High-strength Alloy Steel Research Articles

Analysis and application of high strength alloy steel flywheel structure and material

Analysis and application of high strength alloy steel flywheel structure and material

Investigation of Process Stability and Weld Quality of Underwater Wet Flux-Cored Arc Welding of Low-Alloy High-Strength Steel with Oxy-Rutile Wire

Abstract The paper described the experimental findings of underwater wet welding of E40 steel using self-shielded flux-cored wire with a TiO2-FeO-MnO slag system. The arc stability, weld quality and corrosion resistance with different heat inputs were studied. The results showed that the wet welding process of the designed wire displayed good operability in the range of investigated parameters. The microstructure and mechanical properties of the weld metal depended on the heat input. Due to the high fraction of acicular ferrite in the weld metal, the mechanical properties of the weld metal under low heat input had better tensile strength and impact toughness. Fracture morphologies at low heat input had uniform and small dimples, which exhibited a ductile characteristic. The diffusible hydrogen content in the deposited metal obtained at a heat input of 26 kJ/cm significantly reduced to 14.6 ml/100g due to the combined effects of Fe2O3 addition and the slow solidification rate of molten metal. The microstructure also had a significant effect on the corrosion resistance of the weld metal. The weld metal with high proportions of acicular ferrite at low heat input exhibited the lowest corrosion rate, while the base metal possessed a reduced corrosion resistance. These results were helpful to promote the application of low alloy high strength steel in the marine fields.

Effect of machining on performance enhancement of superficial layer of high-strength alloy steel

The microstructure of machined superficial layer significantly affects the mechanical properties and service life of mechanical components. Herein, to obtain a machined surface with excellent properties, a comprehensive application of theoretical calculations and test analysis research methods was conducted to investigate the influence mechanism of machining on performance and quality of machined superficial layer of high-strength alloy steel during machining, and reveal the intrinsic correlation between microstructure evolution, quality and performance of machined superficial layer. The results indicate that the machining can achieve gradient microstructure on the machined surface, which can improve the performance of machined surface greatly. From the surface to the inside region, the layers are respectively the recrystallized layer where compact nano-sized equiaxed grains are located, the rheological layer with clusters of high-density sub-grain structures, and the distorted layer with residual distorted grains. The maximum strain of superficial layer in the machined state is 2.81 times that of the original state. The grains are evidently refined and the grain size is reduced by 49.03%. The dislocation density is enhanced by 100.69%, while the number of small-angle grain boundaries (SAGB) and other substructures increase sharply, being 5.26 times that in the original state. By performance testing, the machining substantially enhances the hardness of the superficial layer of high-strength alloy steel with certain rise in toughness simultaneously, which is exactly the result of the combined effect of fine-grain strengthening and dislocation strengthening caused by the machining process above.

Effect of tempering temperature on hydrogen embrittlement in V-containing low alloy high strength steel

Three different tempering temperature were designed to investigate the effect of tempering temperature on microstructure, tensile behavior and hydrogen embrittlement sensitivity in a V-containing low alloy high strength steel. Results showed that with increasing tempering temperature, on one hand, the steel displayed decrease in strength and increase in ductility as usual, on the other hand, the susceptibility to hydrogen-induced embrittlement reduced on the same precharging hydrogen condition. These changes on properties were explained from their microstructure variation observed by X-ray diffraction (XRD) and electron backscatter diffraction (EBSD).

Interpreting the radiative properties of advanced high strength steel using the geometric optics ray-tracing approximation

This study investigates the relationship between surface topography and radiative properties of advanced high strength steel (AHSS) alloys using the geometric optics approximation (GOA) with ray tracing. Five AHSS coupons with different alloy compositions and surface topographies are investigated. The directional-hemispherical and specular reflectance of samples are measured using a UV-Vis-NIR spectrophotometer (0.25–2.5 μm) and two FTIR spectrometers (2.5-20 μm), while surface profiles used in the ray tracing model are obtained using an optical profilometer. Predictions of directional-hemispherical reflectance are consistent with the experimental data when the surface parameters and incident wavelengths are within the valid GOA domain. Reflectance predictions in the specular direction are also in line with the measurements when the roughness parameters are in the specular approximation domain.

