Study of microstructural evolution of friction taper plug welded joints of C–Mn steels

Abstract

This paper describes the microstructural evolution of friction taper plug welded joints of C–Mn steels. Experimental and numerical analyses included calculations based on Calphad and continuous cooling transformation curves, and characterisation techniques. The studied friction taper plug welded joint contains three macroregions: plug material, thermomechanically affected zone (TMAZ) and base material. The thermomechanical conditions imposed in the studied friction taper plug welded joint precluded the formation of a heat affected zone. However, seven subregions were identified within the TMAZ region and details are discussed. The interface zone is found in the TMAZ region, where the most relevant phase transformations take place. It is suggested that the phase transformations in TMAZ region depend on local conditions, such as chemical composition, deformation rate, thermal history and the previous thermomechanical history of the parent materials.     

Macro—and microstructural changes in hydrogenated TiMn2 and Ta

Binary TiMn2 alloys with various compositions were arc melted in an Ar atmosphere.These alloys consist of TiMn2 and a small amount of TiMn depending on alloy composition.Annealed Ti-59.4%Mn exhibits the greatest capacity for hydrogen absorption and the smallest degradation of capacity during repeated hydrogen absorption and desorption.No apparent macro-and microstructural chanes are observed in Ti-59.4%Mn by repeated hydrogenation of 30cycles.At Mn content higher than 59.4%Mn,the formation of nano-sized Ti-hydride and the lattice expansion due to retained interstitial hydrogen were confirmed in repeatedly hydrogenated alloys.Pulverized powders were refined in all the alloys with increasing the number of repeated hydrogenation cycles.Many onion-like cracks are introduced in annealed pure Ta with 100℃m equi-axed grains by holding at 1473K followed by furnace cooling to room temperature in a hydrogen atmosphere,but no crack is observed after holding at 1473K in a hydrogen atmosphere followed by furnace cooling in an Ar atmosphere.It is concluded that the surface activation is attained in a hydrogen atmosphere at 1473K and multiple cracking occurs by absorbing a large amount of hydrogen at lower temperature.Volume expansion and dislocations generated by hydrogenation and hydride formation are responsible for multiple cracking.Hydrogen-induced multiple cracking in Ta occurs in the following sequence:hydrogen absorption,lattice expansion,hydride formation,and crack nucleation and propagation.Powder fabrication of Ta by hydrogenation is discussed in comparison with the hydrogen pulverization of intermetallic alloys.     

Wear resistance of high chromium—high carbon cast irons

High chromium—high carbon experimental castings were produced using chilled moulds to study their resistance while subjected to erosive conditions. An experimental design in which the ratio of chromium over carbon equivalent, the amount of molybdenum and that of vanadium plus titanium were varied each in two different levels to obtain eight different casting conditions, The average size and volume fraction of the carbides present in the castings were determined by quantitative analysis. Samples cut from the ingots were subjected to wear in a specially designed rig that used directly reduced iron pellets as an erosive agent; the design is such that these particles impinge the samples after being impulsed by commercial purity nitrogen heated up to maintain a temperature of 550 °C. A multi-linear statistical model was developed to relate the wear resistance of the samples. It was found that resistance to wear was related to chemical composition, in such a way that the samples that exhibit higher wear were those with the higher amount of molybdenum. It was also found that the distribution of primary carbide sizes could affect resistance to wear.     

Optimizing hardenability of high chromium white cast iron

H igh Cr white cast irons possess a combination of excel lent abrasion resistance and a reasonable degree of toughness. The microstructure of high-Cr white cast irons consists of a composite of large primary and/or eutectic carbides in type M7C3 (where M=Cr, Fe, Mo, Mn, etc.) and a softer matrix. The matrix structure favored in the as-cast irons is predominantly austenite which can be changed to predominantly martensite after air quenching. At present, when factories produce high-Cr white …     

