Strength Low Alloy Steel Plates Research Articles

Variations in microstructure and mechanical properties along thickness direction in a heavy high strength low alloy steel plate

A thermal-mechanical control process (TMCP) followed by tempering at 600 °C was applied to produce 420 MPa grade high strength low alloy (HSLA) steel heavy plates. The microstructure and mechanical properties through the thickness were analyzed using various techniques including optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), electron back-scattered diffraction (EBSD), tensile and impact tests. Microscopy analyses showed that a fine-grained structure with an average grain size of 6–10 μm could be obtained by TMCP. After subsequent tempering, the microstructure near the surface of the plate was dominated by bainite, while the microstructure of the core was mainly characterized by aggregated carbides and ferrite. In addition, the density of high-angle grain boundaries (HAGB) on the surface was significantly higher than that in the core. Tensile tests showed a decrease in both yield and tensile strengths from 530.1 and 626.9 MPa on the surface to 384.3 and 496.7 MPa in the core, respectively. The contribution of different strengthening mechanisms to the variations in strengths along the thickness was clarified. In addition, the deformation of ferrite and the initiation of micro-voids during tensile tests were also analyzed.

Characterization of ultrafine grain tungsten carbide tool and its wear investigation in friction stir welding of HSLA steel

In this work, cemented carbides with different cobalt content were developed by using medium and ultrafine tungsten carbide grains. The GGI, (Cr3C2), was added in small amount (0.5 wt. %) to restrict the grain growth. The effect of particle size, reinforcement content and sintering temperature on metallography, densification and mechanical properties is investigated. At 1680 ºC, Co phase was uniformly distributed at WC interface by particle rearrangement and resulted in fully dense microstructure. The fine particle enhanced the sintering rate due to large specific surface area and surface energy. The developed tool was used to join 4 mm thick high strength low alloy steel plates without severe wear and degradation of the tool. Tool oxidation and interface degradation associated to extreme tribological welding condition is observed.

Mechanical properties of corroded high strength low alloy steel plate

Seven groups of copper accelerated acetate spray (CASS) corrosion tests were carried out for high strength low alloy steel plate specimens. The main parameters are corrosion time and tensile pre-stress. Through the mass loss method and the measurement of the corroded surfaces, several parameters of corrosion damage were determined. Then the tensile tests were conducted to investigate the mechanical properties of the steel plate before and after corrosion. The relationship between the corrosion damage and the mechanical properties were also analyzed. The experimental results showed that as corrosion time increased, the total corrosion loss of the specimens without pre-stress kept increasing with a gradually decreasing corrosion rate. Besides, over the corrosion time, the roughness experienced an upward trend and the bottom surface was rougher than the top surface. Separating the corrosion components, the total corrosion loss was dominant by pitting corrosion, although the proportion of uniform corrosion increasingly grew. For long-term corrosion, elastic tensile pre-stress might lead to some inhibition of pitting corrosion while contribute to the slight development of uniform corrosion. As a result, compared with the specimens without pre-stress, the tensile capacity and deformation ability of the specimens with elastic tensile pre-stress were both a little improved. Considering the effects of corrosion components on the mechanical properties separately, uniform corrosion mainly affected the tensile capacity while pitting corrosion dominantly attributed to the deterioration of deformation performance.

Cyclic behavior and constitutive model of high strength low alloy steel plate

Cyclic loading tests with different protocols were conducted for a high strength low alloy steel. Based on the test results, the low cycle fatigue and extremely low cycle fatigue performance of the high strength steel was discussed and an appropriate constitutive model was established. The experimental results implied that the low and extremely cycle fatigue failure showed different fracture features. For low cycle fatigue, there was a strong negative linear correlation between the fatigue life and the strain amplitude in the log–log scale. However, they did not conform the linear relation when transiting to the low cycle fatigue. The steel represented obvious cyclic softening and good energy dissipation capacity. With the increase of strain amplitude, the softening degree decreased and equivalent damping ratio increased. The cyclic stress–strain curve could be descried by the Ramberg-Osgood model, and the strength coefficient and strain hardening exponent of this steel were larger than those of steel with lower strength. A combined hardening model was calibrated to describe the cyclic plasticity of the steel, and it was verified by the simulation results.

Interactions of the process parameters and mechanical properties of laser butt welds in thin high strength low alloy steel plates

High strength low alloy steels subjected to the thermomechanical control process present excellent strength–toughness combination, high strength/weight ratio, and weldability. Therefore, they are widely used in structural components, such as pressure vessels, oil/gas transportation pipes, lifting equipment, vehicles, shipbuilding and offshore industries, and in the automotive industry where low thickness (0.8–3 mm thickness) is of great importance. Usually, these steels are welded by conventional gas metal arc welding, which creates wide heat-affected zones, large residual stresses, and distortion in the welded parts. Laser welding is nowadays an alternative process to weld high strength low alloy steel parts due to its advantages. The aim of this work is to understand the effect of process parameters on defects, weld bead geometry, microstructure, and mechanical properties, namely hardness and tensile strength. We identify the main laser welding parameters and their influence on the weld bead geometry and defects, for a 3 mm thick high strength low alloy steel welded under a maximum power of 2 kW. A cross section of the weld seam was optimized achieving a good geometry without porosity. The threshold value of the heat input to achieve complete penetration was determined for different focus diameters. The microstructure, size, and hardness of the heat-affected zone and of the fusion zone are strongly influenced by the heat input. The values of the tensile strength achieved in butt welds were close to the base metal by an appropriate selection of the laser welding parameters and the heat input.

