Preparation and Mechanical Behavior of Ultra-High Strength Low-Carbon Steel

Abstract

The low-carbon steel (~0.12 wt%) with complete martensite structure, obtained by quenching, was cold rolled to get the high-strength steel sheets. Then, the mechanical properties of the sheets were measured at different angles to the rolling direction, and the microstructural evolution of low-carbon martensite with cold rolling reduction was observed. The results show that the hardness and the strength gradually increase with increasing rolling reduction, while the elongation and impact toughness obviously decrease. The strength of the sheets with the same rolling reduction are different at the angles of 0°, 45°, and 90° to the rolling direction. The tensile strength (elongation) along the rolling direction is higher than that in the other two directions, but the differences between them are not obvious. When the aging was performed at a low temperature, the strength of the initial martensite and deformed martensite increased with increasing aging time during the early stages of aging, followed by a gradual decrease with further aging. However, the elongation increases with increasing aging time. The change of hardness is consistent with that of strength for the cold-rolled martensite, while the hardness of the initial martensite decreases gradually with increasing aging time.

Microstructure Evolution and Mechanical Properties of X6CrNiMoVNb11-2 Stainless Steel after Heat Treatment

“…It is should be noted that Ni 3 Mo is rod-shaped, where the length direction of the rod and matrix is in the <111> direction [ 2 ]. The close-packed surface and direction of δ-Ni 3 Mo and η-Ni 3 Nb phases are parallel to the matrix, with the existence of the coherent or semicoherent relation between δ-Ni 3 Mo/η-Ni 3 Nb and matrix, thus the strength is remarkably improved [ 1 , 2 , 51 , 52 , 53 , 54 ].…”

“…As can be seen in Table 7 , it can be concluded that the cooling ability of the steel core is insufficient when quenching with oil, which results in lower hardness at the central core without meeting the engineering requirements for the intended application, and the hardness difference between the surface and center is about 27 HV. The tempered hardness of the steel core can reach the standard requirement when the PAG polymer medium is used for quenching and tempering; however, the hardness difference between the surface and center is still large, due to the precipitation of carbide during the tempering process [ 53 , 54 ].…”

“…As can be seen in Table 7, it can be concluded that the cooling ability of the steel core is insufficient when quenching with oil, which results in lower hardness at the central core without meeting the engineering requirements for the intended application, and the hardness difference between the surface and center is about 27 HV. The tempered hardness of the steel core can reach the standard requirement when the PAG polymer medium is used for quenching and tempering; however, the hardness difference between the surface and center is still large, due to the precipitation of carbide during the tempering process [53,54] From Figure 12a, with an increase in quenching temperature from 1020 to 1060 °C, the yield strength and tensile strength increase. However, with an increase in tempering temperature from 630 to 670 °C, the diffusion of carbon in martensite leads to the decrease in carbon content in martensite; as a result, the tensile strength and yield strength show a decreasing trend.…”

Characterisation of the plane anisotropy and its effect on interstitial free steel thin sheet metal forming simulation

“…According to the experimental tests (see Figure 5), the considered steel exhibits an anisotropic behaviour which is demonstrated by the variation of the mechanical properties with the in-plane direction. 31,[50][51][52] It is noticed that the hardening curves corresponding to the directions 00°, 30°a nd 45°from the rolling direction had extremely similar mechanical properties up to 20.8% in strain. In addition, the values of yield strength and maximum tensile strength were close.…”

The study of influence of heat treatment procedures on structure and properties of the new high-strength steel with increased cold resistance

“…Respectively, the complex properties are required for mechanical parameters of materials used for fabrication of welding elements of a frame construction. The following properties can be mentioned here: high strength (600-1100 N/mm 2 ) with reservation of sufficient level of tough and ductile parameters at low temperatures (KCV -60 t 50 J/sm 2 ) as well as weldability (C eq d 0.53) [1][2][3][4][5][6].…”