DE1949380C3 - Process for the treatment of cast iron melts for the purpose of spheroidal graphite formation - Google Patents

Description

10 <

Mg
B.

100 mechanical properties ferritic, pearlitic or to make ferritic-pearlitic.

In the first stage of treatment is the melt often pure or alloyed magnesium, e.g. B. an Fe-Si-Mg alloy added as spheroidal graphite former, while subsequently seeding with silicon, e.g. B. takes place in the form of an Fe-Si alloy.

Accordingly, a method of the type mentioned is known (GB-PS 1117 467), according to

Magnesium and boron contents of the relationship in which an alloy consisting essentially of iron, cerium or mischmetal, magnesium and boron is used as the spheroidal graphite former, and in particular an iron-silicon alloy for inoculation. Further so-called doping elements are also sufficient, treated and then become known for these alloys or an alloy containing counter-iron and silicon has been subjected to operational tests. For example, when inoculated, characterized in that in addition to cerium and yttrium, rare earths and that to be added nodular forming LE calcium doping elements for the nodular bildengierung next inevitable Production Organization alloys and barium DonereJement for-related impurities of iron, silicon, 20, the inoculants. A known process (US-PS magnesium and boron and which is to be used 25 27 037) provides, after the melting of the

treated cast iron first an additive from the group lithium, calcium, barium, magnesium, Strontium and cadmium all or in combination with substances such as iron, copper, zinc and manganese to use and add a certain amount of a graphitizing agent for inoculation.

It is also a one-step approach to treatment of cast iron melts for the purpose of spherical

2. The method according to claim 1, characterized by ₃₀ known graphite formation (ÜE-PS 1 75 911), iiemäß that shows that the contents of magnesium and boron are the only added alloy at least three or silicon and barium in the elements to be added Group boron, potassium, sodium, lithium,

Contains calcium, magnesium, barium, cerium, etc. The known processes lead to castings, which still contain unwanted carbides in the unannealed cast state and their ferritization in the Matrix not yet reached the optimal level. The heat treatment time required is relative high.

The invention is based on the object of modifying the method mentioned at the beginning so that the treated cast iron is largely free of carbides in the unannealed cast state, an improved one Ferritization effect on the matrix is achieved and the duration of the heat treatment required can be shortened significantly.

According to the invention, this object is achieved in that the nodular graphite-forming Alloy in addition to unavoidable manufacturing-related

end ternary inoculant silicon and barium in those expressed in percent by weight Contains quantities that the relationship

3 ■: - * - <60 Ba

correspond.

both alloys the relationships

Mg

15th

^ - <30

or.

suffice.

Ba

<12

The invention relates to a method for treating molten cast iron for the purpose of spheroidal graphite formation in two successive stages,

the melt initially with a ball 50th impurities of iron, silicon, "Magne-

graphite former in the form of an alloy containing iron, boron and magnesium, in percent by weight expressed levels of magnesium and boron of the relationship

10 <

Mg
B.

sium and boron and the one to be used ternary inoculating alloy contains silicon and barium in such amounts expressed in percentages by weight, that of the relationship

100

Ba

60

correspond.

suffice, treated and then with an iron ,,. ,,,. ,,

and silicon-containing alloy is seeded. 6c ^Vorzu 8 ^sweise g ^enu g ^{s doing dle Genalte to}

It is common practice to cast a molten cast iron shortly before casting a spheroidal graphitization treatment and then subjected to an inoculation treatment to form a structure with spheroidal graphite to obtain.

The castings then undergo a heat treatment with the aim of dissolving the carbides and the matrix of the cast iron depending on the desired sium and boron or silicon and barium in the the two alloys to be added to the relationships

Mg

15th

or.

Si
Ba

<30

12th

As will be explained in more detail with reference to the exemplary embodiments, the inventive combined addition of the two alloys in two successive stages in the non-annealed As-cast state largely from carbides frek castings, an almost complete degree of ferritization of the matrix and a significant reduction in the cost of the heat treatment required for this.

Examples

Examples 1, 2 and 3 do not correspond to the invention and on the one hand describe the result according to the prior art (Example 1) and on the other hand the result when using only one of the Elements boron and barium.

Examples 4, 5 and 6 correspond to the invention; the spheroidal graphite alloy contains boron, and the inoculant contains barium.

Example 7 shows the superiority of the method using barium according to the invention over the known methods according to which the inoculant contains calcium.

example 1

2.250 kg of a spheroidal graphite-forming alloy made of Fl- - Si - · Mg (Mg ------ 9.1%) are introduced into a pan with 75 kg of cast iron melt at 1510 ° C.

After lifting the immersion device again, it is inoculated with 0.375 kg of Fc-Si (Si -75 ° ,,).

The metal is poured 9 minutes after this treatment.

Example 2

The procedure is as above, but using 2.250 kg Fe-Si - Mg - B (Mg = 9.1%; B = 0.48%) and then 0.375 kg Fe-Si (Si = 75%).

Example 3

One works as above, but uses

ίο 2.250 kg Fe-Si —Mg (Mg = 9.25%) and thereafter 0.420 kg Fe-Si-Ba (Si = 59.5%; Ba = 9.8%).

