Showing papers by "Matthias Militzer published in 1998"

Precipitation hardening of HSLA steels

Abstract: A process model to describe the strength contributior from precipitation hardening during coiling after hot rolling has been developed for V and Nb HSLA steels. Experimental measurements of ageing behaviour on the V steel were conducted on coil material which was received in an underaged condition. The size and composition of precipitates was examined on replicas using scanning transmission electron microscopy. The precipitates were observed to be V rich and a substantial increase in precipitate size occurred as a function of ageing time. The modelling approach developed by Shercliff and Ashby for aluminium alloys was extended to microalloyed steels. The model assumes particle coarsening is the rate controlling process and that the precipitates are initially sheared by dislocations with a transition to non-shearable precipitates at peak strength. After calibration of the model, good agreement was observed between the model predictions and-experimental data. A model for ageing in a Nb HSLA steel was also developed using literature values for the ageing behaviour.

Monitoring of Attenuation During Phase Transformations in Steel using Laser-Ultrasonics

Abstract: Ferrite grain size strongly influences the mechanical properties of steels. In hot rolled steels, the ferrite grain size is determined by the austenite microstructure during the finish rolling, and by the rate of cooling through the transformation temperature range. A sensor to monitor phase transformations and grain sizes in strips during hot rolling would allow to control the process parameters, optimize the ferrite grain size, and better achieve the desired mechanical properties. Unfortunately, such a sensor is presently not available in hot strip mills.