Impact Toughness of Heat-Affected Zones of 11Cr Heat-Resistant Steels

doi:10.1007/s40195-020-01014-2

Abstract

Abstract:

Aiming at the requirements of structural steel in Gen-IV nuclear reactor, the high-chromium martensitic heat-resistant steels containing 10-12% chromium were developed. The toughness of heat-affected zones (HAZs) is one of the important factors for evaluating the weldability of steels. In this paper, the simulated HAZs were fabricated using tempered SIMP steels. The effects of microstructures on the impact toughness of materials were analyzed using Vickers hardness tester, optical microscope, transmission electron microscope. Experimental results demonstrated that the HAZs of weldment were poor in toughness, much lower than that of the base metal. However, after experiencing post-weld heat treatment, the toughness of the HAZs increased greatly. The toughness became better in terms of CG-HAZ, FG-HAZ and IC-HAZ for the two steels, regardless of as-welded or after PWHT. Compared with SIMP7 steel, chemical compositions, such as C, Si, Mn and Cr, were adjusted to a lower content; the toughness of base metal and simulated HAZs was better in the case of SIMP11. The conjunct roles of dislocation density and carbon contents retained in the martensite led to poor impact toughness of the as-welded HAZs, because dislocations and carbon atoms affected the inner stresses within lattices.

Key words: High-Cr F/M heat-resistant steel, Heat-affected zones, Impact toughness, Carbide precipitations

Yongkui Li, Jianxin Lou, Hongtao Ju, Li Lin. Impact Toughness of Heat-Affected Zones of 11Cr Heat-Resistant Steels[J]. Acta Metallurgica Sinica (English Letters), 2020, 33(6): 821-827.

Figures/Tables 10

Table 1 Chemical compositions of the materials

Steels	Chemical compositions (wt%)
SIMP7	C	Si	Mn	P	S	Cr	W	V
	0.29	1.77	0.7	0.007	0.001	11.24	1.38	0.18
	Ta	Fe
	0.14	Bal
SIMP11	C	Si	Mn	P	S	Cr	Ni	Ti
	0.22	1.22	0.52	0.004	0.0043	10.24	0.008	< 0.01
	Al	Cu	W	V	Nb	Ta	Fe
	< 0.01	0.008	1.45	0.18	< 0.01	0.11	Bal

Fig.1 Phase transformation temperatures (A1 and A3) for SIMP7 and SIMP11 steels during heating

Fig.2 Characteristic thermal curves of CG-HAZ, FG-HAZ, IC-HAZ for SIMP11 steel

Fig.3 Microstructures of a as-welded CG-HAZ, b as-welded FG-HAZ, c as-welded IC-HAZ, d base metal of SIMP11 steel by OM

Fig.4 Microstructures of a CG-HAZ, b FG-HAZ, c IC-HAZ of SIMP11 steel after PWHT by OM

Fig.5 Microstructures of a CG-HAZ, b FG-HAZ, c IC-HAZ of SIMP7 steel after PWHT by OM

Fig.6 Charpy impact energies of as-welded CG-HAZ, FG-HAZ, IC-HAZ and base metal of SIMP7 and SIMP11 steels

Fig.7 Charpy impact energies of CG-HAZ, FG-HAZ, IC-HAZ and base metal of SIMP7 and SIMP11 steels after PWHT

Fig.8 Microhardness of HAZs of SIMP11 before and after PWHT

Fig.9 Microstructures of CG-HAZ of SIMP11 steel: a before, b after PWHT

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