Carbon steel properties

Low Alloy Steels. These aHoys are carbon steels to which other elements have been deHberately added to impart a particular property. 

Fluorosulfuric acid can be very corrosive. A study of the corrosive properties of fluorosulfuric acid during preparation and use showed carbon steel to be acceptable up to 40°C, stainless steel up to 80°C, and aluminum alloys up to 130°C (52). 

Soft magnetic materials are characterized by high permeabiUty and low coercivity. There are sis principal groups of commercially important soft magnetic materials iron and low carbon steels, iron—siUcon alloys, iron—aluminum and iron—aluminum—silicon alloys, nickel—iron alloys, iron-cobalt alloys, and ferrites. In addition, iron-boron-based amorphous soft magnetic alloys are commercially available. Some have properties similar to the best grades of the permalloys whereas others exhibit core losses substantially below those of the oriented siUcon steels. Table 1 summarizes the properties of some of these materials. 

The uses of steel are too diverse to be Hsted completely or to serve as a basis of classification. Inasmuch as grades of steel are produced by more than one process, classification by method of manufacture is not advantageous. The most useful classification is by chemical composition into the large groups of carbon steels, alloy steels, and stainless steels. Within these groups are many subdivisions based on chemical composition, physical or mechanical properties, or uses. 

The physical and mechanical properties of steel depend on its microstmcture, that is, the nature, distribution, and amounts of its metaHographic constituents as distinct from its chemical composition. The amount and distribution of iron and iron carbide determine most of the properties, although most plain carbon steels also contain manganese, siUcon, phosphoms, sulfur, oxygen, and traces of nitrogen, hydrogen, and other chemical elements such as aluminum and copper. These elements may modify, to a certain extent, the main effects of iron and iron carbide, but the influence of iron carbide always predominates. This is tme even of medium alloy steels, which may contain considerable amounts of nickel, chromium, and molybdenum. 

Properties. The properties of plain carbon steels are governed principally by carbon content and microstmcture. These properties can be controlled by heat treatment as discussed. About half the plain carbon steels are used in the hot-roUed form, although increasingly the property combinations are enhanced by controlled cooling following the last stand of the hot mill for stmctural shapes, sheet, and strip. The other half are cold-roUed to thin sheet or strip and used direcdy or with an annealing treatment such as described. 

Eig. 25. Variations ia average mechanical properties of as-roUed 2.5-cm bars of plain carbon steels, as a function of carbon content (1). 

Heat Treatment. Although many wrought (roUed or forged) carbon steels are used without a final heat treatment, this may be employed to improve the microstmcture and properties for specific apphcations if the cost can be justified. 

For slightly less than 10% of products, alloying elements are introduced to produce properties not available for carbon steels where the functional elements are usually considered to be carbon, siHcon (to 0.6%), and manganese (to 1.65%). Copper, which may be present up to 0.6 wt %, is relatively rare compared to the ubiquitous siHcon and manganese. 

The effect of the ahoying elements on AISI steels is indirect because ahoying elements control microstmcture through their effect on hardenabhity. These elements permit the attainment of desirable microstmctures and properties over a much wider range of sizes and sections than is possible with carbon steels. 

States or Australia. In some cases, pot stills, arranged in cascade, are still used. The more sophisticated plants employ one or more carbon steel or cast-iron vessels heated electrically and equipped with temperature controls for both the bulk Hquid and the vessel walls. Contact time is usually 6—10 h. However, modem pitches are vacuum-distilled, producing no secondary quinoline insolubles, to improve the rheological properties. 

Thiols are shipped ia every conceivable container size. Dmms and cans can be of carbon steel for most thiols, provided color is not a determining factor. Tmck, rail, and isocontainer shipments should be set up to utilize a vapor return line from the tank to the shipping container. This substantially minimizes the amount of odor that escapes. Phillips Petroleum Company and Atochem North America can supply further information regarding the handling and properties of many thiols. 

Low-Alloy Steels Alloy steels contain one or more alloying agents to improve mechanical and corrosion-resistant properties over those of carbon steel. 

As you can see from the tables in Chapter 1, few metals are used in their pure state -they nearly always have other elements added to them which turn them into alloys and give them better mechanical properties. The alloying elements will always dissolve in the basic metal to form solid solutions, although the solubility can vary between <0.01% and 100% depending on the combinations of elements we choose. As examples, the iron in a carbon steel can only dissolve 0.007% carbon at room temperature the copper in brass can dissolve more than 30% zinc and the copper-nickel system - the basis of the monels and the cupronickels - has complete solid solubility. 

The most important displacive transformation is the one that happens in carbon steels. If you take a piece of 0.8% carbon steel "off the shelf" and measure its mechanical properties you will find, roughly, the values of hardness, tensile strength and ductility given in Table 8.1. But if you test a piece that has been heated to red heat and then quenched into cold water, you will find a dramatic increase in hardness (4 times or more), and a big decrease in ductility (it is practically zero) (Table 8.1). 

We already know quite a bit about the transformations that take place in steels and the microstructures that they produce. In this chapter we draw these features together and go on to show how they are instrumental in determining the mechanical properties of steels. We restrict ourselves to carbon steels alloy steels are covered in Chapter 12. 

Carbon is the cheapest and most effective alloying element for hardening iron. We have already seen in Chapter 1 (Table 1.1) that carbon is added to iron in quantities ranging from 0.04 to 4 wt% to make low, medium and high carbon steels, and cast iron. The mechanical properties are strongly dependent on both the carbon content and on the type of heat treatment. Steels and cast iron can therefore be used in a very wide range of applications (see Table 1.1). 

Figure 11.7 shows how the mechanical properties of normalised carbon steels change with carbon content. Both the yield strength and tensile strength increase linearly with carbon content. This is what we would expect the FejC acts as a strengthening phase, and the proportion of FojC in the steel is linear in carbon concentration (Fig. 11.6a). The ductility, on the other hand, falls rapidly as the carbon content goes up (Fig. 11.7) because the a-FejC interfaces in pearlite are good at nucleating cracks.

Fig. A1.41. Pearlite in a eutectoid-composition plain-carbon steel, x500. (After K. J. Pascoe, An Introduction to the Properties of Engineering Materials, Van Nostrand Reinhold, London, 1978.)...

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