Application Of High Strength Steel Research Articles

Investigation on new steel grades for construction of wind energy mills for sustainable energy supply

In regard to the sustainability of future cities, an increase in sustainable energy sources needs to be managed. Therefore, the German government decided on increasing the ratio of green energy up to 20% by 2020. In accordance with this, offshore wind energy parks will be constructed, as they provide the advantage of lasting air cleanliness and pre- serving natural resources. To ensure construction safety, wind energy mills are constructed using ductile steels of large thickness. Here, an application of high-strength steels provides the possibility of reducing the amount of material while construction safety is still ensured. Considering the long life cycle of wind energy mills' foundation structures and the recy- clability of the steel grades used, their construction becomes a relevant factor in reducing CO2 emissions. Furthermore, the use of less material reduces CO2 emissions. Due to exist- ing safety concepts, however, the application of high-strength steels is only conditionally allowed. Thus, the current study concerns the development of a safety concept based on the existing concepts to allow the application of high-strength steels. Furthermore, as the structural steel parts need to be joined, an energy-efficient welding process is utilised: elec- tron beam welding. The structural steel parts and weld joints are investigated with respect to their mechanical properties by analysing their loadability in combination with safety concepts. The load on the material is evaluated to ensure construction safety. In addition to the investigation of safety requirements, the supplied mechanical properties are investi- gated. As the weld joints show different properties from the base material, the joints are considered the critical part. The joints are investigated concerning strength and toughness. Afterwards the mechanical properties are correlated with the wind energy structures. The prevention of failure is fulfilled when the mechanical properties of the weld joints exceed the required mechanical properties.

Springback Analysis of High Strength Dual-phase Steels

Car manufacturing was always the key industry behind sheet metal forming thus the requirements and developments in car manufacturing have decisive role in the development of sheet metal forming, too. The automotive industry faces with very contradictory demands and requirements: better performance with lower consumption and lower harmful emissions, more safety and comfort that are hardly available simultaneously with conventional materials and conventional manufacturing processes. These requirements are the main driving forces in the automotive industry and in the material and technological developments in sheet metal forming, as well. During the recent years significant developments can be observed in the application of high strength steels. In this respect the application of various dual-phase steels is one of the best examples to meet these contradictory requirements. However, the application of these high strength steels often leads to formability problems. Among them the springback occurring after sheet metal forming should be mentioned first. In this paper, some recent results will be given obtained by using the new device together with a sensitivity analysis done by numerical simulation.

Evaluation of Applicability on a High-rise Building for the Effective Usage of High Performance Steel for Building Structures

최근 건축물의 초고층화, 대형화 및 장경간화에 따른 요구 성능의 증대에 따라 강재 및 콘크리트 등의 구조재료가 지니는 재료강도 및 사용성 등을 향상시키고자 하는 노력이 지속적으로 이루어지고 있다. 본 연구에서는 개발된 건축구조용 고성능 강재의 기계적, 화학적 소재 특성을 평가하고, 실제 Project를 대상으로 대안설계를 수행하여 고강도 강재의 경제성을 평가하였다. HSA800은 고강도와 좋은 용접성을 갖추기 위해 TMCP 방식으로 제조되었으며, 기계적, 화학적 성질 모두 KS규격을 만족하였다. 또한 HSA800의 고층건물의 적용성 및 경제성 평가를 위해 SM490강재 모델과 사용성에 초점을 두고 비교 평가를 수행하였다. 그 결과 SM490대비 약 30% 물량절감이 가능하였다. HSA800의 사용은 추후 건축구조의 제작, 시공 뿐만아니라 공사비 절감에도 기여할 것으로 기대되어진다. As building height and span is getting taller and longer, the researches to increase material's strength and serviceability are continuously performed. This study evaluated mechanical and chemical properties of newly developed high-strength steel (HSS) for building structures, namely HSA800 and verified cost-effectiveness and applicability of HSS for a tall building by comparing the analysis results of normal strength steel (SM490) model. HSA800 was manufactured by TMCP to have a good weldability in spite of HSS and satisfied Korean Industrial Standards (KS). The analysis results for evaluating cost-effectiveness show that total steel quantity could be saved approximately 30% when using HSS compared to SM490. It is expected that HSA800 will contribute to enhance constructability of building.

