Effect of Y_2O_3 on Cracking Susceptibility of Laser-Clad Ti-Based Composites Coatings

Ti-based composite coatings reinforced by in situ synthesized TiB and TiC were deposited on Ti6AlaV substrates by laser cladding. The effects of Y2O3 on the microstructure and cracking susceptibility of the coatings were investigated in details. It is shown that a small amount of Y2O3 addition can significantly refine the microstructure of the coatings by hastening spheroidization of the primary phase structure. The maximum refinement in microstructure was obtained with the optimum （2 wt%） addition of Y2O3. Moreover, it can increase the volume fraction of TiC and reduce the residual stress of the coatings due to the decrease in lattice distortion of the α（Ti） matrix. All of these factors lead to the reduction in cracking susceptibility of the coatings containing Y2O3 on the premise that the hardness of the coatings is improved. The fracture toughness of the coatings without and with Y2O3 （2 wt%） is 8.32 and 17.36 MPa.m1/2, respectively. Scanning electron microscope examination reveals a transition of the fractured surfaces from cleavage fracture to quasi-cleavage fracture resulting from the Y2O3 addition.

Oblique Y-groove cracking test of the welding cold cracking susceptibility of domestic X-70 pipeline steel

Gas Transmitting From West to East Project' is significant. It should ensure the welding quality and safety of pipeline. The task is very arduous to guarantee the quality of the project in the condition of long line, complex weather and geology features. In this paper, the welding cold cracking susceptibility of domestic X 70 pipeline steel adopted by the project, which is one of the most interesting questions of welding quality about petrol pipeline, was studied by means of oblique Y groove cracking test. The crack ratio of surface and section was tested under the conditions of different welding materials and preheat temperature .The thickness of plate steel was 14.7 mm and 10.3 mm . The results reveal that X 70 pipeline steel has good crack resistance. The research has important value for the construction of large scale pipeline engineering and the application of domestic X 70 pipeline steel.

Hot cracking susceptibility research in BTW1 austenitic high-manganese wear-resistant steel

Baosteel’s first BTW1 austenitic high-manganese wear-resistant steel exhibits strong deformation-induced hardening characteristics.Compared with common low-alloy martensitic wear-resistant steels in the market, it has improved impact wear resistance, hard abrasive wear, erosion wear performance, and impact toughness.The metallurgical properties of such austenitic wear-resistant steel lead to the risk of failure because of hot cracking defects in the welded structure.In wear-resistant applications, evaluating hot cracking susceptibility is necessary to avoid the effect of welding defects.In this study, the Varestraint test is used to quantitatively analyze and evaluate the hot cracking susceptibility of BTW1 austenitic high-manganese wear-resistant steel.The test results show that by controlling the content of impurity elements and grain refinement, BTW1 austenitic high-manganese wear-resistant steel effectively reduces hot cracking tendency and has a low incidence of hot cracking under small strain conditions.The developed matching welding process can effectively avoid the influence of hot cracking susceptibility.

Effect of pre-deformation on the stress corrosion cracking susceptibility of aluminum alloy 2519

The effects of pre-deformation and strain rate on the stress corrosion cracking （SCC） behavior of aluminum alloy 2519 in air and in 3.5% NaCI water solution were investigated by means of slow strain rate tension （SSRT）, scanning electron microscopy （SEM）, and transmission electron microscopy （TEM）. The results indicate that the alloy is susceptible to SCC in 3.5% NaCI water solution and not in air. At the same pre-deformation, the alloy is more susceptible to SCC at 1.33 × 10^-5 s^-1 than at 6.66 × 10^-5 s^-1. Moreover, it is more susceptible to SCC at free pre-deformation than at 10% pre-deformation at the same strain rate. The number of 0 precipitated along the grain boundaries is reduced and distributed discontinuously, at the same time, the precipitate-free zones （PFZ） become narrow and the susceptibility to stress corrosion cracking is reduced after 10% pre-deformation.

Solidification behaviour and hot cracking susceptibility of a novel Ni-based superalloy

A novel Ni-based superalloy GH4151,with a γ′ volume fraction of about 55%and a service temperature capability up to 8oo oC,was investigated.Due to the different cooling conditions of various regions during the solidification of ingots,significant cooling rate variations may lead to the occurrence of hot cracking.Conventional scanning laser microscope was utilised to investigate the solidification process and phase precipitation behaviour of the GH4151 under wide range cooling rates.The characteristics of L→γ transformation were analysed,and the growth rates of at each stage were calculated.The segregation behaviour was predicted using the Scheil equation,and the predicted results match well with the experimental results.The sensitivity coefficient for hot cracking was modified,and cracking sensitivity coefficient values for the alloy under different cooling rates were computed,revealing that the alloy is most susceptible to hot cracking at 10℃/min cooling rate.Therefore,controlling the cooling rate can reduce the possibility of hot cracking in ingot.

