Yong’an Min

Alloy optimisation of bainitic steel for large plastic mould

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.

Study on the Microstructure and Properties of Prehardened Plastic-Mould SWFT Steel for Big Section

In order to develop the prehardened plastic-mould SWFT steel for big section without quenching and tempering, the influence of carbon on the microstructure and corresponding hardness of steel under both air and sand cooling were investigated. It was demonstrated that when the carbon content of steels increased, the stability of overcooling austenite increased and the hardness difference decreased because of the decrease of bulk ferrite and the increase of bainite. The microstructure of No.8 steel under both air and sand cooling was mostly bainite and the hardness difference was less than 3HRC.And the No.8 steel had good machineability by the turning comparative experiment of No.8 steel and 45# steel. The prehardened plastic mould SWFT steel for big large section was produced successfully based on the experiment result.

Uniform Design and its Application in the Chemical Composition Design of Hot Work Die Steel

According to the conditions that hot work die steels, for example H13 and HOTVAR, were used, the main chemical compositions and the ranges of their contents were determined as follows: 0.25~0.6%C, 0.5~1.5%Si, 0.2~1%Mn, 2~6%Cr, 1~3%Mo and 0.3~1.5%V. Based on uniform design, six kinds of steels and the following heat treatment schemes were designed. The tempering resistance and the impact toughness at room temperature were measured. The results were analyzed by quadratic stepwise regression analysis, the relationships between the chemical compositions, the heat treatment processes and the properties were studied in detail, the influence coefficients and the influence tendencies of the main variables were also given in this paper.

Study of Identifying the Banded Structure of 8620 Steel Bars

The level of ferrite/pearlite banding in gear steel can be affected significantly by cooling rates, however, different sizes own diverse bands in the same cooling rate. The lower-level degree banding was got under the faster cooling speed, whereas the higher-level degree banding under the slower cooling speed. The alloying elements segregation can be characterized in the fixed speed according to the banding. Banded segregation in a hot rolled SAE8620 gear steel was investigated by DIL805A dilatometer, OM, electron microprobe analysis(EPMA). The transformation temperature of rich solute and poor solute were calculated by JMatPro software. Meanwhile, the diffusion distance of carbon was also figured by DICTRA. Results showed that the difference of Ar3 temperatures for solute-depleted and solute-rich zones will impact the banded intensity, while the diffusion distance of carbon decrease with an increasingly of cooling rate, the banded structure relieved. The corresponding band adopted 0.2 °C/s cooling rate can characterize the first banded segregation of alloy elements.

Study of the microstructure and properties of a precipitation-hardened steel-10Ni3MnCuAl block

A study is made of the microstructure, mechanical properties, machinability, and service properties of a 250 × 800 × 2000 mm block of 0.15% C – 1.87% Mn – 3% Ni – Cr – Cu – Al steel after its continuous cooling. The steel has good hardenability and polishability, and a pattern can easily be etched on its surface.

Study on Machinability of Pre-Hardened Plastic Mould Steel

The relationship between machinability and microstructure of plastic mould steel is still not clear enough, despite the application of plastic mould steel is more and more wide. In this study, two typical plastic mould steels, namely, 718 (DIN 1.2738) and SDP1 steel with the same hardness are chosen to investigate turning force, tool wear and milling force by experimental test. Combining with the turning and milling test, discussions about cutting force and the relationship between machinability and microstructure are made. And it’s found that the micro-uniformity has a great effect on the machinability of plastic mould steel.

Microstructural evolution in 10Ni3MnCuAl precipitation hardened steel after aging at 510°C

Abstract The precipitate hardened plastic mould steel 10Ni3MnCuAl after aging at 510°C 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 510°C 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.

Comparison on the Compositions, Microstructure and Hardness of Super Large Section Prehardened Steels for Plastic Mould Block

Compositions and hardness of four prehardened steels for plastic mould blocks with more than 1 m thick, named QTPA, QTPB, QTPC and QTPD were tested, and microstructures at center and surface of blocks were observed. The results show that hardness uniformity of the QTPC steel block is less than ± 4 HRC, its center appears pearlite, while microstructures at center of the other three steel blocks are martensite and bainite, hardness uniformity of the QTPA steel is less than ±1 HRC, hardness uniformity of the QTPB and QTPD steels are less than ±2 HRC. Combined with the compositions analysis, molybdenum has bigger effect on the hardenablity and hardness uniformity of the large section prehardened steels for plastic mould block, and QTPC steel with higher carbon and lower Molybdenum content makes the hardness uniformity be less than the others.

Comparison of Property of Dynamic Melting-Loss H13 Steel by Different Surface Treatment

In order to prolong the service life of Aluminum alloy die casting dies, different surface treatments were adopted to avoid melting loss on the surface of the dies. In this paper, the dynamic melting-loss properties of H13 steel were compared among non-treatment, vapor oxidation treating, carbonitriding and composite treatment of nitirding and vapor oxidation in liquid aluminum of ADC12 at 700 °C by the weight loss method. The surface structures of the specimens after treatments were analyzed by the optical microscopy (OP); the patterns of specimens on the surface were observed by measuring microscope and the melting-loss characteristics of specimens with different treatment were analyzed. The results showed that the melting-loss property was heightened obviously by different surface treatments; especially the melting-loss property of the specimens with composite treatment of nitirding and vapor oxidation was the best.