Advanced Materials in Sheet Metal Forming

In this paper, some recent developments in materials applied in sheet metal forming processes will be overviewed mainly from the viewpoint of automotive industry as one of the most important application fields. If we consider the main requirements in the automotive industry we can state that there are very contradictory demands on developments. Better performance with lower consumption and lower harmful emission, more safety and comfort are hardly available simultaneously with conventional materials and conventional manufacturing processes. These requirements are the main driving forces behind the material and technological developments in sheet metal forming: application of high strength steels, low weight light alloys and the appropriate non-conventional forming processes are the main target fields of developments summarized in this paper.

Hot Stamping of Two Different High Strength Steel with Tailored Properties

With the increasingly widespread application of high-strength steel (HSS), tailored properties, namely different mechanical properties required in different regions of the same part, have been proposed, in order to achieve the matching between mechanical properties and safety performance of motor vehicle parts. In this paper, the influence of air gap on the final hardness and strength distribution is discussed in terms of two different HSS, namely LG1500HS and WHT1500HF. As for steel LG1500HS, regardless of the location of samples in the formed part, the final fracture area is in the vicinity of the air gap center, proving the lowest hardness and strength in transition zones. Compared to steel LG1500HS, steel WHT1500HF exhibits gradient hardness distribution from the cooling zone to the heating zone, with no minimal value discovered in transition zones.

Local buckling in the stub columns fabricated with HSA800 of high performance steel

Recently, high-performance steels have been increasingly used for structural materials in buildings and bridges with the demand for high-rise and long-span of main structures. This paper is a series of basic study for the design specification of structural members using new high-performance steel with the material properties of HSA800 (High-performance Steel having tensile strength of 800 MPa for building structures). The steel stub columns of built-up H-section and square hollow section with various width-to-thickness ratios are experimentally planned to investigate the local buckling behaviors and then to check their current design limits. The nonlinear three-dimensional finite element models are also constructed to verify the experimental results. The present experimental results are seen to closely agree with those from finite element analysis. In addition, the verified finite element models are used for extensive parametric studies to check up the applicability of highstrength steel in current design specification.

The Research on Ultimate Displacement Angle of Concrete Columns with High-Strength Materials

Not collapse under strong earthquake is an important goal of the seismic design of reinforced concrete structure, seismic collapse resistance performance is directly affected by the deformation behavior of reinforced concrete column. The application of high-strength steel, high-strength stirrup and high-strength concrete can enhance the concrete material properties and mechanical properties of reinforced concrete column, but their deformation behavior have large differences. The research on the seismic performance of columns with high-strength materials, especially its deformation behavior, become the most important issue of anti-collapse analysis. In this paper, the ultimate displacement angle of concrete columns with high-strength materials were collected, the ultimate displacement angle and inter-story drift angle 1/50 were compared and analyzed. The results show that the average of ultimate displacement angle of the reinforced concrete column with high-strength stirrup and high-strength longitudinal bars are 0.0469, 0.0312, respectively, greater than inter-story drift angle 1/50, while the average of ultimate displacement angle with high-strength concrete and high-strength core concrete are 0.0147, 0.0167, less than 1/50, therefore, it is not suitable for taking 1/50 as the critical value of structure collapse with high-strength concrete. The inter-story drift angle should be different in the anti-collapse analysis.

국부좌굴을 고려한 건축구조용 고성능강(HSA800) 조립각형강관 압축재의 적용성 평가

Recently, high-performance steels have been increasingly used for structural materials in buildings and bridges with the demand for high-rise and long-span of main structures. This paper offers a series of basic study for the design specification of structural members using high performance steel, that is material properties of HSA800 (High-performance rolled steel for building structures). Built-up square tube stub columns with variables of width-to-thickness ratios are planned as a parametric study in order to investigate the local buckling behaviors and check the current design limit of width-to-thickness ratio. In addition, the buckling behaviors of stub columns obtained finite element (FE) analysis were compared with those from experimental tests. The verified FE model was used for parametric study and checked applicability of high-strength steel on current design specification.

