M50-type steel

Two approaches for the synthesis of nanostructured M50 type steel (composed of 4.0% Cr, 4.5% Mo, 1.0% V, 0.8% C and balance Fe) powders and their consolidation are reported in this chapter. One approach involved the sonochemical decomposition of organometallic precursors and the other involved the reduction of the metal halides with lithium triethyl borohydride followed by vaccum sublimation of the powders to remove lithium chloride. The as-synthesized powders are amorphous by X-ray diffraction (XRD) but the peaks corresponding to bcc a-Fe are observed in the compacts. The morphology and composition of the powders synthesized by both techniques, as well as the compacts, were examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Hardness, density, particle size and impurity contents were also determined for the compacts. In addition, pure nanosized iron particles obtained by the ultrasound decompositon of iron pentacarbonyl were consolidated and the properties of the latter were studied. 

Powder Synthesis. Two synthetic approaches to produce M50 type steel nanopowders are outlined in Scheme 1. Due to the repeated segregation of vanadium in the M50 powders produced in earlier experiments by using either V(CO)6 or CpV(CO)4 as a vanadium precursor during ultrasound decomposition, vanadium has been excluded in the following reported sonochemical synthesis of M50 type steel, however efforts are currently in progress to remedy this segregation. 

Sonochemical Synthesis of M50 Type Steel Nanopowders. A dispersion of 15g (0.0765 mol) of Fe(CO)5, 0.66g of Cr(EtxC6H6-x)2, 0.75g (0.0015 mol) of CpMo(CO)3 and 1.0 g of polyoxyethylene sorbitan trioleate (surfactant) in dry decalin was sonicated at 50% amplitude for 7h at room temperature in a sonochemical reactor fitted with a condenser and gas inlet and outlet tubes connected to a mercury bubbler. The color of the solution turned dark and then black within a few minutes and this reaction mixture was sonicated until the formation of shiny metallic particles was observed on the walls of the reaction vessel. The sonication was then stopped and the decalin solvent was removed from the reaction flask via vacuum distillation. Fine black powder (Yield 4.448g) remained at the bottom of the reactor, which was then isolated, transferred to a vial and coated with mineral oil before the compaction. 

The sonochemlcal method can also be used to prepare complicated nanoscale mixtures. For example, Gonsalves et al. used the sonochemical decomposition of organometallic precursors to prepare powders of M50-type steel (4% Cr, 4.5% Mo, 1% V, 0.8% C, with the balance being Fe) (140). 

X-ray diffraction spectrum of the M50 type consolidated steel r dmen showing the major peaks due to a-Fe. 

Memo for the Secretary, Ordnance Technical Committee. 1 Apr 4l, sub Bombs. Standardization by Army, Navy, British Purchasing Committee. Cited as ref a, CWTC Item 1220, Obsoletion of 40-lb Steel Case Type Incendiary Bombs and Clusters for Same, 11 Jan 45. (2) Bomb, Incendiary, 4-lb, and Bomb, Incendiary, 40-lb, Classified as Standard and Designated Bomb, Incendiary, 4-lb, AN-M50, and Bomb, Incendiary, 40-lb, AN-M51, 19 May 4l. OCM 16816. (3) Bombs, Incendiary, 4-lb, AN-M50-X, 4-lb, AN-M50, and 40-lb, AN-M51, Clearance for Procurement and Classification as Standard, 22 Jul 41. OCM 17028. 

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