Papers by Keyword: Low Alloy Steel

Abstract: Regulations governing welding in the oil and gas industry mandate post-weld heat treatment (PWHT) for all welded joints, regardless of pipe wall thickness. The maximum permissible hardness is limited to 248 HV to prevent cracking. However, PWHT is time-consuming, energy-intensive, and costly. This study investigates the use of interpass temperature control and the temper bead welding technique as alternative methods for reducing weld hardness without PWHT. SA-335 Grade P11 low alloy steel pipes were welded using the GTAW process with ER80S-B2 filler metal and 99.99% argon gas. A preheat temperature of 250 °C was applied in all conditions. Four experimental groups were investigated: (1) PWHT at 650 °C for 1 hour, (2) low interpass temperature at 250 °C, (3) high interpass temperature at 600 °C, and (4) temper bead welding with 17 overlapping beads. The first three groups used 7 beads for comparison. Weld quality was assessed using VT, PT, and RT. Hardness testing served as the primary evaluation method, followed by tensile, bend, macrostructural, and microstructural analysis. Hardness results showed that the PWHT and high interpass groups remained below 248 HV, with the temper bead group achieving the lowest weld metal hardness (215.5 HV). The low interpass group exceeded the limit (up to 256.3 HV). All specimens failed in the base metal during tensile testing, with average strengths ranging from 498.3 MPa (PWHT) to 526.3 MPa (temper bead). No critical defects were found in bend tests. Microstructural comparison revealed that temper bead welding produced finer and more uniform grains, contributing to lower hardness and improved thermal softening in the HAZ.

Abstract: The pull out and well drop accident caused by serious thread galling damage of low alloy steel tubing connections were investigated in this paper. Representative samples were selected from five failure accidents, and the test and verification program were designed. Based on the experiment and analysis it is considered that the material used for tubing and the quality of thread processing meet the requirements of the standard. The field end of tubing connection pull out may be due to the serious thread galling damage, which reduced the joint strength. Using the torque-position control method to make-up the thread connections in oil field may ensure the connection quality and the connection strength, meanwhile, and hence to avoid the occurrence of tubing pulling out effectively.

Abstract: Wear-resistant low alloy steels containing elements like Cr, Mo, attain their properties due to precipitation of carbides upon heat treatment. These steels are widely used for components in earthmoving and mining equipment. Even though the mechanical properties and wear behaviour of these steels are studied extensively, the studies on nature of carbide precipitation and their influence on corrosion behaviour are very rare. The present work attempts to correlate the microstructure with corrosion properties of low alloy wear resistant steel. After quenching from hot working temperature of about 900 °C, the alloy is subjected to tempering at two different temperatures i.e. 150 °C & 300 °C for durations of 1 h and 4 h. Two competitive process occur simultaneously effecting the hardness of the alloy during tempering i.e. (i) Softening due to transformation of martensite with depleting carbon (ii) Increase in hardness due to formation of carbide precipitates in the matrix. Transmission electron microscopy (TEM) of as quenched condition revealed fully martensite structure in the alloy. TEM investigation of 150 °C/ 4 h tempering condition, revealed presence of some amount of martensite and fine carbide precipitates in the alloy. TEM micrographs of 300 °C/ 4 h condition revealed relatively coarse carbides in a softer ferrite matrix. The presence of martensite and fine precipitates, resulted in relative improvements in wear and corrosion resistance respectively, for the alloy tempered at 150 °C for 4 h, when compared to the alloy tempered at 300 °C for 4 h.

Abstract: We have investigated a possibility of obtaining high-quality welded joints after oxygen and plasma cutting of steel С355 without removing the heat-affected zone (HAZ), in which the changes in chemical, phase and structural compositions are observed. Numerical and experimental studies of the effect of heat input of MAG and Submerged Arc welding on the quality of welded joints are performed. In particular, it was found that when the heat input of welding is at least 6.5 kJ/cm, the metal of HAZ of the edges after cutting is heated during the welding to temperatures above Ас3, which leads to its full recrystallization. When the heat input of welding is at least 10 kJ/cm, the edges after cutting are completely melted and become a part of the welding seam metal. The presence of extensive areas of melting and recrystallization of the edges in the welding process contributes to obtaining high-quality welded joints without removing the HAZ of the edges after cutting. To verify the results of numerical studies, experimental tests of control welded joints were conducted, which showed that the values of bending angle and impact toughness of the welding seam metal and heat affected zone are significantly above the regulatory requirements to quality of welded joints, and not less than the same requirements for steel С355. The obtained results confirm the possibility of revising domestic regulatory requirements for the steel constructions production in terms of the preparation of edges for welding using technologies of thermal cutting without subsequent machining.

