The Experts below are selected from a list of 261 Experts worldwide ranked by ideXlab platform
Wolfgang Bleck - One of the best experts on this subject based on the ideXlab platform.
-
Delayed Cracking behavior of a meta-stable austenitic stainless steel under bending condition
Materials Science and Engineering: A, 2019Co-Authors: Xiaofei Guo, Junhe Lian, Sebastian Münstermann, Wolfgang BleckAbstract:Abstract The Delayed Cracking behavior of a meta-stable austenitic stainless steel AISI 301 under bending condition has been investigated at different temperatures, hydrogen contents and external holding forces. The results reveal that the investigated material with an initial hydrogen content of 1 ppm has good bendability at the temperature range between −20 °C and room temperature, which is not susceptible to Delayed Cracking in atmospheric condition. When the material is pre-charged with 50 ppm hydrogen, the material still shows good bendability. However, it is susceptible to Delayed Cracking under an external holding force during interrupted bending test. By the measurement of martensitic transformation, the simulation of the stress/strain distributions in the bending specimens and the characterization of fracture surfaces, the effects of hydrogen, stress state and external holding force on Delayed Cracking behavior have been assessed.
-
stress oriented Delayed Cracking induced by dynamic martensitic transformation in meta stable austenitic stainless steels
Steel Research International, 2011Co-Authors: Xiaofei Guo, Jan Post, Manso Groen, Wolfgang BleckAbstract:Delayed Cracking in meta-stable austenitic stainless steels AISI 304 and AISI 301 has been investigated by deep drawing test in this study. Specimens from both steels were deformed at different drawing ratios, forming temperatures and hydrogen pre-charged conditions. The strain, martensitic fraction and residual stress distributions were characterised on the deep drawn specimens. Their influences on Delayed Cracking behaviours were quantitatively studied. We found that the incubation time to fracture and the fracture length depend chiefly on the amount of strain induced phase transformation and transformation induced residual stresses when the materials contain ∼1ppm hydrogen. When the materials were electrochemically charged with hydrogen up to the amount of 20ppm, the incubation time to fracture declined with increasing hydrogen contents following a power law relation. Besides, the fracture mode turned from a ductile nature to trans-granular and later on to inter-granular fracture feature with increasing hydrogen contents.
-
Stress Oriented Delayed Cracking Induced by Dynamic Martensitic Transformation in Meta‐Stable Austenitic Stainless Steels
steel research international, 2010Co-Authors: Xiaofei Guo, Jan Post, Manso Groen, Wolfgang BleckAbstract:Delayed Cracking in meta-stable austenitic stainless steels AISI 304 and AISI 301 has been investigated by deep drawing test in this study. Specimens from both steels were deformed at different drawing ratios, forming temperatures and hydrogen pre-charged conditions. The strain, martensitic fraction and residual stress distributions were characterised on the deep drawn specimens. Their influences on Delayed Cracking behaviours were quantitatively studied. We found that the incubation time to fracture and the fracture length depend chiefly on the amount of strain induced phase transformation and transformation induced residual stresses when the materials contain ∼1ppm hydrogen. When the materials were electrochemically charged with hydrogen up to the amount of 20ppm, the incubation time to fracture declined with increasing hydrogen contents following a power law relation. Besides, the fracture mode turned from a ductile nature to trans-granular and later on to inter-granular fracture feature with increasing hydrogen contents.
