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

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) ha...

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Main Authors:	Yun Zong, Chun-Ming Liu
Format:	Article
Language:	English
Published:	MDPI AG 2019-08-01
Series:	Metals
Subjects:	SH-CCT diagram low-carbon bainite E550 steel welding heat affected zone thermal expansion method low temperature impact toughness vickers hardness
Online Access:	https://www.mdpi.com/2075-4701/9/9/939

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spelling	doaj-7142028a0cf14857a03d4c832d99ea0c2020-11-25T02:01:02ZengMDPI AGMetals2075-47012019-08-019993910.3390/met9090939met9090939Continuous Cooling Transformation Diagram, Microstructures, and Properties of the Simulated Coarse-Grain Heat-Affected Zone in a Low-Carbon Bainite E550 SteelYun Zong0Chun-Ming Liu1Key Laboratory for Anisotropy & Texture of Materials, Ministry of Education, Northeastern University, Shenyang 110819, ChinaKey Laboratory for Anisotropy & Texture of Materials, Ministry of Education, Northeastern University, Shenyang 110819, ChinaIn 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 HV<sub>10</sub>. When the cooling time from 800 °C to 500 °C (<i>t</i><sub>8/5</sub>) is 5−15 s, it presents excellent −40 °C impact toughness (273−286 J) of the CGHAZ beyond the base material (163 J).https://www.mdpi.com/2075-4701/9/9/939SH-CCT diagramlow-carbon bainite E550 steelwelding heat affected zonethermal expansion methodlow temperature impact toughnessvickers hardness
collection	DOAJ
language	English
format	Article
sources	DOAJ
author	Yun Zong Chun-Ming Liu
spellingShingle	Yun Zong Chun-Ming Liu Continuous Cooling Transformation Diagram, Microstructures, and Properties of the Simulated Coarse-Grain Heat-Affected Zone in a Low-Carbon Bainite E550 Steel Metals SH-CCT diagram low-carbon bainite E550 steel welding heat affected zone thermal expansion method low temperature impact toughness vickers hardness
author_facet	Yun Zong Chun-Ming Liu
author_sort	Yun Zong
title	Continuous Cooling Transformation Diagram, Microstructures, and Properties of the Simulated Coarse-Grain Heat-Affected Zone in a Low-Carbon Bainite E550 Steel
title_short	Continuous Cooling Transformation Diagram, Microstructures, and Properties of the Simulated Coarse-Grain Heat-Affected Zone in a Low-Carbon Bainite E550 Steel
title_full	Continuous Cooling Transformation Diagram, Microstructures, and Properties of the Simulated Coarse-Grain Heat-Affected Zone in a Low-Carbon Bainite E550 Steel
title_fullStr	Continuous Cooling Transformation Diagram, Microstructures, and Properties of the Simulated Coarse-Grain Heat-Affected Zone in a Low-Carbon Bainite E550 Steel
title_full_unstemmed	Continuous Cooling Transformation Diagram, Microstructures, and Properties of the Simulated Coarse-Grain Heat-Affected Zone in a Low-Carbon Bainite E550 Steel
title_sort	continuous cooling transformation diagram, microstructures, and properties of the simulated coarse-grain heat-affected zone in a low-carbon bainite e550 steel
publisher	MDPI AG
series	Metals
issn	2075-4701
publishDate	2019-08-01
description	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 HV<sub>10</sub>. When the cooling time from 800 °C to 500 °C (<i>t</i><sub>8/5</sub>) is 5−15 s, it presents excellent −40 °C impact toughness (273−286 J) of the CGHAZ beyond the base material (163 J).
topic	SH-CCT diagram low-carbon bainite E550 steel welding heat affected zone thermal expansion method low temperature impact toughness vickers hardness
url	https://www.mdpi.com/2075-4701/9/9/939
work_keys_str_mv	AT yunzong continuouscoolingtransformationdiagrammicrostructuresandpropertiesofthesimulatedcoarsegrainheataffectedzoneinalowcarbonbainitee550steel AT chunmingliu continuouscoolingtransformationdiagrammicrostructuresandpropertiesofthesimulatedcoarsegrainheataffectedzoneinalowcarbonbainitee550steel
_version_	1724959309844971520

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

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