Effect of ferrite transformation on the tensile and stress corrosion properties of type 316 L stainless steel weld metal thermally aged at 873 K
01 Jul 1995-Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science (Springer-Verlag)-Vol. 26, Iss: 7, pp 1859-1868
TL;DR: In this article, the effect of microstructural changes, due to transformation of delta ferrite, on the associated variations that take place in the tensile and stress corrosion properties of type 316 L stainless steel weld deposits when subjected to postweld heat treatment at 873 K for prolonged periods (up to 2000 hours).
Abstract: This article deals with the effect of the microstructural changes, due to transformation of delta ferrite, on the associated variations that take place in the tensile and stress corrosion properties of type 316 L stainless steel weld deposits when subjected to postweld heat treatment at 873 K for prolonged periods (up to 2000 hours). On aging for short durations (up to 20 hours), carbide/ carbonitride was the dominant transformation product, whereas sigma phase was dominant at longer aging times. The changes in the tensile and stress corrosion behavior of the aged weld metal have been attributed to the two competitive processes of matrix softening and hardening. Yield strength (YS) was found to depend predominantly on matrix softening only, while sig-nificant changes in the ultimate tensile strength (UTS) and the work-hardening exponent, n, occurred due to matrix hardening. Ductility and stress corrosion properties were considerably affected by both factors. Fractographic observations on the weld metal tested for stress-corrosion cracking (SCC) indicated a combination of transgranular cracking of the austenite and interface cracking.
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01 Jan 2011
TL;DR: In this paper, the mechanisms by which microstructural changes occur during welding and the ways they can be minimised are reviewed and discussed. But, the authors do not consider the effects of welding on structural engineering.
Abstract: Welded steels are widely used in structural engineering. However, welding introduces potentially unwelcome microstructural changes, stresses and contaminants which can weaken the metal and make it prone to stress corrosion cracking. This chapter reviews the mechanisms by which these changes occur during welding and the ways they can be minimised.
6 citations
TL;DR: The role of N as an alloying element towards the above failures is discussed in this paper, where various factors that are associated with pitting corrosion and stress corrosion cracking problems are reviewed.
Abstract: Weldments are susceptible zones of localized attack in austenitic stainless steel components, as they are characterized by chemical and microstructural inhomogeneities. No review exists in the literature that brings out the complex and diverse nature of localized corrosion of weldments. This paper, therefore, reviews various factors that are associated with pitting corrosion and stress corrosion cracking problems. In addition, the role of N as an alloying element towards the above failures is discussed.
6 citations
TL;DR: In this article, welded and base material of two types of 316 stainless steel were exposed in either s-CO2 or argon at 550 °C or 750 °C for 1000 h.
Abstract: The supercritical carbon dioxide (s-CO2) Brayton cycle is currently being explored as a replacement for the steam Rankine cycle due to its potential for higher efficiency and lower cycle cost. 316 stainless steel is a candidate alloy for use in s-CO2 up to roughly 600 °C, but the mechanical effects of prolonged exposure of base and welded material in s-CO2 have not been analyzed. The potential for carburization makes this an important concern for the implementation of 316 and similar austenitic stainless steels in the s-CO2 environment. In this study, welded and base material of two types of 316–316L and 316H–were exposed in either s-CO2 or argon at 550 °C or 750 °C for 1000 h. 550 °C s-CO2 exposure yielded a thin (< 1 µm) Cr oxide with occasional nodules of duplex Fe oxide and Fe–Cr spinel that were up to 5 microns thick. However, tensile results from s-CO−2 exposure matched those of 550 °C thermal aging in Ar, indicating that no mechanically detrimental carburization occurred in either 316 variant after 1000 h exposure. Conversely, 750 °C s-CO2 exposure produced roughly 10 × the oxide thickness, with a more substantial Fe oxide (3–5 µm) on the majority of the surface and nodules of up to 40 µm thick. In comparison to aged samples, tensile testing of 750 °C CO2-exposed samples revealed ductility loss attributed to carburization. Projections of 316L performance in s-CO2 indicate that mechanically detrimental carburization—equal to that shown here for 750 °C, 1000 h—will likely be present after 7–14 years of service at 550 °C.
6 citations
TL;DR: In this paper, the authors investigated the stress corrosion cracking (SCC) initiation and propagation behavior of a longitudinally welded 304 austenitic stainless steel in an aqueous solution of 1M NaCl + 05M HCl.
