scholarly journals Effect of retained austenite transformation on the fatigue behaviour of aluminum containing TRIP steels

2017 ◽  
Author(s):  
Πέτρος Χριστοδούλου
Keyword(s):  
Retained Austenite ◽  
Fatigue Behaviour ◽  
Austenite Transformation ◽  
Trip Steels

Οι χάλυβες με TRIP προσφέρουν σημαντικά πλεονεκτήματα στην σύγχρονη αυτοκινητοβιομηχανία, όπως η υψηλή αντοχή και η διαμορφωσιμότητα λόγω του σταδιακού μηχανισμού σκλήρυνσης που προκαλείται από το φαινόμενο του μετασχηματισμού του παραμένοντα σε μαρτενσίτη. Η συμπεριφορά τους σε κόπωση έχει επίσης βρεθεί ότι επηρεάζεται από την επίδραση του μετασχηματισμού TRIP, ειδικά υπό συνθήκες ολιγοκυκλικής κόπωσης, οι οποίες συνοδεύονται από κυκλικά πλαστικά φορτία, τα οποία βοηθούν τον μετασχηματισμό του παραμένοντα ωστενίτη. Παρά τις υπάρχουσες ερευνητικές προσπάθειες, εξακολουθούν να υπάρχουν ανεπαρκείς πειραματικές ενδείξεις για την επίδραση του μετασχηματισμού στη μηχανική συμπεριφορά, συγκεκριμένα υπό ελαστικά και πλαστικά κυκλικά φορτία. Στην παρούσα εργασία διεξάγεται εμπεριστατωμένη πειραματική έρευνα για να διερευνηθεί η επίδραση του φαινομένου TRIP στην μονοτονική και κυκλική συμπεριφορά χαλύβων TRIP που περιέχουν αλουμίνιο. Η συμπεριφορά κόπωσης των υλικών εξετάζεται στις περιοχές ολιγοκυκλικής και πολυκυκλικής κόπωσης ενώ δίδεται και ιδιαίτερη προσοχή στο πρόβλημα της έναρξης της ρωγμής κόπωσης. Τα πειραματικά αποτελέσματα υποστηρίζονται από μετρήσεις του μετασχηματισμού του παραμένοντα ωστενίτη χρησιμοποιώντας την τεχνική της μαγνήτισης κορεσμού. Ο ρόλος της μικροδομής των χαλύβων TRIP λαμβάνεται υπόψη κατά την έρευνα, ο οποίος περιλαμβάνει την εξέταση χαλύβων TRIP με διαφορές στις συνθήκες θερμικής κατεργασίας ή/και τη χημική σύσταση.Τα πειραματικά ευρήματα υποδεικνύουν ότι η συμπεριφορά κόπωσης σχετίζεται με την ποσότητα του μετασχηματισμού κατά την κυκλική φόρτιση και τα αποτελέσματα είναι διαφορετικά κάτω από ελαστικές ή πλαστικές κυκλικές τάσεις. Όσον αφορά τη μικροδομή, η επίδραση του μετασχηματισμού στη μηχανική συμπεριφορά σχετίζεται κυρίως με το μέγεθος των σωματιδίων του παραμένοντα ωστενίτη και του φερρίτη.Στο δεύτερο μέρος της εργασίας αναπτύσσεται μια αναλυτική μεθοδολογία για την εκτίμηση της διάρκειας ζωής για την εκκίνηση ρωγμής στη ρίζα μιας εγκοπής υπό κυκλική φόρτιση. Στην ανάλυση, το τοπικό πεδίο τάσεων- παραμορφώσεων στην αιχμή της εγκοπής υπολογίζεται αριθμητικά με τη χρήση της μεθόδου των πεπερασμένων στοιχείων. Συνεπώς, τα αριθμητικά αποτελέσματα χρησιμοποιούνται ως είσοδο σε ήδη υπάρχοντα εδραιωμένα μοντέλα κόπωσης, για να εκτιμηθούν οι κύκλοι κόπωσης που απαιτούνται για την δημιουργία μιας μικρής ρωγμής στην ρίζα της εγκοπής μήκους 250 μm. Τα αναλυτικά αποτελέσματα συγκρίνονται με τα πειραματικά με σκοπό την αξιολόγηση της αξιοπιστίας της μεθόδου να εκτιμά την έναρξη της ρωγμής κόπωσης στους χάλυβες TRIP και τα ευρήματα είναι ικανοποιητικά.

