Continuous Cooling Transformation Behavior Research Articles

Continuous cooling transformation behavior of V microalloyed hot-bent X80 pipeline steel

Abstract Continuous cooling transformation (CCT) behavior of a vanadium-microalloyed hot bent pipeline steel was studied by using Gleeble 3800 thermal simulation machine, and the hot-rolling technique of the tested steel was designed. Acicular ferrite and granular bainite can be observed with the cooling speeds ranging from 1~ 40 °C/s. Higher cooling speed leads to grain refinement. The yield strength is 570 MPa. The ultimate tensile strength (UTS) is 757 MPa. The fracture elongation is 22.50 %. The low temperature toughness at -40 °C is 325 J. The tested steel has both high strength and good low temperature toughness, and meets the mechanical performance requirement of API Spec 5L specification for X80 pipeline steel.

Study on the continuous cooling transformation behavior of X65 hydrogen transportation pipeline steel

Abstract In this work, the continuous cooling transformation (CCT) behavior of X65 hydrogen transportation pipeline steel was studied by Gleeble-3800 machine. The CCT curve was constructed by temperature-dilation curves and microstructures of samples at different cooling speeds. The Ac1 and Ac3 temperatures of the tested steel are 715 °C and 901 °C. Polygonal ferrite and pearlite can be recognized when the cooling speed is between 0.2 °C/s ~ 5 °C/s, bainite and polygonal ferrite can be recognized when the cooling speed is higher than 10 °C/s. The hot-rolling process was designed according to CCT. After finishing rolling, the air cooling steel plates possesses higher hydrogen diffusion coefficient, and the steel plates coiled at 650 °C possesses lower hydrogen diffusion coefficient.

Effect of Combined Addition of Molybdenum and Tungsten on Continuous Cooling Transformation Behavior of High Chromium Cast Iron

Effect of Combined Addition of Molybdenum and Tungsten on Continuous Cooling Transformation Behavior of High Chromium Cast Iron

Continuous Cooling Transformation Behavior in Welding Coarse-Grained Heat-Affected Zone of G115 Steel With the Different Content of Boron

Continuous Cooling Transformation Behavior in Welding Coarse-Grained Heat-Affected Zone of G115 Steel With the Different Content of Boron

Research on 20CrMnTi gear steel continuous cooling transformation behavior

Mechanical properties are essential for gear steel, so as the microstructure. The gear steel’s continuous cooling transformation behavior has influence on both. The performance of 20CrMnTi gear steel has a lot of room for improvement, if the continuous cooling transition behavior is clear. By using the expansion method and microstructure observation, the transformation behavior of 20CrMnTi gear steel under various cooling rates has been investigated. Through these experiments, the 20CrMnTi gear steel continuous cooling transformation curves can be getted. Through this curve, the microstructure of 20CrMnTi gear steel under different conditions can be determined. The research results of 20CrMnTi gear steel are very helpful to the industrial production of gear steel.

Simulated Coarse Grain Heat‐Affected Zone Transformation Behavior of Newly Developed Zr–Ti–RE Deoxidized High‐Strength Low‐Alloy Steels with Extremely High Impact Toughness

The continuous cooling transformation behavior of the Zr–Ti–RE deoxidized high‐strength low‐alloy steel in the simulated coarse grain heat‐affected zone at different cooling rates (corresponding to different t8/5) is investigated by a Gleeble 3800 thermomechanical simulator in combination with microstructure and mechanical properties analysis. The continuous cooling transformation curve in the simulated heat‐affected zone is plotted, and the transformation law of M/A constituents is systematically investigated. It is found that with the increase of the cooling rate, the dominated microstructure is transformed from pearlite + ferrite into granular bainite and, finally, into lath bainite with the further refinement of M/A constituents. The steel exhibits excellent V‐notch Charpy impact properties at −20 °C under typical heat inputs (20, 100, 500 kJ cm−1). Moreover, acicular ferrite formed on spherical Zr–Ti–RE composite inclusions are observed at the heat input of 100 kJ cm−1. The low‐temperature impact absorbed energy gradually decreases with the increasing heat input due to the coarsening of the microstructure, larger effective grain size, and the reduction in the number of high‐angle variant pairs.

Effect of Complex Strengthening on the Continuous Cooling Transformation Behavior of High-Strength Rebar.

