Acceptable Toughness Research Articles

Effect of post-weld heat treatment on the mechanical properties of electron beam welded joints for CLAM steel

In this paper the microstructure and mechanical properties of electron beam weld (EBW) joints for China low activation martensitic (CLAM) steel, which underwent a series of different post weld heat treatments (PWHTs) were studied. The aim of the study was to identify suitable PWHTs that give a good balance between strength and toughness of the EBW joints. The microstructural analyses were performed by means of optical microscope (OM) and scanning electron microscope (SEM). The mechanical properties were determined via tensile tests and Charpy impact tests. The results showed that the tensile strength of the as-weld joint (i.e. without any PWHT) were close to that of the base metal, but the impact toughness was only 13% of that of the base metal due to the existence of a delta-ferrite microstructure. To achieve a significant improvement in toughness a PWHT needs to be performed. If a one-step PWHT is applied tempering at 760°C for 2h gives EBW joints with high strength at a still acceptable toughness level. If a two-step PWHT is applied, a process involving quenching at 980°C for 0.5h followed by tempering at 740°C or 760°C for 2h gives EBW joints with high strength and toughness properties. Whenever possible a two-step PWHT should be applied in favor of a one-step process, because of higher resulting strength and toughness properties.

Welding Advanced Martensitic Creep-Resistant Steels With Boron Containing Filler Metal

Within the last years, the beneficial effect of boron addition in order to increase the creep strength of martensitic 9–12 % Cr steels has been widely investigated and demonstrated. Several boron-strengthened alloys Care the outcome of an intensive European research activity within the scientific framework of COST. The most promising alloy for castings with a targeted application temperature of 650 °C for use in future ultra-super critical steam power plants is a modified 0.1 C-9Cr-1.5Mo steel with the addition of approximately 110 ppm boron. For joining of this advanced steel grade, new “chemically matching” welding consumables have to be developed to provide similar creep strength in the weld. Within this paper, the development of an advanced flux-cored wire with a good “out of position weldability” — based on a rutile slag system is presented. The work discusses the optimization of the chemical composition of the filler, the influence of various post-weld heat treatments on short term mechanical properties, first results of creep tests and results of thick section welds. The boron content of the consumable was optimized to achieve highest creep strength combined with acceptable toughness and lowest hot cracking sensitivity. For a butt weld of a 34 mm-thick casting, the optimum welding parameters and layer sequence were determined. A post-weld heat treatment consisting of stress relieving twice at 730 °C for 12 h seemed to be the best compromise between applicability in the manufacturing of large turbine casings and achievement of acceptable weld toughness.

Effects of Alloying Concepts on Ferrite Morphology and Toughness of Lean Duplex Stainless Steel Weld Metals

Alloying concepts for lean duplex weld metals have been explored. Focus was on compositions with 21.5–24 % Cr with different levels of Ni and Mn in combination with N producing a minimum PREn value of 26. Microstructures and properties of weld metals produced with experimental covered electrodes or metal-cored wires were evaluated. The electron backscattered diffraction (EBSD) technique combined with scanning electron microscopy (SEM) was used to explore relations between weld metal morphology and crystallographic orientation relationships between ferrite and austenite. A duplex microstructure with Widmanstatten type ferrite characteristic of a ferritic solidification was found throughout most weld metals. Regions with a morphology suggesting a mixed ferritic-austenitic solidification occurred particularly for higher Ni- and N-contents. EBSD studies showed that most of the austenite formed following a ferritic solidification was near either the Nishiyama-Wasserman (NW) or Kurjdumov-Sachs (KS) relationships with adjacent ferrite. More phase boundaries in the mixed mode solidification regions had a random orientation relationship. Strength, ductility and PREn requirements were readily matched but the combined Mn, Ni and N alloying levels and the ferrite morphology affected toughness significantly. Both a fully ferritic solidification and a sufficient Ni-content were necessary to produce acceptable and reproducible impact toughness at room and sub-zero temperatures. It was concluded that a composition of 23–24 % Cr, 7–8 % Ni and 0.12–0.16 % N was well suited to fulfil requirements.

