Metallurgical Microstructure Research Articles

Microstructure and corrosion resistance of radial friction welded supermartensitic stainless steels

In this work, supermartensitic stainless steel pipes were radial friction (RF) welded and their corrosion behaviours were studied based on potentiodynamic polarisation and double-loop electrochemical potentiokinetic reactivation tests. Measurements were performed on samples taken from the base metal (BM), weld interface and consumable ring (CR) of the RF weldment. The corrosion properties are discussed in terms of their resulting metallurgical microstructure. The precipitation of Cr carbides that takes place during the tempering treatment induces a substantial Cr depletion value (Ir/Ia = 54.22%). On the other hand, CR and weld interface regions, which had their microstructure transformed and their Cr carbide precipitates redissolved by the RF welding thermomechanical cycle, present a low level of Cr depletion (Ir/Ia < 1%). The AC microstructure, which is composed of a mixture of virgin martensite and stable retained austenite, presents an increase in pitting corrosion resistance compared to the tempered structure of the BM region. It was also observed that the δ-ferrite decreases the pitting resistance of the weld interface region.

Effect of Laser Beam Alloying Strategies on the Metallurgical and Mechanical Properties of Hot Forming Tool Steels

In terms of increasing lightweight designs of car body parts, the machining of high strength steels in hot stamping processes becomes of particular interest. Due to high process forces at hot stamping, the surface of such tools in the area of maximal stress is subject wear, which necessitate some local increase of microhardness to enhance the mechanical performance. Especially laser beam alloying using filler wire and beam oscillation is some suitable method to modify the mechanical properties of tool surfaces to emcompass some continuous martensitic structure, featuring a certain microhardness. Nevertheless the thermal energy input during laser beam alloying induces tempering in the heat affected zone and reduces the hardness.This paper discusses the influence of alloying strategies on the thermal energy input and the resulting metallurgical structure of modified tool surfaces. Also the cooling behavior of alloyed lines for different energy inputs per unit length is of interest. Therefore, the metallurgical microstructure is analyzed regarding microhardness as well as formation of carbides. Furthermore, a numerical thermal simulation is developed to investigate the temperature profile in the heat affected zone of the specimen. These investigations permit the control of the spatiotemporal energy input to avoid tempering of the microstructure.

Constitutive behaviour in as quenched Al–5Cu–0·4Mn alloy during hot deformation

The overburning temperature of the ZL205A (Al–5Cu–0·4Mn) alloy is first determined by differential scanning calorimetry analysis. Then, the solid solution temperature of ZL205A was determined by metallurgical microstructure observation. Isothermal compression tests of the as quenched ZL205A were conducted in temperature from 25 to 500°C and the strain rate from 0·001 to 1 s−1. The deformation behaviour of the as quenched ZL205A was investigated. The prediction of the flow stresses were studied using artificial neural network. The average absolute relative error between the predicted flow stresses and experimental results is 4·4%, which demonstrates that the network proposed in the present paper has high precision. Therefore, it can be chosen as a thermomechanical model to treat the distortion problems of components during quenching process.

Experimental Platforms and Finite Element Analysis on Hot Stamping Processes

Due to the complexity of hot stamping mechanism, including the coupling of material formability, thermal interaction and metallurgical microstructure, it makes the process design more difficult even with the aid of the finite element analysis. In the present study, the experimental platforms were developed to measure and derive the friction and heat transfer coefficients, respectively. The experiments at various elevated temperatures and contact pressures were conducted and the friction coefficients and heat transfer coefficients were obtained. A finite element model was also established with the experimental data and the material properties of the boron steel calculated from the JMatPro software. The finite element simulations for the hot stamping forming of an automotive door beam, including transportation analysis, hot forming analysis and die quenching analysis were then performed to examine the forming properties of the door beam. The validation of the finite element results by the production part confirms the efficiency and accuracy of the developed experimental platforms and the finite element analysis for the process design of hot stamping.

Mechanism Analysis of a Boiler Economizer Corrosion

Reasons for boiler economizer tube corrosion were discussed based on results of macroscopic inspection, metallurgical microstructure examination, SEM and EDS fracture analysis. Results showed that the tube corrosion was due to sulfur corrosion that resulted in matrix exposure and led to further oxygen corrosion.

Research on the Optimal Design of Soccer Robot Based on the Mechanical Analysis

Leakage causes of branch pipe of unit thermal networks were discussed based on macroscopic observation, chemical composition analysis, metallurgical microstructure inspection, mechanical property tests, SEM and EDS analysis. The experimental results showed that frequent contact of outer pipe wall with corrosion media and thermal fatigue load led to early crack of the pipe. During compression test, the crack propagated under increased compression stress and burst finally. Suggestions were provided to prevent similar events happening.

Corrosion behavior of radial friction welded supermartensitic stainless steel pipes

Supermartensitic stainless steel pipes were radial friction (RF) welded and their corrosion properties were determined based on electrochemical tests. Measurements were performed on samples taken from the base metal (BM), weld interface, and consumable ring (CR) of the RF weldment. The corrosion properties are discussed in terms of their resulting metallurgical microstructure. In acid media, RF weldment regions presented better corrosion performance than the tempered structure of the BM. The Cr carbide precipitation that occurs during tempering causes substantial depletion of Cr, while δ-ferrite formation during welding cycle decreases the pitting corrosion resistance of the material.

