀10 × 110 mm) are moved in a waterjet pulp consisting of abrasive and water at a ratio of 2: 1.3 (by volume). Electrocorundum with a grain size of 0.6-1.5 mm was used as an abrasive. The test duration is 1.5 hours. The disk rotation frequency was 500 rpm ^-1 and was controlled by a stroboscopic tachometer, the linear velocity of the sample was 4.7 m / s ^-1 .

The use of the proposed chrome-nickel cast iron with spherical graphite for castings having a complex configuration, for example, wheels of working pumps for pumping abrasive mixtures, pulps and suspensions, can significantly (by 30-40%) increase the service life of parts in operation while reducing the cost of their manufacture by 20- thirty%.

Table 1 Cast iron No. of swimming trunks The content of chemical elements, wt.% FROM Si Mn Cr Ni V Mo Ti AT Xie Mg Ca Al Pre-lag eleven 3.2 0.5 0.8 3.0 2.0 0.4 0.1 0.1 0.2 0,03 0.02 0.05 0.05 12 2.7 1.8 2.2 8.5 33.0 0.7 0.8 0.35 0.3 0.12 0.06 0.13 0.13 13 4.0 3.0 3,5 10.0 4.0 1,0 0.5 0.4 0.4 0.2 0.1 0.2 0.2 Prototype one 3.6 1.9 0.8 8.5 4.0 0.8 - - 0.3 0.12 0.8 0.1 0.3

table 2 No. of swimming trunks The chromium content in the metal base,% Strength, MPa Hardness HRC The corrosion rate in the sulfuric acid environment, g / m ² · n Relative wear coefficient in conditions of hydroabrasive wear eleven 12,2 905 62 0.44 6.8 12 12.8 910 63 0.41 7.0 13 13,4 902 64 0.38 7.2 one 11.8 900 62 0.55 6.4

Information sources

1. Tomashev N.F., Chernova G.L. Corrosion and corrosion resistant alloys. M .: Metallurgy, 1973.- 232.

Claims (1)

Corrosion-resistant nodular cast iron containing carbon, silicon, manganese, chromium, nickel, boron, vanadium, aluminum, cerium, magnesium, calcium and iron, characterized in that it additionally contains molybdenum and titanium in the following ratio of components, wt. %:
carbon 3.2-4.0 silicon 1.5-3.0 manganese 0.8-3.5 chromium 7.0-10.0 nickel 2.0-4.0 boron 0.2-0.4 vanadium 0.4-1.0 molybdenum 0.1-0.5 titanium 0.1-0.4 aluminum 0.05-0.2 cerium 0.03-0.2 magnesium 0.02-0.1 calcium 0.05-0.2 iron rest