scholarly journals Optimization of post weld heat treatment cycle of fiber laser welded bainitic steel

2020 ◽  
Vol 184 ◽  
pp. 01039
Author(s):  
VSM Ramakrishna R ◽  
JP Gautam
Keyword(s):  
Heat Treatment ◽  
Fiber Laser ◽  
Retained Austenite ◽  
Treatment Cycle ◽  
Bainitic Ferrite ◽  
Welding Process ◽  
Fusion Welding ◽  
Bainitic Steel ◽  
Heat Treatment Cycle ◽  
Weld Heat

Automobile industry has always been in look out for advanced materials that would account for greater crash resistance, high fatigue strength, optimum ductility and longer service life despite heavy mechanical loads applied on these engine components. These critical requirements are met through maintaining the complex microstructures and optimum phase constituents. The retention of microstructural constituents has always been a key parameter while fabricating these advanced automobile materials by fusion welding process. Carbide free bainitic steels are emerging out to be the candidate materials for automobile applications. Owing to their microstructure consisting fine bainitic ferrite laths that are interwoven with retained austenite in their lath boundaries. The fine Bainitic laths provide enough strength and the retained austenite phase facilitates the desired ductility. The current paper critically discusses the microstructural and microhardness variation across the zones during Fiber Laser welding of bainitic steel sheets. Keeping the phase transformations during welding in view, post weld heat treatments were undertaken. The welded steel was austenitized at 820 OC, rapidly cooled to 390 OC, and soaked at different durations before furnace cooing. The microstructure variation and microhardness profiling were done at all these heat treatment conditions. Basing on the analyses, the heat treatment cycle has been optimized.

Microstructure and mechanical properties of a high-carbon bainitic steel containing Si/Al by different heat treatment processes

2020 ◽  
Vol 10 (11) ◽  
pp. 1932-1940
Author(s):  
Sufyan Naseem ◽  
Enzuo Liu ◽  
Xuefei Huang ◽  
Weigang Huang
Keyword(s):  
Mechanical Properties ◽  
Heat Treatment ◽  
Electron Microscope ◽  
Retained Austenite ◽  
Bainitic Ferrite ◽  
Bainitic Steel ◽  
Boundary Misorientation ◽  
Treatment Processes ◽  
Microstructure And Mechanical Properties ◽  
The Impact

The present study aims to investigate the microstructure and mechanical properties of 0.79 C wt% bainitic steel containing Si and Al by three heat treatment processes: austempering and tempering (B-T), two-step austempering (2S-A) and the austempering-quenching-partitioning (AQP). The optical microscope (OM), scanning electron microscope (SEM), X-ray diffraction (XRD), transmission electron microscope (TEM) and electron backscatter diffraction (EBSD) were employed to analyze the microstructure of samples. The results demonstrate that the sample subjected to the AQP process exhibited a multiphase microstructure with martensite, filmy retained austenite (RA) and fine bainitic laths. The AQP sample evidenced a high tensile strength of 1705 MPa, yield strength of 1254 MPa, a better total elongation of 16.6%, product of strength and elongation (PSE) of 28 GPa% and the impact toughness of 33 J among all heat treatment processes. The higher strength and toughness could be ascribed to the fine bainitic ferrite as well as an appropriate amount of filmy retained austenite. A fraction of martensite that was formed during the quenching step at 110 °C possibly divided the untransformed austenite into small areas, which could refine the microstructure. EBSD analysis showed that the AQP sample exhibited a higher proportion (64%) of boundary misorientation angle greater than 15° than that of the 2S-A. These high angle boundaries can improve the toughness of steel.

scholarly journals Influence of post weld heat treatment on tensile properties of cold metal transfer (CMT) arc welded AA6061-T6 aluminium alloy joints

2019 ◽  
Vol 28 (1) ◽  
pp. 135-145 ◽  
Author(s):  
Addanki Ramaswamy ◽  
Sudersanan Malarvizhi ◽  
Visvalingam Balasubramanian
Keyword(s):  
Heat Treatment ◽  
Tensile Properties ◽  
Gas Metal Arc Welding ◽  
Weight Ratio ◽  
Welding Process ◽  
Metal Transfer ◽  
Post Weld Heat Treatment ◽  
Cold Metal Transfer ◽  
Cold Metal ◽  
Weld Heat

