Improvement of High-Temperature Mechanical Properties of Low-Carbon RAFM Steel by MX Precipitates

doi:10.1007/s40195-018-0703-y

Abstract

Abstract:

To investigate the influence of tantalum content on high-temperature mechanical properties of low-carbon reduced activation ferritic/martensitic (RAFM) steels, RAFM steels containing different tantalum contents (0 and 0.073%) were fabricated, and the tensile tests at room temperature and high temperature were performed, as well as the creep tests were conducted at 550 °C with the applied stress of 180 and 220 MPa. It was found that 0.073% tantalum addition results in the increase in amount of stable carbonitrides (MX), and the creep rupture time of the steel under 180 MPa is obviously increased. In addition, the increase in MX caused by tantalum addition also leads to the improvement of high-temperature tensile strength. The improvement of high-temperature mechanical properties of RAFM steels is primarily related to the evolution of precipitates.

Key words: Low-carbon RAFM steels, Tantalum addition, Precipitates, High-temperature mechanical properties

Jianguo Chen, Yongchang Liu, Yantong Xiao, Yihuan Liu, Chenxi Liu, Huijun Li. Improvement of High-Temperature Mechanical Properties of Low-Carbon RAFM Steel by MX Precipitates[J]. Acta Metallurgica Sinica (English Letters), 2018, 31(7): 706-712.

Figures/Tables 8

Table 1 Chemical compositions of the RAFM steels in wt%

	C (%)	N (%)	Cr (%)	W (%)	Mn (%)	Si (%)	V (%)	Ta (%)
1#	0.06	0.02	8.91	1.73	0.37	0.05	0.22	0
2#	0.04	0.02	8.93	1.71	0.44	0.04	0.22	0.073

Fig. 1 TEM images of RAFM steels before creep tests: a, b M23C6 of 1# specimen (without Ta), c MX of 1# specimen (without Ta), d, e M23C6 of 2# specimen (with 0.073% Ta), f MX of 2# specimen (with 0.073% Ta)

Fig. 2 Number density of a M23C6, b MX in the normalized and tempered RAFM steel samples

Fig. 3 Effect of Ta addition on the tensile strength of RAFM steels at room temperature (25 °C) and high temperature (800 °C)

Fig. 4 Effect of Ta addition on the a creep behavior, b creep rate of RAFM steels at 550 °C under 220 and 180 MPa

Fig. 5 Comparison of creep rupture times under 180 and 220 MPa at 550 °C for RAFM steels with and without Ta

Fig. 6 TEM images of RAFM steels after creep tests: a, b M23C6 of 1# specimen (without Ta) and 2# specimen (with 0.073% Ta) after 550 °C and 220 MPa, c M23C6 and MX of 1# specimen (without Ta) after 550 °C and 180 MPa, d, e M23C6 and MX of 2# specimen (with 0.073% Ta) after 550 °C and 180 MPa, f, g electron diffraction pattern of M23C6 and MX

Fig. 7 Average sizes of precipitates for specimens (without Ta and with 0.073% Ta) before and after creep tests

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