Analysis of the Surface Defects in a Hot-Rolled Low-Carbon C–Mn Steel Plate

Journal of Failure Analysis and Prevention - In the present study, a microstructural investigation was conducted on surface defects occurring in a 28 mm thick low-carbon C–Mn steel...     

Characterization and Properties of Nanostructured Surface Layer in a Low Carbon Steel Subjected to Surface Mechanical Attrition

A nanostructured surface layer was synthesized on a low carbon steel by using surface mechanical attrition (SMA)technique. The refined microstructure of the surface layer was characterized by means of different techniques,and the hardness variation along the depth was examined. Experimental results show that the microstructure is in homogeneous along the depth. In the region from top surface to about 40 /zm deep, the grain size increases fromabout 10 nm to 100 nm. In the adjacent region of about 40~80 /zm depth, the grain size increases from about 100nm to 1000 nm. The grain refinement can be associated with the activity of dislocations. After the SMA treatment,the hardness of the surface layer is enhanced significantly compared with that of the original sample, which canprimarily be attributed to the grain refinement.     

Characterization and Properties of Nanostructured Surface Layer in a Low Carbon Steel Subjected to Surface Mechnaical Attrition

A nanostructured surface layer was synthesized on a low carbon steel by using surface mechanical attrition (SMA) technique,The refined microstructure of the surface layer was characterized by means of different techniques, and the hardness variation along the depth was examined,Experimental results show that the microstructure is inhomogeneous along the depth ,In the region from top surface to about 40 μm depth,the grain size increases from about 100 nm to 1000 nm ,The grain refinement can be associated with the activity of dislocations After the SMA treatment, the hardness of the surface layer is enhanced significantly compared with that of the original sample ,which cam primarily be attributed to the grain refinement.     

Two Hypotheses of “Melanization” on Electrogalvanized Steel Surface

Melanization is harmful to the lightness of galvanized steel surface and also reduces the bonding force between a paint coat and the steel sheet. Experimental results showed that the hypothesis of Zn-Pb codeposition does not hold true, while the fact that PbSO4 micelles in sulfate bath settle on the coating surface support the second hypothesis. The authors come to the conclusions that (1) Any measure to eliminate PbSO4 micelles before or after passivation of the coating will prevent melanization, (2) PbSO4 micelles adsorbed on the surface of passivated film promote the growth of oxygen-deficient Zn oxide and result in the generation of melanization.     

The Variation of “Surface” Pressure in a Nanocrystal as a Function of Temperature

The Mie-Lennard-Jones potential of interatomic interaction is used to derive an expression for “surface” pressure in a nanocrystal with free surface. The nanocrystal has the form of a parallelepiped with a square base. The number of atoms N may vary from eight to ∞. It is found that a certain “inversion temperature” T _i exists for any substance, where the temperature dependences of surface pressure for different sizes of nanocrystal intersect. When the crystal disperses in the T < T _i region, the “surface” pressure increases, and in the T > T _i region decreases, with decreasing size of nanocrystal: P _sf(N) ～ N ^?1/3. The greater the deviation of the nanocrystal shape from cubic, the stronger the dependence P _sf(N). It is demonstrated that, at some temperatures (T < T ₀), the “surface” pressure compresses the nanocrystal, and at other temperatures-stretches this nanocrystal, as its size decreases. The more clearly the quantum effects are defined in the crystal, the lower the value of the “temperature of zero surface pressure” T ₀, which depends on the nanocrystal size and shape.     

Laser Surface Hardening of 9CrSi Steel

The effects of laser hardening parameters such as beam power,beam diameter and scanning rate on microstructure and mardness of 9CrSi steel were investigated.The microstructure of the surface layer of 9CiSi steel was changed from pearlite to martensite,retained austenite and carbide by laser hardening .The depth of the hardened layer increased with increasing laser energy density and the surface hardeness increased by 3-5times as high as the untreated steel.The laser hardened surface had good wear resistance due to martensite and carbide in the surface layer.The wear mode at low speed was abrasive,while the wear mode at high speed was adhesive.     

Modeling of the Thermal Field of a Workpiece in Milling of Austenitic Steel by a Finger‐Type Cutter

The authors report results of modeling thermal fields by the method of finite elements under conditions of milling of 00H17N14M2A austenitic steel by a fingertype cutter. A solution of the problem of unsteady nonlinear heat conduction has made it possible to find the temperature distribution in the surface layers of a workpiece as a function of the cutting rate and the position of the tip of the cutter edge.     

SCC of Stainless Steel Furnace Tubes in a Heating Furnace

Some furnace tubes made of the austeniticstainless steel 1Cr18Ni9Ti for heating crude oil ex-hibited leakage and were on fire in a refinery.Cor-rosion failure analysis was conducted to explore thecause of failure.Macro-and microexamination in-dicated the failure to be stress corrosion cracking bychloride and sulphide with cracks initiating on theinner surface in weld or heat affected zone.Veri-fying tests demonstrated that the cracks occurredduring operating period.The cause of failure wasrelated to the critical situation of the refinery:lackof desalination equipment,lots of steam with liquidfilm on inside tube walls owing to mixing crude oilwith a great amount of water,increasing decompo-sition of inorganic salts and lowering the tempera-ture in furnace tubes.     

On a Thomas-Fermi Model of “Hollow” Atom

Abstract

A Thomas-Fermi model of a spherical shell of positive charge is investigated, under various boundary conditions. The electron distribution and the ionization charge are given particular attention.     

