Welding iron-carbon alloys

Stainless steels are iron-based alloys which contain more than 12% chromium. A common composition contains 18% Cr and 8% Ni, and is designated as either 18 8 or type-304 stainless steel. Unlike ordinary carbon steel, the stainless steels in the 300 series do not become brittle at low temperatures. Stainless steel has a rather low thermal conductivity. It may be welded, brazed, or soldered and is machinable with some difficulty. Type 303 is the easiest to machine. 

E6.2. Predict whether or not galvanic corrosion will cause the following alloys to be subjected to leaching (i) carbon and carbon steel alloys in an oxidizing atmosphere, (ii) steel rivets in aluminum drain gutters, (iii) copper-nickel alloy in refinery condenser tubes, (iii) graphite fiber-reinforced aluminum composites, (iv) brass in water, (v) iron-chromium alloys, and (vi) carbon steel pipe in contact with the weld to stainless steel pipe. 

Weld hardfacing coatings, for example, high-carbon iron-chromium alloys, tool steels, nickel-chromium-boron alloys, cobalt-base alloys, and austenitic manganese steels... 

Certain alloys of iron, nickel, and cobalt (Kovar, Fernico, etc.) have thermal expansion curves which nearly match those of borosilicate glasses, and a good bond may be formed between the two. Kovar is similar to carbon steel in its chemical properties. For example, it oxidizes when heated in air and is not wet by mercury. It may be machined, welded, copper brazed, and soft soldered. Silver solders should not be used with Kovar since they may cause embrittlement. At low temperatures Kovar undergoes a phase transformation, and the change in expansion coefficient below this temperature may be sufficient to cause failure of a glass-to-Kovar seal. The transformation temperature usually is below... 

This group of steels are used in industry extensively. The versatility and low cost are attractive features. As opposed to pure iron, alloying iron with small amounts of carbon results in improved strength and hardness without loss of ductility. These alloys are attractive from the points of view such as ease of fabrication, machinability and welding as well as good corrosion resistance. 

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