Transformation in Stir Zone of Friction Stir Welded Carbon Steels with Different Carbon Contents

Abstract

Five types of ferrite-pearlite structure carbon steels with different carbon contents (IF steel, S12C, S20C, S35C, S50C) were friction stir welded under various welding conditions, and the mechanical properties and microstructures of the FSW carbon steel joints were evaluated. Compared with IF steel, the microstructures and mechanical properties of the carbon steel joints are significantly affected by the welding conditions. When the carbon content is less than or equal to 0.12 mass%, the welding produces ferrite-pearlite structures, and the strength slightly increases compared to the base metal due to the refined microstructure; when the carbon content is above 0.2 mass%, the welding produces ferrite-pearlite plus harder phases like the martensite and bainite microstructures, resulting in a significantly increased strength of the joints. These are dependent on each of the thermal-mechanical cycles.

Microstructure and Toughness of Friction Stir Weld of Thick Structural Steel

“…In recent years, the advances in the tool materials have improved their durability and enabled the welding of steels in a laboratory scale. A number of studies have been reported on the FSW of steels, such as the interstitial free (IF) steel, 4) carbon steels [5][6][7][8][9] and stainless steels. [10][11][12][13] Some of them especially detailed the FSW process for ferrous materials, investigating the influence of the thermal history and the carbon content on the microstructures of the welds.…”

The Status of Friction Stir Welding Applications to Ferrous Materials

“…2.2.1 페라이트계 강 페라이트계 강에 대한 FSW 보고는 지금 까지 연강 8) , 각종 탄소강 [9][10][11][12][13][14] , DH36강 15) , C-Mn강 16,17) , 라인 파이 프용강 18,19) , 12%Cr강 20,21) , HSLA-65강 [22][23][24][25][26] , DP강 [27][28][29][30] , B첨가강 . 그러나 접합조건을 조절하여 냉 각속도 및 최고도달온도를 제어하면 FSW후 경화조직 의 형성을 억제할 수 있다 [10][11] .…”

Characteristics of Microstructure in Ultrahigh Carbon Steel Produced during Friction Stir Welding

“…Cui et al 19) have reported that the martensitic transformation occurs in the carbon steels during FSW at the high travel speeds. The 0.5 % C steel experienced the martensitic transformation at the rotational speed of 400 rpm during cooling cycle of FSW when the travel speed was higher than 0.42-0.83 mm/s (25-50 mm/min).…”

“…31,32) Hardness of the martensitic structure formed in 1.0 % C steels has been reported to be about 850 HV, 31,32) which is roughly the same as that in the central zone. Cui et al 19) have shown that the hardness in the weld depends on the martensite fraction and the hardness of the martensite in carbon steels when the martensite is formed. This situation suggests that the high hardness in the central zone can be attributed to the martensitic structure.…”

“…Recently, several welding tools with high temperature strength and wear resistance have been developed. 16) Various papers on FSW of steels, such as carbon steels having carbon contents up to 0.70 wt%, [17][18][19] mild steel, 20) DH36 steel, 21) pipeline steel 22) and stainless steels, [23][24][25][26][27][28] have been also published, showing that FSW can produce defect-free welds in these steels even if the fusionweldability is poor.…”