Improving the Toughness of the Weld-Heat-Affected Zone of Cu-Containing Low-Alloy Steel for Offshore Applications by Optimizing Chemical Composition

2020 ◽  
Vol 143 (1) ◽  
Author(s):  
Yuta Honma ◽  
Gen Sasaki ◽  
Kunihiko Hashi ◽  
Fumiyoshi Minami
Keyword(s):  
Chemical Composition ◽  
Alloy Steel ◽  
Heat Affected Zone ◽  
Negative Influence ◽  
Area Fraction ◽  
Test Results ◽  
Low Alloy Steel ◽  
Potential Factors ◽  
Structural Parts ◽  
Haz Toughness

Abstract Copper-containing low-alloy steel based on the ASTM A707 5L grade is widely used for structural parts of offshore wells. However, it is difficult to stably obtain good weld joint toughness. With this background, this paper focuses on the metallurgical factors controlling the heat-affected zone (HAZ) toughness of A707 modified steel. Potential factors considered are the grain size, the martensite–austenite constituent (M-A), and precipitates. Thus, the purpose was to clarify the effect of M-A and precipitates on HAZ toughness. Furthermore, Cu, Si, and Mn contents, which affect M-A and precipitates generations, were focused on and tried to improve HAZ toughness by optimizing their contents in ASTM A707 steel. The weld test results showed that the toughness of an intercritically coarsened grain HAZ (ICRCGHAZ) was remarkably lower than that of the other heat cycle pattern due to the formation of M-A. It is, therefore, essentially important to suppress the formation of M-A in order to improve toughness in the HAZ of the steel. Therefore, the chemical composition was optimized in an effort to improve HAZ toughness. Copper had no negative influence on the HAZ toughness. It was found that when the Mn and Si contents of the steel decreased, the area fraction of M-A decreased. Consequently, the ICRCG HAZ toughness is improved because the toughness increases with the decrease in the area fraction of M-A. The recommended amounts of Cu, Mn, and Si to ensure HAZ toughness are more than 1.0 wt%, less than 0.6 wt%, and less than 0.1 wt%, respectively.

Improvement on Toughness of Weld Heat Affected Zone of Cu-Containing Low Alloy Steel of Long Scale Forging for Offshore Applications by Optimizing Chemical Composition

2019 ◽  
Author(s):  
Yuta Honma ◽  
Gen Sasaki ◽  
Kunihiko Hashi ◽  
Fumiyoshi Minami
Keyword(s):  
Chemical Composition ◽  
Alloy Steel ◽  
Heat Affected Zone ◽  
Heat Input ◽  
Low Alloy Steel ◽  
Crack Tip Opening Displacement ◽  
Welding Condition ◽  
Input Condition ◽  
Haz Toughness ◽  
Weld Heat

Abstract Copper-containing low alloy steel based on ASTM A707 5L grade is widely used for structural parts of offshore wells. Applications of the steel for Ultra-deepwater development require excellent low temperature toughness from the viewpoint of marine accident prevention. However it is difficult to stably obtain good weld joint toughness because the welding condition is inevitably scattering. With those backgrounds, this paper focuses on metallurgical factors controlling the HAZ toughness of A707 modified steel. Potential factors considered are the grain size, M-A and precipitates. A challenge is demonstrated to improve the HAZ toughness by optimizing the Cu and Mn contents. In this study, we investigated mechanical properties including crack tip opening displacement (CTOD) and we observed microstructure using welding tests or various weld heat cycle specimens. The weld heat affected zone (HAZ) of a conventional material had good toughness for the low heat input condition. However it was remarkably decreased for the high heat input condition due to the precipitating martensite-austenite constituent (M-A) in local brittle zones (LBZ). The weld test results indicated the importance of suppressing the formation of M-A in order to improve toughness in the HAZ of the steel. Thereby, we challenged the optimization of chemical composition for HAZ toughness improvement. Cu had no bad influence on the HAZ toughness. It was demonstrated that the HAZ toughness is recovered by good use of Cu precipitates in SC cycle. Moreover the area fraction of M-A is decreased in keeping with Mn content, which leads to the improvement of the ICCG HAZ toughness. Based on our study, the recommended amounts of Cu and Mn are more than 1.0 mass% and less than 0.6 mass%, respectively, to ensure the HAZ toughness, especially ICCG HAZ toughness.

