دنیای جوشکاری

دنیای جوشکاری

دنیایی از مطالب جوشکاری و بازرسی فنی
دنیای جوشکاری

دنیای جوشکاری

دنیایی از مطالب جوشکاری و بازرسی فنی

اثر هیدروژن بر روی تافنس شکست فلز جوش در فولاد زنگ نزن دوفازی


Hydrogen influence on fracture toughness of the weld metal in

super duplex stainless steel (UNS S32750) welded with two different heat input

اثر هیدروژن بر روی تافنس شکست فلز جوش در فولاد زنگ نزن دوفازی

(UNS S32750) جوشکاری شده با دو حرارت ورودی مختلف

ABSTRACT

The super duplex stainless steels have a microstructure composed by two phases, ferrite (α) and austenite (γ). This dual microstructure improves simultaneously the mechanical and corrosion resistance properties. However, the welding of these steels is often a critical operation. The present work evaluated the fracture toughness through critical tip open displacement (CTOD) tests of welded joints, with two different heat input, 1.1 kJ mm−1 and 2.0 kJ mm−1. The steel used was a super duplex stainless steel (UNS S32750) in presence of hydrogen. The CTOD tests (according BS 7448-1 and BS 7448-2 standards) were performed in air and under different times of hydrogenation. The procedure of hydrogenation has been performed using cathodic potential of −1400 mVSCE by 96 and 360 h. The microstructural analysis allowed to determine relevant aspects (α/γ balance, inter austenitic spacing and γ morphology) and to compare with CTOD results. The results showed strong evidence that the reductions of CTOD values is related to differences in the γ2 morphologies. Another important result was the high statistic dispersion in the measures of austenitic spacing, according DNV RP F112-08, which implies in low reliability of using this standard in presence of high anisotropy. The paper also aims to discuss and evaluate which is the best approach to hydrogenated duplex stainless steels: linear elastic fracture mechanics or elasto plastic fracture mechanics.


  

ادامه مطلب ...

اتصالات بین فولاد زنگ نزن سوپر دو فازی و فولاد HSLA

Effect of heat input on microstructure and mechanical properties of

dissimilar joints between super duplex stainless steel and high strength low alloy steel

اثر حرارت ورودی بر ریزساختار و خواص مکانیکی اتصالات غیر مشابه بین

فولاد زنگ نزن سوپر دو فازی و فولاد کم آلیاژ با استحکام بالا

ABSTRACT

In the present study, microstructure and mechanical properties of UNS S32750 super duplex stainless steel (SDSS)/API X-65 high strength low alloy steel (HSLA) dissimilar joint were investigated. For this purpose, gas tungsten arc welding (GTAW) was used in two different heat inputs: 0.506 and 0.86 kJ/mm. The microstructures investigation with optical microscope, scanning electron microscope and X-ray diffraction showed that an increase in heat input led to a decrease in ferrite percentage, and that detrimental phases were not present. It also indicated that in heat affected zone of HSLA base metal in low heat input, bainite and ferrite phases were created; but in high heat input, perlite and ferrite phases were created. The results of impact tests revealed that the specimen with low heat input exhibited brittle fracture and that with high heat input had a higher strength than the base metals.

 

  

ادامه مطلب ...

خوردگی حفره‌ای در جوش فلزات فولاد ضد زنگ سوپر دوبلکس

Effects of Heat Input on Pitting Corrosion in

Super Duplex Stainless Steel Weld Metals

اثر حرارت ورودی بر خوردگی حفره‌ای در جوش فلزات فولاد ضد زنگ سوپر دوبلکس

ABSTRACT

Due to the difference in reheating effects depending on the heat input of subsequent weld passes, the microstructure of the weld metal varies between acicular type austenite and a mixture of polygonal type and grain boundary mixed austenite. These microstructural changes may affect the corrosion properties of duplex stainless steel welds. This result indicates that the pitting resistance of the weld can be strongly influenced by the morphology of the secondary austenite phase. In particular, the ferrite phase adjacent to the acicular type austenite phase shows a lower Pitting Resistance Equivalent (PRE) value of 25.3, due to its lower chromium and molybdenum contents, whereas the secondary austenite phase maintains a higher PRE value of more than 38. Therefore, it can be inferred that the pitting corrosion is mainly due to the formation of ferrite phase with a much lower PRE value.

