Steel Filler Metal Research Articles

Effect of modes of metal transfer and microstructure on corrosion behavior of welded modified ferritic stainless steel in acidic environments

The effects of modes of metal transfer, i.e., short-circuit (SC) and spray (S) modes in single-pass gas metal arc welding of modified ferritic stainless steel using two types of austenitic stainless steel filler metals on microstructure as well as corrosion behavior of weld metal and high-temperature heat-affected zone (HTHAZ), were investigated. The results show that primary solidification modes (PSM) of the welds were exclusively dependent upon the Creq/Nieq ratio of the respective welds. However, the amount of grain boundary austenite and martensite transformation in the welds were solely dependent upon the mode of metal transfer and the extent of cooling rate. Regarding the corrosion mechanism, grain boundary corrosion (GBC) behavior of welds and HTHAZ relied on the microstructural changes along the grain boundary due to the variation in mode of metal transfer. The results show that S-mode resisted grain boundary corrosion of the welds and both GBC as well as pitting corrosion of the HTHAZ. On the other hand, SC-mode improved only pitting corrosion resistance of the welds. Between the filler wires used, 316L welds, in general, provided better corrosion resistance compared with 308L welds.

Effect of the Gmaw and the Gmaw-P Welding Processes on Microstructure, Hardness, Tensile and Impact Strength of Aisi 1030 Steel Joints Fabricated by ASP316L Austenitic Stainless Steel Filler Metal

Effect of the Gmaw and the Gmaw-P Welding Processes on Microstructure, Hardness, Tensile and Impact Strength of Aisi 1030 Steel Joints Fabricated by ASP316L Austenitic Stainless Steel Filler Metal In this study, medium-carbon steel (AISI 1030) plates of 10 mm thickness, were welded by using the synergic controlled pulsed (GMAW-P) and manual gas metal arc (GMAW) welding techniques. Constant wire feed speed, voltage, welding speed and gas flow rates (3.2 m/min, 22.5 V, 4 mm/s, 16 1/min) and ASP316L austenitic stainless steel filler metal were used in these techniques. The interface appearances of the welded samples were examined by optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectrometry (EDS) and X-Ray diffraction (X-RD). In order to determine mechanical properties of samples, the tensile, impact and microhardness tests were conducted. The GMAW-P joints of AISI 1030 steel couples showed superior tensile strength, less grain growth and narrower heat affected zone (HAZ) when compared with GMAW joints, and this was mainly due to lower heat input, fine fusion zone grain and higher fusion hardness.

Residual Stress Fields after Heat Treatment in Cladded Steel of Process Vessels

The influence of the heat treatment on the residual stress fields of weld cladded samples is discussed in this paper. The samples were elaborated from carbon steel plates, cladded in one of the faces with stainless steel filler metals by submerged arc welding. After the cladding process some of the samples were submitted to heat treatments with different parameters: one at 620° C for a holding time of 1 hour and the other at 540° C for a period of ten hours. The in‑depth residual stress profiles were determined by neutron diffraction. The results shown that the sample treated to 620 °C, presented the highest residual stress relaxation. The corresponding heat treatment has the industrial benefit to be shorter than the other heat treatment.

Fatigue Crack Growth Behavior of Gas Metal Arc Welded AISI 409 Grade Ferritic Stainless Steel Joints

The effect of filler metals such as austenitic stainless steel, ferritic stainless steel, and duplex stainless steel on fatigue crack growth behavior of the gas metal arc welded ferritic stainless steel joints was investigated. Rolled plates of 4 mm thickness were used as the base material for preparing single ‘V’ butt welded joints. Center cracked tensile specimens were prepared to evaluate fatigue crack growth behavior. Servo hydraulic controlled fatigue testing machine with a capacity of 100 kN was used to evaluate the fatigue crack growth behavior of the welded joints. From this investigation, it was found that the joints fabricated by duplex stainless steel filler metal showed superior fatigue crack growth resistance compared to the joints fabricated by austenitic and ferritic stainless steel filler metals. Higher yield strength and relatively higher toughness may be the reasons for superior fatigue performance of the joints fabricated by duplex stainless steel filler metal.

