Influence of Multi-Step Austempering Temperature on Tensile Performance of Unalloyed Ductile Iron

2019 ◽  
Vol 803 ◽  
pp. 3-7
Author(s):  
Wei Ci Zhuang ◽  
Ying Ming Jiang ◽  
Wen Tao Zhou ◽  
Zhong Yang Liang ◽  
Derek O. Northwood ◽  
...  
Keyword(s):  
Ductile Iron ◽  
Isothermal Holding ◽  
Bainitic Ferrite ◽  
High Strength ◽  
Rapid Quenching ◽  
Air Cooling ◽  
Strengthening Effect ◽  
Multiphase Structure ◽  
Tensile Performance ◽  
Austempering Temperature

Austempered ductile iron (ADI) has been widely used in various industries due to its excellent combination of high strength, ductility and good wear resistance. The tensile behavior of an unalloyed commercial ADI with a multiphase structure designed by a novel multi-step austempering treatment is investigated. The developed austempering process consists of austenitizing at 890°C for 20min, then initial rapid quenching to 180°C, and isothermal holding at 190, 220, 250°Cfor 120min, and finally air cooling to room temperature. The optimum mechanical properties with an ultimate tensile strength of 1350MPa, a yield strength of 1090MPa, as well as an elongation of 3.5% is achieved at 220°C. This is attributed to a synergistic strengthening effect of multiphase structure including a prior martensite with fine needle bainitic ferrite and film retained austenite.

scholarly journals Effect of Quenching and Partitioning Temperatures in the Q-P Process on the Properties of AHSS with Various Amounts of Manganese and Silicon

2012 ◽  
Vol 706-709 ◽  
pp. 2734-2739 ◽  
Author(s):  
Hana Jirková ◽  
Ludmila Kučerová ◽  
Bohuslav Mašek
Keyword(s):  
Tensile Strength ◽  
Retained Austenite ◽  
Isothermal Holding ◽  
Bainitic Ferrite ◽  
High Strength Steels ◽  
High Strength ◽  
Experimental Program ◽  
Quenching Temperature ◽  
Quenching And Partitioning ◽  
Advanced High Strength Steels

The use of the combined influence of retained austenite and bainitic ferrite to improve strength and ductility has been known for many years from the treatment of multiphase steels. Recently, the very fine films of retained austenite along the martensitic laths have also become the centre of attention. This treatment is called the Q-P process (quenching and partitioning). In this experimental program the quenching temperature and the isothermal holding temperature for diffusion carbon distribution for three advanced high strength steels with carbon content of 0.43 % was examined. The alloying strategies have a different content of manganese and silicon, which leads to various martensite start and finish temperatures. The model treatment was carried out using a thermomechanical simulator. Tested regimes resulted in a tensile strength of over 2000MPa with a ductility of above 14 %. The increase of the partitioning temperature influenced the intensity of martensite tempering and caused the decrease of tensile strength by 400MPa down to 1600MPa and at the same time more than 10 % growth of ductility occurred, increasing it to more than 20%.

High Performance Unalloyed Ductile Cast Iron with Multiphase Structure

2019 ◽  
Vol 295 ◽  
pp. 43-48
Author(s):  
Wen Tao Zhou ◽  
Chen Yang ◽  
Xi Xi Cui ◽  
Zhong Yang Liang ◽  
Xuan Wang ◽  
...  
Keyword(s):  
Cast Iron ◽  
Retained Austenite ◽  
High Performance ◽  
Bainitic Ferrite ◽  
Rapid Quenching ◽  
Ductile Cast Iron ◽  
Fine Needle ◽  
Multiphase Structure ◽  
Matrix Microstructure ◽  
The Matrix

An unalloyed ductile cast iron with a multiphase structure is designed by a novel austempering process. The designed austempering treatment consists of initial rapid quenching to 180°C after austenizing at 890°C for 20min, and finally austempering at 220°C for 240min. A multiphase structure comprising lenticular/needle-like prior martensite, fine needle bainitic ferrite and film retained austenite is obtained. The excellent mechanical properties, with a tensile strength of 1530MPa and an elongation of 3.1% can be achieved by controlling the matrix microstructure of 12% prior martensite, 15% retained austenite with 1.64% carbon content, and 73% bainitic ferrite. This is mainly attributed to prior marteniste which can promote refinement of multiphase colonies.

