Thermomechanical processing of high-strength low-alloy steels

A Gleeble® thermo-mechanical simulator combined with microstructure characterization using a field emission scanning electron microscope was used to provide insights into the seam weld formation during resistance welding (RW). Gleeble® was used to physically/microstructurally simulate the seam weld formation during RW for the first time. It was found that a peak temperature of 1500 ̊C and 10-mm stroke produced a microstructure in the solid-state bondline, the flash, and the heat-affected zone similar to the resistance welded pipe manufactured in an industrial scale. Using the force response obtained during seam weld formation in Gleeble®, microstructure characterization of the seam weld, and thermodynamic calculations, it is proposed the seam weld in a resistance weld consists of a mushy zone with delta ferrite and solute-enriched liquid, which solidifies into austenite, and on post welding cooling, transforms into ferrite and stringers of M/A, respectively. The presence of a mushy zone in the weld joints provides a physical explanation for the “decarburization” phenomenon observed in the seam of resistance welds.

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Bond Formation Mechanism for Resistance Welding of X70 Pipeline Steel

In this investigation, microstructural development and mechanical properties of an automotive grade AISI 4130 steel were explored through various heat treatment routes In that regard, first of all the effect of austenitization temperature and time on the mechanical properties were assessed Then, an optimum austenitization temperature was obtained for austempering at 400 °C and for the duration of 20, 40 and 60 min Finally, under the optimum austenitization condition, austempering temperatures from 300 °C to 500 °C, with 50 °C interval, was evaluated in terms of mechanical properties changes and microstructural development Optical microscope (OM) and Field Emission Scanning Electron Microscope (FE-SEM) equipped with Electron backscattered diffraction (EBSD) detector were employed for microstructural studies Tensile tests, hardness measurements and Charpy impact tests were done to define the mechanical properties of the steels Results show that austenitization at 900 °C for 15 min gives the highest hardness value This was related to the development of bainite microstructure at the expense of martensite Also, under different austenitization temperatures, austempering time of 20 min at 400 °C provides the highest strength level As well, austempering temperature of 400 °C was determined as the best temperature to obtain optimum amount of bainite while strength and ductility levels are acceptable {100} pole figures for some of the austempering steps were gauged and showed a random texture for the initial steel However, after austempering process at different temperatures and times, textured structures with the main components of Cube ({100} ), Copper({112} ), S ({123} ), and Brass ({110} )were obtained Texture components were substantially changed with changing the austempering temperature and time Out of these texture components, non-cube textures were developed for the best combination of austempering temperature and time This latest finding could explain satisfactory levels of mechanical properties under the optimum condition of heat treatment

Texture development during austempering process of an AISI 4130 steel

This work focuses on the effect of Up-Quenching experimentation on mechanical properties of SAE 4130 steel. In that sense, the effect of time and temperature of Up-quenching on hardness, yield strength (YS), ultimate tensile strength (UTS), elongation, and toughness of this automotive steel were investigated. Up-quenching of the austenitized specimens were performed in the temperatures range between 350 to 500 °C for the times period between 20 to 60 min. Mechanical properties were evaluated by means of tensile and hardness tests. In addition, Charpy impact tests were done to measure the fracture energy of the specimens. Microstructural analyses, including texture development and fracture surfaces analyses, were done using Scanning Electron Microscope (SEM) equipped with Electron backscattered diffraction (EBSD) and Transmission Electron Microscope (TEM). Results showed that UP-quenching has positive contribution on hardness, UTS, Elongation% (EL%) and toughness. The results of the present work are useful to control the mechanical properties of SAE 4130 steel via changing the heat treatment parameters. Electron microscopy results showed that the maximum amount of bainite was observed at 450 °C. And the optimum microstructure, that provides the best mechanical properties, is formed in the case of Up-quenching at 450 °C for 20 min {100} pole figures for the Up-quenching in 20 min were constructed and showed that at different Up-quenching temperatures, textured structures with the main components of S, Brass, Copper and Cube are attainable. Texture components were substantially weak in the cases of non-optimum temperatures of Up-quenching. Texture intensity was quite high for the Up-quenching case situation of 450 °C. As well, non-cube textures of S, Brass, and to some extent Copper, were developed for the Up-quenching condition of 450 °C, which clarified the acceptable combination of mechanical properties in this condition. Finally, fracture surfaces examination showed that increasing the temperature and time of Up-quenching leads to lower of porosity that is better distributed in the microstructure.

UP-quenched SAE 4130 steel: Mechanical properties assessment and bainite formation

Textural development, martensite lath formation and mechanical properties variation of a super strength AISI4340 steel due to austenitization and tempering temperature changes

Properties changes of an X52 microalloyed steel processed by a full-scale industrial electric resistant welding (ERW) equipment was studied. Lack of proper toughness level in the weld zone was investigated. Results show that the low toughness value could only be satisfactorily addressed after a two-stage annealing process. {100} pole figures for each processing step revealed a completely random texture for the initial plate. However, after the ERW process, a textured structure with the main components of brass, S and copper was obtained. Texture components were substantially weakened after the second stage of annealing and instead a cube texture was developed which could explain satisfactory level of toughness for the ERW pipe after conducting the two-step annealing process.

S. H. Mousavi Anijdan

Papers

Role of cube texture on toughness variation of electric resistance welded steel