DE1125462B - Process for the heat treatment of solidified cast iron in the production of very tough, e.g. pearlitic malleable cast iron - Google Patents

Description

Process for the heat treatment of solidified cast iron in the production of very tough, e.g. B. pearlitic malleable cast iron Addition to patent 1 005 541 The main patent 1005 541 relates to a process for the heat treatment of white solidified cast iron in the production of pearlitic malleable cast iron, in which to produce the subsequently to be made in the furnace and then cast in sand molds or metal molds Melt the cupola is applicable, with the wall thickness and shape of the castings adapted, completely white solidification securing ratio values of Mn: C and Mn: Si, z. B. the compositions (in 0/0): carbon = 2.35; Silicon = 1.15; Manganese = 0.40; Phosphorus = 0.10; Sulfur = 0.12.

The process according to the main patent is characterized by the following, measures to be taken one after the other: 1. The white solidified castings are at a temperature only slightly above the eutectoid transformation, e.g. B. at 810 ° C, subjected to a solution heat treatment, then by brief, for example 1 minute immersion in a liquid medium, such as a salt bath of minor above Ar ", e.g. 180 ° C, quenched temperature and then on the temperature of the surrounding air cooled; 2. then the castings by, if necessary, gradually heating to a temperature dependent on the casting composition, however, always tempered temperatures above 400 ° C and not higher than approx. 500 ° C, z. B. Chill casting 3 hours at 500 ° C and sand casting 48 hours at 450 ° C; 3. in conclusion the casting becomes above the temperature of the eutectoid transformation of a graphitization annealing until the iron carbide decomposes, e.g. B. 3 hours at 875 ° C for permanent mold casting and 12 hours at 895 ° C or 3 hours at 900 ° C for sand casting, subjected and then cooled in still air.

The method described in the main patent is opposite to the present one Invention described above. The invention is based on the object, once the To simplify the hardening process according to the main patent; on the other hand the formation of Germination of elemental carbon causing treatment stage (measure 2) after Shorten main patent.

The simplification of the hardening process is achieved according to the invention by either using oil at a temperature of about 100 ° C as the liquid quenching medium while maintaining the gradual hardening, or hardening immediately after the solution heat treatment by immersing the pieces in cold oil is carried out.

It has been shown that this results in smaller workpieces that have a regular shape, the martensite structure can be achieved without hardening cracks can, with no hardenability-promoting additives, such as nickel and chromium, necessary are.

According to the main patent, the duration of the maintenance of the nucleation temperature is provided under the best conditions with 3 to 6 hours.

According to the present invention, the nucleating treatment shortened to periods of time that vary between a few minutes and 3 hours, when the castings are a) thin (less than about 10 mm), b) the martensite hardening Favorable additives, such as Ni (0.4 to 2%), Mn (increased to 1.3%), or graphite nucleation contain promotional additives such as Al (0; 1%). If the mentioned under b) Additives are used and if the casting is thin the degradation will change the duration of the nucleation treatment has nothing to do with the number of nodules in that direction, that the mechanical properties of the material produced are impaired could become.

This applies to both sand mold and gravity die casting Parts.

Claims (2)

PATENT CLAIMS: 1: Modification of the method for heat treatment of white solidified cast iron in the production of very tough, e.g. B. pearlitic Malleable cast iron, with the castings following a solution heat treatment by brief Immersion in a liquid at a temperature slightly above Ar ' and then cooling to the temperature of the surrounding air in stages Subjected to hardening, then tempered and subsequently graphitized annealing with subsequent cooling in air, according to patent 1005 541 for the treatment of castings with a wall thickness of less than 10 mm and without sharp edges Edges and sudden changes in cross-section, characterized in that either while maintaining the gradual hardening here as a liquid quenching medium Oil with a temperature of about 100 ° C is used or the solution heat treatment subsequent hardening by dipping the pieces in cold oil as immediate hardening is carried out. 2. Modification of the process for the heat treatment of white solidified Cast iron in the production of very tough, e.g. B. pearlitic malleable cast iron, the Castings following a solution heat treatment by brief immersion in a Liquid at a temperature slightly above Ar "and thereafter Cooling down to the temperature of the surrounding air gradually, eventually subjected to hardening leading to martensite formation, then for the purpose of nucleation Elemental carbon annealed and then graphitized annealing with subsequent cooling in air, according to patent 1005 541 for the treatment of castings with a wall thickness of less than 10 mm and without sharp edges Edges and sudden changes in cross-section, characterized in that the nucleation treatment for castings following martensite pre-hardening, the elements that promote martensite hardening (such as Ni, Mn) or the formation of nuclei of elemental carbon-promoting elements (like Al) is reduced to periods of time between a few minutes and fluctuate 3 hours. Documents considered: French patent specification No. 1050 927.