Elimination of extraordinarily high cracking susceptibility of aluminum alloy fabricated by laser powder bed fusion

Using the calculation of phase diagrams approach and Scheil solidification modeling,the Al-2.5Mg-1.0Ni-0.4Sc-0.1Zr alloy was designed,intentionally with an extraordinarily high cracking susceptibility,making it prime for solidification cracking during laser powder bed fusion.This study demonstrates the ability to mitigate even the most extreme solidification cracking tendencies in aluminum alloys with only minor alloying additions of Sc and Zr,0.5 wt.%max.Furthermore,by employing a simple direct ageing heat treatment,good tensile mechanical properties were observed with a yield strength of 308 MPa,an ultimate tensile strength of 390 MPa,and a total elongation of 11%.

Investigation of reheat cracking susceptibility in CGHAZ of modified T23 steel

T23 steel(2.25Cr–1Mo–1.6W–0.24V–0.05Nb,in wt.%)has been widely used as water walls in ultra-supercritical(USC)power plants.However,high reheat cracking susceptibility of T23 steel hazarded the safety of USC power plants.It is aimed to improve the reheat cracking susceptibility of T23 steel from the perspective of modifying chemical composition.Gleeble-3800 thermal simulator was used to simulate the coarse-grained heat-affected zone(CGHAZ)in T23 and modified T23 steels via thermal simulation of welding,and then evaluate the reheat cracking susceptibility in CGHAZ of T23 and modified T23 steels by the isothermal slow strain rate tensile test.The microstructure was systematically investigated by optical microscopy,scanning electron microscopy and transmission electron microscopy.The results show that the reheat cracking susceptibility of modified T23 steel is extremely improved.Compared with T23 steel,there are fewer M23C6 particles at the grain boundaries in modified T23 steel,and the degree of intergranular weakening is smaller.At the same time,not only MX in the grain interiors but also the solid-solutioned C and W in the matrix decrease in modified T23 steel,leading to the decline of intragranular strengthening.In addition,small grain size is beneficial to the improvement of the reheat cracking susceptibility of modified T23 steel.The decreased number of M23C6 at grain boundaries helps to retard the formation and propagation of reheat cracks because of decreased denuded zones.

Investigation of Stress Corrosion Cracking Initiation of 7A52 Aluminum Alloy

The stress corrosion cracking（SCC） behaviour of 7A52 aluminum alloy in air and in 3.5% NaCl solution was researched by slow strain rate test（SSRT） and SEM-EDS. The SCC susceptibility was estimated with the loss of the reduction in area. The experimental results indicate that the SCC susceptibility of 7A52 aluminum alloy in 3.5% chloride solution is the highest at strain rate of 1×10-6 s-1. The lowest one is under the condition of 1×10-5 s-1. Stress concentration and anode dissolving around Al-Fe-Mn intermetallics initiate micropores which will result in microcracks. The existence of intermetallics in the microstructure may play an important role in understanding the SCC initiation mechanisms of 7A52 aluminum alloy.

Effects of applied potential on the stress corrosion cracking behavior of 7003 aluminum alloy in acid and alkaline chloride solutions

Potentiodynamic polarization tests and slow strain rate test（SSRT） in combination with fracture morphology observations were conducted to investigate the stress corrosion cracking（SCC） behavior of 7003 aluminum alloy（AA7003） in acid and alkaline chloride solutions under various applied potentials（Ea）. The results show that AA7003 is to a certain extent susceptible to SCC via anodic dissolution（AD） at open-circuit potential（OCP） and is highly susceptible to hydrogen embrittlement（HE） at high negative Ea in the solutions with p H levels of 4 and 11. The susceptibility increases with negative shift in the potential when Ea is less than-1000 m V vs. SCE. However, the susceptibility distinctly decreases because of the inhibition of AD when Ea is equal to-1000 m V vs. SCE. In addition, the SCC susceptibility of AA7003 in the acid chloride solution is higher than that in the alkaline solution at each potential. Moreover, the effect of hydrogen on SCC increases with increasing hydrogen ion concentration.

