Structure and phase composition of granular bainite in the region of complete recrystallisation of the heat-affected zone of welded joints in low-carbon low-alloy steels

AbstractIntragranular ferrite (IGF), which nucleates from specific inclusion surfaces in low alloy steels, is the desired microstructure to improve mechanical properties of steel such as the toughness. This microstructure is especially important in the coarse grain heat affected zone (CGHAZ) of weldments. The latest review paper focusing on the role of non-metallic inclusions in the IGF formation in steels has been reported by Sarma et al. in 2009 (ISIJ int., 49(2009), 1063–1074). In recent years, large amount of papers have been presented to investigate different issues of this topic. This paper mainly highlights the frontiers of experimental and theoretical investigations on the effects of inclusion characteristics, such as the composition, size distribution and number density, on the IGF formation in low carbon low-alloyed steels, undertaken by the group of Applied Process Metallurgy, KTH Royal Institute of Technology. Related results reported in previous studies are also introduced. Also, plausible future work regarding various items of IGF formation is mentioned in each section. This work aims to give a better control of improving the steel quality during casting and in the heat affected zone (HAZ) of weldment, according to the concept of oxide metallurgy.

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Dependence of impact toughness of heat affected zone metal of welded joints in low alloy steels on specific energy in welding

Welding International ◽

10.1080/09507118809451121 ◽

1988 ◽

Vol 2 (1) ◽

pp. 12-15

Author(s):

B F Lebedev ◽

A N Pashchin ◽

G A Ivashchenko ◽

S M Dudko

Keyword(s):

Impact Toughness ◽

Specific Energy ◽

Heat Affected Zone ◽

Welded Joints ◽

Low Alloy Steels ◽

Alloy Steels

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DIFFUSION OF HYDROGEN IN WELDED JOINTS OF STRUCTURAL STEELS

Proceedings of Southwest State University ◽

10.21869/2223-1560-2017-21-6-85-95 ◽

2017 ◽

Vol 21 (6) ◽

pp. 85-95 ◽

Cited By ~ 3

Author(s):

N. N. Sergeev ◽

A. N. Sergeev ◽

S. N. Kutepov ◽

A. E. Gvozdev ◽

E. V. Ageev

Keyword(s):

Diffusion Coefficient ◽

Weld Metal ◽

Heat Affected Zone ◽

Welded Joints ◽

Chemical Potential ◽

Weld Zone ◽

Base Material ◽

High Strength ◽

Low Alloy Steels ◽

Alloy Steels

High-strength low-alloy steels are widely used in the construction of welded metal structures. The main advantage of these steels is good combination of strength and toughness, and weldability. However, when welding high strength low alloy steels during cooling of the weld to a temperature below 150-100 °C there may be a risk of formation of bulk crystal structures defects in the weld zone - cold cracks. It was experimentally established that one of the factors contributing to the formation of cold cracks may be the occlusion of hydrogen in the atmosphere of arc plasma in the solidifying weld metal, from which diffusion hydrogen may diffuse to different areas of the weld after cooling. Hydrogen cracking typically has a tendency to slow down i.e. cracks can occur several days after the completion of welding process. As a rule, hydrogen induced cracking occurs either in the original steel in the heat-affected zone or in the weld metal, which is important, topical and long been researched by various scientific schools. Modern technologies of high strength low alloy steels processing have significantly improved the quality of the base material by reducing the amount of carbon and impurities, which has increased the stability of weld in the heat affected zone (HAZ) to hydrogen induced cold cracking. The paper presents modern approaches to the definition of diffusion coefficient of hydrogen in welded joints of high-strength low-alloy steels. Taking into account the temperature, the gradient of chemical potential and continuity conditions there has been considered the process of mass transfer of hydrogen under the influence of diffuse inhomogeneous mediums. It has been shown that the local effects of changing pressure and chemical potential are described using the equation of generalized potential of the diffusing substance. Our paper presents analytical expressions to determine the apparent diffusion coefficient of hydrogen in different local areas of a welded joint depending on temperature.

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Effect of Nb on Microstructure Evolution of Coarse-Grained Heat-Affected Zone with Large Heat Input Welding

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.284-286.1174 ◽

2011 ◽

Vol 284-286 ◽

pp. 1174-1179 ◽

Cited By ~ 1

Author(s):

Xue Li Tao ◽

Kai Ming Wu ◽

Xiang Liang Wan

Keyword(s):

Grain Boundary ◽

Heat Affected Zone ◽

Heat Input ◽

Acicular Ferrite ◽

High Strength ◽

Coarse Grained ◽

Granular Bainite ◽

Low Alloy Steels ◽

Alloy Steels ◽

Grain Boundary Ferrite

The effect of Nb microalloying on microstructure transformation of coarse-grained heat-affected zone of high strength low alloy steels were investigated utilizing different heat input welding simulation. For the low-Nb steel, the microstructures of coarse-grained heat-affected zone mainly consisted of acicular ferrite, bainite and grain boundary ferrite for small heat input welding; the amount of acicular ferrite decreased whereas grain boundary ferrite, polygonal ferrite and pearlite increased with increasing heat input. In constrast, for the high-Nb steel, granular bainite was the dominant microstructure. The formation of granular bainitic microstructure was associated with the solid solution of Nb, which suppressed ferrite transformation and promoted the formation of granular bainite. The hardness of coarse-grained heat-affected zone increased with increasing Nb content, and decreased with decreasing heat input, which was attributed to the microstructural change.

