Takehide Senuma

Okayama University · Division of Mechanical and Systems Engineering

The demand for higher-strength automotive steel sheets has increased significantly for lightweight and safe body concepts. However, the increment of the steel strength is often limited by the potential occurrence of delayed fracture. This paper discusses proper microstructure control and alloy design to improve the resistance against the delayed fr...

The hydrogen embrittlement (HE) characteristics of Fe–0.33C–1.2Mn–xNb–xMo steels were investigated experimentally using various samples with differing microstructural characteristics. HE in steels was affected by hydrogen trapping sites: ε-carbide-based, Nb-based, and Mo-based precipitates, which were effective at enhancing HE resistance. In contra...

In this study, the decarburization behavior, and its effect on mechanical properties of 2000 MPa class martensitic steel were investigated with the purpose of collecting the basic data to realize the further strengthening of structural members for automobiles. Concerning the decarburization behavior, the maximum of the decarburization rate of 2000...

Press hardening steel (PHS) is widely applied in current automotive body design. The trend of using PHS grades with strengths above 1500 MPa raises concerns about sensitivity to hydrogen embrittlement. This study investigates the hydrogen delayed fracture sensitivity of steel alloy 32MnB5 with a 2000 MPa tensile strength and that of several alloy v...

Hydrogen embrittlement (HE) characteristics in Fe–C–Mn-xNb steels were examined via various analyses, including electron backscatter diffraction analysis, scanning transmission electron microscopy and three-dimensional atom-probe tomography. For the investigation, the steel samples were prepared with varying Nb contents and heat treatment processes...

Considerable progress in developing flat-rolled steel grades has been made by the Chinese steel industry over the recent two decades. The increasing demand for high-performance products to be used in infrastructural projects as well as in production of consumer and capital goods has been driving this development until today. The installation of sta...

In this article, the characteristics of hot stamping steels and their coatings are described. At first, the characteristics of the conventional 1500 MPa class hot stamping steel such as mechanical properties, hardenability, fluctuation of strength etc., are described, and then the present status and future perspectives of the development of hot sta...

Toward a high demand for ultrahigh strength automotive components for reducing body weight and increasing crashworthiness, hot stamped components have been employed worldwidely, and the further increase in strength of hot stamped components is being requested. A large obstacle of the strength increase is the concern about the occurrence of delayed...

In typical (cold) stamping operations, the dies are only used to plastically deform the metal material. In hot stamping, on the other hand, the dies are used to form the material and extract the heat energy from the blank. All this has to be done as quickly as possible to improve the part quality (to ensure martensite formation is completed) and pa...

A near-β-type Ti-5Al-2Fe-3Mo alloy (Super-TIX®523AFM) was developed as a low-cost and high-strength material for automotive components such as intake valves. Its mechanical properties, such as strength, elongation and Young's modulus, are adjustable via the solution treatment temperature. Furthermore, a unique phenomenon different from the shape me...

As a method for producing ultrahigh strength automotive steel components with high gauge accuracy the hot stamping technology draws attention and is practiced widely today. For supporting and developing this technology, numerous researches have been actively carried out all over the world. It is a good timing to review this technology on this speci...

As a method for producing ultrahigh strength automotive steel components with high gauge accuracy, the hot stamping technology draws attention and the amount of hot stamped automotive components has exponentially increased in the last decade. The concerns about the potential danger of embrittlement and delayed fracture, however, limit the strength...

In this study, the precipitation hardening behavior of middle carbon steels with single and multiple additions of 0.3mass%V and 2mass%Cu has been investigated. The precipitation treatment was carried out isothermally at 550ºC, 600ºC and 650ºC. In the 0.3mass%V bearing steel, precipitation hardening was observed at 600ºC and 650ºC while no significa...

The transformation behavior and microstructural changes of Ti-4Fe-7Al alloy during tempering were investigated by performing a hardness test and using X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques. Within a brief time of 30 s during tempering at 450°C, the hardness rapidly increased to a maximum value of 600 Hv. The...

