Effect of Austempering on the Structures and Performances of Cast High Carbon Si‐Mn Steel

Abstract

The effects of austempering on the microstructures and mechanical performances of cast high carbon silicon and manganese steel (HC-SMS) containing 1.0 wt.%C-2.5 wt.%Si-1.5 wt.%Mn-1.0 wt.%Cr-0.5 wt.%Cu were studied. The test results show a plate-like morphology of bainitic ferrite. Each plate of the ferrite is surrounded by a thin layer of retained austenite when the austempering temperature is low, whereas large blocky areas of retained austenite are observed when the temperature is higher. The amount of retained austenite in the bainitic structure increases with increasing isothermal quenching temperature. Austempering results in a significant improvement in the mechanical performances of HCSMS. The main effect of the austempering temperature on the mechanical performances is that hardness and strength are decreased and elongation, impact toughness and fracture toughness are increased with increasing temperature. Cast HCSMS has excellent comprehensive mechanical performance when austenized at 593K.

Effect of Microsegregation and Bainitic Reaction Temperature on the Microstructure and Mechanical Properties of a High-Carbon and High-Silicon Cast Steel

“…Such microstructures are obtained through isothermal heat treatments similar to those used in the production of conventional bainitic steels, and they show excellent mechanical properties compared with other more expensive steels [21][22][23][24]. As it was reported, exceptional results were achieved in terms of tensile, toughness, and wear properties using steels with high carbon content (0.6-1.0 wt.%C) and austempering at low temperatures (250-300 • C); this carbon content allows obtaining carbide-free bainitic steels with a tensile strength of 1600-2000 MPa [25][26][27][28]. Toughness values of nearly 130 MPa m 1/2 have been obtained for strength values in the range of 1600-1700 MPa.…”

“…Putatunda [26] has obtained cast carbide-free bainitic steels with tensile strengths in the range 575-2100 MPa with a maximum elongation of 7%. Fu et al [27] also reported tensile strengths ranging from 1180 to 1730 MPa and elongations up to 3.5%, while Mandal [28] developed microstructures with an elongation of 27%, but with a tensile strength lower than 700MPa.…”

“…These alloying elements improve hardenability, avoiding the formation of any other undesired transformation products, such as pearlite, before the isothermal holding in the bainite temperature range, but the alloying additions need to be kept to a minimum in order to accelerate the bainite formation kinetics and to control alloying costs. Typically, additions ranging about 0.5-2.0 wt.%Cr and 0.5-2.0 wt.%Mn are chosen [25][26][27][28].…”

Mechanical properties of a carbide-free bainitic cast steel with dispersed free ferrite

“…At present, just a limited number of studies were conducted on CFB microstructures obtained from cast steels [8-16]. As expected, mechanical properties obtained for cast CFB steels are below those reported for wrought steels, particularly regarding ductility, as a consequence of the presence of some defects in the cast parts, such as microsegregation, inclusions and micro-shrinkage cavities.…”

“…Putatunda [8] has obtained cast CFB steels with tensile strength ranging from 575 to 2100 MPa with maximum ductility of 7%. Fu et al [16] also reported tensile strengths of 1180–1730MPa and ductility ranging from 0.75 to 3.5%, while Mandal [15] developed microstructures with ductility of 27%, but with a tensile strength lower than 700 MPa. In comparison, wrought CFB steels can develop the extraordinary combination of a tensile strength of 2068 MPa with a total elongation of 21.3% [5].…”