Effect of Heat Input in Dissimilar Welding on SS304H and T22 to Hardness Distribution and Delta Ferrite Content with GTAW Process

As the design life of new nuclear power plant increases, the austenitic stainless cladding integrity of reactor vessel becomes one of the new concerns. Since 1970’s, there have been some specific recommendations on delta ferrite content of austenitic cladding of reactor vessels and welds. It has been known that the delta ferrite is beneficial for reducing micro-fissure in welds, though the high delta ferrite content increases the probability of embrittlment of welds. In this study, the mechanical and microstructural properties of austenitic weld metals with the limit values of the recommended range (5 ∼ 18 FN) of the delta ferrite control on low alloy steels were characterized by using bending test and scanning electron microscopy. The base metal was ASME Code Sec. II specification SA 508 Gr. 3 Cl. 1 plate and weld materials were EQ308L and EQ309L strips. Four kinds of cladding were deposited with submerged arc welding process on SA508 cl.3 plates. The bending tests were performed through ASME code Sec. IX and the microstructure of fractured surfaces was analyzed by scanning electron microscopy (SEM). In bending tests, there were no fractures except the highest delta ferrite content specimens (28FN). From the SEM observation of fractured surfaces, cracks initiated from the interface between austenite and ferrites phases in the cladding layer and propagated through the continuous interfaces between two phases. For specimens without continuous interfaces of two phases, though the cracks were observed in the interface of phases, the propagation of cracks was not observed. From the test results, continuous interfaces between austenite matrix and ferrite phase provide the path for crack propagation. And the delta ferrite content affects the integrity of cladding of reactor vessel.

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Heat Input Effect on the Microstructure of Twinning-Induced Plasticity (TWIP) Steel Welded Joints Through the GTAW Process

MRS Advances ◽

10.1557/adv.2018.597 ◽

2018 ◽

Vol 3 (64) ◽

pp. 3949-3956

Author(s):

H. Hernández-Belmontes ◽

I. Mejía ◽

V. García-García ◽

C. Maldonado

Keyword(s):

Phase Transformations ◽

Heat Input ◽

Twip Steel ◽

Research Work ◽

Second Phase ◽

Current Electrode ◽

Weld Joints ◽

Average Grain Size ◽

Gtaw Process ◽

Twip Steels

ABSTRACTHigh-Mn Twinning Induced Plasticity (TWIP) steels are an excellent alternative in the design of structural components for the automotive industry. The TWIP steels application allows weight reduction, maintaining the performance of vehicles. Nowadays the research works focused on TWIP steel weldability are relative scarce. It is well-known that weldability is one of the main limitations for industrial application of TWIP steel. The main goal of this research work was studied the effect of heat input on the microstructural changes generated in a TWIP steel microalloyed with Ti. A pair of welds were performed through Gas Tungsten Arc Welding (GTAW) process. The GTAW process was carried out without filler material, using Direc Current Electrode Negative (DCEN), tungsten electrode EWTh-2 and Ar as shielding gas. The microstructure and average grain size in the fusion (FZ) and heat affected zone (HAZ) were determined by light optical metallography (LOM). Elements segregation in the FZ was evaluated using point and elemental mapping chemical analysis (EPMA) by Scanning Electron Microscopy and Electron Dispersive Spectroscopy (SEM-EDS). Phase transformations were evaluated using X-ray diffraction (XRD). Finally, the hardness were measured by means of Vickers microhardness testing (HV500). The results show that the FZ is characterized by a dendritic solidification pattern. Meanwhile, the HAZ presented equiaxed grains in both weld joints. On the other hand, the TWIP-Ti steel weldments did not present austenite phase transformations. Nevertheless, the FZ exhibited variations in the chemical elements distribution (Mn, Al, Si and C), which were higher as the heat input increases. Finally, the heat input reduced the microhardness of TWIP-Ti steel weld joints. Although post-welding hardness recovery was detected, which is associated with precipitation of Ti second-phase particles.

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Improving the Corrosion Resistance of AISI 316L Steel for Semiconductor Piping by Controlled Delta-Ferrite Content

Korean Journal of Metals and Materials ◽

10.3365/kjmm.2022.60.1.46 ◽

2022 ◽

Vol 60 (1) ◽

pp. 46-52

Author(s):

Young Woo Seo ◽

Chan Yang Kim ◽

Bo Kyung Seo ◽

Won Sub Chung

Keyword(s):

