Large Forgings Research Articles

Non-Destructive Hardness Indentation Measurement of Residual Stress on Large Aerospace Forged Components at the Engineering Site Based on Impact Hardness Tester.

Large forgings are crucial in aerospace applications; however, the residual stresses generated during their forming and heat treatment seriously affect their serviceability. Therefore, the non-destructive detection of residual stresses in large forgings is of far-reaching significance for ensuring the quality of forgings and realising precision machining. Although a variety of detection methods are available, there is still a lack of a programme that can comprehensively, accurately and non-destructively measure the residual stresses in large forgings. This study is dedicated to exploring the application of the bouncing impact indentation method in the non-destructive testing of residual stresses in large forgings. Through in-depth finite element simulations and orthogonal scheme analyses, we found that the elastic modulus, yield strength and work hardening indexes have significant effects on the impact indentation process. Further, we establish the dimensionless function of residual stress and indentation parameters, and successfully obtain the inversion algorithm of residual stress. The relative error of the calculated values of the indentation curves hm and hr in the simulation with reference values is not more than 3%, and the relative error of the corrected Pm inversion values for most virtual materials is not more than 5%. The folding elastic modulus and apparent elastic modulus obtained by inversion are controlled within 10%, which demonstrates a high value for engineering applications. In addition, we innovatively express the research results in the form of 3D stress diagrams, realising the digital expression of 3D residual stresses in large forgings based on feature point measurements and contour surface configurations, which provides intuitive and comprehensive data support for engineering practice.

Hybrid manufacturing approach for landing gear applications: WAAM Ti–6Al–4V on forged Ti–5Al–5Mo–5V–3Cr

High-strength metastable β-titanium alloys like Ti-5553 (Ti–5Al–5Mo–5V–3Cr) are frequently used in highly loaded aerospace components. Such aerospace parts tend to be expensive to traditionally manufacture due to current industry process limitations such as inflexibility for complex geometries, costs related to tooling for large forgings, extended lead times, poor machinability and high material waste. These challenges are leading to increased interest in exploring alternative manufacturing routes. This work investigates the use of additive manufacturing to deposit cost-effective and machinable Ti-64 (Ti–6Al–4V) alloy onto a forged Ti-5553 alloy substrate. The microstructure evolution, microhardness and tensile properties have been investigated for both the as-deposited as well as for stress relief heat-treated conditions. The results confirmed the formation of coarse columnar β grains with a fine basketweave α structure. The heat affected zones (HAZs) developed in the Ti-5553 substrate material from the cyclic thermal fluxes introduced from the melt-pool were characterized by a gradient microstructure of dissolving constituent phases with nearing proximity to the fusion zone. Tensile testing in the as-deposited condition was characterised with a UTS of 884 MPa and a ductility of 15%. Tensile samples extracted across the substrate-deposit interface all failed in the WAAM Ti-64 material and demonstrated comparatively greater strength but poorer ductility. A band of tensile residual stresses was imparted along the substrate, but was adequately stress relieved after heat-treatment at 600 °C. The heat-treatment led to the formation of more homogeneous α-phase laths throughout the HAZ of the Ti-5553 material and provided overall improvements to the strength and ductility.

Physical simulation of the underclad heat affected zone in a reactor pressure vessel to study intergranular cracking

Underclad cracking in nuclear pressure vessels was of significant concern in the 1970s and 1980s before mitigating adjustments were made both to steel compositions and manufacturing practice. Unfortunately, the cracking mechanisms are still not well understood, and this can undermine confidence when changes to cladding operations are under consideration. In this work, Charpy-sized test coupons of 18MND5 steel were subject to a range of thermal cycles that can be experienced by the substrate immediately adjacent to the interface with the overlay. The Charpy test results are considered in combination with analysis of the samples through field emission gun (FEG) scanning electron microscopy (SEM) and wavelength dispersive X-ray spectroscopy (WDXS). The findings suggest that the heat affected zone subject to the coarse grained plus intercritical thermal cycle, before post weld heat treatment, has a peculiar and potentially brittle microstructure. However, in a steel with no obvious macrosegregation, no clear evidence of intergranular cracking in the early stages of the post weld heat treatment could be found. The second part of the work focuses on the effects of segregation regions in large forgings, more specifically ghost lines, on the tendency for underclad cracking. Ghost line regions that subsequently form a coarse grained heat affected zone (CGHAZ), and are then heated to just under the A1 temperature, seem to be the most prone to intergranular cracking. Cracking susceptibility appears to be associated with elevated concentrations of alloying and impurity elements at grain boundaries.

