Microstructural characterization of nanostructured steels

• Grant number: 11/19495-4
• Support type: Scholarships in Brazil - Scientific Initiation
• Effective date (Start): December 01, 2011
• Effective date (End): May 31, 2012
• Field of knowledge: Engineering - Materials and Metallurgical Engineering
• Principal Investigator: Conrado Ramos Moreira Afonso
• Grantee: Vítor Deghaid Pereira
• Home Institution: Centro de Ciências Exatas e de Tecnologia (CCET). Universidade Federal de São Carlos (UFSCAR). São Carlos , SP, Brazil
• Associated research grant: 05/59594-0 - Properties of amorphous, metastable and nano-structured metallic alloys, AP.TEM

Abstract

The development of high strength low alloy steels (HSLA) and higher grades of microalloyed steels with higher strength, was influenced by the need to manufacture large diameter pipes, with thinner wall thickness and operating under higher pressures, which increase productivity, both by reducing the weight of the structure, and increasing the volume of fluid safely transported over great distances.The steel pipes for the oil industry are classified according to the API ("American Petroleum Institute") as a function of its application, chemical composition and mechanical strength. The steels used specifically in the manufacture of pipes for oil and gas transportation lines follow the classification API 5L. For example, to API 5L X80 steel, the last two digits after the letter X specify minimum yield of the steel equal to 80 ksi (550 MPa).The alternatives for the manufacture of metallurgical steel classification and API 5L X70 and X80 vary between 50 and 60 options, which are predominantly related to chemical compositions and the lamination process. It is noticed that there are several options for making these materials, since the standard API does not make a severe restriction in relation to the alloying elements. As a requirement of mechanical properties, the yield strength (Ãy) of the material (mentioned above) must be greater than or equal to 80 ksi (550MPa). For the tensile strength (Ãr) the range is between 620 and 827MPa. The objective of this work is to evaluate, through the microstructural characterization and measurement of mechanical properties such as Vickers hardness, the effect of two processing routes: (i) rapid cooling from the liquid and (ii) severe plastic deformation of steels of different classes including mostly high-strength low alloy (HSLA) and microalloyed steels.