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Evaluation of Microstructure and Fatigue Properties of HSLA-100 Steel Welded by SMAW and FCAW Methods

Shahrani, Siamak | 2015

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 48363 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Ekrami, Ali Akbar
  7. Abstract:
  8. After World War II, steel bearings containing copper element have been developed by the Navy of the United States of America with the HSLA-100 brand. Since 1890 and in order to manufacture tanks and tools for the body of navy equipment, the steel HY 80 was used instead of HSLA-100. Because of the high carbon content, the welding properties of the HY 80 are low. Furthermore, increasing of hardness and decreasing of toughness in the heat-affected zone generated during the welding process lead to susceptibility of this alloy to hydrogen cracking and brittle fracture. Therefore, in order to minimize the cost of welding, low-alloy high strength steel (HSLA) is used which contain copper. Reducing the carbon content is the main method for improving toughness and weldability of this alloy. In this type of steel, the strengthening process was enhanced by the formation of tempered martensitic structure with a high density of dislocations and copper containing precipitates existing in the matrix. Due to the good weldability and toughness, this grade of steel is used in critical navy equipments and other components which performed under dynamic loading which are too complex. The aim of present work is to investigate the effect of coated electrode arc welding and flux cored arc welding electrode on the microstructure and especially the fatigue behavior of HSLA-100. In order to do so, HSLA-100 sheets with a dimension of 18 mm in thickness, 150 mm in width and 400 mm in length were prepared by building edge and according to the instructions in the navy. Three samples including the sample which was prepared by using the coated electrode arc welding process methods, the sample which was made by using the flux cored electrodes and the non-welded sample were prepared to investigate the welding condition on the properties of this steel. To study the effect of process parameters, tensile test, hardness measurement, impact test and microscopic studies were used. In the next step, fatigue tests were performed on three samples of each mode. Also, the fracture surfaces were examined by scanning electron microscopy (SEM). Both welding processes enhanced the ultimate tensile strength compared to the non-welded samples. However, the welding process decreased the toughening behavior of the HSLA-100. Microscopic studies showed an increase in grain size near the heat-affected zone. Also, results showed the formation of martensite, bainite and Widmanstatten ferrite as the main phases in the weld zone. Results of fatigue test showed a reduction of about 96.5 % in fatigue life according to SMAW process. However, this value was 77.2% for the FCAW process
  9. Keywords:
  10. Fatigue ; High Strength Low Alloy (HSLA)Steel ; Fatigue Properties ; Shielded Metal Arc Welding (SMAW) ; Flux Cord Arc Welding (FCAW)

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