THERMAL STABILIZATION OF AUSTENITE IN HIGH NICKEL-CARBON STEELS

High resolution electron microscopy has been shown to give new information on defects(1) and phase transformations in solids (2,3). In a continuing program of lattice fringe imaging of alloys, we have applied this technique to the martensitic transformation in steels in order to characterize the atomic environments near twin, lath and αmartensite boundaries. This paper describes current progress in this program.Figures A and B show lattice image and conventional bright field image of the same area of a duplex Fe/2Si/0.1C steel described elsewhere(4). The microstructure consists of internally twinned martensite (M) embedded in a ferrite matrix (F). Use of the 2-beam tilted illumination technique incorporating a twin reflection produced {110} fringes across the microtwins.

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Observations on the structure at the transformation interface of pearlite in steel

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100174138 ◽

1990 ◽

Vol 48 (4) ◽

pp. 200-201

Author(s):

F. A. Khalid ◽

D. V. Edmonds

Keyword(s):

Room Temperature ◽

Thin Foil ◽

Carbon Steels ◽

Model Alloy ◽

Growth Interface ◽

Medium Carbon ◽

Solution Treated ◽

Medium Carbon Steels ◽

Alloy Carbide ◽

Hot Rolled

The austenite/pearlite growth interface in a model alloy steel (Fe-1 lMn-0.8C nominal wt%) is being investigated. In this particular alloy pearlite nodules can be grown isothermally in austenite that remains stable at room temperature, thus facilitating examination of the transformation interfaces. This study presents preliminary results of thin foil TEM of the austenite/pearlite interface, as part of a programme of aimed at studying alloy carbide precipitation reactions at this interface which can result in significant strengthening of microalloyed low- and medium- carbon steels L Similar studies of interface structure, made on a partially decomposed high- Mn austenitic alloy, have been reported recently.The experimental alloys were made as 50 g argon arc melts using high purity materials and homogenised. Samples were hot- rolled, swaged and machined to 3mm diameter rod, solution treated at 1300 °C for 1 hr and WQ. Specimens were then solutionised between 1250 °C and 1000 °C and isothermally transformed between 610 °C and 550 °C for 10-18 hr and WQ.

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Precipitation at the transformation interface of pearlite in steel

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100177696 ◽

1990 ◽

Vol 48 (4) ◽

pp. 912-913

Author(s):

F. A. Khalid ◽

D. V. Edmonds

Keyword(s):

Thin Foil ◽

Carbon Steels ◽

Model Alloy ◽

Low Carbon ◽

High Carbon ◽

Growth Interface ◽

Medium Carbon ◽

Interphase Precipitation ◽

Solution Treated ◽

Wide Range

The austenite/pearlite growth interface in a model alloy steel (Fe-1lMn-0.8C-0.5V nominal wt%) is being studied in an attempt to characterise the morphology and mechanism of VC precipitation at the growth interface. In this alloy pearlite nodules can be grown isothermally in austenite that remains stable at room temperature thus facilitating examination of the transformation interfaces. This study presents preliminary results of thin foil TEM of the precipitation of VC at the austenite/ferrite interface, which reaction, termed interphase precipitation, occurs in a number of low- carbon HSLA and microalloyed medium- and high- carbon steels. Some observations of interphase precipitation in microalloyed low- and medium- carbon commercial steels are also reported for comparison as this reaction can be responsible for a significant increase in strength in a wide range of commercial steels.The experimental alloy was made as 50 g argon arc melts using high purity materials and homogenised. Samples were solution treated at 1300 °C for 1 hr and WQ. Specimens were then solutionised at 1300 °C for 15 min. and isothermally transformed at 620 °C for 10-18hrs. and WQ. Specimens of microalloyed commercial steels were studied in either as-rolled or as- forged conditions. Detailed procedures of thin foil preparation for TEM are given elsewhere.

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