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"Wear It's At"
Volume 1, Issue 8
Monday, November 15, 1999
In This Issue
Greetings friends, clients and interested parties. Throughout the week I receive a number of interesting questions asked of me regarding hardfacing and wear. These questions are probably many of the same ones you have, so I thought I would share them with you. I will attempt to issue these as often as I can They have been edited for publication. Feel free to pose any
questions you might have and I will try my best to answer and if I cannot I will refer you to other sources. I will keep your identity confidential if you so desire.
I recently overlayed some ground engaging teeth made of 8630. The hardfacing material was 1 layer of Stoody Build UP and 3 layers of Stoody 102 open arc. The welding process was carried out under 400F preheat and interpass temperatures. After welding, the teeth were inspected, cleaned, painted and shipped.
There were no cracks in the hardfacing when they left the shop, but when they arrived at the customers facility, every tooth was cracked down to the base material. Was it faulty welding material, faulty base material, faulty procedure or something else?
It sounds to me like we have a hydrogen cracking problem here. It is also known as delayed cracking. It most often occurs when hydrogen, which is present in water, oil or grease is introduced into the weld pool during the welding procedure. Water or moisture can come from improper preheat, but that doesn’t appear to be the case here. Stoody makes very good, consistent products and I seriously doubt it is a faulty welding material problem. Having said that however, it is possible that the wires might have picked up moisture if they were exposed for a long period of time in humid or wet conditions. Another source of hydrogen is oil or grease on the component to be welded and has not been eliminated prior to welding. Here is what happens when hydrogen is introduced into the weld pool. Hydrogen, being a very small element, roams pretty freely within the weld pool and adjacent Heat Affected Zone (HAZ). When the weld cools the hydrogen is still in movement. Sort of like when you were a kid, and your parents closed the bedroom door thinking you were off to sleep. From outside the door, all seemed OK and quiet, but behind the door, there was plenty of activity. You were busy under the covers reading comic books with a flashlight. Well, the same is true in this case. The hydrogen atom is busy finding other hydrogen atoms, forming gas, and collecting on some defect well within the steel long after it has cooled. After
hours and perhaps days enough hydrogen collects and causes enough pressure to lead to cracking. This usually occurs well after the material has been welded and according to Murphy’s Law, occurs on the customers workplace. Check the cracks for paint. If the paint is not present inside the crack, it most likely occurred after the weld cooled and can be attributed to hydrogen.
How can this be avoided? Quite simple. Make sure all weld materials and base materials are dry and free of water, grease, oil and dirt. Use proper preheat and interpass temperatures. Slow cool the part to about 250F after welding and hold for 2 hours per 1 inch of thickness to allow the hydrogen to escape. After the time at 250F, cool to room temperature and check for hardness. It should be where you want it, and the component will be free of any hydrogen.
Hope this is some help to you if you are suffering from such a problem.
Have a great week.