Effect of Nitrogen on Formation of Martensite-Austenite Constituent in Low Carbon Steels.

Staiger, Mark P.; Jessop, B; Hodgson, Peter; Brownrigg, Allan; Davies, Christopher H J

doi:10.2355/isijinternational.39.183

Cited by 12 publications

(7 citation statements)

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“…22) In contrast, in agreement with the results shown in Fig. 5, steel 11VN has lower hardenability after schedule B, mainly due to the effect of accumulated strain.…”

Section: Pearlite Microstructuresupporting

confidence: 88%

“…21) It is worth emphasizing that Staiger et al observed a similar effect when nitrogen content increased from 30 to 70 ppm in the formation of hard constituents in the case of low carbon wire-rods. 22) In contrast, in agreement with the results shown in Fig. 5, steel 11VN has lower hardenability after schedule B, mainly due to the effect of accumulated strain.…”

Section: Pearlite Microstructuresupporting

confidence: 88%

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Influence of Thermomechanical Processing on the Austenite–Pearlite Transformation in High Carbon Vanadium Microalloyed Steels

et al. 2010

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Multipass torsion tests were carried on with several V-microalloyed high carbon steels, using different deformation sequences in order to modify the austenite state prior to transformation. Both recrystallized and deformed austenite microstructures were studied. After deformation, different cooling rates were applied. The results show that accumulating strain in the austenite before transformation seems to slightly increase the interlamellar spacing for a given cooling rate, this increase being related to the pearlite transformation taking place at higher temperatures because of the increase in the austenite grain boundary area per unit volume (S V ). On the other hand, the retained strain significantly contributes to a refinement of the "ferrite units", this effect being more significant as vanadium and nitrogen contents rise. A relationship between the mean "ferrite unit" size with S V and cooling rate was determined. Similarly, empirical expressions to predict strength as a function of vanadium microalloying addition, S V and cooling rate were derived.KEY WORDS: eutectoid steel; pearlite transformation; vanadium microalloying; thermomechanical processing.tion. This means that when defining the "ferrite unit" the misorientation criterion used is an important factor. A 15°m isorientation criterion was used in Ref. 11) for an eutectoid Nb microalloyed steel, whereas in Ref. 12), where several V microalloyed steels were studied, it was observed that the application of the above criterion led to an "orientation unit" mean size larger than the "facet size" measured on fracture surfaces. In the latter a 12°misorientation criterion provided better results.In a recent paper Jorge-Badiola et al. evaluated the beneficial effect of combining strain induced vanadium nitride precipitation in austenite with proper deformation schedules to accumulate strain in the austenite in eutectoid steels.13) As occurs in low carbon steels, the accumulation of strain produces a significant refinement in the austenite, this leads to high values in the specific grain boundary area (S V ) which may produce, after transformation, a refinement in the "ferrite unit" in pearlite. In the aforementioned paper the work was mainly focused on analyzing the relevance of VN precipitation on austenite conditioning and the subsequent influence on the size of "ferrite units" obtained after transformation compared with a plain C-Mn steel.The precipitation of VN in austenite and the subsequent grain size refinement will affect the CCT curve and consequently, the resulting interlamellar spacing as well as the V(C, N) precipitation hardening can be modified for a given cooling schedule. This paper attempts to evaluate the interaction between these factors considering the influence of different vanadium and nitrogen contents in eutectoid steels. Experimental ProcedureThe composition of the vanadium microalloyed eutectoid steels used in this study are indicated in Table 1. Steels 5V and 10V were provided in the form of 16 mm diameter bars forged from laborat...