AbstractAluminium alloys of 6xxx series are widely used in the fabrication of light weight structures especially, where high strength to weight ratio and excellent weld-ability characteristics are desirable. Gas metal arc welding (GMAW) is the most predominantly used welding process in many industries due to the ease of automation. In this investigation, an attempt has been made to identify the best variant of GMAW process to overcome the problems like alloy segregation, precipitate dissolution and heat affected zone (HAZ) softening. Thin sheets of AA6061-T6 alloy were welded by cold metal transfer (CMT) and Pulsed CMT (PCMT). Among the two joints, the joint made by PCMT technique exhibited superior tensile properties due to the mechanical stirring action in the weld pool caused by forward and rearward movement of the wire along with the controllable diffusion rate at the interface caused by shorter solidification time. However, softening still exists in the welded joints. Further to increase the joint efficiency and to minimize HAZ softening, the joints were subjected to post weld heat treatment (PWHT). Approximately 10% improvement in the tensile properties had been observed in the PWHT joints due to the nucleation of strengthening precipitates in the weld metal and HAZ.

scholarly journals Tempering and Austempering of Double Soaked Medium Manganese Steels

2021 ◽  
Vol 7 ◽  
Author(s):  
Alexandra Glover ◽  
John G. Speer ◽  
Emmanuel De Moor
Keyword(s):  
Heat Treatment ◽  
Tensile Strength ◽  
Ultimate Tensile Strength ◽  
Retained Austenite ◽  
Bainitic Ferrite ◽  
Total Elongation ◽  
Uniaxial Tensile ◽  
Present Contribution ◽  
Uniaxial Tensile Testing ◽  
Manganese Steels

The addition of a tempering or austempering step to the double soaking of a 0.14C–7.17Mn (wt pct) steel was investigated in the present contribution. The double soaking heat treatment is a two-step intercritical annealing heat treatment, which generates microstructures of athermal martensite, retained austenite and ferrite when applied to medium manganese steels. Microstructures following double soaking and (aus)tempering contained a combination of retained austenite, athermal or tempered martensite, and blocky or bainitic ferrite. X-ray diffraction, dilatometry and transmission Kikuchi diffraction were utilized to investigate microstructural changes which occurred during tempering or austempering. The resulting mechanical properties were measured using uniaxial tensile testing. The double soaking plus tempering heat treatment was shown to generate an ultimate tensile strength of 1,340 MPa in combination with 28 pct total elongation while the double soaking plus austempering heat treatment resulted in an ultimate tensile strength of 1,675 MPa and total elongation of 22 pct. Overall, both novel heat treatments produced a combination of strength and ductility desired for the third generation of advanced high strength steels.

Isothermal Transformation, Microstructure and Mechanical Properties of Ausformed Low-Carbon Carbide-Free Bainitic Steel

2018 ◽  
Vol 941 ◽  
pp. 329-333 ◽  
Author(s):  
Jiang Ying Meng ◽  
Lei Jie Zhao ◽  
Fan Huang ◽  
Fu Cheng Zhang ◽  
Li He Qian
Keyword(s):  
Mechanical Properties ◽  
Retained Austenite ◽  
Volume Fraction ◽  
Bainitic Ferrite ◽  
Isothermal Transformation ◽  
Bainitic Transformation ◽  
Isothermal Treatment ◽  
Bainitic Steel ◽  
Low Carbon ◽  
Microstructure And Mechanical Properties

In the present study, the effects of ausforming on the bainitic transformation, microstructure and mechanical properties of a low-carbon rich-silicon carbide-free bainitic steel have been investigated. Results show that prior ausforming shortens both the incubation period and finishing time of bainitic transformation during isothermal treatment at a temperature slightly above the Mspoint. The thicknesses of bainitic ferrite laths are reduced appreciably by ausforming; however, ausforming increases the amount of large blocks of retained austenite/martenisite and decreases the volume fraction of retained austenite. And accordingly, ausforming gives rise to significant increases in both yield and tensile strengths, but causes noticeable decreases in ductility and impact toughness.

Synthesis of Si3N4 Powder by Thermal Decomposition of SI(NH)2

1992 ◽  
Vol 287 ◽  
Author(s):  
Silvia Ampuero ◽  
Paul Bowen ◽  
Terry A. Ring
Keyword(s):  
Heat Treatment ◽  
Thermal Decomposition ◽  
Thermal Treatment ◽  
Treatment Cycle ◽  
Heat Treatment Cycle ◽  
Si3n4 Powder

ABSTRACTA fine white α-Si3N4 powder has been produced by the thermal decomposition of the coprecipitation product of the reaction between SiC14 and NH3. The Cl content, due to a reaction between Si(NH)2 and the NH4Cl by-product during the thermal treatment of the coprecipitate, has been reduced by using an isothermal step at ≈ 250°C in the heat treatment cycle.

