• Transactions of Materials Processing
• /
• v.30 no.1
• /
• pp.22-26
• /
• 2021

The present study demonstrated the effects of processing variable and alloying elements on the processing window of austempered cast iron, one of the heat-treatable cast irons, in order to elucidate the relation between heat treatment and microstructure in terms of time and temperature. Such microstructure is strongly affected by austenitizing conditions and alloying elements. The size of processing window tends to increase initially with increasing austenitizing temperature from 1123 to 1173 K, followed by a decline in the reverse direction between 1173 and 1223 K. Thus, the optimized processing window with large frame was found at an austenitizing temperature of 1173 K. To determine the effect of Sn addition, the processing window in the sample was created by the addition of 0.08 wt.% Sn, which appeared larger than that without Sn and with 0.06 wt.% Sn.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 1995.10a
• /
• pp.921-924
• /
• 1995

Case hardening behavior of carbon tool steel(SK5) was investigated after pulsed YAG laser irradiation. In the case od beam passes,martensite formed in the melt zone and in former pearlite regions of the austenitization zone exhibits vary high Vickers hardness values. The molten depth and width decrease as the beam power density increase. The influence of depth and width of color painted specimen was also investigated. The molten zone of the black painted specimen was the largest. The were loss of the black painted specimen was smaller than any other painted or raw material.

• Transactions of Materials Processing
• /
• v.14 no.3 s.75
• /
• pp.215-223
• /
• 2005

A numerical analysis program is developed by FDM scheme for the prediction of microstructural transformation during heat treatment of steels. In this study, multi-phase model was used fur description of diffusional austenite transformations in low-alloy hypoeutectoid steels during cooling after austenitization. A fundamental property of the model consisting of coupled differential equations is that by taking into account the rate of austenite grain growth, it permits the prediction of the progress of ferrite, pearlite, and bainite transformations simultaneously during quenching and estimate the amount of martensite also by using K-M eq. In order to simulate the microstructural evolution during tempering process, another Avrami-type eq. was adopted and method for vickers hardness prediction was also proposed. To verify the developed program, the calculated results are compared with experimental ones of casting product. Based on these results, newly designed heat treatment process is proposed and it was proved to be effective for industry.

• Journal of the Korean Society for Heat Treatment
• /
• v.5 no.2
• /
• pp.111-121
• /
• 1992

For the purpose of investigating the effect of austenitizing temperatures on the mechanical properties of 0.23% C-13.6%Cr martensitic stainless steel, tensile properties, hardness, impact value and carbide extraction were examined after changing the austenitizing temperatures and tempering temperatures. The results obtained are summerized as follows. The carbide laminations formed from hot rolling before austenitization could not be eliminated after austenitizing at $950^{\circ}C$. With increasing austenitizing temperature, hardness increased and showed maximum value at $1050^{\circ}C$ and then slightly decreased. With increasing tempering temperature up to $500^{\circ}C$, impact value and elongation appeard to be decreased but hardness showed nearly unchanged at austenitizing temperature of $1150^{\circ}C$ due to the fine $M_7C_3$ carbides precipitation. The abrupt increase in impact value, hardness and elongation above the tempering temperature of $500^{\circ}C$ appeared to change in carbide structure from fine $M_7C_3$ to coarse $M_{23}C_6$.

• Journal of the Korean Society for Heat Treatment
• /
• v.30 no.5
• /
• pp.197-206
• /
• 2017

The microstructure of a high-carbon and high-chromium cast steel (HK700) for cold-work die inserts was analyzed by advanced scanning electron microscopy. A continuous network of primary $M_7C_3$ carbide was developed among austenitic matrix after casting. A small amount of $M_2C$ was added to the carbide network owing to the enrichment of Mo and W during the solidification. After quenching in which the austenitization was performed at $1030^{\circ}C$ and double tempering at $520^{\circ}C$, the network structure of $M_7C_3$ was preserved while most of the matrix was transformed to martensite because of additional carbide precipitation. The $M_2C$ in the as-cast microstructure was also transformed to $M_6C$ due to its instability. The continuous network of coarse carbides owing to the absence of hot-working had little influence on the hardness after quenching and tempering, whereas it resulted in severe brittleness upon flexural loading.

• Journal of the Korean Society for Heat Treatment
• /
• v.18 no.4
• /
• pp.247-255
• /
• 2005

Although heat treatment is a process of great technological importance in order to obtain desired mechanical properties such as hardness, the process was required a tedious and expensive experimentation to specify the process parameters. Consequently, the availability of reliable and efficient numerical simulation program would enable easy specification of process parameters to achieve desired microstructure and mechanical properties without defects like crack and distortion. In present work, the developed numerical simulation program could predict distributions of microstructure and thermal stress in steels under different cooling conditions. The computer program is based on the finite difference method for temperature analysis and microstructural changes and the finite element method for thermal stress analysis. Multi-phase decomposition model was used for description of diffusional austenite decompositions in low alloy steels during cooling after austenitization. The model predicts the progress of ferrite, pearlite, and bainite transformations simultaneously during quenching and estimates the amount of martensite also by using Koistinen and Marburger equation. To verify the developed program, the calculated results are compared with experimental ones of casting product. Based on these results, newly designed heat treatment process is proposed and it was proved to be effective for industry.

• Korean Journal of Metals and Materials
• /
• v.46 no.8
• /
• pp.477-481
• /
• 2008

The secondary hardening and fracture behavior in P/M high speed steels bearing V content of 9 to 10 wt% have been investigated in terms of austenitizing temperature and precipitation behavior. Austenitizing was conducted at 1,100 and $1,175^{\circ}C$ of relatively low and high temperatures. Coarse primary carbides retained after austenitization were mainly V-rich MC type. They give a significant influence on hardeness and toughness, as well as wear resistance. Tempering was performed in the range of $500{\sim}600^{\circ}C$. The peak hardness resulting from the precipitation of the fine MC secondary carbides was observed near 520, irrespective of austenitizing temperature. Aging acceleration(or deceleration) did not occur with increasing austenitizing temperature because it mainly influences contents of V and C of matrix through the dissloution of coarse primary MC containing lots of V and C. The precipitation of secondary MC carbides, which also contain V and C, did not change the aging kinetics itself. In the 10V alloy containing much higher C content, the impact toughness was lower than 9V alloy, because of the larger amount of primary carbide and high hardness.