Effect of Welding Processes on Tensile and Impact Properties, Hardness and Microstructure of AISI 409M Ferritic Stainless Joints Fabricated by Duplex Stainless Steel Filler Metal

The effect of welding processes such as shielded metal arc welding, gas metal arc welding and gas tungsten arc welding on tensile and impact properties of the ferritic stainless steel conforming to AISI 409M grade is studied. Rolled plates of 4 mm thickness were used as the base material for preparing single pass butt welded joints. Tensile and impact properties, microhardness, microstructure and fracture surface morphology of the welded joints have been evaluated and the results are compared. From this investigation, it is found that gas tungsten arc welded joints of ferritic stainless steel have superior tensile and impact properties compared with shielded metal arc and gas metal arc welded joints and this is mainly due to the presence of finer grains in fusion zone and heat affected zone.

Effect of weld metal properties on fatigue crack growth behaviour of gas tungsten arc welded AISI 409M grade ferritic stainless steel joints

The effect of filler metals such as austenitic stainless steel, ferritic stainless steel and duplex stainless steel on fatigue crack growth behaviour of the gas tungsten arc welded ferritic stainless steel joints was investigated. Rolled plates of 4 mm thickness were used as the base material for preparing single ‘V’ butt welded joints. Centre cracked tensile (CCT) specimens were prepared to evaluate fatigue crack growth behaviour. Servo hydraulic controlled fatigue testing machine was used to evaluate the fatigue crack growth behaviour of the welded joints. From this investigation, it was found that the joints fabricated by duplex stainless steel filler metal showed superior fatigue crack growth resistance compared to the joints fabricated by austenitic and ferritic stainless steel filler metals. Higher yield strength, hardness and relatively higher toughness may be the reasons for superior fatigue performance of the joints fabricated by duplex stainless steel filler metal.

Microstructure, hardness and residual stress distribution in maraging steel gas tungsten arc weldments

The distribution of residual stresses due to welding has been studied in maraging steel welds. Gas tungsten arc welding process was used and the effect of filler metal composition on the nature of residual stress distribution has been investigated using X-ray diffraction technique with Cr Kα radiation. Three types of filler materials were used, they include: maraging filler, austenitic stainless steel and medium alloy medium carbon steel filler metal. In the case of maraging steel weld, medium alloy medium carbon filler, the residual stress at the centre of the weld zone was more compressive while, less compressive stresses have been identified in the heat affected zone of the parent metal adjacent to the weld metal. But, in the case of austenitic stainless steel filler the residual stresses at the centre of the weld and heat affected zone were tensile. Post-weld aging treatment reduced the magnitude of stresses. The observed residual stress distribution across the weldments has been correlated with microstructure and hardness distribution across the weld.

Effect of preheating temperature and filler metal type on the microstructure, fracture toughness and fatigue crack growth of stainless steel welded joints

It is known that the main problem related with the welding of low carbon 12% Cr stainless steels is its hydrogen induced cracking susceptibility. Thus, it is common practice to perform welding with two alternative ways, preheating the welded parts and using similar filler material or using an austenitic stainless steel filler metal without preheating. This research work consists in identifying and comparing, for these two alternatives, the effect on microstructure, fracture toughness and fatigue crack growth rate of the welded joint. On the first alternative, using a GMAW welding process and similar filler metal, the variable is preheating temperature, with the purpose of minimizing internal residual stresses and the level of diffusible hydrogen. On the second alternative, also using a GMAW welding process and austenitic stainless steel filler metal (greater hydrogen solubility), the variable is hydrogen concentration in the argon shielding gas with the purpose of diffusing hydrogen to the heat affected zone. The results indicate how the thermal cycle, different hydrogen levels and hydrogen trapping sites affect the mechanical properties.

