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

Metals ◽  
2019 ◽  
Vol 9 (9) ◽  
pp. 939 ◽  
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).

Effect of Heat Imput on Microstructure and Toughness of High Strength Bridge Steel

2011 ◽  
Vol 194-196 ◽  
pp. 255-258
Author(s):  
Kun Ning Jia
Keyword(s):  
Grain Size ◽  
Crack Propagation ◽  
Heat Affected Zone ◽  
High Strength ◽  
Thermal Simulation ◽  
Granular Bainite ◽  
Coarse Grain ◽  
Bridge Steel ◽  
Lath Bainite

The coarse grain heat affected zone(CGHAZ) at different parameters t8/5 of high-strength bridge steel Q460q were simulated with thermal simulation machine. the microstructure of CGHAZ and the effect of granular bainite on the toughness were analyzed in this paper.The results show that: When t8/5<60s, lath bainite and granular bainite intertwine, and the quantity of strip M-A constituents in granular bainite decreased, so toughness is higher.When t8/5>60s, the quantity of eutectoid ferrite and granular bainite increased, coarse M-A constituent resulting in the grain size of effective crack propagation becoming coarser and toughness decreased significantly.

scholarly journals Change of mechanical properties in substrate during rewelding deposit

2011 ◽  
Vol 57 (No. 3) ◽  
pp. 105-109 ◽  
Author(s):  
R. Chotěborský ◽  
P. Hrabě ◽  
A. Kabutey
Keyword(s):  
Mechanical Properties ◽  
Impact Toughness ◽  
Heat Affected Zone ◽  
Impact Test ◽  
Low Carbon Steel ◽  
Charpy Impact ◽  
Charpy Impact Test ◽  
Optical Metallography ◽  
Coarse Grain ◽  
Low Carbon

A study was carried out to examine the influence of rewelding deposit of structural low carbon steel and also the changes which occur in heat-affected zone and subcritical zone during rewelding. Optical metallography, microhardness Vickers method and Charpy impact test were employed to analyze these differences. The results show that rewelding deposit increased the heat-affected zone and fine coarse grain heat-affected zone and also has influence on impact toughness of substrate and their microhardness. Again, it was found that rewelding increased the fine coarse grain heat-affected zone. This effect resulted in increasing impact toughness in the heat-affected zone. However, submicroscopic change in substrate ferrite showed decreasing impact toughness.

Microstructures and Toughness in Simulated Coarse Grain Heat-Affected Zones of Copper-Bearing Steel

2008 ◽  
Vol 575-578 ◽  
pp. 910-914
Author(s):  
Wen Yan Liu ◽  
Lai Wang ◽  
Ji Bin Liu ◽  
Ping He Li ◽  
Kai Miao ◽  
...  
Keyword(s):  
Impact Toughness ◽  
Heat Affected Zone ◽  
Physical Simulation ◽  
Bearing Steel ◽  
Granular Bainite ◽  
Coarse Grain ◽  
Factors Influencing ◽  
Visible Effect ◽  
Main Factors ◽  
The Impact

Microstructures and toughness of simulated coarse grain heat-affected zone of hot continuously rolled copper-bearing steel were investigated using physical simulation. The results showed that brittlement is easy to happen in the region of CGHAZ with slower thermal cycles (t8/5≥45s). Granular bainite transformed from austenite led to brittlement. The dimensions of granular martensite and austenite (M-A) constituents are main factors influencing the impact toughness. There is no visible effect on the toughness when the dimensions of M-A constituents are less than 1μ m. However, the toughness decreases greatly once the dimensions exceed 1μ m. Therefore, decreasing the dimensions of M-A constituents by controlling weld heat input will do good to improve the impact toughness of copper-bearing steel.

scholarly journals Influence of Chromium Content on the Microstructure and Mechanical Properties of Thermomechanically Hot-Rolled Low-Carbon Bainitic Steels Containing Niobium

2020 ◽  
Vol 10 (1) ◽  
pp. 344 ◽  
Author(s):  
Mohammed Ali ◽  
Tun Nyo ◽  
Antti Kaijalainen ◽  
Jaakko Hannula ◽  
David Porter ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Impact Toughness ◽  
Cooling Rate ◽  
Chromium Content ◽  
Bainitic Ferrite ◽  
Polygonal Ferrite ◽  
Granular Bainite ◽  
Low Carbon ◽  
Cr Content ◽  
Hot Rolled