Analysis on Fracture Causes of Condensate Water Pump Shaft

Failure causes on a condensate pump shaft were discussed by means of macroscopic observation, chemical composition analysis, metallurgical microstructure inspection, mechanical property tests and stress analysis. The experimental results showed that the improper material with disqualified chemical composition, improper microstructure and poor mechanical properties acted as inherent factor. In addition, structure design that led to stress concentration contributed to the failure as external factor. Finally, fatigue fracture happened at the reduce section of the pump shaft.

Hydrogen diffusion into three metallurgical microstructures of a C–Mn X65 and low alloy F22 sour service steel pipelines

This paper describes the process of hydrogen diffusion in API 5L X65 and ASTM A182 F22 steels with three different metallurgical microstructures (quenched and tempered, quenched and annealed) by an electrochemical technique which is a modified Devanathan and Stachurski's cell. The analysis of experimental results compares different measurement methods for hydrogen diffusion coefficients: 1) charge method; 2) partial charge and partial discharge method; 3) discharge method. For the steel, cathodically polarized in acidic medium (pH ≈ 4.2), the less dispersed and more meaningful results are obtained by partial charge and partial discharge method after about one hundred hours of polarization, i.e., when a stationary regime was reached. The discharge method, carried out after one hundred hours of polarization, provides analogous results by extrapolation of the experimental results obtained during the initial phase of hydrogen desorption. The hydrogen diffusion coefficients measured would appear dependent only on the hydrogen migration processes in the crystal lattice regular sites and corresponding values DL increase as follows: quenched < quenched and tempered < annealed.

Multiple-shocks induced nanocrystallization in iron

We found that multiple shots of femtosecond laser-driven shock pulses changed coarse crystalline iron grains with a size of 140 μm into nanocrystals with a high density of dislocations, which had never been observed in conventional shock processes. We performed metallurgical microstructure observations using transmission electron microscopy (TEM) and hardness measurements using nanoindentation on cross-sections of shocked iron. TEM images showed that grains with sizes from 10 nm through 1 μm exist within 2 μm of the surface, where the dislocation density reached 2 × 1015 m−2. Results of the hardness measurements showed a significant increase in hardness in the nanocrystallized region. We suggest that the formation of a high density of dislocations, which is produced by a single shock, induces local three-dimensional pile-up by the multiple-shocks, which causes grain refinement at the nanoscale.

The Effect of Relative Thickness on Microstructures of TiB2/TiC Particles Reinforced Carbon Steel Matrix Surface Composite

This paper introduces a process that combines a vacuum expandable pattern casting V-EPC with self-propagation high–temperature synthesis SHS of TiB2/TiC particles for fabricating the TiB2/TiC duplex particulates reinforced carbon steel matrix surface composite, and the effect of relative thickness δ on metallurgical quality and microstructures. FeTi-FeB-FeCr system with low cost is adopted as the SHS reactant. Experimental results show that with increasing δ, the surface composite is gradually formed and the metallurgical quality improved. The typical microstructures of the composite from surface to core are consisted of three different layers, i.e., the surface compound layer, the interim transitional layer and the carbon steel base. A certain amount of fineTiB2/TiC particles is distributed in the matrix of the surface compound layer.

Study of laser butt welding of SUS301L stainless steel and welding joint analysis

This paper describes a study on laser butt welding of 4 and 2 mm SUS301L stainless steel and a detailed analysis of welding joints. The gap tolerance of butt joint was also studied with optimized process parameters. The electrolytic etching in 10 % oxalate solution was used to test the intergranular corrosion of the 4 mm SUS301L welded joint. Fatigue property of the 2 mm SUS301L welded joint was tested under the conditional cycle times of 1 × 107. Using optical microscopy, the changes of metallurgical microstructure in the weld zone of 4 mm SUS301L were also studied. It has been found that laser butt welding of 4 mm SUS301L is able to achieve sound metallurgical morphology and high strength weld joint when the butt gap is within certain tolerance. The weld joint also has good resistance to intergranular corrosion and has a fatigue limit of 310 MPa.

Fracture of the Leads of Integrated Circuits with TO Package

The Kovar alloy leads broke from two integrated circuits (ICs) with TO (Tin Outline) package. Through the metallurgical microstructure analysis, energy dispersive spectrometer (EDS) analysis and fractography analysis, the failure mode of the leads was found to be stress-corrosion-cracking. After checking the whole plating process, it was found that the residual chloride ions resulted in stress-corrosion-cracking. The chloride ions were absorbed inside the residual organic containment below Ni-plating layer. And a corrective measure was proposed.

