Depth-hardened steel

The structure is manufactured from pre-hardened mold steel such as 1.2312 or from a corrosion-resistant steel 1.2085, while the splits are available in different materials. Here, case-hardening steels and depth-hardened steels such as 1.2343 are available. 

An alternative to the measurement of the dimensions of the indentation by means of a microscope is the direct reading method, of which the Rockwell method is an example. The Rockwell hardness is based on indentation into the sample under the action of two consecutively applied loads - a minor load (initial) and a standardised major load (final). In order to eliminate zero error and possible surface effects due to roughness or scale, the initial or minor load is first applied and produce an initial indentation. The Rockwell hardness is based on the increment in the indentation depth produced by the major load over that produced by the minor load. Rockwell hardness scales are divided into a number of groups, each one of these corresponding to a specified penetrator and a specified value of the major load. The different combinations are designated by different subscripts used to express the Rockwell hardness number. Thus, when the test is performed with 150 kg load and a diamond cone indentor, the resulting hardness number is called the Rockwell C (Rc) hardness. If the applied load is 100 kg and the indentor used is a 1.58 mm diameter hardened steel ball, a Rockwell B (RB) hardness number is obtained. The facts that the dial has several scales and that different indentation tools can be filled, enable Rockwell machine to be used equally well for hard and soft materials and for small and thin specimens. Rockwell hardness number is dimensionless. The test is easy to carry out and rapidly accomplished. As a result it is used widely in industrial applications, particularly in quality situations. 

Quantitative tests of hardness involve indenting a material with a ball, cone, or wedge of hardened steel or other metal under a pre-determined pressure for a specific amount of time. The size and depth of the cavity left in the material being tested is then measured and a formula applied. The resulting value is the hardness, which, like Moh s hardness, has no units of measure. 

An example of stress measurements in depth is given in Fig. 16-11, which shows the residual stress produced in hardened steel by grinding. The extremely... 

The long-chain structure by itself, as exemplified by n-aliphatic hydrocarbons, shows no extreme-pressure lubricant functionality. Evidently the additive action is connected with the carboxylate ester and the sulfide structures. To demonstrate this, Dorinson isolated an ester/ sulfide component from sulfurized methyl undecylenate, identified its structure, synthesized an organosulfide-ester with this structure, and showed that the lubricant additive activity was the same for the fraction separated from sulfurized methyl undecylenate end for the synthetic material. The data, summarized ib Fig. 11-15, were obtained tiy pin-and-disk wear tests with hardened steel rubbing specimens and show the effect of contact pressure on the depth-rate of wear. The significant feature is the change from a low rate of wear, relatively insensitive to increase of pressure in the range 0.276-1.724 GPa (40,000-250,000 Ib/in ), to pressure-sensitive increase of wear rate at 1.724 GPa and higher. 

The standard test methods for determining Rockwell hardness are listed in Table 12.6 and the Rockwell scales are given in Table 12.7. For example, ISO 2039 employs a hardened steel ball, 5 mm diameter. The ball is pressed into the specimen under a specified load selected to give an indentation between 0.07 and 0.10 mm (Method A) or between 0.15 and 0.35 mm (Method B). The recommended thickness of the specimen is 4 mm and the suggested time of application of the load is 30 s before the depth reading is taken. 

The Rockwell test differs fi om the other three tests because the depth of the indent rather than its surface area is taken as a measure of hardness. A hardened steel ball is used as the indentor. A major advantage of the Rockwell test is that no visual measurement of the indentation is necessary, and the depth of the indent is read directly as a hardness value on the scale. 

Carburizing n. A process for case-hardening steels in which the objects to be hardened are heated with carbonates and charcoal in the absence of air for bout 24 h at 840-950° C, then quenched in oil. The depth of hardening is about 1.7 mm and the surface hardness is from 50 to 55 on the Rockwell C scale. 

Rockwell hardness n. The Rockwell hardness test method consists of indenting the test material with a diamond cone or hardened steel ball indenter. The indenter is forced into the test material under a preliminary minor load Fq, usually lOkgf When equilibrium has been reached, an indicating device, which follows the movements of the indenter and so responds to changes in depth of penetration of the indenter is set to a datum position. While the preliminary minor load is still applied an additional major load is applied with resulting increase in penetration. When equilibrium has again been reached, the additional major load is removed but the preliminary minor load is still maintained. Removal of the... 

Submarine development and construction involves a number of industries. Besides shipbuilding, submarines, especially military ones, require specialized equipment and materials to operate in their harsh underwater environment. Submarines need special hardened steel to survive the crushing depths, sophisticated communications and electronics gear, and modified weapons systems that no other naval vessel uses. None of this is cheap. The standard ballistic missile submarine of the U.S. Navy, the Ohio class, each cost more than 1 billion, and each of their twenty-four Trident D-5 ballistic missiles costs 29 million. The most modem U.S. attack submarine, the Virginia class, costs 1.8 billion. That high cost limits the number of submarines that a navy can acquire. Consequently, only a few countries can afford submarines, especially nuclear-powered ones. 

When the appropriate spindle speed, abrasive, and grinding ball (usually made of hardened steel) are selected, it is possible for the ball to penetrate the hard coating to the required depth within 20-30 s in practical applications. A concave depression with a circular or elhptical shape and a depth of 5-20 pm is produced in the test surface. The functional principle is represented schematically in Fig. 137. 

In bottle blow molds, there will be a hardened steel insert with a land of 0.076-0.13 mm (0.003-0.005 in.), a relief angle of 20° with a total depth of 0.76 mm (0.030 in.) measured from the inside bottom of the blow mold, and then a 45° cut to the bottom of the relief section in the pinch-off area. Normally, the total of this relief section will be 90% of the parison wall thickness to be pinched (see Fig. 31). This design will also minimize residual flash. It is best to design the pinch land at 0.25-0.4 mm (0.010-0.015 in.) and have metal to remove, if the pinch is not adequate. 

Electroexplosive copper plating of steel 45 is accompanied by the saturation of the surface layer of atoms of copper, carbon and oxygen. Subsequent high-speed cooling of steel is accompanied by the separation of the liquid phase and the formation of a surface layer with the stmcture of the cellular crystallization. The thickness of cellular stmcture is about 5 pm. The thickness of the layer of hardened steel 45, located at a depth of 5 pm, is about 7 pm. 

Despite all the new developments, the long-standing DIN steels still play an important role. Often, in standard applications, depth-hardened or hot work mold steel is sufficient enough, and the cost of brand-name steel would not pay for itself with the application of the mold. The selection of steels should therefore always be considered from two aspects technical feasibility and economic benefits. 

Indentation hardness involves taking an object, often a hardened steel ball, and pressing it against the material with a defined force, and then measuring the depth of the resulting indentation after the ball is removed. 

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