本文研究了HR3C钢在750℃下时效500 h前后的显微组织变化和第二相的种类.研究结果表明, 时效后HR3C钢中的析出物主要为形状各异的M23C6和NbCrN,其中M23C6在晶界和晶内均有析出, NbCrN以极其细微的尺寸大量弥散分布于晶内; 时效过程中弥散析出的M23C6和极其细微的NbCrN提高了HR3C钢的硬度. 晶内及晶界析出的M23C6晶格常数均为基体的3倍, 并与基体保持完全共格的关系, 晶界处部分 M23C6转变成了高Cr的$\sigma$相.
HR3C steel (Fe-25Cr-20Ni-Nb-N) is a new type of austenitic heat-resistant steel which has been widely used for super-heater and re-heater tubes in the ultra supercritical pressure (USC) boiler. The mechanical properties of HR3C steel were dependent on the stability of the microstructure, particularly the large amount of precipitates formed during service. This work was focused on the change of microstructure and the precipitations of HR3C steel after thermal aging for 500 h at 750℃. The results indicated that the major precipitates were variform M23C6 carbides and NbCrN nitrides. M23C6 carbides precipitated on grain boundaries and in intragranular. Fine and dispersed NbCrN nitrides were found to precipitate in intragranular. The hardness of HR3C steel had been improved through dispersed M23C6 and fine NbCrN precipitates after thermal aging for 500 h at\linebreak 750℃. All the M23C6 carbides, with lattice parameter of three times of the austenite matrix, grown in a cube to cube orientation relationship with the matrix. Some of the M23C6 carbides which precipitated on grain boundaries were transformed into σ phase.
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