In Situ Repair Welding of Steam Turbine Shroud for Replacing a Cracked Blade

A root-cracked blade in a high-pressure steam turbine of a nuclear power plant had to be replaced with a new blade by cutting the shroud to remove the cracked blade. This necessitated in situ welding of a new shroud piece with the existing shroud after the blade replacement. The in situ welding of the shroud, a 12% Cr martensitic stainless steel with tempered martensite microstructure, was carried out using gastungsten arc welding and 316L austenitic stainless steel filler metal followed by localized postweld heat treatment at 873 K for 1 h using a specially designed electrical resistance-heating furnace. Mock-up trials were carried out to ensure that sound welds could be made under the constraints present during the in situ repair welding operation. In situ metallography of the repair weld after postweld heat treatment confirmed the adequate tempering of the martensitic structure in the heat-affected zone. Metallurgical investigations carried out in the laboratory on a shroud test-piece that had been welded using the same procedure as employed in the field confirmed the success of the in situ repair operation. The alternate option available was replacing the cracked blade and the shroud piece to which it is riveted with a new one, reducing the height of all the blades attached to the shroud by machining, riveting the blades with reduced height to the new shroud, and, finally, dynamic balancing of the entire turbine after completion of the repair. This option is both time-consuming and expensive. Hence, the successful completion of this repair welding resulted in enormous savings both in terms of reducing the downtime of the plant and the cost of the repair. The turbine has been put back into service and has been operating satisfactorily since December 2000.

Study of restoration by welding of pearlitic ductile cast iron

The objective of this investigation is to study the restoration and/or hardfacing by welding of worn-out parts manufactured from pearlitic ductile cast iron. The work may be divided into two sections. The first deals with studying the weldability of pearlitic ductile cast iron by means of five different types of filler material, namely, pure Ni, Fe–Ni alloy, Ni–Cu alloy, stainless steel and ferritic steel. Particular attention was directed towards the parameters affecting welding by ferritic steel filler metal. This material is attractive because of its low cost. In addition, weldments produced are characterized by excellent colour match, satisfactory hardness and the variety of austenitic transformation products which occur on cooling. Process variables such as preheating, heat input, post weld heat treatment (PWHT), multipass and multilayer techniques, and hardfacing process were studied in detail. Microstructural analysis, microhardness distribution of the melt region (MR) and heat affected zone (HAZ), and nondestructive evaluation were all applied to assess the weldment quality.

Dilution in single pass arc welds

A study was conducted on dilution of single pass arc welds of type 308 stainless steel filler metal deposited onto A36 carbon steel by the plasma arc welding (PAW), gas tungsten arc welding (GTAW), gas metal arc welding (GMAW), and submerged are welding (SAW) processes. Knowledge of the arc and melting efficiency was used in a simple energy balance to develop an expression for dilution as a function of welding variables and thermophysical properties of the filler metal and substrate. Comparison of calculated and experimentally determined dilution values shows the approach provides reasonable predictions of dilution when the melting efficiency can be accurately predicted. The conditions under which such accuracy is obtained are discussed. A diagram is developed from the dilution equation which readily reveals the effect of processing parameters on dilution to aid in parameter optimization.

高純度フェライト系ステンレスクラッド鋼の溶接に関する研究 （第６報） ３０Ｃｒ‐２Ｍｏ鋼肉盛溶接金属の耐食性評価

In the previous report, it was indicated that the usage of 19Cr-2Mo-0.25Zr steel filler metal for the first layer and 30Cr-2Mo steel filler metal for the upper layers respectively was effective to ensure a good weld ductility in the overlay welds of the 30Cr-2Mo steel cladding steel.The corrosion resistance of the overlay welds is also important in the practical use of this material.Therefore, the corrosion resistance in such overlay welds has been investigated in this report.The corrosion resistance was compared with ones of 30Cr-2Mo steel base metal and cladding metal of 30Cr-2Mo clad steel. Measurement of anodic polarization curves and pitting corrosion potentials, grain boundary corrosion test, stress corrosion cracking test and crevice corrosion test were performed.The excellent corrosion resistance, which was almost same level as ones of 30Cr-2Mo steel base metal and cladding metal of 30Cr-2Mo clad steel, was obtained by using 19Cr-2Mo-0.25Zr steel filler metal for the first layer and 30Cr-2Mo steel filler metal for 2nd, 3rd and 4th layers.On the basis of these results, the overlay welding procedure by using 30Cr-2Mo steel filler metal for the upper 3 layer after using 19Cr-2Mo-0.25Zr steel filler metal for the first layer was recommended in order to ensure a good corrosion resistance of the overlay welds.

