On the Step Cooling Treatment for the Assessment of Temper Embrittlement Susceptibility of Heavy Forgings in Superclean Steels

Abstract

When subjected to extended exposure to intermediate service temperatures, Cr-Mo steels, Ni-Cr steels, and 5% Ni steels can become embrittled, with an associated decrease in fracture toughness and a shift in the ductile-to-brittle transition temperature to higher temperatures. Two methods for the investigation of temper embrittlement phenomena are isothermal aging or the use of a step cooling aging treatment, which is less time consuming and is considered to be the most severe test to evaluate steel's susceptibility to this phenomenon. In the present work, the effectiveness of the step cooling treatment in the assessment of temper embrittlement in a superclean 26NiCrMoV14.5 steel for heavy section forgings has been studied. Some isothermal aging treatments in the critical temperature range have also been carried out. Results of a Charpy V impact test on not-aged and aged specimens, and observation of the fracture surfaces led to the following conclusions: the steel does not undergo temper embrittlement upon step cooling treatment or after aging at different temperatures and times in the critical temperature range; the most negative effect on the shift of the ductile-to-brittle transition curve-compared with not aged steel-has been observed after aging at 593 • C for 2 h (∆T54J = 9 • C); further aging up to 8 h produced a ∆T54J of only 1 • C. Neither step cooling nor aging at various critical temperatures gave rise to an intergranular brittle fracture; the amount of embrittling impurity elements in a superclean steel does not seem to be enough to cause embrittlement and a pure intergranular decohesion.

Elucidating the Effect of Step Cooling Heat Treatment on the Properties of 2.25 Cr–1.0 Mo Steel Welded with a Combination of GMAW Techniques Incorporating Metal-Cored Wires

“…The indentations were made using a standard load of 10 kg for 10 s. Three indentations were taken at each location approximately 1 mm apart to ascertain the values at same location and average values were taken for analysis purposes. Step cooling heat treatment [14]. For analyzing the temper embrittlement susceptibility of the weldment after SCHT, chemical analysis was carried out using the spectroscopy technique at the center of the weld.…”

“…This may cause a loss of toughness over some time. The X-factor is a numerical value calculated by the levels of residual elements in the weld deposit as per Equation (1) [14]. X = (10P + 5Sb + 4Sn + As)/100 (Content in ppm)…”

“…Thus it becomes necessary to assess the welded joints for their susceptibility to the temper embrittlement phenomenon. This phenomenon takes place after a longer duration of service and hence the assessment of its susceptibility is often time-consuming and tedious [14], as chemical composition plays an important role in temper embrittlement, the selection of welding filler metal also plays an important role [14]. Gas metal arc welding (GMAW) is one of the major processes used in fabrication incorporating solid wires [15][16][17].…”

Effects of Long-Term Service on Microstructure and Impact Toughness of the Weld Metal and Heat-Affected Zone in CrMoV Steel Joints

“…The susceptibility to temper embrittlement increased as J increased. For the low-alloy Cr-Mo steels, when J exceeded 100, temper embrittlement would occur under embrittlement conditions [29,30]. The content of Mn, Si, and P in WMs was 1.37, 0.53, and 0.011 wt.%, respectively.…”

Brittle Fracture Behaviors of Large Die Holders Used in Hot Die Forging

“…Additionally, there is no original material of the die holder, so region 6, which suffered the least temperature and mechanical load effects, are used for comparison with region 4. Furthermore, the tempering and water-cooling experiment was designed to simulate the practical environment stress of the die holder, and the effect of cyclic tempering and water cooling on the material impact property was studied as well [14]. That is, the samples of region 6 were tempered for 40 min at the temperature of 150 °C, 250 °C, 350 °C and 450 °C, respectively, and then water-cooled.…”