Abstract: Corrosion problem which exists in every stage of oil and gas production has been a great challenge to the operators in the industry. The conventional carbon steel with all its inherent advantages has been adjudged susceptible to the aggressive corrosion environment of oilfield. This has aroused increased interest in the use of micro alloyed steels for oil and gas production and transportation. The corrosion behavior of three commercially supplied micro alloyed steels designated as A, B, and C have been investigated with API 5L X65 as reference samples. Electrochemical corrosion tests were conducted in an unbuffered 3.5 wt% NaCl solution saturated with CO2 at 30 0C for 24 hours. Pre-corrosion analyses revealed that samples A, B and X65 consist of ferrite-pearlite microstructures but with different grain sizes, shapes and distribution whereas sample C has bainitic microstructure with dispersed acicular ferrites. The results of the electrochemical corrosion tests showed that within the experimental conditions, the corrosion rate of the samples can be ranked as CR(A)< CR(X65)< CR(B)< CR(C). These results are attributed to difference in microstructures of the samples as depicted by ASTM grain size number in accordance with ASTM E112-12 Standard and ferrite-pearlite volume fractions determined by ImageJ Fiji grain size analysis software.
Abstract: Proper selection of welding parameters for getting
excellent weld is a challenge. HAZ simulation helps in identifying
suitable welding parameters like heating rate, cooling rate, peak
temperature, and energy input. In this study, the influence of weld
thermal cycle of heat affected zone (HAZ) is simulated for
Submerged Arc Welding (SAW) using Gleeble ® 3800 thermomechanical
simulator. A (Micro-alloyed) MA steel plate of thickness
18 mm having yield strength 450MPa is used for making test
specimens. Determination of the mechanical properties of weld
simulated specimens including Charpy V-notch toughness and
hardness is performed. Peak temperatures of 1300°C, 1150°C,
1000°C, 900°C, 800°C, heat energy input of 22KJ/cm and preheat
temperatures of 30°C have been used with Rykalin-3D simulation
model. It is found that the impact toughness (75J) is the best for the
simulated HAZ specimen at the peak temperature 900ºC. For parent
steel, impact toughness value is 26.8J at -50°C in transverse
direction.
Abstract: Micro-alloyed steel components are used in
automotive industry for the necessity to make the manufacturing
process cycles shorter when compared to conventional steel by
eliminating heat treatment cycles, so an important saving of costs and
energy can be reached by reducing the number of operations. Microalloying
elements like vanadium, niobium or titanium have been
added to medium carbon steels to achieve grain refinement with or
without precipitation strengthening along with uniform
microstructure throughout the matrix. Present study reports the
applicability of medium carbon vanadium micro-alloyed steel in hot
forging. Forgeability has been determined with respect to different
cooling rates, after forging in a hydraulic press at 50% diameter
reduction in temperature range of 900-11000C. Final microstructures,
hardness, tensile strength, and impact strength have been evaluated.
The friction coefficients of different lubricating conditions, viz.,
graphite in hydraulic oil, graphite in furnace oil, DF 150 (Graphite,
Water-Based) die lubricant and dry or without any lubrication were
obtained from the ring compression test for the above micro-alloyed
steel. Results of ring compression tests indicate that graphite in
hydraulic oil lubricant is preferred for free forging and dry lubricant
is preferred for die forging operation. Exceptionally good forgeability
and high resistance to fracture, especially for faster cooling rate has
been observed for fine equiaxed ferrite-pearlite grains, some amount
of bainite and fine precipitates of vanadium carbides and
carbonitrides. The results indicated that the cooling rate has a
remarkable effect on the microstructure and mechanical properties at
room temperature.