scholarly journals Phase and structural transformations when forming a  welded joint from rail steel. Report 3. The use of thermokinetic and isothermal diagrams of austenite decomposition for selection of optimal modes of electric contact welding

2021 ◽  
Vol 64 (6) ◽  
pp. 420-426
Author(s):  
E. V. Polevoi ◽  
Yu.  N. Simonov ◽  
N. A. Kozyrev ◽  
R. A. Shevchenko ◽  
A. R. Mikhno
Keyword(s):  
Pulse Heating ◽  
Welded Joint ◽  
Rail Steel ◽  
Metal Structure ◽  
Coarse Grained ◽  
Minimum Length ◽  
Austenite Decomposition ◽  
Contact Heating ◽  
Thermal Influence ◽  
Isothermal Diagrams

During contact flash welding of rails, the metal is heated and continuously cooled in the zone of thermal influence. Accelerated heating and subsequent intensive cooling, implemented by the pulsed flashing-off method, lead to the formation of quenching structures. Subsequently, during the operation of the rails welded joint, this leads to the formation of cracks and to brittle destruction. We have investigated the possibilities of using contact heating after welding to avoid the formation of quenching structures in the metal of the welded joint made of R350LHT rail steel. The thermal cycles during welding and subsequent contact heating were recorded. The regularity of formation of the weld metal structure was established including the zone of thermal influence during pulsed contact heating for R350LHT rail steel. It is shown that contact pulse heating slows down the welded joint cooling and prevents the formation of quenching structures. However, contact pulse heating when using suboptimal modes can also lead to the opposite effect. It is determined that with a significant investment of heat by contact heating, cooling rate of the metal exceeds the critical one, transformation process passes through a diffusion-free mechanism with the formation of martensite coarse-grained structure. The use of thermokinetic and isothermal diagrams of austenite decomposition at known thermal welding cycles allows us to significantly narrow the search limits for optimal modes of contact butt welding of railway rails and subsequent contact heating. The use of optimal contact heating modes makes it possible to obtain a minimum length of heat-affected zones with reduced hardness without the formation of quenching structures in the welded joint of railway rails.

scholarly journals Phase transformations occurring during the formation of a welded joint from rail steel

2021 ◽  
Vol 330 ◽  
pp. 02007
Author(s):  
Alexey Yuryev ◽  
Nikolay Kozyrev ◽  
Roman Shevchenko ◽  
Alexey Mikhno ◽  
Olga Gutak
Keyword(s):  
Phase Transformations ◽  
Welded Joint ◽  
Rail Steel ◽  
Supercooled Austenite ◽  
Austenite Decomposition ◽  
Hardness Testing ◽  
Continuous Cooling Transformation ◽  
Continuous Cooling ◽  
Continuous Cooling Transformation Diagrams ◽  
Transformation Diagrams

The results of dilatometry, metallography and hardness testing of the decomposition process of supercooled austenite of R350LHT steel are presented. During continuous cooling and in isothermal conditions, continuous cooling transformation diagrams of supercooled austenite decomposition of steel R350LHT are constructed.

scholarly journals Elaboration of a technology of long rail lashes production without induction heat treatment application

2019 ◽  
Vol 75 (4) ◽  
pp. 488-497
Author(s):  
N. A. Kozyrev ◽  
R. A. Shevchenko ◽  
S. N. Krat’ko ◽  
R. E. Kryukov ◽  
A. R. Mikhno
Keyword(s):  
Heat Treatment ◽  
Welded Joint ◽  
Rail Steel ◽  
Theoretical Calculations ◽  
Local Heating ◽  
Latency Period ◽  
Metal Structure ◽  
Butt Welding ◽  
Technical Requirements ◽  
Current Pulses