The effects of niobium and composite strengthening on the phase transformation characteristics and precipitation behavior of continuous cooling transformation of high-strength rebar during thermal deformation and subsequent cooling were investigated. The results show that when the cooling rate was within 0.3-5 °C/s, ferrite transformation and pearlite transformation occurred in the experimental steels. The Nb content increased to 0.062 wt.%, and the starting temperature of the ferrite transformation decreased. Meanwhile, the ferrite phase transformation zone gradually expanded, and the pearlite phase transformation zone gradually narrowed with the increase in the cooling rate. When the cooling rate was 1 °C/s, bainite transformation began to occur, and the amount of transformation increased with the increase in the cooling rate. It was found that the main precipitates in the experimental steels were (Nb, Ti, V)C, with an average particle size of about 10-50 nm. When the Nb content was increased to 0.062 wt.% and the cooling rate was increased to 5 °C/s, the ferrite grain size was reduced from 19.5 to 7.5 μm, and the particle size of the precipitate (Nb, Ti, V)C could be effectively reduced. The strength of the steel was significantly improved, but the elongation of the steel was reduced. However, the comprehensive mechanical properties of 0.062 wt.% Nb experimental steel was significantly improved at a cooling rate of 5 °C/s.

Effect of Tungsten Addition on Continuous Cooling Transformation and Precipitation Behavior of a High Titanium Microalloyed Steel

Effects of tungsten addition on the continuous cooling transformation (CCT) characteristics and precipitation behavior of a high titanium microalloyed steel were investigated by dilatometry, optical microscopy, scanning and transmission electron microscopy, and hardness measurements. The results showed that the ranges of transformation products were moved to the right side of the CCT diagram when the 0.4% W was added. Accordingly, the following observations were made: (i) the ferrite phase transformation was shifted to the side of lower cooling rates and reduced temperatures; (ii) the bainite phase transformation region ran throughout the whole cooling rate range studied. Addition of W had a positive effect on the particle size refinement and number density increase of the precipitates. At the low cooling rates, in the range of <14 °C/s, W addition shifted the precipitation hardening peak to the low cooling rate side as the ferrite transformation induced stronger precipitation strengthening than the bainite one. Furthermore, the effect of W addition on phase transformation strengthening was obvious (increase in hardness: ~40Hv) at the high cooling rate range, over 14 °C/s.

Continuous Cooling Transformation Behavior and Microstructure Control of Nb Microalloyed Reinforcing Bars

Continuous Cooling Transformation Behavior and Microstructure Control of Nb Microalloyed Reinforcing Bars

Continuous Cooling Transformation Behavior of High Carbon Pearlitic Steel

The continuous cooling transformation behavior of high-carbon pearlitic steel was studied by employing optical microscopy, scanning electron microscopy, and the Vickers hardness test. The results show that the microstructure of the test steel is composed of proeutectoid cementite and lamellar pearlite in the cooling rate range of 0.05–2 °C/s and lamellar pearlite in the range of 2–5 °C/s. Further, martensite appears at 10 °C/s. With the increase in the cooling rate, the Vickers hardness of the test steel first decreases and then increases. In the industrial production of high-carbon pearlite steel, the formation of proeutectoid cementite at a low cooling rate needs to be avoided, and at the same time, the formation of martensite and other brittle-phase at a high cooling rate needs to be avoided.

Continuous Cooling Transformation Behavior in Welding Coarse-Grained Heat-Affected Zone and Microstructure Evolution of G115 Steel with the Different Content of Boron

Continuous Cooling Transformation Behavior in Welding Coarse-Grained Heat-Affected Zone and Microstructure Evolution of G115 Steel with the Different Content of Boron

Continuous cooling transformation behaviour of 30CrMo steel simulated by CSP process

ABSTRACT The continuous cooling transformation (CCT) diagram of 30CrMo steel simulated by compact strip production process was constructed. And the effect of austenite deformation on the CCT behaviour was investigated. The results showed that the microstructure gradually transformed from proeutectoid ferrite and pearlite to bainite and martensite with the increase of cooling rate, accompanying a refined microstructure and an increasing hardness. When the cooling rate was lower than 0.1°C s−1, the desired microstructure of ferrite and pearlite could be obtained. And the austenite deformation strongly promoted the formation of proeutectoid ferrite, which led to a decreasing hardness of deformed steel. When the cooling rate was larger than 10°C s−1, the fully martensite microstructure was obtained. And the austenite deformation inhibited martensite transformation, resulting in a decrease of the martensite transformation starting (M s) temperature from 391°C to 368°C.