Topology Optimization of a Car Seat Frame

The optimization of consumer products through the use of numerical simulations has become a key factor to a continuously increasing requirement for time and cost efficiency, for quality improvement and materials saving, in many manufacturing areas such as automotive, aerospace, building, packaging and electronic industries. Environmental protection, fuel economy and safety specifications are today major concerns in automotive industry. Part of the overall strategy is a lower weight car which means increased performance, reduction of fuel consumption achieving a lower vehicle exhaust emissions to the environment. At the same time, the occupant safety must be continuously improved, as the safety specifications are more demanding. To meet these requirements, a call for new lightweight’s concepts and crash structures was raised, using lighter and/or stronger materials. In the last decade we have assisted to a development and application of high-strength steels and aluminum alloys in the manufacture of automotive structures. This paper presents a structural design problem of a car seat frame, aiming the desired weight reduction while satisfying a set of performance constraints. The numerical model of the seat frame has been developed and the numerical results were validated against experimental data obtained during static loading tests. Using the developed computational model, an optimized topology of the linear elastic structure has been determined, reaching a significant weight reduction.

Steels for vessels of water-moderated water-cooled reactors of a new generation with enhanced radiation resistance

A path of the formation of schools of thought on the development of high-strength vessel steels which were created by Academician of the Russian Academy of Sciences I.V. Gorynin is shown from the beginning of the 1950s to the present time. Results achieved in the field of development and application of high-strength steels for nuclear reactor vessels of a new generation with enhanced radiation resistance are represented.

Key Issues of Using High Strength Steels in Seismic Structures and some Recent Progress

Since recent advances of technology in material science and increasing demand for high strength steel, Q460 high strength steel has been applied to several landmark buildings and major projects. However, the application of high strength steel in seismic structures is limited by the relative worse ductility, which is usually decreasing with the increasing on yield strength. For this purpose, key issues of using high strength steels in seismic structures are discussed and two design methodologies are proposed. Recent research progress on application of high strength constructional steel achieved at Tongji University is introduced. Finally, future work related to the application of high strength steels are recommended.

Field of application of high strength steel circular tubes for steel and composite columns from an economic point of view

This paper presents the results of a global comparison between high strength steel and normal steel circular tube used to build steel and composite columns submitted to static loading, as regards the economic aspects. The comparison is based on an optimum design taking into account the strength, stability and stiffness conditions of Eurocode 3 and 4. The automatic implementation of the algorithms allows achieving a high amount of case studies, covering the realistic possibilities of building columns. The investigations are realized on simple columns, columns included in braced or un-braced frames and whole frames. The field of application of high strength steel (vs normal steel), regarding the total cost of the member, is provided in a chart clearly indicating where the use of high strength steel becomes economic.

Investigation of High Strength Steel for Automotive Roll-Forming Parts

In recent years, the number of automobiles has been steadily increasing, which has significantly impacted on the society and human life, and led to many social problems such as fuel crisis, environment pollution. Therefore, lightweight designing becomes a focused issue. Lightweight materials application, optimized structure design and advanced manufacturing process are the main ways to achieve the lightweight. However, low plasticity and ductility of high strength steel constrain the application of high strength steel. In this paper, the basic principle of roll forming for automotive parts is investigated, and it is innovatively applied in the hot roll forming process of the ultra high strength steel.

600MPa급 고강도 원형강관 부재의 성능 평가

현재 토목 및 건축구조에서 고성능 고강도 강에 대한 수요가 증가함에 따라 고성능 재료개발의 필요성이 증대되고 있다. 특히 초고층 건물과 장경간을 가지는 구조에서는 고강도, 고인성, 우수한 용접성 등이 요구된다. 이에 따라 현재 국내에서는 600MPa 급 강재의 개발이 진행 중에 있다. 그러나 고강도 강재는 일반 강재와는 전혀 다른 기계적 특성을 갖고 있다. 그러므로 고강도 강재를 구조물에 적용하기 위해서는 비탄성영역에서의 거동이 일반 강재와 동등한가를 확인해야 한다. 본 연구에서는 600MPa급 원형 강관의 기둥 및 보부재 실험을 통해 구조적 거동을 파악하였다. 각각 3개의 기둥 및 보 실험이 수행되었으며, 현행설계규준과의 적합성을 평가하였다. Recent advances of technology in materials science have made it easy to respond to user's needs on high performance steel in civil and building structures. The high-performance and high-strength steel are required for large scale structure and high-rise building to have high-strength, high fracture toughness and better weldability etc. Therefore development of 600MPa class steel for mega structure is necessary. high strength steels, however, may have mechanical properties that are significantly different from those of the conventional steels. The application of high-strength steels to building structures should be reviewed as to whether inelastic behavior equivalent to that of conventional steels can be attained or not. This study researched the structural behavior of high strength circular tubes compression and under flexure. Three column tests and three flexural tests were carried out. The suitability of existing design formulae(KBC 2009) and the structural behavior were investigated through these columns and beams with various types.