Optimal heat treatment conditions and properties of bimetal (high Cr cast iron/alloyed steel) hammers

This study intended to establish the optimal heat treatment conditions for the desired hardness and wear resistance property for the bimetal hammers developed by the authors. The objective of this study is to attain bimetal hammers that have a tough Cr–Ni alloyed steel shank and a high wear resistant high Cr cast iron head to replace conventional single alloy (high Mn steel) hammers. The results show that the optimal heat treatment condition obtained for the bimetal hammers is: destabilisation: 1000–1050°C for 2 h, quench: FAC and tempering: 480–500°C for 6 h. By employing this optimal heat treatment condition, the highest hardness value can be attained along with the best wear resistance property for the head portion and acceptable toughness for the shank portion. The microstructure of the head portion that corresponds to the optimal properties consists of eutectic M7C3 carbides, secondary M7C3 carbides, tempered martensite and almost nil retained austenite.

Effect of Cobalt to Bronze Ratio on Transverse Rupture Strength of Diamond Segments

Diamond segments were fabricated by cold pressing and sintering under pressure at the temperature up to 750 °C. It was obtained from this study that if we increase the cobalt ratio, the hardness of the matrix increases and the wear rate of the segments decreases. But the optimum matrix composition with less wear rate must ensures that the acceptable matrix toughness. Because the harder matrix wears more slowly than the diamonds, the space between the cutting edges and the matrix is constantly reduced. Because the swarf cannot be carried away properly, and the segment will continuously lose its ability to cut. From this point of view, the cobalt ratio in matrix composition for this formulation should not be higher than the 60 wt.% in order to have a good cutting ability.

Influence of forging and cooling rate on microstructure and properties of medium carbon microalloy forging steel

In view of their capacity to develop high strength following limited alloying and ease of processing medium carbon microalloyed (MA) steels are very cost-effective compared to quenched and tempered steels for the production of automotive components. To be able to substitute quenched and tempered steels, MA steels must be processed to similar strength levels and acceptable toughness [1]. The increased use of microalloyed forging steels in production applications should be supplemented with an increased understanding of not only the strengthening mechanisms that occur in these steels, but also the effects of the composition and forging parameters on these mechanisms. The size and percentage distribution of ferrite and pearlite within the microstructure play an important role on the final mechanical properties. Each of the microstructure variables is highly influenced by the composition of the microalloyed steels, the forging parameters utilized, and the post-forging cooling rate [2–4]. The aim of the present study is to investigate the influence of different cooling rates on structure and properties of MA steel processed through forging route. The chemical compositions of the steels used in this study are shown in Table I. The steels are medium carbon microalloyed steel with different vanadium and aluminum contents. Specimens obtained from steels 1 and 2 were heated at 1100 ◦C for 30 min and forging operation was carried out. Thirty-six percent deformation was applied by repeated strokes in temperature range of 1000–1100 ◦C. Then forged steel samples were cooled either in water, air, or sand. Room temperature tensile strength was measured by using an Instron machine at a crosshead speed of 1 mm/min. The pearlite grain size, volume fraction of ferrite, and pearlite were determined by using mean linear intercept (mli) method and point counting. Hardness measurement was also carried out using the Vickers hardness test. Fig. 1 shows the evaluation of the microstructure for both of the microalloyed steel under various cooling condition. Table II also shows volume fraction of ferrite and pearlite and mli grain sizes of pearlite in as-received,

Toughness measurements on steel fibre-reinforced high strength concrete

The paper reports on strength and toughness measurements on a range of normal and high strength concrete mixes, with and without steel fibre reinforcement. Cube strength, modulus of rupture, cylinder splitting and torsional-tension test results are reported together with toughness measurements determined via two fracture-type test specimens (standard RILEM three-point notched beams in flexure and eccentrically loaded notched cubes). In the toughness tests, crack mouth opening displacement (CMOD) was measured and used in a closed loop testing mode to achieve complete load/displacement curves. Good correlation was observed in the strength tests and the two toughness tests showed similar load-CMOD curves and toughness indices. However, traditional toughness indices are unsatisfactory with load-CMOD tests, and further work is necessary to define acceptable toughness measurements, which may also have to account for size effects. The effect of steel fibre reinforcement on high strength (up to 120 N mm 2 ) and normal strength concrete is similar.