 

  

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جوشکاری آلیاژ Al–Cu–Mg–Mn به روش تیگ

Effect of welding parameters on the solidification microstructure

of autogenous TIG welds in an Al–Cu–Mg–Mn alloy

تاثیر پارامترهای جوشکاری بر میکروساختار انجمادی جوش های TIG

بدون ماده پر کننده در یک آلیاژ Al–Cu–Mg–Mn

ABSTRACT


The weld metal microstructures of autogenous TIG welds have been investigated for a range of welding conditions using an Al–Cu–Mg–Mn alloy. It was found that a combination of high welding speeds and low power densities provide the thermal conditions required for the nucleation and growth of equiaxed grains in the weld pool, providing heterogeneous nucleation sites are available. The most likely origin of the nucleants is from a combination of dendrite fragments and TiB2 particles that survive in the weld pool. The finest microstructure was observed in the centre of the weld and is attributed to the higher cooling rates which operate along the weld centreline. Composition profiles across the dendrite side arms were measured in the TEM and were found to follow a Scheil type segregation behaviour where there is negligible back diffusion in the solid. The measured core concentration of the dendrite side arms was found to rise with increasing welding speed and was attributed to the formation of significant undercoolings ahead of the primary dendrite tip, which enriched the liquid surrounding the dendrite side arms.

 

  

ادامه مطلب ...

اثر ارتعاش مکانیکی روی ریزساختار ماده‎ی جوشکاری

Studies on the Effect of Mechanical Vibration on 

the Microstructure of the Weld Metal

تحقیقات در مورد اثر ارتعاش مکانیکی روی ریزساختار ماده‎ی جوشکاری

ABSTRACT

The solidification process in the weld metal produces solidification structure. The solidification process depends on the thermal gradient, solidification speed and the alloy content. These structures can be planar, cellular, columnar dendritic and equiaxed dendritic. The solidification process may change from planar to cellular, columnar dendritic and equiaxed dendritic across the weld metal zone as shown in fig.1. Three grains are shown to grow epitaxially from the fusion line. A short distance away from the fusion line, solidification changes to the cellular mode. Further away from the fusion line, the solidification changes to columnar dendritic mode. Near the weld centre line equiaxed dendrites nucleate and grow, blocking off the columnar dendrites. Each one of these structures would affect the hot cracking susceptibility in greater or smaller extent.

 

 

ادامه مطلب ...

تنش‌های پسماند در جوش‌های لب به لب اتصالات لوله غیرمشابه

Effect of the welding heat input on residual stresses in butt-welds of dissimilar pipe joints

اثر ورودی حرارت جوشکاری بر تنش‌های پسماند در جوش‌های لب به لب اتصالات لوله غیرمشابه

ABSTRACT

This study used finite element techniques to analyse the thermo-mechanical behaviour and residual stresses in dissimilar butt-welded pipes. The residual stresses at the surface of some weld specimens were measured experimentally by using the hole-drilling method. The results of the finite element analysis were compared with experimentally measured data to evaluate the accuracy of the finite element modelling. Based on this study, a modelling procedure with reasonable accuracy was developed. The developed finite element modelling was used to study the effects of welding heat input on magnitude and distribution of welding residual stresses in butt-welded pipes made of ferritic and austenitic steels. The hoop and axial residual stresses in dissimilar pipe joints of 8 mm thick for V-groove shape were studied. It is shown that the welding heat input has a significant effect on magnitude and distribution of residual stresses in the stainless steel side of the studied joints.

 

  

ادامه مطلب ...

تنش پسماند حرارتی در فرآیند جوشکاری لیزری هیبریدی-GMA welding process

Numerical and experimental study of thermally induced residual stress in the hybrid laser–GMA welding process

مطالعه عددی و تجربی تنش پسماند حرارتی در فرآیند جوشکاری لیزری هیبریدی-GMA


ABSTRACT

A model based on a double-ellipsoidal volume heat source to simulate the gas metal arc welding (GMAW) heat input and a cylindrical volume heat source to simulate the laser beam heat input was developed to predict the temperature field and thermally induced residual stress in the hybrid laser–gas metal arc (GMA) welding process. Numerical simulation shows that higher residual stress is distributed in the weld bead and surrounding heat-affected zone (HAZ). Effects of the welding speed on the isotherms and residual stress of the welded joint are also studied. It is found that an increase in welding speed can reduce the residual stress concentration in the as-weld specimen. A series of experiments has been performed to verify the developed thermo-mechanical finite element model (FEM), and a qualitative agreement of residual stress distribution and weld geometrical size is shown to exist.

