Characterization of the microstructure and hardness of the HAZ in a 800MPa grade RPC steel

0Introduction Intheprojectof“NewGenerationSteelMaterials”, oneoftheeffectiveapproachestoachieve800MPagrade steelsistoadoptRPCphasetransformationtechnique[1]. Atpresent,12 millimeter thickplatesteelwithyield strengthover800MPahasbeenobtainedbymeansofthis…     

Study on improving properties of welded joints of 400 MPa ultra fine grained steel by mechanical surface hardening

0IntroductionOn the premise almost changeless primary materialconstitutions,no increase of primary material cost,and nodecrease of other properties,ultra fine grained steels aregained by extreme refining on grain through the control ofsmelting process and rolling technique.Ultra fine grainedsteels can have double yield strength than traditional mate-rials,hence they have higher cost performance and wideapplication prospect[1].In the practical application of ultrafine grained steels,they often …     

Microstructure and mechanical properties of a laser welded low carbon–stainless steel joint

This article reports on an experimental investigation to understand and subsequently control the alloying composition in laser welding of austenitic stainless steel and low carbon steel. An energy dispersive spectrometer was used to analyse the alloying composition, while microscopy and tensile tests were used to study the microstructure, and mechanical performance of the welded joint respectively. The investigation revealed that above a certain specific point energy the material within the melt pool is well mixed and the laser beam position can be used to control the mechanical properties of the joint. This finding was confirmed using a numerical model based on computational fluid dynamics (CFD) of melt pool dynamics. Strategies to control the composition leading to dramatic changes in hardness, microstructure and mechanical properties of the dissimilar laser welded joint are discussed.     

Microstructure and mechanical properties of Zr-Cu-Al bulk metallic glasses

Zr49Cu46Al5 and Zr48.5Cu46.5Al5 bulk metallic glasses（BMGs） with diameter of 5 mm were prepared through water-cooled copper mold casting. The phase structures of the two alloys were identified by X-ray diffractometry（XRD）. The thermal stability was examined by differential scanning calorimetry（DSC）. Zr49Cu46Al5 alloy shows a glass transition temperature, Tg, of about 689 K, an crystallization temperature, Tx, of about 736 K. The Zr48.5Cu46.5Al5 alloy shows no obvious exothermic peak. The microstructure of the as-cast alloys was analyzed by transmission electron microscopy（TEM）. The aggregations of CuZr and CuZr2 nanocrystals with grain size of about 20 nm are observed in Zr49Cu46Al5 nanocrystalline composite, while the Zr48.5Cu46,5Al5 alloy containing many CuZr martensite plates is crystallized seriously. Mechanical properties of bulk Zr49Cu46Al5 nanocrystalline composite and Zr48.5Cu46.5Al5 alloy measured by compression tests at room temperature show that the work hardening ability of Zr48.5Cu46.5A15 alloy is larger than that of Zr49Cu46Al5 alloy.     

Microstructure and mechanical properties of Al-Fe-V-Si/SiCp composites

The characteristics of microstructures and mechanical properties of the multi-layer spray deposited SiCp/A1-6.SFe-0.6V-1.3Si, SiCp/A1-8.SFe-1.3V-1.7Si and SiCp/Al-10Fe-1.3V-2Si composite sheets obtained by rolling after extruding were investigated. The evolution of the grain and phases of these composites during processing were examined, and the influence of the microstructures on the mechanical properties was analyzed. The experimental results show that the ultimate tensile strengths σb of the three kinds of composite sheets are 420, 535, 470 MPa respectively at room temperature, and 232, 285, 300 MPa at 315℃ and 148, 180, 200 MPa at 400 ℃. The excellent mechanical properties can be attributed to the high solid solubility, fine grain size, Al12（Fe,V）3Si precipitation particles and the SiC particles. And the composition of the matrix alloy has an obvious effect on the mechanical properties of the as-rolled sheets.     

Microstructure and mechanical properties of Al-Cu-Mg-Ag alloyed with Ce

The aged characteristics and microstructure of two Al-Cu-Mg-Ag alloys with and without Ce addition are investigated by TEM and mechanical properties test. The results show that trace Ce addition inhibits precipitating process and delays peak aging time 0.25% Ce additions decrease both tensile strength and ductility. TEM observation shows that the morphology of Ω precipitate can be modified by the small addition of Ce, The trace Ce affects the microstructure by reducing the volume fraction of Ω precipitate. It can be concluded that the intensive interaction between Ce and Cu decreases the Cu atom concentration in alloy matrix and reduces the precipitated kinetics for Ω phase.     