-
Methods of improving the deep drawing properties of austenitic stainless steels
Europace, 2006Co-Authors: Wolfgang Bleck, A. Frehn, E. Ratte, E. Schedin, L. Staubwasser, J. L. Avendano, N. Akdut, E. Brasseur, P. Karjalainen, P. JuntunenAbstract:Austenitic stainless steels have been developed for various purposes because of their combination of corrosion resistance with outstanding mechanical properties. Besides the remarkable strength properties, they are also known for their superior formability behaviour. Especially the stretch forming characteristics outstrip those of conventional ferritic steels by far, which is supposed to be explained by transformation of the cubic face centred austenitic phase to the cubic body centred respectively hexagonal martensite during straining, which is called TRIP-effect (Transformation Induced Plasticity). With regard to light-weight constructions and safety solutions especially in the automotive and transportation industry austenitic stainless steels with excellent cold formability gain much interest [1-4]. However, with a change of the stress state from stretch-forming to deep drawing, austenitic stainless steels lose their favourable combination of properties. That means that specific new applications, i.e. parts with high deep drawing depths, for those austenitic stainless steels would be suitable for, cannot by now be produced by using the deep drawing process. Furthermore, problems with deep drawing parts may occur as using unstable high strength austenitic stainless steels, which is expressed in a phenomenon called Delayed Cracking and in an increased springback behaviour [5-9]. The first aim of this project was to perform a quantitative evaluation of the above mentioned influencing parameters concerning the deep drawability of austenitic stainless steels. Therefore, various steel grades, including austenitic, partly austenitic and conventional ferritic deep drawing steels, had been examined, which differ in chemical composition, content of austenitic fraction, mechanical properties and topography. The second aim was to carry out formability benchmark tests and FEM-modelling of pilot components in order to achieve a more comprehensive description of press shop behaviour of the steel grades. The third aim was the development and production of an "ideal" austenitic stainless steel for deep drawing and stretch forming operations with an increment of the limiting drawing ratio from the current level of 2.0 up to ≥ 2.15. In this way the application potential of austenitic stainless steels should be enlarged, above all in the automotive industry.
Hannu Hanninen - One of the best experts on this subject based on the ideXlab platform.
-
Hydrogen-Induced Delayed Cracking in TRIP-Aided Lean-Alloyed Ferritic-Austenitic Stainless Steels
Materials (Basel Switzerland), 2017Co-Authors: Suvi Papula, Juho Talonen, Teemu Sarikka, Severi Anttila, Iikka Virkkunen, Hannu HanninenAbstract:Susceptibility of three lean-alloyed ferritic-austenitic stainless steels to hydrogen-induced Delayed Cracking was examined, concentrating on internal hydrogen contained in the materials after production operations. The aim was to study the role of strain-induced austenite to martensite transformation in the Delayed Cracking susceptibility. According to the conducted deep drawing tests and constant load tensile testing, the studied materials seem not to be particularly susceptible to Delayed Cracking. Delayed cracks were only occasionally initiated in two of the materials at high local stress levels. However, if a Delayed crack initiated in a highly stressed location, strain-induced martensite transformation decreased the crack arrest tendency of the austenite phase in a duplex microstructure. According to electron microscopy examination and electron backscattering diffraction analysis, the fracture mode was predominantly cleavage, and cracks propagated along the body-centered cubic (BCC) phases ferrite and α’-martensite. The BCC crystal structure enables fast diffusion of hydrogen to the crack tip area. No Delayed Cracking was observed in the stainless steel that had high austenite stability. Thus, it can be concluded that the presence of α’-martensite increases the hydrogen-induced Cracking susceptibility.
-
Delayed Cracking of low-nickel austenitic stainless steel studied with constant load tensile testing
Fatigue & Fracture of Engineering Materials & Structures, 2015Co-Authors: Suvi Papula, Juho Talonen, Hannu HanninenAbstract:Delayed Cracking in unstable low-Ni austenitic stainless steel 204Cu was studied by constant load tensile testing. The developed testing arrangement enabled a systematical examination on the effect of applied stress, strain-induced α′-martensite and internal hydrogen content on time to fracture. Volume fraction of strain-induced α′-martensite was shown to affect Cracking kinetics, except at a very high stress level. Hydrogen content had a marked effect on time to fracture, also at the highest applied stress level. When hydrogen content was reduced by annealing, Delayed Cracking kinetics and susceptibility were suppressed, and Cracking required a considerably higher stress level. The apparent critical hydrogen content, below which Delayed Cracking was not observed, was about 0.85 wppm. According to scanning electron microscope and electron backscattering diffraction examination, fracture mechanism in the constant load test specimens was mainly transgranular quasi-cleavage, and Cracking propagated along α′-martensite.