Continuous Cooling Transformation Behavior in Welding Coarse-Grained Heat-Affected Zone and Microstructure Evolution of G115 Novel Martensitic Heat-Resistant Steel

Continuous Cooling Transformation Behavior in Welding Coarse-Grained Heat-Affected Zone and Microstructure Evolution of G115 Novel Martensitic Heat-Resistant Steel

Continuous Cooling Transformation Behaviour and Bainite Transformation Kinetics of 23CrNi3Mo Carburised Steel

In this study, the phase transformation behaviour of the carburised layer and the matrix of 23CrNi3Mo steel was comparatively investigated by constructing continuous cooling transformation (CCT) diagram, determining the volume fraction of retained austenite (RA) and plotting dilatometric curves. The results indicated that Austenite formation start temperature (Ac1) and Austenite formation finish temperature (Ac3) of the carburised layer decreased compared to the matrix, and the critical cooling rate (0.05 °C/s) of martensite transformation is significantly lower than that (0.8 °C/s) of the matrix. The main products of phase transformation in both the carburised layer and the matrix were martensite and bainite microstructures. Moreover, an increase in carbon content resulted in the formation of lamellar martensite in the carburised layer, whereas the martensite in the matrix was still lath. Furthermore, the volume fraction of RA in the carburised layer was higher than that in the matrix. Moreover, the bainite transformation kinetics of the 23CrNi3Mo steel matrix during the continuous cooling process indicated that the mian mechanism of bainite transformation of the 23CrNi3Mo steel matrix is two-dimensional growth and one-dimensional growth.

Continuous cooling transformation behaviour and toughness of heat-affected zones in an X80 line pipe steel

A continuous cooling transformation (CCT) diagram was developed using thermal simulation techniques to replicate the coarse-grain heat-affected zone (CGHAZ) of an X80 line pipe steel. Specimens were heated to a peak temperature of 1350 °C with a 1 s hold time, followed by cooling at several rates between 7.6 and 356 °C/s. The thermo-mechanical specimen design was compatible with sub-size instrumented Charpy impact testing, which allowed the toughness to be evaluated. Following dilatometry measurements during continuous cooling, specimens were prepared and examined using optical and scanning-electron microscopy. In addition, the initial CGHAZ microstructure (upper bainite) was reheated to a peak temperature of 850 °C for 1 s (double cycled) and cooled at three different cooling rates (10, 5 and 2 °C/s). This allowed the influence of intercritical reheating, which occurs in multi-pass welds to be investigated in terms of microstructure, tensile strength and notch toughness. It was observed that the microstructure consisted of effective grain (matrix) and untempered MA when cooling at 10 or 5 °C/s. However, when reheating was followed by a cooling rate of 2 °C/s, the microstructure consisted of a combination of effective grain and a more benign distribution of tempered MA, which provided better low temperature impact toughness.

Study on the continuous cooling transformation behavior of heavy thickness X80 pipeline steel

In this paper, the continuous cooling transformation behavior of heavy thickness X80 pipeline steel after two steps deformation was studied by Gleeble1500 thermal simulator. The continuous cooling transformation (CCT) curve of the sample was set up according to the thermal dilation curve and microstructure. The results show that during the continuous cooling process, ferrite and degenerated pearlite in the X80 are obtained in the high temperature phase transformation region. The bainite in the X80 was obtained in the medium temperature transformation region, and when the cooling rate is less than 20°C/s, the micro structure is granular bainite. When the cooling rate is between 20∼30C/s, the mixed microstructure of granular bainite and lath bainite were obtained. According to the CCT curve, in the production, the start cooling temperature and cooling rate should be controlled properly to get expected microstructure so as to ensure the property requirements of the steel plate.

