The investigation of applicability of the Hollomon-Jaffe equation on tempering the HSLA steel

Abstract

High strength low-alloyed (HSLA) Cr-Mn-Si steels belong to a group of steels that can reach their full mechanical properties after quenching and tempering. Those properties depend both on the temperature and time of tempering. Knowing the tempering parameters, it is possible to reach the desired properties of the treated steel. Some results on investigating the Hollomon-Jaffe equation (in parametric form) application for tempering of HSLA steel, are shown in this paper. The experiments were performed in real production conditions, using a standard material. The quenching was performed at 870 °C, the heating period was always 30 min, with subsequent cooling into the oil bath. The tempering was carried out in temperature range from 480 to 680 °C, while tempering time varied from 15 min to 24 h. The degree of tempering is referred through the hardness values changing. The experimental results have shown a pretty well agreement to tempering parameters, included in Hollomon--Jaffe equation, for this kind of HSLA steel.Quenched steels, from a group of heat-treatable steels, always have high values of both hardness and strength, but pretty low values of impact properties. The residual stresses are also on a high level. So, any kind of tempering has to be done -depending of the steel type. However, the tempering [1-4] is provided in a wide temperature range (even up to Ac 1 point), and then a wide diapason of structures will appear: from the untransformed martensite (with differrent amounts of retained austenite) to the structure, which contains carbide globules into ferrite matrix.Although the tempering temperature shows a dominant influence on the structure changes, the tempering time also has a strong influence but is usually less investigated. One more reason for investigating the tempering time is a fully diffusion character of all processes which are involved in tempering processes [1,4]. In relation with the processes mentioned, many efforts are still made to find out one proper parameter, which will include both the temperature and time of tempering. Only in that way, i.e., on the equivalency of a simultaneous influence of tempering temperature

Mathematical Description of the Microstructural Modifications and Changes in the Mechanical Properties during Spheroidization of Medium‐Carbon Steel

“…Figure (left) shows the measured hardness with the tempering parameter using a calculated constant C = 12.69 and the composition‐dependent tempering parameter from Equation , respectively. The data are from the present investigation and from Jusevic et al for a high‐strength low‐alloyed steel with a composition (wt%) of 0.30C, 0.90 Si, 0.98 Mn, and 1.0 Cr after quenching at 870 °C and annealing at two different temperatures of 600 and 650 °C for 0.25 to 24 h. Despite the different hardness values due to the different chemical compositions of the steels, the measured hardness values decrease with increasing tempering parameter. The linear relationships show a good correlation.…”

Optimization of furnace residence time and loading pattern during heat treatment of large size forgings

“…These microstructural changes have a determining effect on the hardness, as the most common qualification criteria for successful heat treatment in the steel industry. According to Janjušević et al [3] the final mechanical properties and microstructural features are affected significantly by tempering temperature and holding time inside the furnace. Therefore, uniformity of the heating process, in other words, the temperature distribution's uniformity during the non-isothermal tempering up to the target temperature is of great importance for the quality of final products [4], specifically for large size products.…”

Hardness Prediction in Quenched and Tempered Nodular Cast Iron Using the Hollomon-Jaffe Parameter

“…Figure 7 shows the value of R 2 when different values of C are used. As that figure shows, the range of values from which C can be chosen and still have a coefficient of determination R 2 over 0.95 goes from 17 to 39, what explains the different values proposed by different authors or the aforementioned negligible influence of C in the applicability of the tempering parameter [24]. Evidently, the value of TP will change with C. In this case, as the use of C = 20 gives good results (R 2 = 0.971), it was decided to maintain that value in pursuit of a better comparability with bibliographic results.…”

“…Although this value has been widely used [15][16][17][18] even for new steels [19,20], other values have also been proposed for different alloys, basically through the fit of experimental data [16,[21][22][23]. Even a negligible influence of the value of C in the applicability of the tempering parameter has been suggested [24], which could explain the aforementioned wide and appropriate use of a value of 20 for C.…”