Evaluation of cracking risk of 80MnSi8-6 nanobainitic steel during hot forging in the range of lower temperature limits

Abstract Nanobainitic steels exhibit an exceptional combination of high strength, good plasticity, impact toughness, and wear resistance. They are suitable for the production of large mass components through the open-die forging process. Subsequently, the forgings are air-cooled. An obstacle of this method is the extended time required for the large forgings to undergo a bainitic transformation, making the industrial implementation of this process economically unjustifiable. Nevertheless, nanobainitic steels also allow for the open-die forging of small batches of structural elements with high property requirements. A technological limitation lies in the necessity of performing a series of operations, leading to a prolonged processing time dependent on the shape of the product and the degree of deformation. Therefore, inter-operational reheating is often necessary, incurring costs and time consumption. This is particularly relevant to forgings with a mass ranging from a few to several dozen kilograms, which, due to their low thermal capacity, rapidly dissipate heat to the surroundings and tools. Designing an economical process with a limited number of reheating cycles requires advanced knowledge of material behavior under thermo-mechanical deformation parameters, including boundary conditions where a significant decrease in plasticity occurs and the risk of crack initiation. To obtain this information, a comprehensive analysis of the influence of thermo-mechanical parameters applied during the deformation of nanobainitic steel at relatively low temperatures on the flow characteristics and crack formation was conducted. To achieve this goal, the Digital Image Correlation method, the finite element method modeling considering damage criteria, and the macrostructural evaluation of deformed specimens were employed.

Measurement method of hot forging dimension based on green laser depth information.

The application field of large forgings is extensive. Accurate dimensional measurement is an important factor to ensure the quality of the finished forging product when it is forged at high temperature. Therefore, this paper proposes a green laser scanning measurement method based on depth information. First, a geometric measurement model based on depth information is established by studying the relationship between green laser depth information and forging dimension. Then, based on the heat transfer theory, distribution of the temperature field around hot forgings is studied, and an error function caused by light refraction is established using a ray tracing algorithm. After that, the error function is used to modify the measurement model to obtain the accurate distance between the forging and background plane and then obtain the dimensional information of the forging. Finally, this measurement method was experimentally verified in the laboratory, and the experimental results show that the measurement error of this method meets the dimensional measurement requirements of large hot forgings.

О возможности локального измерения трещиностойкости конструкционных сталей с привязкой к структуре

The scale of heterogeneity of the structures of steels and alloys can be rather large both within one sample and within a product. The procedure adopted in practice for determining the integral values of crack resistance characteristics cannot always reflect this circumstance. In this regard, it is necessary to develop methods for assessing the crack resistance of a medium with a heterogeneous structure. In this work, the authors determined the crack resistance of large forgings made of heat-hardenable 38KhN3MFA-Sh steel (0.38%C–Cr–3%Ni–Mo–V) based on the critical crack opening δс and the J-integral. The presence of critical stages in the development of a ductile crack during testing was assessed by acoustic emission measurements. In combination with the obtained methods of digital fractography of 3D images of fractures, this allowed relating the shape and position of the leading edge of each crack jump to the load-displacement diagram. Measuring the crack opening geometry during the test showed the possibility of determining directly the coefficient of crack face rotation when estimating δс. In general, this allowed constructing a map of the distribution of parameter δс values over the thickness of the sample and estimating the scale of the scatter in crack resistance within one sample – up to 30 %. Such a localization of measurements, primarily of the δc parameter, is comparable to the scale of heterogeneity in the morphology of various types of structures, which was assessed based on the measurement of digital images of the dendritic structure, the Bauman sulfur print, non-metallic inclusions on an unetched section, and ferrite-pearlite banding in the microstructure. This makes it possible to link local crack resistance values to various fracture mechanisms and their accompanying structural components.

