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

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 aswelded HAZs, because dislocations and carbon atoms affected the inner stresses within lattices.

Effect of Microstructural Evolution on the Mechanical Properties of Intercritical Heat‐Affected Zone of Quenched‐and‐Tempered Ultrahigh‐Strength Steel

“…[ 43 ] The study suggested that the decrease of carbon content was beneficial to the toughness of HAZ. [ 44 ] Therefore, the C and Mn content of austenite in IC‐100% was lower and more homogeneous than the partially austenitized ICHAZs, resulting in the decline of the embrittlement of FM and GB (Figure 12a). Therefore, the grain refinement, high density of HAGBs, and the less embrittlement of microstructure improved the impact toughness of IC‐100% to some extent.…”