Microstructure Evolution of HSLA Pipeline Steels after Hot Uniaxial Compression

Abstract

The mechanical properties of the high-strength low-alloy pipeline steels were mainly controlled by the subsequent phase transformations after rolling. The influence of hot uniaxial compression on the phase transformation of acicular ferrite was explored by viewing of the deformation degree, the deformation temperature, and the strain rate. The results show that the increase of deformation amounts raises the transformation starting and finishing temperature during the subsequent cooling and also promotes the polygonal ferrite transformation, which leads to the decrease of Vickers hardness accordingly. With the increasing of the deformation temperature, the achieved microstructure becomes coarsened and thus decreases the hardness. As the strain rate increases, the microstructure is refined and thus the hardness increases gradually; increasing the strain rate appropriately is beneficial to the refinement of the microstructure.

Effect of Cooling Path on Microstructure Features and Tensile Properties in a Low Carbon Mo-V-Ti-N Steel

“…In addition to previously mentioned micro-alloying methods, the reasonably-designed schedule for Thermo-Mechanical Controlled Processing (TMCP) is also essential for the desired microstructure and mechanical properties. Previous studies [12,13] have extensively estimated the effects of TMCP parameters for two-stage controlled rolling and cooling including the finish rolling temperature (FRT) [14] and the hot rolling reduction (HRR) [13,15], which accelerated the cooling rate (ACR) [16] on the γ→α phase transformation, the final microstructure, and the mechanical properties. These investigations reported that the microstructure comprising quasi polygonal ferrite (QPF), acicular ferrite (AF), granular bainitic ferrite (GBF), and/or lath bainitic ferrite (LBF) as well as a small amount of martensite-austenite (M-A) constituent normally developed in a low-C niobium (Nb)-microalloying steel.…”

Microstructure Formation of Low-Carbon Ferritic Stainless Steel during High Temperature Plastic Deformation

“…In general, this dynamic formation of fine ferrite during deformation is considered to be a dynamic strain-induced transformation (DSIT) [18]. When deformation is in the meta-stable austenite phase region, the dynamic strain-induced ferrite nucleates at the defects [19]. The movement of austenite-ferrite phase boundaries is hindered, due to the enhanced strength of the matrix caused by strain hardening, accompanied by dynamic recrystallization of ferrite grains.…”

“…Firstly, during deformation at high temperature, dynamic recovery and recrystallization occurs, offsetting the work hardening effect resulting from dislocation multiplication [21,22]. Secondly, according to the microstructural observation, the higher deformation temperature promotes the DSIT ferrite formation, accompanied by the movement and annihilation of dislocation, which also results in the loss of work hardening effect [19]. Figure 10 shows the values for Vickers hardness of the samples deformed at the different temperatures.…”

Corrosion Behavior of Welded Joints of X70 Pipeline Steel Produced by High-frequency Welding

“…It is well-known that pipes of big diameter from 530 to 1420 mm for pipelines are manufactured using arc welding under flux [1][2][3]. In this case the effectively of such type of welding significantly decreasing with decreasing of the thick of pipe wall.…”