Killed Steel

July 20, 2010

Some things you want to have bubbles, some you don’t.

Usually, Bubbles are good.

In beermaking, yeast consumes the sugars in the wort and convert them into CO2 gas bubbles- carbonation.

In steel making the main reaction is the combination of Carbon in the melt with Oxygen to form a gas. At the high temperatures involved, this gas is very soluble in the molten bath.

If the Oxygen that is available for this chemical reaction isn’t completely removed before the steel is cast the gases will continue to be forced out of the melt during solidification, resulting in porosity in the steel.

Bubbles and where the gas goes can be important in your steel part.

In order to control the evolution of gas, chemicals called deoxidizers are added to the steel. These chemicals, Silicon or Aluminum, Vanadium, Columbium, Niobium scavenge the available oxygen in the molten steel, react chemically to form solid oxide particles dispersed throughout the steel, rather than bubbles of Carbon Dioxide.

The amount and type of deoxidizer added determines the type of steel. If sufficent deoxidizers are added, no gas is evolved from the solidifying steel, and the steel is said to be “killed.” The ingot drawing labelled number 1 shows a fully killed (deoxidized) steel showing only a shrinkage cavity, and no bubbles or porosity. ( This shrinkage cavity would be cropped off in normal rolling practice.)

Because gas is still evolving, this beer is NOT KILLED.

Killed steel has more uniform chemical composition and properties than rimmed, semi-killed, or non-killed steels, and generally less segregation. The uniformity of killed steel and and its freedom from porosity makes these steels more suitable for critical components and for applications involving heat treatment.

Killed steels generally contain 0.15-.35 weight percent Silicon as a deoxidizer, and may contain  some of the other elements as mentioned above. These other elements may be used as deoxidizers or as grain refiners.

Steel grades with a Carbon maximum of 0.30 weight % and above, and all alloy steels are typically provided as “killed steels.”

Free machining steels such as 12L14, 1215, and some 11XX series steels are not “killed” with Silicon, Aluminum, etc., due to their deleterious effects on tool life and machinability. The high amounts of Manganese  in these steels form Manganese Sulfides to promote machinability, and also the Manganese scavenges excess Oxygen, preventing  evolution of CO2.

Killed steel is specified so your critical parts won't have bubbles in them.

Killed steel- for critical parts. Non-killed beer for critical  after work down time.

Cheers!

Beer Bubbles Photo Credit

Ingot scan from a handout in my files originally after Making Shaping and Treating of Steel.

 Beer Head Photo Credit

Bread with Holes

Share


Chinese Resource Hoarding Dispute Before WTO

November 4, 2009

The US, EU and Mexico have just  (2 hours ago) jointly made a formal request to the WTO for a dispute-settlement panel to address China’s export restraints on a number of  raw materials  of interest to our precision machining industry.  Bloomberg coverage here.

Raw materials such as

  • coke ( used in steel), 
  • zinc (used in brass),
  •  bauxite (aluminum ore),
  •  fluorspar (steelmaking slag conditioner),
  • magnesium,
  • manganese (steelmaking ingredient),
  • silicon metal (steelmaking deoxidizer),
  • silicon carbide (desulfurizer)

 These are among the materials listed in the filing. These are important (essential!)  ingredients into the steel and metallic raw materials our industry consumes. We remember reading about this as an emerging concern in June in the Globe and Mail.

r-china-wheeler24_88661gm-a

How they load steel in Hubei, China.

 The economic issue is that this “resource hoarding” results in artificially lowered cost for these raw materials in China  and in effect becomes a subsidy for those  manufacturing operations that China deems “strategic.”  While at the same time making these materials more difficult (and Expensive) to obtain for non Chinese companies.

Peace” according to Ambrose Bierce, in The Devil’s Dictionary, “in international affairs is a period of cheating between two periods of fighting.”  I think that this is a particularly useful perspective in this situation.

Diplomacy,” according to my 8th grade History teacher, Mrs. Abernathy, “is war by other means.”

Our industry, the EU, Mexico, and the United States- all of us  are certainly looking forward to some diplomatic success. 

The panel is expected to be convened Nov. 19th.

China_from_space

We all live here together. Why not trade fairly?

Steel loading Photo via  Globe and Mail originally Shanghai Reuters.

Earth photo credit: NASA.