Influence of cutting velocity on gradient microstructure of machined surface during turning of high-strength alloy steel

The microstructure of machined surfaces is crucial to the overall performance and service life of mechanical structures. In this study, we performed cutting experiment, test analyze, and theoretical calculation to investigate the evolution in gradient microstructures of the superficial layer on machined surface, including grain size, dislocation density, grain boundary and misorientation angle, in the turning of high strength alloy steel with a self-developed coated carbide microstructure turning tool under different cutting velocities. Single-factor cutting experiments and corresponding tests were carried out using X-ray diffraction (XRD) and electron back scattered diffraction (EBSD) to investigate effects of cutting velocity on the microstructure of the machined surface during the cutting process. In addition, the performance and quality of the machined surfaces were assessed using a micro-hardness tester, laser scanning confocal microscopy, and atomic force microscopy. The relationship between microstructure and performance of the machined surface was explored by establishing a cutting model. The results showed that higher cutting velocities before exceeding the transition threshold with a larger relative evaluation coefficient can raise the thickness of the strengthening layer. This changes the gradient-distribution of dislocation density, grain boundary, and misorientation angle in the machined surface resulting in finer grains, thereby strengthening the machined surface. Moreover, the thickest agglomerate layer of equiaxed crystals was also observed under the higher cutting velocity, which was found to improve the performance of the workpiece (Micro-hardness of 318.07 HV and roughness of 0.05 μm), suggesting the approach to control cutting conditions to achieve better machined surfaces by evaluating the comprehensive function of mechanical load and thermal load in the metal machining process is effective.

Evolution of Residual Stress and Microstructure during Annealing of 30SiMn2MoVA High-Strength Alloy Steel Tube Processed by Cold Radial Forging

Evolution of Residual Stress and Microstructure during Annealing of 30SiMn2MoVA High-Strength Alloy Steel Tube Processed by Cold Radial Forging

Development of a multivariate spectral emissivity model for an advanced high strength steel alloy through factorial design-of-experiments

Variations in the spectral emissivity of advanced high strength steels (AHSS) during intercritical annealing leads to errors in pyrometry measurements, which, in turn, cause thermal excursions that impact the mechanical properties of the steel. This paper presents an empirical approach for modelling the spectral emissivity of advanced high strength steel. Samples of two dual-phase steel (DP980) alloys, having Si/Mn ratios of 0.04 and 0.23, are heated within a galvanizing simulator in atmospheres of 95%/5% N2/H2 and dew points of 10°C and −30°C. The spectral hemispherical reflectance of the annealed samples was measured with an FTIR spectrometer. The variation of the spectral emissivity with dew point, alloy composition, pre-annealed surface state, and wavelength is analyzed using full factorial designs. The significant main and interaction effects vary across the spectral range, with the ratio of alloy components and pre-annealed surface state dominating at shorter and longer wavelengths, respectively. The predicted spectral emissivity values obtained from the model fitted for a three-channel pyrometer shows good agreement with the measurements. This study shows response surface methods (RSM) to be a viable approach for developing spectral emissivity models for pyrometry applications.

Study on formation mechanism and regularity of residual stress in ultrasonic vibration grinding of high strength alloy steel

The surface residual stress of the part has a crucial influence on its service performance. This paper studies the formation mechanism of residual stress in Ultrasonic Vibration Grinding (UVG) of high strength alloy steel, and obtains the correlation law between processing parameters and residual stress. First, based on the kinematics analysis of UVG, the formulas of ultrasonic grinding force and ultrasonic grinding transient moving heat source temperature field are analyzed. A thermal-mechanical coupled ultrasonic vibration grinding residual stress prediction model was established by FEM and verified by experiments. Second, the thermal behavior of the workpiece surface during UVG is analyzed, and the formation mechanism of the residual stress on the workpiece surface is explained. Finally, combining simulation and experimental results, a comprehensive correlation law between multiple grinding process parameters and residual stress is obtained. The research results show that compared with common grinding (CG), UVG can reduce the grinding temperature by about 8%. Both UVG and CG will reduce the original compressive stress on the surface, but UVG can make the surface of the workpiece retain greater compressive residual stress and prevent the emergence of tensile residual stress. This work of the thesis provides a basis for the research of residual stress in UVG.

