Effect of Wave Thermal Deformation Hardening on the Microhardness of the Surface Layer of Steel Parts

Preliminary experimental studies of the possibility of increasing the microhardness of the surface layer of the material by the method of wave thermodeformational hardening on the example of austenitic steel class 12X18H10T are carried out. Comparative studies on the hardening of the material with and without heating were also carried out. The possibility of a significant increase in the maximum microhardness in the range from 25 to 50% at a depth of up to 0.6 mm, depending on the hardening mode, in comparison with the deformation treatment in the “cold” state is established. The area of technological modes providing the maximum increase of microhardness in the surface layer is revealed, in particular, the temperature of the treated surface should be in the range from 200°C to 400°C. At the same time, the achieved microhardness values exceed the initial one by 1.8…2.2 times, depending on the processing modes. It is also found that when choosing rational processing modes, the combined wave thermal strain hardening can significantly increase the hardening depth to 4.2 mm of the surface layer compared to the initial state. To establish the possibility of improving the performance of combined processing requires additional research.

Transition from engineering strain to the true strain in analytical description of metals hardening

Purpose of the work is related with the impossibility of correctly estimating the strain hardening of metals (alloys) in the area of their large total deformations due to absence of additivity in the traditionally used value of engineering strain g, its nonlinear change in the area of large values, and absence of data in the technical literature Hall-Petch coefficient Ai for logarithmic true deformations, which led to the task of correct transition from the values of the engineering strain 0 < g < 50...60 % to the value of the true logarithmic strainn 0 < e < 1...3. Methodology. The theoretical analysis of the regularities of deformation hardening of metals (alloys) from the engineering strain is carried out, the transition from engineering to logarithmic ("true") strain of metals (alloys) by analytical representation of metal hardening graphs as a function of logarithmic (true) strain. in contrast to the degree of engineering strain is presented. Originality. Analytical expressions are presented that allow the use of known theoretical data on the strain hardening of metals (alloys) at small (50...60 %) total engineering strains g during cold pressure treatment to transition to logarithmic (true) strain e with large total deformations. Practical value. The obtained mathematical expressions allow to use the accumulated in the technical literature experimental data on the hardening of metals and alloys with small engineering strains in the processes of cold processing of metals (alloys) by pressure to determine the hardening with large total logarithmic (true) strains. These data can also be used to solve metallophysical problems of metal processing by pressure associated with large total compressions. Keywords: cold forming of metals and alloys; hardening; degree of deformation

Research of stamping of unequal channel bars. Part 4. Deformed state of the workpiece when extruding channels. 1. Deformations in the area of wall formation

Determination of the deformed state of the workpiece at free extrusion of channels is considered. Formulas are obtained that make it possible to determine the accumulated deformations at a given point of the center of plastic deformation and the extruded walls of the product for any working stroke of the punch. Keywords: die forging, extrusion, misalignment, punch, matrix, plane deformation, accumulated deformation, hardening. [email protected]

The Influence of Magnetic Field on Fatigue and Mechanical Properties of a 35CrMo Steel

The influence of a magnetic field of 1.2–1.3 T on the variation of the fatigue behaviors and the mechanical properties of a 35CrMo steel after fatigue tests are investigated in this paper, in order to provide a basic guidance on the application in the similar environment of electrical machinery or vehicles. The microstructures of samples tested with and without magnetic fields are observed and analyzed by XRD, SEM, and TEM techniques. The fatigue life cycles are slightly increased by about 10–15% under magnetic field of 1.2–1.3 T according to the experimental results. A small increment of yield strength under fatigue life cycles of 10,000, 50,000, and 100,000 times is caused by the magnetic field, although the enhancement is only of 5–8 MPa. The dislocation density of the specimen is increased and the uniformity of dislocations is improved by magnetic fields applied during fatigue tests under the same load and cycles. The formation of micro-defects or micro-cracks will be postponed by the improvement in homogeneity of the material, leading to the increase of mechanical properties. The strengthening mechanisms such as deformation hardening and dislocation hardening effects are enhanced by the dislocation entangled structures and the higher density caused by magnetic field.

Methodology for calculating the technological parameters of preventive deformation of the hardened parts of the "wall" type

The article aims to establish the effect of preventive deformation on the accuracy of aircraft parts made from the thermally hardened aluminium alloy 1933T2, after blasting hardening. Determination of the impact of preventive deformation was carried out by analysing structural parts of the "wall" type produced using various technological sequences. Sample 1 was produced using a standard manufacturing sequence: milling – blasting hardening – blasting correction. Sample 2 was produced as follows: milling – preventive deformation – hardening – blasting correction. The deformation of the samples was determined at checkpoints by deviations from flatness based on bending deflections. In sample 2, preventive deformation was performed on its ridges by a rolling device. The calculation of the technological parameters of the rolling device was conducted following the principle of superposition of individual operations, such as rolling and blasting hardening. The definition of the parameters of preventive deformation of sample 2 was based on the results ob tained for sample 1. It was established that, for both samples, the deviation from flatness after milling comprised 2.5 mm. The maximum deviation of sample 1 (without preventive deformation) after blasting hardening was 2.6 mm under a high degree of surface saturation. The maximum deviation of sample 2 (with preventive deformation) after blasting hardening did not exceed 0.4 mm, which corresponds to the acceptable deviation of such structural parts. Thus, the inclusion of the preventive deformation stage in the manufacturing process, with consideration of the deviations resulting from the milling stage, allows minimisation of deviations from the required form after blasting hardening. An analysis of the obtained re[1]sults confirmed that preventive deformation of structural parts reduces distortions after blasting hardening. Therefore, it is advisable to use the following manufacturing sequence: preventive deformation → hardening by a blasting method → correction by a blasting method.

Effect of deformation hardening intensity, contact friction and back tension on indicators of wire drawing process

Dependences on the hardening factor for the drawing stress, the safety factor of I.L. Perlin and the stress state indicator V.L. Kolmogorov at different values of the drawing angle, coefficient of friction and stress of back tension are presented. For the first time, the nature of the dependences for the limiting and permissible values of delta-criterion is shown for the shape of the deformation zone of round solid profile on the coefficients of friction, hardening and safety factor and the back tension stresses. The limiting and permissible values of the delta-criterion increase from increase in the coefficients of friction and safety factor, the back tension stress and decrease from increase in the hardening coefficient. It is shown that for small values of the criterion ∆ < 1.5, the drawing stress can be higher than the yield point at the die output. As result, the wire material may be destroyed and the drawing process cannot be realized. Assessment of the change degree in the limiting and permissible values of the elongation coefficient and delta-criterion is carried out with increase in the friction coefficient from 0.05 to 0.15, the back tension from 0 to 85 MPa, the safety factor from 1.0 to 1.4, the hardening coefficient from 0 to k.

Processing of teeth of saw blades of cotton processing machines with a stream of compressed air with abrasive particles

In the article, it is presented materials on abrasive blasting of teeth of saw blades of cotton processing machines with particles of black silicon carbide. The micro-profile of the surface, characterized by the height and pitch of irregularities, after microcutting with abrasive particles is able to intensify the process of fiber separation by activating the tank surfaces of the teeth. This machining process is also accompanied by deformation hardening of the surface layer of the teeth, leading to an increase in the wear resistance and durability of the saws.