Accelerated Nano Super Bainite in Ductile Iron

MRS Advances ◽  
2018 ◽  
Vol 3 (45-46) ◽  
pp. 2789-2794
Author(s):  
Eric Jiahan Zhao ◽  
Cheng Liu ◽  
Derek O. Northwood
Keyword(s):  
Ductile Iron ◽  
Retained Austenite ◽  
Bainitic Ferrite ◽  
Isothermal Treatment ◽  
Strengthening Effect ◽  
Matrix Microstructure ◽  
Upper Bainite ◽  
Multi Phase ◽  
Step Heat Treatment ◽  
Kinetics Of

ABSTRACTA commercial unalloyed ductile iron has been developed to produce a multiphase matrix microstructure consisting of lenticular prior martensite, feathery upper bainite and a nano-scaled super bainite of lath bainitic ferrite and carbon-enriched film retained austenite. Multi-step heat treatment composed of austenizing, rapidly quenching and isothermally holding at low temperature have been developed. A tensile strength of more than 1.6 GPa, a hardness higher than HRC 54, and an elongation in excess of 5%, are achieved. This is attributed to a synergistic multi-phase strengthening effect. The developed nano super bainite exhibits a good balance between strength and toughness. The presence of martensite formed during the quenching prior to the isothermal treatment, accelerates the kinetics of subsequent nano super bainitic transformation by bainitic laths nucleating quickly at the martensite-austenite interfaces.

scholarly journals Influence of the Quenching and Partitioning Process on the Transformation Kinetics and Hardness in a Lean Medium Manganese TRIP Steel

Metals ◽  
2019 ◽  
Vol 9 (3) ◽  
pp. 353 ◽  
Author(s):  
Simone Kaar ◽  
Reinhold Schneider ◽  
Daniel Krizan ◽  
Coline Béal ◽  
Christof Sommitsch
Keyword(s):  
Isothermal Holding ◽  
Bainitic Ferrite ◽  
High Strength ◽  
Quenching Temperature ◽  
Quenching And Partitioning ◽  
Novel Approach ◽  
Medium Mn Steel ◽  
C Partitioning ◽  
Mn Steel ◽  
Isothermal Bainitic Transformation

The quenching and partitioning (Q&P) process of lean medium Mn steels is a novel approach for producing ultra-high strength and good formable steels. First, the steel is fully austenitized, followed by quenching to a specific quenching temperature (TQ) in order to adjust an appropriate amount of initial martensite (α’initial). Subsequently, the steel is reheated to a partitioning temperature (TP) in order to ensure C-partitioning from α’initial to remaining austenite (γremain) and thus retained austenite (RA) stabilization. After isothermal holding, the steel is quenched to room temperature (RT), in order to achieve a martensitic-austenitic microstructure, where the meta-stable RA undergoes the strain-induced martensitic transformation by the so-called transformation induced plasticity (TRIP) effect. This paper systematically investigates the influence of the Q&P process on the isothermal bainitic transformation (IBT) kinetics in a 0.2C-4.5Mn-1.3Al lean medium Mn steel by means of dilatometry. Therefore, the Q&P annealing approach was precisely compared to the TRIP-aided bainitic ferrite (TBF) process, where the samples were directly quenched to the temperature of the IBT after full austenitization. The results indicated an accelerated IBT for the Q&P samples, caused by the formation of α’initial during quenching below the martensite start (MS) temperature. Furthermore, a significant influence of the annealing parameters, such as TQ and TP, was observed with regard to the transformation behavior. For further characterization, light optical microscopy (LOM) and scanning electron microscopy (SEM) were applied, showing a microstructure consisting of a martensitic-bainitic matrix with finely distributed RA islands. Saturation magnetization method (SMM) was used to determine the amount of RA, which was primarily depending on TQ. Furthermore, the hardness according to Vickers revealed a remarkable impact of the annealing parameters, such as TQ and TP, on the predicted mechanical properties.

Monitoring Phase Transition Kinetics in Austempered Ductile Iron (ADI)

2010 ◽  
Vol 638-642 ◽  
pp. 3394-3399 ◽  
Author(s):  
Leopold Meier ◽  
Peter Schaaf ◽  
S. Cusenza ◽  
D. Höche ◽  
Menachem Bamberger ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Phase Transition ◽  
Heat Treatment ◽  
Ductile Iron ◽  
Bainitic Ferrite ◽  
High Strength ◽  
Austempered Ductile Iron ◽  
Design Engineers ◽  
Phase Transition Kinetics ◽  
Complementary Techniques

Austempered ductile iron (ADI) is a very attractive material for applications where high strength, good ductility, wear resistance and fatigue strength are required. Thus, it offers design engineers an alternative to steel and aluminium alloys. ADI essentially is a cast ductile iron that undergoes a specially designed austempering heat treatment, which creates a microstructure of high carbon austenite and bainitic ferrite along with graphite nodules. The final proportion of these phases (and thus the mechanical properties) depends on the phase transformation kinetics which is strongly affected by composition, as-cast microstructure and heat treatment parameters (austempering). ADI samples were austempered (heat treated) and the phase transitions were analysed after interrupted austempering. The phase fractions (austenite, ferrite, martensite, etc.) and their relation to bulk properties, like electrical resistivity, magnetic properties and mechanical properties (e.g. strength, hardness), and others were measured using optical and electron microscopy, X-ray and neutron diffraction, Mössbauer spectroscopy, and micro hardness measure¬ment. This combination of complementary techniques allows the correlation of the phase transition kinetics with the resulting properties.

scholarly journals Austempering Experiments of Production Grade Silicon Solution Strengthened Ductile Iron

