Effect of Deformation Temperature on the Microstructure and Mechanical Properties of High-Strength Low-Alloy Steel Durin
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Effect of Deformation Temperature on the Microstructure and Mechanical Properties of High-Strength Low-Alloy Steel During Hot Compression Chengzhi Zhao, Wilasinee Kingkam, Li Ning, Hexin Zhang, and Li Zhiming (Submitted August 24, 2017; in revised form June 28, 2018) The microstructure and mechanical properties of high-strength low-alloy steel were investigated at deformation temperatures of 800-1100 °C and strain rates of 0.1-10 s21 using an MMS-200 thermal mechanical simulator. The results indicated that the increased deformation processes observed between the starting and finishing temperatures during hot compression testing caused a polygonal ferrite transformation in the material. The polygonal ferrite grain sizes increased with increasing transformation temperatures and gradually grew larger at higher deformation temperatures. Widmansta¨tten ferrite and acicular ferrite were also formed at high temperatures from 1000-1100 °C, which accordingly led to an increase in Vickers microhardness. In addition, the flow stress in the material increased with an increase in the strain and a decrease in the deformation temperature. Keywords
flow stress, high-strength low-alloy steel, polygonal ferrite, microstructure
1. Introduction High-strength low-alloy (HSLA) steel and microalloy (MA) steel are low-carbon or low-alloy types of steel that contain microadditions of small alloying elements such as Nb, V, Cr, or Ti for better mechanical properties and higher corrosion resistance than conventional steels (Ref 1-3). These steels have been under development since the 1960s with many applications in oil and gas pipelines, large ship construction, transport engineering, and heavy industrial applications (Ref 4, 5). Over the past few decades, a great deal of interest has been shown in the development and use of HSLA steel for pipeline applications with the goal of maximizing strength while retaining toughness (Ref 6, 7). For structural construction and pipeline applications, HSLA steel requires high toughness, high tensile strength, and weldability. Currently, improving these properties by grain refinement through controlled rolling and cooling rates is the most utilized method to improve both strength and toughness. These techniques are called thermomechanical controlled processes (TMCP) (Ref 8-10). Many researchers have extensively studied the refinement of the grain size in HSLA steel by various processes, such as hot deformation, multivariant applications, and multi-axis deforChengzhi Zhao and Hexin Zhang, College of Materials Science and Chemical Engineering, Harbin Engineering University, Harbin 150001, China; and Key Laboratory of Superlight Materials and Surface Technology, Ministry of Education, Harbin Engineering University, Harbin 150001, China; Wilasinee Kingkam and Li Ning, College of Materials Science and Chemical Engineering, Harbin Engineering University, Harbin 150001, China; and Li Zhiming, College of Power and Energy Engineering, Harbin Engineering University, Harbin 150001, C
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