Cr-Mo-Ni HSLA Steel Welding HAZ On Microstructure And Properties Of Research

Mining machinery hydraulic support mainly uses the tensile strength is more than 670MPa HSLA and manufactured, but with lowalloy high strength steel strength increasing,the decrease of plasticity and toughness, welding stability becomes worse, the welding heat affected zoneperformance deterioration, cold cracking sensitivity on the rise,it is significant to study the low alloy high strength steel welding HAZ microstructure and properties. In this paper,the welding research and properties of thermaleffects on four kinds of low alloy high strength Cr-Mo-Ni steel used in the production of a mine machinery factory.In this paper, by using the four Cr-Mo-Ni low alloy high strength steel gradesare: Q690,AH70, BG690 and A700. Using Fomastor-D automatic rapid thermal expansion of the welding heat affected zone thermal cycle simulationinstrument, obtained at different cooling rate (i.e. the different welding conditions) welding heat affected zone, through the microstructure analysis,hardness testing methods developed four kinds of steel welding CCT diagrams based on the national standard "bolt welding; the cold cracksensitivity test method"and "Y shape crack sensitivity test method" to get the four steel cold cracking sensitivity and different restraint stress under the minimum preheat temperature of weiding,and simulates the working condition,the joint of four steels welding test and mechanical property test,the welding production provides certain theory and technical support.The results show that,through the analysis of the microstructure of four steels and welding CCT diagrams of the Q690, BG690 and A700, found that three kinds of steel in welding the fast cooling rate, HAZ is easy to get martensite organization, and high hardness,strong hardening tendency, while AH70 steel heat affected zone get martensite and bainite microstructure,hardenability is relatively low, but the four steel welded joints were producedand conditions of welding cold cracking; through "implant test" and "Y shapetest",when in the low degree of constraint conditions, the Q690 and AH70 twofor steel at room temperature (17 ?), without preheating welding, welding cold cracks can be avoided, and the welding of BG690 and A700 two kinds ofsteel, the steel preheating above to 60 ? can effectively avoid cold crack in the welding process; when the degree of constraint is high. The weldability of AH70 steel, the most excellent, only needs to be heated to 60 ?,it can avoid the welding cold cracking, while Q690, BG690 and A700 three kinds of steelmust be the preheating temperature up to 100 ?, can effectively avoid thewelding cold cracking; pass Detection of mechanical properties of welded jointof four steel, found in previousexperiments to determine the preheating temperature of four kinds of high strength low alloy steel welding,welding process is not stable, defects of cold cracking, the mechanical properties of the welding joint can meet the production requirements of enterprises.