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"Wear It's At"

Volume 2, Issue 3

Monday, April 3, 2000

 

In This Issue

 

1. Welcome
2. Carbides - Part 1
3. Interest Topic on Sleep


1. Welcome

Well it's been a few weeks since our last get together.  And during that time we have had quite a few new subscribers added to the list.  Welcome to all.


2. Carbides - Part 1

Due to numerous requests, I have put together a series of articles on Carbides.  This is a vast subject area and encompasses many base materials other than Iron, but for the preliminary discussions, I will focus on the Iron Base Alloys.


There probably isn't a single element that is so important to metallic wear resistance than Carbon.  Carbon in Iron does two things; (1) Forms Martensite, a very hard phase of Iron, (2) Forms Carbides, hard components made up of a Metal (M) and Carbon (C).  For clarity we will refer to Carbides in general as MC, the M standing for Metal, and C for Carbon.  There are many forms of Carbides, depending upon the Metal component of the Carbide.  Each has its own properties.  For example, Iron and Carbon form Fe3C, Chromium forms Cr23C6, Cr3C2, etc.  The point is not how many there are, but which ones are stable in metallic alloys and which ones contribute to abrasion resistance.  

Before we jump into the real popular Carbides such as Chromium, Tungsten, Titanium, etc. Let's explore how carbon hardens steel.  Because it is from there we can better understand how Carbon reacts with Metals to form this important group of compounds.

Carbon is very fickle.  It wants to marry with any Metal atom, if given enough time and temperature.  It is so fickle, that it will often partition itself between many Metal atoms in the same alloy.  Polygamy, if you will.  When robbed of this ability to marry a Metal atom, and instead becomes entrapped in a Metal matrix, it becomes very angry and causes tension.  This tension results in a very hard matrix.  And this is exactly what happens in quenched Iron that contains Carbon.  

In the molten state, the Carbon floats around amongst its potential partner, Iron.  As the temperature is lowered into the solid state, it continues to roam around.  It is from this high temperature solid that determines the matrimonial state of the Carbon at room temperature.  If slowly cooled to room temperature, it will get its way and marry an Iron atom to form Iron Carbide.  But if it is quenched in water or oil, it becomes entrapped in the Iron Atom Matrix and results in a matrimonial state that is highly stressed.  This stressed state is known as Martensite.  Generally, the higher the carbon content, the higher the Martensite Hardness.  Martensites are a major contributor to hardfacing products and are usually used where metal to metal or frictional  wear is a problem. They are tough and hard.  But let's look at the Iron Carbide (Fe3C).  This is a hard carbide and forms when cooling rates are slow enough or when there is a great deal of carbon, usually over 0.50%.  These alloys can approach the Cast Iron varieties and are valuable for certain types of grinding media.  But just adding Carbon to the melt can has other consequences, which is beyond the scope of this article.  Suffice it to say that Chromium and other Metals help solve the problems of just adding Carbon.

It is here then, where we will break off and continue our exploration of Carbides until the next Issue of Wear It's At.  We will explore the world of Chromium Carbides, probably the most popular and most economical of all Carbides to combat abrasive wear.

3. MOST AMERICANS WOULD GIVE UP SOME SLEEP TO WORK

According to a study funded by the National Sleep Foundation, nearly half those surveyed said they’d be willing to sleep less in order to get more work done. More than half of those aged 18 to 29 said they stay up too late in order to watch TV or surf the Net. Only slight fewer older people said they do the same thing. Not a great idea in light of the fact that being sleepy can impair your performance at work, your driving ability and your mood in general. “Most people will admit they don’t feel as good when they get too little sleep, but research shows that the consequences of sleep deprivation are far more severe than most people realize,” said Richard Gelula, the foundation’s executive director on the occasion of National Sleep Awareness Week. “Memory, mood, reaction time and alertness are diminished when we are sleep deprived, and recent research has also found that our metabolism and endocrine functions are affected as well.”  And although doctors say adults generally need about eight hours of sleep a night to be at their best the following day, most adults say they get less than seven hours on weeknights and less than eight on weekends.



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