The effect of chromium content in the range of 1 wt.%–4 wt.% on the microstructure and mechanical properties of controlled-rolled and direct-quenched 12 mm thick low-carbon (0.04 wt.%) steel plates containing 0.06 wt.% Nb has been studied. In these microalloyed 700 MPa grade steels, the aim was to achieve a robust bainitic microstructure with a yield strength of 700 MPa combined with good tensile ductility and impact toughness. Continuous cooling transformation diagrams of deformed and non-deformed austenite were recorded to study the effect of Cr and hot deformation on the transformation behavior of the investigated steels. Depending on the cooling rate, the microstructures consist of one or more of the following microstructural constituents: bainitic ferrite, granular bainite, polygonal ferrite, and pearlite. The fraction of bainitic ferrite decreases with decreasing cooling rate, giving an increasing fraction of granular bainite and polygonal ferrite and a reduction in the hardness of the transformation products. Polygonal ferrite formation depends mainly on the Cr content and the cooling rate. In both deformed and non-deformed austenite, increasing the Cr content enhances the hardenability and refines the final microstructure, shifting the ferrite start curve to lower cooling rates. Preceding austenite deformation promotes the formation of polygonal ferrite at lower cooling rates, which leads to a decrease in hardness. In hot-rolled and direct-quenched plates, decreasing the Cr content promotes the formation of polygonal ferrite leading to an increase in the impact toughness and elongation but also a loss of yield strength.

scholarly journals Effect of Welding Heat Input on Microstructure and Impact Toughness in the Simulated CGHAZ of Low Carbon Mo-V-Ti-N-B Steel

Metals ◽  
2021 ◽  
Vol 11 (12) ◽  
pp. 1997
Author(s):  
Mingliang Qiao ◽  
Huibing Fan ◽  
Genhao Shi ◽  
Leping Wang ◽  
Qiuming Wang ◽  
...  
Keyword(s):  
Impact Toughness ◽  
Heat Input ◽  
Acicular Ferrite ◽  
Granular Bainite ◽  
Equivalent Diameter ◽  
Low Carbon ◽  
Welding Heat Input ◽  
Lath Bainite ◽  
Gleeble 3500 ◽  
The Impact

Welding thermal cycles with heat inputs ranging from 25 to 75 kJ/cm were performed on a Gleeble 3500. The impact energy improved significantly (from 10 to 112 J), whereas the simulated coarse-grain heat-affected zone (CGHAZ) microstructure changed from lath bainite ferrite (LBF) and granular bainite ferrite (GBF) + martensite/austenite (M/A) to acicular ferrite (AF) + polygonal ferrite (PF) + M/A as the heat input increased. Simultaneously, the mean coarse precipitate sizes and the degree of V(C,N) enrichment on the precipitate surface increased, which provided favorable conditions for intragranular ferrite nucleation. The Ar3 of CGHAZ increased from 593 °C to 793 °C with increasing heat inputs; the longer high-temperature residence time inhibited the bainite transformation and promoted the ferrite transformation. As a result, acicular ferrite increased and bainite decreased in the CGHAZ. The CGHAZ microstructure was refined for the acicular ferrite segmentation of the prior austenite, and the microstructure mean equivalent diameter (MED) in the CGHAZ decreased from 7.6 µm to 4.2 µm; the densities of grain boundaries higher than 15° increased from 20.3% to 45.5% and significantly increased the impact toughness. The correlation of heat input, microstructure, and impact toughness was investigated in detail. These results may provide new ideas for the development of high welding heat input multiphase steels.

Microstructure and Properties of HAZ in Low-Carbon Bainite E550 Steel during Double-Pass Welding Thermal Cycle

2018 ◽  
Vol 913 ◽  
pp. 317-323 ◽  
Author(s):  
Yun Zong ◽  
Chun Ming Liu
Keyword(s):  
Impact Toughness ◽  
Heat Affected Zone ◽  
Thermal Cycle ◽  
Coarse Grained ◽  
Granular Bainite ◽  
Low Carbon ◽  
Microstructure And Properties ◽  
Welding Thermal Cycle ◽  
Low Carbon Bainite ◽  
The Impact