A discussion on “On the solution of a class of fuzzy system of linear equations”

The paper is a discussion on the results obtained by Salkuyeh in the article (Sādhānā 40(2):369–377, 2015). Salkuyeh considers the solution of the fuzzy system of linear equations (FSLE) and gives numerical examples where the results of FSLE are calculated. It was shown that the results by Salkuyeh are not full solutions and do not satisfy equivalent forms of the analysed FSLE. The paper presents a multidimensional approach to finding the solution of the FSLE. On the basis of the notation of the horizontal fuzzy number, a full solution that satisfies the FSLE and its equivalent forms is obtained.     

Gaseous Nitriding Process of Surface Nanocrystallized （SNCed） Steel

The behavior of gaseous nitriding on the surface nanocrystallized(SNCed) steel was investigated.The mild steel discs were SNC ed on one side by using the method of ultrasonic shot peening.The opposite side of the discs maintained the original coarse-grained condition.The gaseous nitriding was subsequently carried out at three different temperatures;460,500 and 560℃ .The compound layer growth and diffusion behavior were then studied.It was revealed that SNC pretreatment greatly enhances both diffusion coefficient D and surface reaction rate.As a result ,nitriding time could be reduced to the half.It was also found that the growth of compound layer with nitriding time conformed with parabolic relationship from the start of nitriding process in the SNCed samples.     

On the “Anomalous” hardness of nanocrystalline materials

The present paper is a further contribution on a rule of mixtures approach for the prediction of hardness dependence on grain size for nanocrystalline metals and intermetallics. Different behavior for the “bulk” and the “grain boundary” regions is assumed in order to consider the special features of nanocrystalline materials, such as the arrangement of geometrically necessary dislocations and disclinations. The usual Hall-Peteh (HP) relationship is assumed to describe the hardness dependence for each one of the two regions. A “correction” term is introduced for the HP slope of the boundary region as compared to the grain interior HP slope. An integrated formula for the total hardness H is obtained involving the grain size, the grain boundary width, the hardness characteristics of coarse grain counterparts and an extra parameter describing the arrangement of triple junctions. This formula compares well with a large set of experimental data.     

Influence of Surface Nano-structured Treatment on Pack Boriding of H13 Steel

In order to lower the boriding temperature of hot work steel H13, method of surface mechanical attrition treatment （SMAT）, which can make the grain size of the surface reach nano-scale, was used before pack boriding. The growth of the boride layer was studied in a function of boriding temperature and time. By TEM （transmission electron microscopy）, SEM （scanning electron microscopy）, XRD （x-ray diffraction） and microhardness tests, the grain size, thermal stability of the nano-structured （NS） surface and the thickness,appearance, phases of the surface boride layer were studied. Kinetic of boriding was compared between untreated samples and treated samples. Results showed that after SMAT, the boride layer was thicker and the hardness gradient was smoother. Furthermore, after boriding at a low temperature of 700℃ for 8 h, a boride layer of about 5 μm formed on the NS surface. This layer was toothlike and wedged into the substrate, which made the surface layer combine well with the substrate. The phase of the boride layer was Fe2B. Research on boriding kinetics indicated that the activation energy was decreased for the treated samples.     

Corrosion Failure of the External Surface of Chlorinator’s Copper Pipes in a Water Disinfection Station

This work investigates the corrosion failure of the chlorinator’s copper pipes in a rural water disinfection station. For this purpose, some corroded samples were provided from the failed pipes and investigated using the X-ray diffraction (XRD) and the scanning electron microscope (SEM) equipped with the energy-dispersive X-ray spectroscopy (EDS). Also, an experimental setup was designed to study the role of the electrolyte formation on the copper pipes. This experimental setup demonstrated that the main factor of pipe failure was the formation of a corrosive electrolyte layer with varying chlorine (presented due to gas leakage) concentration during a day. The electrochemical impedance spectroscopy (EIS) confirmed that variations in the chlorine concentration had an unexpected effect on the corrosion rate. Furthermore, it was found that the main phase in the corrosion products was cupric chloride hydroxide (Cu₂(OH)₃Cl) with many porosities and cracks. These defects provide suitable places for the formation of the corrosive electrolyte and the following corrosion which ultimately led to the failure of the copper pipes.     

Occurrences of bimolecular C-H···O synthons in organic crystal structures in the Cambridge Database

The control of molecular aggregation in the solid state is a current challenge in crystal engineering and materials chemistry. Supramolecular retrosynthesis via recurring synthons is an attractive strategy for the design and self-assembly of target crystal structures. This database study deals with occurrences of two- and three-point intermolecular C-H···O hydrogen bonded synthons in fragments of DAD, DDA and DDD type in organic crystals, where D=C(sp²)-H and A=O-atom. The number of hits with fragments DAD>DDA>>DDD (2606, 1485, 461 hits). Two-point recognition synthon DA⋅AD occurs more frequently in DAD and DDA structures (225, 111 hits) than DD⋅AA motif in DDA and DDD structures (34, 5 hits). Three-point recognition synthons DAD⋅ADA, DDA⋅AAD and DDD⋅AAA are extremely rare (3, 0, 1 hits). These frequency data are rationalised in terms of the molecular complexity of fragments, the overriding preference for centrosymmetric packing, and the stringent requirements of donor-acceptor and solubility match in binary crystals.