DE1608239C2 - Use of a cast iron alloy as a material for castings with lamellar graphite formation, high toughness and high thermal conductivity in the as-cast state - Google Patents

Description

The subject of previously filed patent 1,250,643 is the use of a cast iron alloy as a material for castings with lamellar graphite, high toughness and high thermal conductivity in As-cast state. The patent relates in particular to the use of a cast iron alloy consisting of 2.5 to 3.8 carbon, below 0.08%, preferably below 0.04% phosphorus, below 0.08%, preferably below 0.04% chromium, below 3 ml / 100 g hydrogen, below 0.3%, preferably below 0.15% manganese, below 0.03% Sulfur, the remainder iron, with the lowest levels of interfering elements such as arsenic, boron, antimony, lead, tellurium, Selenium, as well as with a silicon content that is around 0.8% lower than in castings of the same wall thickness made of conventional cast iron or that is reduced by up to half of this conventional silicon content, with the manganese-sulfur ratio is set to be greater than 5: 1, preferably greater than 7: 1, as the material for castings with a pearlitic structure and lamellar graphite formation of high toughness (measured according to ISO proposal 1197), which roughly doubles the tensile strength of conventional cast iron is, and high thermal conductivity, which is comparable to that of a conventional cast iron alloy Graphite content is increased by about a third in the as-cast state.

It has now been found that for the same purpose as a material for castings with pearlitic Structure and lamellar graphite formation, high toughness and high thermal conductivity in the Cast state, also those cast iron alloys are suitable, which with the same high purity requirement for the Base mass have a higher manganese content. Accordingly, the invention is in use a cast iron alloy, consisting of 2.5 to 3.8% carbon, below 0.08%, preferably below 0.04% Phosphorus, below 0.08%, preferably below 0.04% Chromium, below 3 ml / 100 g hydrogen, below 0.03% Sulfur, the remainder iron, with the lowest levels

ίο interfering elements such as arsenic, boron, antimony, lead, tellurium, Selenium, as well as with a silicon content that is around 0.8% lower than in castings of the same wall thickness made of common cast iron or which is reduced by up to half of this common silicon content, wherein the manganese-sulfur ratio is set to be greater than 5: 1, preferably greater than 7: 1, than Material for castings with a pearlitic structure and lamellar graphite formation of high toughness (measured according to ISO proposal 1197), which is about is doubled; and high thermal conductivity compared to that of a conventional cast iron alloy with comparable graphite content is increased by about a third, in the as-cast state, and it is characterized by that the manganese content is greater than 0.3% and up to 2.25%, preferably up to 1.75% Manga ι.

It was also found that too low sulfur contents of the range to be used according to the application Cast iron alloy increases the toughness when the manganese content is kept constant.

The cast iron alloy to be used according to the invention has the good casting properties of normal cast iron and enables casting of castings with lamellar graphite formation with high values for toughness and elongation. Leave it Furthermore, workpieces of high thermal conductivity with increased compared to cast parts made of normal cast iron Establish toughness.

Toughness is understood here to mean:

Z =

log α μ -j- 0.7
log σ β

In this equation au denotes the modulus of impact, measured in kp · cm / cm ^3, and σ β denotes the tensile strength, measured in kp / mm ² .
The silicon contents in the casting made from the cast iron alloy to be used according to the invention are remarkably low and are greatly reduced compared to castings of the same wall thickness made from conventional normal cast iron. In contrast, up to a value of 1.6% silicon in the casting made of normal gray cast iron, a casting made of tough gray cast iron with a silicon value lower by at least half is cast.

Is z. B. a casting made of normal gray cast iron with a cast iron alloy with 1.5% silicon, in contrast, when casting the same casting from tough gray cast iron, half is at most this value, d. H. at most 0.75% silicon in the cast iron alloy is required.

Castings made of a cast iron alloy with a silicon content of above 1.6% are tough Cast iron with a silicon value lower by at least 0.8% absolute. For example a casting made of conventional gray cast iron with 2.5% SiIi-

cium is poured off, the same casting made of tough gray cast iron with a maximum of 1.7% silicon is poured off.

How high the absolute silicon content of the casting made of normal gray cast iron is set in the individual case must be, is familiar to the relevant person skilled in the art. It should be noted that this content as is known, it also depends on the wall thickness of the casting. This results, as in the individual case the silicon content must be adjusted in the case of tough gray cast iron.

An inoculation treatment of the melt, known per se for gray cast iron, is expedient according to the invention / u made using cast iron alloy to bring about the gray solidification. Here is only to note that by the inoculation alloy, the is generally based on silicon, a certain silicon content in the cast iron alloy melt is introduced. This silicon value, which gets into the melt via the impurity, is for to take into account the final silicon value, and there is a correspondingly lower silicon content Provide base melt. In particular, these ratios are the case with extremely small silicon values Cast iron melt to take into account.

