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Superior Mechanical Properties Obtained by HIP Heat Treatment for Machinery Applications

  • : Larker, Richard1
  • : 1Indexator AB
  • : PDF Download
  • : 2012

Abstract

Austempering is a heat treatment where austenitized parts of iron/steel are quenched to avoid pear-lite, followed by isothermal transformation at 250?400�C (above Ms), usually in a salt bath. For steels, bainite is commonly formed. When Ductile Iron cast with >2 % silicon are austempered to form ADI, carbon released from growing acicular ferrite stabilizes the surrounding austenite instead of forming bainitic carbides, resulting in a fine duplex ferritic-austenitic microstructure named ausferrite. Recent concurrent HIP developments in heat treatment parameters and equipment enable Uniform Rapid Quenching (URQ?) for austempering in the AusFerHIP concept. Numerous advantages in-clude faster heating and austenitization kinetics concurrent with elimination of porosity, and improved hardenability during quenching. In addition, the isothermal transformation to ausferrite can be pro-moted by rapid nucleation of acicular ferrite at lower temperature followed by rapid growth at higher temperature, this two-step austempering resulting in better properties and reduced process time
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