Stainless Steel ◽

Corrosion Resistance ◽

316L Stainless Steel ◽

Sem Analysis ◽

Ferrite Content ◽

Aisi 316L ◽

Delta Ferrite ◽

Aisi 316L Stainless Steel ◽

316L Steel ◽

The Difference

This study evaluated changes in delta-ferrite content depending on the preheating of AISI 316L stainless steel. We also determined the reasons for the variation in delta-ferrite content, which affects corrosion resistance. Changes in delta-ferrite content after preheating was confirmed using a Feritscope, and the microstructure was analyzed using optical microscopy (OM). We found that the delta-ferrite microstructure size decreased when preheating time was increased at 1295 oC, and that the delta-ferrite content could be controlled through preheating. Potentiodynamic polarization test were carried out in NaCl (0.5 M) + H2SO4 (0.5 M) solution, and it was found that higher delta-ferrite content resulted in less corrosion potential and passive potential. To determine the cause, an analysis was conducted using energy-dispersive spectroscopy (EDS), which confirmed that higher delta-ferrite content led to weaker corrosion resistance, due to Cr degradation at the delta-ferrite and austenite boundaries. The degradation of Cr on the boundaries between austenite and delta-ferrite can be explained by the difference in the diffusion coefficient of Cr in the ferrite and austenite. A scanning electron microscopy (SEM) analysis of material used for actual semiconductor piping confirmed that corrosion begins at the delta-ferrite and austenite boundaries. These results confirm the need to control delta-ferrite content in AISI 316L stainless steel used for semiconductor piping.

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Effect of weld cooling rate on delta-ferrite content of austenitic weld metals

Journal of Materials Science Letters ◽

10.1007/bf00721800 ◽

1990 ◽

Vol 9 (6) ◽

pp. 675-677 ◽

Cited By ~ 16

Author(s):

K. Prasad Rao

Keyword(s):

Cooling Rate ◽

Ferrite Content ◽

Delta Ferrite ◽

Weld Metals

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Experimental review of thermal analysis of dissimilar welds of High-Strength Steel

REVIEWS ON ADVANCED MATERIALS SCIENCE ◽

10.1515/rams-2019-0004 ◽

2019 ◽

Vol 58 (1) ◽

pp. 38-49 ◽

Cited By ~ 2

Author(s):

Francois Njock Bayock ◽

Paul Kah ◽

Belinga Mvola ◽

Pavel Layus

Keyword(s):

Heat Treatment ◽

Thermal Analysis ◽

Heat Input ◽

Power Plants ◽

Welding Process ◽

Postweld Heat Treatment ◽

High Strength ◽

Dissimilar Welding ◽

Dissimilar Welds ◽

Wide Range

Abstract Dissimilar welding offers exiting benefits for a wide range of engineering applications, such as automotive bodies, piping systems of nuclear power plants, health equipment. The main advantages of dissimilarwelding applications areweight reductions, lower costs, unique properties combinations, and improved energy-efficiency. The properties of dissimilar weld depend on the type of welding process used, the accuracy of the process parameters control, the characteristics of the base metal and the heat treatment procedures. The current study reviews the scientific literature on the topic of thermal analysis of dissimilar high-strength steels (HSS) welding. The review of experimental data was carried out to analyze the variable heat input effect on dissimilar welds. The results indicate the welds mechanical properties irregularity and reduction in toughness and tensile strength due to uneven changes in the microstructure. Furthermore, postweld heat treatment (PWHT) often resulted in the formation of intermetallic compounds whose properties are dependent on the duration of treatment. The research results can be used to optimize the heat input of the HSS welding process.

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Hot-Deformation Behavior and Hot-Processing Maps of AISI 410 Martensitic Stainless Steel

High Temperature Materials and Processes ◽

10.1515/htmp-2015-0145 ◽

2016 ◽

Vol 35 (9) ◽

pp. 929-940

Author(s):

Rong-Sheng Qi ◽

Miao Jin ◽

Bao-Feng Guo ◽

Xin-Gang Liu ◽

Lei Chen

Keyword(s):

Stainless Steel ◽

High Temperatures ◽

Hot Deformation ◽

Martensitic Stainless Steel ◽

Ferrite Content ◽

Optimum Process ◽

Processing Maps ◽

Delta Ferrite ◽

Deformation Behaviors ◽

Measured Flow

AbstractThe compressive deformation behaviors of 410 martensitic stainless steel were investigated on a Gleeble-1500 thermomechanical simulator, and the experimental stress–strain data were obtained. The measured flow stress was corrected for friction and temperature. A constitutive equation that accounts for the influence of strain was established, and the hot-processing maps at different strain were plotted. The microstructure evolution of the hot-deformation process was studied on the basis of microstructural observations at high temperatures. Phase-transformation experiments on 410 steel were conducted at high temperatures to elucidate the effects of temperature on the delta-ferrite content. The initial forging temperature and optimum process parameters were obtained on the basis of the processing map and the changes in the delta-ferrite content at high temperatures.

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