Assessment of the Effect of Laser Welding on the Properties and Structure of TMCP Steel Butt Joints

Abstract

The research work and related tests aimed to identify the effect of filler metal-free laser beam welding on the structure and properties of butt joints made of steel 700MC subjected to the TMCP (thermo-mechanically controlled processed) process. The tests involved 10-mm thick welded joints and a welding linear energy of 4 kJ/mm and 5 kJ/mm. The inert gas shielded welding process was performed in the flat position (PA) and horizontal position (PC). Non-destructive testing enabled classification of the tested welded joints as representing the quality level B in accordance with the requirements set out in standard 13919-1. Destructive tests revealed that the tensile strength of the joints was 5% lower than S700MC steel. The results of tensile tests and changes in structure were referred to joints made using the MAG (Metal Active Gas) method. The tests of thin films performed using a high-resolution scanning transmission electron microscope revealed that, during laser beam welding, an increase in dilution was accompanied by an increase in the content of alloying microadditions titanium and niobium, particularly in the fusion area. A significant content of hardening phases in the welded joint during cooling led to significant precipitation hardening by fine-dispersive (Ti,Nb)(C,N) type precipitates being of several nanometres in size, which, in turn, resulted in the reduction of plastic properties. An increase in the concentration of elements responsible for steel hardening, i.e., Ti and Nb, also contributed to reducing the weld toughness below the acceptable value, which amounts to 25 J/cm2. In cases of S700MC, the analysis of the phase transformation of austenite exposed to welding thermal cycles and the value of carbon equivalent cannot be the only factors taken into consideration when assessing weldability.

Heat Source Models in Numerical Simulations of Laser Welding

“…However, this also causes a problem in choosing the right device for a particular application, especially taking into account the constantly shortening response time required by the market. The degree of complexity of current, modern welding technologies based on this type of equipment, along with the mentioned advantages and requirements, forces engineers and constructors to take a different approach to the design stage and search for modern tools supporting the preparation of welding and heat treatment technologies themselves [ 2 , 3 , 4 , 5 , 6 , 7 ].…”

Remote Fibre Laser Welding of Advanced High Strength Martensitic Steel

“…Steel had a carbon equivalent CE of 0.38%, calculated using equation CE = C + Mn/6 + (Cr + Mo + V)/5 + (Ni + Cu)/15 [2,18]. Due to the low weldabilty these steels are welded with a preheating or low energy input or PWHT is used to improve the microstructure and properties of welded joint [11,[13][14][15]18,24].…”

“…Steel had a carbon equivalent CE of 0.38%, calculated using equation CE = C + Mn/6 + (Cr + Mo + V)/5 + (Ni + Cu)/15 [2,18]. Due to the low weldabilty these steels are welded with a preheating or low energy input or PWHT is used to improve the microstructure and properties of welded joint [11,[13][14][15]18,24]. The implemented robotic laser system consisted of: a fibre laser YLR-400AC (IPG Photonics, Oxford, MA, USA) with power 400 W, wave length 1070 nm and beam quality M2 = 1.03, a head for a remote laser welding was model RLSK (HighYAG, Oxford, MA, USA), a robotic arm YR-MC2000-A00 (Yaskawa, Ribnica, Slovenia), and a 3-D module (with accuracy of 0.2 mm).…”

“…The tensile strength and elongation of laser welded specimens remained the same than that of the base materials. Górka [24] laser welded 10 mm thick butt joints made of steel 700 MC subjected to the TMCP (thermo-mechanically controlled processed) process. Laser welding was done using linear energies of 4 kJ/mm and 5 kJ/mm.…”

Autogenous Fiber Laser Welding of 316L Austenitic and 2304 Lean Duplex Stainless Steels

“…Lasers as a heat source have been widely applied in industrial processes [1,2]. Currently, they are used for welding, cutting, remelting, and various processes with surface modification of materials [3][4][5][6]. Laser sources are characterized by: high energy density, high efficiency, large temperature gradients, high repeatability of the process, and formation of a narrow heat affected zone (HAZ).…”