Thermo-mechanical Control Process Steel Research Articles

Buried Arc Application in Hybrid Laser-Arc Welding of Thermo-Mechanical Control Process Steels

Buried Arc Application in Hybrid Laser-Arc Welding of Thermo-Mechanical Control Process Steels

Comparative study on the stress corrosion cracking of a new Ni-advanced high strength steel prepared by TMCP, direct quenching, and quenching & tempering

The stress corrosion cracking (SCC) behaviors of Ni-advanced steels prepared by thermo-mechanical control process (TMCP), direct quenching (DQ), and quenching & tempering (QT) are examined by microstructural characterization, electrochemical test, hydrogen permeation test, and slow strain rate tensile test under different applied potentials. The results show that the SCC susceptibility of these Ni-advanced steels is low at open circuit potential in the simulated environment, and the SCC mechanism is mainly controlled by the anodic dissolution process. However, the SCC sensitivity increases significantly at −1200 mV, and the SCC mechanism becomes hydrogen-induced cracking. The SCC sensitivity of the test steels decreases in the following order: TMCP steel > QT steel > DQ steel, which is primarily attributed to the microstructural difference.

Effect of heat treatment on the mechanical properties and microstructure of HSLA steels processed by various technologies

This study presents a striking advance in investigating the influence of heat treatment on the microstructure and properties of high strength low-alloyed steels obtained using various technologies. In contrast to the normalization treatment, the application of the thermo-mechanical control process (TMCP) offers higher strength characteristics but less stable properties during consequent high-temperature heat treatment. It has been established that the mechanical properties of both the steels are stable up to 650 °C. With an increase in the treatment temperature, the mechanical properties of the TMCP steel (grade S460M) are strongly degraded, while the normalized steel (grade S355J2) remains stable up to 950 °C. This is attributed to intensive grain growth at a temperature higher than Ac3 for TMCP steel and to the microstructural stability of the normalized steel. It is shown that the structural stability during high-temperature heat treatment is controlled by a number of factors such as heating temperature and holding time, grain growth, accumulated strain, the presence of deformation texture, steel deoxidation, and dissolution/uncontrolled growth of precipitations. Data availabilityThe raw/processed data required to reproduce these findings cannot be shared at this time due to technical or time limitations.

Welding Thermal Cycle Impact on the Microstructure and Mechanical Properties of Thermo–Mechanical Control Process Steels

Steels obtained by the thermo–mechanical control process (TMCP) possess a higher level of strength than conventional normalized steels due to the fine‐grained microstructures generated during TMCP. Such enhancement opens ways to decrease metal construction weight. At the same time, TMCP steels have less thermal stability, in connection with a lot of factors affecting and governing grain growth during the heating of TMCP steels. Herein, the effects of the welding thermal cycle (WTC) on the structure and properties of TMCP steels of ferritic–perlite (S460M) and bainitic (alform 620M) types are systematically investigated.

Crack Behavior and Crystallographic Feature for TMCP690 Steel under Fatigue Loading

For a new type of thermomechanical controlled process steel, when stress intensity factor was about 32 MPa m1/2, several slip bands with different orientations occurred in cyclic plastic zone. Some slip bands had strong interaction with dominant crack, which led to crack bifurcation and aggregation. After that, electron back-scattered diffraction technique was employed to evaluate the cyclic plasticity effect on crystallographic features of kernel average misorientation (KAM), strain distribution and fraction of different categories of grains for fatigue loading sample in crack tip zone. Before fatigue loading, KAM distribution map revealed relatively homogeneous plastic deformation and few grains displayed distortion based on strain distribution map. After fatigue loading, KAM showed higher cyclic plasticity in the middle, and lower value on both sides. Strain network structure formed. Meanwhile, when fatigue loading was executed, proportion of recrystallized grains had a little variation from 3.15 to 5.58%. Ratio of substructured grains increased to 19.63%, and deformed grains reduced to 74.79%.