The toughness and the resistance to delayed fracture are deteriorated with increasing strength of martenstic steels. It has been reported that these properties could be improved by grain refinement of martensite. In this study, the influence of both hot stamping conditions such as heating rate, heating temperature, cooling rate, and material condit...

Disclosed are a high-strength, high-toughness hot-pressed steel plate member and a manufacturing method therefor. A specified hot-press process is performed on a steel plate member that, with respect to the chemical composition of the steel plate, includes: 0.15 to 0.4 wt % of C; 1.0 to 5.0 wt % of Mn or of a total of Mn and at least one of Cr, Mo,...

抄録 In this study, the precipitation behavior of middle carbon steels with single and multiple additions of 0.3mass%V and 2mass%Cu has been investigated. The precipitation treatment was carried out isothermally at 600°C. In the 0.3mass%V bearing steel, precipitates were observed in rows, indicating the occurrence of the interphase precipitation. On...

抄録 Unprecedented phenomena were discovered by tempering the Ti-4Fe-7Al alloy quenched from the β (bcc) field. The alloy became very hard when it was tempered at 450℃ for several minutes, and severely rugged surface was generated. The inverse shape recovery phenomenon was also discovered when a quenched specimen that had been bent at room temperatur...

抄録 The tensile deformation behavior of single and poly-crystal Fe-3%Al alloys was investigated at room temperature. The work hardening rate (WHR) of the polycrystalline alloy monotonously decreased with increasing strain and increased with decreasing grain size. The WHR of the single crystal alloy was remarkably lower than that of the polycrystalli...

抄録 The influence of Al content on the evolution of microstructures and mechanical properties of Ti-xFe-yAl alloys quenched from a β field was investigated via hardness measurements, tensile tests, scanning electron microscopy (SEM) equipped with electron back scattering pattern (EBSP) analyzer, and conventional transmission electron microscopy (TEM...

Hot stamping is a very promising method for producing ultrahigh-strength automotive components. The heating and cooling conditions in the conventional hot stamping process are quite limited. To improve the productivity of the process and/or the mechanical properties of the product, optimizing the heating and cooling conditions is an important and u...

Annealing treatment of cold-rolled steel sheets are mostly subjected to the continuous annealing line. In such process recovery, recrystallization, reverse transformation and dissolution or formation of precipitates occur during heating and homogenizing treatments, and the transformation and precipitation in the steel during the subsequent cooling...

To satisfy the demand for high-strength steel sheets with excellent strength–ductility–hole expansion ratio balance, high-strength steels consisting of a ferrite or bainitic ferrite matrix strengthened by a large amount of finely dispersed precipitates have been developed. In this study, the influence of the precipitation-forming elements Ti and Nb...

Microstructual observations indicate that the recrystallization of cold rolled extralow carbon steel sheets occurs due to the abnormal growth of selected subgrains in recovered subgrain microstructures. The authors measured the orientations of a recovered microstructure of a cold rolled extralow carbon steel sheet by SEM-EBSP and classified the def...

For lightening the hot forged automotive components such as connecting rods, crank shafts etc. the increase in their yield strength is an important technical issue. Recent developments indicate that it is a promising way to increase the yield strength of the components using the ferrite-pearlite microstructure strengthened by precipitation hardenin...

Nowadays, most of cold rolled steel sheets are produced in continuous annealing lines. In continuous annealing lines, the recovery, recrystallization, reverse transformation and dissolution of precipitates occur in the heating and homogenizing process and the transformation and precipitation occur in the cooling and aging process. The required micr...

Microstructual observations indicate that the recrystallization of cold rolled extralow carbon steel sheets occurs due to the abnonnal growth of selected subgrains in recovered subgrain microstructures. Based on this recrystallization mechanism, a new model for predicting the recrystallization behavior of a material with idealized microstructure wa...

Hot stamping is an attractive method to produce extra high strength automotive components. In the conventional hot stamping, the furnace heating is employed and the heating rate is quite low. To improve the productivity of the hot stamping technology, the reduction of time for the heating process is required. In this study, the influence of the hea...

