Effect of N on the Microstructure and Mechanical Properties of High Si Martensitic Heat-Resistant Steels

doi:10.1007/s40195-014-0095-6

Abstract

Abstract:

In order to investigate the effect of N on the microstructure and room temperature mechanical properties of new-type high silicon martensitic heat-resistant steels, three steels containing the same total content of C and N but different N contents have been designed and prepared according to the thermo-calc calculation. The thermodynamic calculation and experiments indicate that the replacing of C by N changes the kind and volume fraction of precipitates of the high Si martensitic steel significantly. Along with the N content increasing, the precipitates in the samples after 750 °C tempering change from (Cr₂₃C₆ + VN + TaC) to (Cr₂₃C₆ + VN + TaC + TaN) and finally to (Cr₂₃C₆ + VN + Cr₂N) according to both experimental results and thermodynamic calculations. The room temperature mechanical tests show that the strength of the steel decreases as the N content increases. However, the Charpy impact toughness increases with N content increasing. According to the calculation and SEM observation, it is inferred that the decrease of amount and size of precipitates accounts for the changes of the mechanical properties.

Key words: Martensitic heat-resistant steels, Nitrogen, Thermo-calc, Precipitates, Mechanical properties

Jia Sun, Yutuo Zhang, Pei Wang, Zhongfei Ye, Dianzhong Li. Effect of N on the Microstructure and Mechanical Properties of High Si Martensitic Heat-Resistant Steels[J]. Acta Metallurgica Sinica (English Letters), 2014, 27(4): 573-584.

Figures/Tables 20

Table 1 The designed chemical composition of the steel (wt%)

C	Cr	Si	Mn	W	V	Ta	C + N	N	Fe
x	10.0	1.5	0.65	2.0	0.2	0.1	0.22	y	Bal.

Table 2 The measured chemical composition of the experimental steels (wt%)

Steel	C	Cr	Si	Mn	W	V	Ta	N	Fe
No. 1	0.22	9.65	1.55	0.62	1.79	0.21	0.09	0.023	Bal.
No. 2	0.21	9.48	1.57	0.68	1.79	0.21	0.10	0.047	Bal.
No. 3	0.13	9.63	1.40	0.72	1.70	0.26	0.05	0.11	Bal.

Fig. 1 The pseudo-binary phase diagrams of the steel with designed composition

Fig. 2 The pseudo-binary phase diagrams of the steels: a steel No. 1; b steel No. 2; c steel No. 3

Fig. 3 The phase composition diagrams of the M23C6 in the steels: a steel No. 1; b steel No. 2; c steel No. 3

Fig. 4 The phase composition diagrams of the fcc-2 in the steels: a steel No. 1; b steel No. 2; c steel No. 3

Fig. 5 The phase composition diagrams of the fcc-3 in the steels: a steel No. 1; b steel No. 2

Fig. 6 The phase composition diagrams of the HCP in the steel No. 3

Fig. 7 XRD patterns of the three steels tempered at 750 °C

Fig. 8 TEM micrograph and SAED pattern a and EDX result of M23C6b from steel No. 1 specimen tempered at 750 °C

Fig. 9 TEM micrograph a and EDX result of Ta-MXb from steel No. 1 specimen tempered at 750 °C

Fig. 10 TEM micrograph a and EDX result of Ta-MXb from steel No. 2 specimen tempered at 750 °C

Fig. 11 TEM micrograph a and EDX result of V-MXb from steel No. 2 specimen tempered at 750 °C

Fig. 12 TEM micrograph and SAED pattern a and EDX result of V-MXb from steel No. 3 specimen tempered at 750 °C

Fig. 13 TEM micrograph a and EDX result of Cr-rich nitride b from steel No. 3 specimen tempered at 750 °C

Fig. 14 The tensile strength of No. 1, No. 2, and No. 3 steels tempered at different temperatures: a yield strength Rp0.2; b tensile strength Rm; c elongation

Fig. 15 The SEM photos of the steels tempered at 750 °C: a steel No. 1; b steel No. 2; c steel No. 3

Fig. 16 Mass fraction of different phases in the steels: a steel No. 1; b steel No. 2; c steel No. 3

Fig. 17 Approximate maximum and minimum total content of (Cr23C6 + Cr2N + TaC + VN + TaN) during tempering at 700–800 °C as function of N content according to the mass phase fraction diagrams in Fig. 16

