Date

May 1986

Document Type

Dissertation

Degree Name

Ph.D.

Department

Dept. of Materials Science and Engineering

Institution

Oregon Graduate Center

Abstract

Chromium and cobalt are strategic materials in the U.S. and both are major constituents in many weld hardfacing alloys. Substitution for these materials or alternatives to their use was a primary direction of this investigation which was conducted in conjunction with the U.S. Bureau of Mines. Minimization of the use of strategic materials was the criteria guiding the development of intermetallic-hardened abrasion resistant weld hardfacing materials. Other criteria were that the new alloy contain a hard intermetallic compound in an FCC matrix, and that these intermetallic compounds be stable at room temperature. A survey of ternary systems was made and the Fe-Mo-Ni system was selected to provide a basis for alloy development. Powder metallurgical techniques and arc-melting provided samples for initial examination. Further development was performed using the submerged-arc welding process with alloyed metal powder additions. Specimens were examined and wear resistance tested using the pin-on-drum abrasive wear test. Final compositions were also subjected to heat treatment and melting point analysis. Fe-Mo-Ni alloys synthesized by arc-melting and similar alloys made by welding possessed similar microstructures, a (Fe,Ni)[subscript 7]Mo[subscript 6] intermetallic plus austenite eutectic in an austenitic matrix. These materials exhibited poor abrasive resistance. Silicon additions to the alloy promoted formation of a Laves phase FeMoSi intermetallic which helped increase the abrasive wear resistance. Through a series of alloy chemistry iterations a final composition of Fe-2OMo-15Ni-5Si was selected. Heat treatment of this alloy at 550 to 650°C caused second phase precipitation in the matrix and raised the hardness about 14 points HRC to 50 HRC. The alloy's wear rate, measured with the pin-on-drum abrasive wear test, was 6.3 to 6.5 mg/m. However this was twice the wear rate observed in commercial high-carbon high-chromium alloys. Based on examination of the alloy microstructures, their chemistry, and an analysis of the Fe-Mo-Si phase system; directions for further research are to increase the molybdenum and silicon content to produce a Fe-2OMo-10Ni-15Si composition. Based on the phase diagram analysis this alloy promises better abrasive wear resistance through a larger volume fraction of hard phases formed and the formation of a harder ternary intermetallic compound, Fe[subscript 2]MoSi[subscript 2].

Identifier

doi:10.6083/M4765C7N

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