 

 

ادامه مطلب ...

اثر سرعت جوشکاری بر تنش پسماند در طول جوشکاری قوس با الکترود تنگستن تحت پوشش گاز

Influence of welding speed and power on residual stress during gas tungsten arc welding (GTAW) of thin sections

with constant heat input: A study using numerical simulation and experimental validation

اثر سرعت جوشکاری و توان بر تنش پسماند

در طول جوشکاری قوسی الکترود تنگستن (GTAW) مقاطع نازک با ورودی گرمای ثابت

مطالعه ای با استفاده از شبیه سازی و اعتبارسنجی تجربی

ABSTRACT

The temperature distribution and residual stresses for a GTAW circumferential butt joint of AISI 304 stainless steel using numerical simulation have been evaluated. For evaluation of weld induced residual stresses, the analysis of heat source fitting was carried out with heat inputs ranging from 200 to 500 J/mm to arrive at optimal heat input for obtaining proper weld penetration and heat affected zone (HAZ). For this chosen heat input, the influence of different weld speeds and powers on the temperature distribution and the residual stresses is studied. The heat source analysis revealed the best choice of heat input as 300 J/mm. The residual stresses on the inner and outer surfaces, and along the radial direction were computed. Increase in temperature distribution as well as longitudinal and circumferential residual stresses was observed with the increase in weld speed and power. The validity of the results obtained from numerical simulation is demonstrated with full scale shop floor welding experiments.

   

ادامه مطلب ...

جوشکاری GTAW آلیاژ آلومینیوم تیتانیوم

Effect of Vibration during GTAW Welding on Microstructure and Mechanical Properties of Ti6Al4V

تاثیر ارتعاش در طی جوشکاری GTAW روی ریزساختار و خواص مکانیکی Ti6Al4V 

ABSTRACT

The drive to improve weld quality and process parameters demands the use of improved welding tech niques and materials [1]. Titanium and its alloys are considered to be the best engineering metals for indus trial applications because of their excellent strengthto weight ratio, high fatigue life, toughness, resistance to corrosion and good fatigue strength [2, 3].

Welding methods such as gas tungsten arc, resis tance, and diffusion welding have been developed in response to the expansion of the titanium industry. 

Titanium alloys easily absorb harmful gases because of their high chemical activity, resulting in poor mechanical properties and unstable structure [4, 5]. Gas tungsten arc welding is the preferred method for avoiding these deficiencies [6]. The weld ing of titanium alloys often increases grain size in the welded metal and heat affected zones [7]. Fusion zones typically exhibit coarse columnar grains in response to prevailing thermal conditions during welded metal solidification [6]. These columnar grains produce inferior mechanical properties in the welds [1]. Methods of weld grain refinement include inocu with heterogeneous nucleants, surface nucleation induced by gas impingement, introduction of physical disturbance through techniques such as elec tromagnetic stirring [4]. Vibratory techniques, and pulsed current welding techniques [8].

 

 

ادامه مطلب ...

ابزار جوشکاری اصطکاکی اغتشاشی friction stir welding tools

friction stir welding tools

ابزار جوشکاری اصطکاکی اغتشاشی

ABSTRACT

Friction stir welding (FSW) is a widely used solid state joining process for soft materials such as aluminium alloys because it avoids many of the common problems of fusion welding. Commercial feasibility of the FSW process for harder alloys such as steels and titanium alloys awaits the development of cost effective and durable tools which lead to structurally sound welds consistently. Material selection and design profoundly affect the performance of tools, weld quality and cost. Here we review and critically examine several important aspects of FSW tools such as tool material selection, geometry and load bearing ability, mechanisms of tool degradation and process economics.

ادامه مطلب ...