Welding butts of rail lashes after resistance butt-welding are subjected to heat treatment to eliminate heat-affected zones. At present facilities of induction heating are used in Russia for the heat treatment and compressed air as a quenching media. However, this method of quenching has significant drawbacks, including appearance of new heat-affected zones at the local heating of the welded butts, deterioration of the welded butts’ straightness after cooling. Shlatter Company proposed a solution of this problem by application of the process of resistance butt-welding by rails fusion. Theoretical calculations and laboratory studies of the thermal cycle of rail steel samples welding were made in the Siberian State Industrial University, which showed a principal possibility of this method application under industrial conditions. The method assumes after the welded butt settling and cooling to keep the preset temperature from the moment of its reaching by passing alternative electric current pulses through the welded butt. The temperature of exposure is selected based on obtaining necessary fine grain seam metal structure. The duration of exposure is determined by latency period of the structure formation and is controlled by the number of current pulses. The carried out industrial experiments at the МСР-6301 resistance butt welding machine resulted in determining parameters of cooling time after settling, heating and cooling after the heating, as well as the number of heating pulses. A method of resistance butt welding was tested, enabling to obtain the welded joint of details of the P65 ДТ350 category rail steel. The welded joint had mechanical properties exceeding technical requirements of СТО РЖД 1.08.002–2009 specifications.

Effect of Microstructure on High-Strength Low-Alloy Steel Welded Joint Toughness with Simulation of Heat-Affected Zone Coarse-Grained Area

Metallurgist ◽  
2021 ◽  
Vol 64 (9-10) ◽  
pp. 875-884
Author(s):  
K. G. Vorkachev ◽  
P. P. Stepanov ◽  
L. I. Éfron ◽  
M. M. Kantor ◽  
A. V. Chastukhin ◽  
...  
Keyword(s):  
Alloy Steel ◽  
Heat Affected Zone ◽  
Welded Joint ◽  
High Strength ◽  
Coarse Grained ◽  
Low Alloy Steel ◽  
Effect Of Microstructure

scholarly journals Effect of Cooling Rate on Microstructure and Mechanical Properties in the CGHAZ of Electroslag Welded Pearlitic Rail Steel

Metals ◽  
2019 ◽  
Vol 9 (7) ◽  
pp. 742 ◽  
Author(s):  
Khan ◽  
Yu ◽  
Wang ◽  
Jiang
Keyword(s):  
Mechanical Properties ◽  
Tensile Strength ◽  
Cooling Rate ◽  
Rail Steel ◽  
Interlamellar Spacing ◽  
Coarse Grained ◽  
Microstructure And Mechanical Properties ◽  
Confocal Scanning Laser ◽  
Start Temperature ◽  
Pearlitic Rail Steel

The effect of cooling rate, ranging from 6 to 1 °C/s, on microstructure and mechanical properties in the coarse-grained heat affected zone (CGHAZ) of electroslag welded pearlitic rail steel has been investigated by using confocal scanning laser microcopy (CSLM) and Gleeble 3500 thermo-mechanical simulator. During heating, the formed austenite was inhomogeneous with fractions of untransformed ferrite, which has influenced the pearlite transformation during cooling by providing additional nucleation sites to pearlite. During cooling, at 6 °C/s, the microstructure was composed of martensite and bainite with little pearlite. From 4 to 1 °C/s, microstructures were completely pearlite. Lowering the cooling rate of the CGHAZ from 4 to 1 °C/s increased the pearlite start temperature and reduced the pearlite growth rate. Meanwhile, this increase in pearlite start temperature enlarged the pearlite interlamellar spacing. Alternatively, increasing pearlite interlamellar spacing in the CGHAZ by lowering the cooling rate from 6 to 1 °C/s reduced the hardness and tensile strength, whereas toughness was found unaffected by the pearlite interlamellar spacing. It has been found that a cooling rate of 4 °C/s leads to the formation of pearlite with fine interlamellar spacing of 117 nm in the CGHAZ of electroslag welded pearlitic rail steel where hardness is 425 HV, tensile strength is 1077 MPa, and toughness is 9.1 J.

The Mechanism of Failure of the Axisymmetrical Welded Joint under Thermomechanical Loading

2010 ◽  
Vol 638-642 ◽  
pp. 3805-3810
Author(s):  
Piotr Lacki ◽  
Kwiryn Wojsyk ◽  
Andrzej Służalec
Keyword(s):  
Welded Joint ◽  
Relevant Literature ◽  
Coarse Grained ◽  
Thermomechanical Loading ◽  
Deformation And Failure ◽  
Minimal Impact ◽  
Failure Initiation ◽  
Welded Structure ◽  
Von Mises ◽  
New Generation

