Laser beam welding of advanced high strength steels in the bainitic range for aerospace applications

• Grant number: 14/26930-7
• Support Opportunities: Scholarships abroad - Research
• Start date: December 01, 2015
• End date: May 31, 2016
• Field of knowledge: Engineering - Aerospace Engineering
• Principal Investigator: Milton Sergio Fernandes de Lima
• Grantee: Milton Sergio Fernandes de Lima
• Host Investigator: Stephen Liu
• Host Institution: Instituto de Estudos Avançados (IEAv). Departamento de Ciência e Tecnologia Aeroespacial (DCTA). Ministério da Defesa (Brasil). São José dos Campos , SP, Brazil
• Institution abroad: Colorado School of Mines, United States

Abstract

Advanced high strength steels (AHSS) and ultra high strength steels (UHSS) have been used in a number of applications such as automobile construction and petroleum and natural gas pipelines. In the aerospace industry, these steels are suited for use in motor engines, landing gears and armoring. Although these metallic alloys are well known in terms of microstructure and mechanical and chemical behavior, welding is still a huge issue. Welding usually loss the well balanced phases ratio and the microconstituents morphology and thus many macroscopic properties get unpredictable. This is particularly true in conventional processes, such as Gas Metal Arc Welding, Submerged Arc Welding and Resistance Welding, since the heat input cannot be strictly controlled. The use of laser beam welding greatly helps controlling the heat input and distortion in steel parts of complex geometries. Nevertheless, the high cooling rates observed during laser welding might produce martensite, which is known to be a hard and fragile phase in AHSS and UHSS. As long as the martensite transformation can be considered intrinsic to the welding practice, engineers usually apply post-welding heating treatments to produce tempered martensite, that is substantially tougher than the as-welded martensite. Heat treatment for large and complex components, such as subsea trees and rocket motors, are very expensive. Additionally, due to environmental regulations, salt bath treatments are no longer available for tempering and stress relief. One possible solution could be to produce high strength steels welds directly in the correct microstructural condition. According to the metallurgical experience, bainite is the best candidate to produce tough and reliable weld joints. However, the laser beam is too fast to generate bainite in AHSS and UHSS welds, and thus the piece should be heated in the bainitic range during and after the welding. The temperatures are sufficiently low (480-660°F) to be achievable in industries using conventional radio frequency or resistance furnaces. The overall objective of the proposal is to offer an alternative route to the joint of high strength steels through hot laser welding, avoiding martensite and inducing the bainitic transformation. The specific objectives of this proposal are the following: a) establish the thermodynamic and kinetic basis for the bainite formation in advanced high strength steel welds; b) Perform welds with metallurgical and tensile mechanical properties suitable for use in mechanical engineering and c) Prepare a report with detailed procedures to enable the manufacture of advanced steel parts with high mechanical strength by laser welding. (AU)

Scientific publications

(References retrieved automatically from Web of Science and SciELO through information on FAPESP grants and their corresponding numbers as mentioned in the publications by the authors)

LIMA, M. S. F.; GONZALES, D.; LIU, S.. Microstructure and Mechanical Behavior of Induction-Assisted Laser Welded AHS Steels. WELDING JOURNAL, v. 96, n. 10, p. 376S-388S, OCT 2017. (14/26930-7)

CORREARD, G. C. C.; MIRANDA, G. P.; LIMA, M. S. F.. Development of laser beam welding of advanced high-strength steels. INTERNATIONAL JOURNAL OF ADVANCED MANUFACTURING TECHNOLOGY, v. 83, n. 9-12, p. 1967-1977, APR 2016. (14/26930-7)