Applicability of Hybrid Built-Up Wide Flange Steel Beams

To accommodate growing demands on either heavy steel structures or unique buildings with irregular configurations, built-up wide-flange steel (BWS) beams are being popularly used in modern steel construction. In current fabrication practices of BWS members, high-performance steels produced in steelmaking factories under the thermo-mechanical control process (TMCP) are typically utilized to achieve proper welding performances. However, since its basic unit price is quite higher than typical hot-rolled steel materials, this study introduced a hybrid BWS section for cost saving with no performance degradation, where high-performance TMCP steel was used in flanges, and conventional hot-rolled steel was adopted in web plate. To verify the tensile performances of a hybrid BWS section with non-uniform properties, split T tension and Charpy impact tests were conducted, and flexural tests were also carried out on hybrid and homogeneous BWS beam members. On this basis, it was confirmed that the structural performance of the hybrid BWS member is comparable with that of the conventional one with a uniform section property.

Waveform and frequency effects on corrosion-fatigue crack growth behaviour in modern marine steels

The primary focus of this work is to investigate the sensitivity of cyclic waveform, frequency (f), load level and microstructure on the corrosion-fatigue crack growth rate (CFCGR) in modern normalised-rolled (NR) and thermomechanical control process (TMCP) ferrite-pearlite steels in the Paris Region of the da/dN vs. ΔK log-log plot. Constant amplitude sinewave (si) and trapezoid waveform (generally referred to here as hold-time (h-t)) were used under frequencies of 0.2 Hz, 0.3 Hz and 0.5 Hz and stress ratio of 0.1. Comparison is also made between the crack path in the S355 TMCP steel under si and h-t in seawater (SW). The role of microstructure in retarding or accelerating fatigue crack growth in SW is also discussed. Experimental results showed that the CFCGR corresponding to the si is higher than that of the h-t for all the load levels and frequencies examined. It was observed that reduction in the f and fatigue load level increased the CFCGR for the h-t but had little effect on the si. Generally, f in the range 0.2–0.5 Hz had little effect; and for a given f an increase in load led to a reduction in the CFCGR, in the Paris Region (PR) for both si and h-t in SW. Under both si and h-t, the CFCGR in the TMCP steels (e.g. S355G8 + M, S355G10 + M) is lower than that of the normalised steels (e.g. S355J2 + N). Metallurgical analyses on the fractured surface of corrosion-fatigue specimens show that the main active crack tip blunting process is the primary factor controlling the CFCGR of steel at high stress intensity factor range (SIFR) and low f in SW. The results obtained from this study have been discussed in terms of the potential impact on the structural design and integrity of offshore wind turbine foundations.

Microstructure and mechanical properties of high strength TMCP steel hybrid disk laser-MAG welded joint

Hybrid laser-arc welding (HLAW) was carried out on high strength thermo-mechanical controlled process (TMCP) steel of 14 mm thickness using single-pass welding (SPW) and multi-pass welding (MPW) processes. Well-formed weld joints with good performance were successfully obtained. The results showed that the microstructure of weld was pre-eutectoid ferrite, acicular ferrite and some granular bainite. There were mainly lath bainite, granular bainite and acicular ferrite in the heat-affected zone. The grain sizes of SPW were thicker than MPW, and the bainite content of MPW was higher than SPW. The average hardness value of the fusion zone was lower than that of the Heat affected zone, but higher than that of the base material. The weld was divided into upper arc domain zone (ADZ) and lower laser domain zone (LDZ). The ADZ was harder than the LDZ. The average absorbed energy of SPW and MPW in the fusion zone at −40[Formula: see text]C was 125.5 and 92 J/cm2, respectively. The influences of microstructure on impact toughness were summarized by analyzing the hardness distribution and microstructure of the welded joint. The brittle transition temperatures of the two processes obtained by the energy criterion and the morphology criterion were close to each other.

