welding carburized, high carbon steel

By concutter Date 04-11-2003 18:47

Hey all, does anyone have any experience with welding to carburized steel? Especially one with a high initial carbon content? We weld the steel to Cobalt, and have had some very sporadic porous welds. We have narrowed the issue down to some sort of an interaction/contaminant in the material (presumably the steel, not the Cobalt). The steel is cold rolled and oil hardened, then formed and heat treated. We have found if we ECM the material (Hydrochloric bath plus electrolydic application), we can 'cleanse' the steel of the contaminant and weld well... but now they flash rust. In addition, the acid bath and electrolydic process can induce hydrogen embrittlement. Any insight to welding this this type of steel is welcome. Thanks in advance!!!

By kk_chiong (*)

Date 04-13-2003 12:55

How thick is the steel and in what type of structure? Can you grind the surface to remove the harden layer before welding the cobalt materials on to this carbon steel. Grinding off the top layer is important to reduce the carbon content and others impurity if any before applying the cobalt. May I know the purpose of applying cobalt on to these surface (for what kind of prevention or solely for joining purpose). Have you ever try to used cobalt from other supplier and see what is the result. As I experience, impurity in cobalt always give porous weld. (Experience this problems with Stellite 1 materials with oxy-acy weld. Hope you can solve your problems very soon.

By concutter Date 04-14-2003 15:16

The app is a diamond cutting tool, much like a circular saw... a steel core with diamond impregnated Cobalt 'segments' welded to it. The steel is about 1.25mm thickness, and we want to penetrate all the way through it. The cobalt is in the form of a sintered-power block. We have several vendors of this product and require specific density levels. We too weld to Stellite, and have no problems with that process. It's something in our heat treat with the thinner steel that gives us problems. We have tried some grinding, but with results no different than production. We have found we can weld with low penetration (wide spot size and lower power) and get 'nice' results, but they don't have the strength we need. When we push to get the penetration and strength, the welds become porous. We'll keep trying. If nothing, we can send out for a chromate treatment. They have a descalling process in the chromate that solves our problem, they don't rust, plus they are esthetically pleasing when they are finished. Thanks for the input... take care.

By arcblue (*)

Date 04-15-2003 14:47

The actual weld defect is porosity? I am a little surprised given the metallurgical factors involved (high carbon, Cobalt & such) that cracking is not an issue.

Consider the mechanism for the formation of porosity, you have to chemically reduce a substance (manganese oxides, carbon, hydrocarbons, something in or on the material) from the elevated temperature interaction of the welding event. Even if it is a high energy density process like LBW, there is a required interval of time for “out gassing” within the weld pool. After solidification occurs the “trapped gas bubbles” may be deemed a “defect”. So if you do not feel like having pores in your welds consider increasing the time of solidification.

Short answer: repass the welds
If you rerun the weld it can drive out the pores and increase the weld penetration as well as improve the weld appearance. In EB welding it is called a cosmetic pass but it is a really useful means of cleaning up a weld.