Steel Kh12M Research Articles

Wear-resistant diffusion coatings on steels for punching and coining dies

1. For punching and coining die parts the optimum combination of properties (high hardness of the base and wear resistance of the surface and sufficient core toughness) is obtained with a combination of chemicothermal and heat treatments (with water quenching of the container) only for Kh12M and KhVG steels (and primarily with use of carbide coatings). 2. The following processes are recommended: for Kh12M steel chemicothermal treatment in a container with a fusible seal at 1050°C for 5 h, water quenching of the container with the parts; for KhVG steel chemicothermal treatment in a container with a fusible seal at 1000°C for 5 h, furnace cooling of the container, austenitizing in the same sealed container at 850°C for 2 h, water quenching of the container with the parts. 3. For punching and coining dies (taking into consideration the proposed chemicothermal and heat treatment process) use of high-chromium type Kh12M steel is most desirable.

Semiautomatic welding of 15Kh5M steel in a carbon dioxide atmosphere without heat treatment of the weld joints

Semiautomatic welding of 15Kh5M steel in a carbon dioxide atmosphere without heat treatment of the weld joints

Improving the stability of a cold-worked tool

The recommended heat-treatment regime—quenching in the melt of a salt mixture and tempering at 380–400°C for 2 h—tends to produce an optimal combination of hardness, strength, and ductility, and ensures higher operational stability of punches formed from steels Kh12M and Kh12F1 as compared with those treated in accordance with the technology of series production. The annual saving generated from the implementation of this heat treatment is 12,000 rubles.

Effect of metastable residual austenite on the mechanical properties of steels Kh12M

1. An increase in austenitizing temperature for steel Kh12M increases austenite stability in relation to martensitic transformation during cooling, but it confusingly affects its intensity during subsequent loading. Depending on its temperature, tempering may both stabilize and destabilize austenite. 2. The level of mechanical properties for steel Kh12M is governed not only by the original phase composition, but also the degree of γres → α-transformation development during mechanical testing. Achievement of 15–20% metastable residual austenite and its conversion into martensite makes it possible to provide the best combination of strength and ductility properties with static torsion tests. A predominatly austenitic structure with a certain degree of stability causes an increase in the level of ductility and impact resistance for steel Kh12M. 3. For specific loading conditions it is necessary to control the amount and degree of residual austenite stability, which provides achievement of the required mechanical and service properties.

Change in structure, properties, and accumulation of damage in Kh12M and R6M5 steel in elastoplastic loading

1. An increase in hardening temperature of Kh12M steel to 1050°C leads to strengthening of its sensitivity to hardening in elastoplastic loading and intense formation of microcracks at the grain boundaries as the result of transformation of a large quantity of residual austenite into martensite. Therefore for tools operating under high specific loads treatment by preliminary high-temperature thermomechanical working is preferable. 2. Low-cycle loading of hardened Kh12M and R6M5 steels leads to gradual relaxation of first order residual stresses as the result of formation of microcracks for R6M5 steel and for Kh12M as the result of deformation of the residual austenite, which causes the formation of martensite and also leads to the appearance of microcracks, the quantity of which steadily increases. 3. Fracture of tools of hardened Kh12M and R6M5 steels is a multistage process and is determined by the length of each of the five stages (accumulation of damage, formation of a system of microcracks in local areas, formation of the initial macrocrack, cyclic growth of the initial crack, and transition to the unstable condition), the lengths of which depend upon the heat treat cycles and the effective loads.

Formation of the structure and properties of Kh12M steel in partial bainitic decomposition of austenite

1. To improve the mechanical properties of Kh12M steel, a stepped heat treatment including partial transformation of austenite in the bainitic transformation range for the purpose of obtaining structures of primary and secondary bainite in the hardened structure is proposed. 2. As the result of stepped heat treatment using the optimum cycles an α-solid solution with a high degree of homogeneity is formed in the structure of Kh12M steel after tempering. 3. To evaluate the effectiveness of the use of partial transformation of austenite in hardening heat treatment of Kh12M steel it is desirable to use a structural criterion taking into consideration the degree of homogeneity of the α-solid solution.

Stability of the properties of a steel Kh12M tool

1. After heat treating (annealing) steel Kh12M forgings, which is carried out under industrial conditions, scatter is observed in the hardness of a batch of tools, which is described well by a normal distribution. 2. Preliminary refinement (quenching from 950°C and subsequent high tempering) leads to a reduction in the mathematical expectancy of the hardness and to a reduction in the dispersion of its distribution, and tends to improve the stability of the properties of the tool consignment. 3. Holding of the finished tool at normal temperatures gives rise to an increase in the hardness of the entire consignment of tools; this must be considered during actual production.

Influence of the original structure, heat-treatment cycles, and deformation on the mechanical properties of Kh12M steel

1. In the as-received condition pearlite of different degrees of dispersion, which has a substantial influence on the phase composition and properties of the steel after hardening, is observed in the structure of Kh12M steel. 2. The preliminary thermomechanical working cycle developed (heating of the billets to 1020–1050°C, deformation by forging with e=25–30%, temperature of the finish of forging of not less than 870°C, and air cooling) makes it possible to eliminate nonuniformity in the pearlite, to obtain a structure with a constant degree of dispersion, and to increase the mechanical properties and life of a forming tool of Kh12M steel designed for cold extrusion.

Influence of the temperature and rate conditions of deformation on the mechanical properties of 15Kh5M steel

1. Relationships of the characteristics of strength and plasticity of 15Kh5M steel to the temperature and rate conditions of deformation in the range of test temperatures of 293–273°K and of deformation rates of 8.33 (10−3–10−7) sec−1 were established. 2. It was shown that in the 773–873°K service temperature range 15Kh5M steel possesses a significant deformation capacity (δ>7%). Under service conditions failure of 15Kh5M steel tubes must be preceded by significant local plastic deformation.

