Simple Steels Research Articles

Strengthening in low carbon pearlitic steels

The microstructure-flow stress relationship has been examined in two simple ferrite-pearlite steels. As in fully pearlite steels, a Hall-Petch equation was shown to be applicable, when care is taken in obtaining the appropriate mean slip distance in ferrite for each microstructure.

Mechnism for ablation of metals by explosion plasmas

The authors present results from a study of the gasdynamic and thermal phenomena that occur when an explosion plasma comes into contact with metals. Metals include commercial-grade iron, copper and aluminum as well as iron alloys including the simple carbon steels, alloy' steels and cast irons. Aluminum alloys are represented here by silumins with 6-38% Si, Amg6 an alloy with magnesium, and auraluminum D16. From the experiments conducted it is concluded that: under the pressure of an explosion the surface layer of a metal is heated by the plasma to critical temperature, but vaporization of the metal is low owing to screening of the surface by vapor; and that most of the removal of metal occurs at the end of the interaction owing to vaporization and sputtering of the alloy when the pressure drops.

Determination of thermal-hardening stress in steels by use of thermoplasticity theory

The problems of quenching-stress analysis are critically reviewed and an adequate simple theory is discussed. The theory accounts for both plasticity and volumetric changes due to phase transformation accompanying the thermal-hardening of a group of simple steels that are characterized by C-shaped time-temperature-transformation diagrams. The volume dilatation in the absence of stress is assumed to be a linear function of the separate specific volumes and weight fractions of the constituents (pearlite, austenite and martensite). With use of the classical relationships of a formal theory of transformation kinetics, the amounts of pearlite and martensite are expressed in terms of the temperature and the temperature-history. The specific forms of such functions are given. In order to account for the influence of phase transformation on plastic properties, the non-isothermal plastic flow-rule is generalized, and a thermal-hardening parameter is introduced which is identified with the amount of pearlite. Variational principles and bounding inequalities associated with the fundamental rate-problem are considered. As an example, the problem for a rapidly, uniformly-cooled half-space is solved. The variations of the residual stress and the final amount of martensite with distance from the outer surface are given, for several values of the rate-of-cooling. The results suggest that the residual stress vanishes on the plane containing approximately 30–35 per cent of martensite.

Strengthening of titanium steels by carbide precipitation

AbstractThree simple high-purity steels containing between 0.10 and 0.55 wt.-% titanium and 0.02–0.11% carbon have been examined after direct transformation of austenite to ferrite by subcritical isothermal transformation in the range 600–800°C and by continuous cooling. Electron microscopy has shown that titanium carbide occurs in a fine banded form during the γ→α transformation, the dispersion parameters being very dependent on the transformation temperature. The finer dispersions were measured by field ion microscopy. The mechanical properties in tension at room temperature were determined as a function of transformation temperature for the three alloys and compared with the properties obtained by quenching and tempering in the, same temperature range. Fracture toughness measured by a COD test was determined on two titanium steels with 0.26% and 0.48%Ti. The results emphasize the importance of transformation temperature or rate of cooling through the transformation in determining the fracture toughness...

The Formation of Oxide Films On Chromium and 18 Cr-8 Ni Steels

Abstract The formation of oxide films on simple chromium steels and 18-8 stainless steels oxidized in air at temperatures of 300 C to 700 C has been studied by electron microscopy, electron diffraction and X-ray diffraction methods. A thin uniform film forms in the first few minutes of oxidation and grows very slowly thereafter. As oxidation proceeds the protectiveness of the base film fails at randomly distributed positions, permitting the rapid growth of localized polycrystalline nodules of oxide. These nodules continue to grow and new ones are formed until the base film is completely covered. The rate at which the process proceeds depends on alloy composition and temperature in the same way as does the scaling rate at higher temperatures. There is no evidence that the failure is due to cracking of the base film. There seems to be no detrimental effect produced by the usual amounts of minor constituents in the alloys. Local failure may be due to blistering or recrystallization. The principal component of the base film is a solid solution of ferric and chromic oxides preferentially oriented with the (111) plane parallel to the surface. The degree of the orientation and the chromic oxide content of the solution increase with time of oxidation. A small amount of spinel may be present also. In the case of the 18Cr-8Ni alloy the spinel contains some Ni. The nodules are principally αFe2O3 or a low chrome ferric-chromic oxide solution and contain somewhat more spinel than does the base film. 3.2.3