Example 4

The procedure is as in Example 1, but using 2.250 ke in accordance with the invention Fe - Si - Mg - B (Mg = 9.1%; B - ^ 0.48%) and then 0.420 kg Fe-Si-Ba (Si = 59.5%; Ba -9.8%).

The following table 1. which shows the composition of iron after casting and the properties of thin castings before any heat treatment summarizes, and the F i g. 1 to 4 clearly show that only the inventive method castings results that are almost free of carbides, have a substantial proportion of ferrite in the matrix and are high Have elongation and breaking strength values.

These results could also be obtained by following the procedures of Example 1, 2, or 3, for which it would be however, a time-consuming heat treatment is required to dissolve the carbides and distribute the carbon to change.

table

example 1 Example 2 Example i Example ·> without B with B without B invention without ba without ba with Ba Chemical composition according to sphere graphite formation and vaccination in the invention moderate procedures (° / ₀ ) C. 3.60 3.58 3.65 3.55 Si 2.60 2.65 2.54 2.70 Mn 0.05 0.06 0.05 0.08 P. 0.023 0.021 0.025 0.026 S. 0.007 0.007 0.009 0.010 Mg 0.040 0.046 0.038 0.048 Properties of castings from heat treatment Ferrite in the matrix Ferrite perut Ferrite perut 90% ferrite 90% ferrite Number of balls per mm ² 80 i 10 70 L 10 85 i 15 105 ± 10 Carbides present present little very little Tensile strength, kg / mm ² *) 43.4 44.2 48 51.8 Strain, %*) 6.7 9.4 13.4 18.9 Yield strength, kg / mm ² *) 25.5 26.3 22.5 28.2

*) Standard test samples.

Table I and the figures further show that the method according to the invention leads to a better Magnesium utilization (calculated according to the residual magnesium content of the cast iron) leads to an increase the number of graphite spheres and a greater regularity in their size.

Example 5

200 kg of cast iron are converted to 5 kg of Fe - Si - Mg - B (Mg = 9.1% and B = - 0.48%) at 1500 C and 0.960 kg Fe - Si - Ba (Si - = 60%; Ba = 9.8%) after one currently used in foundries

and »sandwich process called cast. A second partial inoculation is then carried out using 0.300 kg of the same Fe-Si-Ba solution. The cast after 12 minutes of cast iron biding is kugelgraphitisch, and metallographic examination shows a 90 ⁰ / "ig ferritic microstructure. The composition is as follows _{:, 6} o ρ

Ö'oi9 ^{0 /} 'p

, _'78 ";'" n- '

OOP "p

0 05 ^ "Mp

The mechanical properties measured on test objects in the unannealed as-cast state are:

"
Tensile strength 50 kg, .mm-

Elongation at break 17, ₀

η · · 1C

A ton of cast sea salt of 1480 "C will be according to the "sandwich" method with 14 kg Fe - Si - Mg - B of the composition

45.6% Si,
8.1% Mg.
0.45% B and
0 07 ° approx

treated. 0.2 kg of mixed silicon metal is then introduced with the immersion device and then inoculated by means of 12 kg Fe-Si-Ba (Si -60.1%; Ba = 9.4%). A completely nodular, strongly ferritic cast iron is obtained, the properties of which are in the unannealed The as-cast condition is as follows:

Yield strength 38 kg / mm ²

Tensile strength 52.3 kg / mm =

Elongation at break 13.2%

^Beis P ' ^cI7

150 kg of the same cast iron melt are added split two equal parts A and B of 75 kg each, both of which are kept at 1520 C. You wcrdci both according to the »sandwich method using 2.250 kj Fe --Si --- Mg B of the composition with

47 4 ⁿ Si
7 * 95 "" Mc and

treated. The following quantities are then introduced with the immersion device:

ίο In the subset A according to the invention 0.420 kg Fe-Si-Ba (Si = 61 ° ": Ba - 9.6 °") One receives a cast iron of the same quality ^{as that according to Be) s} P ^lel4 ·

In subset B 0.420 kg of a known Fe-Si-Ca alloy (Si 62.4%; Ca - 10.3 "). In subset A, the exposure of the parts obtained with subset B is good, but it shows sii _{CJNE leichti} tendency to shrinkage; further illustrates setting _the cast iron B, as shown in Table II, meh:

Carbides and less ferrite.

Table II

Subset A part according to the amount: 1 lInvention "" Composition of the casting iron according to the spheroidal graphite 30 educational and vaccination treatments lung C. 3.67 3.61 Si 2.07 2.75 35 ρ 0.02 0.02 S. 0.006 0.008 Mg 0.04S 0.044 Properties of cast iron ₄₀ before heat treatment Ferrite in the matrix 90% 75% Presence of carbides <1% about

1 sheet of drawings

Claims (1)

Patent claims: 1. Process for the treatment of molten cast iron for the purpose of spheroidal graphite formation in two successive stages Stages, whereby the melt is first treated with a spheroidal graphite former in the form of an alloy containing iron, boron and magnesium, their expressed in percent by weight