scholarly journals Effect of the Heating Rate on Austenite Formation

2021 ◽  
Vol 100 (10) ◽  
pp. 338-347
Author(s):  
ALEJANDRO HINTZE CESARO ◽  
◽  
PATRICIO F. MENDEZ
Keyword(s):  
Transformation Temperature ◽  
Pipeline Steel ◽  
Continuous Heating ◽  
Microalloyed Steels ◽  
Austenite Formation ◽  
Heating Rates ◽  
X80 Pipeline Steel ◽  
Bainitic Microstructure ◽  
The One ◽  
Two Stages

The extent of the heat-affected zone (HAZ) in welding is typically estimated from thermodynamic considerations of austenization; however, thermodynamics are a poor predictor of the HAZ location in microalloyed steels. This work addresses the problem through the study of austenite formation during continuous heating on a grade X80 pipeline steel with an initial ferritic and bainitic microstructure. The methodology involved dilatometry, electron microscopy, and thermodynamic calculations. A continuous heating transformation diagram was developed for heating rates varying from 1˚ to 500˚C/s. For the slower heating rates, austenite start-transformation temperature was higher than the one dictated by the equilibrium, while for the faster heating rates, start-transformation temperature gradually approached the theoretically calculated temperature at which the ferrite can transform (possibly through a massive transformation) without a long-range diffusion into austenite. Partial-transformation experiments suggested that austenite formation occurs in the following two stages: 1) the transformation of bainitic zones into austenite, and later, 2) the transformation of polygonal ferritic grains.

Investigation on the Austenizing Transformation Process in Continuously Heated X65 Microalloyed Pipeline Steels

2013 ◽  
Vol 756-759 ◽  
pp. 72-75
Author(s):  
Dan Tian Zhang ◽  
Zhi Xia Qiao ◽  
Jie Huo ◽  
Yong Chang Liu ◽  
Hui Jun Li ◽  
...  
Keyword(s):  
Heat Treatment ◽  
Pipeline Steel ◽  
Interface Energy ◽  
Ferrite Matrix ◽  
Transformation Process ◽  
Continuous Heating ◽  
Second Stage ◽  
Fine Carbide ◽  
Two Stages ◽  
Carbide Particles

Austenization is an important stage during the quenching-tempering heat-treatment process of X65 microalloyed pipeline steel, because it can influence the development of final microstructure and mechanical properties. In this paper, a detailed investigation was carried out on the austenizing transformation process in X65 microalloyed pipeline steel using high-resolution dilatometric technique and microstructure observations. According to the obtained dilatometric curve during continuous heating, the austenizing transformation process in X65 steel was apparently composed of two stages, 740-765°C and 765-875°C respectively. In order to clarify the microstructure evolution during the two stages, interrupt heat treatment tests were performed and subsequent microstructural observations showed that the first stage (740-765°C) was corresponding to the dissolution of fine carbides particles and the second stage (765-875°C) was corresponding to αγ phase transformation. Firstly, austenite nucleates at interfaces between fine carbide particles and ferrite matrix due to the high interface energy there and then the carbide particles dissolve into the austenite nucleus, which constitutes the first stage. After the fine carbide particles dissolve completely into the austenite nucleus, the ferrite matrix relatively far from the original carbide particles needs higher thermal driving force to transform to austenite, therefore the major αγ transformation occurs at higher temperature range (the second stage).

Austenite Formation in C35 and C45 Alloys

2007 ◽  
Vol 539-543 ◽  
pp. 4637-4642
Author(s):  
V.I. Savran ◽  
Y. van Leeuwen ◽  
Dave N. Hanlon ◽  
Jilt Sietsma
Keyword(s):  
Heat Treatment ◽  
Continuous Heating ◽  
Austenite Formation ◽  
Dual Phase ◽  
Heating Rates ◽  
Austenitic Phase ◽  
Step Process ◽  
Austenite Transformation ◽  
Treatment Processes ◽  
Scanning Electron

