TRỊNH VĂN TRUNG, NGUYỄN ANH SƠN, LÊ THIÊM TUẤN
Viện Khoa học và Kỹ thuật Vật liệu, Trường Đại học Bách khoa Hà Nội, Số 1, Đại Cồ Việt, Hai Bà Trưng, Hà Nội
NGUYỄN THÀNH HỢP
Viện Ứng dụng Công nghệ, Số 25, Lê Thánh Tông, Hoàn Kiếm, Hà Nội
VÕ THỊ KIỀU ANH
Viện Kỹ thuật Nhiệt đới, Viện Hàn lâm Khoa học và Công nghệ Việt Nam, Số 8, Hoàng Quốc Việt, Cầu Giấy, Hà Nội
NGUYỄN VĂN THÀNH*
1. Viện Khoa học và Kỹ thuật Vật liệu, Trường Đại học Bách khoa Hà Nội, Số 1, Đại Cồ Việt, Hai Bà Trưng, Hà Nội
2. Viện Ứng dụng Công nghệ, Số 25, Lê Thánh Tông, Hoàn Kiếm, Hà Nội
The AISI 420 stainless steel is commonly used in parts such as steam generators, chemical mixer blades, plastic molds that required high hardness and medium corrosion resistance. To improve the hardness of the parts from this steel, it is required a heat treatment such as quenching and tempering. However, the tempering process affects both hardness and corrosion properties at tempering temperatures higher than 500 oC or long tempering duration, especially. This study focuses on the influence of both tempering temperatures (200, 300, 400, 500, 600, and 700 oC) and time (1, 4, and 8 hours) on the microstructures and properties of as-quenched specimens after austenitizing at 1030 oC for 1.5 hours. Hardness tester, X-ray diffractometer, optical microscope, corrosion resistance tester, and the field-emission scanning electron microscope were used for the hardness, microstructure, phase composition, and corrosion resistance evaluation. The results show that tempering at temperature lower than 400 oC for holding time less than 4 hours improved the hardness and corrosion resistance of this steel compared with as-received steel. The highest corrosion resistance was observed when tempering at 200 oC for holding time
no longer than 4 hours. The second hardness of around 53 HRC was achieved after tempering at 500 oC for 4 hours because of the precipitation of secondary M7C3 carbides with high hardness. However, the hardness and the corrosion resistance decrease when tempering duration increases from 4 hours to 8 hours. When the tempering temperature is above 500 oC and tempering duration is around 8 hours, the hardness and corrosion resistance were significantly decreased because of the martensitic decomposition and precipitation of M23C6 carbides.
# AISI 420 steel, tempering, corrosion resistance, carbides precipitation.
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