In this study, the precipitation and precipitation hardening behavior of a 0.3%V and 2%Cu bearing middle carbon steel has been investigated in comparison with that of a 0.3%V bearing steel and a 2%Cu bearing steel. The precipitation treatment was carried out isothermally at 600 degrees C. The amount of the precipitation hardening of the 0.3%V and 2...

抄録 Over the past decades, hot stamping technology has been gradually applied to the production of ultra high-strength automotive components. Although automotive components such as bumpers, door impact beams, center pillar reinforces have been produced by hot stamping and installed in many cars worldwide, this promising technology has not spread as...

In this study, we investigated the microstructure, hardness, Young's modulus, and tensile behavior of binary Ti-4∼9 mass% Mo alloys, quenched from a temperature of 1223 K. Among the solution-treated binary Ti-Mo alloys, the lowest Young's modulus was observed in the case oftheTi-6Mo alloy, which was the border composition of α′ /α′. When the rollin...

The microstructural evolution of extralow carbon steels in hot working processes has been studied. Considering the experimental results of the microstructural evolution of austenite and the transformation behavior, a metallurgical model for predicting the microstructural evolution of extralow carbon steels in hot working processes was developed. Th...

抄録 For the past decade, hot stamping technology has been gradually applied to the production of super high strength automotive parts. Although auto-parts such as bumpers, door impact beams, center pillar reinforces have been produced by hot stamping and installed in many cars all over the world, this promising technology has not spread as much as w...

In this paper, the qualities and characteristics required from an engineer who works globally are discussed based on my own experience of a joint research project with a European company. The most important qualities and characteristics are integrity, one‧s own initiative, basic and expert knowledge, creativity, communicative skills and broad world...

The effect of various operational parameters such as the finishing temperature, the final reduction, the cooling rate, the onset time for cooling after the final rolling in a hot strip rolling process on the grain refinement of hot rolled extralow carbon steel bands has been investigated. To analyze the experimental results, a metallurgical model f...

Quenching and annealing experiments with electrical resistivity measurements, were applied to magnesium to investigate the formation of thermal vacancies. Two specimens made from materials differing in impurity contents were examined. One of the specimens quenched in a methanol bath at -80 degrees C from elevated temperatures ranging from 160 degre...

The nitriding process is one of the common methods for surface hardening, and consists of heat treatment in a furnace for many hours. The nitriding behavior and strengthening mechanism of Ti added steels in the nitriding process, which is applicable to a high temperature and rapid process such as the continuous annealing of steel strip, were invest...

In this paper, recent research and development of modern steel sheets for automobiles has been reviewed. Therefore, the steel sheets introduced here are not only types in commercial production but also those until now only reported in technical papers. Besides steel sheets themselves, some technologies contributing to promoting the use of the steel...

The influence of a heating rate up to 1000 degrees C/s on recrystallization behavior and texture formation of an extralow carbon steel sheet was investigated. To discuss the experimental results of this investigation, a mathematical model for predicting recrystallization behavior was developed. An analysis using the model shows that the heating rat...

The aim of this study is to systematically investigate the elastic behavior with deformation of the binary titanium alloys of TiMo, Ti-Nb and Ti-V. The stress-strain curve using cyclic load-unloading tensile test of alloys composed of alpha '' martensite, e.g. 20Nb and 8Mo, showed the peculiar pseudo-elastic behavior. A little higher content of bet...

High strength steels have been developed in order to improve fuel economy as well as to increase safety. The conventional Si-Mn bearing high strength steels have the drawback of poor galvanisability due to the presence of complex Si-Mn oxides on their surface. In order to improve the galvanisability of Si-Mn steels, the effect of the addition of Ni...

Japanese Specification for Highway Bridges [Japan Road Association: Specification for Highway Bridges—I & II, 2002.3] has been revised in 2002, which clearly states that degradation of bridge members, including those of weathering steels, to occur in prolonged period of time must be taken into account at the design stage to realize long term struct...

