Research On The Weldability Of B-HARD360 High Strength Wear Resistant Steel

B-HARD360 is a new kind of high strength low alloy steel, due to special heat treatment process and alloy component design, it is with high strength, high toughness, excellent formability and wearability, which has been widely used in mining machinery, earthmoving machinery and excavator industry. Many defects may be crised during welding B-HARD360, including cold cracks, joint softening, which restricted the promotion of this steel. In this paper, B-HARD360 used in the scoop of excavator has been studied. B-HARD360 was welded by gas metal arc welding without pre-heating, the mechanical properties, the microstructure and cracks of welded joint are researched to analyse the relationship between welding parameters and abo-mentioned aspects.Oblique Y-groogve cracking tests are performed to analyse the influence of heat input on the cracking sensitivity of B-HARD360 joints. The penetration ratio of welded joint has been calculated. The result shows that with the increase of welding heat input, the cracking ratio of joint increased at first and then decreased. The cracking ratio is over 20%, when welding heat input is too high or too low. The penetration ratio of welded joint is about 35% when heat input changed. The heat input have great impact on the cold cracking sensibility of B-HARD360 welding joint, Choosing a suitable heat input can reduce the cracks. The preferred welding heat input is about 12-19kJ/cm.The influence of welding heat input has been discussed on microstructure and mechanical property of the B-HARD360 welding joint. The microstructure of weld seam contains acicular ferrite, proeutectoid ferrite and ferrite side plate. The microstructure of HAZ coarse grain zone and fusion-line is bainite and martensite, with the increase of heat input from 10.4kJ/cm to 30.2kJ/cm, the acicular ferrite decreased from 80% to 20%. The shape of proeutectoid ferrite changed from strip to bulky block. With the increase of heat input, the amount of martensite in HAZ coarse grain zone and fusion-line reduced rapidly, and the amount of bainite increased. With the increase of heat input, the vickers-hardness, strength and toughness of the joint decreased, meanwhile the width of softened layer and soften degree increased.Controlled thermal severity test and straight Y-groove cracking test were conducted to research the influence of heat input on the cracking sensitivity of SHT1080 and Q460 joints, we laid special stress on analysing the microstructure and vickers-hardness of the welding crack. The microstructure of HAZ coarse grain zone and fusion-line in SHT1080 joints contain bainite and a little martensite, martensite disappeared when heat input increased, which caused a low hardness. When the heat input increased, the microstructure of HAZ coarse grain zone in Q460 steel joints remained martensite, which caused stability hardness. The microstructure of HAZ coarse grain zone in Q460 steel joints is martensite with 9.8kJ/cm heat input, which caused a 43% cracking ratio.