High-temperature Thermomechanical Working Research Articles

Martensitic transformations and martensite structure in thermomechanically strengthened high-nitrogen steels

Structure and properties formed as a result of martensitic transformations during cooling and cold working, and subsequent tempering in metastable carbon- and nitrogen-containing austenitic iron alloys were studied using magnetometric, X-ray diffraction and electron microscopy analyses as well as mechanical tests. Hot deformation in a cycle of high-temperature thermomechanical treatment influences the martensitic transformations, martensite structure and tempering processes in dependence on steel composition, structure and treatment regime. The austenitic high-nitrogen chromium and chromium-manganese steels are noticeably strengthened under rather small strain. At high strains, they are inclined to the martensitic transformation. The cold working accelerates the tempering processes in all the steels studied. The strengthening by high-temperature thermomechanical treatment or cold working of the nitrogen-containing steels remains up to higher heating temperatures. Alloying of nitrogen-containing steels by vanadium retards the decomposition processes during tempering and aging and makes dispersion hardening of the austenite and martensite more effective.

An investigation of the uniformity of mechanical properties of forgings of VT9 titanium alloy after superplastic deformation and high-temperature thermomechanical processing

The results are presented of evaluation of the uniformity of mechanical properties and structure of VT9 alloy after deformation with different degrees under conditions of superplasticity and high-temperature thermomechanical working. It is shown that the strength and plastic properties of forgings of this alloy after superplastic deformation with degrees from 10 to 70% are stable and quite high. The macro- and microstructures of such forgings and uniform. High-temperature thermomechanical working with an increase in the degree of deformation leads to a reduction in plasticity an an increase in strength with a significant spread in properties apparently related to the structural nonuniformity. The results obtained make it possible to evaluate the advantages of treatment under conditions of superplasticity and in comparison with high-temperature thermomechanical working. 7 refs., 1 fig., 1 tab.

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.

Influence of preliminary heat treatment or thermomechanical working on the properties of 51KhFA steel wire after high-temperature thermomechanical working

1. Preliminary heat treatment of the wire rod provides an improvement in the combination of mechanical properties of the wire which it acquires after high-temperature thermomechanical working and in the service properties of the springs. 2. In preparation of the structure of the steel for high-temperature thermomechanical working it is necessary to create a uniform ferritic-pearlitic structure with lamellar or rodshaped carbide particles 0.01–0.05 μm thick. 3. For 51KhFA steel the highest combination of properties after high-temperature thermomechanical working is obtained with the use of normalizing with heating in a salt bath and also of patenting with subsequent tempering at the patenting temperature as the preliminary heat treatment. 4. Cold deformation after preliminary heat treatment does not have a significant influence on the properties of high-temperature thermomechanically worked wire.

The influence of rate-earth metals on the physicomechanical properties of steel in thermomechanical working

The authors study the stabilizing influence of rare-earth metals on the structural condition of thermomechanically worked steels. 45, 60, U8A, 50KhGA, and 70S2KhA steels were used for the investigation. The rare-earth metals used were lanthanum, cerium, and a mixture of rare-earth metals called mischmetal. Impact strength tests of Mesnager specimens at room temperature showed that the favorable influence of high-temperature thermomechanical working is strengthened with an increase in carbon content in the steel. Results are shown of investigations at sub-zero temperatures of Charpy specimens with an initiated fatigue crack. Rare-earth metal microadditions are shown to have a good influence on the structurally sensitive characteristics of the steel, the contact strength and the corrosion resistance. Rare-earth metals also retard the development of the recrystallization processes of the deformed austenite.

Structure and properties of constructional steels after high-temperature thermomechanical isothermal working

Structure and properties of constructional steels after high-temperature thermomechanical isothermal working

Influence of thermomechanical working on the failure resistance of U8A steel

1. With a decrease in austenitic grain size and the creation of a developed substructure within the limits of a single grain size with high-temperature thermomechanical working the impact strength, work for crack propagation, and share of ductile constituent in the fracture increase in comparison with induction hardening. 2. High-temperature thermomechanical working promotes the obtaining of martensite in which the processes of self-tempering to a two-phase mechanism occur more fully than with treatment by other methods.

What is high-temperature thermomechanical working?

What is high-temperature thermomechanical working?

Corrosion resistance of 12Kh18N10T steel after high-temperature thermomechanical working

Corrosion resistance of 12Kh18N10T steel after high-temperature thermomechanical working

Influence of the change in grain shape in high-temperature thermomechanical working on the strength of steel

1. The increase in high-temperature thermomechanical working in the yield strength of 40Kh2N2VA steel with an increase in the degree of deformation is caused by the formation of an austenitic substructure and the inheritance of this substructure by the martensite crystals. 2. The increase in yield strength with an increase in the degree of deformation is more significant in fine-grained steel than in coarse-grained. 3. The increased strength after high-temperature thermomechanical working accompanied by recrystallization is to a significant degree caused by the fine-grained structure (average grain size no more than 10 μm).

The influence of high-temperature thermomechanical working on the amount of the Bauschinger effect in 40S2Kh and 60S2Kh steels

The influence of high-temperature thermomechanical working on the amount of the Bauschinger effect in 40S2Kh and 60S2Kh steels

The thermomechanical working of carbon steel

1. Plastic deformation of stable austenite with limitation of the development of recrystallization, provides strengthening of the final structure in all forms of transformation-martensitic, intermediate, and pearlitic. 2. The strengthening effect is different with different forms of transformation in eutectic carbon steel. Strengthening as the result of deformation is a maximum in the martensitic transformation, with the tensile strength increasing 30% and the ductility dropping by half; a minimum in the pearlitic transformation, with an increase in ductility of 20% and in strength of 15–20%; and with an intermediate value for intermediate transformation, an increase in strength of 20% and in ductility also of 20%. 3. The maximum strengthening is obtained with an austenite deformation of 25–35% for the martensitic transformation; of 15–20% for the intermediate transformation; and of 6–8% for the pearlitic transformation. 4. As a result of changes in the fine structure of the strengthened steel the addition of a small quantity of titanium provides high ductility. 5. The desirability of using particular methods of treating eutectic carbon steel, such as high temperature thermomechanical working, high temperature thermomechanical working with isothermal transformation, and high temperature thermomechanical working with diffusion transformation, is determined by the dimensions of the starting piece, service conditions, and production conditions.

The stability of the influence of high temperature thermomechanical working on the properties of 1Kh12VNMF steel

1. The increased mechanical properties of 1Kh12VNMF as a result of high temperature thermome chanical working remained at high tempering temperatures and is preserved after repeated heat treatment. 2. The use of high temperature thermomechanical working and tempering at 200°C of 1Kh12VNMF makes it possible to increase the erosion resistance of the steel by more than five times in comparison with the use of the normal heat treatment consisting of hardening and tempering at 680°C. 3. High temperature thermomechanical working with rehardening, which provides high properties in 1Kh12VNMF, may be used for the production of machined parts.