Studies On Strength And Toughness Of Ultra-high Hardness,Wear-resistance And Cracking-resistance Hardfacing Materials

The cold working roll repairing is always a meaningful research project in the metallurgical industry. Ultra-high hardness, high cracking resistance, strength and toughness are desired by the deposited metal, whereas the toughness and cracking resistance decrease significantly with the hardness going up and the requirement from the cold working roll can't be satisfied. It is imperative to explore the surfacing material with ultra-high hardness, wear-resistance and crack-resistance. Based on phase transition strength, solution strength, grain-refining strength and precipitation strength of metallic material, mathematic models on hardness, wear volume, impact work and cracking length of deposited metal with alloying elements (C,Cr,Mo,W,V) are established by first applying quadratic rotary regress optimum design in developing surfacing flux–cored wires alloy system. Qualitative and quantitative analysis between deposited metal performances and alloying element factors in flux-cored wires are also discussed. Surfacing flux-cored wire prescription for cold working roll repairing is optimized. It is revealed by optic microscope (OM) and scan electronic microscope (SEM) that the microstructures of deposited metal mostly consist of reticular white eutectic structure along grain boundary, light gray quenched martensite, black gray temper martensite and fine disperse precipitated multielement carbides with shapes of block, herringbone and strip. Strength and toughness mechanism of ultra-high hardness surfacing materials are brought forward according to the cracking in deposited metal and impact fracture observed. Through different temper processing of deposited metal, mathematic model between precipitation carbides particle and temper temperature is set up in terms of phase transition thermodynamics. Calculation regarding decomposing of retained austenite and quenched martensite is carried out, and cementite precipitated from martensite and austenite is also investigated. According to the microalloy technology applied and the constituents of surfacing metal designed from structure project aspect, the effects of different modificator such as Y-based rare earth alloy, rare earth oxide, titanium, niobium and tantalum on surfacing performances are discussed and different additions optimum are generated. It is concluded that strength and toughness can be increased by using microalloy technology to fine grain, improve shape and distribute of eutectic carbides, homogenize composition, and modify inclusion. Better surfacing performances can be acquired by first applying electromagnetic stirring in improving primary crystallization of deposited metal. By working on the relationship with weld shape, quantity and dimension of inclusion and microstructure, the optimized electromagnetic parameters (electromagnetic stirring frequency, magnetic induction intensity) have been found.