Regulation Law of Tempering Cooling Rate on Toughness of Medium-Carbon Medium-Alloy Steel.

Temper embrittlement is a major challenge encountered during the heat treatment of high-performance steels for large forgings. This study investigates the microstructural evolution and mechanical properties of Cr-Ni-Mo-V thick-walled steel, designed for large forgings with a tensile strength of 1500 MPa, under different tempering cooling rates. Optical microscopy (OM), scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD) were employed to analyze the microstructural features. The results demonstrate that the embrittlement occurring during air cooling after tempering is attributed to the concentration of impurities near Fe3C at the grain boundaries. The low-temperature impact toughness at -40 °C after water quenching reaches 29 J due to the accelerated cooling rate during tempering, which slows down the diffusion of impurity elements towards the grain boundaries, resulting in a reduced concentration and dislocation density and an increased stability of the grain boundaries, thereby enhancing toughness. The bainite content decreases and the interface between martensite and bainite undergoes changes after water quenching during tempering. These alterations influence the crack propagation direction within the two-phase microstructure, further modifying the toughness. These findings contribute to the understanding of temper embrittlement and provide valuable guidance for optimizing heat treatment processes to enhance the performance of high-performance steels in large forgings.

PREDICTION OF MICROSTRUCTURE EVOLUTION OF 316LN AUSTENITIC STAINLESS STEEL USING CELLULAR AUTOMATA AND A NOVEL EVALUATION METHOD FOR GRAIN SIZE INHOMOGENEITY

Inhomogeneous grain size is a significant structural defect in large forgings. This study employed cellular automata to simulate the dynamic recrystallization (DRX) of 316LN steel and analyzed the grain distribution during DRX. The accuracy of the CA method was verified by comparing its results with the results of a thermal simulation test on Gleeble 1500D. Subsequently, a novel method for evaluating grain size inhomogeneity was proposed. The grain size inhomogeneity coefficient Gu was introduced to determine the evolution of grain size inhomogeneity during DRX. This coefficient accurately and objectively reflects grain inhomogeneity. The impact of the initial and recrystallized grain size on the inhomogeneity during DRX was also analyzed.

Equivalent initial damage sizes (EIDS) for type 1C anodised aluminium alloy 7085-T7452 under variable amplitude loading

Aluminium alloy (AA) 7085-T7452 is a high strength, low weight alloy used in large forgings in primary airframe applications. For corrosion protection, airframe components are anodised and this study looks at the influence of type 1C anodising on the fatigue crack growth behaviour in AA 7085-T7452 specimens that were fatigue tested with fighter wing spectrum loading. Surface etch pits formed during essential anodising preparatory processes were the primary cause of fatigue crack nucleation. The severity of the early crack growth caused by those etch pits that nucleated the worst crack in each specimen was evaluated using quantitative fractography-based fatigue crack growth measurements and the equivalent initial damage size (EIDS) of those etch pits was determined. Characterising the EIDS distribution of aircraft alloys with representative surface treatments is a fundamental input into Linear Elastic Fracture Mechanics (LEFM) based fleet failure analysis of aircraft structures. In this study, a notable increase in the average EIDS value for the worst crack present was observed whenever material or loading condition changes led to a significantly increased number of crack nucleation sites. In particular, an increase in the cyclic stress spectrum’s severity increased the number of nucleation sites in a specimen and significantly increased the average EIDS. It appears that due to variable nucleating discontinuity properties (e.g. size, shape and orientation) and material property variations, an increased number of nucleation sites increases the probability that the worst crack present will nucleate at a location that is conducive for relatively fast early crack growth. This will potentially cause shorter overall airframe component fatigue lives and so both the mechanisms and conditions of etch pit fatigue nucleation in this material and material finish shall be discussed for the benefit of failure analysts evaluating unexpected fleet fatigue cracking.

