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 Volume 1    Issue   4

October 25, 2001

The welding show in Essen, Germany, despite the overshadow of the Sept. 11 events, was a huge success.  This show is active every four years and it was quite evident that all participants were well prepared.  Approximately 93,000 attended the event.  This was down from the previous show in 1997, but many folks from the US and the Americas could not get flights at that time.  I have been in the hardfacing and welding business for over 30 years and this was my first trip to the Essen Show.  I was quite impressed by the size of it all.  Much bigger than AWS shows by a wide margin.  I learned a lot, saw a lot, and ate a lot.  Great show.  Great Food.   If you have the opportunity to visit the next one four years from now, make it a point to go. 

The topic of hardfacing alloys is not complete without a discussion of Chromium Carbide alloys.  Although many think of hardfacing alloys as strictly the Martensitic types as we discussed in a previous issue, it is the Chromium Carbide class of alloys that really shine when it comes to abrasion resistance.  There are a number of alloys in this class, each having its own abrasion resistance and impact properties.  Increasing abrasion resistance is usually associated with decreasing impact resistance. 

If there is one property that characterizes these alloys, it is their CHECK CRACKING tendency.  What do I mean by check cracking?  Check cracking is simply a crack that develops perpendicular to the length of deposited bead as it cools.  Very often one can hear the "ping", "ping" emanating from the deposit as it cracks.  The crack goes down to the base material and in most cases, stops there.  If the base material is very hard and brittle, there is a chance that the crack will continue into the base material and possible cause a major crack or failure.  Ductile deposits, such as the Austenitics we discussed in the last issue are used here as a buttering layer that will blunt all check cracks.  Check cracks are really quite good.  I know, you're probably saying to yourself, "Cracks in weld metal are GOOD?"  Yes, that is what I said.....for the simple reason that they relieve stresses within the deposit itself.  One must remember also that hardfacing alloys are not used for joining, where cracks are certainly undesirable. If the hardfacing deposit did not check crack, it is quite possible that the stresses would build to such a level that under-bead cracking would occur and possibly lead to spalling or complete separation of the weld bead from the base material.  By depositing very thin wide beads and maximizing the cooling rate, it is possible to enhance the number of check cracks.  The thinking here is; the more check cracks, the more stress relieved, the less likelihood of spalling.  Sooo, cracks are GOOD.

Metallurgically speaking, Chromium Carbide alloys are the result of adding substantial amounts of Carbon (~3.0%) and Chromium (>18%) to Iron.  Small amounts of Manganese and Silicon are also added.  In the alloys where Carbon and Chromium are minimum, Austenite forms first as the deposit cools, followed by Chromium Carbide formations at grain boundaries.  

Question Wait a minute--, didn't we say that Austenite was a tough structure in our last Issue (3)?    

Answer: Yes, we did.  

Question: Then how come these alloys are so brittle and check crack?

Answer:  Austenite is tough in these alloys also, however the Chromium Carbide that forms on the grain boundaries weakens them drastically and causes the deposit to check crack.

As Chromium and Carbon is added in greater proportions, Chromium Carbide is formed first and then followed by our old friend, grain boundary carbides mixed with Austenite.  This makes for great abrasion resistance but because of  less Austenite, the impact and toughness properties are much less.  Depositing more than two layers is not recommended because of the lack of ductility. 

Within this class of alloys resides a subgroup know as Complex Carbide alloys.  Complex Carbide alloys are really Chromium Carbide alloys with additions of exotic elements such as Columbium, Molybdenum, Tungsten, Vanadium and Titanium.  These elements are added to enhance abrasion resistance at both room temperature and high temperatures (~1500ºF).  Complex Carbide alloys are complex in themselves and probably beyond the scope of this newsletter.  Perhaps we can address these alloys in depth at a later time.

Where can we use these alloys?  Wherever we encounter high abrasion and medium to light impact:

Tampers, Coal pulverizing hammers, Grizzly bars, Bulldozer blades, Dragline buckets, Power shovel buckets and teeth, Road rippers, Scraper blades, Dredge bucket lips, Dredge pump side plates, Dredge cutter head & teeth, Clamshell bucket lips, Crusher jaws, Crusher cones, Gyrator crusher mantles, Muller tires, just to name a few.

Within this group of alloys, increasing hardness is usually associated with increasing abrasion resistance, but is not always the best indicator.  Hardness numbers can be very misleading in this class of alloys.  Abrasion test results are more reliable and definitive.   We will cover hardness and abrasion testing in later Issues.

Chromium Carbide alloys come in a variety of forms; Open Arc & Gas Shielded Wires, and Stick Electrodes.  Wire sizes range from .045" to 1/8", while stick electrodes range from 3/32" to 3/16".  Smaller size wires are ideal for shop work as well as field work.  Most can operate from a Constant Current (Drooper) DC Power Supply and a voltage sensing wire feeder or a Constant Voltage DC Power Supply.  The following Postle wires and electrodes are in the Chromium Carbide class.  Abrasion resistance increases as the numbers increase below.

1. Postalloy 2820SPL (Open Arc & Gas Shielded)
2. Postalloy 2832SPL (Open Arc or Gas Shielded) and Postalloy 214 Electrode
3. Postalloy 2834SPL (Open Arc or Gas Shielded)
4. Postalloy 2836SPL* (Open Arc or Gas Shielded) and Postalloy 248CB Electrode

* Complex Carbide

Data sheets are available on our Website .  Feel free to browse.  If you don't find what you are looking for, just email me, Bob Miller. 

In Issue 3, I spoke of an article that I wrote regarding how hardfacing is a part of everyday life and is related to just about everything we touch.  I have had numerous emails requesting the article.  It is now available as a PDF file on our Website.  It is in a self extracting Zip file that will automatically download the file to your desktop so you can find it easily.  Just click here and your downloading process will start.  

Thanks for the interest.

Thought you might enjoy these signs.  Have a great day, and I will be talking with you again real soon.

*** On a plumber's truck: "We repair what your husband fixed."

*** On the trucks of a local plumbing company in Pennsylvania:

         "Don't sleep with a drip. Call your plumber."

*** Pizza shop slogan: "7 days without pizza makes one weak."

*** Outside a muffler shop: "No appointment necessary. We

         hear you coming."

*** In a veterinarian's waiting room: "Be back in 5 minutes.

         Sit! Stay!"

*** On an electrician's truck: "Let us remove your shorts."

*** On a maternity room door: "Push. Push. Push."

*** At an optometrist's office: "If you don't see what

       you're looking for, you've come to the right place."