Evaluation of the cracking and aging susceptibility of asphalt mixtures using viscoelastic properties and master curve parameters

Aging can significantly affect the performance of asphalt mixtures, causing increase in stiffness, reduction in relaxation capability and increase in cracking susceptibility. It is also well known that fundamental viscoelastic properties are used for design and modelling of asphalt mixtures and pavement structures to addressing rutting, fatigue and thermal cracking concerns. The objective of this paper is to study how the viscoelastic properties of asphalt mixture change over time, and evaluate and identify the cracking and aging susceptibility of asphalt mixtures with different mix variables during material selection and mixture design. Ten mixtures are evaluated using different laboratory conditioning protocols to simulate a range of aging levels in the field. The complex modulus test is then conducted on the lab aged mixtures to measure the viscoelastic properties in order to construct the dynamic modulus and phase angle master curves. The mixture Glover-Rowe(G-Rm) parameter and the shape parameters of the dynamic modulus and phase angle master curves, including inflection point frequency(-β/γ), difference between the glassy modulus and the inflection point modulus(γ), peak value of phase angle(a) and the horizontal position(frequency) of the peak phase angle value(c), are determined and evaluated for the mixtures with different aging conditions and mix variables. The study indicates the ability of the G-Rmparameter and all the master curve shape parameters to capture the effect of different aging conditions on linear viscoelastic mixture properties, as well as the cracking and aging susceptibility of asphalt mixtures.

Hydrogen trapping and electrochemical corrosion behavior of V–N microalloyed X80 pipeline steels consisting of acicular ferrite and polygonal ferrite

Hydrogen trapping behavior of V–N microalloyed X80 pipeline steels was studied by means of hydrogen permeation and hydrogen induced cracking(HIC)tests.In addition,the electrochemical performance of the steels in 3.5 wt.%NaCl solution was investigated.Results indicated that the microstructure of experimental steels mainly consisted of acicular ferrite and polygonal ferrite(PF).When the fraction of PF was 9.1%and 30.4%,hydrogen effective diffusion coefficient was 1.624×10^(−6) and 3.121×10^(−6) cm^(2)/s,respectively.The pipeline steels were not susceptible to HIC.Numerous potential hydrogen traps distributed in homogeneous dispersion were conducive to high HIC resistance.With increasing the fraction of PF from 9.1%to 30.4%,the corrosion current density increased from 5.39×10^(−6) to 9.49×10^(−6) A cm^(−2),the corrosion potential decreased from−0.48 to−0.57 V,and the charge transfer resistance decreased from 2301 to 2068Ωcm^(2),respectively.Increased fraction of PF was disadvantageous for corrosion resistance because of galvanic corrosion.

Weldability of Low Carbon Transformation Induced Plasticity Steel

Transformation induced plasticity （TRIP） steel exhibited high or rather high carbon equivalent （CE） because of its chemical composition, which was a particularly detrimental factor affecting weldability of steels. Thus the weldability of a TRIP steel （grade 600） containing （in mass percent, %） 0.11C-1. 19Si-1.67Mn was extensively studied. The mechanical properties and impact toughness of butt joint, the welding crack susceptibility of weld and heat affected zone （HAZ） for tee joint, control thermal severity （CTS） of the welded joint, and Y shape 60° butt joint were measured after the gas metal arc welding （GMAW） test. The tensile strength of the weld was higher than 700 MPa. Both in the fusion zone （FZ） and HAZ for butt joint, the impact toughness was much higher than 27 J, either at room temperature or at -20 ℃, indicating good low temperature impact ductility of the weld of TRIP 600 steel. In addition, welding crack susceptibility tests revealed that weldments were free of surface crack and other imperfection. All experimental results of this steel showed fairly good weldability. For application, the crossmember in automobile made of this steel exhibited excellent weldability, and fatigue and durability tests were also accomplished for crossmember assembly.

Effect of Tempcore Processing on Mitigating Problems of Tramp Elements in Low C Steel Produced from Recycled Material

The effect of tramp elements in the steel was intensively studied. It was found that the solubility of tramp elements decreased as the temperature decreased under normal cooling conditions. The tramp elements （Cu, Pb, and Sn） diffused toward the grain boundaries, and intermetallic compounds or rich phases which have low melting points were formed, causing reduction in ductility and failure during the bending test. Rebars with Cu content which were left to air cooling after the last step showed drop in elongation, up to 32 %. On contrast, the samples with high per- centage of tramp elements （Cu, Pb, and Sn） in the billet, which were rolled and subjected to Tempcore process, did not show drop in elongation or failure in bending test （especially for rebar with diameter less than 32 mm）; however, copper must be less than 0.35 mass% to prevent the precipitation of Cu-rich zones of critical size in 32 mm. When quench- ing was applied, the tramp elements remained in the interstitial supersaturated solid solution positions inside the grains and would not have the chance to diffuse and form precipitates, hindering the copper precipitates from reac- hing the critical size necessary for impairing the properties. This would hinder the occurrence of the harmful effect of the tramp elements on the elongation or the hot shortness after rolling.