Investigations on the microstructure and properties of the Coarse-Grained Heat-Affected Zone (CGHAZ) and intercritical reheated Coarse-Grained Heat-Affected Zone (ICCGHAZ) of a low-carbon bainite E550 steel were carried out using thermal simulation technology in this paper.Double-pass welding thermal cycle were performed on Gleeble-3800 thermal simulator, tempering heat treatment of the critical coarse crystal zone carried out in a box resistance furnace, low impact energies at -40 °C and Vickers hardness determined, and the microstructure were observed. The experimental results show that the microstructure of CGHAZ (Tp1 is 1320 °C) was dominated by coarse granular bainite and Lath bainite Ferrite, the impact toughness of CGHAZ was poor. The toughness of the CGHAZ was improved after second welding heat cycle except intercritical two-phase heating. When the peak temperature of the second thermal cycle(Tp2) was 650 °C, martensite-austenite (M-A) constituent of original CGHAZ wasdecomposed and refined, impact toughness and hardness were all higher than that of CGHAZ; When Tp2 is 750 °C, there was a ” necklace” distribution of massive M-A constituent in this ICCGHAZ, the impact energy at -40 °C prominently decreased and Hardness went up; When Tp2 was in the temperature range of 850 °C ~1100 °C, the microstructure was mainly finer granular bainite, the toughness of CGHAZ could be effectively improved; When Tp2 was over 1100 °C, M-A constituents become coarse, the toughness declined slightly . The changing of hardness was the opposite of toughness but the hardness fluctuation was comparatively small. After tempering at different temperature (520 °C~640 °C) , the grain boundary "necklace" structure of ICCGHAZ was still obvious, some of the M-A constituent were decomposed, the hardness decreased, the lowest hardness was obtained in 610 °C.

Continues Cooling Transformation Behavior of Low Carbon Mn-Nb-B Steel

2011 ◽  
Vol 335-336 ◽  
pp. 595-598 ◽  
Author(s):  
Zheng Tao Duan ◽  
Yan Mei Li ◽  
Fu Xian Zhu ◽  
Hui Yun Zhang
Keyword(s):  
Cooling Rate ◽  
Acicular Ferrite ◽  
Granular Bainite ◽  
Low Carbon ◽  
Transformation Behavior ◽  
Cct Curve ◽  
Lath Bainite ◽  
Left Corner ◽  
Cct Diagrams

The continues cooling transformation (CCT) of a low carbon Mn-Nb-B steel in the undeformed and deformed conditions were investigated, respectively. The CCT diagrams of the steel were constructed. The microstructures and microhardness were analysized. The results showed that the microsructures contains ferrite, pearlite, granular bainite, acicular ferrite and lath bainite depending on cooling rate; Deformation moved the CCT curve to the top left corner, increased the transformation start temperatures slightly, and promoted the formation of ferrite and pearlite. Furthmore deformation also fined the transformed microstructures.

scholarly journals Morphological and Crystallographic Characteristics of α Structure in a Low-Carbon Iron–Nickel Alloy

Crystals ◽  
2018 ◽  
Vol 8 (12) ◽  
pp. 468 ◽  
Author(s):  
Gaojun Mao ◽  
Cyril Cayron ◽  
Xiuli Mao ◽  
Rui Cao ◽  
Roland Logé ◽  
...  
Keyword(s):  
Lath Martensite ◽  
Granular Bainite ◽  
Body Centered Cubic ◽  
Low Carbon ◽  
Electron Backscattered Diffraction ◽  
Dislocation Densities ◽  
Lath Bainite ◽  
Crystallographic Characteristics ◽  
Iron Nickel ◽  
Relationship Of

The features of α (body-centered cubic) structures were investigated in a low-carbon multicomponent alloy from morphological and crystallographic perspectives. In addition to apparent features of granular bainite and lamellar martensite, a morphological similarity can be found between lath martensite and lath bainite. Therefore, it is of interest to explore possible discrepancies between lath martensite and lath bainite from a crystallographic perspective. These microstructures were obtained by various cooling rates (i.e., water quenching, 5 °C/s, and 0.05 °C/s) and then were characterized by a combination of scanning electron microscopy and electron backscattered diffraction techniques. It is shown that: (1) Lath martensite (LM) formed in the samples that were water-quenched, and a mixture of LM and lath bainite (LB) and granular bainite (GB) formed in the samples cooled at rates of 5 °C/s and 0.05 °C/s, respectively; (2) A Kurdjumov-Sachs relationship was mostly found in as-quenched martensite, while a Greninger-Troiano relationship represented the orientation relationship of LB and GB; (3) As the cooling rate decreased, the dislocation densities in corresponding microstructures were reduced, while the tendency of variant grouping was enhanced.

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