Evaluation of the long-term strength of 15Kh15M steel by extrapolation to 200,000 h

1. It was shown that the change of the fracture mechanisms from intergranular at the grain contacts to failure through the pores at the grain boundaries in 15Kh5M steel in the as-received condition at 570°C takes place in the time to fracture range 1300–1700 h. 2. The long-term strength of the specimens of 15Kh5M steel in the as-received condition at 570 and 620°C was determined by means of experiments. These results can be used to extrapolate the long-term strength of this steel to a life of up to 200,000 h.

Surface hardening with formation of ?-phase and its effect on the wear resistance of high-chromium stainless steels

1. A new method of surface hardening of high-chromium stainless steels of type 70Kh29N8M2 is suggested; the method is based on the predominant separating out of σ-phase in the specially decarburized surface layer. Decarburization is attained by vacuum heat treatment of previously oxidized steel. Such treatment yields a nonferromagnetic hardened surface layer 0.8 mm thick with hardness better than HRC 50. 2. When the structure of the investigated austenitic steels contains a large amount of σ-phase, their wear resistance increases in friction with lubricant when paired with steel Kh12M, and also in friction against fixed abrasive. Under these conditions the wear resistance of hardened steel Kh29N8M2 is equal to that of steel 9Kh18. In dry friction, which entails adhesional interaction of the metal surfaces, precipitation of σ-phase does not ensure high resistance to wear, because of the great brittleness of this phase.

Mechanical properties of die steels after low-temperature mechanical treatment

1. After LTMT, medium-carbon die steels 4Kh4VMFS, 4Kh5MF1S, and 6KhV2S obtain a better set of mechanical properties, compared with the properties of high-chromium steels Kh12F1, Kh12M, and Kh6VF, and fast-cutting steels R18, R12, and R6M5. 2. In order to provide the optimum set of mechanical properties after LTMT, the hardness of steels 4Kh4VMFS and 4Kh5MF1S should be HRC 58–60, and for steels Kh6VF and 6KhV2S it should be HRC 60-62.

Stress-rupture strength of 15Kh5M steel after long service in the tube furnaces of oil-refining equipment

1. The failure of 15Kh5M steel after 100,000 h of service under the conditions of a petroleum refining tube furnace in stress-rupture strength testing at temperatures of 570 and 620°C occurs according to a single type-failure at voids. 2. On the basis of the results of a probability determination of the mean and minimum values of stress-rupture strength of 15Kh5M steel after long service, the stress-rupture strength curves were extrapolated in the area of the experiment and the stress-rupture strengths were determined to a base of up to 40,000 h.

Modification of Kh12M steel

1. In practice it is advisable to modify steels of the Kh12M type with aluminum, yttrium, and boron, since this helps to achieve more uniform distribution of eutectic carbides, to decrease segregation of alloying elements, and to decrease sensitivity of the steel to overheating. 2. Carbide inclusions in forged and annealed modified steel Kh12M are small in size and of characteristic shape. 3. Modification of steel Kh12M promotes transformation of austenite during tempering, promotes precipitation hardening, improves mechanical properties, and increases by 1.5–2 times the wear resistance of tools.

Effect of annealing on the structure and properties of molybdenum coatings on steel Kh12M

1. Molybdenum coatings obtained by the method of CIB on steel Kh12M, during the process of high-temperature annealing, become saturated with the carbon of the base, and the solid phase Mo2C forms. 2. In consequence of the opposite diffusion of carbon and molybdenum, a zone of increased hardness forms in the surface layer of the steel. The thickness of this zone depends on the annealing temperature.

Residual austenite in tool steel Kh12M

1. With increased quenching temperature, high-chromium tool steels contain much more residual austenite than other tool steels. 2. With a residual austenite content >40%, the bending strength of steel Kh12M is reduced. Each additional 1% >40%) of austenite causes a reduction in bending strength by ∼0.8%. 3. Impact strength of quenched steel Kh12M increases markedly with increasing residual austenite content. With an increased quenching temperature, the positive effect of austenite on impact strength increases. 4. There is a parabolic relationship between the amount of residual austenite and the hardness of quenched steel Kh12M. 5. With increased quenching temperature the effect of residual austenite on linear quench deformation of a component decreases. 6. Repeated heating of a quenched component of steel Kh12M above 400°C and cooling causes residual austenite breakdown and a change in dimensions and hardness.

Features of the structure of Kh12M steel in the hardened and tempered conditions

Features of the structure of Kh12M steel in the hardened and tempered conditions

Automatic welding of circular joints in chemical apparatus of steel 15Kh5M

Automatic welding of circular joints in chemical apparatus of steel 15Kh5M

Electrothermal treatment of high-alloy die steels

1. Electrothermal treatment (electrohardening+electrotempering) of complex alloy steel 8Kh4V2S2MF increases the hardness to HRC 65-67. 2. Electrothermal treatment (hardening with holding 20 sec at austenitizing temperature and electrotempering) of ledeburitic steel Kh12M makes it possible to obtain a hardness of HRC 61-63. 3. To obtain a long service life for tools subject to large alternating loads it is expedient to have some amount of retained austenite in the structure.

Vacuum quenching of steel Kh12M

Vacuum quenching of die steel Kh12M in argon and in VM-1 vacuum oil after heating to 1030° (10−1 mm Hg) ensures a hardness of HRC 63-64 with retention of a bright surface and reduction of distortion.