Effect Of Deoxidization Process On The Microstructure And Properties Of Low Carbon Steel

Using the high heat input welding is more and more popular in recent years. As the long holding time of high temperature and slow cooling rate in phase transformation during high heat input welding, the grain rapidly grew in heat affected zone, and the toughness of steel were very poor after welding, and it was easy to product welding crack, which is bad for the microstructure of steel. Oxide metallurgy technology has become the most effective technical for high heat input welding steel by significantly improving the microstructure of heat affected zone through stimulating intragranular ferrite in austenite grain by making use of fine inclusions in steel.In this paper, Ti and Mn were added in different order and different holding time. Ti, Zr and Mg were added in different amount, and then welding thermal simulation, strength-toughness tests were carried out after rolling.Quantitative metallographic and SEM analysis show that Mn first added induce more amount of inclusions, smaller average diameter, and fewer large inclusions. The main inclusions are TiN, and the composition of inclusions has not changed after30min. The acicular martensite and a little of acicular ferrite was found in this series of experiment.The characteristics of inclusions, mechanical properties and microstructure and property after welding are analyzed after adding different Ti and Mg. The results show that:(1) After adding0.032%Ti and0.01%Ti-0.01%Mg, larger amount of inclusions, smaller average diameter, and more inclusions per square millimeter can be found. The most of inclusions components are TiN-ZrO2-MnS-Al2O3, and TiN is the main body. When a little Mg is added, the components of inclusions are MgO-Al2O3-MnS-ZrO2-TiOx, and MgO is the main body.(2) Finer average ferrite grain size after adding0.032%Ti and0.01%Ti-0.01%Mg can be got. What’s more, they have better mechanical properties, and the tensile strength reaches respectively495MPa and500MPa. There are a lot of dimples in the fracture.(3) After welding thermal simulation, the grain rapidly grows, which is up to100μm in welding heat affected zone when not add Mg, and the impact energy is no more than10J, and it is brittle fracture. However, when adding a little Mg, coarsening rate of the grain is small, which is only20μm, and the impact energy is up to249J.