Quenching iron-carbon alloys

Part V. Compendium of Phase Diagram Data , Tech. Rep. AFML-TR-65-2, Part V, Air Force Materials Laboratory, Wright-Patterson AFB, OH, 1969 (Phase Diagram, Experimental, 1) [1969Ruh] Ruhl, R.C., Cohen, M., Splat Quenching of Iron-Carbon Alloys , Trans. AIME, 245, 241-251 (1969) (Crys. Structure, Experimental, Phase Relations, 50)... 

Yet another microconstituent or phase called martensite is formed when austenitized iron-carbon alloys are rapidly cooled (or quenched) to a relatively low temperature (in the vicinity of the ambient). Martensite is a nonequilibrium single-phase structure that results from a diffusionless transformation of austenite. It may be thought of as a transformation product that is competitive with pearlite and bainite. The martensitic transformation occurs when the quenching rate is rapid enough to prevent carbon diffusion. Any diffusion whatsoever results in the formation of ferrite and cementite phases. 

Ben] Benabder, A., Faivre, R, Influence of Formation and Decomposition of Low-Temperature Carbides on Graphitisation of Some Iron-Carbon-Silicon Alloys after a Martensitic-Type Quench (in French), Mem. Sci. Rev. Metall, 65(4), 309-315 (1968) (Experimental, Crys. Stmcture, Morphology, 15)... 

Ruh] Ruhl, R.C., Cohen, M., Splat Quenching of Carbon-Iron Alloys , Trans. AIME, 245, 241 (1969) (Experimental, Crys. Stracture, 50)... 

In addition, the carbon further strengthens the alloy considerably. The solubility of carbon is much smaller in the body-centred than in the face-centred crystal structure because the interstitial spaces are smaller. If 7 iron with a sufficient amount of dissolved carbon (> 0.008 wt-%) is quenched, the carbon remains dissolved in the body-centred lattice. The carbon atoms strongly distort the body-centred cubic cell to a tetragonal one (figure 6.54). This distorted lattice structure has an extreme strength when highly oversaturated because the stress field cannot be passed by dislocations. As a rule of thumb. 

Heat Treatment of Steel. Steels are alloys having up to about 2% carbon in iron plus other alloying elements. The vast application of steels is mainly owing to their ability to be heat treated to produce a wide spectmm of properties. This occurs because of a crystallographic or aHotropic transformation which takes place upon quenching. This transformation and its role in heat treatment can be explained by the crystal stmcture of iron and by the appropriate phase diagram for steels (see Steel). 

Steels are alloys of iron and up to 1.7% carbon, although steels are not usually found with more than 1.2% carbon. The importance of steels is that their mechanical properties are greatly influenced by their carbon content. As the carbon increases in the steel, the ductility goes down while the hardness and tensile strength go up. A further important consideration is that the hardness of steels can be dramatically increased to even higher levels by a process of heating to above 800°C and quenching in water or some other fluid such as urine... 

The material of construction for the Grignard reactors and feed vessels R-1. R-2, T-1, and T-2 is typiciilly stainless steel, carbon steel or glass-lined cat bon steel. (For convetiiencc the charge tanks anil the reactors are numbered in Figure 6.1. so that T-l refers to Tank I and R-l refers to Reactor I.) The use of carbon steel must be considered carefully, however, due to the potential introduction ol iron which can be a probletn in some reactions. The material of construction for R-3 and T-3, the quench equipment, can be glass-lined steel or an acid resistant metal alloy such as Hastelloy C. 

Wil] Chemical analysis of carbon content and calculation of carbon activity in (yFe) phase. Pure iron-copper strip and metastable iron carbide as a carbon source placed in the sealed tubes were heated in furnace from 24 h at 1050°C to 7 d at 850°C, then the tubes were quenched to room temperature. Fe-alloys with 0.72, 1.36, 3.13, 5.61, 6.74 mass% Cu and 0.2 to 1.5 mass% C. Measurements at 850, 925 and 1050°C. 

Iron containing carbon at a percentage of some tenths, is a forgeable alloy. Unlike pure iron it can also be hardened by heating to a high temperature and quenching in water. By an after-treatment, a tempering, it is possible to get a desired combination of... 

The vast majority of vessels are constructed of ferrous and nonferrous alloys. Ferrous alloys are defined as those having more than 50% iron. They are used in the ASME Code, VIII-1 and 2, and include carbon and low-alloy steels, stainless steels, cast iron, wrought iron, and quenched and tempered steels. Nonferrous alloys include aluminum, copper, nickel, titanium, and zirconium. The ASTM designates all ferrous alloys by the letter A and all nonferrous alloys by B. ASME uses the prefixes SA and SB, respectively, In most cases the ASME and ASTM specifications are identical. However, vessels built to the ASME Code usually refer to the ASME specifications. 

The flame-hardening process is used for a wide variety of applications. These include (1) parts that are so large that conventional furnace treatments are impractical or uneconomical, (2) prevention of detrimental treatment of the entire component when only small segments of die part require heat treatment, and (3) use of less costly material to obtain the desired surface properties where alloyed steels would be normally applied. Flame hardening is limited to hardenable steels (wrought or cast) and cast iron. Typical hardnesses obtained for the flame-hardened grades depend on the quench media (Table 1). The practical level of minimum surface hardness attainable with water quenching for various carbon contents is shown in Fig. 1. 

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