The stress corrosion cracking of high strength CrMnSiNi and CrMo steels

Practically all constructional steels are working under applied loads and environments. Below some stress levels the deterioriation of the material occurs by typical corrosion modes. Modern constructions are often loaded with enough high stresses to promote catastrophic failures due to stress corrosion crack propagation. Actually the whole range of metallic materials used in reliable constructions which are exposed to corrosive environments should be tested for their sensitivity to stress corrosion cracking. By measuring the material constant K_ISCC (critical stress intensity factor for stress corrosion cracking) it is possible to construct the reliable parts working in a safe range of stresses, which cannot be computed knowing yield strength of the material only. For measuring K_ISCC values of high strength CrMnSiNi and CrMo steels, original stands were built and long-term (> 10³h) tests applied by means of the cantilever beam method. Sensitivity of tested steels to stress corrosion cracking was expressed as a ratio K_ISCC:K_IC. Some other observations concerning kinetics of crack propagation and other properties of the materials have been carried out.     

Corrosion of two kinds of cast steels containing chromium in hot concentrated alkaline

A typical hot concentrated alkaline corrosion environment exists in alumina metallurgical industry, so that steel materials with outstanding alkaline corrosion resistance are strongly demanded for its processing equipment. In this paper, the corrosion resistance of two kinds of martensitic cast steels containing chromium in static 303g/L NaOH alkaline solution at 85℃ was studied through polarization and potential-time curves, corrosion weight loss and corrosion morphology analysis. Experimental results showed that protection effect by passive film of cast steel containing Cr was temporary. The low carbon steel without Cr content also exhibited chemical passivity in the same solution. The corrosion mode of the tested Cr-containing cast steel was composed of active dissolving corrosion and caustic embrittlement cracking. Dissolving corrosion was the primary mechanism for the induced weight loss, while severe caustic embrittlement cracking was secondary. With the increase of chromium content in the cast steel, the tendency of the caustic embrittlement cracking decreased, while the active dissolving corrosion increased.     

Néel temperature of high Mn austenitic steels

The predictive equations for the Néel temperature (T_N) of high Mn austenitic steels were reviewed and reevaluated using 116 different measured T_N values. The previous equations gave good predictions for T_N values of high Mn-low C austenitic steels, but not for those of medium and low Mn-high C austenitic steels, including TWIP steels with less than 20 at.% Mn. Therefore, an improved T_N equation for medium and low Mn-high C as well as high Mn-low C was newly suggested. To improve the accuracy of the new equation, especially for high C TWIP steels, the T_N values of three different high C TWIP steels were experimentally measured using a superconducting quantum interference device (SQUID) because there are few measured T_N values of high C TWIP steels in the literature.     

Effect of heat treatment on microstructure and high temperature tensile properties of cast nickel-base superalloy with high W, Mo and Nb contents

The microstructural features and high temperature tensile properties of M963 superaUoy at as-cast, as-solutioned and as-aged conditions were investigated in detail. The results show that the solution treatment at 1220℃ for 4 h,AC causes an increase in high temperature yield strength but a drastic drop in high temperature ductility due to the precipitation of both the secondary carbide M6C along grain boundaries and at the interdendritic regions and very fine γ‘ particles in the dendrite cores. Aging treatment following the solution treatment can improve the high temperature tensile properties of M963 superalloy due to the coaraing of the γ’ precipitate. One stage aging at 850℃ for 16 h following the solution treatment causes an increase in both strength and ductility d alloy M963, and two-stage aging of 1089 ℃/2 h, AC plus 850℃/16 h, AC following the solution treatment further increases the ductility d alloy M963 but slightly decreases its strength.     

Experimental and numerical analysis of effect of cooling rate on thermal–microstructural response of spheroidal graphite cast iron solidification

This work presents an experimental and numerical study of the solidification process of an eutectic spheroidal graphite cast iron (SGI). The effect of the cooling rate on the thermal–microstructural response is particularly analysed. To this end, experiments as well as numerical simulations were carried out. The experiments consisted in a solidification test in a wedge-like casting such that different cooling rates were measured at specific positions along the part. A metallographic analysis was also performed in five locations of the sample with the aim of obtaining the number and size of graphite nodules at the end of the process. The numerical simulations were made using multinodular based and uninodular based models. These two models predicted similar results in terms of cooling curves and nodule counts. Besides, good experimental–numerical agreements were obtained for both the cooling curves and the graphite nodule counts.     

