Compacting of gas atomized metal powder to a part

Abstract

A process for making full dense components of a carbon-containing steel, comprises the steps of: a) making a powder of the carbon-containing steel by gas atomization wherein the carbon content is low, less than 0.15 wt %, b) agglomerating the powder from step a) with at least one hydrocolloid and elemental carbon, c) compacting the agglomerated powder from step b) to a density of at least 80% of theoretical density, with the proviso that the compacted agglomerated powder still is porous allowing transport of gas to and from its interior, and d) sintering the compacted powder to a density of more than 98% of theoretical density, preferably more than 99% of theoretical density, wherein a gas comprising carbon is added during sintering and finally subjecting the component to HVC. Advantages include that it is possible to manufacture a dense component of powders which otherwise are difficult to compact.

1 . A process for making full dense components with a density of more than 98%, of the theoretical density of a material selected from the group consisting of a carbon-containing steel and a carbon containing alloy, said process comprising the steps of:
 a) making a powder of the carbon-containing steel by gas atomization, wherein the carbon content is less than 0.15 wt %,   b) agglomerating the powder from step a) with at least one hydrocolloid, wherein carbon in elemental form is added in the form of a colloid of insoluble particles comprising carbon suspended throughout a liquid, during the agglomeration,   c) compacting the agglomerated powder from step b) in a first compacting step to a density of at least 80% of theoretical density, with the proviso that the compacted agglomerated powder still is porous allowing transport of gas to and from its interior,   d) further compacting the compacted agglomerated powder from step c) to a density of more than 98% of theoretical density using at least sintering followed by HVC (high velocity compacting) with a ram speed exceeding 5 m/s, wherein a gas comprising carbon is added during sintering.   
     
     
         2 . The process according to  claim 1 , wherein the carbon in elemental form added during the agglomeration in step b) is added in an amount corresponding to the difference between the carbon content in the carbon-containing steel in step a) and the desired carbon content of the finished steel after step d). 
     
     
         3 . The process according to  claim 1 , wherein the carbon in elemental form in step b) is added in the form of graphite. 
     
     
         4 . The process according to  claim 1 , wherein the carbon in elemental form in step b) is added in the form of a carbon powder. 
     
     
         5 . The process according to  claim 1 , wherein the carbon in elemental form in step b) is added in the form of particles with an average size in the interval 0.1-10 μm. 
     
     
         6 . The process according to  claim 1 , wherein the carbon-containing steel prior to gas atomization in step a) is treated so that the carbon content is reduced to a carbon content less than 0.10 wt %. 
     
     
         7 . The process according to  claim 1 , wherein the carbon-containing steel prior to gas atomization in step a) is treated so that the carbon content is reduced to a carbon content less than 0.050 wt %. 
     
     
         8 . The process according to  claim 1 , wherein the carbon-containing steel prior to gas atomization in step a) is treated with argon oxygen decarburization. 
     
     
         9 . The process according to  claim 1 , wherein the carbon-containing steel prior to gas atomization in step a) is treated in a vacuum furnace. 
     
     
         10 . The process according to  claim 1 , wherein the carbon-containing steel is hardenable after step c). 
     
     
         11 . The process according to  claim 1 , wherein the gas comprising carbon is methane. 
     
     
         12 . A full dense component manufactured according to  claim 1 , with a density of more than 98% of the theoretical density, wherein the component comprises a carbon-containing steel. 
     
     
         13 . The full dense component according to  claim 12 , wherein the density is more than 99% of the theoretical density. 
     
     
         14 . The process according to  claim 1 , wherein in step d), the compacted agglomerated powder from step d) is further compacted to a density of more than 99% of theoretical density.