2208 スプリングバック抑制を目的とした可変ブランクホルダー力の最適軌道設計(OS7-1 近似最適化I,OS7 近似最適化)

In order to meet the current requirement of lightweight, energy conservation in car development, high strength steel (HSS) is widely applied. But too much springback and poor dimensional accuracy are fatal problems in the application of HSS, so precise predication of springback and an effective control method become urgent in the sheet metal forming area. In the previous study, we know that we can use Variable Blank Holder Force (VBHF) to decrease the springback. Therefore the VBHF approach is popular approach in industries, and it's important to design the VBHF trajectory. However, the information about how to optimize the VBHF Trajectory in previous study is limited. In this paper, we tried to develop an effective way to obtain the VBHF trajectory by using sequential approximate optimization (SAO) approach. The objective is taken as the minimization of springback. The constraints are quantitatively defined with the Forming Limit Diagram (FLD), in which no wrinkling and tearing can be observed. The design variables are the blank holder force. The Radial Basis Function (RBF) network is employed for the response surface, and the validity of the VBHF we obtained is examined through the numerical simulation.

水素侵入による980MPa級溶接金属の低温割れ限界条件

Prevention of weld cracking is primely important for ensuring the integrity of steel construction. Especially, for high strength steel weld, which is susceptible to hydrogen cold cracking, it is important to clarify the critical condition for cracking in order for expanding use of high strength steel applications. In this study, critical conditions of hydrogen content and residual stress in the high strength steel weld with tensile strength level of over 980MPa were investigated. Cold cracking test was conducted using Y-grooved constraint weld joint by intentionally introducing hydrogen gas, and critical hydrogen content in the weld metal to cold cracking was determined. Cold cracking occurred in the weld metal from the root, bottom portion in the weld metal, when hydrogen content exceeds about 2ppm, and fracture surface was typical grain boundary fracture caused by hydrogen embrittlement. Then, residual stress distribution in the weld meal was measured by neutron diffraction technique. Same Y-grooved weld joint with no cold cracking was used for stress measurement. Neutron beam was filtered by 2mm×2mm slit to measure the residual stress in the small region. Reference sample without residual stress was prepared by introducing multiple saw cuts with small intervals in the same weld joint, and lattice spacing of stress free condition was first measured. Then, lattice spacing in the three different directions along the centerline of the weld metal were measured to calculate residual stress in the three directions. All portions in the weld metal center showed tensile residual stress. The root portion showed highest tensile stress of over 1110MPa in the transverse direction, which is the same as the crack opening direction. Therefore, it is considered that high level of tensile residual stress is the key factor for cold cracking. Hydrogen concentration to the root region by pressure stress was discussed in terms of local hydrogen content condition for cracking.

초고성능 콘크리트(UHPC)의 부착특성에 관한 연구

초고성능 콘크리트(ultra high performance concrete, UHPC)는 종래의 보통 콘크리트와 다른 새로운 재료로써 높은 강도와 향상된 인성을 그 특징으로 한다. 이러한 새로운 재료의 활용을 위하여 이 연구에서 초고성능 콘크리트의 부착 성능을 평가하고자 하였다. 수정된 RILEM 방법을 사용하여 초고성능 콘크리트와 이형 철근의 인발실험(pull-out test)을 수행하였으며 보통 콘크리트와 비교하여 5~10배에 달하는 부착강도를 확인하여 기존의 설계 기준에 비하여 현저하게 감소한 정착길이와 피복 두께를 제안하였다. 700 ㎫급 고장력 철근의 실험 결과의 비교로부터 초고성능 콘크리트에서 고강도 철근 활용의 유효성을 확인하였다. 강연선의 응력전달길이 측정실험을 통하여 현재 전달길이 기준이 UHPC의 경우 매우 보수적이라는 것을 확인하였다. 또한 유한요소해석을 통하여 실험 결과를 검증하였다.