Influence of welding sequence on residual stress distribution and deformation in Q345 steel H-section butt-welded joint

Abstract Based on Marc. MSC software, this paper developed a thermo-elastic-plastic finite element method (FEM) to simulate the welding residual stresses and deformation in the low alloy high strength steel joints. The welding residual stresses and deformation in the Q345 Steel H-section butt-welded joints were calculated using this method. An H-section butt-welded joint was fabricated and the welding residual stresses were measured. Based on the simulation and experiment, the influence of welding sequence on the residual stress distribution and deformation in the Q345 steel H-section butt-welded joint was investigated. The results indicate that the welding sequence has a relatively small effect on the residual stress distribution in the flanges of the H-section joints, but a significant influence on that in the web. Under three different welding sequences, the welding deformations in the joints were similar. In the view of controlling welding residual stress, welding the web first is recommended in the fabrication of the H-section butt-welded joint.

Friction stir riveting (FSR) of AA6061-T6 aluminum alloy and DP600 steel

The increasing demand for lightweighting in the automobile industry drives the mix-use of high specific strength materials, such as aluminum alloy and advanced high strength steel (AHSS). However, the differences in physical and metallurgical properties of aluminum alloy and steel, and the increase of steel strength have brought great challenges to the traditional spot joining technologies. This paper proposed a novel friction stir riveting (FSR) process to join aluminum alloy and AHSS sheets. In the FSR process, a high-speed rotating semi-hollow rivet penetrates through the aluminum sheet and is then friction welded with the steel sheet to form an annular solid phase welding zone, which mechanically locks the aluminum sheet between the rivet cap and the steel sheet, creating a solid phase-mechanical hybrid joint. The joint macro morphology formation, the solid phase welding mechanism, the thermo-mechanical coupled effects on microstructures and microhardness, and the tensile-shear performance of the joints were investigated. The results indicate that the FSR process achieved successful joining of AA6061-T6 and DP600. However, the joint performance was limited by a thin layer of inclusion in the solid phase welding zone, which was produced after the rivet cavity being fully filled by the trapped aluminum alloy. Further optimization of the rivet cavity and corresponding process parameters is necessary to obtain an inclusion-free FSR joint. The FSR process is expected to provide a new industrial solution for the joining of light alloy to steel and offers new insight into the solid phase joining of tube-sheet structures.

Automatic Control System of Hydraulic Tension Pilot Warm Rolling Mill

In order to meet the warm rolling demand and deal with the inefficiency of cold-rolled deformation metals such as high-strength steel, silicon steel and magnesium-nickel alloy, etc., The state key Laboratory of Rolling technology and Automation of Northeastern University(NEU-RAL) designed and manufactured a new pilot warm rolling mill that can achieve heating on line in the rolling process. This paper introduces equipment constitutes, and its main functions and features. The paper also describes its temperature control system, AGC system and ATC system during the warm rolling process in details. Multiple experiments have proven that the pilot warm rolling mill can not only simulate the actual production process to produce the hard-deformed metals, provide innovative technology, but also offer easy to use experimental equipment for steel industry researchers.

Welding stability and fatigue performance of laser welded low alloy high strength steel with 20 mm thickness

The butt joint of low alloy high strength steel with 20 mm thickness was joined by combining with high power laser welding and narrow gap hybrid laser-arc welding. For the high power laser welding, the laser power was a decisive factor of the weld formation: excessive laser power lead to unstable behavior of molten pool and key hole, while insufficient laser power resulted in the lack of penetration. For the narrow gap hybrid laser-arc welding, arc behavior was closely related to the dynamic behavior of the molten metal at tip of the wire. Unstable behavior of the molten metal at tip of the wire caused variable arcing positions, leading to the arc deflection and arc burning up. The narrow gap grooves were heated unevenly when the arc was whether deflection or burning up, leading to the formation of the sharp corner areas and lack of fusion defects. The fatigue fractures of both laser weld and hybrid weld were made up of the crack initiation areas, the crack propagation areas and the transient fracture areas. Fatigue property of the laser weld was better than that of the hybrid weld, which was thought to be strongly associated with the fine multidirectional grains within the laser weld and the precipitation of particle phases inside the hybrid weld.

