Duohui BEI
,
Jianfeng GU
,
Jiansheng PAN
,
Jian Leür
,
Ke LU
材料科学技术（英）
The behavior of gaseous nitriding on the surface nanocrystallized (SNCed) steel was investigated.The mild steel discs were SNCed on one side by using the method of ultrasonic shot peening. The opposite side of the discs maintained the original coarse-grained condition. The gaseous nitriding was subsequently carried out at three different temperatures: 460,500 and 560°C. The compound layer growth and diffusion behavior were then studied. It was revealed that SNC pretreatment greatly enhances both diffusion coefficient D and surface reaction rate. As a result, nitriding time could be reduced to the half.It was also found that the growth of compound layer with nitriding time conformed with parabolic relationship from the start of nitriding process in the SNCed samples.
关键词:
Nitriding process
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Dongli SONG
,
Jianfeng GU
,
Jiansheng PAN
,
Xin YAO
材料科学技术（英）
For large-sized AISI P20 steel block used as plastic die with a thickness of more than 200~mm, appropriate quenching processes are the key to obtain much thick hardened layer. In this paper, different quenching processes of AISI P20 steel block such as oil quenching, direct water quenching, water quenching with pre-cooling and water quenching with pre-cooling and self-tempering were numerically investigated by computer simulation based on the detailed discussion on the mathematical models of quenching processes including partial differential equations of heat transfer, thermal physical properties, latent heat, heat transfer coefficient and calculation of phase transformation, The results show that the water quenching with pre-cooling and self-tempering process can not only effectively avoid quenching cracks, but also obtain deeper harden depth than oil quenching.
关键词:
Computer simulation
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