CZ129192A3 - spheroidal graphite cast iron for low temperatures - Google Patents

Abstract

Low-alloyed spheroidal graphite cast iron for low temperatures with a basic chemical composition of 3.0 to 4.0% of carbon, 1.5 to 2.5 % of silicon, 0.1 to 0.5 % of manganese, up to 0.070% of phosphorus, up to 0.030% of sulphur, traces of 0.080 % of magnesium, containing at least 0.1 to 2.5% of one of the alloying constituents of nickel, 0.03 to 0.50 % of vanadium, 0.10 to 1.0% of copper, 0.01 to 0.15 % of aluminium and traces of 0.1% of noble earth elements, is modified by 0.03 to 0.90 % by weight of niobium, with a total content of the combination of nickel and alloying constituents of 0.04 to 4.0%.

Description

Technical field

The present invention relates to the chemical composition of a low-alloy ductile iron with a ferritic matrix for use in low temperature castings.

BACKGROUND OF THE INVENTION

At present, large-scale components of vehicles, especially rail vehicles, and some components used in the fields of refrigeration and petrochemistry are mainly made of cast low-alloy steels or ferritic ductile iron. Unalloyed ductile iron or low-alloy ductile iron with nickel additives is used (Ductile Iron Data for Design Engineers. Sorelmetal Technical Service QIT - Fer et Titan lne. 1991) or modified copper (Sýkora, P. - Mahďák, V.- Malec, M .: Ferritic ductile iron with high toughness after heat treatment, especially at negative temperatures, Authorized Certificate No. 196567 of June 30, 1982). These ferritic cast iron complies with the conditions of work at reduced temperatures in terms of strength, ductility, and with the exception of cast iron with added copper and toughness.

A common drawback of said cast irons after ferritic annealing is the low yield strength. For unalloyed ductile iron, min. 230 MPa, in the case of cast iron with addition of nickel up to 1% of c. Although ferritic ductile iron with copper additive has a yield strength somewhat higher (approx. 320 MPa), its notch toughness KCV decreases at low temperatures below 10 0.cm.

For a cost-effective dimensioning of machine parts in terms of shape and weight, this relatively low yield strength value in conjunction with other favorable low-temperature plastic and brittle fracture characteristics is a significant limitation.

SUMMARY OF THE INVENTION

The above-mentioned drawbacks of existing ductile cast iron are overcome by the present invention by adjusting their chemical composition.

The low alloy low temperature ductile iron according to the invention has a basic chemical composition of 3.0 to 4.0% carbon, 1.5 to 1.5% carbon

2.5% silicon, 0.1 to 0.5% manganese, up to 0.070% phosphorus, up to 0.030% sulfur, up to 0.080% magnesium ^ 0.1 to * 2.5% ⁷ nickel , '7

0.03 to 0.50% vanadium, 0.1 to 1.0% copper, 0.01 to 0.15% aluminum, up to 0.1% rare earth elements, iron remainder - all in weight, yodsia ^ ov VyKQlezy engrave contains niobium in an amount of from 0.03 to 0.90% / in combination with at least one SZ abovementioned alloying c.ílk.c characterized 0R · _f 0 to 1 ° / o

In order to achieve the desired properties, it is necessary that the low-temperature ductile iron castings for low temperatures are subsequently heat treated to undergo annealing with recrystallization and then ferritizing annealing below temperatures A. This results in a very fine ferritic grain in the structure of the cast iron. a hardness not exceeding approximately 200 Brinella units.

The advantage of the proposed solution according to the invention is that the above-mentioned chemical composition of the ductile iron castings achieves an increase in yield strength and an optimal combination of strength, deformation, brittle fracture and fatigue characteristics at normal but especially at low temperatures.

DETAILED DESCRIPTION OF THE INVENTION

Example 1

A melt cast iron having a basic composition of 3.4% is prepared.

carbon, 2.0% silicon, 0.2% manganese, 0.020% phosphorus, 0.010%, V Ι Ι Ι Ι κ κ o κ κ κ κ κ s s s s s iry s iry 0.2% Ni from 1.0% Nickel 0.3% Copper - all in amounts by weight, in total, 1.5%, the rest iron. Castings of 30 to 60 mm wall thickness are cast from this low-alloy nodular cast iron, which is heat treated to achieve optimum properties by heating to 830 ° C, holding for 4 h followed by cooling in air and then ferritizing annealing at 680 ° C for 16 h with subsequent cooling in an oven. By this heat treatment, mechanical properties with these values are achieved in the above-mentioned melting;

hardness HB 185 breaking strength in thrust R _m (19 ° C) • 440 MPa yield strength R 0 , 2 (15 ° C) 340 MPa P ductility A- (15 ° C) 25 notch natost ^KCV -40 ° C 18 3. cm fatigue limit θ '. (15 ° C) 203 MPa

Example 2

A melt cast iron having a base composition of 3.5% carbon, 2.1% silicon, 0.2% manganese, 0.030% phosphorus, 0.010% α, 3S% mSubstitute sulfur, 0.050 ¾ magnesium / and a total additive content of 2.0 was prepared. namely, 0.35% niobium, 1.5% nickel, 0.1% vanadium, 0.05% aluminum - all in weight amounts - the rest iron. Castings of hay thickness of 40 to 80 mm are cast from this cast iron, which are heat treated as follows: annealing at 850 ° C for 5 h followed by cooling in air and then heating to a ferritizing annealing temperature of 700 ° C with a holding time of 20 h. air. The achieved mechanical properties can be characterized by the following values:

hardness HB 190 breaking strength in tension R m ⁽¹⁹ ° ^C) 450 MPa yield strength R n 0.2 (15 ° C) 350 MPa Ductility A ₅ (15 ° C) 24% notch toughness ^KCV -40 ° C - 19 3.cm fatigue limit <5 * C (15 ° C) 210 MPa

Industrial applicability

The low temperature ductile iron according to the invention is applicable to castings of machine parts of vehicles, tractors, rail vehicles and refrigeration components.

Claims (1)

PATENT CLAIMS Low temperature ductile iron with basic chemical composition 3.0 to 4.0% carbon, 1.5 to 2.5% silicon, 0.1 to 0.5% manganese, up to 0.070% phosphorus, up to 0.030 % sulfur, ς-lops <> 0,080¾ magnesium containing at least one of the alloys in an amount 0.1 to 2.5% nickel, 0.03 to 0.50% vanadium, 0.10 to 1.0% copper, 0.01 to 0.15 ¾ aluminum, fáyy ^ 2 0.1% element $ t rare earths, all in mass amounts, the rest of the iron, marked by dzle. it contains niobium in an amount by weight of 0.03 to 0.90 ¾ _f k-ether in combination with all alloys containing 0.04 and 4.0%.