-
effect of internal hydrogen on Delayed Cracking of metastable low nickel austenitic stainless steels
Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science, 2014Co-Authors: Suvi Papula, Olga Todoshchenko, Juho Talonen, Hannu HanninenAbstract:Metastable austenitic stainless steels, especially manganese-alloyed low-nickel grades, may be susceptible to Delayed Cracking after forming processes. Even a few wppm of hydrogen present in austenitic stainless steels as an inevitable impurity is sufficient to cause Cracking if high enough fraction of strain-induced α′-martensite and high residual tensile stresses are present. The role of internal hydrogen content in Delayed Cracking of several metastable austenitic stainless steels having different alloying chemistries was investigated by means of Swift cup tests, both in as-supplied state and after annealing at 673 K (400 °C). Hydrogen content of the test materials in each state was analyzed with three different methods: inert gas fusion, thermal analysis, and thermal desorption spectroscopy. Internal hydrogen content in as-supplied state was higher in the studied manganese-alloyed low-nickel grades, which contributed to susceptibility of unstable grades to Delayed Cracking. Annealing of the stainless steels reduced their hydrogen content by 1 to 3 wppm and markedly lowered the risk of Delayed Cracking. Limiting drawing ratio was improved from 1.4 to 1.7 in grade 204Cu, from 1.7 to 2.0 in grade 201 and from 1.8 to 2.12 in grade 301. The threshold levels of α′-martensite and residual stress for Delayed Cracking at different hydrogen contents were defined for the test materials.
-
Characterization of Delayed Cracking in deep drawn swift cups of metastable austenitic stainless steels
Fatigue & Fracture of Engineering Materials & Structures, 2014Co-Authors: S. Ortega, Suvi Papula, Juho Talonen, Tapio Saukkonen, Hannu HanninenAbstract:Fracture behaviour of metastable austenitic stainless steels (Cr-Ni grade 301 and low-Ni high-Mn grades 201 and 204Cu) that suffer of Delayed Cracking after deep drawing was examined. The phenomenon of Delayed Cracking is known to be related to the coexistence of internal hydrogen, strain-induced α′-martensite and tensile residual stresses. The objective of this study was to maximize the information attainable from the common Swift cup test, which is used to evaluate the formability and Delayed Cracking susceptibility of sheet metals. Fractures in deep-drawn Swift cups were analysed macroscopically, by fracture surface study and electron backscatter diffraction analysis. Residual stresses in the cups were measured with X-ray diffraction and α′-martensite content using a Ferritescope. Estimation of fracture toughness of the materials was made using two different approaches: measuring the width of shear lips and relating it to the plastic zone size, and measuring the crack-tip opening angle CTOA. On the basis of the results, grade 301 presents the highest fracture toughness, and 204Cu the lowest. Toughness of the materials seems to correlate with their nickel content. The order between the studied materials is similar when considering the susceptibility to Delayed Cracking.
-
effect of residual stress and strain induced α martensite on Delayed Cracking of metastable austenitic stainless steels
Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science, 2014Co-Authors: Suvi Papula, Juho Talonen, Hannu HanninenAbstract:The role of residual stresses and strain-induced α′-martensite in Delayed Cracking of metastable austenitic stainless steels was studied by means of Swift cup tests, measurement of residual stresses by X-ray diffraction and ring slitting, and α′-martensite content determination. Low-Ni, high-Mn austenitic stainless steels, e.g., AISI 201, were compared with Fe-Cr-Ni austenitic stainless steels. The presence of α′-martensite seemed to be a necessary prerequisite for Delayed Cracking to occur in austenitic stainless steels with typical internal hydrogen concentrations (<5 ppm). Stable low-Ni austenitic stainless steel was not prone to Delayed Cracking. The low-Ni metastable grades showed more severe Cracking at lower degree of deformation and lower volume fraction of α′-martensite than that of the metastable 300-series grades. The limiting α′-martensite content, below which Delayed Cracking did not occur, decreased along with the nickel content of the material. The strain-induced martensitic transformation substantially increased the magnitude of residual stresses in deep-drawn cups. One explanation for high sensitivity of the low-Ni grades to Delayed Cracking after deep drawing is their higher residual stresses compared to that of the Fe-Cr-Ni grades. Alloying elements of the stainless steels, nickel, and carbon in particular, influence the sensitivity to Delayed Cracking through their effect on the properties of the α′-martensite.
Xiaofei Guo - One of the best experts on this subject based on the ideXlab platform.
-
Delayed Cracking behavior of a meta-stable austenitic stainless steel under bending condition
Materials Science and Engineering: A, 2019Co-Authors: Xiaofei Guo, Junhe Lian, Sebastian Münstermann, Wolfgang BleckAbstract:Abstract The Delayed Cracking behavior of a meta-stable austenitic stainless steel AISI 301 under bending condition has been investigated at different temperatures, hydrogen contents and external holding forces. The results reveal that the investigated material with an initial hydrogen content of 1 ppm has good bendability at the temperature range between −20 °C and room temperature, which is not susceptible to Delayed Cracking in atmospheric condition. When the material is pre-charged with 50 ppm hydrogen, the material still shows good bendability. However, it is susceptible to Delayed Cracking under an external holding force during interrupted bending test. By the measurement of martensitic transformation, the simulation of the stress/strain distributions in the bending specimens and the characterization of fracture surfaces, the effects of hydrogen, stress state and external holding force on Delayed Cracking behavior have been assessed.