The first step in the heat-treatment processes for a vast majority of commercial steels is austenitization. There is much less research put in this field comparing to the cooling transformation, but the interest is continuously increasing especially in view of the development of TRIP and Dual-phase steels. The microstructural evolution during continuous heating experiments has been studied for a series of C-Mn steels with carbon contents in the range 0.35-0.45 wt. % using optical and scanning electron (SEM) microscopy. It is shown that the formation of the austenitic phase is possible in pearlitic as well as in ferritic regions, although in the former it proceeds at a much faster rate due to the shorter diffusion distances. Thus a considerable overlap in time of the ferriteto- austenite and the pearlite-to-austenite transformations is likely to occur. Another observation that was made during the experiments is that depending on the heating rate, the pearlite-to-austenite transformation can proceed in either one or two steps. At low heating rates (0.05 °C/s) ferrite and cementite plates transform simultaneously. At higher heating rates (20 °C/s) it is a two-step process: first ferrite transforms to austenite within pearlite grains and then the dissolution of the cementite lamellae takes place.

Global Reaction Model to Describe the Kinetics of Catalytic Pyrolysis of Coffee Grounds Waste

2017 ◽  
Vol 899 ◽  
pp. 173-178 ◽  
Author(s):  
Ronydes Batista Jr. ◽  
Bruna Sene Alves Araújo ◽  
Pedro Ivo Brandão e Melo Franco ◽  
Beatriz Cristina Silvério ◽  
Sandra Cristina Danta ◽  
...  
Keyword(s):  
Thermal Decomposition ◽  
Large Scale ◽  
Catalytic Pyrolysis ◽  
Petroleum Products ◽  
Reaction Model ◽  
Heating Rates ◽  
Coffee Grounds ◽  
One Step ◽  
Global Reaction ◽  
The One

In view of the constant search for new sources of renewable energy, the particulate agro-industrial waste reuse emerges as an advantageous alternative. However, despite the advantages of using the biomass as an energy source, there is still strong resistance as the large-scale replacement of petroleum products due to the lack of scientifically proven efficient conversion technologies. In this context, the pyrolysis is presented as one of the most widely used thermal decomposition processes. The knowledge of aspects of chemical kinetics, thermodynamics these will, heat and mass transfer, are so important, since influence the quality of the product. This paper presents a kinetic study of slow pyrolysis of coffee grounds waste from dynamic thermogravimetric experiments (TG), using different powder catalysts. The primary thermal decomposition was described by the one-step reaction model, which considers a single global reaction. The kinetic parameters were estimated using nonlinear regression and the differential evolution method. The coffee ground waste was dried at 105°C for 24 hours. The sample in nature was analyzed at different heating rates, being 10, 15, 20, 30 and 50 K/min. In the catalytic pyrolysis, about 5% (w/w) of catalyst were added to the sample, at a heating rate of 30 K/min. The results show that the one-step model does not accurately represent the data of weight loss (TG) and its derivative (DTG), but can do an estimative of the activation energy reaction, and can show the differences caused by the catalysts. Although no one can say anything about the products formed with the addition of the catalyst, it would be necessary to micro-pyrolysis analysis, we can say the influence of the catalyst in the samples, based on the data obtained in thermogravimetric tests.

Study on Corrosion of X80 Pipeline Steel in Different Water Content of Soil

2014 ◽  
Vol 1015 ◽  
pp. 655-658
Author(s):  
Shu Zhen Yu ◽  
Guang Jun Xu ◽  
Han Hua Song ◽  
Xun Zhu ◽  
Wen We Lu ◽  
...  
Keyword(s):  
Water Content ◽  
High Frequency ◽  
Pipeline Steel ◽  
Electrochemical Corrosion ◽  
High Water ◽  
High Water Content ◽  
Linear Segment ◽  
X80 Pipeline Steel ◽  
The Third ◽  
In The Beginning

The electrochemical corrosion of X80 pipeline steel in Xinzhou’s soil with different water content is tested and analyzed. The corrosion signal time and frequency domain figure show that the corrosion signal fluctuates all the time in 30 days’ test with low water content (14%). The slope of high-frequency linear segment in the potential PSD is smaller than it is at the beginning. In the soil with the middle water content (18%), the intense wave motion lasts for 15 days. The noise fluctuation only exists before the third days when in the high water content soil (22%). After the third day, linear drift can be observed but no transient peak. The slope of high-frequency linear segment changes obviously compared with the situation in the beginning. And the high-frequency white noise appears.