Investigation on grinding-induced dynamic recrystallization behavior of 40Cr alloy steel

This study aims to investigate the metallurgical behavior of high strength alloy steel 40Cr during the grinding strengthening (GS) process. The grinding heat can cause phase transformation, which increases surface hardness during the GS process. It is worthwhile mentioning that the severe plastic deformation can easily lead to dynamic recrystallization (DRX) under the high temperature on the grinding strengthening layer (GSL). It can improve the mechanical properties of metal components significantly. Firstly, the relations between true stress and strain of 40Cr alloy steel are obtained by the split Hopkinson pressure bar (SHPB) experiment under high temperature and high strain rate. The critical conditions and key simulation parameters of DRX are determined. Secondly, the temperature field and plastic strain field of the GSL are solved with the analytical method and finite element method, respectively. The results show that there is a large temperature gradient in GSL. The maximum temperature of the ground surface can reach 1060 °C. And the austenite transformation occurs within 150 µm. The severe plastic deformations generated within 60 µm in the grinding subsurface can reach the critical conditions of DRX. Thirdly, a cellular automaton (CA) model is established to simulate DRX of the microstructure evolution of the grinding enhancement layer. The comparison between simulation and experimental indicates that the plastic strain of the strengthening layer increases and the degree of refinement of the microstructure becomes higher with the increase of the grinding depth.

Friction - wear modeling in drilling process of H-13 tool steel

Simulation of metal cutting is complex both from numerical and physical perspective. The scope of this work is to elaborate on the process and physics of metal cutting, and more specifically drilling. The description of H-13 steel dry drilling with the use of a single-layer TiN coated carbide twist drill is presented. H-13 is a high strength alloy steel used in demanding applications and elevated temperatures. A simulation model was developed with use of Deform-3D software, and an experiment was conducted in order to evaluate the acquired simulation results, meaning the wear mechanisms and thermal loads implemented during the process of drilling. The Usui wear model was used for the calculation of the wear rate of the drill. Regarding the experiment, a thermal camera was used in order to record the temperature of the drill after the process. The comparative analysis of the simulation models and the experiment showed that adhesion is the dominant wear mechanism. Higher wear values were observed in the rake faces of the drill, where the coating starts to fade, due to built-up edges (BUE). The tool and workpiece temperatures reach near steady state conditions during process. Elevated temperatures are applied on the removed material. Good chip evacuation and chip length indicate that coated drills with optimized geometry are suitable for drilling tough materials.

Mechanical clinching and self-pierce riveting for sheet combination of 780-MPa high-strength steel and aluminium alloy A5052 sheets and durability on salt spray test of joints

To increase the usage of high-strength steel and aluminium alloy sheets for lightweight automobile body panels, the joinability of sheet combinations including a 780-MPa high-strength steel and an aluminium alloy A5052 sheets by mechanical clinching and self-pierce riveting was investigated for different tool shapes in an experiment. All the sheet combinations except for the two steel sheets by self-pierce riveting, i.e., the two steel sheets, the two aluminium alloy sheets, and the steel-aluminium alloy sheets, were successfully joined by both the joining methods without the gaps among the rivet and the sheets. Then, to show the durability of the joined sheets, the corrosion behaviour and the joint strength of the aged sheets by a salt spray test were measured. The corrosion and the load reduction of the clinched and the riveted two aluminium alloy sheets were little. The corrosion of the clinched two steel sheets without the galvanized layer progressed, and then the load after 1176 h decreased by 85%. In the clinched two galvanized steel sheets, the corrosion progress slowed down by 24%. In the clinched steel and aluminium alloy sheets, the thickness reduction occurred near the minimum thickness of the upper sheet and in the upper surface on the edge of the lower aluminium alloy sheet, whereas the top surface of the upper sheet and the upper surface of the lower sheet were mainly corroded in the riveted joint. The load reduction was caused by the two thickness reductions, i.e., the reduction in the minimum thickness of the upper sheet and the reduction in the flange of the aluminium alloy sheet. Although the load of the clinched steel without the galvanized coating layer and aluminium alloy sheets decreased by about 20%, the use of the galvanized steel sheet brought the decrease by about 11%. It was found that the use of the galvanized steel sheets is effective for the decrease of strength reduction due to corrosion.

