Long Term Microstructural Evolution of 9-12%Cr Steel Grades for Steam Power Generation Plants

Performance of HIPIMS deposited CrN/NbN nanostructured coatings exposed to 650 °C in pure steam environment

“…P92 substrates and coated samples were oxidised at 650 °C in 100% steam atmosphere up to 2000 h, in order to simulate the future operation conditions of steam turbines employed in power plants [16,17,18]. Figure 2 shows the experimental laboratory setup for the steam oxidation test procedure.…”

Analysis on Degradation in Creep Strength of 9Cr-W Martensitic Steel

“…It has been discussed that the rupture strength of the martensitic steel is lowered unexpectedly in creep testing longer than several tens of thousands of hours (Kushima, Kimura, & Abe, 1999;Sawada, Kushima, Kimura, & Tabuchi, 2007). The formation of both coarse Z-phase particles consuming finely dispersed MX particles and recovery zones in the vicinity of the primary austenite grain boundaries (PAGBs) is pointed out as major causes of the unexpected drop in strength (Kushima, Kimura, & Abe, 1999;Suzuki, Kumai, Kushima, Kimura, & Abe, 2003;Sawada, Kushima, & Kimura, 2006;Danielsen, 2007;Hald, 2008;Kimura, Sawada, Kushima, & Toda, 2013), where MX denotes carbonitride with cubic structure and M denotes metallic elements mainly Nb, V, and Cr and X denotes carbon and/or N. On the otherhand, Hu et al (2009) and Di-Gianfransesco, Vipraio, & Venditti (2013) proposed a question that the direct cause of the unexpected drop in rupture strength may possibly depend on the stability of Laves phase. Though the proposed question is not accepted in general, it is important to investigate the actual cause of the unexpected drop in rupture strength for the purpose of improving rupture strength of high Cr martensitic heat resistant steel.…”

Damage characterization of an ASTM A 213 grade 91 tube after 116.000 h of service in a reforming plant

“…The loss of creep rupture strength of T91 steels is due also to recovery of original microstructure, preferentially near prior austenitic grain boundaries (PAGB). Crept specimens showed characteristic increasing in lath and subgrain size [9,10,13,14]. Well developed subgrains of low dislocations density in the interior are typical feature of long term exposed specimens [13].…”

“…Although very detrimental effect on creep strength has been ascribed to Z phase in 12% Cr steels [9,10,12], in grade 91 steels modified Z phase precipitation starts only after 30.000e40.000 h at 650 C, whereas at lower temperatures it does not play a significative role on long term microstructural evolution and stability. The loss of creep rupture strength of T91 steels is due also to recovery of original microstructure, preferentially near prior austenitic grain boundaries (PAGB).…”