NbC-TiN co-precipitation behavior and mechanical properties of X90 pipeline steels by critical-temperature rolling process

The X90 pipeline steels containing Nb and Ti elements have been produced by special critical-tempering rolling process (CTRP) and conventional thermomechanical controlled process (TMCP) respectively. Microstructure was investigated with field emission scanning electron microscopy (FESEM) and field emission transmission electron microscopy (FETEM), and Mechanical properties were measured by tensile test and charpy impact test. Results show that almost two times impact toughness with similar strength level for CTRP steel was obtained compared with TMCP steel. The averaged thickness of pancaked austenite grain is 7.8 μm for CTRP steel, which is less than a half of TMCP steel whose averaged thickness is 18 μm. In addition, high density NbC-TiN co-precipitates in CTRP steel have been found. However, a small quantity of single NbC and TiN precipitates are observed in TMCP steel. The reason is that CTRP process induced co-precipitation of NbC-TiN particles that promoted epitaxial precipitation of NbC on pre-existing TiN precipitate. High intensity TiN-NbC co-precipitates in CTRP steel promoted adequate Zener drag to retard pancaked austenite growth and improved mechanical properties.

Assessment of Steel Subjected to the Thermomechanical Control Process with Respect to Weldability

The study is concerned with the assessment of the weldability of steel S700MC subjected to the thermomechanical control process (TMCP) and precipitation hardening and characterised by a high yield point. Appropriate mechanical and plastic properties of steel S700MC were obtained using the thermomechanical control process through precipitation, solution, and strain hardening as well as by using grain-refinement-related processes. Constituents responsible for the hardening of steel S700MC include Ti, Nb, N, and C. The hardening is primarily affected by (Ti,Nb)(C,N)-type dispersive precipitates sized from several nanometres to between ten and twenty nanometres. The welding process considerably differs from TMCP conditions, leading to the reduction of plastic properties both in the heat-affected zone (HAZ) and in the weld area. This study demonstrates that in cases of TMCP steels, where the effect of precipitation hardening is obtained through titanium and niobium hardening phases, the carbon equivalent and phase transformation γ–α cannot constitute the basis of weldability assessment. The properties of welded joints made from the above-named group of steels are primarily affected by the stability of hardening phases, changes in their dispersion, and ageing processes. The most inferior properties were identified in the high-temperature and coarse-grained HAZ area, where the nucleation of hardening phases in the matrix and their uncontrolled reprecipitation in the fine-dispersive form lead to a sharp decrease in toughness.

Assessment of the Weldability of EH36 TMCP Shipbuilding Steel Welded by High Heat Input Submerged Arc Welding

High heat input welding is one of the alternatives adopted by the world’s major shipyards for increasing productivity in operations for joining materials in shipbuilding. However, the thermal cycles generated during welding may cause microstructural transformations that are detrimental to the mechanical properties, mainly toughness in the heat-affected zone (HAZ). The main aim of this study was characterization of the microstructure and assessment of the mechanical properties of the HAZ of EH36 shipbuilding steel produced by controlled rolling followed by accelerated cooling (Thermo Mechanical Control Process (TMCP) – thermo-mechanically controlled process) compared to a steel of the same grade produced by conventional rolling, both welded by the submerged arc process with two levels of heat input: 76 and 130 kJ/cm. It was observed that the presence of a more refined microstructure in the different regions of the HAZ, associated with the smaller grain size of the base metal and the lower carbon equivalent, were the main factors contributing to the excellent toughness of the HAZ of TMCP steel compared to conventional steel. The results achieved show that it is possible to obtain welded joints with excellent mechanical properties and toughness when using TMCP steel for high heat input welding, and its use is a possible strategy for optimizing fabrication times and costs in the shipbuilding industry.

Advanced TMCP Steel Plates for Pipelines and Structurals

The developments of plates are strongly driven by demands from high-sophisticated pipeline and structural applications. Such needs reflect in plates with higher thickness, larger width, higher toughness also at lower temperatures, higher strength and/or better resistance to sour environments. The requirement profiles are, in some cases, exceptional and have become achievable, in an extreme combination of alloying and processing technologies, only as a result of comprehensive development work and plant investments. An outline of modern production facilities is given. A broad potential for innovation derives by the utilization of the key-technology TMCP (Thermo-Mechanical Controlled Process). As a central element to achieve high-class requirements, aspects and parameters of the metallurgical design are explained. The utilization is explained and illustrated with selected recent applications.