Abstract: Spark Plasma Sintering (SPS) process is a relatively new PM technology used to fabricate metallic parts in shorter time and lower temperature than traditional press-to-sintering technology. In this study, sintering cycles by SPS process were performed in Astaloy CrM steel powder at temperatures between 950 and 1100 °C, with 5 minutes of dwell time and under 60 MPa of uniaxial compaction pressure. The apparent density measured by Archimedes principle, the microstructural investigation by optical microscopy (OM) and scanning electron microscopy (SEM) and the hardness tests by Vicker’s indentation were carried out with the sintered samples. It was observed that at 1050°C more than 98 % of densification was attained. As a low alloy steel powder sintered by SPS an expected high level of densification by the solid state sintering was achieved while hardness is lower than that expected for the Astaloy CrM when sintered mixed with graphite particles.

Abstract: Large-scale forging segments with two different section thicknesses (100 and 250 mm) were separately subjected to water, polymer solution and vegetable oil quenching and then tempered to evaluate the influence of cooling rate on microstructure and mechanical properties under industrial conditions. Regardless of quenching media, the fastest cooling rates are obtained in the thin (100 mm) sections of the ring segments. For the two cross sections, water and vegetable oil generated the faster and slower cooling times, whilst an intermediate cooling timebetween that of water and oil was achieved with polymer solution. Slightly enhanced mechanical properties in the thin sections are associated to the presence of fine mixtures of tempered martensite and tempered bainite (lower type morphology) compared to the thick section microstructure mostly composed of coarse tempered bainite with granular and lower type morphologies and small amounts of tempered martensite. The results obtained in this study also suggest the possibility of using vegetable oil as an alternative quenching media for large-scale forgings with high-specification requirements.

Abstract: In the fabrication process of medicine tablets, working speed of the tablet compressing is an important factor to realize the high fabricating efficiency together with the low cost. Thus, a number of loadings would be applied with very high frequency to tips of a couple of compressing punches. Sometimes, the tablet compressing speed exceeds 150 tablets per second. Due to such a circumstance, the very high cycle loadings are applied to the tips of the compressing punches making medicine tablets. The high strength steel of KNS-ES was specially designed and fabricated for the particular use as the compressing punches. In this study, very high cycle fatigue tests were performed in the loading type of rotating bending in order to obtain the fundamental S-N property of this steel. Based on experimental results, the S-N property in giga-cycle regime was discussed including the effect of the residual stress on the S-N properties. Consequently, the duplex S-N curves were clearly found, but the surface-induced fractures were often found in the fatigue data belonging to the second S-N curve in the longer life region.

Abstract: The paper presents results of researches carried out to establish the causes that led to the cracking of forgings made of manganese low alloy steel microalloyed with boron. The researches includes analysis of samples taken from the forgings in the cracked surface area and also analysis of a sample from forged material. The following methods and techniques were used for investigation:metallographic analysis by optical microscopy;visual macroscopic examination by scanning electron microscopy (SEM) at low magnification, using scanning electron microscope;examination by scanning electron microscopy on the material cracks area and its adjacent area;investigation of material by X-ray microanalysis in energy dispersive (EDAX) for its characterization, in terms of microcomposition;

Abstract: The galvanic corrosion behavior of titanium (TA2)/Cu-Ni alloy (B10)/low alloy steel (921A) multi-material system has been studied using a zero-resistance ammeter (ZRA) in seawater at different temperatures. After the tests, the surface morphologies of the samples were detected by SEM. Results showed galvanic corrosion behavior of TA2/B10/921A fulfill the mixed potential theory, 921A acts as the anode and both TA2 and B10 act as the cathodes. The effect of temperature on the galvanic corrosion is important, the corrosion rate increases with increasing temperature.

Abstract: Materials are subjected to low temperatures either intentionally as in the case of cryogenic fuels or non-intentionally as in the case of aerospace environment and are observed to undergo changes in their properties. Microstructural changes are the premier indications of changes in the properties of materials. This paper investigates the effect of cryogenic temperature on the microstructure of low alloy steel weldments. The weldments were subjected to liquid nitrogen temperature of 77K and the microstructures were analyzed using optical microscope and transmission electron Microscope. A distinct change in the microstructure was observed which would reason out the changes in the mechanical properties of weldments.