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"Wear It's At"

Volume 2 Issue 5

Monday, August 7, 2000

 

In This Issue

1. Welcome and Thanks
2. Chromium Carbides Part III
3. Beer Marinade


1. Welcome and Thanks


A hardy hello and a warm welcome to all our new subscribers.  I just want to let you know that any and all comments and contributions will be cordially accepted.  If you have an article or a topic you would like to share with others, please email or fax us and we will include it in one of our issues.


2. Chromium Carbides – Part III

In previous issues we discussed the various types of chromium carbide deposits.  Each type being dependent upon the levels of both Chromium and Carbon and the unique combinations that result in a wide range of wear resistance.  In this issue I would like to address some of the unique attributes of chromium carbide deposits.

You may recall that chromium carbide deposits are basically very hard particles buried in a tough matrix.  The hard Chromium Carbide particles are what give these deposits their great wear resistance and the matrix is what holds it all together.  Despite this great combination, these deposits “Check Crack”.  What is Check Cracking?  A check crack is nothing more than a crack that develops perpendicular to the bead direction. Let’s face it, these deposits are brittle and they crack because they have no ductility.  These cracks usually go to the bottom of the deposit and stop at the interface of weld metal and base metal.  They also act as stress relievers.  Without them there would be a danger of spalling.  Spalling is the separation of the deposit from the base material.  So check cracks are good, at least from a welding standpoint.  The downside of check cracking is that they accelerate abrasive wear.  A free edge anywhere invites chipping, even on a microscopic scale. 

Check cracking can be controlled by chemistry and heat.  Usually the higher the alloy content, i.e. carbon and chromium, the more numerous the check cracks.  While most high chromium carbide deposits are limited to two layers, inducing the volume of check cracking allows multiple layers to be deposited.  A tight and numerous check cracking pattern can be achieved by keeping weld beads thin and flat, and by quenching in a water jet or water mist.  This practice is highly successful in the hardfacing of Nihard coal pulverizer rolls; an otherwise un-weldable type material.  The number of layers deposited using this technique is unlimited.  Despite the fact that numerous check cracks contribute to accelerated abrasive wear, the trade off for multiple abrasive resistant layers is quite acceptable.  I should mention that it is possible to deposit “check crack free” weld metal using the opposite approach than what has been described, but that is another subject matter, and perhaps a topic for further issues of “Wear It’s At”.

3.  Coming Attractions

In the next issue I plan to continue our discussion about Chromium Carbides and will address the topic of Complex Carbides.   These are cousins to the Chromium Carbide family.  They add a unique advantage over traditional chromium carbides when it comes to high temperature wear. 

So until then, have a great day.  Thanks for your interest and I’ll be looking forward to our next meeting.  Be sure to visit our sponsors web sites for more information.

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Our Sponsors

Bohler Thyssen Welding USA Inc.  (http://www.btwusa.comis a single source supplier for practical high quality electrodes, wires, and fluxes.

Postle Industries Inc.  http://www.postle.com
Postle offers a complete range of hardface welding alloys to protect equipment from all types of wear.

Sure Alloy Steel Corporation (http://www.surealloy.com)
Wear Control - Design, engineering, and fabrication with over 40 years experience.