The methodology for testing pipeline steels is suggested on the assumption that for the destruction of pipes in field oil pipelines by the mechanism of grooving corrosion the simultaneous fulfillment of such conditions as the occurrence of scratches on the lower generatrix of the pipe, eventually growing into a channel in the form of a groove, emulsion enrichment with oxygen, presence of pipe wall metal in a stressed state, presence of chlorine-ion in the oil-water emulsion is required. Tests are suggested to be carried out in 3 % aqueous solution of NaCl with continuous aeration by air on bent plates 150×15×3 mm, made of the analyzed steel, the middle part of which is under the action of residual stresses σ res , close to the level of maximum equivalent stresses σ eqv in the wall of the oil pipeline, with the presence of a cut on this part on the inner side of the plate as an initiator of additional mechanical stresses. Using the value of the modulus of normal elasticity of the analyzed steel, the degree of residual strain of the elastic-plastic body from this material, corresponding to the value σ res ≈ σ eqv is calculated, based on which the plates are bent to the required deflection angle, after which the cut is applied to them. After keeping the plates in the corrosive medium for each of them the increase in depth of the cut as a result of corrosion of the walls by the corrosive medium is analyzed, from which the rate of steel K by the mechanism of grooving corrosion is calculated taking into account the duration of tests. Corrosion rate values for two pipe steel grades determined by the suggested procedure are given. The comparison of K values obtained leads to the conclusion about the higher resistance to grooving corrosion of 09G2S steel.
The technique and the results of experiments on the study of the laws of the process of the cone-shaped tip of a freely falling impactor made of 38HM, U8, H12MF steels, subjected to typical heat treatment and additionally treated with cold, when they apply multiple (up to 10000) single impacts on granite under conditions approaching hydraulic impactor peaks. To explain the processes, we used the values of stresses σ к , arising at the contact area of the impactor and the rock, calculated using the developed mathematical model. It has been established that the process of wear of an impactor with multiple single blows proceeds in three stages separated by critical values, , which correspond to the strength characteristics of the material of the impactor demonstrated in these dynamic conditions. With a small number of strokes (n ≤ n * ) and the small size of the blunting area (stage I interaction) values σ c exceed of steel and it is exposed to local destruction at the contact site, which is recorded as a significant loss of the impactor’s mass; with n * < n ≤ n ** (stage II) the resulting stresses are not enough to destroy the material, but it is enough for its plastic deformation, accompanied by the movement of metal from the central part of the contact area to the peripheral and the destruction of part of the deformed metal by rock; with n > n ** (stage III) arising σ к do not reach the level and the decrease in the mass of the impactor is determined by the resistance of the steel to abrasion by the products of rock destruction, displaced by the impactor from the well. The treatment of impactors from all tested steels with cold leads to an increase in their wear resistance; The total depth of the holes punctured by the cold-treated H12MF steel impactor at the time of the interruption of the rock penetration is four times higher than that of the 38HM steel impactor subjected to typical heat treatment.
Hadfield steel (110G13L) is the basic material for fast wornout items of mining equipment: beaters, hammers, liners, refractory plates of crushers and mills. By way of example, the effect of cold hardening was specifically analyzed on the rate of wear of mining equipment parts for various types of wear by hard (more than 1100 HV) and soft rock. A unique ability of that steel to resist shock wear is noted. It is shown that this steel exhibits low resistance to abrasive rock wear. Meanwhile wear by rock of hardness lower than steel (less than 1100 HV), may be substantially increased by pre-hardening of samples (up to 10-fold). In case of wear by high hardness rocks, shock impact that should contribute to hardening of the material, fails to increase abrasive wear resistance of Hadfield steel, and in that parameter it does not differ from the conventional medium carbon steel 45. Also, the authors of this article describe a technique they developed of high-temperature thermomechanical treatment of specimen of Hadfield steel (free forging at 1150-950ºC and subsequent quenching in water) and experiments in their abrasion. The results of tests show that hardness and wear resistance of Hadfield steel to hard abrasive (corundum 25A with aggregate hardness of ~2500 HV) increases with plastic deformation at HTMT. For maximum plastic deformation intensity (deformation magnitude of α = 2.25), reached in the experiments by the authors, wear resistance grew by 70% as compared to undeformed steel. The dependence is presented of wear resistance of steel on hardness, HV, achieved in the result of plastic deformation. Since a similar positive effect was obtained earlier by the authors for 35HGSA steel, also used in mining machinery, they conclude that the HTMT technique may be recommended for treating short lived parts of the mining and mineral processing equipment to increase their service life.
For example, steel 110G13L as the material of teeth of excavator buckets, shows that the work hardening (hardening) is an effective means to increase (up to 10 times) the wear resistance of components in contact with abrasive media, such as marble, yielding the steel in a state of hard-ening of hardness. In the case of wear on the rocks (granite, gabbro) with a hardness greater than the hardness of steel, the effect of hardening has almost no effect. It was found that high-temperature thermomechanical treatment of steel 35HGSA as the material of holders of rotary cut-ters (strain at 900 С, water quenching, tempering at 230 С) leads to a substantial increase of its hardness (23 %) and durability (38 %) compared to typical heat treatment used in the manufacture of cutting tools at the factory.
Regularities abrasion steel 110G13L with a significant load on the sample and impact. Found that increasing the load to the point where the voltage on the surface of the sample achieved a true rupture stress of the material, does not increase the wear resistance of steel. Shown that the impact and, therefore, have no hardening significant influence on the wear rate of steel in its work on the solids (granite, gabbro). In the case of soft rocks (marble) concomitant impact effect is exceeds durability of the material. Designed conclusion on whether the elements are made of mining and processing equipment from steel 110G13L depending on the hardness of the destroyed rock.
Taking a grinding of coal ball mill (type: BTM 400/800) operating without rocks as an example it is shown that a bombardment of the armour by grinding bodies made of steel 110G13L directly is capable to raise its hardness from 200 to 320HB at the depth of the cold-hardened layer up to 6,7 mm that will approximately 2 times increase its firmness to an abrasion. The time needed for the realization of an effective bombardment is 11 minutes, the period between strengthening cold – work hardenings is 25 days.
In article the analysis data of mechanical and metallographic researches of tangential rotary cutters of the Russian and foreign manufacturers is resulted. The reason of fragility of tangential cutters of the Russian manufacture is specified.
The method is offered which allows to increase the wear resistance of bit bodies for continuous miners by means of their additional full hardening. This results in increasing the bit body hardness from 37-42 HRC up to 49-51 HRC, which must bring to increasing in wear resistance approximately of 25 %. The suggestion has been tested with a batch of bits spec. RKS-2 (РКС-2) in the mines of Vorkuta and have demonstrated an increasing in wear resistance compared with that of the bits which had not been exposed to an additional hardening.
It is shown that X-ray fluorescence method can be utilized to determine composition of steels used for manufacturing the rockbreaking tools. A conclusion is derived that one of the possible cause of low wear resistance of miner bits in «Vorkutaugol» is their bodies manufacturing from the steels, which do not meet the Mining Code specifications.