Metallurgical microstructure control in metal-silicon reactions

A comprehensive review on interfacial reactions to form silicides between metal and Si nanowire or wafer is given. Formation of silicide contacts on Si wafers or Si nanowires is a building block needed in making current-based Si devices. Thus, the microstructure control of silicide formation on the basis of kinetics of nucleation and growth has relevant applications in microelectronic technology. Repeating events of homogeneous nucleation of epitaxial silicides of Ni and Co on Si in atomic layer reaction is presented. The chemical effort on intrinsic diffusivities in diffusion-controlled layer-typed intermetallic compound growth of Ni2Si is analyzed.

Influence of Cutting Speed on Surface Plastic Deformation and White Layer Formation of FGH95

The superalloy parts in the aeronautical field demand high reliability, which is largely related to surface integrity. Surface integrity generally includes three parameters, such as geometric parameter, mechanical parameter and metallurgical parameter. The paper presents the influence of cutting speed on surface plastic deformation and white layer formation through orthogonal milling of FGH95 superally material. The influence of cutting speed on grain refinement of machined surface is also investigated. It is found that cutting speed has significantly effect on the surface metallurgical characteristic microstructure. The increasing of cutting speed creates severer plastic deformation. Surface plastic shear strain increases with the increasing of cutting speed, while the depth of plastic deformation decreases on contrary. White layer thickness is increased with the increasing of cutting speed. Through statistical analysis for grains number, it can be drawn that the higher the cutting speed, the more serious grains refinement.

Failure Analysis on Boiler Industrial Extraction Steam Pipe

Failure reason of boiler extraction steam pipe was discussed by means of macro-observation, chemical composition analysis, metallurgical and SEM microstructure examination and EDS analysis. Results showed that the crack initiated from original corrosion flaw on outer wall of the extraction pipe, propagated rapidly under large pressure caused by water-hammer due to no drainage design in the unit pipe system until final bursting.

Analysis and Suggestions on Leakage of Boiler Low Temperature Reheater

Leakage causes of boiler low temperature reheater were discussed by means of macroscopic inspection, chemical composition analysis, metallurgical microstructure examination, SEM and EDS fracture analysis. Results showed that the reheater leakage occurred for cracks originating from the fillet seam of ear plate. The main causes lie in improper structural design of the ear plate welding directly on the reheater elbow where suffered from complicated stress condition, wall thinning and out-of-round. In addition, as a weak zone, heat effect zone of the fillet welding seam was more likely to crack under fatigue stress for frequent unit start and stop and pipeline vibration. Installation stress existed between the ear plate and support block also contributed to the cracking. Suggestions were provided to avoid similar accident based on the comprehensive analysis of leakage causes.

The Thermomechanical Controlled Processing of High-Strength Steel Plate: A New View of Toughness Based on Modern Metallography

Modern thermomechanical controlled processing (TMCP) of advanced steels is now an important processing route in the production of engineering structures and products that are of value to society. The principles of TMCP are now practiced in the hot mill, cold mill and press forming shops around the world. Successful TMCP means that the proper metallurgical microstructure has been obtained in the required areas of the steel. The ideal microstructure is often defined by the correct phase balance and dimensions either of the parent austenite or final ferritic phase. Technological and economic demands have led to ever increasing levels of strength, especially for applications such as large diameter linepipe. The operative yield strengths in 18mm hot rolled plate have increased from X52(ferrite pearlite) in 1970 to X80(ferrite-bainite) today. The next frontier is the X100-X120 strength range, where bainitic or martensitic microstructures are required. It is clear that achieving a high-strength bainitic microstructure in heavy plate requires a high Carbon Equivalent value (C. E. II or Pcm), a rapid cooling rate, and a low water-end temperature. The requirement of high toughness and good weldability also means a low carbon content. This paper will describe the results of a research program where a steel of C. E. 0.56 and Pcm 0.23 was reheated, rough rolled for grain refinement, finish rolled for austenite pancaking, and direct quenched to below the Bs temperature. It was found that the strength and especially the toughness of the fully processed plates could not be explained using conventional metallographic techniques in conjunction with known structure-property relationships. However, the application of modern metallographic techniques based on FEG-SEM incorporating OIM led to microstructural characterization that more fully explained the observed mechanical properties. Of particular importance were the amount of MA micro-constituent, the crystallographic packet size of the bainite, and the high angle boundary character, especially the CSL boundaries, found in the microstructure. In the future, improved modeling of microstructural evolution and attendant mechanical properties will incorporate these important features.

Fracture Analysis on Drainage Pipe Socket of Boiler

Rupture reason of boiler drainage pipe socket was analyzed by means of chemical composition analysis, macro-observation, metallurgical and SEM microstructure examination. Results showed that the rupture of the drainage pipe socket was a result of creep cracking initiated in intercritical zone of HAZ due to long period operation under high temperature. During creep process, carbides precipitated on fine grain boundaries of intercritical zone and grew up gradually into new coarse carbides as favorite nucleation site for creep void. With the growth, coalesce and connection of creep voids carries on, micro-cracks formed on original austenite boundaries and finally led to fracture of weld joint.

室町時代末期から江戸時代に製作された槍刀身の金属組織

室町時代末期から江戸時代に製作された槍刀身の金属組織