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Papers by ya min

Materials Science and Technology, 2014

Based on the phase transformation theories, especially the T0 concept of bainite transformation, ... more Based on the phase transformation theories, especially the T0 concept of bainite transformation, alloy optimisation of bainitic steel with carbides has been carried out aiming at the produce of plastic mould with large cross-section. The effect of manganese and silicon on proeutectoid ferrite and bainite transformation is explored by dilatometric analysis, XRD and different microscopy techniques. The results show that after the alloy optimisation, the transformation of proeutectoid ferrite is suppressed and when the cooling rate is lower than 0·1°C s− 1, the new lower bainite transformation appears by decreasing carbon capacity of austenite and promoting carbide precipitation. Industrial production proves that the optimised alloy SDP1 can meet the demand for the plastic mould with the thickness of 1050 mm.

Materials Science and Technology, 2012

The precipitate hardened plastic mould steel 10Ni3MnCuAl after aging at 510uC is investigated by ... more The precipitate hardened plastic mould steel 10Ni3MnCuAl after aging at 510uC is investigated by optical microscopy, X-ray diffractometry, TEM and three-dimensional atom probe. The results show that its microstructure is granular bainite with a certain amount of retained austenite after soluted and cooled in furnace, and its content decreases until close to 0. By TEM observation, the age hardening of the 10Ni3MnCuAl steel is mainly ascribed to the precipitation of a high density, ultrafine and fully coherent NiAl precipitation with the B2 structure at 510uC for 4 h, and a multicomponent precipitate can be found in steel for 100 h aging. The three-dimensional atom probe researches show that its age hardening derives from a spherical multicomponent precipitate containing Fe, Ni, Al, Mn and Cu, and the content of Fe decreases with aging time, while those of Ni, Al, Mn and Cu are opposite, and the ratio between Ni and Al is roughly 1, and the Cu precipitates are surrounded by Ni, Al and Mn clusters for 100 h aging. The hardness variation is related to the size and number density of the precipitates, and it follows the cutting mechanism during early aging while obeys Orowan mechanism during overaging.

Surface and Coatings Technology, 2013

Abstract Plasma boriding of high strength alloy steel (AISI H13) with nanostructured surface laye... more Abstract Plasma boriding of high strength alloy steel (AISI H13) with nanostructured surface layer fabricated by air blast shot peening(ABSP) was performed at 580 °C for 4 h. A continuous coating layer with thickness of about 4 μm was composed with two phases of Fe 2 B and FeB, and the nanohardness of borided layer was as high as 20 GPa. These results indicate that cyclic deformation and the angle between shot jet and sample surface play a critical role in the process to produce nanocrystalline in the surface layer. By using ABSP as pre-treatment, boron diffusion and the nucleation rate of boride can be remarkably enhanced in nanostructured surface layer. In addition, the weight loss rates of borided samples in molten aluminum alloy were only as much as ~ 40% of that of untreated ones, and the main reason was that the coating layer can effectively prevent the substrate directly contacting with molten aluminum alloy.

Metal Science and Heat Treatment, 2010

Effects of the initial structural state and of the rate of subsequent heating on inheritance of s... more Effects of the initial structural state and of the rate of subsequent heating on inheritance of structure in steel 718 are studied. Metallographic analysis of the steel after various modes of heat treatment is performed. The critical temperatures of the steel are determined. Heating curves are plotted for specimens in different initial states with the help of a DIL-805A dilatometer. Recommendations are given on lowering the inheritance of structure in large-section preforms from steel 718.

Materials Science and Engineering: A, 2010

ABSTRACT A study of 40SiMnNiCr steel subjected to a two-step quenching and partitioning process (... more ABSTRACT A study of 40SiMnNiCr steel subjected to a two-step quenching and partitioning process (Q&P) is presented. The result suggests that strength variation of Q&P steels during the two-step Q&P process was a cumulative effect of increase of retained austenite fraction, decrease of carbon supersaturation of virgin martensite, and particularly much of lower bainite formation. A trade-off between high strength and good ductility of two-step Q&P steels can be tailored and adjusted by controlling lower bainite fraction. The final amount of austenite was influenced by the transformation kinetics of lower bainite during the partitioning process.

