Weld Heat-Affected Zone Properties in AISI 409 Ferritic Stainless Steel

Abstract

Although welding of thin-gage ferritic stainless steels is well documented, little information is available on the response of thicker (4.5 to 12.0 mm) sections to welding. With increasing interest in the use of heavier gages, it has become necessary to rectify this gap in knowledge. The work reported herein was undertaken to examine the metallurgical response of titanium-stabilized 11.5Cr steels to welding in terms of heat-affected zone (HAZ) structure, mechanical properties, and corrosion behavior. Welds were made in four heats of steel to determine the thermal cycles occuring in the weld HAZ and to examine structures and give a general indication of joint properties. In order to examine the characteristics of different regions in the HAZ, a thermal simulation technique was used to produce specimens for examination and testing which had undergone a thermal cycle appropriate to a specific part of the HAZ. Parent steel, weldments, and simulated specimens were examined by optical microscopy, hardness testing, notch impact testing, and corrosion testing. Four distinct regions of the HAZ were distinguished, as the HAZ was traversed from the unaffected parent steel to the fusion boundary. The amount of martensite formed reached a maximum where the HAZ peak temperature was in the duplex α + γ range. Impact transition temperature increased as the grain size increased, and martensite appeared to have little effect. In direct HAZ tests the transition temperature increased by 30 to 70 deg C irrespective of arc energy. Corrosion resistance deteriorated as the martensite content increased. Variations in nickel, manganese, and titanium within the steels used gave only minor variations in HAZ structure and properties, and it is concluded that compositional variations within the AISI 409 specification are unlikely to give significant improvements in the weldability of these steels.