Korean Journal of Metals and Materials (대한금속재료학회지)

The Korean Institute of Metals and Materials (대한금속재료학회)
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Microstructures and Hardness of CO2 Laser Welds in 409L Ferritic Stainless Steel

409L 페라이트계 스테인리스강 CO2레이저 용접부의 미세조직과 경도

  • Kong, Jong Pan (Dept. of Material Science and Engineering, Pusan National University) ;
  • Park, Tae Jun (Dept. of Material Science and Engineering, Pusan National University) ;
  • Na, Hye Sung (Dept. of Material Science and Engineering, Pusan National University) ;
  • Uhm, Sang Ho (POSCO Technical Research Laboratories) ;
  • Kim, Jeong Kil (POSCO Technical Research Laboratories) ;
  • Woo, In Su (POSCO Technical Research Laboratories) ;
  • Lee, Jong Sub (POSCO Technical Research Laboratories) ;
  • Kang, Chung Yun (Dept. of Material Science and Engineering, Pusan National University)
  • Received : 2010.01.13
  • Published : 2010.04.15
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Abstract

The microstructure and hardness of $CO_2$ laser welds were investigated in the Ti-stabilized ferritic stainless steel 409L. The observed specimen was welded in a fully penetrated condition in which the power was 5 kW and the welding speed 5 m/min. The grain structure near the bond line of the laser welds was produced by epitaxial growth. The grain size was the largest in the fusion zone, and HAZ showed nearly the same grain size as that of the base metal. The HAZ microstructure consisted of subgrains and precipitates that were less than 100 nm in size and that were located along the subgrain boundaries. On the other hand, the hardness was the highest in the fusion zone due to the large amount of small precipitates present. These were composed of TiN, Ti(C,N) and $TiO_2$+Ti(C,N). The hardness decreased continuously from the fusion zone of the base metal. The HAZ hardness was slightly greater than that of the base metal due to the existence of subgrains and precipitates in the subgrain boundary.

Keywords

Acknowledgement

Supported by : (주)포스코, 과학기술부

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