高純度フェライト系ステンレスクラッド鋼の溶接に関する研究 ＩＶ Ｚｒ添加低Ｃｒ系下盛溶加棒による肉盛溶接部の曲げ延性改善機構

The mechanism of improvement of the bend ductility of the low interstitial ferritic stainless steel overlay welds prepared with zirconium containing low chromium type steel filler metal for the first layer has been investigated.In the previous report, it was indicated that the thickness of chromium carbide, 475°C embrittlement and grain coarsening were factors affecting embrittlement in the overlay welds.Decreasing in chromium content in the first layer of the weld metal contributed to mitigation of 475°C embrittlement and decreasing of the thickness of chromium carbide on the grain boundary in the overlay weld metal. Addition of zirconium to the first layer of the ferritic stainless steel overlay welds made the thickness of chromium carbide decrease and also the grain size refine.These resulted in an excellent weld ductility for the overlay welds.

Performance of Dissimilar Welds in Service

Dissimilar metal welds (DMWs) between austenitic and ferritic steel tubing and piping are commonly employed in high-temperature applications in energy conversion systems. Differences in coefficient of thermal expansion between the two types of steel induce thermal stresses at the welds and local metallurgical changes near the low alloy steel/weld metal interface due to prolonged service at an elevated temperature. These phenomena, together with the differences in creep behavior of the materials joined, render the DMWs more prone to failure than welds between similar steels. This has been reflected in relatively high failure rates in DMWs in certain service applications (e.g., in utility power plant boiler tubing). Typically these welds fail by low ductility cracking in the low alloy steel at, or very close to, the fusion line. A project, sponsored by the Electric Power Research Institute (EPRI) and managed by the Metal Properties Council (MPC), has made significant headway over the last three years in understanding the failure modes and causes involved and in developing methods to assess residual life of DMWs. Welds from service in superheaters and reheater tubes and from laboratory simulation tests were examined to establish metallurgical characteristics and failure modes. Three failure modes were identified: (i) Prior austenite grain boundary cracking in the ferritic steel, one or two grains away from the fusion line; this mode was mainly observed in DMWs made with stainless steel filler metal. (ii) Cracking along the weld interface, which occurred in DMWs made with nickel-base filler metal. (iii) Propagation of cracks initiating from oxide notches formed at the weld outside surface; this mode occurred mainly in thin-walled tubes. Creep damage induced by steady and cyclic loading was found to be the predominant mechanism for damage and failure; therefore a dependence of damage on loading levels and service temperature was established. It was also determined that failure susceptibility in DMWs made with nickel-base filler was strongly influenced by the type of microstructure that formed at the low alloy steel/weld metal interface. The technique developed for estimating the condition and remaining life of DMWs in service involves detailed assessment of loading histories to which the welds are subjected, along with the use of empirical quantitative relationships established from both laboratory and service data. The methodology assumes that damage results from the combined effects of self damage (caused by thermal cycling of materials of different expansion coefficients) and service loadings, including both primary loads (e.g., pressure and deadweight) and secondary, or cyclic, loads due to the constrained thermal expansion of the system as a whole. The technique, Prediction Of Damage In Service (designated PODIS), has been found to adequately predict levels of damage in stainless-based DMWs in service. It is currently being developed further to embrace nickel-based DMWs.

Comportement en fatigue d'assemblages de divers aciers soudés en utilisant un métal d'apport inoxydable

The fatigue properties of heterogeneous welded joints currently considered in heavy steel fabrication have been investigated, in particular butt welds made with or without buttering of a structural steel to a stainless steel and butt or cruciform welds (load carrying welds and non-load carrying welds) of high-strength steels using stainless steel filler metal.12 mm thick plates were butt or cruciform welded. After characterization of the microstructure and residual stresses (by X rays) for each type of joint, tests were conducted on as-welded, ground or flush-ground (butt welds) joints. The characterization of crack initiation sites and the analysis of results made it possible to identify the parameters which appear to play a dominant role in the fatigue performance of these joints.

Creep Behavior of SMA Type 316 Weld Metal With Controlled Residual Elements

Type 316 stainless steel filler metal is a candidate material for welds in piping and other components of Liquid Metal Fast Breeder Reactors. There are few elevated-temperature tensile and creep data for type 316 weld metal in the literature, and reported properties vary widely with material batches or welding process variables. A nuclear components fabricator has developed a type 316 SMA weld that contains controlled amounts of the residual elements (CRE) boron, phosphorus, and titanium, analogous to the chemical element content of an improved type 308 CRE weld that was reported recently. The type 316 CRE weld has good strength and ductility at 649°C in both short-term tensile tests and creep tests lasting up to about 6000 hr. No tendency for cracking along interphase boundaries or substructural boundaries was found in these limited tests.