Thermal modelling of cutting tool temperatures and heat partition in orthogonal machining of high-strength alloy steel

Cutting temperatures and heat partition into the cutting tool are critical factors that significantly affect tool life and part accuracy during metal removal operations, especially in dry machining. Among many thermal modelling studies, uniform heat partition ratio, and/or uniform heat intensity along the tool-chip interface are frequently assumed. This assumption is not valid in actual machining and can lead to erroneous estimated results in the presence of sticking and sliding friction zones. Therefore, it is necessary to accurately predict the cutting tool temperature and heat partition during machining. This paper presents an analytical thermal modelling approach which considers the combined effect of the primary and the secondary heat sources and determines the temperature rise and non-uniform heat partition ratio along the tool-chip interface. Cutting tests were conducted on AISI/SAE 4140 high-strength alloy steel using carbide cutting tools over a wide range of cutting speeds. Cutting temperatures were measured experimentally using an infrared thermal imaging camera. Experimentally established sticking and sliding friction regions were used to evaluate non-uniform frictional heat intensity along the tool-chip interface. The temperature matching condition along the tool-chip interface leads to the solution of distributed non-uniform heat partition ratio by solving a set of linear equations through programming in MATLAB®. Experimental results show to be consistent well with those obtained from the thermal model, yielding a relative difference of predicted average tool-chip interface temperature from −0.8% to 6.3%. It is found that average heat partition into the cutting tool ( RT) varies from 35% down to 15% for the entire range of cutting speeds. These results suggest that, to address the thermal problem in metal cutting, the research and development of tooling should also focus on reducing friction on the tool rake face in addition to the contribution of the combined effect of primary and secondary heat sources on temperature rise at the tool-chip interface.

A New Drilling Tool for Machining of CFRP-Metal-Hybrid Components

In many industrial sectors, lightweight construction with fiber-reinforced plastics have been in use for many years. In aviation, for example, about half of the aircraft weight of current airliners consists of carbon fiber reinforced plastics (CFRP). These materials are combined with metals to obtain hybrid materials in order to improve their mechanical properties. For a secure and accurate fitting connection of the resulting components, both materials must be drilled simultaneously in one machining operation. This represents a significant technological challenge due to the contrasting requirements of both material groups on the machining process and the tools used. Standard tools are only adapted to one material at a time and the machining parameters can only be adjusted to a limited extent during the drilling process. As a result, one component of the hybrid material is damaged during the drilling process. This damage must be removed in an additional machining step in order to meet the high quality requirements. In this paper, a new tool concept is presented, which allows high-quality drilling of hybrid materials made of CFRP and metal in a single manufacturing operation without subsequent rework. For high quality machining, the drilling process is carried out in three steps. At first, the hybrid material is pre-drilled with a universal cutting edge. The resulting material damage occurs in a small area around the bore edge, depending on the selected cutting parameters. Then, two independent sets of cutting edges, which are adapted to the respective material components, are used in a finishing process to remove the damage caused during the pre-drilling. By using a movable cutting edge, the tool works in two directions during the drilling process. Machining tests proved that the tool concept is able to achieve reproducible high-quality bores in hybrid materials made of CFRP in combination with high-strength aluminum, steel and titanium alloys.

Behavior Strengthening of Superficial Layer of High Strength Alloy Steel in Machining Process

Behavior Strengthening of Superficial Layer of High Strength Alloy Steel in Machining Process

INFLUENCE OF DIFFERENT ASSEMBLIES ON PRE-HEATING THE HSLA SAR 80T STEEL ON COATED ELECTRODE WELDING

The present work evaluated the influence of assemblies other than preheating in the welding process obtained by coated electrode, using high strength and low alloy steel SAR 80T as the base metal and the AWS E7018 electrode as the addition metal. In order to prevent cracks, preheating and interpassing for low alloy steel was performed. Depending on the way the preheating equipment is installed, it may take more or less time to reach the preheat temperature. Different assembly arrangements for top joints were evaluated, aiming at cost reduction, in addition to evaluations of the mechanical properties of the joint. Visual testing, ultrasound, micrography, macrography and cross-sectional traction were performed. The results obtained were considered acceptable and showed that there was an influence on time, cost of preheating and resistance to impact.