Fig. 18 Charpy impact energy of No. 1, No. 2, and No. 3 steels tempered at different temperatures

References 23

[1]	J.S. Zhang, N. Li, J. Nucl. Mater. 373, 351(2008)10.1016/j.jnucmat.2007.06.019
[2]	A.L. Johnson, E.P. Loewen, T.T. Ho, J. Nucl. Mater. 350, 221(2006)10.1016/j.jnucmat.2005.12.007
[3]	D. Koury, A.L. Johnson, J. Welch, J.W. Farley, J. Nucl. Mater. 429, 210(2012)10.1016/j.jnucmat.2012.05.041
[4]	P. Hosemann, R. Dickerson, P. Dickerson, N. Li, S.A. Maloy, Corros. Sci. 66, 196(2013)10.1016/j.corsci.2012.09.019
[5]	J.S. Zhang, N. Li, Y.T. Chen, A.E. Rusanov, J. Nucl. Mater. 336, 1(2005)10.1016/j.jnucmat.2004.08.002
[6]	A. Hojna, F.D. Gabriele, J. Nucl. Mater. 413, 21(2011)10.1016/j.jnucmat.2011.03.044
[7]	C. Schroer, Z. Voss, O. Wedemeyer, J. Novotny, J. Konys, J. Nucl. Mater. 356, 189(2006)10.1016/j.jnucmat.2006.05.009
[8]	J. Van den Bosch, D. Sapundjiev, A. Almazouzi, J. Nucl. Mater. 356, 237(2006)10.1016/j.jnucmat.2006.05.034
[9]	Y.Z. Shen, S.H. Kim, H.D. Cho, C.H. Han, W.S. Ryu, J. Nucl. Mater. 400, 94(2010)10.1016/j.jnucmat.2010.02.016
[10]	P. Hosemann, J.G. Swadener, J. Welch, N. Li, J. Nucl. Mater. 377, 201(2008)10.1016/j.jnucmat.2008.02.073
[11]	Y. Kurata, J. Nucl. Mater. 437, 401(2013)10.1016/j.jnucmat.2013.02.022
[12]	J. Van den Bosch, G. Coen, P. Hosemann, S.A. Maloy, J. Nucl. Mater. 429, 105(2012)10.1016/j.jnucmat.2012.05.017
[13]	J. Van de Bosch, P. Hosemann, A. Almazouzi, S.A. Maloy, J. Nucl. Mater. 398, 116(2010)10.1016/j.jnucmat.2009.10.020
[14]	S.A. Bashu, K. Singh, M.S. Rawat, Mater. Sci. Eng. A l27, 7(1990)10.1016/0921-5093(90)90184-5
[15]	P. Hu, W. Yan, L.F. Deng, W. Sha, Y.Y. Shan, K. Yang, Fusion Eng. Des. 85, 1632(2010)10.1016/j.fusengdes.2010.04.066
[16]	D. Preininger, J. Nucl. Mater. 307–311, 514(2002)10.1016/S0022-3115(02)01210-2
[17]	U.E. Klotz, C. Solenthaler, P.J. Uggowitzer, Mater. Sci. Eng. A 476, 186(2008)10.1016/j.msea.2007.04.093
[18]	K. Kaneko, S. Matsumura, A. Sadakata, K. Fujita, W.J. Moon, S. Ozaki, Mater. Sci. Eng. A 374, 82(2004)10.1016/j.msea.2003.12.065
[19]	Z.X. Xia, C. Zhang, Z.G. Yang, Mater. Sci. Eng. A 528, 6764(2011)10.1016/j.msea.2011.05.084
[20]	B.S. Srinivas Prasad, V.B. Rajkumar, K.C. Hari Kumar, Calphad 36, 1(2012)10.1016/j.calphad.2011.10.006
[21]	K. Maruyama, K. Sawada, J.I. Koike, ISIJ Int. 41, 641(2001)10.2355/isijinternational.41.641
[22]	X.C. Hao, M. Gao, L. Zhang, X.J. Zhao, K. Liu, Acta Metall. Sin. 47, 912(2011)
[23]	Q.X. Dai, Z.Z. Yuan, X.M. Luo, X.N. Cheng, Mater. Sci. Eng. A 385, 445(2004)10.1016/j.msea.2004.07.003