A new-type of weathering steel containing 3.0 mass% Ni and 0.4 mass% Cu (“advanced weathering steel”) exhibits good atmospheric-corrosion resistance in an atmosphere containing relatively high air-born salinity. Here, we show that the high performance was successfully achieved by controlling Fe(O,OH)6 nano-network structures of rust formed on their...

The present status and future perspectives of steel sheets and electrical steel sheets for automobiles are introduced. Concerning the steel sheets, the control for minimizing the deterioration of formability caused by increasing strength is important and the physical metallurgy for obtaining the appropriate microstructure of modern high strength st...

Pitting corrosion behavior of austenitic stainless steels with Mo was investigated in chloride and bromide solutions. The steels with higher S content as 0.009 mass% showed higher pitting potential in 1 kmol/m(3) bromide solution than 1 kmol/m(3) chloride solution. On the other hand, the steels with lower S content as 0.0003 mass% showed opposite r...

It has been reported that the characteristic of rolling contact wear of rail steels varies depending on the microstructure of steels. However, the reasons for such variations have not been fully elucidated yet. Accordingly, a two cylinder rolling contact wear test was conducted by using pcarlitic steels, tempered martensite steels, spheroidal carbi...

The nitriding process is one of the common methods for surface hardening, and consists of heat treatment in a furnace for many hours. The nitriding behavior and strengthening mechanism of Ti added steels in the nitriding process, which is appli- cable to a high temperature and rapid process such as the continuous annealing of steel strip, were inve...

To reduce the emissions of CO2, weight reduction of cars is required. One promising solution is the application of high strength steel sheets. For the widespread use of high strength steel sheets, the required formability must be achieved.In this paper, the processing and properties of advanced high strength steels produced by sophisticated control...

The influence of heating and coiling temperatures on recrystallization of Ti added high purity ferritic stainless steels (17Cr-0.1Ti-ultra low C, N) was investigated to claryfy the conditions of accelerating recrystallization in the coiling processes. The recrystallization during coiling significantly retarded when the heating temperature before ro...

Precipitation is one of the most important phenomena for controlling the properties of steel. Therefore, numerous studies have been performed in this field. Since 1998, the ISIJ has held a research workshop on precipitation control consisting of around forty members from academia and industry. This workshop held a seminar in autumn 2001 in which so...

It has been reported that the characteristic of rolling contact wear of rail steels varies depending on the microstructure and carbon content of steels. However, the reasons for such variations have not been fully elucidated yet. Accordingly, the authors conducted two-cylinder rolling contact wear test by using pearlitic steels with carbon content...

Lightening of automobile bodies is required from the viewpoint of saving energy which contributes to ameliorating an ecological problem. A useful means of doing this is the application of high strength steel sheets to automobile bodies. The inferior formability of high strength steel sheets in comparison with that of mild steel sheets, however, hin...

Experiments have been conducted to investigate the effect of hot- and cold-rolling conditions on earing. It was shown that the earing of cold-rolled and annealed sheets increases with an increase in cold-rolling reduction. On the other hand, the earing decreases with a finishing temperature below Ar3 temperature in hot rolling, the effect of the fi...

The nitriding process is one of the common methods for surface hardening, and consists of heat treatment in a furnace for many hours. The nitriding behavior and strengthening mechanism of Ti added steels in the nitriding process, which is applicable to a high temperature and rapid process such as the continuos annealing of steel strip, were investi...

It is well known that nickel is a beneficial alloying element in copper bearing steels as it prevents hot shortness. On the other hand, the addition of tin promotes hot shortness. Though some mechanisms for promoting these phenomena have been suggested, a quantitative discussion has still failed to establish the cause. In the present study, changes...

The final report on the university of the 21st century and measures for necessary reform submitted by the university council in October 1998 described many of the problems in the present university education and proposed the necessary measures for improvement. The report was fundamentally written from a viewpoint of university representatives altho...