Microstructure and mechanical properties of hot-rolled Mg-Zn-Y-Zr magnesium alloy

Fine-grained magnesium alloys strengthened by quasicrystalline particles were easily developed by thermomechanical process for Mg-Zn-Y-Zr alloys. The microstructure evolution of Mg-Zn-Y-Zr alloys hot rolled with different reductions at different temperatures was studied. Tensile tests and fracture observation were carried out to study the mechanical properties of this alloy. The thin magnesium sheets hot rolled at 380 ℃ exhibit better combination of high strength and ductility than that hot rolled at lower temperature. The results show that the grains become equiaxed and uniform as compared with those of the extruded materials because of recrystallization and repeated heating between rolling passes. It is also found that with the increasing rolling temperature and strain the I-phase particles become much smaller and are homogeneously distributed in the matrix, which enhances both strength and ductility.     

Microstructure and properties of composite of stainless steel and partially stabilized zirconia

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Microstructure and high-temperature mechanical properties of Nb-silicide based in-situ composites

Nb-15W-18Si-xHf （x = 0, 5, 10 and 15, mole fraction, %） alloys were prepared by arc melting and then homogenized at 1 750 ℃ for 50 h. The microstructure and mechanical behaviors, such as Vickers hardness, fracture toughness, room- and hightemperature strength of the alloys were investigated. The microstructure of the annealed Nb-15W-18Si-xHf alloys is composed of large primary Nbss dendrite and fine eutectic mixture of Nbss and MsSi3 silicide. Both the hardness and the fracture toughness show an increase tendency at room temperature with increase of Hf content. The 0.2% compressive yield strength, σ0.2 of the alloys with 5 %Hf and 10%Hf are larger than 960 MPa at 1 200 ℃, and about 500 MPa even at 1 500 ℃.     

Microstructure and toughness of local brittle zone of HSLA steel multipass weld metals

By using thermo-simulation,Auger analysis and Charpy Ⅴ impacttest and with the observation of the microstructures in which cleavage crack wasinitiated,the morphology and toughness of the local brittle zone of C-Mn andCr-Ni-Mo multipass weld metals have been investigated.The results indicatedthat the local brittle zone in C-Mn weld metals with low and high Mn％ and Cr-Ni-Mo weld metals is different.With statistical analysis,it has been revealedthat the more the local brittle zone and the lower their toughness,the lower thetoughness of the entire weld metals.The alloy elements have a noticeable influ-ence on the toughness of the local brittle zone,thereby changing the toughnessof weld metals.     

Microstructure, mechanical properties and age-hardening of Mg-Li alloy sheets

Mg-（5-22）（mass fraction, %）Li alloys with Zn addition were produced and studied. The density of studied alloys is 1.19- 1.62 g/cm^3. It is found that the alloy has excellent cold-workability and can be rolled to thin sheets at room temperature. The tensile tests were carried out at various tensile temperatures and strain rates. It is remarkable that the superplasticity occurs during uniaxial tensions at 150℃. In addition, the sheet is very sensitive to strain-rate even at room temperature. The age-hardening of the sheets at room temperature and 50℃ was investigated. The hardening may be caused by the precipitation of MgLi2Zn phase, and overaging occurs owing to the phase transformation from MgLi2Zn to MgLiZn observed by X-ray diffractometry.     

Effect of secondary weld thermal cycle on structure and properties

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Microstructure and wear properties of tungsten carbide reinforced steel matrix composites

WC（27%） reinforced steel matrix composites were produced by using an electroslag melting casting technique. The microstructure of the material was characterized using scanning electron microscopy（SEM）, optical microscopy and X-ray diffraction （XRD）. Energy dispersive spectroscopy（EDS） and transmission electron microscopy were performed to investigate the interracial composition between WC particle and steel matrix. The results reveal that the WC particles are partially melted into the steel substrate. At the same time, a reaction layer was detected along with the periphery of WC particle, which significantly enhances the bonding strength of the interface. A slipping wear （high stress abrasion） test was utilized to understand the wear behavior of this material. Abrasive experiment displays a better wear resistance than unreinforced steel matrix when coarse WC particles are dispersed into it. The coarse particles provide greater wear-resistance than the fine particles and operatively takes on the most applied loads. Additionally, the large particles have not been peeled during the wear process for a long time, which indicates the effect of interfacial reaction on wear behavior at the ambient temperature. A double carbide （Fe, W）3C is detected in the interface zone between particles and matrices using transmission electron microscopy.     