Effect of Different Coiling Temperature on Mechanical Properties in Hot Rolled TRIP Steel

2011 ◽  
Vol 239-242 ◽  
pp. 1092-1095
Author(s):  
Xu Tao Gao ◽  
Ai Min Zhao ◽  
Zheng Zhi Zhao ◽  
Ming Ming Zhang ◽  
Di Tang
Keyword(s):  
Mechanical Properties ◽  
Retained Austenite ◽  
X Ray Diffraction ◽  
Coiling Temperature ◽  
Experimental Steel ◽  
Transformation Induced Plasticity ◽  
X Ray ◽  
Trip Steels ◽  
Hot Rolled ◽  
Scanning Electron

By means of optical microscopy(OM), scanning electron microscopy(SEM),X-ray diffraction(XRD),And tensile test, Mechanical Properties of hot rolled transformation -induced plasticity (TRIP) steels which were prepared through three different coiling temperature was investigated. Result reveals that the formability index of the experimental steel descends when the coiling temperature becomes low. Different coiling temperature has greater impact on retained austenite. Amount and carbon content of retained austenite in the experimental steel get less with lower coiling temperature.

Influence of the Processing Variables on the Microstructure Evolution of a Bainitic Carbide-Free Steel

2016 ◽  
Vol 879 ◽  
pp. 867-872 ◽  
Author(s):  
M.C. Taboada ◽  
I. Gutiérrez ◽  
D. Jorge-Badiola ◽  
S.M.C. van Bohemen ◽  
F. Hisker ◽  
...  
Keyword(s):  
Retained Austenite ◽  
High Strength Steels ◽  
High Strength ◽  
High Volume ◽  
X Ray Diffraction ◽  
Tempered Martensite ◽  
Trip Steels ◽  
Volume Fractions ◽  
Advanced High Strength Steels ◽  
Processing Variables

New trends focused on achieving higher performance steels has led to a so-called 3rd Generation Advanced High Strength Steels (AHSS), in which the typical polygonal ferrite found in TRIP steels as a matrix phase is replaced by harder phases as Carbide-Free Bainite (CFB) and/or (tempered) martensite. Besides, large volume fractions of retained austenite (R.A.) with adequate stability are aimed for to improve the formability of the steels. Si containing steels are regarded as the most suitable to retard cementite formation and consequently reach high volume fractions of RA. In this work, CFB annealing schedules were applied to dilatometer samples of Fe-0.22C-2.0Mn-1.3Si. The overaging temperature TB was varied between 390 oC and 480 oC, and other processing variables investigated were the austenitizing temperature Taus, and the overaging holding time tB. The annealed samples analyzed with LOM, FEG-SEM, EBSD and X-ray diffraction techniques show that markedly different complex microstructures made up of bainite, ferrite, MA phase and retained austenite (R.A) are accomplished depending on the specific thermal cycle. These results are described in detail and discussed in relation to the dilatometry measurements.

Retained Austenite Transformation-Induced Residual Stress Change in Carburized 16MnCr5 Steel

2022 ◽  
Vol 50 (3) ◽  
pp. 20210457
Author(s):  
Wanhua Liang ◽  
James Pineault ◽  
F. Albrecht Conle ◽  
Timothy H. Topper
Keyword(s):  
Residual Stress ◽  
Retained Austenite ◽  
Stress Change ◽  
Austenite Transformation

Influence of Chromium and Niobium on the Press-Hardening Process of Multiphase Low-Alloy TRIP Steels

2021 ◽  
Vol 1016 ◽  
pp. 636-641
Author(s):  
Hana Jirková ◽  
Jiří Vrtáček ◽  
Michal Peković ◽  
Tomáš Janda ◽  
Ludmila Kučerová
Keyword(s):  
Retained Austenite ◽  
High Energy ◽  
Experimental Program ◽  
Chemical Compositions ◽  
Body Parts ◽  
Press Hardening ◽  
Trip Steels ◽  
Forming Technology ◽  
Suitable Heat Treatment ◽  
High Energy Absorption

Press-hardening is an intensively developing forming technology which is mainly used for the production of car body parts. Because it is a hot forming technology, small forming forces can be utilized and, due to the lower spring-back effect, more accurate products are achieved. In car bodies, materials with high energy absorption and a sufficient hardening coefficient are mainly used in impacted parts. One of these materials is TRIP multiphase steels with different chemical composition. In these steels, it is possible to achieve an ultimate strength up to 1000 MPa with the ductility of 20-30%. In order to achieve the desired properties, it is necessary to select a suitable heat treatment that allows to achieve a multiphase structure. Phase transformations and mechanical properties are influenced by the use of suitable alloying elements. Three low-alloy, multiphase TRIP steels with different chemical compositions with a carbon content of 0.2% were chosen for the experimental program. The first steel was alloyed only with manganese and silicon, in the second niobium was added, and in the third the influence of chromium on increase of hardenability and strength was investigated. Press-hardening was performed in a heated forming tool. To describe the effect of the cooling rate, the forming was carried out in a tool at room temperature and after preheating to 425°C. The influence of holding time in the tool at 425°C to support the formation of bainite and retained austenite stabilization was also investigated. Mixed ferritic-bainitic-martensitic structures with some retained austenite content were obtained.

