Selection of the chemical composition of steels and their thermal hardening mode using a computer program

The relationships between the parameters of the structure of heat‑treated steels and their abrasive wear resistance are established. At all temperatures of the final tempering of hardened steel, there is a direct relationship between its structure parameters (the number of elements in a solid solution, the density of dislocations, the size of cementite particles and the intercementite distance) and wear resistance when sliding friction against loose abrasive particles. A computer program has been developed to select the chemical composition of the steel grade and methods of thermal hardening in order to ensure the required wear resistance.

Quantified Static Recovery Trend of Constricted Jogs of Aluminium Alloys During Annealing

The static recovery of dislocations in aluminium alloys is known to observe during re-heating and inter-annealing of aluminium alloys, so that the fully recrystallised and partially recrystallised grain structures are deliberated respectively for a judicious control on their final tempering of strength, ductility, toughness and crystallographic texture to eliminate the earing related problems. An elaborate physical based static recovery simulator is required to address the trend of dislocation recovery during the time of industrial annealing to evaluate the extent of discontinuously and continuously developed recrystallised aluminium alloys. New industrial annealing practices to develop an extensively wide range of aluminium alloys with the medium to low stacking fault energy range, suitable for their plenty of use in defence vehicles, inevitably demand quantified dislocation density, the decisive element of flow strength. The formulated static recovery rate of the constricted dislocation jogs increases with the stacking fault energy and increases with the industrial annealing temperature. The formulated static recovery of dislocations is found to be very precise and concentric to address the process and materials characteristics, so that it would be liable to define the minute change in the processing temperature, i.e. 50K.

Impact Toughness Modification of NIST Low-Energy Charpy Verification Specimens for Testing at Room Temperature

The possibility for the National Institute for Standards and Technology (NIST) to certify Charpy reference specimens for testing at room temperature (21 °C ± 1 °C) instead of −40 °C was investigated in a previous study, in which a slightly increased likelihood of specimen jamming was observed at the low-energy level (13 J to 20 J). Moreover, there is a concern that the higher impact toughness of low-energy verification specimens at room temperature would not allow the same Charpy machine features to be verified as in the case of low-temperature (−40 °C) tests, namely, the linear elastic behavior of the sample and the very high maximum forces (typically larger than 33 kN). In this paper, we report on the change in the mechanical properties (hardness and absorbed energy) of the American Iron and Steel Institute (AISI) 4340 steel low-energy specimens that ensues from the modification of the temperature of the final tempering heat treatment. We established that, if low-energy verification specimens are tempered at 300 °C for 2 h and then air cooled, they exhibit equivalent impact toughness (13 J to 20 J) and postimpact behavior (specimen halves projected backward at high speed) at room temperature as compared to specimens currently on sale for testing at −40 °C. Their hardness is however increased to above 49 HRC on the Rockwell scale. The minimum hardness requirement for low-energy verification specimens, currently set at 44 HRC in NIST specifications, will have to be increased to 49 HRC.

Study by Differential Thermal Analysis of Reverse Spinodal Transformation in 15-5 PH Alloy.

Alloy 15-5 PH is a stainless steel with 15 wt.% Cr and 5 wt.% Ni that is precipitation hardened by addition of Cu. In its semi-finished state, this alloy consists in Cu-supersaturated soft martensite; its high specific properties come from a final tempering consisting in a heating to 550-600°C, holding for 4 hours, and then air cooling. This treatment leads to nanometric Cu precipitation that hardens the material and to transformation of some martensite to reverted austenite which is then stable and provides ductility. While a' embrittlement of such steels is known to occur at temperature in the range 450-520°C, it has been reported that they can be sensitive to the same phenomenon after long term ageing at temperature as low as 300°C, with a significant loss of ductility and an increase of the ductile-to-brittle transition temperature. Atom probe studies showed that this degradation is related to demixtion of martensite into Fe-rich and Cr-rich phases. Depending on the ageing temperature, demixtion can proceed through a nucleation and growth precipitation or by spinodal decomposition of the martensitic matrix. The present study reports differential thermal analyses (DTA) performed upon heating samples of material held at various temperatures (290-525°C) for various times (410 h to 8500 h) that have been characterized by atom probe. A clear DTA signal is obtained upon the reverse spinodal transformation that is further found to depend on ageing conditions.

Effect of a Complex Heat Treatment on the Structure of 300M Steel

Intermediate high temperature tempering prior to subsequent reaustenitization has been shown to double the plane strain fracture toughness as compared to conventionally heat treated UHSLA steels, at similar yield strength levels. The precipitation (during tempering) of metal carbides and their subsequent partial redissolution and refinement (during reaustenitization), in addition to the reduction in the prior austenite grain size during the cycling operation have all been suggested to contribute to the observed improvement in the mechanical properties. In this investigation, 300M steel was initially austenitized at 1143°K and then subjected to intermediate tempering at 923°K for 1 hr. before reaustenitizing at 1123°K for a short time and final tempering at 583°K. The changes in the microstructure responsible for the improvement in the properties have been studied and compared with conventionally heat treated steel. Fig. 1 shows interlath films of retained austenite produced during conventionally heat treatment.

The Embrittlement of Low-Carbon Steel

The paper deals with those changes in the mechanical properties of steel having a low carbon content, which occur as a result of quenching from temperatures up to 900 deg. C. Attention is directed mainly to brittleness, especially to that resulting from ageing at atmospheric temperature, which the authors term “age embrittlement.” The range of temperature in which this occurs appears to include those temperatures used in the carburizing treatment of steel as well as lower temperatures. It is suggested that case-hardened steels should be subjected to a final tempering treatment after quenching to avoid the possibility of core brittleness. Theories are briefly discussed, but at present no direct explanation of the phenomenon is forthcoming, as X-ray and microscopic examination reveal no abnormalities in the age-embrittled steel. Ageing at 100 deg. C., after quenching, shows distinct age hardening, but this is found to be dissociated from age embrittlement.