Experimental Analysis of Ratcheting Failure Based on the Piezomagnetic Response of X80 Pipeline Steel

2017 ◽  
Author(s):  
Sheng Bao ◽  
Shengnan Hu ◽  
Yibin Gu
Keyword(s):  
Magnetic Field ◽  
Hysteresis Loop ◽  
Mechanical Response ◽  
Pipeline Steel ◽  
Failure Process ◽  
Failure Behavior ◽  
X80 Pipeline Steel ◽  
Test Analysis ◽  
Number Of Cycles ◽  
The Magnetic Field

The objective of this research is to explore the correlation between the piezomagnetic response and ratcheting failure behavior under asymmetrical cyclic stressing in X80 pipeline steel. The magnetic field variations from cycle to cycle were recorded simultaneously during the whole-life ratcheting test. Analysis made in the present work shows that the piezomagnetic hysteresis loop evolves systematically with the number of cycles in terms of its shape and position. Corresponding to the three-stage process in the mechanical response, piezomagnetic response can also be divided into three principal stages, but the evolution of magnetic parameter is more complex. Furthermore, the loading branch and unloading branch of the magnetic field-stress hysteresis loop separate gradually from each other during ratcheting failure process, leading to the shape of hysteresis loop changes completely. Therefore, the progressive degradation of the steel under ratcheting can be tracked by following the evolution of the piezomagnetic field. And the shape transition of the hysteresis loop can be regarded as an early warning of the ratcheting failure.

Effect of Ferrite Volume Fraction on Mechanical Properties of X80 Pipeline Steel

2014 ◽  
Vol 989-994 ◽  
pp. 212-215
Author(s):  
J. Liu ◽  
G. Zhu ◽  
W. Mao
Keyword(s):  
Mechanical Properties ◽  
Heat Treatment ◽  
Work Hardening ◽  
Single Phase ◽  
Volume Fraction ◽  
Pipeline Steel ◽  
X80 Pipeline Steel ◽  
Hardening Behavior ◽  
Two Phases ◽  
Better Than

The effect of volume fraction of ferrite on the mechanical properties including strength, plasticity and wok hardening was systematically investigated in X80 pipeline steel in order to improve the plasticity. The microstructures with different volume fraction of ferrite and bainite were obtained by heat-treatment processing and the mechanical properties were tested. The work hardening behavior was analyzed by C-J method. The results show that the small amount of ferrite could effectively improve the plasticity. The work hardening ability and the ratio of yield/tensile strength with two phases of ferrite/bainite would be obviously better than that with single phase of bainite. The improvement of plasticity could be attributed to the ferrite in which more plastic deformation was afforded.

Fracture Toughness of Different Locations in API X80 Pipeline Steel on Low Constraint SENT Specimens

2016 ◽  
Vol 853 ◽  
pp. 251-255
Author(s):  
Hong Sheng Lu ◽  
Yong He Yang ◽  
Gang Chen ◽  
Xu Chen ◽  
Xin Wang
Keyword(s):  
Welded Joints ◽  
Weak Link ◽  
Pipeline Steel ◽  
Welding Process ◽  
Resistance Curve ◽  
X80 Pipeline Steel ◽  
Three Samples ◽  
Inner Surface ◽  
Notch Orientation ◽  
Low Constraint

With the considerable use of high-grade pipeline steel in onshore and offshore project, welded joints are recognized as the weak link in pipeline because of the non-uniform microstructural regions induced by welding heat input. At first, the microstructural of different regions in API X80 pipeline welded joints was characterized and quantified by SEM, which indicate that the pipeline steel is a typical acicular ferrite steel. In this paper we investigated the J-integral resistance curve (J-R curve) in different locations of API X80 pipeline welded joints through low constraint SENT specimens with side grooves at room temperature. The effect of notch orientation (longitudinal-radial (L-R) and transverse-radial (T-R)) on resistance curve were investigated in base metal, which reveal the orientation almost have no effect on resistance curve. As the welded joints adopted in this study is two-pass steel arc welds, so the J-R curves of the inner surface, the outer surface and through-thickness surface notches specimens in the weld metal were investigated. The inner surface sample have the highest toughness through three samples because of the effect of second pass welding process. The effect of constraint on resistance curve was conduct between low constraint SENT specimen and high constraint SENB specimen, which found that the lower constraint corresponding to the higher resistance curve. After finishing the test, crack advancing plan of different positions were etched and observed by OM to demonstrate that the crack path always in the region which we would like to test.

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