Comparison of Two Different Rolling Processes on Microstructure and Properties of Ferrite-Bainite Dual-Phase Pipeline Steels

The microstructure and mechanical properties of ferrite-bainite dual-phase pipeline steels respectively produced by thermomechanical control process (TMCP) and intercritical annealing were studied using optical microscope, scanning electron microscope (SEM), Vickers hardness tester and MTS 810 servo-hydraulic machine. The results show that these two processes obtain different morphology and distribution of microstructure, but the mechanical properties of them are similar and superior, especially the yield ratios are low. It is found that for TMCP steel, the grains of ferrite are large and the average ferrite grain size is approximately 6.1µm. The bainite structures are lump-shaped with concentrated distribution in the ferrite matrix and the band structure is obvious. For steels produced by intercritical annealing process, the grains are finer and the distribution of bainite is uniform on the ferrite grain boundaries. From the rolling plane to the centre, the grain sizes of ferrite in these two microstructures increase obviously, and the volume fraction of bainite first increases significantly, then decreases slightly in the TMCP steel and the average volume fraction is approximately 60.1%. However, the bainite volume fraction in the intercritical annealing steel decreases gradually and the average volume fraction is approximately 35.4%. Moreover, hardness values in through-thickness direction are uniform in the TMCP steel and these values are also similar in the intercritical annealing steel except the values in the region near the rolling plane are much larger.

Recent developments and applications of TMCP steel plates

The developments of plates are strongly driven by demands from high-sophisticated pipeline and structural applications. Such needs reflect in plates with higher thickness, larger width, higher toughness also at lower temperatures, higher strength and/or better resistance to sour environments. The requirement profiles are, in some cases, exceptional and have become achievable, in an extreme combination of alloying and processing technologies, only as a result of comprehensive development work and plant investments. A broad potential for innovation derives by the utilization of the key-technology TMCP (Thermo-Mechanical Controlled Process). The status of present-day heavy plate production will be presented. An outline of the production facilities, routes and process variants will be given. As a central element to achieve high-class requirements, aspects and parameters of the metallurgical design will be explained. The utilization will be explained and illustrated with selected recent applications.

Development of 7%Ni-TMCP Steel Plate for LNG Storage tanks

LNG storage tanks made of 9%Ni steel plate have safely been operated at the many LNG export and import terminals in the world for the last half-century. Over the years extensive improvement and enhancement have been achieved on the 9%Ni steel plate in terms of toughness in steel to withstand the cryogenic temperatures under an operating condition with LNG.This paper reports research and development of the 7%Ni - TMCP steel plate. As nickel is an expensive and valuable rare metal, it was aimed to reduce nickel content to 7% to save investment costs for constructions of LNG storage tanks. Inferiority of the lower nickel content was compensated by adjusting chemical contents of Mn, Si, Cr etc. and by Thermo-Mechanical Controlled Process (TMCP) with an intermediate heat treatment.In order to evaluate fitness of the 7%Ni - TMCP steel plate and its weld for LNG storage tanks a series of testing was conducted. Three different kinds of plate thicknesses of 40, 25 and 10 mm were chosen to run large scale fracture toughness tests such as duplex ESSO tests, cruciform wide plate tests as well as small scale tests. Those mechanical tests showed excellent quality of the steel and demonstrated safety of the steel which was considered the same safety level as the conventional 9%Ni steel plate.Hence, it is considered that the 7%Ni - TMCP steel plate warrants serious consideration for use in LNG storage tanks.

Thermal distortion analysis method for TMCP steel structures using shell element

As ships become larger, thicker and higher tensile steel plate are used in shipyard. Though special chemical compositions are required for high-tensile steels, recently they are made by the TMCP (Thermo-Mechanical control process) methodology. The increased Yield / Tensile strength of TMCP steels compared to the normalized steel of same composition are induced by suppressing the formation of Ferrite and Pearlite in favor of strong and tough Bainite while being transformed from Austenite. But this Bainite phase could be vanished by another additional thermal cycle like welding and heating. As thermal deformations are deeply related by yield stress of material, the study for prediction of plate deformation by heating should niflect the principle of TMCP steels. The present study is related to the development of an algorithm which could calculate inherent strain. In this algorithm, not only the mechanical principles of thermal deformations, but also the initial portion of Bainite is considered when calculating inherent strain. Distortion analysis results by these values showed good agreements with experimental results for normalized steels and TMCP steels during welding and heating. This algorithm has also been used to create an inherent strain database of steels in Class rule.

