CH655950A5 - WORKPIECE IN CAST IRON WITH BALL GRAPHITE. - Google Patents

Description

The invention relates to a workpiece with wall thicknesses greater than 10 mm made of spheroidal graphite cast iron with a maximum of 1.0 mass% silicon (Si), preferably 0.2-0.6% silicon.

. Cast iron with a Si content of at most 1% by mass - all percentages are to be understood as% by mass - is known (CH-PS 508 729). To remove carbon as graphite during the solidification process, this cast iron contains 1-3% aluminum (AI), which partially replaces the silicon as a graphitizing element. Silicon and aluminum are known to have an embrittling effect in the material structure. In order to obtain the highest possible toughness, it is therefore necessary to keep the Si and Al contents in the cast iron as low as possible.

The invention is therefore based on the object of creating a cast iron with spheroidal graphite, the Si contents of which are clearly below 1%, without another alloying element for graphitization - in particular, therefore, no AI - being added to it.

According to the invention, this object is achieved in that it is free of aluminum (AI) replacing Si as a graphitization element, that its structure is free of primary carbides, and that at least one of the following basic structures is ferrite, pearlite, bainite or martensite; a

The process for its production is characterized in that, after the Mg treatment necessary for the formation of spheroidal graphite, an inoculant is added to the melt shortly before solidification, by which 5 0.1-0.2% Si is added to the melt, and after that Solidification to produce the above-mentioned structure, a heat treatment is carried out.

“Shortly before solidification” means that the vaccination is carried out in the mold, in the pouring stream or in the pouring well. "> This relatively late vaccination means that graphite precipitation is achieved even without the usual amounts of graphitizing elements. Si is advantageously added by the melt containing 0.15 to 0.3% ferro-silicon, 80% Si (FeSi-80) The 15 Mg treatment of the melt necessary for spheroidal graphite formation can be carried out with pure Mg, Ni-MG, Cu-Mg or a high-percentage FeSi-Mg.

In the as-cast state, the workpiece is generally in a pearlitic structure without primary carbides. The 20 required structures are achieved by heat treatments as are known per se for the production of these structures. The workpiece is e.g. from the as-cast state in the austenite range - i.e. to 700-950 ° C - heated, held in this area for 0.25-10 hours and then cooled down to the speed required for the desired structure. A ferritic structure can be obtained by slow furnace cooling down to a maximum of 20 ° C / h, while perlite is formed when it is cooled in air. Bainite is obtained by isothermal conversion in a salt, oil or lead bath between 30 250 and 450 ° C.

An additional object is furthermore to create a workpiece from the aforementioned cast iron with a low Si content, in which a martensite tempering structure 35 is obtained by tempering at different tempering temperatures, without secondary graphite being precipitated . This can be done by quenching the workpiece from the austenite area in air, oil or water to produce a martensite tempering structure with certain strength and ductility and then 40, depending on the desired strength and ductility, at a temperature between 400 and 720 ° C is started.

A certain combination of strength and ductility can be achieved by a suitable choice of tempering temperatures.

The invention is explained in more detail below on the basis of an exemplary embodiment in which a workpiece is produced with a pure martensite tempering structure.

In an induction furnace, which is provided with an acid or basi-50 see lining, equal amounts of low-siliconized pig iron and unalloyed steel scrap, each with a maximum Si content of 0.2%

with the addition of a carburizing agent, e.g. Graphite to achieve the desired carbon content in the white

55 ter final composition of the melt given below

- melted and heated to a temperature of 1550 ° C.

At this temperature, the Mg treatment of the melt necessary for spheroidal graphite formation is carried out by adding 0.5% 60 of the additional alloy FeSi-Mg-40 (containing about 40% Mg) by dipping the melt.

Next, the melt treated with Mg is poured into the casting in a sand mold, whereby according to the invention, a vaccination 65 takes place during the casting process; 0.2% FeSi-80, which contains 80%, serves as inoculant.

A sample is taken from the cast melt for analysis purposes, with the aid of which the following final composition of the melt is determined:

3rd

655 950

Chromium 3.40-3.70 mass%

Silicon 0.40-0.60% by mass

Manganese 0.10-0.20 mass%

Magnesium 0.04-0.06 mass%

Pmax 0.08

Smax 0.01

After cooling in the as-cast state, the workpiece has a pearlitic structure that contains no primary carbides.

As a heat treatment, the heating is first carried out to 900 ° C in the austenite area, which comprises approximately 720 to 1145 ° C. The workpiece is held at the specified temperature for 0.25 h, although holding times of 0.25-10 h are generally permissible. From the austenite area, the workpiece is quenched in oil, creating a martensite structure.

A tempering treatment is then carried out at temperatures of 400 to 700 ° C - the tempering temperature is selected in a known manner in accordance with the desired mechanical properties, in particular the strength s and plasticity - and cooling in the oven or in air. The structure of the workpiece subjected to the heat treatment described is a purely martensitic tempering structure, which is free of secondary graphite deposits, its mechanical properties depending on the tempering temperatures, resulting in:

0.2% proof stress

Rp0.2

N / mm2

300-900

tensile strenght

Rm

N / mm2

500-1200

Elongation at break

As

%

12-2

Brinell hardness

HB

200-350

Impact work

Av

J

12-2

G

Claims (5)

655 950 1. Workpiece with wall thicknesses greater than 10 mm made of spheroidal graphite cast iron with a maximum of 1.0% by mass of silicon (Si), characterized in that it is free of aluminum (AI), which replaces Si as a graphitization element, that its structure free of primary carbides and that at least one of the following basic structures ferrite, pearlite, bainite or martensite is present. 2. Workpiece according to claim 1, characterized, apart from impurities, by Vanadium (V) Chromium (Cr) Manganese (Mn) Nickel (Ni) Copper (Cu) Molybdenum (Mo) 0-0.5 mass% 0-0.5 mass% 0-1.0 mass% 0-10 mass% 0-3.0 mass% 0-1.0 mass% as an alloying element. 2nd PATENT CLAIMS 3. A process for the production of a workpiece according to claim 1, characterized in that an inoculant is added to the melt after the Mg treatment necessary for spheroidal graphite formation shortly before solidification, through which the melt 0.1-0.2 mass% of Si is added, and that after solidification to produce the above-mentioned structure, a heat treatment is carried out. 4. The method according to claim 3, characterized in that the workpiece is heated from the as-cast state to the austenite region, held in this region for 0.25-10 hours (h) and then cooled at a speed adapted to the desired structure. 5. The method according to claim 4, characterized in that the workpiece is quenched from the austenite region in air, oil or water and then, depending on the desired strength and ductility, at a temperature between to produce a martensite tempering structure without the elimination of secondary graphite 400 and 720 ° C is left on.