DC-MSIP/HPPMS (Cr,Al,V)N and (Cr,Al,W)N thin films for high-temperature friction reduction

The application of high-strength steel and aluminum alloys entails increasing demands on the surfaces of tools used for forming processes. A promising approach towards the reduction of friction forces and thus towards the wear of tools is the application of self-lubricating coatings. Due to the high number of crystallographic shear planes and a partially low melting temperature, the so-called Magnéli-phases offer excellent possibilities for the reduction of friction in tools at application temperatures between 600 °C and 800 °C. In order to achieve the aforementioned gliding planes vanadium (V) and tungsten (W) containing (Cr,Al)N thin films deposited via a combination of Magnetron Sputter Ion Plating (MSIP) and High Power Pulse Magnetron Sputtering (HPPMS) Physical Vapor Deposition (PVD) were activated in a high-temperature environment. In this context, the (Cr,Al)N matrix provides for wear protection while vanadium and tungsten are developing friction-reducing oxides under temperature influence. Hence, a diffusion of these metals to the surface during application is necessary for a continuous generation of dry or liquid lubricants. Within this paper a scanning electron microscope (SEM) was used for the analysis of the cross-section fractures of the coatings in order to allow statements about the coatings' morphology and thickness; further, annealing tests in an atmosphere furnace at 600 °C, 800 °C and 1000 °C were carried out. X-ray diffractometry (XRD) served for documentation of phase transformations. With an electron probe micro analysis (EPMA) the diffusion of elements was observed. To investigate the friction reduction high-temperature pin-on-disk (PoD) tribometer measurements (room temperature (RT), 600 °C and 800 °C) using a 100Cr6 counterpart were, moreover, carried out in atmosphere. Within these investigations we could show a reduction in the friction coefficient from 0.6 at room temperature to 0.05 at 800 °C for the (Cr,Al,V)N coating. Furthermore, a diffusion of V to the surface of the coating was demonstrated. However, a positive effect by using (Cr,Al,W)N cannot be verified.

Springback Calculation and Compensation System Based on Rail Member Panel

Springback problem is always a hotspot in automotive industry and academia, especially when the application of high strength steel in automotive panel is more and more popular. Based on the modeling characteristics of rail panel, a complete system able to calculate and compensate springback and modify the profile is presented. The system includes three main aspects. Firstly, springback of sections can be calculated by 2D section method and finite element method (FEM) codes and the accurate springback results can be obtained in the system. Secondly, the section nodes can be compensated by node-offset algorithm and the nodes information of each section before springback and after compensation can be obtained. And thirdly, according to the matching relationship of the section nodes before springback and after compensation, the compensated profile can be obtained by shape global deformation (SGD) algorithm based on the original profile in this system. This method can ensure the topology consistency of surface before and after modifications and the quality and smoothness of compensated curved surface. The practice proves that this system can save time and cost to a great extent in dealing with springback of rail panel and also a great improvement in surface-smoothness and more accurate compensation can be achieved.

Investigation of fracture behaviour in TRIP steels

In automotive body designing high strength steels are used to achieve weight reduction together with an improvement of crashworthiness. The most important representatives of the AHSS steels are Dual Phase (DP) steels and TRansformation Induced Plasticity (TRIP) steels. The application of high strength steels requires a detailed knowledge about the formability and the forming limits. While the true stress strain curve describes a material’s forming behaviour, the Forming Limit Diagram (FLD) is the common criterion used for a Finite Element based process-layout to analyse failure probability and to prevent the occurrence of factures. But forming of multiphase high-strength steels may lead to the occurrence of cracks in regions of a component, which are save in accordance to the results of Finite Element Analysis (FEA). Mostly areas of the part are involved, in which a combination of tension compression- and biaxial tension-stresses can be observed. These results lead to the assumption that depending on the forming history there might be an unknown forming limit. To generate valid forming limits the identification of critical forming operations becomes necessary. Therefore deep drawing operations of cups with geometrically modified specimens have been carried out. The aim of this modification is to influence the stress and strain condition during forming as well as the corresponding microstructural evolution. Experimental work in combination with numerical investigations shows interdependencies between the forming behaviour of the material, stress condition, strain path and maximum drawing ratio. X-ray, light optical and electron microscopes, thermography, computer tomography and metallography are used to describe the fracture mechanism.