Thermal distortion analysis method for TMCP steel structures using shell element

ABSTRACT As ships become larger, thicker and higher tensile steel plate are used in shipyard. Though special chemical compositions are required for high-tensile steels, recently they are made by the TMCP (Thermo-Mechanical control process) methodology. The increased Yield / Tensile strength of TMCP steels compared to the normalized steel of same composition are induced by suppressing the formation of Ferrite and Pearlite in favor of strong and tough Bainite while being transformed from Austenite. But this Bainite phase could be vanished by another additional thermal cycle like welding and heating. As thermal deformations are deeply related by yield stress of material, the study for prediction of plate deformation by heating should reflect the principle of TMCP steels. The present study is related to the development of an algorithm which could calculate inherent strain. In this algorithm, not only the mechanical principles of thermal deformations, but also the initial portion of Bainite is considered when calculating inherent strain. Distortion analysis results by these values showed good agreements with experimental results for normalized steels and TMCP steels during welding and heating. This algorithm has also been used to create an inherent strain database of steels in Class rule.

Strain-rate dependence of mechanical behavior and hysteretic characteristics of TMCP steel (SM570-TMC) and its modeling

Abstract The stress–strain response of TMCP (Thermo-Mechanical Control Process) steels during dynamic deformation is different toward that during static deformation due to strain rate- and temperature-dependences of mechanical behavior. To predict static or dynamic behavior of SM570-TMC under monotonic and cyclic loadings, it is necessary to investigate characteristics of static–dynamic mechanical behavior by experimental approaches and to develop a strain rate-dependent model which can describe the non-linearity and hysteresis of complicated stress–strain relationship in the static and dynamic conditions. Therefore, strain-rate dependence of mechanical behavior and hysteretic characteristic of SM570-TMC is investigated by performing the tensile and low-cycle fatigue experiments as a function of strain rate. And based on the experiments, the strain rate-dependent hysteresis model is proposed by the authors. A three-dimensional elastic–plastic finite element analysis is developed by using the formulated hysteresis model and verified by comparing between the structural analyses and the experiments.

TMCP 강판의 고유변형도 기반 열변형 해석법 개발

As ships become to be larger than ever, the thicker plate and the higher tensile steel plate are used in naval shipyard. Though special chemical composition is needed for high-tensile steels, recent high-tensile steels are made by the TMCP(Thermo-Mechanical control process) skill. The increase of yield stress and tensile stress of TMCP steels is induced from bainite phase which is transformed from austenite, but that increased yield stress can be vanished by another additional thermal cycle like welding and heating. As thermal deformations are deeply related by yield stress of material, the study for prediction of plate deformation by heating should reflect principle of TMCP steels. This study developed an algorithm which can calculate inherent strain. In this algorithm, not only the mechanical principles of thermal deformations, but also the predicting of the portion of initial bainite is considered when calculating inherent strain. The simulations of plate deformation by these values showed good agreements with experimental results of normalizing steels and TMCP steels in welding and heating. Finally we made an inherent strain database of steels used in Class rule.

Impact Toughness Prediction for TMCP Steels Using Knowledge-based Neural-fuzzy Modelling

As one of the most important characteristics of structural steels, toughness is assessed by the Charpy V-notch impact test. The absorbed impact energy and the transition temperature defined at a given Charpy impact energy level are regarded as the common criteria for toughness assessment. This paper aims at establishing generic toughness prediction models which link materials compositions and processing conditions with Charpy impact properties. Hybrid knowledge-based neural-fuzzy modelling techniques which incorporate linguistic knowledge into data-driven neural-fuzzy models have been used to develop the Charpy impact properties prediction models for thermo-mechanical control process (TMCP) steels. Two basic ways of knowledge incorporation are discussed and used to improve the performance of the obtained fuzzy models. Simulation experiments show that both numeric data and linguistic information can be combined in a unified framework and that both Charpy impact energy and the impact transition temperature (ITT) can be predicted by the same model.