In order to meet demanding service applications, offshore structures have to withstand severe loads and harsh environments. This requires steels with low sulfur contents, good through-thickness ductility and toughness and also the ability to suppress lamellar tearing during welding and fabrication.
Statistical analysis of height change maps of corrosion surface topographies show that the addition of Ca(NO3)2 significantly reduces both general recession and fast localized corrosion at pitting sites.
This alloy is characterized by high tensile and impact strengths at room temperature, good weldability (as based on Charpy V-notch tests), excellent hardenability, and exceptional ductility. The low carbon content allows for excellent machinability. It also provides for excellent toughness and fatigue resistance. Vanadium is added to provide grain boundary pinning and prevent excessive grain growth during the high-temperature treatment.
This treatment is performed in the form of a calcium silicon alloy, CaSi. This is fed deep into the liquid steel at a high concentration. The CaSi melts and reacts with inclusions, oxygen, and sulfur. It also prevents nozzle clogging during the casting process.
Mechanical characterization of the samples, such as Vickers hardness and densification after SPSing, deformation site and indented volume, and average maximum acceleration values during multiple impact tests were conducted. The results indicated that coated 316L spent most of the impact energy on plastic deformation. This was reflected in the dynamic hardness graphs of SPS-sintered, SLM/PBF-fabricated and PVD-coated metallic alloys.
The tensile strength of a material is the amount of force that can be applied to stretch or pull it apart. It measures how much a material can be stretched or pulled before it will break.
The Mohs scale of mineral hardness classifies minerals according to their ability to scratch other materials. Calcium has a hardness of approximately 1.5.
In tensile tests, calcium treated steels showed greater levels of ductility and room temperature impact resistance compared to non-calcium treated steels. They also had higher notch toughness and fatigue thresholds.
In addition to improving tensile properties, calcium treatment also enhances formability. This is because it combines with Sulphur to form round CaS inclusions that can control their shape and size, preventing nozzle clogging during casting. The resulting formations can then be removed by electromagnetic swirl stirring during the casting process. This can significantly reduce the slag deposition rate during casting and improve the through-thickness property distribution.
Fatigue threshold is a point that indicates the limit of the material to sustain load cycles without failing. It’s similar to your body’s signals that you are tired and should take a break from exercise or perhaps stop training altogether (muscle twinges, soreness, general feeling of fatigue).
Performing simulations of the crack growth process up to very high cycle counts in 2D hexagonal lattice models reveals that the phenomenon of near-threshold fatigue crack growth cannot be explained by simple mechanisms such as shielding or antishielding, slip irreversibility, or preexisting dislocation sources. Instead, sustained near-threshold fatigue crack growth is the result of a dense persistent slip band (PSB) that can send antishielding dislocations to the crack tip and promote crack growth.
The effect of calcium treatment on the fatigue threshold and fatigue crack propagation properties in A5l6-70 has been investigated by comparing specimens tested as hot-rolled, quenched and tempered and as cold-rolled with and without additional requenching. It was found that additional requenching can lead to an enhancement of the fatigue endurance limits and fatigue crack propagation rates.
Fatigue crack growth rate, or m
Fatigue-crack-growth rate data is usually presented as a curve with log(DK) plotted against Log(Da/dn). For many materials, the Paris region shows a linear relationship where DK is above the threshold stress intensity factor (Kmax) and Da/dn is less than the specimen thickness.
However, it is important to remember that these curves are not geometry-independent, especially if the test specimens come from components that embody residual stresses such as weldments or complex shape forged, extruded, cast or machined thick sections. In addition, the effect of load history on fatigue crack growth during variable amplitude loading may be significant and must also be considered. This complicates the use of constant-amplitude fatigue test data when attempting to estimate life under variable-amplitude loading conditions.
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