Brinell scale - Wikipedia
In the case of steel, there is a common relationship between the Brinell hardness number (BHN) and the ultimate tensile strength (UTS) given in pounds force. As the hardness increased the tensile strength also increased for a There is a linear correlation between hardness and fatigue strength to Brinell. of the ultimate tensile strength throughout the entire hardness range. The hardness test is a mechanical test for material properties which are used in to do with the relationship between hardness and other properties of material. The Brinell hardness test method consists of indenting the test material with a 10 prediction of ultimate tensile strength may also be obtained using the relation.
The melt stir casting is a very good option for fabricating MMCs due to its inherent advantages such as the flexibility, simplicity, applicability to a lot of volume, wide processing conditions and selection of materials, large sized parts can also be fabricated easily.
Moreover, stir casting is one of the economical ways of distributing the reinforcement particles uniformly in the MMC system .
Stir casting make sure that the reinforcement material is not damaged . It is a popular method as its cost of processing is just one third or half of the cost of the other fabrication methods. The thing which is the most important during fabrication of MMC by stir casting method is that the reinforcement in the matrix should be uniform otherwise the properties will not be uniform in the specimen.
Some of the common problem in stir casting methods is sedimentation and agglomeration of reinforcing particles, solidification of melt; impurities can get mixed with the melt, sometimes air gets trapped in the melt deteriorating the quality of MMC fabricated. The stir casting normally consist of the melting the matrix material in a crucible followed by stirring of that molten material to from a vortex and then reinforcement particles are incorporated in the vortex. After that the mixture of both the metals was stirred at - rpm for some time.
Figure 1 and four different specimens of composites were prepared see Figure 2. Tensile Testing A tensile test measures the resistance of a material to a static or slowly applied force. A machined specimen is placed in the testing machine and load is applied. A Strain Gage Figure 1.
Sand casting being done to prepare the specimens. The stress obtained at the highest applied force is the Tensile Strength. The yield Strength is the stress at which a prescribed amount of plastic deformation commonly 0. Elongation describes the extent to which the specimen stretched before fracture. Information concerning the strength, stiffness and ductility of a material can be obtained from a tensile test.
The readings got are given in Table 1 and a corresponding graph is also shown in Figure 3. Rockwell Hardness Testing The Rockwell Hardness test makes use of indentation to measure the hardness of the different specimens. The machine generally has different types of scales to get the readings but here C scale was used to check the readings.
The specimen is first loaded with the help of minor load then after that major load is applied with the minor load still applied. The increasingly pronounced curvature, with increasing bar diameter, of the curves in Figure 3. The resultant reduced rate of increase of graphite volume with increased carbon would be reflected in flatter curves at higher carbon levels.
Graphite flotation can cause a serious degradation of properties near the upper cope surface of large Ductile Iron castings. However, this phenomenon is readily avoided by reducing the carbon equivalent as the casting section size increases. Effect of Carbide Content Carbide content has both direct and indirect effects on the properties of Ductile Iron castings. As discussed earlier, this convergence of yield and tensile strengths produces a decrease in elongation with increasing carbide content.
The presence of carbides in a Ductile Iron matrix also increases the dynamic elastic modulus and significantly reduces machinability. The formation of eutectic carbide during solidification affects the volume fraction of graphite produced because carbide and graphite compete for the carbon contained in the liquid iron.
Fifteen volume per cent of carbide would require 1 per cent carbon, reducing the carbon available for graphite by approximately one third.
Hardness conversion table
The formation of carbide thus increases the likelihood of internal casting porosity by reducing the expansion effects produced by the formation of graphite during solidification. These levels can usually be achieved as-cast by reducing the levels of carbide forming elements through the use of high purity pig iron in the furnace charge and by increasing the nodule count through the application of good inoculation practices. When required, heat treatment can be used to eliminate carbides.
Effect of Matrix In Ductile Irons with consistent modularity and nodule count and low porosity and carbide content, mechanical properties are determined primarily by the matrix constituents and their hardness. Ferrite is the purest iron phase in Ductile Iron. It has low strength and hardness, but high ductility and toughness and good machinability.
Pearlite is an intimate mixture of lamellar cementite in a matrix of ferrite. Compared to ferrite, pearlite provides a combination of higher strength and hardness and lower ductility. This ratio is controlled in the as-cast condition by controlling the composition of the iron, taking into account the cooling rate of the casting. It can also be controlled by an annealing heat treatment to produce a fully ferritic casting, or by normalizing to maximize the pearlite content.