scholarly journals Effect of Molybdenum on the Impact Toughness of Heat-Affected Zone in High-Strength Low-Alloy Steel

Materials ◽  
2021 ◽  
Vol 14 (6) ◽  
pp. 1430
Author(s):  
Xiaoyan Wu ◽  
Pengcheng Xiao ◽  
Shujing Wu ◽  
Chunliang Yan ◽  
Xuegang Ma ◽  
...  
Keyword(s):  
Chemical Composition ◽  
Alloy Steel ◽  
Heat Affected Zone ◽  
Laser Scanning ◽  
Lattice Misfit ◽  
High Strength ◽  
Optical Microscope ◽  
Low Alloy Steel ◽  
Number Density ◽  
The Impact

The microstructure, precipitates, and austenite grain in high-strength low-alloy steel were characterized by optical microscope, transmission electron microscope, and laser scanning confocal microscopy to investigate the effect of Mo on the toughness of steel. The microstructure was refined and the toughness was enhanced after the addition of 0.07% Mo in steel. The addition of Mo can suppress the Widmanstätten ferrite (WF) formation and promote the transformation of acicular ferrite (AF), leading to the fine transformed products in the heat-affected zone (HAZ). The chemical composition of precipitates changed from Nb(C, N) to (Nb, Mo)(C, N) because of the addition of Mo. The calculated lattice misfit between Nb(C, N) and ferrite was approximately 11.39%, while it was reduced to 5.40% for (Nb, Mo)(C, N), which significantly affected the size and number density of precipitates. A detailed analysis of the precipitates focusing on the chemical composition, size, and number density has been undertaken to understand the contribution of Mo on the improvement of steel toughness.

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

Effect of Chemical Composition and Microstructure Parameters on Carbon and Low-Alloy Steel Corrosion Resistance

Metallurgist ◽  
2018 ◽  
Vol 61 (9-10) ◽  
pp. 770-776
Author(s):  
I. G. Rodionova ◽  
M. V. Feoktistova ◽  
O. N. Baklanova ◽  
A. V. Amezhnov ◽  
D. L. D’yakonov
Keyword(s):  
Corrosion Resistance ◽  
Chemical Composition ◽  
Alloy Steel ◽  
Steel Corrosion ◽  
Low Alloy Steel ◽  
Microstructure Parameters ◽  
Steel Corrosion Resistance

Fracture Toughness in the Ductile-Brittle Transition and Thermal Ageing Behavior of Decarburized Heat Affected Zone of Alloy 52 Dissimilar Metal Welds of Nuclear Components

2014 ◽  
Author(s):  
Pierre Joly ◽  
Miguel Yescas ◽  
Elisabeth Keim
Keyword(s):  
Fracture Toughness ◽  
Stainless Steel ◽  
Alloy Steel ◽  
Heat Affected Zone ◽  
Power Plants ◽  
Base Alloy ◽  
Thermal Ageing ◽  
Low Alloy Steel ◽  
Dissimilar Metal ◽  
Brittle Transition

Dissimilar metal welds (DMW) are used in nuclear power plants between the nozzles of main components in low alloy steel and stainless steel pipes, or safe-ends connected to the main coolant line pipes. AREVA proposes for EPR™ an improved design of DMW involving narrow gap welding without buttering between the low alloy steel nozzles and the stainless steel safe-ends, and the use of a corrosion resistant weld filler metal (Alloy 52). AREVA performed a thorough characterization of this type of welds, which shows a particular microstructure close to the fusion line between the low alloy steel and the nickel base alloy, where the heat affected zone of the low alloy steel is decarburized. This paper presents results of fracture toughness tests performed with the crack tip located in this area, in the ductile to brittle transition in the as post-welded heat treated condition and after thermal ageing. The results show an excellent fracture toughness behavior of this particular area, compared to that of low alloy steel parent metal.

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