Research On The Weidability Of WELDOX960

As one of the newly developed high strength low alloy structural steel, WELDOX960 is characterized by fine grain,super-metallurgical purification and homogenization,high strength and toughness,and it is widely applied in the field of mine-machine,bridge,railway and mobile crane etc.This article according to the actual working condition,and basis on the principle of "the low strength match" select welding wire E-FK1000 which is produced by Sweden as well as the high strength steel of WELDOX960 to design the welded process which Ar+CO₂ mixed gas to protect.The preheating temperature 80～100℃,100～120℃,120～150℃respectively carries on the multi-layers and multi-passes welding.Mechanical properties tests(tensile test, bending test and impact test)and crack tests(Y-groove and CTS cracking test,peak hardness of HAZ test) were carried out to study its weldability,and microstructures of fusion zone,weld metal,HAZ and fractography of welded joint were investigated by means of optical microscopy and SEM,the effect of processing factors and microstructures of welded joint on strength and toughness of welded joint was analyzed.The experimental result shows that cold crack and the thermal crack sensitivity of WELDOX960 is small at the experimental condition,and the attachment tensile strength,the anti-impact and so on meets the design requirements.The welding preheated temperature has greatly influenced to the joint performance.The microscopic analysis indicated that the low-carbon martensite within weld metal and the heat-affected zone is basic condition to keep high strength and the toughness of the joint. With the welding technology optimized,so as to keep the welded joint structure containing a few low-carbon martensite,thus the strength and toughness of joint was guaranteed.This topic basis on tests filler metal and the base material,form which the result may know that the butt joint,the corner joint and the lap joint surface and the cross section crack rate is zero,which it shows that the weldability of the steel is feasible. According to factory standard QJ/CQ05.01.00-93,at the room temperature,the low temperature(-20℃,-40℃) the joint properties attained the value to be able to guarantee the design request.The experiment also proved that selecting E-FK1000 with 1.2mm diameter as welding wire to weld the WELDOX960 steel,of which welded joint machine capability feasible.According to the carbon equivalent value and the highest hardness value of HAZ,the material must be preheated during welding,the preheating temperature guarantee the welded joint quality for choosing 130～150℃,the layer temperature should not be over 250℃.Along with the weld structure rigidity increasing, the preheating temperature should be enhance to 150～180℃,and after welding it may not keep the temperature,but the forced cooling can not be conducted to the welded joint.The controlled atmosphere must use mixed gas 80%Ar+20%CO₂,and it has not been to use the rich argon gas allocated proportion afflux.If heat temperature up to 600～650℃,the material properties basically maintains to be invariable as the performance parameter of 100kg level.When heating up to 800～850℃,the material properties reduces,tensile strength value equal to 80kg level material.Therefore,the steel heat up with the hot sizing,the highest heating temperature should be lower than 650℃.