Engineering Critical Assessment of Post Weld Heat Treatment for Full-Encirclement Tees Greater Than 1.25 Inches

2019 ◽  
Author(s):  
Kolton Landreth ◽  
Qi Li ◽  
Raghav Marwaha
Keyword(s):  
Heat Treatment ◽  
Residual Stresses ◽  
Welding Process ◽  
Post Weld Heat Treatment ◽  
Critical Assessment ◽  
Material Strength ◽  
Mechanical Reinforcement ◽  
Element Analysis ◽  
Pipeline Design ◽  
Weld Heat

Abstract Full-encirclement split tee fittings for hot tapping and plugging (HT&P) wrap completely around the pipeline and are welded in place. The welded joint provides mechanical reinforcement of the pipe and branch. When full-encirclement hot tap tees are welded to pipelines 24 inches in diameter or larger, the header must often be at least 1.25 inches thick to pass the required calculations for reinforcement. This means the joint will require post weld heat treatment (PWHT) according to ASME B31.8 and CSA Z662. However, PWHT can be extremely dangerous and impractical, potentially elevating temperature to the point where material strength of the pressurized pipeline is compromised. An engineering critical assessment per ASME FFS-1/API 579 indicated PWHT may not be required for a full-encirclement hot tap tee over 1.25 inches thick. Specifically, research showed that the residual stresses developed during the welding process may not limit the design of a full-encirclement tee or lead to shorter pipeline design life. This paper illustrates how a “more rigorous analysis” per paragraph 802.2.2[b] of ASME B31.8 and paragraph 4.3.12.2 of CSA Z662 may help operators avoid the PWHT requirement. It discusses the finite element analysis (FEA) simulations researchers used to induce residual stresses in a carbon steel fitting. The residual stresses induced in the fitting were used as initial condition for plastic collapse and fatigue evaluations.

scholarly journals Influence of Prior Martensite on Bainite Transformation, Microstructures, and Mechanical Properties in Ultra-Fine Bainitic Steel

Materials ◽  
2019 ◽  
Vol 12 (3) ◽  
pp. 527 ◽  
Author(s):  
Hui Guo ◽  
Xianying Feng ◽  
Aimin Zhao ◽  
Qiang Li ◽  
Jun Ma
Keyword(s):  
Mechanical Properties ◽  
Retained Austenite ◽  
Bainitic Ferrite ◽  
Growth Direction ◽  
Bainitic Transformation ◽  
Bainitic Steel ◽  
Bainite Transformation ◽  
Multiphase Microstructure ◽  
Microstructures And Mechanical Properties ◽  
The Impact

A multiphase microstructure comprising of different volume fractions of prior martensite and ultra-fine bainite (bainitic ferrite and retained austenite) was obtained by quenching to certain temperatures, followed by isothermal bainitic transformation. The effect of the prior martensite transformation on the bainitic transformation behavior, microstructures, and mechanical properties were discussed. The results showed that the prior martensite accelerated the subsequent low-temperature bainite transformation, and the incubation period and completion time of the bainite reaction were significantly shortened. This phenomenon was attributed to the enhanced nucleation ratio caused by the introduced strain in austenite, due to the formation of prior martensite and a carbon partitioning between the prior martensite and retained austenite. Moreover, the prior martensite could influence the crystal growth direction of bainite ferrite, refine bainitic ferrite plates, and reduce the dimension of blocky retained austenite, all of which were responsible for improving the mechanical properties of the ultra-fine bainitic steel. When the content of the prior martensite reached 15%, the investigated steels had the best performance, which were 1800 MPa and 21% for the tensile strength and elongation, respectively. Unfortunately, the increased content of the prior martensite could lead to a worsening of the impact toughness.

Effect of the FCAW Welding Process and Post Weld Heat Treatment on the Properties and Microstructure of the Weld Joints of Heat Treated 4330V Steel

2015 ◽  
Vol 809-810 ◽  
pp. 437-442
Author(s):  
Jacek Górka ◽  
Michał Miłoszewski
Keyword(s):  
Mechanical Properties ◽  
Heat Treatment ◽  
Weld Metal ◽  
Heat Input ◽  
Large Diameter ◽  
Welding Process ◽  
Post Weld Heat Treatment ◽  
High Toughness ◽  
Interpass Temperature ◽  
Weld Heat

4330V is a high strength, high toughness, heat treatable low alloy steel for application in the oil, gas and aerospace industries. It is typically used for large diameter drilling parts where high toughness and strength are required. The research describes the effect of preheat temperature, interpass temperature, heat input, and post weld heat treatment on strength, hardness, toughness, and changes to microstructure in the weld joint. Welding with the lower heat input and no post weld heat treatment resulted in optimal mechanical properties in the weld metal. Austempering at 400 °C resulted in optimal mechanical properties in the HAZ. Increasing preheat and interpass temperature from 340 °C to 420 °C did not improve Charpy V-notch values or ultimate tensile strength in the weld metal or heat affected zones. The higher temperature increased the width of the heat affected zone. Austempering at 400 °C reduced HAZ hardness to a level comparable to the base metal. Both tempering and austempering at 400 °C for 10 hours reduced toughness in the weld metal.

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