Abstract: The stress corrosion cracking (SCC) initiation and propagation behaviour of a longitudinally welded 304 austenitic stainless steel has been investigated in an aqueous solution of 1M NaCl + 05M HCl The SCC in the base metal and heat affected zone (HAZ) initiates and propagates perpendicular to the applied tensile stress and the cracks initiate and propagate, initially, in the transgranular mode The crack growth mechanism changes into the intergranular mode when the crack size attains a particular value The cracks in the fusion zone are likely to initiate and to propagate in planes inclined at an angle of ~30° to the maximum principal tensile stress Optical microscopy and SEM observations show that the cracks propagate along the boundary of dendrites where δ ferrite exists, indicating that δ ferrite tends to dissolve preferentially In spite of the difference in microstructure, no remarkable difference is found in the kinetics of crack initiation and propagation among the three zones investigat
4 citations
TL;DR: In this article, a 15Cr-15Ni-2.2Mo titanium modified austenitic stainless steel was thermomechanically worked to a strain of 30% in a single stage at temperatures between 873 and 1473 K and at strain rates of 0.15, 1.0, and 100S-l. These strain rates were obtained by working the alloy in a hydraulic press, a rolling mill, and aforge hammer, respectively.
Abstract: A 15Cr-15Ni-2.2Mo titanium modified austenitic stainless steel was thermomechanically worked to a strain of 30% in a single stage at temperatures between 873 and 1473 K and at strain rates of 0.15, 1.0, and 100S-l. These strain rates were obtained by working the alloy in a hydraulic press, a rolling mill, and aforge hammer, respectively. At all strain rates, the yield strength (YS) increased while ductility and stress corrosion cracking (SCC) resistance significantly decreased on thermomechanically working the solution annealed alloy at temperatures below 1173 K. Thereafter, the YS decreased and ductility along with SCC resistance increased substantially towards valuesfor the solution annealed alloy on thermomechanical treatment at and above 1273 K. The highest ductility was obtained on working the alloy at a strain rate of less than 1.0 S-l. However, the best SCC resistance was obtained on working the material at the highest strain rate of l00 S-l. The improvement in SCC resistance has been attr...
3 citations
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TL;DR: In this article, the authors studied the stress corrosion cracking of a sensitized Type 304 stainless steel at room temperature using controlled potentials and two concentrations of sodium thiosulfate.
Abstract: The stress corrosion cracking of a sensitized Type 304 stainless steel has been studied at room temperature using controlled potentials and two concentrations of sodium thiosulfate. In both constant extension rate and constant load tests, the crack velocities attain extremely high values, up to 8 μm s-1. Scratching electrode experiments conducted at various pH values on simulated grain boundary material show that both the crack initiation frequency and crack velocity are closely related to the repassivation rate of the grain boundary material as expected on a dissolution-controlled mechanism; however, the maximum crack velocity at any potential is consistently about two orders of magnitude higher than that predicted from the electrochemical data. Frequent grain boundary separation ahead of the crack tip is thought to occur, but retarded repassivation of the grain boundary material is a necessary feature of the cracking. Effects of strain-generated martensite are discussed.
64 citations
54 citations
TL;DR: In this paper, Potentiostatic and isothermal immersion tests have been used to investigate pitting corrosion in the weld metal of low carbon (<0.03%C) austenitic stainless steels.
Abstract: Potentiostatic and isothermal immersion tests have been used to investigate pitting corrosion in the weld metal of low carbon (<0.03%C) austenitic stainless steels. The experiments were co...
46 citations
TL;DR: In this paper, the microstructure changes and consequent deterioration in the room temperature tensile properties of type 316L stainless steel weld metal when exposed to elevated temperatures (773 to 973 K) for prolonged periods (up to 5000 hours).
Abstract: This paper deals with the microstructural changes and consequent deterioration in the room temperature tensile properties of type 316L stainless steel weld metal when exposed to elevated temperatures (773 to 973 K) for prolonged periods (up to 5000 hours). The microstructure-property correlation derived in this study is based on a variety of techniques: Magne-Gage, electrochemical extraction, X-ray diffraction, tensile testing, and both optical and electron microscopy. It has been established that the amount and morphology of the sigma phase are the key factors in determining the changes in the strength levels, total elongation, and extent of work hardening. The amount and morphology of sigma, in turn, is seen to depend on the relative kinetics of the various transformations, such as dissolution of delta-ferrite, growth of carbides,etc., shape changes in sigma, and the relative stabilities of the phases at the corresponding temperature of aging. The complicated dependence of the tensile properties on the microstrutural changes has been explained with direct quantitative evidence.
44 citations