Morphology and Crystallography of Ausferrite in Austempered Ductile Iron

et al. 2022

Crystals

Five types of ductile cast irons (DCIs) were fabricated by crystallizers with different inner diameters, as well as five different austempered ductile cast irons (ADIs) after the same isothermal quenching process. The effects of amount, diameter, and morphology of graphite on the mechanical properties of DCI and ADI and the effect of the original as-cast microstructure on the microstructure after austempering were studied. The microstructures were characterized by optical microscopy, scanning electron microscopy, and X-ray diffraction. Their mechanical properties were examined by tensile, U-shaped impact, and hardness tests. As the diameter of the crystallizer increases from 60 mm to 150 mm, the diameter of the nodular graphite increases from ~10 to ~50 μm, and the nodularity rate decreases from 100 to 70%. The average ultimate tensile strength increases from ~500 MPa in the as-cast state to 1100 MPa in the austempered state and the hardness increases from ~180 HB to 400 HB. The elongation in cast state decreases from 11 to 4.6% and the elongation in ADI state decreases from 7 to 4.5%. Through the research in this paper, it can be seen that ADIs with different matrix microstructures can be obtained from different original as-cast microstructures through the same isothermal quenching process, and different casting crystallizers can be selected according to different performance requirements, which can reduce the nitrite pollution and reduce cost.

Section: Discussionmentioning

confidence: 99%

Microstructures and Mechanical Properties of Ductile Cast Iron with Different Crystallizer Inner Diameters

Jiaojiao

et al. 2022

Crystals

“…Then, the fully austenitized GI samples were quickly transferred to another pre-heated low temperature salt bath furnace (50% KNO3 + 50% NaNO3) for the austempering process at various austempering temperatures (232 °C, 260 °C, 288 °C, 316 °C, 343 °C, and 371 °C) and holding times (1 min, 2 min, 3 min, 6 min, 10 min, 20 min, 30 min, 60 min, 90 min, and 120 min). The above parameters were selected in terms of the previous related research [6,10,[15][16][17][18][19]. Then, the AGI samples were cooled to room temperature by water.…”

Section: Austempering Heat Treatmentmentioning

confidence: 99%

Wear Behavior of Austempered and Quenched and Tempered Gray Cast Irons under Similar Hardness

Han

Barber

et al. 2019

Metals

In this research, an austempering heat treatment was applied on gray cast iron using various austempering temperatures ranging from 232 °C to 371 °C and holding times ranging from 1 min to 120 min. The microstructure and hardness were examined using optical microscopy and a Rockwell hardness tester. Rotational ball-on-disk sliding wear tests were carried out to investigate the wear behavior of austempered gray cast iron samples and to compare with conventional quenched and tempered gray cast iron samples under equivalent hardness. For the austempered samples, it was found that acicular ferrite and carbon saturated austenite were formed in the matrix. The ferritic platelets became coarse when increasing the austempering temperature or extending the holding time. Hardness decreased due to a decreasing amount of martensite in the matrix. In wear tests, austempered gray cast iron samples showed slightly higher wear resistance than quenched and tempered samples under similar hardness while using the austempering temperatures of 232 °C, 260 °C, 288 °C, and 316 °C and distinctly better wear resistance while using the austempering temperatures of 343 °C and 371 °C. After analyzing the worn surface, abrasive wear and fatigue wear with the presence of pits, spalls, voids, long cracks, and wear debris were the main mechanisms for austempered gray cast iron with a low austempering temperature. However, only small pits and short cracks were observed on the wear track of austempered gray cast iron with high austempering temperature. Furthermore, the graphite flakes were exposed and ground by the counterpart surface during wear tests. Then, the graphite particles would form a tribo-layer to protect the contact surface.

“…The microstructure of ausferrite is usually investigated by scanning electron microscopy (SEM) or optical microscopy (OM) with its crystallographic feature unknown. Recently, we have found for the first time that acicular ferrite has the G-T relationship in ADI by electron backscatter diffraction (EBSD) [26]. In this paper, we have mainly investigated the effects of austempering temperature on crystallography of ausferrite.…”

Section: Introductionmentioning

confidence: 99%

Effect of austempering temperature on microstructure of ausferrite in austempered ductile iron

Materials Science and Technology

Liu

et al. 2019

The effect of austempering temperature on the microstructure of ausferrite in austempered ductile iron was investigated. The results show that the grain sizes of retained austenite and acicular bainitic ferrite both become larger with the increase of austempering temperature. As the austempering temperature is 240°C, the crystallographic relationship between ferrite and austenite in ausferrite follows Greninger-Troiano relation. However, Nishiyama–Wassermann relation and Greninger-Troiano relation both appear in ausferrite austempered at 300°C. At this temperature, the point-to-point misorientations of individual ferrite needle austempered at 300°C are less than 1°, being less than those at 240°C. This means the ferrite needles at 300°C contain fewer defects. However, some poles of ferrite needles obviously deviate from their ideal positions, which mainly comes from some ends of ferrite needles.