Oxidation Behavior of Advanced Intermetallic Compounds

ABSTRACTThe oxidation behavior of a number of ordered high melting point intermetallic materials has been studied in flowing air in the temperature range 1000 to 1500°C. The alloys were selected for acceptable toughness and ductility at temperatures above 1000°C. Included were ruthenium aluminides, chromium silicide and compounds of iridium and ruthenium with elements such as titanium, tantalum, nickel, iron, cobalt, silicon, vanadium and rhenium. In general, alloys containing the metals iron, cobalt and nickel, and also titanium and tantalum, oxidized rapidly at 1000°C and above. Oxidation-resistant materials were those capable of forming scales of chromia/silica or alumina. Intermetallic compounds of chromium and ruthenium formed volatile oxides above 1200°C, but binary compounds of these elements with silicon and aluminum were highly oxidation resistant at lower temperatures.

Microstructure and mechanical and electrochemical properties of martensitic weld deposits developed for welding of a 12%Cr duplex stainless steel

AbstractThe microstructure and mechanical and electrochemical properties of martensitic weld deposits developed for the welding of a duplex 12% Cr corrosion resisting steel, as well as the experimental procedures used, are described. During the development, it was found that weld metals having matching compositions (and thus duplex structures) to those of 3CR12 had very poor impact properties. This was largely because of the inability to control weld metal grain size. By increasing the proportion of austenite stabilising elements, to produce a predominantly low carbon martensitic weld deposit, it was found that acceptable toughness (≥30 J at 20°C) could be achieved in the as welded condition. The electrochemical properties were designed to be similar to, yet slightly more noble than, those of the wrought 3CR12 plate, thus guarding against possible inhomogeneities in the as cast structure. Cost was also an important consideration throughout the development of these closely matching consumables, since the a...

Microstructure and mechanical and electrochemical properties of martensitic weld deposits developed for welding of a 12%Cr duplex stainless steel

The microstructure and mechanical and electrochemical properties of martensitic weld deposits developed for the welding of a duplex 12% Cr corrosion resisting steel, as well as the experimental procedures used, are described. During the development, it was found that weld metals having matching compositions (and thus duplex structures) to those of 3CR12 had very poor impact properties. This was largely because of the inability to control weld metal grain size. By increasing the proportion of austenite stabilising elements, to produce a predominantly low carbon martensitic weld deposit, it was found that acceptable toughness (≥30 J at 20°C) could be achieved in the as welded condition. The electrochemical properties were designed to be similar to, yet slightly more noble than, those of the wrought 3CR12 plate, thus guarding against possible inhomogeneities in the as cast structure. Cost was also an important consideration throughout the development of these closely matching consumables, since the austenitic filler metals used (e.g. AWS E 309 Mo) were substantially more expensive than the parent plate. It has been shown that cost effective, metallurgically compatible filler metals for 3CR12 can be produced.MST/651

Quenching, Tempering, and Aging Chromium-Molybdenum-Vanadium Cast Steels

Abstract The usual specifications for Cr-Mo-V steel castings fix modest levels of yield strength (350 to 450 MPa) in the hope of obtaining acceptable toughness. But this optimism sometimes leads to disappointment when only the components themselves are considered and not the attached parts. Tests carried out on Cr-Mo steel casings that have 100 000 h or more of service life show that, if toughness is sufficiently high in the as-received condition, and if certain precautions are taken into account at start-up, one may accept service embrittlement and even allow casings that reveal cracks caused by creep or thermal fatigue to remain in service. The aim of the work discussed in this paper has been to compare different grades of Cr-Mo steel distinguished in particular by chromium and nickel contents. Two subjects have been dealt with: the influence of the chemical composition on the optimal conditions of hardening and tempering and the preliminary study of age embrittlement (evaluated by the translation of Charpy V-notch and ductile fracture toughness transition curves).