To predict and control the planar plastic anisotropy of metal sheets, it is necessary to clarify the quantitative relationship between the texture and anisotropy. In this paper, prediction of earing of drawn cup by three-dimensional texture analysis based on the vector method and quantitative evaluation concerning the relation between texture and e...

In this paper, the effect of various operational parameters in a hot strip rolling process on the grain refinement of hot rolled plain extralow-carbon steel bands has been investigated. The finishing temperature and the onset time of cooling after hot rolling influence the grain refinement significantly. The finishing temperature just above Ar3 is...

The evolution of texture due to recrystallization was investigated in cold rolled Ti-bearing IF steel sheets using Electron Back Scattering Pattern (EBSP). The aim of this study was to obtain a real picture of the formation of the recrystallization texture of IF steel sheets, which would contribute to proper texture control for improving deep drawa...

The evolution of texture due to recrystallization was investigated in cold rolled Ti-bearing IF steel sheets using Electron Back Scattering Pattern (EBSP). The aim of this study was to obtain a real picture of the formation of the recrystallization texture of IF steel sheets, which would contribute to proper texture control for improving deep drawa...

A textural analysis was carried out to explain the cause of the planar anisotropy of r -value of cold rolled plain extralow-carbon steel sheets. For a detailed analysis, a model for calculating r -values from ODF-data of texture was applied and the influence of each or a group of crystal orientations of the recrystallization texture on the planar a...

The effect of the hot band grain sizes of 28 μm and 54 μm on the r value and the texture formation of cold rolled plain extra low carbon steel sheets has been investigated in a range of cold rolling reductions from 70 to 90%. The results are concluded as follows. 1. In the formation of the cold rolling texture, the refinement of the hot band micros...

In this paper, a textural analysis on the planer anisotropy of r-value was carried out using extra low carbon steel sheets cold rolled at 80% and 90% with a hot band grain size of 28μm and 54μm respectively. For a detailed analysis, a model for calculating r-values from ODF-data of texture was used and the influence of each or a group of crystal or...

To realize a remarkable improvement of the deep drawability of steel sheets, the formation of texture of Ti-bearing IF(Interstitial atoms free) steel sheets has been investigated throughout the rolling and annealing processes. The textures formed by rolling and annealing has been studied at the surface and the midplane of IF steel sheets. The forma...

To realize a remarkable improvement of the deep drawability of steel sheets, the formation of texture of Ti-bearing IF steel sheets has been investigated throughout the rolling and annealing processes. Initially, the formation of hot band textures has been investigated in terms of the influence of rolling temperature and reduction. A low carbon ste...

To predict solute carbon and nitrogen in Nb and Ti added extra-low carbon steels quantitatively, the phase stability of the carbonitride in austenite and/or ferrite has been calculated by using Thermo-Calc software to which some thermodynamic parameters were added for the Fe-Nb-Ti-C-N system. It has been confirmed that the (Nb,Ti)(C,N) phase has a...

Although thin slab-direct hot rolling process is expected as a future process of steel sheet production, its metallurgy has not been investigated thoroughly. In this paper, the metallurgy of mild steel in thin slab-direct hot rolling process has been discussed with special attention to the precipitation behavior of MnS and its influence on the hot-...

Bake hardenability (BH) of cold rolled titanium-bearing extra low carbon steel sheets has been investigated by examining the precipitation behavior of sulfides and titanium-compounds in hot bands with varying sulfur and manganese content. In high sulfur steels (0.0050mas%) without manganese, Ti4C2S2 mainly precipitated in hot bands, while through t...

The isothermal precipitation behavior of Nb(C, N) in austenite has been investigated using steels of different carbon contents. The observed progress of the precipitation in extra low carbon steel ismuch faster and size of the precipitates is apparently larger than those in steels with higher carbon content even though their supersaturations are th...

The isothermal precipitation behavior of Nb(C, N) in austenite has been investigated using steels of different carbon contents. The observed progress of the precipitation in extra low carbon steel is much faster and size of the precipitates is apparently larger than those in steels with higher carbon content even though their supersaturations are t...

