Details
| Original language | English |
|---|---|
| Title of host publication | 6th International Conference Hot Steel Metal Forming of High-Performance Steel, CHS2 2017- Proceedings |
| Editors | Mats Oldenburg, Braham Prakash, Kurt Steinhoff |
| Pages | 433-440 |
| Number of pages | 8 |
| ISBN (electronic) | 9781935117667 |
| Publication status | Published - 2017 |
| Event | 6th International Conference on Hot Steel Metal Forming of High-Performance Steel, CHS2 2017 - Atlanta, United States Duration: 4 Jun 2017 → 7 Jun 2017 |
Publication series
| Name | 6th International Conference Hot Steel Metal Forming of High-Performance Steel, CHS2 2017- Proceedings |
|---|
Abstract
Press-hardening of intercritically annealed steel sheets is a promising approach to tailor material properties. Both strength and ductility can be adjusted by varying the annealing parameters and thus controlling the ratio of transformed austenite to untransformed ferrite. During hot deformation and subsequent quenching in the dies, the austenite fraction present is transformed into martensite. As a result, the martensite is located in between the ferritic grains which had not been austenitized during the intercritical annealing. Experiments with the heat treatable steel 22MnB5 show that two-phase microstructures with martensite contents of 60 % to 100 % can been achieved by using annealing temperatures of 750 °C to 850 °C. In addition, more complex heat treatments like the quenching and partitioning (Q&P) process can be integrated in the processing step of press-hardening. However, this requires that the formed parts can be removed from the die prior to reaching the martensite finish temperature or that the die is heated up to the temperature range between the martensite start and finish temperature. The Q&P process aims at overaging of the martensitic microstructure, whereby the martensite formed between the martensite start temperature and the holding temperature is tempered and a small amount of retained austenite is stabilized at low temperatures by carbon diffusing from the martensite to the austenite. Due to the retained austenite, the resulting microstructure features a TRIP-effect (transformation induced plasticity) and thus increased ductility and energy absorption capacity. In combination with an intercritical heating, the strength can be controlled by adjusting the martensite fraction. Here, even a further stabilization of the retained austenite in the multiphase microstructure can be facilitated. This is due to the partial austenitization, which results in a higher fraction of austenite stabilizing alloying elements such as carbon and manganese in the austenite, since their solubility in ferrite is quite low. By isothermal overaging in a salt bath, a tensile strength of 1,045 MPa and a total elongation of 10.8 % were achieved for an initially intercritically annealed microstructure featuring 70 % austenite and 30 % ferrite. XRD-measurements revealed 8 % of retained austenite. Due to the cold-rolled initial state of the steel sheets, the mechanical properties were to some extend anisotropic. To identify microstructure compositions with high energy absorption capacities, various microstructural conditions (quenched, 1 -step and 2-step overaging) were characterized by mechanical tests with a plane strain state and in uniaxial tension.
Keywords
- 22mnb5, Adapted microstructure, Intercritical annealing, Quenching-and-partitioning
ASJC Scopus subject areas
- Engineering(all)
- Mechanical Engineering
- Engineering(all)
- Mechanics of Materials
- Materials Science(all)
- Metals and Alloys
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6th International Conference Hot Steel Metal Forming of High-Performance Steel, CHS2 2017- Proceedings. ed. / Mats Oldenburg; Braham Prakash; Kurt Steinhoff. 2017. p. 433-440 (6th International Conference Hot Steel Metal Forming of High-Performance Steel, CHS2 2017- Proceedings).
Research output: Chapter in book/report/conference proceeding › Conference contribution › Research › peer review
}
TY - GEN
T1 - Intercritical annealing - new heat treatment strategies for tailoring the stress-strain behavior of 22mnb5
AU - Wolf, Lars Oliver
AU - Rodman, Dmytro
AU - Nürnberger, Florian
AU - Cordebois, Jean Pierre
AU - Maier, Hans Jürgen
N1 - Publisher Copyright: © 2017 CURRAN-CONFERENCE. All rights reserved.