Magnetic and mechanical properties of FeSi alloys with high Si content

The chemical vapor（CVD） deposition-diffusion method was applied to prepare FeSi alloys with high silicon content up to 6.5%. In spite of various deposition and post-annealing, the sample remains α-Fe bcc structure. The cross section of the composition was analyzed to evaluate the Si content and distribution before and after annealing. The results show that the soft magnetic properties are improved by increasing the silicon content. For the samples containing about 6.5% Si, the coercivity decreases to 60 from 237.3 A/m of the original. It is also obtained that, in addition to the Si content, Si distribution has a large influence on the core loss due to the effect of resistivity. The micro-hardnesses were also evaluated along the cross-section after various annealings.     

Laser-structured grinding tools – Generation of prototype patterns and performance evaluation

Laser ablation with ultrashort pulsed lasers enables high geometrical flexibility and allows for fabrication of micro scale structures in e.g. ultrahard materials that are hardly possible with any other process. In this work a novel laser structuring method employing picosecond lasers is proposed and applied to produce various micro patterns on the surface of hybrid bonded (metal-vitrified) CBN grinding tools. Grinding performance and wear behaviour of the structured tools are tested and compared to the results of a non-structured tool.It is found that the type of surface pattern has a strong influence on the grinding results. The laser structured tools generally allow for a reduction of grinding forces by up to 54%. However, depending on the pattern geometry, a significant increase in workpiece surface roughness and elevated wear rates (in terms of surface roughness) have to be taken into consideration. Despite this fact, the study does not reveal a significant increase in radial profile wear of the structured tools.     

Use of electron microscopy on microstructure characterization of high chromium cast irons

The physical metallurgy underlying the development of cast microstructures in abrasion resistant high chromium cast irons, and their structural modification by thermal treatments is relatively complex. Structural characterisation via electron microscopy therefore has a key role to play in furthering our understanding of the phase transformations that control the microstructures and hence the service performances of these irons as wear parts. This paper shows how both scanning and especially transmission electron microscopy can provide valuable information on the nature of eutectic and secondary carbides and on the matrix structures in these irons. Particular attention is given to current characterisation research on conventionally cast 30%Cr irons that are used for applications involving corrosive wear e.g. slurry pumps and on a semi-solid cast 27%Cr iron that has a potential for applications in industry.     

Effect of microstructural heterogeneities on scatter of toughness in multi-pass weld metal of C–Mn steels

Often, scatter in mechanical properties of multi-pass steel weldments is qualitatively attributed to the underlying heterogeneous microstructure brought about by spatial variations of multiple thermal cycles. In this research, a method for quantitative heterogeneity calculation based on measured variations of microstructure and hardness throughout the multi-pass weld metals including various reheated regions was explored. Published data from multi-pass welds with controlled titanium additions (7–32 wt ppm) were correlated to comprehensive microstructure characterization. The scatter in 7 wt ppm Ti steel welds was larger than that of 32 wt ppm Ti steel welds. This change in scatter is correlated to spatial distributions of microstructural heterogeneity parameter, rather than the average value of heterogeneity parameter for the whole weldment.     

Macrostructure and Mechanical Properties of Al – Si,Al – Mg – Si,and Al – Mg – Mn Aluminum Alloys Produced by Electric Arc Additive Growth

Metal Science and Heat Treatment - The macrostructure and mechanical properties of clad metal produced by electric arc additive growth using wires of aluminum alloys of three alloying systems (Al...     

Computer-aided designing and manufacturing of advanced steels

Suitable optimization and simulation were performed using a powerful software package with a mature database as well as modem measurement facilities, which led to the successful designing and manufacturing of advanced steels. In the course of designing, the composition of a large section of prehardened mold steel for plastics was estimated so as to lower the quantities of oxide inclusions to change the type of carbides and to raise the machinability. The composition and process were adjusted to obtain satisfactory surface quality for the prevailing galvanization in transformation-induced plasticity （TRIP） steel. The refuting process of low-carbon steel was simulated in the light of both Thermo-Calc and Factsage. Thermodynamic and kinetic analyses were always conducted during the test and the procedure.