With regard to the possibilities of alloying the cast iron alloy to be used according to the invention The statements made in DT-PS 12 50 643 apply accordingly. That is, the alloying element is allowed have no or only a very weak carbide stabilizing effect, it should be similar to iron 1.87 Å Have lattice constant in order to largely avoid a distortion of the l-'errite lattice, and finally the alloying element should not form a bond with carbon. Through these demands There are practically only elements such as nickel (3.52 Å), molybdenum (3.15 Å), copper (3.62 Å) and nobalt (251 Ä) into consideration.

The cast iron alloy to be used according to the invention can be produced by metallurgical processes known per se, as they are also in the I) T-PS 1 250 643 is mentioned.

The invention is explained in more detail with reference to the following examples.

example 1

A cast iron alloy of the following final analysis was found after inoculating with a commercially available Inoculant of the composition

60 to 65% Si,
5 to 7% Mn,
5 to 7% Zr,

Remainder Fe

cast into 30 mm test rods and from these rods samples for tensile strength (short proportional rod according to DIN 50 125 B) and the S: Hagmodul (according to ISO suggestion no. 1197).

% c % Si ° / "Mn % P % s % Cr 3.03 1.31 see table 1 0.022 0.012 0.01

Table I.

° / Mn kp / mm ² "M 7th relationship / 0 ^lvl 'i 38.1 cmkp / Mn: S 40.5 cm ³ 0.31 39.8 18.3 1.24 25: 1 0.59 41.0 17.5 1.21 49: 1 0.98 41.5 15.9 1.19 81: 1 1.72 14.8 1.16 143: 1 2.22 13.0 1.12 185: 1

Table I above illustrates the toughness values of tough gray cast iron, in terms of terms by the toughness index Z with increasing Mn contents and otherwise unchanged analysis.

In order to achieve tensile strength values of 38 to 40 kp / mm ² with normal gray cast iron, test bars made of a cast iron alloy of the following composition would have to be cast on:

% c % Si % Mn % P % s % Cr 2.92 2.12 0.72 0.110 0.095 0.2

In the case of a casting made from a cast iron alloy of this composition, however, the modulus of impact is only 8.5 cmkp / cm ³ . The tensile strength of 38 kp / mm ² results in a value for the toughness index Z of 1.03.

Example 2

A cast alloy of the following final analysis was inoculated with a commercially available inoculant des Example 1 poured into 30 mm test rods and from these rods samples for the tensile strength and the Impact module worked out according to Example 1.

45

% c % Si % Mn % P % s % Cr 2.95 0.96 0.32 0.032 see table !! 0.01

Tabel!!

% Mn 55 0.32 % s (kp / inm ^a ) "Af
(kpem / Z relationship
Mn: S 0.32 cm ³ ) 0.32 39.0 0.32 0.058 40.0 13.5 1.15 5.5: 1 0.043 40.1 16.0 1.190 7.4: 1 0.020 38.5 18.0 1.220 16: 1 0.009 18.5 1,240 35.5: 1

60

From the values in Table II above, the increase in toughness at constant Mn content is but to be taken from decreasing S-content.

Claims (2)

Patent claims: 1. Use of a cast iron alloy, consisting of 2.5 to 3.8% carbon, less than 0.08%, preferably below 0.04% phosphorus, below 0.08%, preferably below 0.04% chromium, below 3 ml / 100 g Hydrogen, below 0.03% sulfur, the remainder iron, with the lowest levels of interfering elements such as arsenic, Boron, antimony, lead, tellurium, selenium, as well as with a silicon content that is about 0.8% less than for castings of the same wall thickness made of conventional cast iron or up to half of this usual Silicon content is reduced, the manganese-sulfur ratio being greater than 5: 1, preferably greater than 7: 1, is set, as a material for castings with a pearlitic structure and lamellar Graphite formation of high toughness (measured according to ISO proposal 1197), which compared to that of conventional cast iron of comparable tensile strength is roughly doubled and has high thermal conductivity, compared to that of a conventional cast iron alloy with a comparable graphite content by about one Third is increased, in the as-cast state, thereby characterized in that the manganese content is greater than 0.3% and up to 2.25%, preferably up to 1.75% manganese. 2. Use of a cast iron alloy according to claim 1, wherein to increase the strength other alloy elements such as nickel, molybdenum, copper or cobalt, the cast iron alloy are added for the purpose mentioned in claim 1.