Research On The Mechanism Of Welding Heat Input On HAZ Structure Of Ship Plate Steel Containing Mg In Different Thicknesses

Large heat input welding has a huge heat input,and it takes a long time to dissipate heat at HAZ.There is a serious growth of austenite grains in HAZ,which causes a significant decrease in the plasticity and toughness of the steel welding area.Therefore,by analyzing the influence of temperature change on the second phase particles,the influence of welding heat input on the welding heat-affected zone is studied.Through the welding heat simulator to simulate different welding heat input,the HAZ metallographic structure analysis results show that the metallographic structure and the original austenite grains are the smallest under the 200 k J/cm heat input.The second phase particles of HAZ are mostly rectangular.The typical elemental composition of the second phase particles is Ti N particles,Ti,Nb(C,N)particles and Ti,N,Composite two-phase particles formed by Nb,Mo and Mg.The size of nano-scale second phase particles is mostly below 80 nm.The calculated min austenite boundary stop growth size is 38.93 ?m.A model of 35 mm plate thickness under different input of input energy is established.The analysis results show that with the increase of input energy,the duration of high temperature at position increases.At 50 k J/cm and 300 k J/cm line energy,it takes 61.5 s and153.5 s to decrease the temperature from the highest temperature to 900 ? at 1 mm from upper surface line.At 7 mm,45 s and 120 s are required respectively.With the increase of heat input,the duration of HAZ high temperature increases,resulting in a decrease in the pinning of the second phase particles in the welding heat-affected zone.Establish 35 mm,40 mm and 50 mm plate thickness models at 200 k J/cm line energy.As the thickness increases,high temperature duration decreases.It takes 118.5 s and 48.5 s for the 35 mm and 50 mm thickness models to decrease from the highest temperature to 900 ?at 1 mm from the fusion line;112 s and 30.5 s at 3 mm.It shows that the thicker the steel plate,the better the heat dissipation,the higher the applicable welding heat input.Figure 68;Table 15;Reference 48...