Microstructure and Mechanical Properties of an Austenitic Heat-Resistant Steel after Service at 570\xa0\xb0C and 25.4\xa0MPa for 18\xa0Years

Xu Yang,Xianbo Shi,Gong Qian,Xisheng Yang,Chengwei Yu,Wei Yan,Baochen Wang,Kai Yan

doi:10.1007/s11665-020-05420-6

Abstract

Microstructure and mechanical properties of an austenitic heat-resistant steel (12Cr18Ni12Ti) serviced in a supercritical power plant at 570 °C/25.4 MPa for 160,000 h were investigated. The results show that the hardness and the tensile strength did not decrease; however, the impact toughness was remarkably reduced. The TiC precipitate shows excellent thermostability; for example, it hardly grew up, and no big M23C6 carbides were found. However, large Fe, Cr-rich σ-phase was doomed to precipitate along grain boundary, which should be responsible for the reduced toughness. The growth of σ-phase was observed to have an interaction with the preexisted carbides.

Highlights

Austenite stainless steels are the most widely used in power plants due to the excellent creep strength, high resistance to oxidation and mature manufacturing process (Ref [1,2,3])
It indicates that under the long-term high-temperature condition, austenite grain is still under the control of thermodynamics and reaching for equilibrium, during which the growth of the big grains was through sacrificing the small ones
The large TiC precipitates could be existed before the steam tubes made of 12Cr18Ni12Ti steel was carried into practice and always are accepted as the primary carbides

Summary

Introduction

Austenite stainless steels are the most widely used in power plants due to the excellent creep strength, high resistance to oxidation and mature manufacturing process (Ref [1,2,3]) Such austenite stainless steels generally include S304, S310, S316, S316L, and so on. The experimental steel (12Cr18Ni12Ti) is such kind of modified S316 steel by adding the element of Ti. Since Ti has a very strong bonding force with C so as to get TiC precipitates, Cr has little chance to form carbides with C at grain boundaries, and the intergranular corrosion resistance could be improved (Ref [4,5,6]). Compared with S316 steel, 12Cr18Ni12Ti steel has better intergranular corrosion resistance and higher creep strength (Ref [4,5,6,7])

Methods

Results

Discussion

Conclusion