Microstructure and mechanical properties of Mg-xLi-3Al-1 Ce alloys

Several Mg-xLi-3Al-lCe alloys were prepared by vacuum induction heating. These alloys are Mg-5Li-3Al-lCe, Mg-8Li-3Al-lCe and Mg-14Li-3Al-1C e, respectively. The microstructure and phase composition of these alloys were analyzed by optical microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffractometry. The mechanical properties of these alloys were measured with tensile tester. The results show that, Mg-5Li-3Al-1Ce has a single phase （α） structure, Mg-8Li-3Al-lCe has a double phases （α＋β） structure, Mg-14Li-3Al-1Ce has a single phase （β） structure. And some compounds distribute in the matrix. After being rolled, the grain size of all the alloys is refined. Under the condition of the same content of other alloying elements, the mechanical properties of Mg-5Li-3Al-1Ce are relatively high. With increasing Li content, the strength of both as-cast and as-rolled alloy decrease. For the as-cast alloys, with increasing Li content, the elongation increases. While for the as-rolled alloys, with increasing Li content, the elongation decreases. Ce has refining effect on these alloys.     

Microstructure and mechanical properties of new metastable β type titanium alloy

A new metastable β type titanium alloy called TB-13 with the combination of excellent strength and ductility was developed successfully.In order to develop a perspective on this new alloy,the influence of several commonly used heat treatments on the microstructure and properties was studied.In solution-treated and quenched samples,a low-temperature aging at 480°C results in the precipitation of finerαphase.The precipitation of coarserαphase plate at higher aging temperature(560°C)leads to the increase of tensile ductility but reduction of strength.During low-temperature aging at 300°C,quite homogeneous distribution of fine isothermalωphase particles was found.The isothermalωphase provides nucleation sites forαphase during two-step aging process and makesαphase extremely fine and disperse uniformly in β matrix.Thus,TB-13 alloy is strengthened and its mechanical properties are improved.     

Microstructure and mechanical properties of the pressure die cast magnesium alloy AZ91D after long-term thermal exposure

The thermal resistance of the pressure die cast magnesium alloy AZ91D is yet not investigated sufficiently. In order to assess the effect of a thermal exposure on the microstructural stability and the mechanical properties, the alloy AZ91D is subjected to a long-term annealing for 1 000 h at 80 ℃, 100 ℃, 120 ℃, 150 ℃, 180 ℃ and 200 ℃. After the annealing, the microstructural appearance of the material is investigated by light and scanning electron microscopy and compared with the as-cast condition. Furthermore, tensile tests, hardness measurements and fracture toughness tests are carried out and the measured values are discussed on the basis of the microstructural changes. The results reveal the distinct correlation between the microstructural changes, especially the precipitation of discontinuous and continuous β-particles (Mg17Al12), and the mechanical properties.     

Microstructure and mechanical properties of Mg-Zn-Gd-based alloys strengthened with quasicrystal and Laves phase

One kind of Mg3.5Zn0.6Gd-based alloy strengthened with quasicrystals was designed, and the effect of alloying elements on microstructure and mechanical properties of as-cast Mg-Zn-Gd alloy at room temperature and elevated temperatures were studied. The results indicate that MgZnCu Laves phase, which coexists with quasicrystal at grain boundary, emerges with the addition of copper element in Mg-Zn-Gd alloy. The strength of alloys exhibits the parabola curve with the increase of copper content. The alloy with 1.5% （mole fraction） Cu shows better mechanical properties at room temperature： tensile strength 176 MPa, yield strength 176 MPa and elongation 6.5%. The existence of MgZnCu Laves phase can effectively improve the heat resistance and elevated temperature properties of the alloy. The alloy with 1.5% Cu has better mechanical properties at 200℃ ： tensile strength 130 MPa and elongation 18.5%. The creep test of the alloys at 200℃ and 50 MPa for 102 h indicates that Mg3.5Zn0.6Gd alloy reinforced with quasicrystal has better creep properties than AE42, which can be further improved with the introduction of Laves phase in the alloy.     

Microstructure and properties of Nd:YAG laser welded AZ31B magnesium alloy

Biodegradable magnesium-based alloys are very promising materials for temporary implants. Laser welding is an important joining method in such application. In this study, the as-rolled AZ31B magnesium alloy sheets of 1 mm in thickness were successfully joined by Nd ： YAG laser welding. The microstructure and properties of the welded joint were investigated. The result shows that the welded joint is characterized by a narrow heat-affected zone, finer grains and a large number of precipitates distribute in the matrix in the weld. Microhardness of the weld is significantly improved to 72 HV 0. 05 as compared to 55 HV 0. 05 of the base metal. Tensile strength of butt-welded joint is 180. 24 MPa, which is 76. 8% that of the base metal. The electrochemical corrosion experiment shows that the corrosion resistance of laser welded joint is significantly improved in a 3.5 wt. % NaCl solution.     

Microstructure evolution and mechanical properties of a novel γ'phase-strengthened Ir-W-Al-Th superalloy

The present work introduces a novel γ'phase-strengthened Ir-W-Al-Th superalloy for ultrahigh-temper-ature applications.First,the as-cast microstructure and phas...