The purpose of the paper is to present the mechanism of deformation and failure of welded joints during the process of retrofit. The considered joints are made of conventional steels used in the power industry, as well as new-generation steels. The problems of failure and the design of such joints are considered in the paper. The model of welded joint was built with properties of low alloyed chrome-molybdenum steel and a new-generation steel of P/T91 type. All metallurgical zones, i.e. the weld and the heat-affected zone were considered, modelled and discussed. A simulation of thermomechanical loading was conducted under various loading conditions to explain the causes of the failure of energy structures, which appears more frequently during their loadings or steam dropping (i.e. in conditions of changes of thermal loadings) than during their stable work. The results of calculations were confirmed by experimental metallurgical studies. It is observed that the brittle and soft zones of coarse-grained ferrite with minimal impact strength, resulting from internal and external operation parameters, appear in regions where oscillation of the highest von Mises and normal stresses takes place. The relevant literature does not describe the analysis of the phenomenon of acceleration of the failure of the welded structure leading to its failure, while taking into account the complex thermomechanical conditions of their operation. This mechanism is based on the accumulation of structural weakening of the weld as the result of the diffusion process within the axially symmetrical joint, the growth of the brittle zone and their additional degradation, and the influence of the oscillation of maximal normal and von Mises stresses. It was noted that in the process of thermomechanical loading, the state of failure initiation in circumferential and longitudinal directions appeared in the weld. A few illustrations presenting the mechanism of the deformation and failure of the welded joint are presented. The effects of the distortions of the weld are also discussed in the paper.

scholarly journals Effect of non-metallic inclusions of rail steel on welded joint formation

2016 ◽  
Vol 2016 (6) ◽  
pp. 24-28 ◽  
Author(s):  
S.I. Kuchuk-Yatsenko ◽  
◽  
V.I. Shvets ◽  
A.V. Didkovsky ◽  
E.V. Antipin ◽  
...  
Keyword(s):  
Welded Joint ◽  
Rail Steel ◽  
Joint Formation ◽  
Metallic Inclusions

scholarly journals Phase and structural transformations when forming a welded joint from rail steel. Report 1. Thermokinetic diagram of decomposition of supercooled austenite of R350LHT rail steel

2021 ◽  
Vol 64 (2) ◽  
pp. 95-103
Author(s):  
E. V. Polevoi ◽  
Yu. N. Simonov ◽  
N. A. Kozyrev ◽  
R. A. Shevchenko ◽  
L. P. Bashchenko
Keyword(s):  
Diffusion Processes ◽  
Rail Steel ◽  
Physical And Mechanical Properties ◽  
High Hardness ◽  
Supercooled Austenite ◽  
Austenite Decomposition ◽  
Thermokinetic Diagram ◽  
Optimal Parameters ◽  
Higher Temperature ◽  
Martensite Structure

A thermokinetic diagram of decomposition of supercooled austenite of R350LHT steel was constructed based on the results of its dilatometric, metallographic and hardness analysis during continuous cooling and in isothermal conditions. It was found that cooling at a rate of 0.1 and 1 °C/s causes the austenite decomposition in R350LHT steel by the pearlite mechanism. After cooling at a lower rate, the pearlite structure is coarser and has lower hardness (289 HV). This is due to the higher temperature range of transformation, in which diffusion processes associated with the transformation of austenite into pearlite occur more actively. In the range of rates from 5 to 10 °C/s, the austenite decomposition occurs according to the pearlite and martensitic mechanism, which leads to the formation of a pearlite-martensite structure. When the austenite of the steel under study is cooled at a rate of 30 and 100 °C/s, the austenite transforms according to the martensitic mechanism, and a martensitic structure with high hardness is formed. With an increase in the cooling rate of R350LHT steel, an increase in hardness is observed from 289 (at 0.1 °C/s) to 864 – 0 896 HV (at 100 and 30 °C/s, respectively). The conducted studies allow the boundaries of the search for optimal parameters of welding and heat treatment modes of the investigated rail steel to be narrowed. To obtain the required structures and physical and mechanical properties (austenite of R350LHT steel undergoes decomposition by the pearlite mechanism), cooling should be carried out at a rate of no more than 1 °С/s.