Comparative analysis of continuous cooling transformation behaviour in CGHAZ of API X-80 and X-65 line pipe steels

Continuous cooling transformation diagrams were obtained for a simulated coarse-grain heat-affected zone of API X-80 and X-65 steels using Gleeble-3800 thermo-mechanical simulator. Dilatometry results showed that variable cooling rates have significant effect on phase transformation behaviour and microstructure of the steels. For X-80 steel, a mixture of bainite/martensite at fast and medium cooling rates and ferrite/pearlite at slow cooling rates was obtained and confirmed by microhardness measurements between 340 and 240 HV, whereas, for X-65 steel soft phase such as ferrite was nucleated along with bainite at moderate (15–100 °C s−1) and pearlite at slow cooling rates (3–10 °C s−1). Dilatometry curve comprises inherent noise, and Loess computational filter was used to filter background noise in the curves. Martensite/bainite and ferrite/pearlite coexisted for most cooling rates, which made it difficult to distinguish transformation kinetics of individual phases. In the first derivative analysis d/dT {(ΔL/Lo)} of dilatometry curves, peaks of individual phases were clearly observed. Peaks of individual phase were separated according to their transformation temperature range, and peak rate temperatures were determined. It was confirmed that the first derivative d/dT {(ΔL/Lo)} analysis described phase transformation behaviour precisely and aided in identification of the transformed phases.

Influence of Cu Addition on Microstructure and Mechanical Properties of Fe-0.08C-1Mn-2.5Ni Steel

In addition to precipitation strengthening effect as Cu precipitates in steel, Cu-containing steel is generally believed to have ability to resist corrosion. However, there are some issues, e.g. strengthening mechanism and appropriate copper content, remaining to be clarified. In this presentation, an offshore platform steel Fe-0.08C-1Mn-2.5Ni was used as experimental materials and the emphasis was put on the comparative study of Cu-addition in terms of microstructural evolution and mechanical properties by using microstructural characterization and mechanical properties measurement. The continuous cooling transformation behavior of the two Cu-containing steels with varying contents was first compared. The Cu-containing precipitates were then determined by transmission electron microscopy (TEM) in the hot rolled steel plate after quenching and tempering. Finally, the effect of Cu-addition on precipitation strengthening and low temperature toughness was discussed considering the interaction of Cu precipitates with dislocation and martensite microstructure.

The Effects of Alloying Elements on the Continuous Cooling Transformation Behavior of 2¼Cr-1Mo Steels

The continuous cooling transformation (CCT) behavior of eight 2¼Cr-1Mo steels from a statistically designed matrix was determined. These steels contained two levels of carbon (0.07 and 0.16 wt.%), manganese (0.35 and 0.85%), chromium (1.5 and 2.8%), and molybdenum (0.3 and 1.25%). Each steel was tested in a quenching dilatometer at five to six cooling rates between 725 and 1.2 °C/min. For each CCT sample, the change in length, microstructure, and macrohardness were determined. The ferrite content was also measured for samples cooled near the ferrite nose. Pearson correlation and multiple regression analyses were performed for various CCT diagram parameters. The correlation analysis showed that carbon and chromium contents significantly affected the critical temperatures and the bainite and martensite transformation temperatures. Increasing carbon content significantly increased the hardness for the bainite and martensite range of cooling rates, but hardness at slower cooling rates was unaffected by alloying elements. Regression equations were obtained for the critical temperatures and the ferrite nose cooling rate.

In-situ investigation of phase transformation behaviors of 300M steel in continuous cooling process

Comprehensive understanding of continuous cooling transformation behaviors is important in heat treatment of steels, but there is still a lack of research in the phase transition behaviors of 300M steel, which would greatly hinder the microstructure controlling and finally affect the application of this material. In this work, in-situ observations by high temperature confocal laser scanning microscope (HTCLSM) was introduced by considering its superiorities in clarity, accuracy, and directness, to systemically investigate the microstructure evolutions of 300M steel under various cooling rates (0.01–100 °C/s). Pearlite, bainite, and martensite were observed to form at the cooling rate range of 0.01–0.15, 0.03–1, and 0.3–100 °C/s, respectively. A continuous cooling transformation diagram was constructed based on the in-situ observations, verified by metallography, and compared with dilatometry. Results showed that the transition temperatures by in-situ observations agreed well with the results of dilatometry, while the transition starting temperatures by in situ observation were lower and the phase transition termination temperatures were higher. Finally, models accurately describing the relationships between Vickers hardness, retained austenite content, and cooling rates were established, and the phase transformation mechanisms and kinetics were analyzed. Our finding not only understands fundamentally the transformation mechanisms of different microstructures, but also provides a useful reference for practical microstructure control in heat treatment of 300M steel.