Materials Science and Technology, 2014

Based on the phase transformation theories, especially the T0 concept of bainite transformation, ... more Based on the phase transformation theories, especially the T0 concept of bainite transformation, alloy optimisation of bainitic steel with carbides has been carried out aiming at the produce of plastic mould with large cross-section. The effect of manganese and silicon on proeutectoid ferrite and bainite transformation is explored by dilatometric analysis, XRD and different microscopy techniques. The results show that after the alloy optimisation, the transformation of proeutectoid ferrite is suppressed and when the cooling rate is lower than 0·1°C s− 1, the new lower bainite transformation appears by decreasing carbon capacity of austenite and promoting carbide precipitation. Industrial production proves that the optimised alloy SDP1 can meet the demand for the plastic mould with the thickness of 1050 mm.

Materials Science and Technology, 2012

The precipitate hardened plastic mould steel 10Ni3MnCuAl after aging at 510uC is investigated by ... more The precipitate hardened plastic mould steel 10Ni3MnCuAl after aging at 510uC is investigated by optical microscopy, X-ray diffractometry, TEM and three-dimensional atom probe. The results show that its microstructure is granular bainite with a certain amount of retained austenite after soluted and cooled in furnace, and its content decreases until close to 0. By TEM observation, the age hardening of the 10Ni3MnCuAl steel is mainly ascribed to the precipitation of a high density, ultrafine and fully coherent NiAl precipitation with the B2 structure at 510uC for 4 h, and a multicomponent precipitate can be found in steel for 100 h aging. The three-dimensional atom probe researches show that its age hardening derives from a spherical multicomponent precipitate containing Fe, Ni, Al, Mn and Cu, and the content of Fe decreases with aging time, while those of Ni, Al, Mn and Cu are opposite, and the ratio between Ni and Al is roughly 1, and the Cu precipitates are surrounded by Ni, Al and Mn clusters for 100 h aging. The hardness variation is related to the size and number density of the precipitates, and it follows the cutting mechanism during early aging while obeys Orowan mechanism during overaging.

Surface and Coatings Technology, 2013

Abstract Plasma boriding of high strength alloy steel (AISI H13) with nanostructured surface laye... more Abstract Plasma boriding of high strength alloy steel (AISI H13) with nanostructured surface layer fabricated by air blast shot peening(ABSP) was performed at 580 °C for 4 h. A continuous coating layer with thickness of about 4 μm was composed with two phases of Fe 2 B and FeB, and the nanohardness of borided layer was as high as 20 GPa. These results indicate that cyclic deformation and the angle between shot jet and sample surface play a critical role in the process to produce nanocrystalline in the surface layer. By using ABSP as pre-treatment, boron diffusion and the nucleation rate of boride can be remarkably enhanced in nanostructured surface layer. In addition, the weight loss rates of borided samples in molten aluminum alloy were only as much as ~ 40% of that of untreated ones, and the main reason was that the coating layer can effectively prevent the substrate directly contacting with molten aluminum alloy.

Metal Science and Heat Treatment, 2010

Effects of the initial structural state and of the rate of subsequent heating on inheritance of s... more Effects of the initial structural state and of the rate of subsequent heating on inheritance of structure in steel 718 are studied. Metallographic analysis of the steel after various modes of heat treatment is performed. The critical temperatures of the steel are determined. Heating curves are plotted for specimens in different initial states with the help of a DIL-805A dilatometer. Recommendations are given on lowering the inheritance of structure in large-section preforms from steel 718.

Materials Science and Engineering: A, 2010

ABSTRACT A study of 40SiMnNiCr steel subjected to a two-step quenching and partitioning process (... more ABSTRACT A study of 40SiMnNiCr steel subjected to a two-step quenching and partitioning process (Q&P) is presented. The result suggests that strength variation of Q&P steels during the two-step Q&P process was a cumulative effect of increase of retained austenite fraction, decrease of carbon supersaturation of virgin martensite, and particularly much of lower bainite formation. A trade-off between high strength and good ductility of two-step Q&P steels can be tailored and adjusted by controlling lower bainite fraction. The final amount of austenite was influenced by the transformation kinetics of lower bainite during the partitioning process.