scholarly journals On Mechanical Properties of Welded Joint in Novel High-Mn Cryogenic Steel in Terms of Microstructural Evolution and Solute Segregation

Metals ◽  
2020 ◽  
Vol 10 (4) ◽  
pp. 478
Author(s):  
Jia-Kuan Ren ◽  
Qi-Yuan Chen ◽  
Jun Chen ◽  
Zhen-Yu Liu
Keyword(s):  
Microstructural Evolution ◽  
Welded Joint ◽  
Solute Segregation ◽  
Coarse Grained ◽  
Shielded Metal Arc Welding ◽  
Metal Arc Welding ◽  
Long Time ◽  
Segregation Band ◽  
Lng Tank ◽  
Cryogenic Steel

There is a growing demand for high-manganese wide heavy steel plate with excellent welding performance for liquefied natural gas (LNG) tank building. However, studies on welding of high-Mn austenitic steel have mainly focused on the applications of automotive industry for a long time. In the present work, a high-Mn cryogenic steel was welded by multi-pass Shielded Metal Arc Welding (SMAW), and the microstructural evolution, solute segregation and its effect on the properties of welded joint (WJ) were studied. The yield strength, tensile strength and elongation of the WJ reached 804 MPa, 1027 MPa and 11.2% at −196 °C, respectively. The elongation of WJ was reduced with respect to the BM due to the poorer strain hardening capacity of weld metal (WM) at −196 °C. The WM and coarse-grained heat affected zone (CGHAZ) had the lowest cryogenic impact absorbed energy of ~55 J (at −196 °C). The inhibited twin formation caused by the higher critical resolved shear twinning stress ( τ T ) in the C-Mn-Si segregation band, the inhomogeneous microstructure caused by solute segregation, and the hardened austenite matrix deteriorated the plastic deformation capacity, finally resulting in the decreased cryogenic impact toughness of the CGHAZ. To summarize, the cryogenic toughness and tensile properties of the WJ meet the requirements for LNG tank building.

Study of Welded Joint Metal Structure under Pulsed Impact on Arc Discharge

2021 ◽  
Vol 38 (1) ◽  
pp. 38-43
Author(s):  
S.M. Burdakov ◽  
M.B. Damaskina ◽  
D.I. Zheletskiy
Keyword(s):  
Welded Joint ◽  
Arc Discharge ◽  
Metal Structure

Region-Specified Ratcheting Behavior of API X80 Welded Joint Under Uniaxial Cyclic Loading

2016 ◽  
Author(s):  
Hongsheng Lu ◽  
Yonghe Yang ◽  
Gang Chen ◽  
Xu Chen ◽  
Xin Wang
Keyword(s):  
Weld Metal ◽  
Base Metal ◽  
Heat Affected Zone ◽  
Welded Joint ◽  
Pipeline Steel ◽  
Coarse Grained ◽  
Strain Accumulation ◽  
Lower Strength ◽  
Fine Grained ◽  
Ratcheting Strain

Evaluation of mechanical performance of different regions can be difficult by using standard size samples due to the size limitation of weld metal and heat-affected zone (HAZ). At first, the microstructure of different regions was characterized and quantified by Scanning Electron Microscope, which indicate that the pipeline steel is a typical acicular ferrite steel. In this study the deformation behavior of different regions (base metal, weld metal and heat affected zone) in a welded joint of API X80 pipeline steel were studied by conducting uniaxial loading tests on miniature specimens with the cross section of 2×0.5mm and gauge length of 9mm. From the results of uniaxial tension in base metal and weld metal it is shown that the welding is overmatching. Compared to the base metal, the coarse grained HAZ exhibits a lower strength, while the fine grained HAZ exhibits a higher strength. Under near zero-to-tension cyclic stress loading, all regions of the welded joints exhibit progressive accumulation of plastic strain. Under the same stress level, the base metal shows the fastest ratcheting strain accumulation, which is the result of lower strength than other regions. This fact may indicate that the ratcheting behavior of the overall welded joint is highly dependence on that of base metal for the present case. But when under the same normalized stress level (σ = σ/σYS), the fine grained HAZ has the highest ratcheting strain accumulation, while the coarse grained HAZ has the lowest ratcheting strain accumulation, which reveals that the intrinsic resistance to ratcheting is yield strength dependent.

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