The pearlite content was varied from 15 to per cent by the use of different copper-manganese and tin-manganese combinations.
Alloy levels beyond those required to produce a fully pearlitic matrix were also tested to determine their effects on properties. The effects of Cu and Sn diverge, however, for alloy levels approaching and exceeding those required to produce a fully pearlitic matrix. Additions of copper to a fully pearlitic matrix in the Cu-Mn alloy resulted in further increases in both yield and tensile strengths, probably due to solid solution strengthening.
Additions of tin to the fully pearlitic Sn-Mn alloy did not affect the yield strength, but resulted in a decrease in tensile strength that has been related to the formation of intercellular degenerate graphite. These data, obtained from testing 1 inch 25 mm keel blocks made from irons with average compositions of 3.
As-cast properties Figure 3. Yield and tensile strengths increase, and elongation decreases, until the matrix becomes fully pearlitic at 0. In agreement with Figure 3. Ferritization of the fully pearlitic samples containing more than 0. These Sn levels are of academic interest only, as the Sn content in commercial Ductile Iron is usually limited to less than 0. Both hardness and strength of the normalized keel blocks increase with increasing Cu and Sn contents Figure 3.
In the Cu alloyed material, the increase is due to solid solution strengthening, while the initial increase produced by Sn is caused by the elimination of ferrite rings around the graphite particles, indicating that for the Sn series, the base composition provided insufficient hardenability for complete pearlitization.
The Quality Indices of the heat treated samples, which were taken from different keel blocks, ranged from 90 to Low Temperature Tensile Properties Ductile Irons are structurally stable at very low temperatures, but when designing for low temperature applications, the designer must take into consideration the significant effect of temperature on strength and elongation. Ferritic grades of Ductile Iron are generally preferred for low temperature applications because their ductility at low temperatures is superior to that of pearlitic grades.
As the temperature decreases, both the yield and tensile strengths increase, although the yield strength, which more accurately reflects the effect of temperature on flow stress, rises more rapidly. Pearlitic grades of Ductile Iron exhibit a significantly different response to decreasing temperature.
As a result of the steady deterioration in tensile strength and elongation below room temperature, pearlitic Ductile Irons should be used with caution at low temperatures. High Temperature Tensile Properties Ductile Irons exhibit several properties which enable them to perform successfully in numerous elevated temperature applications. Unalloyed grades retain their strength to moderate temperatures and exhibit significantly better resistance to growth and oxidation than unalloyed Gray Iron.
Alloy Ductile Irons see Section V provide outstanding resistance to deformation, growth and oxidation at high temperatures. The only high temperature applications in which Ductile Irons, with the exception of Type D-5 Ductile Ni-Resist, do not perform well are those involving severe thermal cycling.
In these applications the low thermal conductivity of Ductile Iron, combined with a high modulus of elasticity, can result in internal stresses high enough to produce cracking and warpage.
Hardness and Tensile Strength Charts
However, the successful use of Ductile Iron in millions of exhaust manifolds and turbocharger casings confirms that in specific thermal cycling applications Ductile Iron provides superior performance.
Above this temperature the tensile strengths of both grades decrease rapidly with further increases in temperature. The pearlitic grade exhibits superior strength at all temperatures, due to a combination of higher ambient temperature strength and reduced effect of temperature on strength.
The stress-rupture curves define the stress required to produce rupture failures after 10, and hours. The creep curves define the stress required at a given temperature to produce a minimum creep rate of 0. As with the tensile properties, the short-term stress-rupture strength of the pearlitic grade is approximately twice that of the ferritic grade.
However, the longer term rupture strength and creep strength of both materials are almost identical. The relatively poor longer term rupture and creep properties of the pearlitic iron, compared to its shorter term properties, are partly due to growth from graphitization and ferritization of the pearlite matrix.
For example, a sample subjected to a stress of 4 ksi would be expected to have lives of 10, and hours when tested at temperatures ofand oC, and oF.
The effect of alloying elements on the high temperature properties of Ductile Iron will be presented in greater detail in Section V. Effect of Temperature on Design Stresses When determining design stresses for a Ductile Iron component, the designer must be aware of both the temperature range in which the component will be operated and the effect of temperature on tensile properties.
The increase in yield strength with decreasing temperature for both ferritic and pearlitic Ductile Irons suggests that higher design stresses may be used at low temperatures. Because most low temperature applications also involve performance at room temperatures, the room temperature yield strength must be used in the calculation of design stresses.
However, the use of a yield strength-related design stress is acceptable for low temperature applications only when the applied stress state can be simulated by a quasi-static low strain rate test.