May 2021 Volume 3

MATERIALS

Material Considerations for the Flood Welding Process

By David Mills and Terry McInerney The process of flood welding has been in use for over 70 years. Developed as a solution to repair and refurbish existing die blocks, although it sounds simple, it is a highly complex process. There are specific rules for correctly applying the process that need to be followed to effectively flood weld a die block. Let’s examine. Preheating, Welding, and Tempering When flood welding, the used impression is removed by milling, or arc air scarfing, to the point where none of the existing cracks appear. Before flood welding begins, the die block must be preheated to 800- 900 degrees, andmust maintain ample heat during the flood welding. Weld applications include 'stick' type electrodes and MIG welding units. Welding can be continuous. Once the weld stops and the puddle is in the orange state, peening can begin. The process is continued until the weld is just above the original die height. When this height is reached, the die must be post heated at 800 to 900 degrees for four to six hours then slow cooled to an ambient temperature. Once cooled, the die is stress relieved in a furnace at 1050 degrees for one hour per inch of thickness. This process tempers the weld and stress relieves the die.

All steels have a carbon content, the carbon transforms the elements to carbides in the order of their melting temperatures, referred to as “the call to carbide”, with chrome being the lowest and Tungsten and Vanadium being the highest. However, many do not consider, is the fact that lower carbon tool steels, such as H-13, do not have enough carbon to fully transform the molybdenum to carbides, but get all the chrome, so the remainder goes to the matrix. M-2 and M-4 on the other hand, with over 1.0 carbon have enough to transform all the elements to carbide. M-2 is fully hardened and is therefore brittle and not heavily used as a weld material for flood welding forge dies. All forging dies have unique differences; shallow, deep, thin wall sections etc., and some dies may have all three types of sections in the same die. Flood welding can enhance the different areas by using weld materials suited for the area. Normally shallow dies can be welded with material that reaches the high 40s to low 50s in RC values. Deeper dies can be welded with materials that are slightly harder than the parent material with better heat resistance. Contact time also plays a role in what product to use. The longer the hot steel is in contact, the more reason to use cobalt- enhanced products. Weld Overlays A somewhat newer approach to enhancing die life is weld overlays. It uses less material, but the die preparation is just as important as the procedures for flood welding. All cracks must be removed by milling with either ORBIT EDM or selective scarfing. Pre-heat and post- heat operations are the same as they are with flood welding. There are two welding approaches; the first is to enlarge the desired section or entire die by .060 to .100 in all directions, then weld a 3/16" to 1/4" deposit over the areas. An H-11 or a cobalt-based product is typically used. Notably, the arc at the weld point at 3000 degrees does a good job of drawing carbon from the parent material and remixing it with the higher elements in the product. In cases where there is a certain element in the parent, like Molybdenum or Tungsten, those elements become more fully transformed to their respected carbides. Deeper penetration equals a better mix at the die surface. As for cobalt products such as Stellite 21, the remaining depth back to the surface is critical, (not more than .060). This is called the Fusion Zone and stops the softer cobalt from creeping or mushrooming on flash-lands and extrusion tooling. Again, product choices are determined by what the end-user wants to accomplish. Overlays generally enhance heat resistance, which extends die life by decreasing premature surface breakdown.

WeldMaterials Weld material choices are critical to the process. The selections are made by identifying the premature failure modes or the overall improvement desired. There are many improvement options available from replacing the parent material to enhancing element content. The typical element spectrum contains chrome, nickel, molybdenum, tungsten, vanadium, and cobalt as desired additions to improve performance. In the elements named, all but cobalt and nickel create carbides, as they are in the matrix that hold the carbides in place. Depending on the mix and availability of the elements, determine how they will improve die wear and heat resistance.

FIA MAGAZINE | MAY 2021 23