-
stress oriented Delayed Cracking induced by dynamic martensitic transformation in meta stable austenitic stainless steels
Steel Research International, 2011Co-Authors: Xiaofei Guo, Jan Post, Manso Groen, Wolfgang BleckAbstract:Delayed Cracking in meta-stable austenitic stainless steels AISI 304 and AISI 301 has been investigated by deep drawing test in this study. Specimens from both steels were deformed at different drawing ratios, forming temperatures and hydrogen pre-charged conditions. The strain, martensitic fraction and residual stress distributions were characterised on the deep drawn specimens. Their influences on Delayed Cracking behaviours were quantitatively studied. We found that the incubation time to fracture and the fracture length depend chiefly on the amount of strain induced phase transformation and transformation induced residual stresses when the materials contain ∼1ppm hydrogen. When the materials were electrochemically charged with hydrogen up to the amount of 20ppm, the incubation time to fracture declined with increasing hydrogen contents following a power law relation. Besides, the fracture mode turned from a ductile nature to trans-granular and later on to inter-granular fracture feature with increasing hydrogen contents.
-
Stress Oriented Delayed Cracking Induced by Dynamic Martensitic Transformation in Meta‐Stable Austenitic Stainless Steels
steel research international, 2010Co-Authors: Xiaofei Guo, Jan Post, Manso Groen, Wolfgang BleckAbstract:Delayed Cracking in meta-stable austenitic stainless steels AISI 304 and AISI 301 has been investigated by deep drawing test in this study. Specimens from both steels were deformed at different drawing ratios, forming temperatures and hydrogen pre-charged conditions. The strain, martensitic fraction and residual stress distributions were characterised on the deep drawn specimens. Their influences on Delayed Cracking behaviours were quantitatively studied. We found that the incubation time to fracture and the fracture length depend chiefly on the amount of strain induced phase transformation and transformation induced residual stresses when the materials contain ∼1ppm hydrogen. When the materials were electrochemically charged with hydrogen up to the amount of 20ppm, the incubation time to fracture declined with increasing hydrogen contents following a power law relation. Besides, the fracture mode turned from a ductile nature to trans-granular and later on to inter-granular fracture feature with increasing hydrogen contents.
A. Bouchou - One of the best experts on this subject based on the ideXlab platform.
-
Hydrogen-induced Delayed Cracking in the AISI 301 unstable austenitic steel sheet
Materials & Design, 2010Co-Authors: A. Zinbi, A. BouchouAbstract:Abstract This work aims to study the hydrogen-induced Delayed Cracking related to the martensitic transformation in the AISI 301 unstable austenitic stainless steel. It happens because the metastable austenite is substantially transformed into α ′ -martensite due to the deformation occurring during the clamp-forming operation. To understand this phenomenon, morphological and chemical analyses have been made. The martensite fraction in the inside bend radius was measured by X-ray Diffraction (XRD) and the breaking patterns were observed using a Scanning Electron Microscope (SEM). The clamps breaking patterns observed after Delayed Cracking show a brittle intergranular fracture in the bend radius. Under laboratory conditions and after hydrogen-charged clamps, Delayed Cracking occurred. The main fractographic feature observed in cracked clamps is the intergranular Hydrogen Embrittlement (HE). This brittle behavior is intensified by the high heterogeneous stress state in the material and the high content of martensite.
-
Delayed Cracking in 301 austenitic steel after bending process: Martensitic transformation and hydrogen embrittlement analysis
Engineering Failure Analysis, 2010Co-Authors: A. Zinbi, A. BouchouAbstract:Abstract The aim of this work is to study the Delayed Cracking phenomenon of the unstable austenitic stainless steels (301 grade) deformed by bending operations. During the clamp-forming operation, austenite is transformed to α ′ -martensite. To understand this phenomenon, morphological analysis and hardness measurements were made. Scanning electron microscopy (SEM) was used to perform fracture surface analysis and X-ray diffraction (XRD) to measure the amount of the martensite . The breaking patterns of these clamps obtained after Delayed Cracking are predominantly intergranular. This type of failure is often associated with hydrogen embrittlement. This brittle behavior is accentuated by the presence of internal stresses in the material (cold rolling, forming by bending) and the high content of martensite.
