Iron-graphite composite powders and sintered articles produced therefrom

A process for preparing an iron-graphite composite powder, wherein said powder is comprised of iron-graphite composite powder particles comprising about 2% to about 4.5% by weight carbon and about 0.05% to about 2.5% by weight silicon and having a microstructure comprised of temper carbon clusters embedded in a ferrous matrix, wherein at least 30% of the carbon clusters are fully embedded within the ferrous matrix, said process comprising the steps of:

• (a) atomizing a liquid iron to form an atomized iron powder;
• (b) heating the atomized iron powder to a temperature of greater than about 900° C.;
• and
• (c) cooling the powder from a temperature of greater than about 900° C. to a temperature greater than about 600° C.,
• wherein the powder is heated from a temperature of about 650° C. to greater than about 900° C. at a rate sufficient to permit nucleation of the carbon clusters in the core of the powder particles and wherein the powder is cooled at a rate no faster than about 10° C./minute.

An iron-graphite composite powder comprising composite powder particles comprised of about 2% to about 4.5% by weight carbon and about 0.05% to about 2.5% by weight silicon and having a microstructure comprised of temper carbon clusters embedded in a ferrous matrix, wherein at least 30% of the carbon clusters are fully embedded within the ferrous matrix, wherein said powder is prepared by the process comprising the steps of:

• (a) atomizing a carbon- and silicon-containing liquid iron to form an atomized iron powder;
• (b) heating the atomized iron powder to a temperature of greater than about 900° C.;
• and
• (c) cooling the powder from a temperature of greater than about 900° C. to a temperature of not less than about 700° C.;
• wherein the powder is heated to a temperature greater than about 900° C. at a rate sufficient to permit nucleation of the carbon clusters in the core of the powder particles and wherein the powder is cooled at a rate no faster than about 10° C./minute.

A process for preparing an iron-graphite composite powder comprising powder particles comprising about 3.2% to about 3.7% by weight carbon and about 0.8% to about 1.3% by weight silicon and having a microstructure comprised of temper carbon clusters embedded in a ferrous matrix, wherein at least 30% of the carbon clusters are fully embedded within the ferrous matrix, said process comprising the steps of:

• (a) atomizing a liquid iron to form an atomized iron powder;
• (b) heating the atomized iron powder to a temperature of greater than about 1000° C.;
• and
• (c) cooling the powder from a temperature of greater than about 1000° C. to a temperature greater than about 700° C.;
• wherein the powder is heated from a temperature of about 650° C. to greater than about 1000° C. at a rate of greater than about 30° C./min, maintained at a temperature between about 850° C. and greater than about 1000° C. or at the temperature greater than about 1000° C. for about 5 minutes to about 16 hours and the powder is cooled at a rate no faster than about 10° C./min.

A process of preparing an iron-graphite composite powder, comprising powder particles comprising about 3.2% to about 3.7% by weight carbon and about 0.8% to about 1.3% by weight silicon and having a microstructure comprised of temper carbon clusters embedded in a ferrous matrix, wherein at least 30% of the carbon clusters are fully embedded within the ferrous matrix, said process comprising the steps of:

• (a) atomizing a liquid iron to form an atomized iron powder;
• (b) heating the atomized iron powder to a temperature of greater than about 1000° C.;
• and
• (c) cooling the powder from a temperature of greater than about 1000° C. to a temperature not less than about 700° C.;
• wherein the cooling step comprises a combination of cooling and maintaining steps selected from:
• (i) cooling the powder from a temperature of greater than about 1000° C. to a temperature not less than about 700° C. and maintaining the powder at the temperature of not less than about 700° C.;
• (ii) optionally cooling the powder from the temperature not less than about 700° C. to another temperature not less than about 700° C. and maintaining the powder at said temperature;
• and
• (iii) optionally repeating step (ii);
• wherein in the powder is heated from a temperature of about 650° C. to greater than about 1000° C. at a rate of greater than about 30° C./min, maintained at a temperature greater than about 1000° C. for about 5 minutes to about 16 hours and cooled at a rate no faster than about 10° C./min.

An iron-graphite composite powder comprising composite powder particles comprising about 3.2% to about 3.7% by weight carbon and about 0.8% to about 1.3% by weight silicon and having a microstructure comprised of temper carbon clusters embedded in a ferrous matrix, wherein at least 30% of the carbon clusters are fully embedded within the ferrous matrix, prepared by the process comprising the steps of:

• (a) atomizing a carbon- and silicon-containing liquid iron to form an atomized iron powder;
• (b) heating the atomized iron powder to a temperature of greater than about 1000° C.;
• and
• (c) cooling the powder from a temperature of greater than about 1000° C. to a temperature of not less than about 700° C.;
• wherein in the powder is heated from a temperature of about 650° C. to greater than about 1000° C. at a rate of greater than about 30° C./min., maintained at a temperature greater than about 1000° C. for about 5 minutes to about 16 hours then cooled at a rate no faster than about 10° C./min.