The influence of fiber laser groove distance on microstructure and mechanical properties of brazing Ti-6Al-4V alloy to 17-4PH martensitic stainless steel dissimilar joint

Quenching and partitioning (Q&P) treatment has been proven effective in manufacturing advanced high strength steels with high content of retained austenite, showing the improved balance of high strength and sufficient ductility. This method has been very well elaborated for carbon steel processing over the last two decades. Though it can also be potentially applied for processing other steel families, this has been scarcely studied. This article focuses on the effect of chemistry and heat treatment parameters on the microstructure and properties of Q&P treated martensitic stainless steels. Three different martensitic stainless steels with different contents of alloying elements are subjected to Q&P processing with varying quenching temperature or partitioning temperature and partitioning time. The tensile behavior of the Q&P treated steels is studied. The effect of chemistry and Q&P treatment parameters on the microstructure and tensile properties is analyzed. The effect of plastic deformation on the microstructure of the Q&P treated steels is also investigated. It is demonstrated that the Q&P treated martensitic stainless steels can show a good combination of enhanced strength and sufficient tensile ductility. Their uniform elongation increases with the increasing volume fraction of retained austenite due to the transformation induced plasticity (TRIP) effect. The ability of the martensitic matrix to accumulate plastic deformation also plays an important role. The Q&P process - microstructure - property relationship is discussed.

A series of studies has been carried out to examine the weldability and properties of dissimilar steel joints using martensitic and austenitic stainless steels F6NM (OCr13Ni4Mo) and AISI 347, respectively. This type of joint requires good mechanical properties, corrosion resistance, and a stable magnetic permeability in addition to a good weldability. Weldability tests include weld thermal simulation of the martensitic steel to investigate the influence of weld thermal cycles and post-weld heat treatment (PWHT) on the microstructure and mechanical properties of the heat affected zone (HAZ); implant testing to examine the tendency for cold cracking of martensitic steel; and rigid restraint testing to determine hot crack susceptibility of the multipass dissimilar steel joints. The simulation results indicated that the toughness of the martensitic steel HAZ did not change significantly after the weld thermal cycles. The implant test results indicated that welds produced using nickel based filler show...

Microstructure and Mechanical Properties of Martensitic Stainless Steel 6Cr15MoVn

Martensitic stainless steels are widely used in industries due to their high strength and good corrosion resistance performance. Precipitation-hardened (PH) martensitic stainless steels feature very high strength compared with other stainless steels, around 3-4 times the strength of austenitic stainless steels such as 304 and 316. However, the poor workability due to the high strength and hardness induced by precipitation hardening limits the extensive utilization of PH stainless steels as structural components of complex shapes. Laser powder bed fusion (L-PBF) is an attractive additive manufacturing technology, which not only exhibits the advantages of producing complex and precise parts with a short lead time, but also avoids or reduces the subsequent machining process. In this review, the microstructures of martensitic stainless steels in the as-built state, as well as the effects of process parameters, building atmosphere, and heat treatments on the microstructures, are reviewed. Then, the characteristics of defects in the as-built state and the causes are specifically analyzed. Afterward, the effect of process parameters and heat treatment conditions on mechanical properties are summarized and reviewed. Finally, the remaining issues and suggestions on future research on L-PBF of martensitic precipitation-hardened stainless steels are put forward.

Experimental investigation on microstructure, mechanical properties, and residual stresses of dissimilar welded joint of martensitic P92 and AISI 304L austenitic stainless steel

Microstructure & mechanical properties of dissimilar material joints between T91 martensitic & S304H austenitic steels using different filler wires

Abstract: Hydroturbine blades in hydroelectric power plants are subjected to erosion. Currently these blades are made of 13/4 martensitic stainless steel (ASTM grade A743). This steel suffers from several maintenance and welding related problems. Nitronic steels are being considered as an alternative to martensitic stainless steels since they have good weldability. In present work, erosive behaviour of 13/4 Martensitic and Nitrogen alloyed austenitic stainless steel (23/8N steel) has been studied. Cavitation erosion tests were carried out in distilled water at 20 KHz frequency at constant amplitude. Microstructure of eroded surface, mechanical properties and erosion rate were characterized. It was observed that 23/8N steel possesses excellent resistance to erosion in comparison to 13/4 martensitic steels. 23/8N steel showed good hardness coupled with high tensile toughness and work hardening ability, leading to improved erosion resistance.

AISI 422 martensitic stainless steel with superior hightemperature performance (oxidation resistance and strength) is under evaluation for replacing current heavy-duty piston crown materials, AISI 4140 martensitic steel and microalloyed steel (MAS) 38MnSiVS5, to fabricate a multimaterial piston (Refs. 1, 2). This multimaterial piston concept further improved power density and fuel economy by allowing heavyduty diesel engines to operate at higher temperatures and pressures (Ref. 3). Joining AISI 422 steel piston crowns with AISI 4140 steel piston skirts is a key manufacturing step for this multimaterial piston. However, the significant differences in strength, elevated temperature flow stress, alloy chemistry, and temper resistance between these two martensitic steels cause some weldability issues (cracking) and metallurgical challenges (alloying element migration/segregation) when using conventional fusion-based welding processes (Refs. 4–6). Rotary inertia friction welding (RIFW), a solid-state welding process, has been the preferred method to join 4140 crowns to 4140 skirts (and MAS crowns to MAS skirts) in high-volume production of current heavy-duty diesel engine pistons. It has been used to join these two materials with relatively comparable alloy chemistry to fabricate pistons with MAS skirts and 4140 crowns. Meanwhile, RIFW has also been a preferred method of dissimilar metal welding (Refs. 7, 8). However, RIFW of dissimilar high-strength martensitic steels has yet to be widely pursued. The interfacial microstructure complexities created by the thermomechanical process and highly nonequilibrium phase transformations during RIFW are a significant challenge for understanding and predicting their joining behavior and have not been reported in detail. In this work, defect-free AISI 422 steel-AISI 4140 multimaterial pistons were successfully fabricated using the RIFW process. The interfacial microstructure and mechanical properties of dissimilar 422/4140 steel RIFW in the as-welded condition were experimentally studied in detail. The results provide critical baseline information for understanding RIFW mechanisms and guiding subsequent postweld heat treatment (PWHT) practice.

