Research on Forming Temperature of Metastable Austenitic Stainless Steel Head Based on Strain-Induced Martensitic Transformation

2019 ◽  
Vol 141 (5) ◽  
Author(s):  
Jinyang Zheng ◽  
Qunjie Lu ◽  
Yingzhe Wu ◽  
Xiao Zhang ◽  
Huiming Ding ◽  
...  
Keyword(s):  
Stainless Steel ◽  
Chemical Composition ◽  
Martensitic Transformation ◽  
Austenitic Stainless Steel ◽  
Low Cost ◽  
Tensile Tests ◽  
Delta Ferrite ◽  
Cold Forming ◽  
Metastable Austenitic Stainless Steel ◽  
Forming Temperature

The formation of strain-induced martensite (SIM) is found in metastable austenitic stainless steel (m-ASS) during cold forming, and the presence of SIM may cause reductions in toughness, ductility, and corrosion resistance of m-ASS. These mechanical properties can be restored and improved by proper heat treatment after forming, however, which obviously raises the manufacturing costs. One low-cost way to reduce the SIM amount during m-ASS forming is to maintain the forming temperature at an appropriate level. This paper intends to investigate an approach to determine the optimum forming temperature at which the strain-induced martensitic transformation (SIM-Tr) of m-ASS head during forming can be restrained within a limited intensity. First, static tensile tests were conducted on S30408 conventional cylindrical tensile specimens under different temperatures varying from 20 °C to 180 °C, and then the effect of deformation temperature on SIM was evaluated. Second, according to the stacking fault energy (SFE) calculation method, m-ASS's chemical composition was taken into further consideration to investigate its effect on SIM. Finally, a formula was established based on SIM and chemical composition for optimization of forming temperature. In addition, the results obtained by this formula were compared with those of the experiment by S30408 ASS head stamping tests, and the satisfactory matching is found for the proposed forming temperatures and predicted ferrite number (FN) values (readings of the Ferritescope measurement, as a representation of the amount of martensite in this study). Furthermore, an enhancement in the cryogenic impact properties and a fewer quantity of delta-ferrite in the microstructure of m-ASS heads are observed when warm stamping is performed as compared with the cold stamped head.

Research on Forming Temperature of Metastable Austenitic Stainless Steel Head Based on Strain-Induced Martensitic Transformation

2016 ◽  
Author(s):  
Qunjie Lu ◽  
Jinyang Zheng ◽  
Xiao Zhang
Keyword(s):  
Stainless Steel ◽  
Chemical Composition ◽  
Martensitic Transformation ◽  
Austenitic Stainless Steel ◽  
Tensile Tests ◽  
Manufacturing Cost ◽  
Delta Ferrite ◽  
Cold Forming ◽  
Metastable Austenitic Stainless Steel ◽  
Forming Temperature

Formation of strain-induced martensite (SIM) is found in metastable austenitic stainless steel (m-ASS) during cold forming. The presence of SIM may cause reductions in toughness, ductility and corrosion resistance of the m-ASS. Although these mechanical properties can be restored and improved after cold forming by using proper heat treatment, the manufacturing cost rises greatly. However, the cost of warm forming is cheaper and the SIM reduces with forming temperature increasing. Thus, the main purpose of this research is to investigate a suitable forming temperature, at which the strain-induced martensitic transformation (SIM-Tr) of m-ASS head in forming will reduce. Primarily, a series of static tensile tests were conducted based on several batches of S30408 plates. The tests were carried out at different temperatures varying from 20 °C to 180 °C, with the effect of deformation temperature on SIM evaluated. Moreover, according to the stacking fault energy (SFE) calculation method, the m-ASS’s chemical composition was taken into further consideration to investigate its effect on SIM. Eventually, a formula was established that related to SIM and chemical composition for optimizing the forming temperature. The results obtained by this formula were compared to the experimental results of 304 ASS head stamping tests, and satisfactory matching is found for the proposed forming temperatures and the predicted FN values (readings of the Ferritescope measurement, as a representation of the amount of martensite in this study). Additionally, an enhancement of the cryogenic impact properties and a fewer quantity of delta-ferrite in the microstructure are observed when stamping temperature is higher than 90 °C.

Development of Formability, Microstructure and Martensite Reversion during Intermediate Annealing of Metastable Austenitic Stainless Steel

2014 ◽  
Vol 611-612 ◽  
pp. 49-55
Author(s):  
Philipp Schmid ◽  
Mathias Liewald
Keyword(s):  
Stainless Steel ◽  
Austenitic Stainless Steel ◽  
Tensile Tests ◽  
Local Heat ◽  
Uniaxial Tensile ◽  
Intermediate Annealing ◽  
Austenitic Phase ◽  
Deep Draw ◽  
Multi Stage ◽  
Metastable Austenitic Stainless Steel

Intermediate annealing is a widely used process to recover formability in multi-stage deep drawing of austenitic stainless steel sheets. A special ability of metastable austenitic stainless steel is the so called strain-induced martensite formation, which causes the TRIP-effect (TRansformation Induced Plasticity). Major issues of intermediate annealing in serial production processes are long annealing times and high costs for annealing equipment and consumed heating energy. One suggestion for optimization of this process made in this paper is to anneal austenitic material only in regions of the part where it is required and to use suitable annealing parameters. This annealing parameters need to be optimized to requirements of follow-up forming processes. Therefor, basic intermediate annealing experiments were accomplished for austenitic grade EN 1.4301 within temperature range of 100-1100°C. Measurements of mechanical properties by uniaxial tensile tests, martensite contents measured by Feritscope and micrographs are showing the development of martensite reversion as well as reconstitution of austenitic phase. Especially 400°C, 600°C and 1000°C were identified as most interesting annealing temperature levels due to formation of carbides and recrystallization. This knowledge can be used as base for further local heat treatment concepts and may enhance, simplify and save costs of intermediate annealing process of deep draw components made of stainless steel.

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