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“…22) In contrast, in agreement with the results shown in Fig. 5, steel 11VN has lower hardenability after schedule B, mainly due to the effect of accumulated strain.…”

Section: Pearlite Microstructuresupporting

confidence: 88%

Section: Pearlite Microstructuresupporting

confidence: 88%

Influence of Thermomechanical Processing on the Austenite–Pearlite Transformation in High Carbon Vanadium Microalloyed Steels

et al. 2010

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“…When observing the PM at high magnification under SEM, the dark color regions appear to constitute of M–A constituents and degenerate pearlite ( Figure 7 c). M–A constituents are formed because of austenite stabilizing elements, such as manganese and nickel, that allow austenite to exist at room temperature [ 49 ]. Note in Table 1 , the as-received X70 PM contains some nickel, a strong austenite stabilizer [ 50 ].…”

Section: Resultsmentioning

confidence: 99%

Post-Weld Heat Treatment of API 5L X70 High Strength Low Alloy Steel Welds

et al. 2020

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High Strength Low Alloy (HSLA) steels are the materials of choice in pipeline construction with the API X70 grade as the steel for the majority of pipeline networks constructed during the late 20th and early this century. This paper reports on the influence of Post-Weld Heat Treatment (PWHT) on the reduction of residual stresses, resulting changes in the microstructure, and mechanical properties of a multi-pass, X70 HSLA steel, weld joints made by a combined Modified Short Arc Welding (MSAW) and Flux Cored Arc Welding (FCAW) processes. Neutron diffraction results highlighted high magnitude of tensile residual stresses, in excess of yield strength of both parent and weld metal, in the as-welded specimen (~650 MPa), which were decreased substantially as a result of applying PWHT (~144 MPa). Detailed microstructural studies are reported to confirm the phase transformation during PWHT and its interrelationship with mechanical properties. Transmission Electron Microscopy (TEM) analysis showed polygonization and formation of sub-grains in the PWHT specimen which justifies the reduction of residual stress in the heat-treated weld joints. Furthermore, microstructural changes due to PWHT justify the improvement in ductility (increase in the elongations) with a slight reduction in yield and tensile strength for the PWHT weld joint.

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“…A similar result was found for a soak temperature of 1200 o C, fig. 5b.The actual mechanism for N lowering the transformation is not fully understood, but it has been suggested [9] that nitrogen may hinder nucleation or growth of the pearlite reaction by interfering with diffusional processes or that N rapidly partitions to the last transforming austenite, increasing hardenability. · Specimens experiencing complete transformation prior to coiling have a well-defined dilation trough and peak, indicating the temperature region where the bulk of the transformation occurs.…”

Section: Influence Of C and N On Transformation: I N O R D E R T O E mentioning

confidence: 99%

Influence of chemistry and runout table parameters on hot coil collapse in C–Mn steels

Banks¹,

Tuling²,

Mintz³

2011

Ironmaking & Steelmaking

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The key metallurgical parameters affecting the incidence of coil collapse (soft slump) of C-Mn steels has been investigated using industrial data and laboratory simulation. Runout table (ROT) cooling/coiling simulations were performed on a Gleeble 1500D to study transformation before and during coiling of thin strip. For low C (< 0.07%) grades, coiling temperatures above 650˚C coupled with high nitrogen contents decreased the transformation-end temperature, Ar 1 , and increased collapse. Coiling temperatures above the Ar 1 for ROT cooling increased both dilation and the time to complete transformation during coiling. These effects correlated with industrial conditions where a high frequency of coil collapse was observed.

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Effect of Nitrogen on Formation of Martensite-Austenite Constituent in Low Carbon Steels.

Abstract: (Ti-Low. Ti-High) were microalloyed wlth two levels of titanium while the base composition was kept constant and the total nitrogen level maintained at I 10 ppm.The steel cornpositions are shown in Table 1

Cited by 12 publications

References 1 publication

Influence of Thermomechanical Processing on the Austenite–Pearlite Transformation in High Carbon Vanadium Microalloyed Steels

Influence of Thermomechanical Processing on the Austenite–Pearlite Transformation in High Carbon Vanadium Microalloyed Steels

Post-Weld Heat Treatment of API 5L X70 High Strength Low Alloy Steel Welds

Influence of chemistry and runout table parameters on hot coil collapse in C–Mn steels

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