Austenitic Filler Metal Research Articles

Repair welding of cracked steam turbine blades using austenitic and martensitic stainless-steel consumables

The procedure for repair welding of cracked steam turbine blades made of martensitic stainless steels has been developed using the gas tungsten arc welding process. Weld repair procedures were developed using both ER 316L austenitic and ER 410 martensitic stainless-steel filler wire. The overall development of the repair welding procedure included selection of welding consumables (for austenitic filler metal), optimisation of post-weld heat treatment parameters, selection of suitable method for local pre-heating and post-weld heat treatment (PWHT) of the blades, determination of mechanical properties of weldments in as-welded and PWHT conditions, and microsturctural examination. After various trials using different procedures, the procedure of local PWHT (and preheating when using martensitic stainless-steel filler wire) using electrical resistance heating on the top surface of the weldment and monitoring the temperature by placing a thermocouple at the bottom of the weld was found to give the most satisfactory results. These procedures have been developed and/or applied for repair welding of cracked blades in steam turbines.

Mechanical and Structural Properties of Similar and Dissimilar Steel Joints

The mechanical properties of specimens from similar and dissimilar weld joints were examined. A ferritic steel (St37-2) and an austenitic stainless steel (AISI 304) were joined by the gas tungsten arc weld (GTAW) process using an austenitic filler metal. Mechanical and metallographic properties of the specimens were obtained by means of microhardness testing, tensile testing, bending fatigue testing, and light optical and scanning electron microscopy. The highest microhardness values were recorded on the ferritic–austenitic dissimilar weld joint, whereas the highest tensile strength and bending fatigue life were obtained with the austenitic–austenitic joints. Ferritic and pearlitic structures were observed in the microstructure of the ferritic–ferritic joint. The microstructures of austenitic–austenitic and austenitic–ferritic joints showed small recrystallization grains in addition to the typical austenitic and ferritic structures. Scanning electron microscopy was used to observe the fracture surfaces of the specimens and the origins of the fatigue cracks.

Strength and toughness properties of two nitrogen alloyed stainless steels and their submerged arc weldments at cryogenic temperatures

Submerged arc weldments of the two nitrogen-alloyed stainless steels X2 CrNiN 18 10 (similar to AISI 304 LN) and X4 CrNiMoN 18 14 (similar to AISI 316 LN) welded with the fully austenitic filler metal X2 CrNiMnMoN 20 16 were investigated. Tensile, impact toughness and single-specimen J-integral tests at room temperature, 77 K and 4 K were performed. The strength of the materials increased whereas the impact toughness and the fracture toughness decreased with decreasing temperature. The toughness of the steel X4 CrNiMoN 18 14 was superior to that of X2 CrNiN 18 10, and for the austenitic weld a good combination of strength and toughness was also found. On the fracture surface of the compact tension specimens, a stretch zone was found, the width of which was reduced with decreasing test temperature. For all three materials at all three temperatures the critical values, JIc, of the J integral determined according to ASTM E 813 are approximately twice the respective values for the J integral at physical crack initiation determined according to the German specification DVM 002 using the width of the stretch zone. © 1998 Chapman & Hall

Weldability studies of high-strength low-alloy steel using austenitic fillers

A study was undertaken to establish the weldability of high-strength low-alloy steel (0.3C 3Ni-2.5Si-0. 87Cr-0.52Mn-0.29Mo) using austenitic filler metals (309L and 18Cr-8Ni-6Mn) and the gas tungsten are welding process with a view to securing high toughness in the weldment. Hot and cold cracking tests, carried out to study the cracking tendency in the weldment, showed that these steels are not prone to hot and cold cracking. Weld joints were characterised on the basis of transverse tensile, hardness and impact-toughness properties and microstructural studies. The joint efficiencies of 309L and 18-8-6 austenitic stainless-steel weld deposits were found to be around 72% compared to that of the base metal (with respect to UTS). However, the studies revealed that the toughness of the weld deposit is improved by a factor of nearly 1 1/2 compared to that of the base metal in the case of 309L filler wire, while with 18-8-6 filler wire the toughness of the weld deposit was lower than that of the base metal.

Microstructure and mechanical and electrochemical properties of martensitic weld deposits developed for welding of a 12%Cr duplex stainless steel

The microstructure and mechanical and electrochemical properties of martensitic weld deposits developed for the welding of a duplex 12% Cr corrosion resisting steel, as well as the experimental procedures used, are described. During the development, it was found that weld metals having matching compositions (and thus duplex structures) to those of 3CR12 had very poor impact properties. This was largely because of the inability to control weld metal grain size. By increasing the proportion of austenite stabilising elements, to produce a predominantly low carbon martensitic weld deposit, it was found that acceptable toughness (≥30 J at 20°C) could be achieved in the as welded condition. The electrochemical properties were designed to be similar to, yet slightly more noble than, those of the wrought 3CR12 plate, thus guarding against possible inhomogeneities in the as cast structure. Cost was also an important consideration throughout the development of these closely matching consumables, since the austenitic filler metals used (e.g. AWS E 309 Mo) were substantially more expensive than the parent plate. It has been shown that cost effective, metallurgically compatible filler metals for 3CR12 can be produced.MST/651

Atmospheric corrosion performance of welded stainless steels

The results of a 3 year study of the corrosion performance of welded panels of four types of stainless steel in three atmospheric environments are presented. The alloys chosen were weldable grades used in process industriesfor fabrication of plant for exterior applications such as tankage, pipework, and processing equipment. The grades were AISI types 304L and 316L (austenitic), AISI type 444 (ferritic), and proprietary grade 3RE60 (duplex). The panels were welded with austenitic filler metals and three surface finishes were employed: ground, polished, and pickled. The three environments chosenfor the exposure sites were severe marine, urban–marine, and a geothermal atmosphere.

オーステナイト系溶加材による超高張力鋼及び耐熱超合金のミグ溶接

Fundamental studies on the prevention of welding cracks of heat resistaing superalloys and ultra high strength steels were made and as a result, developed an economical method of obtaining heat resisting .weld metal with low cracking sensitivity by using fully austenitic Cr-NiMn filler metal containing a certain amount of additional elements and Ar-base mixed shielding gases. These methods are already adopted for welding of heat resisting superalloys, hear resisting steels and low alloy high strength steels, obtaining good results.The superior properties of the weld obtained by this method are, described in this paper, which are summarized as follows:(1) High cracking resistance is obtained by eliminating the effects of deleterious impurities such as CrS and NiS.(2) High heat resistance is obtained by the prevention of -phase formation and the uniform deposition of stable carbide M23C6 in the austenitic matrix of weld metal.(3) Good impact properties is obtained at high and low temperatures and also in the case high temperature isheld for a long time.