Papers by Author: L. Zhao

Abstract: The present work investigates the influence of phosphorus addition on the size distribution of retained austenite in TRIP steels containing 0.01%, 0.09% and 0.14% phosphorus. The size of retained austenite is measured by means of neutron depolarization technique and optical microscopy. It is found that the addition of phosphorous increases the size of the larger intergranular and inter-ferritic austenite grains and therefore also increases the volume fraction of retained austenite due to the strengthening effect of phosphorous on the surrounding ferrite and bainite grains. For all phosphorous additions the most frequently observed austenite size is around 0.2 μm, which is probably corresponds to the interlath film-type retained austenite. The average grain size from the neutron depolarization technique agrees in general with that from the optical microscopy and it is suggested that the accuracy can be improved by further development of the data analysis by taking into account the preferred shape and orientation of the austenite grains.

Abstract: The kinetics of isothermal bainite formation at 483 K, 503 K and 533 K in a bearing SAE 52100 steel (1,01% C – 1,36% Cr – 0,32% Mn – 0,25% Si (wt.%)) is investigated theoretically and experimentally. It is found that the bainite formation becomes significantly slower with decreasing temperature. To interpret the results, a physical model with a concept of reconstructive approach proposed in the literature is applied. The model gives a reasonable agreement with experimental results, although a certain deviation exists at the late stage of the transformation. This deviation is attributed to the diffusion coefficient used in the model without considering the effect of alloying elements, mainly chromium.