Solution Annealing Treatment Research Articles

Application of electron backscattered diffraction to cleavage fracture in duplex stainless steel

The mechanical properties and corrosion resistance of duplex stainless steel (DSS) are generally superior to conventional austenite or ferrite grades. DSSs can have yield strengths twice the austenite grades, while retaining good ductility and toughness properties. Commercial wrought duplex stainless steels, either plates or rod, are processed by hot rolling followed by a solution annealing treatment to optimize the austenite-ferrite ratio and dissolve any pre-existing secondary phases. Processing may lead to a significant anisotropy in mechanical properties. For example, the tensile properties in cold-rolled sheet of duplex stainless steel (22Cr5Ni) reveals anisotropy of strength, i.e., the transverse direction tensile strength is 7.3% higher than tensile strength in the rolling direction (RD). It was also shown in a study of the effect of crack orientation on the impact properties of the same steel, that when the crack was oriented parallel to the direction of elongation of the austenite phase, the crack could grow along the more brittle ferrite phase for a longer distance before encountering the more ductile austenite. This decreased impact toughness. These are examples of microstructure texture. Crystallographic texture may also have an effect on properties that are related to specific crystallographic planes; such as brittle cleavage and stressmore » corrosion cracking. This paper describes the application of electron backscattered diffraction (EBSD) to study cleavage fracture and crystal texture in age-hardened DSS.« less

Recrystallization and Related Phenomena. Effect of Carbon on the Cold-worked State and Annealing Behavior of Two 18wt%Cr-8wt%Ni Austenitic Stainless Steels.

The influence of carbon on the work hardening, formation and reversion of deformation induced martensite and on the recrystallization of two austenitic stainless steels 18%Cr-8%Ni type were studied with the help of different microstructural analysis techniques. Two steels were selected: the first an AlSl 304L with low carbon (%C=0.021) content and the second an AlSl 304 with higher carbon (%C=0.065) content. Both steels were heat treated to obtain two different initial conditions: one with the carbon completely in solid solution (after a solution annealing treatment at 1 100°C) and the other with practically all the carbon in the precipitated form, as (Cr,Fe) 23 C 6 (after a precipitation treatment at 750°C). The material having higher carbon content, both in solid solution and precipitated, presented in both cases higher strain hardening, smaller tendency to form strain induced martensite and higher resistance to recrystallization. Carbon in solid solution, as compared to the precipitated condition, led to a material with a higher tendency to strain hardening, less susceptibility to martensite formation and more resistance to recrystallization. Nucleation of recrystallization preferably occurred in the vicinity of grain boundaries. Based on the results of the kinetics of recrystallization and intergranular corrosion tests it was concluded that the usually recommended annealing temperatures (1 000 to 1 120°C) are sometimes unnecessarily high.

Influence of Ti/(C+6/7N) ratio on the recrystallization behaviour of a cold worked 15Cr-15Ni-2.2Mo-Ti modified austenitic stainless steel

The influence of Ti/(C+6/7N) ratio on the recrystallization behaviour of 15Cr-15Ni-2.2Mo-Ti modified austenitic stainless steel was studied. The alloys were given a thermo-mechanical treatment which involved solution annealing at 1343 K for 0.5 h followed by 20% cold work. The cold worked samples were aged at 873–1173 K for times up to 1, 100 and 1000 h. Recrystallization behaviour was studied by carrying out hardness and tensile property measurements supported by optical metallography of microstructural changes on the aged samples. Using a thermodynamic model given in the literature the amount of primary Ti(C,N) precipitates, which remain undissolved after solution annealing treatment, and secondary TiC precipitates, which form during post deformation aging, were estimated. The amount of primary coarse precipitates increased with an increase in the Ti/(C+6/7N) ratio of the alloys and they facilitated earlier onset of recrystallization. The amount of fine TiC precipitates, which retarded recovery and recrystallization was maximum in the alloy with Ti/(C+6/7N) ratio of 3.67 compared to other two alloys. The formation of a maximum amount of TiC precipitates in the matrix along with the formation of grain boundary precipitates in the alloy with Ti/(C+6/7N) ratio of 3.67 provided the best resistance against recrystallization of the cold worked microstructure. The alloy with Ti/(C+6/7N) ratio of 3.67 exhibited higher temperature and time for recrystallization compared to other two alloys.

Microstructural characterization of precipitates formed during high temperature testing and processing of iron-aluminide alloys

Iron-aluminide alloys were examined using analytical electron microscopy after creep-rupture testing at 600–650°C or after thermomechanical processing at 650–1250°C. Various precipitates were found in several different alloys after testing or heat treatments and most were identified as carbide phases. Small Mo 2C grain boundary precipitates and occasional coarse FeAlMo Laves phase particles were found after creep testing at 650°C in ternary Fe 3Al+2Mo alloy, but only after 0.3 h at 275 MPa and not after 90 h at 69 MPa. Large and small niobium- and zirconium-rich MC unintentional impurities) creep tested for 1932 h at 650°C and 69 MPa, whereas no such precipitates were observed when creep-rupture occured after only 0.5 h at 275 MPa. Two different precipitate phases were found in a complex Fe 3Al+Cr, Mo,Ti,Nb,V,C alloy after high temperature processing or mechanical testing, a titanium-rich MC phase and a CrMoFe phase (Fe 2MoC?). Coarse matrix particles of both phases were found after hot rolling at 650°C. The precipitates partially dissolved and only MC remained after solution annealing (SA) at 1100–1200°C, but finer grain boundary MC was found after a SA treatment at 1250°C. The CrMoFe phase was not found after the SA treatments, but was found to form around matrix MC particles during creep at 600°C (207 MPa for 244 h) and during aging for 9 h at 750°C.

Heat Treatment as a Potential Preventive Measure Against IASCC

Abstract Various high-temperature solution-annealing treatments were explored as potential prevention measures against irradiation-assisted stress corrosion cracking (IASCC) of type 304 (UNS S30400) stainless steel (SS). The HNO3/Cr+6 corrosion test was used to measure the effectiveness of the high-temperature heat treatments, since the results of this test can be correlated with IASCC susceptibility. Corrosion rate was found to decrease with increasing solution annealing temperature in the range from 2200°F (1204°C) to 2400°F (1316°C). The same low corrosion rate shown by high-purity type 304 SS could be achieved using appropriate temperature—time combinations.

Effect of niobium on marine crevice corrosion resistance of Inconel alloy 625

Abstract The crevice corrosion resistance of Inconel alloy 625 has been investigated as a function of its niobium content. A technique used primarily for mathematical modelling of crevice corrosion in chloride media has been used to compare the probable resistances to this type of corrosion. It has been shown that the level of niobium can be reduced from that in the commercially available alloy – thereby offering a more cost effective alternative – while maintaining favourable crevice corrosion resistance and mechanical properties. In addition, it was found that a solution annealing treatment of the alloy variations produced further beneficial properties in the alloy.

Strain Fatigue and Tensile Behavior of Inconel® 718 from Room Temperature to 650°C

Abstract Results of tensile and fully reversed strain-controlled fatigue tests, conducted on three heats of Incone® 718 that had been subjected to different solution annealing and aging treatments, are presented. Tests were conducted at temperatures ranging from 22 to 650°C, with fatigue tests defining behavior over the cyclic range from 102 to 106 cycles to failure. Average best fit equations defining true stress-strain, strain-controlled fatigue, and cyclic stress-strain behavior are given for the two heat treatments characterized. Heat-to-heat variations in the elevated temperature tensile and fatigue behavior were found. Fatigue lifetime was seen to be dependent upon grain size, particularly at lower strain ranges.