The effects of austenitizing time on bainite continuous transformation kinetics are investigated for AISI 4340 steel in dilatometric experiments. Dilatometric specimens were heated up to 950°C, and austenitized for 10-120 minutes, followed by rapid cooling to 550°C in 20 s, and in the following 120 minutes cooled to 350°C, and then quenched to room temperature at l00°C/s. The bainite transformation start temperature (Bs) and 50% transformation temperature (Bm) vary obviously with holding time. The bainite transformation finish temperature (Bf) remains almost the same. The reason of Bs raises with the holding time may be due to the precipitation of AlN and TiC or other carbide or nitride particles on prior austenite grain boundaries. In fact the trends that the bainitic transformation rate varied with its volume fraction ξ can be separated into three stages: I. rapid increase stage; II. slowly decrease stage; III. rapid decrease stage. The reasons for the above phenomenon may be due to the effects of the decreasing of temperature, the diffusion of carbon during the continuous transformation process, and effects of the alloy composition, etc.
|Number of pages||4|
|Journal||Cailiao Rechuli Xuebao/Transactions of Materials and Heat Treatment|
|Publication status||Published - 2006 Aug|
All Science Journal Classification (ASJC) codes
- Materials Science(all)
- Physics and Astronomy(all)