CO2 is known as an acid gas and it is commonly found in oil and gas production or in gas lift injection systems used to transport oil to the surface. During the gas injection operation, the CO2 gas in contact with completion fluid promotes the decreasing the pH value. This acidizing promotes a more corrosive environment for martensitic steels used in oil and gas wells, such as 1%Cr low alloy steel, 13%Cr martensitic stainless steel and Super 13%Cr martensitic stainless steel. Electrochemical tests were carried out in static conditions to verify the behavior of martensitic steels in completion fluid, saturated with CO2 and without CO2, at room temperature and at 60°C. According to anodic polarization curves, 1%Cr low alloy steel presented active dissolution in all tested conditions. 13%Cr and SCr13% stainless steels presented passive behavior nearby open circuit potential for both temperatures. Gravimetric tests were carried under static conditions in an autoclave at 50 psi partial pressure of CO2 and at 60° C for 1%Cr low alloy steel, 13%Cr martensitic stainless steel and SCr13% stainless steel, where SCr13% stainless steel presented lower corrosion rate, when compared to 13%Cr and 1%Cr steels. It has been observed that oxygen is an important experimental factor that affects the behavior of martensitic steels during anodic polarization.

Microstructure, strain-rate sensitivity, work hardening, and fracture behavior of laser additive manufactured austenitic and martensitic stainless steel structures

Degradation mechanisms in martensitic stainless steels: Wear, corrosion and tribocorrosion appraisal

The corrosion behavior and pitting corrosion resistance of 439 ferritic, 301 austenitic, 420 martensitic and S32101 duplex stainless steel in 2 M H2SO4 at 0–1.5%NaCl concentrations were studied through potentiodynamic polarization measurement and optical microscopy analysis. Experimental observation shows that corrosion rate, pitting potential and passivation potential are influenced by the Cl− ion concentration, alloy composition and metallurgical properties of the steels. 439 ferritic steel had significantly the lowest corrosion rate and highest pitting corrosion resistance. Surface morphology showed no visible change from comparison of steel samples before and after corrosion. The corrosion rates of the duplex steel were comparably lower than the austenitic and martensitic steel; however, it had the least pitting corrosion resistance with respect to Cl− ion concentration. The martensitic steel despite quenching heat treatment for improved corrosion resistance had the highest corrosion rate values. The surface morphology of the steel samples except 439 ferritic steel showed the presence of micro- and macro-pits, and visible surface deterioration.

<div class="section abstract"><div class="htmlview paragraph">The recent demand for power generation capability has raised the operating temperature of the power plants in the range of 600°C. High operating temperature leads to material degradation or reduced lifespan of boilers, which necessitates the analysis of the high-temperature behavior of welded joints of power plant boilers for a long lifespan and improved efficiency. Gr91 martensitic and SS304 austenitic stainless steel are identified as the primary piping material for these boilers. The boiler piping involves similar weld joints (Gr91/Gr91 and SS304/SS304) and dissimilar weld joints (SS304/Gr91) known as transition joints. These joints are exposed to high temperatures for a long duration during their service and it is therefore necessary to evaluate the high-temperature behavior of these weld joints. The hot tensile test is a short-term high-temperature test that serves as a valuable tool for analyzing the high-temperature behavior of the welds. In this investigation, by using the shielded metal arc welding (SMAW) process, similar joints of Gr91/Gr91 martensitic steel, SS304/SS304 were made using matching electrodes, and dissimilar joints between Gr91/SS304 were welded using INCONEL electrode. The joints were subjected to hot tensile test at temperatures of 550°C, 600°C, and 650°C. The stress–strain behavior of the weld joints at elevated temperatures was studied, compared with each other, and reported.</div></div>

Effect of δ-ferrite on the H-trapping behavior in the martensitic stainless steel

The discovery of the first petroleum off-shore fields 30 meters below sea level in the Brazilian coast in 1968 stimulated the development of new technology for oil extraction and production in increasing water deepness. Outstanding levels such as 6000 meters were expected for oil extraction in the offshore pre-salt reservoirs in the 2010s, which demanded a large amount of material, raising costs to extremely high levels. So, considerable new research efforts are being directed towards the development of new martensitic steels, with improved properties as a lower cost option for such application. In the present work information is gathered about recent developments on new martensitic stainless steels capable of withstanding severe conditions of operation and exploration of petroleum in marine platforms. These materials must present adequate mechanical strength and corrosion resistance in these conditions. With this purpose such information, based on articles and patents published in international databases since the onset of the 21st century (2001) until 2012, is compiled and analyzed in this review article. Keywords: Stainless steels, corrosion, microstructure, mechanical properties, oil and gas, seawater, marine environment.