CLADDING TECHNOLOGY SHANXI CO., LTDDevelopment of Sintered Flux for 1Cr13NiMoVNb Strip High-Speed Cladding
Overview and Background
The 1Cr13NiMoVNb alloy is a high-strength, high-toughness martensitic stainless steel widely used in high-speed strip cladding applications for components requiring excellent wear resistance and mechanical strength, such as rolling mill rolls, extrusion dies, and mining equipment. The development of a specialized sintered flux for high-speed strip cladding of this alloy is critical to achieving the desired overlay properties while maintaining high productivity. Sintered fluxes offer several advantages over metallic fluxes, including lower cost, better weldability, and the ability to tailor the flux composition to optimize the overlay properties.
Core Technical Approach
Sintered fluxes for strip cladding are manufactured by mixing powdered flux materials (such as lime, dolomite, fluorite, and iron oxide) with alloying elements (such as chromium, nickel, molybdenum, vanadium, and niobium) and then sintering the mixture at high temperature to form a porous, cohesive flux. The sintered flux is then used in conjunction with a strip of the desired alloy composition to produce a uniform overlay layer.
| Parameter | Typical Specification |
|---|---|
| Flux composition | CaO-SiO2-Fe2O3-Cr2O3-NiO-MoO3-V2O5-Nb2O5 |
| Strip composition | 1Cr13NiMoVNb (Fe-1C-13Cr-2Ni-1Mo-1V-1Nb, wt.%) |
| Flux thickness | 2-4 mm |
| Strip thickness | 3-6 mm |
| Welding process | Submerged arc welding (SAW) |
| Current type | DC, electrode positive (DCSP) |
| Current density | 30-50 A/mm² |
| Travel speed | 400-800 mm/min |
| Heat input | 0.3-0.8 kJ/mm |
| Overlay hardness | 45-55 HRC |
The key to developing a high-performance sintered flux for 1Cr13NiMoVNb strip cladding is the optimization of the flux composition and the sintering process. The flux must provide adequate deoxidation and slag protection while also contributing the desired alloying elements to the overlay. The sintering temperature and time must be carefully controlled to ensure that the flux has the appropriate porosity and strength for handling and application.
Flux Composition and Sintering Process
The flux composition for 1Cr13NiMoVNb strip cladding is typically based on a lime-dolomite flux with the addition of iron oxide, chromium oxide, nickel oxide, molybdenum oxide, vanadium oxide, and niobium oxide. The iron oxide serves as a deoxidizer and a source of iron for the overlay, while the chromium oxide, nickel oxide, molybdenum oxide, vanadium oxide, and niobium oxide provide the alloying elements required for the overlay.
The sintering process involves mixing the flux powders with a binder (such as bentonite or starch) and water, forming a slurry, and then drying and sintering the mixture at a temperature of 1000-1200°C for 1-4 hours. The sintering temperature and time are critical to achieving the desired flux properties. A temperature that is too low results in a flux with insufficient strength and porosity, while a temperature that is too high results in a flux with excessive density and poor gas permeability.
The flux must also be designed to have an appropriate viscosity and fluidity to ensure good slag coverage and protection of the weld pool. The slag must be easily removable from the weld surface after welding, and it must not contain excessive amounts of sulfur or phosphorus, which can cause hot cracking in the overlay.
Defect Analysis and Countermeasures
The primary defects in high-speed strip cladding with sintered flux include hot cracks, cold cracks, porosity, slag inclusion, and lack of fusion. Hot cracks are caused by the high sulfur and phosphorus content in the flux and the base metal, and can be prevented by using a low-sulfur, low-phosphorus flux and by preheating the base metal. Cold cracks are caused by hydrogen embrittlement in the high-hardness martensitic overlay, and can be prevented by controlling the interpass temperature and by using a low-hydrogen flux.
| Defect Type | Root Cause | Countermeasure |
|---|---|---|
| Hot crack | High S/P in flux or base | Use low-S/P flux, preheat base |
| Cold crack | Hydrogen embrittlement | Control interpass temp, use low-H flux |
| Porosity | Moist flux, contamination | Dry flux storage, clean base surface |
| Slag inclusion | Poor slag fluidity | Optimize flux composition and sintering |
| Lack of fusion | Low current density, high speed | Increase current density, reduce speed |
The flux must also be designed to have an appropriate chemical composition to ensure that the overlay has the desired mechanical properties. The carbon content of the overlay is determined by the carbon content of the strip and the flux, and must be carefully controlled to achieve the desired hardness and toughness. The chromium, nickel, molybdenum, vanadium, and niobium content of the overlay must also be carefully controlled to ensure that the overlay has the desired wear resistance and corrosion resistance.
Integration with Engineering Practice
In practical applications, the sintered flux for 1Cr13NiMoVNb strip cladding must be carefully selected and qualified for each application. The flux must be tested for its chemical composition, mechanical properties, and weldability, and the welding procedure must be qualified according to relevant standards such as NB/T 47014 or ASME IX.
The welding process for high-speed strip cladding with sintered flux requires specialized equipment, including a high-speed welding machine with precise control of the current, voltage, and travel speed. The welding machine must also have a precise strip feeding system to ensure that the strip is fed at a constant rate and at the correct angle to the base metal.
The quality inspection protocol includes visual examination, magnetic particle testing (MT) of the overlay surface, ultrasonic testing (UT) for bond quality, and hardness profiling across the overlay thickness. The overlay must have a hardness of 45-55 HRC, and the hardness profile must be uniform across the overlay thickness.
Study Insights and Reflections
The literature on the development of sintered flux for 1Cr13NiMoVNb strip high-speed cladding highlights the importance of flux design in achieving high productivity and high-quality overlay layers. The sintered flux offers a cost-effective and flexible solution for tailoring the overlay composition and properties, and it can be easily adapted to different welding conditions and base metals.
However, the development of a high-performance sintered flux is a challenging task that requires a deep understanding of the flux chemistry, the sintering process, and the welding process. The flux must be carefully designed to balance the competing requirements of deoxidation, slag protection, alloying, and weldability, and the sintering process must be carefully controlled to achieve the desired flux properties.
From an engineering perspective, the use of sintered flux for high-speed strip cladding offers significant advantages in terms of productivity and cost-effectiveness. However, the flux must be carefully qualified for each application, and the welding procedure must be rigorously followed to ensure reliable performance. The long-term durability of the overlay is also a critical consideration, and the flux must be designed to minimize the risk of cracking and spalling during service.