Free machining

The estimated world production of tellurium from 1991—1994 is shown in Table 4 the average annual production in that time period was 240 tonnes. The data for 1994 are considered to be the most accurate because of the direct reporting, for the first time, of production from plants in the former Soviet Union. The main uses for tellurium are as a free machining additive in ferrous metallurgy (55%), as a free machining additive in nonferrous metallurgy (10%), in chemicals (30%), in electrical appHcations such as solar cells and thermoelectrics (3%), and miscellaneous (2%). 

Figure 2.17 Pitting at a free-machining austenitic stainless steel threaded valve throat. The valve controlled flow of a chlorine-containing, low-pH biocide.

Sampie Specifications % in. (1.39 cm) inner diameter, free-machining carbon steel... 

Figure 7.23/ Free-machining carbon steel hose coupling after 2 months in a solution containing several percent oleic acid.

Where free machining characteristics are required, this may be achieved by additions of cadmium, antimony, tin or lead (e.g. BS 4300/5). Materials for electrical use are of special composition (BS 2627, 3988), while bearings are manufactured from Al-Sn alloys. 

Silicon hydrides, in growing amorphous silicon, 22 129-131 Silicon integrated circuits, 19 167 Siliconized coatings, 10 108 Silicon-killed free-machining steels, 24 424 Silicon lattice, 23 35 Silicon-manganese-zirconium, 26 638 Silicon microelectronics, sensor sensitivity and, 22 269... 

Trethewey, K.R. and Pinwill, I. (1987). The dezincification of free-machining brasses in seawater. Surface and Coatings Technology 30 289-307. 

ASTM A 582, Standard specification for free-machining stainiess steei bars. 

P. It was developed by Chase Division, Kennecott Copper Corp., in 1950. The machinability rating is 80. The hot-working properties are comparable to those of a high copper commercial bronze and are superior to lead-containing free-machining copper alloys. The tensile strength is high, and the electrical and thermal conductivities are similar to those of nickel bronze CDA No. 191, and about one half those of copper (see Copper alloys). 

Selenium copper also available for combining high electrical conductivity with free-machining and hoi-working properties. Alloy makes excellent copper-to-glass seals. 

The corrosion rate depends upon the steel composition surface condition and the angle of exposure. Increase in carbon, manganese and silicon content of the steel results in decrease in corrosion rate although if manganese is present as sulfide as in free-machining steels, corrosion resistance decreases. The presence of copper increases the corrosion resistance. 

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