RU2444578C2 - Growth-resistant cast iron - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: austenitic growth-resistant cast iron contains the following, wt %: Ni 10.0-12.9; Mn 1.5-5.0; Cr 2.8-5.0; C 2.5-3.5; Si 1.5-3.0; Cu 1.5-6.0; S<0.1; P<0.3; Fe - the rest.

EFFECT: cast iron has high operating properties at low temperatures, namely growth resistance, corrosion resistance.

2 cl, 1 tbl, 1 ex

Description

The invention relates to the field of ferrous metal alloys, and in particular to compositions of special alloyed cast irons containing chromium and nickel. Such cast irons can be used for the manufacture of machine parts operating without resizing in cold climates.

In engineering, highly alloyed high-alloy austenitic cast irons are widely used. These cast irons are designed and, as a rule, are used for the manufacture of machine parts operating at elevated operating temperatures. Most often, a large amount of the main alloying element of nickel is introduced into the composition of such cast irons (more than 15%).

Known, for example, the composition of austenitic iron:

FROM <3.0% Si 1.5 ... 3.0% Mn 0.5 ... 1.5% Ni 18.0 ... 22.0% Cr 1.0 ... 3.5% P <0.08%

(B. Voronenko, Yu. I. Romatovsky “Properties and application of austenitic nickel irons with spherical graphite” // MiTOM, 1988, No. 4).

This cast iron has good growth resistance at low temperatures up to -80 ° C. It also has good corrosion resistance. However, it has a drawback, namely, a high cost due to the high nickel content, the price of which is constantly growing.

The composition of austenitic iron is known:

FROM 3.0 ... 3.5% Si 2.6 ... 3.0% Mn 7.0 ... 9.0% Ni 6.0 ... 7.0% Cr 0.2 ... 0.35% V 0.2 ... 0.4% S <0.1% P <0.3% Fe rest

(RF patent No. 2205887, IPC C21C 37/10, publication 2003.06.10)

Such cast iron is much cheaper and has sufficient growth resistance at temperatures up to -60 ° C, however, it has the following disadvantages. The high content of manganese makes its main structural component (austenite) prone to martensitic transformation under mechanical action. Parts during martensitic transformation change size and become unsuitable for further operation. In addition, when working in some aggressive environments, such as formation fluid, a mixture of oil, water and associated petroleum gas, the cast iron in question has low corrosion resistance.

The closest technical solution is the composition of cast iron:

FROM <3.0% Si 2.0 ... 3.0% Mn 6.0 ... 7.0% Ni 12.0 ... 14.0% Cr - P <0.08%

(B. Voronenko, Yu. I. Romatovsky “Properties and application of austenitic nickel irons with spherical graphite” // MiTOM, 1988, No. 4).

The composition provides the necessary growth resistance, has a satisfactory cost. The reason limiting the use of such cast irons for the manufacture of machine parts operating at low temperatures in the Far North is the relatively low and unstable corrosion resistance.

An object of the invention is the creation of structural nickel austenitic iron for operation in cold conditions at temperatures up to -60 ° C with the minimum required nickel content in it. An additional requirement for the cast iron being developed is its good machinability by cutting, which is necessary in the manufacture of parts from cast billets.

The technical result from the implementation of the invention is to obtain parts with high performance properties at minimum cost.

The specified technical result is ensured by the fact that the high performance properties of nickel austenitic iron are formed by the main complex of alloying elements:

Ni 10.0 ... 12.9% Mn 1.5 ... 5.0% Cr 2.8 ... 5.0%

however, cast iron may contain elements in the following concentration ranges:

FROM 2.5 ... 3.5% Si 1.5 ... 3.0% Cu 1.5 ... 6.0% S <0.1% P <0.3%

In addition, the consumer properties of cast iron, especially corrosion resistance, can be increased with the help of spheroidizing modification, for example, magnesium, SchZM and REM-containing modifiers, as a result of which graphite is obtained in spherical or vermicular form in the structure of cast iron.

In addition, consumer properties, especially wear resistance, can be improved by introducing small amounts of refractory metals, such as vanadium, molybdenum, niobium, titanium, and tungsten, which are simultaneously strong carbide-forming elements, into the composition of cast iron.

A nickel content of less than 10.0% to ensure the necessary corrosion resistance requires a chromium content of more than 5.0% in the composition of cast iron. This chromium content leads to the formation of an increased amount of carbides forming a continuous framework in the structure of cast iron, and unacceptably high hardness and poor machinability of cast iron.

Cast iron with a manganese content of more than 5.0% has an increased tendency to harden high-manganese austenite. During the machining of cast iron by cutting, part of such austenite turns into a very solid martensite phase. Martensitic transformation leads to unacceptably poor machinability of cast iron and sharp wear of the tool. During the operation of parts under shock loads, part of such austenite also turns into martensite. Martensitic transformation is accompanied by a change in the linear dimensions of the part and the destruction of equipment.

Cast iron with a manganese content of less than 1.5% has poor growth resistance at low temperatures.

Cast iron with a chromium content of less than 2.8% has poor corrosion resistance.

A nickel content of more than 12.9% is not economically feasible.

Example. Prototype cast iron was smelted in an induction furnace IST-0.06 with an acid lining. As a charge, cast iron scrap SCH20, steel scrap St.3, graphite in the form of chips of graphite electrodes, nickel H1, copper M1, ferromanganese FMn80, ferrosilicon FS75, carbon ferrochrome ФХ800 were used.

Casting was carried out without modifying the melt. Casting molds of test samples and a sample for quantitative chemical analysis were poured with melt from one ladle. The temperature at the outlet of the furnace 1490-1500 ° C. The pouring temperature of the molds is 1390-1420 ° C.

Examples of chemical compositions of cast iron of experimental melts and the results of corrosion resistance tests are presented in the table.

Element The composition of the cast iron experimental swimming trunks No. 1 (famous) Number 2 Number 4 Number 8 Ni 18.1 10.1 11.0 12.9 Mn 1.4 4.9 3.2 1,6 Cr 3,1 5,0 3.4 2,8 FROM 2.9 2.9 2.9 3.2 Si 2.2 2,3 2.2 2.2 S 0,025 0,023 0,025 0,023 R 0,07 0,07 0,07 0,07 The corrosion rate, g / m ² · h 1,655 1,518 1,633 1,620

The study of growth resistance was carried out on 5 samples of each experimental heat. A mixture of ethanol and carbon dioxide, placed in a thermos, was used as a low-temperature medium (-60 ° C). After immersion of the samples in the mixture, the thermos was closed. Samples were kept in this state for one hour. Then the samples were removed from the mixture and allowed to warm. The length of the samples was measured with an accuracy of 0.01 mm at a temperature of (20 ± 2) ° C. All variants of experimental cast irons showed the absence of changes in linear dimensions. All variants of experimental cast irons did not show a tendency to hardening during machining.

Claims (2)

1. Austenitic growth-resistant cast iron for operation at low temperatures, containing chromium and nickel, characterized in that to ensure high consumer properties in operating conditions at low temperatures, it contains, wt.%:
Ni 10.0-12.9 Mn 1,5-5,0 Cr 2.8-5.0 FROM 2.5-3.5 Si 1.5-3.0 Cu 1.5-6.0 S <0.1 R <0.3 Fe rest 2. Cast iron according to claim 1, characterized in that the graphite in the structure of cast iron has a spherical or vermicular shape.