Mathematical models for predicting microstructural evolution and mechanical properties of hot strips have been reviewed. The metallurgical features of the hot strip rolling are discussed and the fundamental idea of their modeling is introduced. As applications of the mathematical models, the on-line prediction of the microstructure and strength, th...

A mathematical model has been developed for predicting phase transformation of hypoeutectoid steels during continuous cooling, with a special reference to the application to the temperature simulation in hot strip rolling. The model contains only a small number of experimental parameters so as to be used in wide ranges of temperature and chemical c...

A mathematical model for predicting microstructural evolution in hot rolling processes and the strength of hot rolled steels has been developed. Application examples are given for hot strip rolling. An accurate online prediction of microstructure and tensile strength is achieved in the whole length of hot strip. Furthermore, an accurate prediction...

The textures of warm rolled low carbon and Ti-bearing extra low carbon steel sheets have been investigated using ODF's ECC-ECP (electron channeling contrast-electron channeling pattern) and selected area electron diffraction and the following results were obtained: (1) The main orientation of the low carbon steel sheet was near {113}〈110〉 while tha...

Recent development in the automobile industry requires higher and higher formability of steel sheets. With an aim of improving the deep drawability, the influence of α-region hot rolling on the texture and r-values of cold rolled Ti-bearing extra low carbon steel sheets has been investigated and the following results were obtained. (1) As for steel...

In order to predict microstructure and mechanical properties in hot rolled HSLA steels, a precipitation model of NbC in austenite was developed. The effects of Nb content, prior austenite grain size and condition of deformation on the precipitation kinetics were quantitatively determined by extraction replica. The modelling was basically constructe...

From a viewpoint of deep drawability, the influence of chemical compositions on the texture formation of steel sheets hot rolled below Ar3 temperature (warm rolled) has been investigated using steels consisting of various combinations of carbon and titanium contents. The formation of texture was greatly influenced by carbon in solution. A steel she...

Textures of warm rolled low carbon and Ti-bearing ultra low carbon steel sheets have been investigated. The main orientation of the recrystallization texture of the low carbon steel sheet is near {114}〈110〉, while that of the Ti-bearing ultra low carbon steel sheet is near ND\varparallel〈111〉. To explain the different formation of texture between t...

In this paper, the texture formation of Ti-added extra low carbon sheet steels hot rolled below Ar3 transformation temperature has been investigated. A remarkable feature of the texture of the sheet hot-rolled below Ar3 is an inhomogeneous formation through the thickness. In the case of Ti-added extra low carbon sheet steels, the recrystallization...

A calculation model for predicting the progress of transformations of low carbon steels during continuous cooling and the microstructure after cooling has been developed. In this model, the progress of tranformations is assumed as follows. The transformation from austenite to ferrite starts at the equilibrium temperature, Ae3. The ferrite transform...

A calculation model for predicting the strength of hot rolled low carbon steel sheets from their chemical compositions and processing variables has been developed as a combination of the hot deformation model, the transformation model, and the relationship between the strength and the microstructure. To make up a comprehensive model based on the pr...

In this paper, the deformation resistance and recrystallization behavior in high temperature working (600-850°C) with high strain rates (2-150 l/s) which covers the most hot rolling conditions have been investigated. In the usual hot rolling condition the dynamic recrystallization does not occur and the resistance to hot deformation is determined b...

This paper is concerned with prediction of mechanical properties of hot rolled carbon steel sheets when the manufacturing conditions are given. By using the calculation models of structure changes during hot deformation and subsequent cooling and the relationship between hardness and the transformation temperature during cooling, hardness can be ca...

In this investigation, the recrystallization behaviour of austenite of carbon steels due to hot working has been studied. To investigate the change of structure of austenite during hot rolling of strip, a newly developed testing machine which enables simulations of hot rolling of plate, strip and wire rod has been used. The results of the experimen...