Silicon Steel

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This is somewhat more of a metallurgy question than a general welding question, but it has to do with welding as well. Apparently the old SF/Oakland Bay Bridge uses some semi-exotic steels. According to an article I found online The bridge was designed and built using state-of-the-art techniques available in the 1930s. For example, the engineers specified the highest-strength steel available for critical elements. Nickel (55 ksi; Grade 380 MPa) and silicon steel (45 ksi; Grade 311 MPa) for the east crossing make up 62% of the total steel used there, and 72% of the cantilever section. Even the carbon steel used in this bridge was higher-strength (37 ksi; Grade 255 MPa) than is normally used today. High-strength cable steel (120 ksi; Grade 828 MPa) was specified for the west crossing suspension cables. The entire bridge required 167,100 tons (151,593 metric tons) of structural steel, or 115 psf (561 kg/m2).
Reply:You know how freezing cider yields regions that freeze quickly without much alcohol/sugar, and regions that freeze later (at a lower temperature) have more alcohol/sugar? I've been reading about welding metallurgy, and the more alloying elements that are added, the more they affect hot metal as it cools and crystallizes. The crystals that form are alloy-poor, while the region between the crystals is alloy-rich. That leads to weakness within the steel.Does this apply to silicon more than other elements? I don't know.
Reply:slotard"From what I've been told . . . "You have asked: a technical/metallurgical question ofdebth without application.  This is 'a folly indicator'.The answers to your questions are in the very specs.that you have: 'Quoted & Referenced'.Until you disclose what are you doing - and why is this info is important . . . You are upside-down, in the barrow pit, and on fire.All of your answers are available at your local . . .    Opus
Reply:piojoIt took a while for us to speak: 'one-on-one'.Do you walk to work - or take your lunch?I was hungry -  but I went down stairs . . .How can you be anti-abortion - and be pro-fracking?Is Mother Nature diminutive to your 'Machismo'?Opus
Reply:Opus - ?
Reply:Originally Posted by OPUS FERROslotard"From what I've been told . . . "You have asked: a technical/metallurgical question ofdebth without application.  This is 'a folly indicator'.The answers to your questions are in the very specs.that you have: 'Quoted & Referenced'.Until you disclose what are you doing - and why is this info is important . . . You are upside-down, in the barrow pit, and on fire.All of your answers are available at your local . . .    Opus
Reply:Slotard,Post the link to the article you quoted, please.  I'm guessing from the context of your quote, but here goes.Nickel is a common alloying ingredient in steels today.  So called high strength, low alloy steels often contain nickel or chromium, or manganese in amounts less than 1%.  Nickel adds some strength to an alloy but is more often looked at as a toughening agent.  It tends to make the steel less brittle, particulary at temperatures below 0°F.Silicon is also an alloying ingredient in steels.  It is added as a de-oxidizing agent.  You may have heard of 'silicon-killed' steel or 'aluminum-killed' steel.  The term 'killed' means that silicon or aluminum were added intentionally to the molten steel as a means of removing excess oxygen.  Excess oxygen in molten steel forms porosity and/or small inclusions, or defects, when the steel is allowed to cool and changes from a liquid to solid.  A small amount of silicon or aluminum remains dissolved in the solidified steel.  Small amounts of these two elements also affect strength and toughness.  Just like so many things in life, a little bit is good, but too much is not.Wikipedia has a good article on this subject.http://en.wikipedia.org/wiki/Deoxidized_steeland http://en.wikipedia.org/wiki/Steel_makingYou'll see in the second article that some new technology in steel making was coming around about the time the bridge was built.  Hence the notation about using better steels in it's construction.Last edited by A_DAB_will_do; 08-05-2014 at 11:58 AM.Benson's Mobile Welding - Dayton, OH metro area - AWS Certified Welding Inspector
Reply:From infrastructureengineers.comLow carbon steel, steel with carbon content less than approximately 0.3%, defines some of the most common steel types: -  A7 steel - the most widely used bridge steel up to about 1967; obsolete due to poor weldability characteristics -  A373 steel - similar to A7 steel but has improved weldability characteristics due to controlled carbon content -  A36 steel - the latest of the low carbon steels, first used in 1960; it features good weldability and improved strength Structural nickel steel (A8) was used widely prior to the 1960's in bridge construction, but welding problems occurred due to relatively high carbon content.Structural silicon steel (A94) was used extensively in riveted or bolted bridge structures prior to the development of low alloy steels in the 1950's. This steel also has poor weldability characteristics due to high carbon content."USMCPOP" First-born son: KIA  Iraq 1/26/05Syncrowave 250 w/ Coolmate 3Dialarc 250, Idealarc 250SP-175 +Firepower TIG 160S (gave the TA 161 STL to the son)Lincwelder AC180C (1952)Victor & Smith O/A torchesMiller spot welder
Reply:http://www.structuremag.org/?p=1544 is the article.Lincoln 175HD
Reply:The old bridge was a riveted structure.    The alloying elements weren't as crucial as a welded steel structure or the distributions of the elements to a point.      As far as welding lifting points, why bother when you can torch holes for slings.    the only welders i have seen during the demo of the bridge have been running light plants and riding service trucks.Vantage 500's LN-25's, VI-400's, cobramatics, Miller migs, synch 350 LX, Powcon inverters, XMT's, 250 Ton Acurrpress 12' brake, 1/4" 10' Atlantic shear,Koikie plasma table W/ esab plasmas. marvel & hyd-mech saws, pirrana & metal muncher punches.