THE MORPHOLOGICAL AND COMPOSITIONAL CHANGES OF THE CARBIDES IN F12 HEAT-RESISTANT ALLOY STEEL FOR LONG-TERM SERVICE AT ELEVATED TEMPERATURE
长期高温时效F12耐热合金钢中碳化物形态和组分变化

The mechanical property and microstructure of the steel X20CrMoV12.1 used as main steam pipe in power plant changed distinctively after long time service at elevated temperature. It exhibited embrittlement at room temperature without softening. Observation by TEM showed clearly the character of creep damage in microstructure. Most carbides are identified as M23C6 and coarsened heavily. The morphologies and compositions of those M23C6 carbides are varied with their locations, which might be relative to their coarsening processes. The precipitation of some fine V-rich MC carbide during long term exposure is the main reason for hardness maintenance.