Correlation of the microstructure and fracture toughness of the heat-affected zones of an SA 508 steel

Abstract

In this study, microstructures of a heat-affected zone (HAZ) of an SA 508 steel were identified by Mössbauer spectroscopy in conjunction with microscopic observations, and were correlated with fracture toughness. Specimens with the peak temperature raised to 1350 ЊC showed mostly martensite. With the peak temperature raised to 900 ЊC, the martensite fraction was reduced, while bainite or martensite islands were formed because of the slow cooling from the lower austenite region and the increase in the prior austenite grain size. As the martensite fraction present inside the HAZ increased, hardness and strength tended to increase, whereas fracture toughness decreased. The microstructures were not changed much from the base metal because of the minor tempering effect when it was raised to 650 ЊC or 700 ЊC. However, fracture toughness of the subcritical HAZ with the peak temperature raised to 650 ЊC to 700 ЊC was seriously reduced after postweld heat treatment (PWHT) because carbide particles were of primary importance in initiating voids. Thus, the most important microstructural factors affecting fracture toughness were the martensite fraction before PWHT and the carbide fraction after PWHT.

Microstructure and mechanical properties of laser welded S960 high strength steel

“…The strengths of the fusion zone and each sub-zone within the HAZ were increased mainly by the generation of martensite. Some researchers [39,40] have investigated the correlation between the microstructure and the fracture toughness within the heat affected zone in SA508 steel. Lee et al [40] reported that the yield strengths were over 1100 MPa within the CGHAZ and FGHAZ, and that these values were approximately double the yield strength of the base material (~500 MPa).…”

Study of Electroslag Remelted and Nitrogen Containing High Speed Tool Steel M41

“…In addition to the location of carbon, the substitutional elements (Mn, Cr, Mo, Si …. etc) are soluble in the BCT martensite structure and they strongly disturb the local environment around iron atoms [12,13]. Thus, the observed three magnetic sub-spectra [MFe1, MFe2 and MFe3] may depend on the location of the carbon atoms and/ or the substitutional elements at the first or the second nearest interstitial sites, and may be further.…”

Effects of alloying elements on fracture toughness in the transition temperature region of base metals and simulated heat-affected zones of Mn-Mo-Ni low-alloy steels

“…The intercritically reheated coarse-grained (ICRCG) HAZ near the weld fusion line, which is generally known as the most brittle region in HAZs, was considered the local brittle zone. [13,27] According to the thermal flow formula of Rosenthal, [27,28] the peak temperature (T p ) and cooling time between 800 °C and 500 °C (᭝t 8/5 ) were set to be 1350 °C and 23 seconds, respectively, for the local brittle zone. Thermal-cycle simulation conditions are shown in Table II.…”