Meltless preparation of martensitic steel articles having thermophysically melt incompatible alloying elements

Abstract

An article of iron base metal base metal alloyed with an alloying element is prepared by mixing a chemically reducible nonmetallic base-metal precursor compound of the iron base metal and a chemically reducible nonmetallic alloying-element precursor compound of an alloying element to form a compound mixture. The alloying element is preferably thermophysically melt incompatible with the iron base metal. The method further includes chemically reducing the compound mixture to a metallic alloy, without melting the metallic alloy, and thereafter consolidating the metallic alloy to produce a martensitic-composition consolidated metallic article, without melting the metallic alloy and without melting the consolidated metallic article.

Description

[0001] This invention relates to the preparation of metallic-alloy articles, specifically martensitic iron-base alloy articles, without melting of the metallic alloy. BACKGROUND OF THE INVENTION [0002] Martensitic steels having a martensitic microstructure are one important class of the ferritic steels. The martensitic steels have wide application in the aircraft propulsion industry and are also used in other industries such as the automotive industry. Metallic articles made of martensitic steels are fabricated by any of a number of techniques, as may be appropriate for the nature of the metal and the article. In one common approach, metal-containing ores are refined to produce molten metal, which is thereafter cast. Ore refinement may take place separately for each of the major alloying elements, or in combination for more than one element. Elements and combinations of elements may take many intermediate forms before being melted to form the final alloy. The metal is refined as nec...

AI Technical Summary

Benefits of technology

[0021] Another such thermophysical melt incompatibility occurs due to elemental segregation during solidification, which causes an unacceptable distribution of the alloying element in the solidified ingot. The degree of segregation may be reduced in melted-and-cast product by lowering the melting power, reducing the ingot diameter, using long post-casting homogenization heat treatments, and the like, but these prior approaches increase cost and limit the type of product that may be produced. In the present process, this type of segregation is avoided because the alloy is never melted and solidified. Examples of such segregating alloying elements for iron-base alloys include arsenic, beryllium, antimony, scandium, and titanium.

[0034] The present approach is advantageously applied to make martensitic steel articles. Contamination and other impurity elements that are almost unavoidable in conventional casting practice, and which may have major adverse effects on the properties of the material, may be eliminated with the present approach. The structure is more uniform and homogeneous than may be produced by conventional casting and working techniques. For the material produced by the present approach that replaces conventionally cast material, there is a reduced incidence of irregularities such as those produced by segregation and inclusions (e.g., white spots, freckles, eutectic nodules, and banding) during conventional casting operations, and those associated with remelted / recycled material. The cost is also reduced due to the elimination of processing steps associated with casting. The reduction in the cost of the final product achieved by the present approach also makes the martensitic steels more economical. Properties are also improved. Material made by the present approach that is a replacement for conventional wrought articles realizes these same benefits. Additionally, large-sized specialty articles, whose size is limited only by compaction capability, may be made while avoiding microsegregation and macrosegregation. Reduced thermomechanical work is required to produce fine microstructures, and there is reduced loading on the mechanical working equipment. More complex processing may be used, because of the initially fine microstructure.

Problems solved by technology

The melting operation, which often involves multiple melting and solidification steps, is costly and imposes some fundamental limitations on the alloy content and hence the mechanical properties of the final martensitic-composition articles.

The method circumvents problems, which cannot be avoided in melting practice or are circumvented only with great difficulty and expense.

The present approach permits a uniform alloy to be prepared without subjecting the constituents to the circumstance, which leads to the incompatibility, specifically the melting process.

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