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Investigations of fracture toughness and reliability of welded joints from low-carbon and low-alloy steels

Welding International ◽

10.1080/09507116.2021.1953290 ◽

2021 ◽

pp. 1-12

Author(s):

V. V. Moskvichev ◽

A. M. Lepikhin ◽

N. A. Chernyakova

Keyword(s):

Fracture Toughness ◽

Welded Joints ◽

Low Alloy Steels ◽

Low Carbon ◽

Alloy Steels

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Analysis of the Effects of Welding Conditions on the Formation of the Structure of Welded Joints of Low-Carbon Low-Alloy Steels

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.844.146 ◽

2020 ◽

Vol 844 ◽

pp. 146-154

Author(s):

Dmytro Laukhin ◽

Valerii Pozniakov ◽

Oleksandr Beketov ◽

Nataliia Rott ◽

Anatolii Shchudro

Keyword(s):

Welded Joints ◽

Special Interest ◽

Welded Joint ◽

Weld Zone ◽

Low Alloy Steels ◽

Low Carbon ◽

Influence Zone ◽

Alloy Steels ◽

Thermal Influence ◽

Welding Processes

To obtain reliable joints in the conditions of open construction is complicated or impossible to use stationary machines and apparatuses, so requirements to welding processes are of special interest. The most interest concerning the support of strength and reliability of welded joint is specific processes developed after the crystallization of weld at weld zone. The value of the zone of thermal influence depends on the welding conditions and properties of metal that is welded. That is why the research on the influence of welding conditions on the formation of the structure of welded zone and thermal influence zone is actual.

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The influence of the carbon equivalent on the weldability of high-strength low-alloy steel in the water environment

Welding Technology Review ◽

10.26628/wtr.v91i5.1001 ◽

2019 ◽

Vol 91 (5) ◽

Author(s):

Jacek Tomków ◽

Michalina Tomków

Keyword(s):

Weld Metal ◽

Yield Point ◽

Heat Affected Zone ◽

Welded Joints ◽

Water Environment ◽

High Strength ◽

Carbon Equivalent ◽

Low Alloy Steels ◽

Low Alloy Steel ◽

Alloy Steels

From many years, the high strength low alloy steels are often used for offshore constructions. This constructions, due to the environment in which they work, require more frequent repairs than the constructions from the land. For economic reasons, repairs take place in the underwater conditions, however water significantly decreases the weldability of steel. The paper presents the results of the CTS weldability test for S460ML and S460 steels, which have a similar value of the yield point, but different carbon equivalent (CeMIS) values. The welded joints were cut into specimens, which were then subjected to Vickers HV10 hardness measurements. The experiment has shown that as the CeMIS value increases, the hardness in the heat affected zone (HAZ) of joints and in the weld metal increases.

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Continuous Cooling Transformation Diagram, Microstructures, and Properties of the Simulated Coarse-Grain Heat-Affected Zone in a Low-Carbon Bainite E550 Steel

Metals ◽

10.3390/met9090939 ◽

2019 ◽

Vol 9 (9) ◽

pp. 939 ◽

Cited By ~ 1

Author(s):

Yun Zong ◽

Chun-Ming Liu

Keyword(s):

Impact Toughness ◽

Cooling Rate ◽

Vickers Hardness ◽

Heat Affected Zone ◽

Granular Bainite ◽

Coarse Grain ◽

Low Carbon ◽

Transformation Diagram ◽

Lath Bainite ◽

Continuous Cooling Transformation Diagram

In order to provide important guidance for controlling and obtaining the optimal microstructures and mechanical properties of a welded joint, the continuous cooling transformation diagram of a new low-carbon Nb-microalloyed bainite E550 steel in a simulated coarse-grain heat-affected zone (CGHAZ) has been constructed by thermal dilatation method in this paper. The welding thermal simulation experiments were conducted on a Gleeble-3800 thermo-mechanical simulator. The corresponding microstructure was observed by a LEICA DM2700M. The Vickers hardness (HV) and the impact toughness at −40 °C were measured according to the ASTM E384 standard and the ASTM E2298 standard, respectively. The experimental results may indicate that the intermediate temperature phase transformation of the whole bainite can occur in a wide range of cooling rates of 2–20 °C/s. In the scope of cooling rates 2–20 °C/s, the microstructure of the heat-affected zone (HAZ) mainly consists of lath bainite and granular bainite. Moreover, the proportion of lath bainite increased and granular bainite decreased as the cooling rate increasing. There is a spot of lath martensite in the microstructure of HAZ when the cooling rate is above 20 °C/s. The Vickers hardness increases gradually with the increasing of the cooling rate, and the maximum hardness is 323 HV10. When the cooling time from 800 °C to 500 °C (t8/5) is 5–15 s, it presents excellent −40 °C impact toughness (273–286 J) of the CGHAZ beyond the base material (163 J).

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