PY - 2017
Y1 - 2017
N2 - Press-hardening of intercritically annealed steel sheets is a promising approach to tailor material properties. Both strength and ductility can be adjusted by varying the annealing parameters and thus controlling the ratio of transformed austenite to untransformed ferrite. During hot deformation and subsequent quenching in the dies, the austenite fraction present is transformed into martensite. As a result, the martensite is located in between the ferritic grains which had not been austenitized during the intercritical annealing. Experiments with the heat treatable steel 22MnB5 show that two-phase microstructures with martensite contents of 60 % to 100 % can been achieved by using annealing temperatures of 750 °C to 850 °C. In addition, more complex heat treatments like the quenching and partitioning (Q&P) process can be integrated in the processing step of press-hardening. However, this requires that the formed parts can be removed from the die prior to reaching the martensite finish temperature or that the die is heated up to the temperature range between the martensite start and finish temperature. The Q&P process aims at overaging of the martensitic microstructure, whereby the martensite formed between the martensite start temperature and the holding temperature is tempered and a small amount of retained austenite is stabilized at low temperatures by carbon diffusing from the martensite to the austenite. Due to the retained austenite, the resulting microstructure features a TRIP-effect (transformation induced plasticity) and thus increased ductility and energy absorption capacity. In combination with an intercritical heating, the strength can be controlled by adjusting the martensite fraction. Here, even a further stabilization of the retained austenite in the multiphase microstructure can be facilitated. This is due to the partial austenitization, which results in a higher fraction of austenite stabilizing alloying elements such as carbon and manganese in the austenite, since their solubility in ferrite is quite low. By isothermal overaging in a salt bath, a tensile strength of 1,045 MPa and a total elongation of 10.8 % were achieved for an initially intercritically annealed microstructure featuring 70 % austenite and 30 % ferrite. XRD-measurements revealed 8 % of retained austenite. Due to the cold-rolled initial state of the steel sheets, the mechanical properties were to some extend anisotropic. To identify microstructure compositions with high energy absorption capacities, various microstructural conditions (quenched, 1 -step and 2-step overaging) were characterized by mechanical tests with a plane strain state and in uniaxial tension.
AB - Press-hardening of intercritically annealed steel sheets is a promising approach to tailor material properties. Both strength and ductility can be adjusted by varying the annealing parameters and thus controlling the ratio of transformed austenite to untransformed ferrite. During hot deformation and subsequent quenching in the dies, the austenite fraction present is transformed into martensite. As a result, the martensite is located in between the ferritic grains which had not been austenitized during the intercritical annealing. Experiments with the heat treatable steel 22MnB5 show that two-phase microstructures with martensite contents of 60 % to 100 % can been achieved by using annealing temperatures of 750 °C to 850 °C. In addition, more complex heat treatments like the quenching and partitioning (Q&P) process can be integrated in the processing step of press-hardening. However, this requires that the formed parts can be removed from the die prior to reaching the martensite finish temperature or that the die is heated up to the temperature range between the martensite start and finish temperature. The Q&P process aims at overaging of the martensitic microstructure, whereby the martensite formed between the martensite start temperature and the holding temperature is tempered and a small amount of retained austenite is stabilized at low temperatures by carbon diffusing from the martensite to the austenite. Due to the retained austenite, the resulting microstructure features a TRIP-effect (transformation induced plasticity) and thus increased ductility and energy absorption capacity. In combination with an intercritical heating, the strength can be controlled by adjusting the martensite fraction. Here, even a further stabilization of the retained austenite in the multiphase microstructure can be facilitated. This is due to the partial austenitization, which results in a higher fraction of austenite stabilizing alloying elements such as carbon and manganese in the austenite, since their solubility in ferrite is quite low. By isothermal overaging in a salt bath, a tensile strength of 1,045 MPa and a total elongation of 10.8 % were achieved for an initially intercritically annealed microstructure featuring 70 % austenite and 30 % ferrite. XRD-measurements revealed 8 % of retained austenite. Due to the cold-rolled initial state of the steel sheets, the mechanical properties were to some extend anisotropic. To identify microstructure compositions with high energy absorption capacities, various microstructural conditions (quenched, 1 -step and 2-step overaging) were characterized by mechanical tests with a plane strain state and in uniaxial tension.
KW - 22mnb5
KW - Adapted microstructure
KW - Intercritical annealing
KW - Quenching-and-partitioning
UR - http://www.scopus.com/inward/record.url?scp=85054171373&partnerID=8YFLogxK
M3 - Conference contribution
AN - SCOPUS:85054171373
T3 - 6th International Conference Hot Steel Metal Forming of High-Performance Steel, CHS2 2017- Proceedings
SP - 433
EP - 440
BT - 6th International Conference Hot Steel Metal Forming of High-Performance Steel, CHS2 2017- Proceedings
A2 - Oldenburg, Mats
A2 - Prakash, Braham
A2 - Steinhoff, Kurt
T2 - 6th International Conference on Hot Steel Metal Forming of High-Performance Steel, CHS2 2017
Y2 - 4 June 2017 through 7 June 2017
ER -