Numerical Analysis of the Influence on High Humidity in a T-Joint Fillet Weld for High Strength Low Alloy Steel

Welding at high humidity is frequently needed for the harbor hoisting machinery of steel structures in the coastal port city. A computational procedure is proposed for analyzing residual stress and temperature distributions induced by the T-joint welding in two types of St52-3 high strength low alloy steel plates both 6 mm in thickness. The relative humidity conditions varied from 75 to 90% at constant pressure. The finite element models are employed to evaluate the transient temperature and the residual stress during welding. According to the analysis results, the higher residual stress and the highest concentration of hydrogen are distributed in and surround the heat affected zone (HAZ), and vary with different humidity.

Weldability of X100 linepipe

Research has been carried out to identify weld metal compositions and microstructures capable of meeting high strength and toughness requirements for X100 seam welded linepipe. Single pass, multiwire submerged arc welds were made in experimental, high strength low alloy steel plates using consumables to give a wide range of weld metal alloying. Work has shown that the optimum strength and toughness are obtained in Mo–B–Ti alloyed weld metals with Pcm values between 0.218 and 0.250. Weld metal microstructures were almost fully acicular ferrite with an ultrafine grain size (1–2 µm). Dilatometric studies demonstrated that at typical weld cooling rates the optimised welds transformed at significantly lower temperatures than those reported for X65 plate deposits, which contain acicular ferrite in the form of idiomorphic primary ferrite and intragranular Widmanstätten ferrite. The maximum rate of transformation in the optimised welds occurred between 515 and 570°C, which indicates that the acicular ferrite in this case consisted of intragranular Widmanstätten ferrite and/or bainite. The ferrite would appear to have a fine plate morphology growing from large as well as small inclusions, but not very far before the onset of hard impingement, thereby ensuring an ultrafine grain size. Tensile strengths of 708–784 MPa were achieved with an 80 J Charpy impact transition temperature toughness between -68 and -115°C. More highly alloyed weld metals containing 2–3%Mn and 1.5%Si transformed at lower temperatures and showed increased strength, but there was a substantial loss of toughness, attributed to the relatively unimpeded growth of large ferrite plates from larger inclusions, and the replacement of ultrafine acicular ferrite between these plates by blocks of martensite–austenite. One pass per side, multiwire submerged arc welds manufactured to the optimum weld metal chemistry confirmed their applicability for thin section X100 linepipe.

Acoustic emission detectability of fatigue cracks in high strength low alloy steel plate during quasi static loading

Acoustic emission detectability of fatigue cracks in high strength low alloy steel plate during quasi static loading

A method for predicting service load from the width and height of striation: Murakami, Y., Kanenawa, K., Furukawa, K., Nishida, S. and Shiraishi, N. J. Soc. Mater. Sci. Jpn. June 1991 40, (453), 706–711 (in Japanese)

Flakes in low carbon high strength low alloy steel plates are not easily identified by macroetching because they form parallel to the plane of rolling and near to porosities and segregation lines in the steel plate. They also overlap each other after heavy deformation. Ultrasonic inspection and macrofracture examinations may be convenient and reliable methods for detecting them. The presence of flakes also results in diminished values for reduction of area in tensile tests, impact toughness in the vertical direction, and fatigue strengths. Flakes in plate mainly exist in granular bainite and other microstructures transformed at lower temperatures where Si, Mn, and V segregate. Scanning electron microscopy of flake fracture after heat treatment reveals a cloudrack morphology in the crack propagation region and a moth-eaten pattern at the edges of the flakes. The reasons for the formation of microstructural features of flakes and for the relation between flakes and inclusions are discussed.

Acoustic emission detectability of fatigue cracks in high strength low alloy steel plate during quasi static loading: Proceedings of the 12th World Conference on Non-Destructive Testing, Amsterdam (Netherlands) 23–28 Apr. 1989, Vol. 1, pp. 484–489. Edited by J. Boogaard and G.M. van Dijk, Elsevier, 1989

Acoustic emission detectability of fatigue cracks in high strength low alloy steel plate during quasi static loading: Proceedings of the 12th World Conference on Non-Destructive Testing, Amsterdam (Netherlands) 23–28 Apr. 1989, Vol. 1, pp. 484–489. Edited by J. Boogaard and G.M. van Dijk, Elsevier, 1989

Flakes in low carbon high strength low alloy steel

Flakes in low carbon high strength low alloy steel plates are not easily identified by macroetching because they form parallel to the plane of rolling and near to porosities and segregation lines in the steel plate. They also overlap each other after heavy deformation. Ultrasonic inspection and macrofracture examinations may be convenient and reliable methods for detecting them. The presence of flakes also results in diminished values for reduction of area in tensile tests, impact toughness in the vertical direction, and fatigue strengths. Flakes in plate mainly exist in granular bainite and other microstructures transformed at lower temperatures where Si, Mn, and V segregate. Scanning electron microscopy of flake fracture after heat treatment reveals a cloudrack morphology in the crack propagation region and a moth-eaten pattern at the edges of the flakes. The reasons for the formation of microstructural features of flakes and for the relation between flakes and inclusions are discussed.