Metallurgical modifications and residual stress in welded steel with average carbon content

Abstract

Welded joints of metallic materials are subject to residual stress and metallurgical transformations, in particular in the thermally affected zone (TAZ), with the possible formation, especially in steels with a high carbon content, of brittle structures and a loss of tenacity. The loss of tenacity in the TAZ facilitates the formation of cracks and possible brittle fracturing or failure, following the progressive propagation of the cracked zone. Moreover, residual stresses may cause premature failure in structural elements as they have an influence on the conditions of collapse, for example on account of instability of the compressed members. In this work, the order of magnitude of residual stress is estimated for a specific case, identifying by means of an empirical–experimental approach, the portion of material more susceptible to the formation of cold cracks under the combined effect of residual stress and brittleness of the microstructure.

Keywords::

• carbon steels
• cold cracking
• cooling rate
• hardness
• hardness tests
• heat-affected zone, martensite, mathematical models
• measurement
• mechanical properties
• mechanical tests
• metallography
• microstructure
• residual stresses
• MMA welding
• stimulating
• transformation
• weldability

Additional information

Notes on contributors

S. Missori

Severino Missori is an Associate Professor at the Department of Mechanical Engineering at the University of Rome ‘Tor Vergata’ for the ING-IND/21 disciplinary group. From 2001-2002 to the present he has been teaching Metallurgy on the Mechanical Engineering degree programme. Author of over 80 scientific papers, he carries out research activity in the following fields: welding of metallic materials with traditional and innovative processes, metallurgy of welding, mechanics of fractures, special steels and light alloys.

G. Costanza

Girolamo Costanza is a researcher in the ING-IND/21 sector (metallurgy) in the Department of Mechanical Engineering at University of Rome ‘Tor Vergata’, where he teaches a course in Thermo-mechanical treatments of Metals. His main fields of research are the production and characterisation of metallic foams; metallurgy of welding; the analysis of the effects of small-charge explosions on cfc metals; composite materials; shape memory forms to be applied as sensors/actuators. He is the author of 65 scientific publications.

A. Sili

Andrea Sili, a Full Professor of Metallurgy at the Faculty of Engineering at the University of Messina, carries out research activity in the following fields: mechanical properties of steels and their behaviour when fracturing, behaviour under fatigue of metallic matrix composites and their surface treatments, mechanical properties of welded joints, the development of new, laser-beam or hybrid laser-electric arc welding techniques with the use of filler materials in the form of powders. He is the author of over 100 scientific papers.

M.E. Tata

Maria Elisa Tata graduated in Mechanical Engineering and was awarded a doctorate-level qualification in Mechanical Metallurgical Engineering at the University of Rome ‘Tor Vergata’. She is a confirmed researcher in the ING-IND21 sector (metallurgy) at the University of Rome ‘Tor Vergata’, where she teaches a Materials for Special Applications course. Her main research topics are the study of ferritic-martensitic stainless steel for applications in nuclear fusion reactors; plastically deformed stainless steels; the production and characterisation of metallic foams; effects of explosions on cfc metals; composite materials; shape memory alloys. She is the author of 94 scientific publications.