2018 ◽  
Vol 925 ◽  
pp. 239-245
Author(s):  
Kaisu Soivio
Keyword(s):  
Ductile Iron ◽  
High Strength ◽  
Heat Treatments ◽  
Strengthening Effect ◽  
Iron Carbides ◽  
The Matrix ◽  
Solution Strengthening ◽  
Grade Silicon ◽  
The Stability

Austempered ductile iron provides a feasible way to produce high strength components. However, in heat treatments resulting in highest strengths some of the ductility is lost due to formation of bainitic carbides. The role of silicon in inhibiting the formation of iron carbides in as-cast ductile irons as well as its solution strengthening effect is well known and acknowledged in industry. The effect of silicon on austemperability, resulting microstructures, and mechanical properties of austempered ductile irons with silicon contents with 3.4-3.8 w-% was researched. Quenching and austempering heat treatments were carried out for production grade silicon solution strengthened ductile irons EN GJS 500-14. Results indicate, that it is possible to manufacture a fully ausferritic structure into a silicon solution strengthened matrix and indeed good ductility can be achieved in combination with ultimate tensile strength of 1600 MPa. Segregation of silicon reduces the solubility of carbon into the matrix especially close to the graphite nodules which reduce the stability of carbon stabilized austenite and leads into compromised machinability.

A Preliminary Study on Machinability Assessment of Nanobainite Steel

2013 ◽  
Author(s):  
Ashwin Polishetty ◽  
Guy Littlefair ◽  
Thomas Musselwhite ◽  
Chinmay Sonavane
Keyword(s):  
Isothermal Holding ◽  
Bainitic Ferrite ◽  
Cutting Speed ◽  
High Strength ◽  
Depth Of Cut ◽  
New Variety ◽  
Treatment Techniques ◽  
Before And After ◽  
Preliminary Study ◽  
Future Work

The demand for high strength materials and improvements in heat treatment techniques has given rise to this new form of high strength steel known as nanobainite steel. The production of nanobainite steel involves slow isothermal holding of austenitic steel around 200°C for 10 days, in order to obtain a carbon enriched austenite and cooling to room temperature using austempering. The microstructure of nanobainite steel is dual phase consisting of alternate layers of bainitic ferrite and austenite. The experimental design consists of face milling under 12 combination of Depth of Cut (DoC)-1, 2 and 3mm; cutting speed-100 and 150m/min; constant feed- 0.15mm/rev and coolant on/off. The machinability of the material is assessed by means of analysis such as metallography and cutting force analysis. The results obtained are used to assess the most favorable condition to machine this new variety of steel. Future work involves study on phase transformation by quantifying the microstructural phase before and after milling using XRD.

scholarly journals Effect of Rare Earth Ce on Deep Stamping Properties of High-Strength Interstitial-Free Steel Containing Phosphorus

Materials ◽  
2020 ◽  
Vol 13 (6) ◽  
pp. 1473
Author(s):  
Hao Wang ◽  
Yanping Bao ◽  
Chengyi Duan ◽  
Lu Lu ◽  
Yan Liu ◽  
...  
Keyword(s):  
Solid Solution ◽  
Grain Size ◽  
Rare Earth ◽  
High Strength ◽  
Rolling Process ◽  
P Element ◽  
Second Phase ◽  
Strengthening Effect ◽  
Interstitial Free ◽  
If Steel

The influence of rare earth Ce on the deep stamping property of high-strength interstitial-free (IF) steel containing phosphorus was analyzed. After adding 120 kg ferrocerium alloy (Ce content is 10%) in the steel, the inclusion statistics and the two-dimensional morphology of the samples in the direction of 1/4 thickness of slab and each rolling process were observed and compared by scanning electron microscope (SEM). After the samples in each rolling process were treated by acid leaching, the three-dimensional morphology and components of the second phase precipitates were observed by SEM and energy dispersive spectrometer (EDS). The microstructure of the sample was observed by optical microscope, and the grain size was compared. Meanwhile, the content and strength of the favorable texture were analyzed by X-ray diffraction (XRD). Finally, the mechanical properties of the product were analyzed. The results showed that: (1) The combination of rare earth Ce with activity O and S in steel had lower Gibbs free energy, and it was easy to generate CeAlO3, Ce2O2S, and Ce2O3. The inclusions size was obviously reduced, but the number of inclusions was increased after adding rare earth. The morphology of inclusions changed from chain and strip to spherical. The size of rare earth inclusions was mostly about 2–5 μm, distributed and dispersed, and their elastic modulus was close to that of steel matrix, which was conducive to improving the structure continuity of steel. (2) The rare earth compound had a high melting point. As a heterogeneous nucleation point, the nucleation rate was increased and the solidification structure was refined. The grade of grain size of products was increased by 1.5 grades, which is helpful to improve the strength and plasticity of metal. (3) Rare earth Ce can inhibit the segregation of P element at the grain boundary and the precipitation of Fe(Nb+Ti)P phase. It can effectively increase the solid solution amount of P element in steel, improve the solid solution strengthening effect of P element in high-strength IF steel, and obtain a large proportion of {111} favorable texture, which is conducive to improving the stamping formability index r90 value.

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