Ken-ichiro Mori - One of the best experts on this subject based on the ideXlab platform.
-
Prevention of Delayed Cracking of punched 1.5 GPa ultra-high strength steel sheets by ironing with punched slug
The International Journal of Advanced Manufacturing Technology, 2020Co-Authors: Ken-ichiro Mori, Yohei Abe, Yusuke MuraiAbstract:Hydrogen-induced Delayed Cracking of punched 1.5 GPa ultra-high strength steel sheets was prevented by ironing with a slug ejected from punching, because the risk of Delayed Cracking for sheared 1.5 GPa sheets is very high due to high tensile residual stress and large plastic deformation. To prevent the occurrence of Delayed Cracking, the sheet was punched, and then, the punched hole was ironed by passing the punched slug. Although the residual stress around the punched edge of the 1.5 GPa sheet was tensile, the stress was turned to compressive stress by slug ironing. In addition, the fracture surface of the sheared edge was changed to a smooth ironed surface. A cathode hydrogen charging test of the punched edge for Delayed Cracking was performed. Although Delayed cracks were caused at the punched hole by hydrogen charging, no cracks occurred at the ironed hole for charging. It was found that slug ironing of the punched hole is effective in preventing Delayed Cracking.
-
Delayed Cracking in hot stamping with hot trimming for ultra-high strength steel components
The International Journal of Advanced Manufacturing Technology, 2019Co-Authors: Yuki Nakagawa, Ken-ichiro Mori, Tomoyoshi Maeno, Ryo UmemiyaAbstract:Hydrogen-induced Delayed Cracking in hot stamping with hot trimming for ultra-high strength steel components at various trimming temperatures was investigated. The trimming temperature of a heated quenchable sheet was adjusted by rapid cooling with the upper punch and die, and then, the sheet was trimmed and die-quenched. A cathode hydrogen charging test was performed to examine the occurrence of Delayed Cracking at trimmed edges, and then, tensile strength and total elongation of the hydrogen-charged specimen were measured from the tensile test. Below, a martensite transformation start temperature of 420 °C, the fracture surface and the tensile residual stress became large, and Delayed Cracking was caused on the fracture surfaces of the sheared edges. Although no Delayed Cracking of the hydrogen-charged specimen occurred above 420 °C, the tensile strength and total elongation were reduced by hydrogen embrittlement. The critical temperature of Delayed Cracking for a thin sheet having 1.0 mm in thickness rose to 600 °C.
-
Delayed fracture in cold blanking of ultra-high strength steel sheets
CIRP Annals, 2019Co-Authors: Ken-ichiro Mori, Yohei Abe, Kyohei SedoguchiAbstract:Abstract Hydrogen-induced Delayed fracture at cold-blanked edges of 1–1.5 GPa ultra-high strength steel sheets was investigated. The blanked edges undergo large shear deformation and tensile residual stress, and thus the risk of Delayed fracture is high, especially for the 1.5 GPa sheet. The effects of residual stress, surface quality and hardness of the sheared edge on the occurrence of Delayed Cracking were examined. Delayed Cracking was caused by press blanking, whereas no Cracking occurred for laser blanking because of compressive residual stress. For the 1.5 GPa sheet, Delayed Cracking was prevented by heating above 250 °C and a stain above 0.005.
-
shearing of ultra high strength steel sheets with step punch
Procedia Manufacturing, 2018Co-Authors: Ryuji Yonekawa, Kyouhei Sedoguchi, Ken-ichiro MoriAbstract:Abstract The punch with a step was applied to improve the punch life in punching of ultra-high strength steel sheets. The contact pressure in punching with the step was reduced due to the early separation of the sheet under tension. Punching with the step punch was carried out for 7000 times in stroke, whereas chipping in the punch occurred at 3000 times in punching without the step. Then, punching with the step punch was applied to the quenched steel sheet to prevent the occurrence of the Delayed Cracking of the sheared edge. The Delayed Cracking occurred, although the residual stress in the sheared edge decreased with increasing the step height. Furthermore, shearing with the step punch was applied to improve the stretch-flangeability of the ultra-high strength steel and high strength steel sheets.