Study on the Influence of Prior Cold Work on Precipitation Behavior of 304HCu Stainless Steel During Isothermal Aging
- PDF / 913,147 Bytes
- 7 Pages / 593.972 x 792 pts Page_size
- 81 Downloads / 176 Views
TION
EXTENSIVE studies are being carried out in developing high-temperature materials for the application of superheater/reheater in advanced ultra-supercritical (AUSC) thermal power plants at extreme operating conditions to achieve high-efficiency and low CO2 emissions.[1,2] The principle objective in the development of different superalloys (Inconels 617, Inconels 740, Hayness 263, Hayness 282) and new generation steels (304HCu, HR3C, HR6W) is to operate these plants at high steam temperatures and pressures of above 600 C and 25 MPa, respectively.[3,4] While Inconel 617 is proposed to be used in higher temperature sections, copper-added steels such as 304HCu steel are proposed to be used in moderately high-temperature sections of superheaters and reheaters of the boilers. The effect of copper addition to steels toward precipitation strengthening and corrosion resistance has been studied extensively.[5–7] The austenitic 304HCu stainless steel is considered for use in the Indian AUSC program.[8,9] The 304HCu steel exhibits excellent creep rupture R. MANOJKUMAR, S. MAHADEVAN, and C.K. MUKHOPADHYAY are with the Non Destructive Evaluation Division, Indira Gandhi Centre for Atomic Research, HBNI, Kalpakkam, 603102, India. Contact e-mail: [email protected] M.N. SINGH is with the Hard X-ray Applications Lab., Synchrotrons Utilization Section, Raja Ramanna Centre for Advanced Technology, Indore, 452013, India. Manuscript submitted March 4, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS A
strength due to coherent as well as dispersion precipitation strengthening resulting from fine precipitate particles of Cu-rich phase, NbCrN, Nb(C, N), and M23C6 formed during thermal aging. The microstructural stability of this steel indicates that it is a suitable candidate for boiler tubes.[10] In 304HCu steel, after aging at 650 C for 1 hour, formation of nano-size Cu-rich phase of about 1.5 nm in radii has been found by three-dimensional atom probe (3DAP) and it grows to 30-40 nm on aging for 10,000 hours retaining the strengthening on long-term aging.[11,12] The MX carbide saturates to a size of 70 nm, whereas M23C6 grows to a size of 500 nm at 5000 hours of aging duration causing dispersion strengthening. The creep rupture studies of 304HCu steel were carried out to confirm the microstructural and phase stability at high temperatures between 600 and 800 C and on aging for longer durations.[13–15] Many attempts have been made to quantify the precipitate fraction and characterize the microstructural changes in 304HCu steel using electrical resistivity, hardness, optical microscopy, XRD, SEM, and TEM.[11,12,16] Ren et al.[16] made micro-hardness measurements on 304HCu steel aged for 1 to 6 hours duration at 700 C and found that the hardness peaks at 2 hours duration from 137 to 157 HV. They have reported that the hardness and electrical resistivity are relatively sensitive to the Cu-precipitation behavior in Cu-bearing austenitic steel. The 304HCu austenitic steel having an fcc crystal structure does not undergo any solid state p
Data Loading...
