Metastable austenitic Cr−Mn steelsFilippov, M.
doi: 10.1007/BF00774728pmid: N/A
1.
The contact strength of machine parts operating under various conditions of contact dynamic loading (cavitation-erosion, gas erosion, friction, and impact-abrasive wear) can be improved substantially by using Cr−Mn MAS steels.
2.
The resistance of Cr−Mn MAS depends on the conditions of CDL, the rate of the martensitic transformation, and the properties of the phases formed. For applications involving cavitation we recommend steels containing 0.1–0.3% (C+N) of the 10Kh14AG12-30Kh10G10 type, in which the γ→ε and γ→α martensitic transformations occur at a high rate; steels with a high carbon content (0.6–0.8%) in which the γ→α transformation is the primary transformation under load (steels of the 60Kh5G10L-70Kh4G8L type) are promising for impact-abrasive wear conditions.
Structure and properties of low-carbon steel alloyed with boron and copperMalinochka, Ya.; Koval'chuk, G.; Yarmosh, V.
doi: 10.1007/BF00774730pmid: N/A
1.
Adding as much as 0.5% Cu to steel microalloyed with boron (as much as 0.003%) increases the solubility of boron in austenite and prevents precipitation of brittle boron-containing phase in austenite grain boundaries. This simplifies the melting procedure for steels with boron.
2.
In steels with a higher boron content (0.003–0.005%) that are additionally alloyed with copper the borides are evenly precipitated within grains and in grain boundaries as small equiaxed inclusions. No boride phase was detected in cast or rolled steel with 0.003% B and 0.41% Cu.
3.
Adding copper to steel with boron increases the stability of supercooled austenite somewhat and has no negative effect on the hardenability of the steel.
4.
After heat treatment, steel with boron and copper has higher values of the strength and especially the fracture toughness as compared with steel with boron but without copper. The ductility of the steel with both additions is fairly high and approaches that of unalloyed steel as the tempering temperature is raised. Adding copper lowers the ductile-brittle transition temperature of steel containing boron.
Microstructure and mechanical properties of 20GTL steel after heat treatment using various cyclesZhukov, A.; Bekerman, F.; Kharitonov, A.; Bondarev, A.; Platonov, A.
doi: 10.1007/BF00774731pmid: N/A
1.
For steel with an unfavorable “balance” of components from the point of view of its tendency toward the formation of a pearlite network microalloying (modification) with titantium, which makes it possible to prevent the formation of Widmanstätten pattern in the cast condition, is insufficient for preventing pearlite network in cooling of austenite in heat treatment with relatively low rates.
In this case the primary method of eliminating the pearlite network is increasing the degree of supercooling of the austenite in the area of subcritical temperatures, which is obtained by overheating in austenitizing and increasing the cooling rate of the metal in normalizing or in the temperature range between austenitizing and the subcritical hold in “isothermal annealing.”
2.
Steel modified with titanium and having a quite high residual aluminum content is relatively insensitive to overheating. 20GTL steel may be austenitized at 920 and even at 970°C. Overheating at 1050°C also does not lead to a significant reduction in its mechanical properties. The impact strength of the normalized steel (including at −60°C) is more sensitive to underheating than to overheating.
3.
The negative influence of the pearlite network in the structure of 20GTL steel is revealed in a reduction in impact strength at +20 and −60°C, primarily after austenitizing at reduced temperatures. Normalizing from 920 and especially from 970°C provides a quite high impact strength.
4.
Tempering of steel after normalizing is relatively ineffective since as the result of tempering only the ductile properties of the steel increase.
5.
After isothermal annealing significant advantages in mechanical properties in comparision with normalizing are not obtained.
6.
Hardening and tempering of cast steel makes it possible to completely homogenize its microstructure and significantly increase the strength properties without a significant reduction in ductility. However, the impact strength at +20 and −60°C does not increase although it remains sufficiently high.
7.
In hardening and tempering 20GTL steel tempering at 550°C is ineffective, especially with a hold of 1.5 h. Tempering of hardened and tempering steel at 650°C leads to reduction in the strength properties with an insignificant increase in ductility and impact strength.
Structure and properties of steel for high-pressure vesselsBalakhovskaya, M.; Nadtsyna, L.; Davlyatova, L.
doi: 10.1007/BF00774732pmid: N/A
1.
The structure of 16GNMA steel in the normalized condition consists of ferrite and bainite or of upper bainite.
2.
The steel with the bainitic structure is characterized by a higher thermal fatigue resistance than that with a ferritic-bainitic structure. When together with thermal fatigue the metal is subjected to the action of shut-down (acid) corrosion, the steel with the bainitic structure is less reliable.
3.
Both in the original (after normalizing and tempering) and the aged conditions 16GNMA steel has sufficiently high resistance to brittle fracture.
Structural formation of high-speed steels during crystallizationNizhnikovskaya, P.; Kalinushkin, E.; Snagovskii, L.; Demchenko, G.
doi: 10.1007/BF00774734pmid: N/A
The L+δ→ψ peritectic transformation in tungsten-molybdenum high-speed steels goes to completion prior to the start of the eutectic reaction (L→ψ+K), which may precede segregation of austenite from the liquid (with a high carbon content). In this case, the eutectic is crystallized on the base of the metastable M2C carbide. Conditions for the formation of thermodynamically more stable MC and M6C carbides are created during slow cooling characteristic for the central zones and upper horizons of an ingot. Eutectics based on these carbides begin to crystallize at comparatively high temperatures, when the peritectic transformation has yet to go to completion. In a certain temperature interval, these transformations occur simultaneously; in this case, they can be suppressed by the eutectic crystallization owing to the characteristic features of the peritectic transformation. As a result, δ-ferrite (the products of its decomposition) is present in the steel.
Modification of Kh12M steelPavaras, A.; Popandopulo, A.; Ambrosa, P.; Vishkarev, A.; Savinov, V.
doi: 10.1007/BF00774737pmid: N/A
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.