Mechanism of mitigating quenching cracking for B-containing 9Cr martensitic heat resistant steel by austempering process

B-containing 9Cr martensitic steels are attractive materials for specific industrial applications due to their excellent high-temperature strength and ductility. However, quenching large forgings with water or oil often results in cracking. The correlation between quenching crack and microstructure was established in this work to evaluate the selection of the quench cooling methods, which make it possible to mitigate the quench cracking by tailoring microstructural evolution. Kinetics dynamic analysis, microstructural characterization, and phase-field simulation were used to clarify the mechanism of mitigating quenching cracking. It is demonstrated that austempering produces a mixed microstructure consisting of lathy martensite, ultra-fine martensite, and a small amount of C-riched retained austensite. This mixed microstructure translates into refining the effective grain size and reducing the internal stress, reducing cracking propagation by reducing phase transformation stress and enhancing the coordinated deformation. Thus, the quenching cracking can be inhibition by tailoring the fraction of ultra-fine martensite and retained austensite in B-containing 9Cr steels.

Research on the behaviour and mechanism of void welding based on multiple scales

Abstract As the core foundation of major national equipment, large forgings have a great influence on the national economic construction, the development of national defence equipment and the development of modern cutting-edge science and technology. In the production of large forgings, welding the internal void of forgings is a technical problem that directly affects the quality of large forgings. In view of the phenomenon of void welding in large forgings, the behaviour and mechanism of void welding were deeply studied based on the stretching test and molecular dynamics simulation, combined with a lot of theoretical analysis. The results show that multi-pass stretching deformation is a kind of plastic deformation process which can eliminate void defects. When the forging ratio reaches 2.2, the void can be welded completely and the tensile strength can be restored to the level of the matrix. With the increase of compression deformation, the stress will increase sharply, especially at the grain boundary. In addition, the main void welding mechanism of 30Cr2Ni4MoV steel is the recrystallization and grain growth mechanism. Recrystallization and grain growth are of great significance for promoting the reduction of void volume and realizing metallurgical bonding of the interface.

Influence of Spacers and Skid Sizes on Heat Treatment of Large Forgings within an Industrial Electric Furnace

The influence of stacking patterns, through the different spacer and skid sizes, on the transient temperature distribution uniformity of large-size forgings in a 112-m3 electrical heat treatment furnace was investigated by conducting CFD simulations and real-scale experimental validation. A 3D CFD model of the electrical furnace was generated, including a heat-treating chamber, axial flow fans, large size blocks, skids, and spacers. Real-scale temperature measurements on instrumented test blocks during the heat treatment process were carried out to validate the CFD simulations. Results indicated that the CFD model was capable enough to determine the transient temperature evolution of the blocks with a maximum average deviation of about 6.62% compared to the experimental measurements. It was found that significant temperature non-uniformities of up to 379 K on the surfaces of the blocks due to the non-optimum stacking pattern were experienced by the blocks. Such non-uniformities could be reduced between 24% to 32% if well-adapted spacer and skid sizes were used in the stacking configurations. Based on simulation results and experimental validation work, optimum spacer and skid sizes for uniform temperature distribution were proposed for different stacking patterns.

New Method and Application of Stress Field Calculation for Large Forgings

New Method and Application of Stress Field Calculation for Large Forgings

Optimization of COMPASS-U Support Structure

The global support structure for Compass Upgrade (COMPASS-U) employs many bolted and pinned components to improve the manufacturability of the whole structures. This is a departure from other designs used for highly loaded tokamaks, like Alcator C-Mod which used large forgings. Modeling of the numerous connections and interfaces was a challenge. This article will describe how to optimize the C-frame support structure with the goal to eliminate differential displacements at those interfaces and, importantly, minimize toroidal mutual displacement at the sliding joint of the toroidal field (TF) coils. The global support structure consists of 16 C-frames, and it can be simplified as a 1/8th cyclic symmetry model due to the eight vertical rods mounting that connect bottom CS and PF1-3 assemblies to the C-frames. Structure variants with different connection webs between two neighboring C-frames have been analyzed. The preloading of bolts can be split into several preload substeps to simulate the real assembly process of the COMPASS-U support structure. The TF crown and the wedge plate can be further improved to become a solid part to better hold the TF coils.

