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Lath martensite has an unusual good toughness compared to its high strength. Lath martensite is formed only in steels with a carbon content of less equal 0.03 wt%. Therefore, a further increase of the yield stress by carbon precipitation was not possible. But by precipitation of the intermetallic phase (Fe, Ni)(16), Ti(8)Si(6) a yield stress of 2000 MPa could by achieved. This intermetallic phase is a coherent precipitation that is cut by dislocations and gives an inhomogeneous glide during plastic deformation and thus low values of the toughness. Therefore, the good values of toughness, measured in the as quenched state, decrease with increasing strength by precipitation hardening, brittle, intercrystalline fracture appears. In the overaged stage the coherent particles become more and more incoherent, but these particles precipitate on grain boundaries with an inhomogeneous distribution and poor toughness. The toughness can be improved by a combination of coherent and incoherent particles, both with a distribution as homogeneous as possible. To check this, the following alloys were investigated:

- Alloys without molybdenum to suppress the precipitation of coarse Fe(2)Mo particles on the grain boundaries;
- Precipitation of one part of the G-phase in the austenite that will be incoherent under these conditions;
- Precipitation hardening by niobium and titanium carbonitrides;
- Precipitation hardening by chromium nitride;
- Precipitation hardening by a combination of the G-phase and nitrides;
- Precipitation by nitrides and carbides.


Additional information

Authors: SCHULZ-BEENKEN A, Max-Planck-Institut für Eisenforschung GmbH, Düsseldorf (DE);PLUTKA B, Max-Planck-Institut für Eisenforschung GmbH, Düsseldorf (DE);HOUGARDY H, Max-Planck-Institut für Eisenforschung GmbH, Düsseldorf (DE)
Bibliographic Reference: EUR 16023 DE (1997) 98pp., FS, ECU 16.50
Availability: Available from the (2)
ISBN: ISBN 92-828-0754-1
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