scholarly journals Quantitative Description of External Force Induced Phase Transformation in Silicon–Manganese (Si–Mn) Transformation Induced Plasticity (TRIP) Steels

Materials ◽  
2019 ◽  
Vol 12 (22) ◽  
pp. 3781
Author(s):  
Zhongping He ◽  
Huachu Liu ◽  
Zhenyu Zhu ◽  
Weisen Zheng ◽  
Yanlin He ◽  
...  
Keyword(s):  
Phase Transformation ◽  
Carbon Steel ◽  
Trip Steel ◽  
Retained Austenite ◽  
Low Carbon Steel ◽  
High Strength ◽  
High Plasticity ◽  
Low Carbon ◽  
Transformation Induced Plasticity ◽  
Trip Steels

Transformation Induced Plasticity (TRIP) steels with silicon–manganese (Si–Mn) as the main element have attracted a lot of attention and great interest from steel companies due to their low price, high strength, and high plasticity. Retained austenite is of primary importance as the source of high strength and high plasticity in Si–Mn TRIP steels. In this work, the cold rolled sheets of Si–Mn low carbon steel were treated with TRIP and Dual Phase (DP) treatment respectively. Then, the microstructure and composition of the Si–Mn low carbon steel were observed and tested. The static tensile test of TRIP steel and DP steel was carried out by a CMT5305 electronic universal testing machine. The self-built true stress–strain curve model of TRIP steel was verified. The simulation results were in good agreement with the experimental results. In addition, the phase transformation energy of retained austenite and the work borne by austenite in the sample during static stretching were calculated. The work done by austenite was 14.5 J, which was negligible compared with the total work of 217.8 J. The phase transformation energy absorption of retained austenite in the sample was 9.12 J. The role of retained austenite in TRIP steel is the absorption of excess energy at the key place where the fracture will occur, thereby increasing the elongation, so that the ferrite and bainite in the TRIP steel can absorb energy for a longer time and withstand more energy.

scholarly journals Effect of Retained Austenite and Non-Metallic Inclusions on the Mechanical Properties of Resistance Spot Welding Nuggets of Low-Alloy TRIP Steels

Metals ◽  
2019 ◽  
Vol 9 (10) ◽  
pp. 1064 ◽  
Author(s):  
Víctor H. Vargas Cortés ◽  
Gerardo Altamirano Guerrero ◽  
Ignacio Mejía Granados ◽  
Víctor H. Baltazar Hernández ◽  
Cuauhtémoc Maldonado Zepeda
Keyword(s):  
Mechanical Properties ◽  
Tensile Test ◽  
Retained Austenite ◽  
High Strength ◽  
Microstructural Characterization ◽  
Spot Welds ◽  
Trip Steels ◽  
Resistance Spot ◽  
Lap Shear ◽  
Metallic Inclusions

The combination of high strength and formability of transformation induced plasticity (TRIP) steels is interesting for the automotive industry. However, the poor weldability limits its industrial application. This paper shows the results of six low-alloy TRIP steels with different chemical composition which were studied in order to correlate retained austenite (RA) and non-metallic inclusions (NMI) with their resistance spot welded zones to their joints’ final mechanical properties. RA volume fractions were quantified by X-ray microdiffraction (µSXRD) while the magnetic saturation technique was used to quantify NMI contents. Microstructural characterization and NMI of the base metals and spot welds were assessed using scanning electron microscopy (SEM). Weld nuggets macrostructures were identified using optical microscopy (OM). The lap-shear tensile test was used to determine the final mechanical properties of the welded joints. It was found that NMI content in the fusion zone (FZ) was higher than those in the base metal and heat affected zone (HAZ). Whereas, traces of RA were found in the HAZ of highly alloyed TRIP steels. Lap-shear tensile test results showed that mechanical properties of spot welds were affected by NMI contents, but in a major way by the decomposition of RA in the FZ and HAZ.

Characteristics of retained austenite in TRIP steels with bainitic ferrite matrix

2011 ◽  
Vol 26 (6) ◽  
pp. 1148-1151 ◽  
Author(s):  
Mingya Zhang ◽  
Fuxian Zhu ◽  
Zhengtao Duan ◽  
Shicheng Ma
Keyword(s):  
Retained Austenite ◽  
Bainitic Ferrite ◽  
Ferrite Matrix ◽  
Trip Steels
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