Abstract
This paper reports a study of the addition effects of either titanium or titanium and nitrogen of steel grade DIN 56NiCrMoV7 on mechanical properties. Three steel grades were produced in 30 kg-induction furnace, one conforms the chemical composition of conventional 56NiCrMoV7 while the other two produced steels were microalloyed by either titanium or titanium and nitrogen. The produced cast steel grades were reheated to 1150°C and hold for 2 hours, followed by forging process. The forging process was carried out in temperature range 950°C - 1100°C. Solution treatment of hot forged steels was conducted at 880°C, 850°C followed by air and oil quenching, respectively. Quenched steel samples of different steel grades were tempered at different temperatures in the range of 300°C to 650°C for 45 min. The hardness variations after tempering of the two modified steels comparing with the conventional 56NiCrMoV7 steel were studied. Microadditions of titanium or titanium and nitrogen were found to produce secondary hardening at 550°C to 575°C (45 min) with a hardness peak higher than that attained in the conventional 56NiCrMoV7 steel. The effect of titanium and nitrogen additions on phases formation was investigated by Thermo-Calc. SEM was used to confirm Thermo-Calc analysis. Interpretation between hardness and formed phases has been illustrated.
Highlights
In tool steels chromium will form carbides of the types Cr23C6 and some Cr7C3 during annealing depending on the chromium content
This paper reports a study of the addition effects of either titanium or titanium and nitrogen of steel grade DIN 56NiCrMoV7 on mechanical properties
Thermo-Calc results showed that the influence of addition of nitrogen and titanium—as given in Figure 9—on phases behavior with increasing tempering temperature from 500 ̊C to 650 ̊C is illustrated as the following: Figure 7
Summary
In tool steels chromium will form carbides of the types Cr23C6 and some Cr7C3 during annealing depending on the chromium content. It was found that vanadium forms very hard and thermally stable MC type carbides usually as isolated particles These carbides improve the resistance against abrasive wear and provide very good cutting performance [4] [5] [12]. Microalloying with vanadium, titanium, niobium and nitrogen was emerged as an attractive technique to enhance the mechanical properties of hot deformed steels through grain refinement and precipitation strengthening [16] [17] and attaining higher hardness levels in quenched-tempered steels through secondary hardening [18]. The objective and novelty of this article is to investigate the effect of micro addition of either titanium or titanium and nitrogen on the carbides formation from the point of their types, compositions and amount and their effect on hardness of tempered steel
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