A calculation method of wavelength range required to acquire image of hot large forging

A calculation method of wavelength range required to acquire image of hot large forging

Structure and Mechanical Properties of Welded Joints of Large Steel Forgings for Nuclear Power Plants of MIR 1200 Type

The paper deals with research, development and verification of production technology of selected welded joints for pressure vessels located in primary circuit of nuclear power plants type MIR 1200. Effects of various welding technologies on mechanical and fracture properties were studied. Four types of weld joints made of 10GN2MFA steel grade were prepared for experimental programme consisted of testing of conventional mechanical (tensile and impact tests) as well as fracture toughness and low-cycle fatigue tests and also stress corrosion cracking test in water environment. Effect of elevated operating temperature on material properties was evaluated, too.

A study on length measurement method of hot large forgings based on binocular vision system

A length measurement method of hot large forgings is proposed in this paper. Firstly, the images of hot forgings are acquired by two monochrome Charge Coupled Device (CCD) cameras, and the light strips are detected according to the characteristics that the value of the pixels in the vertical direction of the light strips is approximate the Gaussian distribution. Secondly, the sub-pixel centers of each light strips in the left and right images are calculated and used for matching and three-dimensional (3D). Finally, the curve represented by quintic polynomial is employed to fit the two-dimensional (2D) points which are projected by 3D points on the fitted plane, and the edge of the forging is calculated by the curvature of the fitted curve. The experimental results in laboratory show that the measurement accuracy can reach 0.547%. The length measurement time of hot forging is 3.7 s.

Review and Prospect of Process Research on Large Forgings

Review and Prospect of Process Research on Large Forgings

On necessity of taking into account statistical nature of the objects using Big Data in metallurgy

Several statistical restrictions, which are critically important for correct use of different Big Data procedures in metallurgy for attestation and management of quality of metal products are evaluated. Representative production control data stores for steel manufacturing technologies are used as the research object. This research covered wide grade and dimension range of steels: large forgings of heat treatable 38KhN3MFA-Sh steel, rolled products of 40KhMFA steel, sheet 17G1S-U, 09G2S and 15KhSND steels. Possible scale of variety of values distribution both for managing parameters and characteristics of strength, plasticity and toughness is shown using the coefficients of asymmetry and kurtosis. These characteristics are varied within the technological tolerance range. Accompanying risk during metal quality prediction and management, e.g. using the methods of parametric statistics, was evaluated for the case when this circumstance was not taken into account. The features of influence of a sample list volume on the results of statistical processing of large production control data stores and metallurgical product are revealed. It is shown how absence of common space of parameters restricts possibilities of classic statistics in metallurgy, makes non-effective the management “by disturbance” principle. In this connection, possibilities of non-parametric statistics, presented by Kolmogorov – Smirnov criterion, which is not depended on distribution of collection of analyzed sample lists, are evaluated. To provide objective selection of the areas with dominating type of relationship, it is necessary to take into account possibility of existence of different evolution scenarios for structure and defects along the technological chain (technological heredity) within the framework of rather wide tolerance range, as well as features of their appearance. Difference in the evolution mechanisms of structures and defects within the framework of separate technological trajectory is a cause of appearances of developed heterogeneity for nominal single-type structures which have, however, different scales, as well as accompanying quality dispersion (which is often essential). Taking this circumstance into account allows to find out the links in the system “managing parameters – final parameters of metal products”, which are not always evident during their search using generally accepted approaches. Development of the complex of rules for online management of metal products quality is possible on this base.

A novel method for measuring the length of hot large forgings based on machine vision system

In order to measure the length of hot large forgings, a novel method based on machine vision system is proposed. Firstly, according to the characteristics that the light strips in the images acquired by machine vision system are continuous and have peaks, the light strip is detected. Secondly, after calculating the sub-pixel edge points of each light strip using an improved sub-pixel edge detection algorithm, the sub-pixel edge points of each light strip are sorted according to the order of the abscissa from small to large. Three-dimensional (3D) points of each edge can be obtained separately by matching and 3D reconstruction. Finally, the 3D points of each edge are projected onto its fitting plane, and the projected points are fitted with a quintic polynomial curve. According to the curvature of the fitted curve, the edge point of the forging can be detected. The distance from the starting point to the edge point is the length of forging at the position of light strip edge. The length measurement experiment shows that the method can be used to measure the length of hot large forgings. The relative error of the length measurement system is 0.547%. The time for measuring the length of hot forging is 6.8 s.