EXPERIMENTAL INVESTIGATION OF WELD JOINTS BETWEEN SINTERED NB MODIFIED HK30 STAINLESS STEEL AND WROUGHT/CAST STAINLESS STEELS

Very important property of powder metallurgy parts is ability to join to components produced by different manufacturing technologies or dissimilar materials. Properties of powder metallurgy Nb modified HK30 components are highly influenced by conditions applied during sintering. Weldability of sintered components can be improved using favorable sintering conditions. In this regard, effect of sintering parameters on fusion weldability of Nb modified HK30 is presented in this paper. Investigation of weld joints between HK30, produced by different sintering conditions, and cast HK30 stainless steel is performed. In addition, examination of welds between sintered HK30 and wrought 304 stainless steel is also performed. Microstructural examination and hardness testing of fusion zones and heat affected zones were done for different combinations of base material.

Study on the hydrogen-induced delayed fracture behavior of Q-P980 and MS980

In this paper, the hydrogen diffusion behavior and hydrogen induced delayed fracture (HIDF) of Q-P980 (Q-P: Quenching and Partitioning) and MS980 (MS: Martensitic steel) steels were investigated using hydrogen penetration, slow strain rate tensile (SSRT) tests, thermal desorption spectroscopy (TDS) tests, fracture analysis, and microstructural examination in this paper. The austenite in Q-P980 is massive retained-austenite (RA) with low stability. The TRIP (Transformation Induced Plasticity) effect will occur in the process of strain and change into high carbon martensite. HIDF is caused by a substantial amount of surplus hydrogen being enriched at the border and flaws. The fracture has a broad cleavage surface and is a typical quasi-cleavage fracture. MS980 has been sufficiently tempered, resulting in a substantial quantity of distributed spherical cementite (150nm) precipitating around the lath martensite. This size and form of cementite may successfully trap hydrogen while maintaining the material's mechanical characteristics. And tempering can effectively reduce the local stress level of steel, so MS980 has a very low HE susceptibility. HIDF is related to local stress and hydrogen accumulation. We suppose that Z is a constant and ZC is a critical value which associated to σ and CH (the local stress and local hydrogen concentration), rising as σ and CH rises. The atomic bonds at the crack tip, lattice position and the phase interface will fracture when ZC reaches a particular value Z. Tempering to minimize local stress and carbide precipitation to capture hydrogen are two strategies for reducing hydrogen embrittlement (HE) susceptibility, particularly for dislocation strengthened steel. Microalloying elements can generate precipitates that function as hydrogen traps and obstruct the HELP (Hydrogen Enhanced Localized Plasticity) process, lowering local stress and hydrogen accumulation.

A metallurgical investigation on a failed superheater tube used in a thermal biomass power plant

This article described the investigation of the failed superheater tube made of SA210 Grade C used in a biomass power plant. Visual inspection, microstructural examination, chemical analysis and hardness measurement were employed to analyze the causes of the superheater tube failure. Results from the investigation showed that the major cause of this failure was mainly related to the long-term overheating, resulting in the occurrence of the excessive thermal oxidation and graphitization. The excessive thermal degradation accelerated the reduction of the wall tube and promoted the build-up of the stress acting on the tube. Graphitization degraded the microstructure of the tube, reducing the mechanical performance of the tube. The combined effects from the severe thermal oxidation and graphitization attributed to the premature failure of the tube. It is therefore advised to use the correct material, SA213 T22, in the failed section. Material specification examination for superheater regions prior to tube installations should be performed to avoid the use of the inappropriate material. The temperature monitoring and mapping in this section were also suggested.

Development and Mechanical Characterisation of Al6061-Al2O3-Graphene Hybrid Metal Matrix Composites

MMC based on aluminium (Al) were produced for light-weight applications especially in aviation and automobile areas. Present paper deals with the fabrication and mechanical performance of AA6061 matrix composites fortified with Al2O3 (alumina) and graphene particulates. Fluid metallurgy method namely stir casting route was employed for fabricating the hybrid composites. Al2O3p and graphene powder are mixed in different weight fractions in which graphene (1 wt. %) particle reinforcement is held consistent and Al2O3 reinforcement is differed freely with 5, 10 and 15 wt. %. Using optical analyser and SEM equipment, microstructural examination is carried out and the result reveals that the graphene and Al2O3 particles prevalently are homogeneously appropriated on the grain limits of Al matrix and Al2O3 particles are disseminated between graphene in the as-cast AA6061 MMC’s. Detailed analysis on investigation of the microstructure and mechanical aspects of Al6061-graphene-Al2O3p composites is presented by following ASTM guidelines; results uncovered that with increment in reinforcement particles, there is an enhancement in the hardness, ultimate strength, yield strength and a decline in the elongation values was however noticed when contrasted with Al6061 alloy. Fractography investigation revealed dimples in unreinforced alloy and the composite.

A Comparative Study on Constant Current GTAW and Constant Current GTAW with Superimposed HF Current of SDSS Grade SAF2507

This present investigation explore the microstructural properties of SDSS grade SAF2507 weldments produced by constant current GTAW and constant current GTAW with superimposed high frequency (HF) current. The macro, microstructural examination and mechanical characterization were performed. From the results, it was found that, the superimposition of high-frequency current on the welding current results in constriction of the arc during constant current GTAW with superimposed HF current. The superimposed HF current restricts the arc with for all intents and purposes a similar root and extended diameter. The weldment region unit considered the standard for mechanical and microstructural properties. The dominance of properties because of the association of inter pulse or HF current is described along with its related science concerned.

Deformation and fracture behaviour of the γ-TiAl based intermetallic alloys

SYNOPSIS The ß-solidifying g-TAl intermetallic alloys of nominal composition Ti-48Al (binary alloy), Ti-48Al-2Nb (ternary alloy), Ti-48Al-2Nb-0.7Cr (quaternary alloy), and Ti-48Al-2Nb-0.7Cr-0.3Si (quinary alloy) (in at.%) were developed. The materials produced were tensile tested at room temperature. The as-cast microstructures and fracture surfaces of the tensile tested specimens were examined using conventional metallographic methods. Microstructural examination indicated that the alloys were comprised of lamellar structures (a2+γ) embedded in columnar dendritic cores in the as-cast condition. However, the quinary alloy contained a T5Si3 second phase. The alloys exhibited no detectable ductility during tensile deformation, indicating the brittleness of all the materials. The fracture surfaces revealed that the alloys failed by translamellar fracture with correspondingly few cleavage facets. Keywords: γ-TlAl based alloys, ß-solidifying, translamellar fracture.

The structural integrity of flash-butt welded premium rail steel – Evaluation of strength, microstructure and defects

Experimental testing of flash-butt welded premium rail steel samples was undertaken to quantify the variation in strength through the cross-section of the weld, with results showing a general correlation between the width of the heat-affected-zone and the ultimate tensile strength. Microstructural examination and fractography revealed the presence of defects in some samples. Large defects can be identified by non-destructive testing methods as part of routine structural integrity assessment; however, small defects may escape detection but could propagate under cyclic loading in service leading to catastrophic failures. This work demonstrates the requirement for stringent control of heat input to prevent the development of defects in premium rail steels with high alloying content.