Effect of carbon concentration on precipitation behavior of M23C6 carbides and MX carbonitrides in martensitic 9Cr steel during heat treatment

Taneike, Masaki; Sawada, Kota; Abe, Fujio

doi:10.1007/s11661-004-0299-x

Cited by 217 publications

(100 citation statements)

References 8 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…twice the size measured in the base metal. The evolution of M 23 C 6 carbide population observed in the present study is consistent with previous results 18) showing that when the carbon content is lowered, the M 23 C 6 carbides exhibit a larger size and are less in number. Extensive lath recovery probably results from a lack in dissolved carbon and from rapid coarsening of the M 23 C 6 carbides not dissolved during the weld thermal cycle.…”

Section: )supporting

confidence: 93%

“…17) When decreasing the carbon content from 0.16 to 0.002 wt% in a 9Cr3W steel, the martensite start temperature increases by 100°C. 18) Here, the maximum variation between M s1 and M s2 occurs for T peak Ϸ990°C. For T peak ϭ1 200°C the average value of M s is nearly the same as that of the base metal.…”

Section: Microstructure Of the Matrix After The Simulatedmentioning

confidence: 86%

See 1 more Smart Citation

High Temperature Creep Flow and Damage Properties of the Weakest Area of 9Cr1Mo-NbV Martensitic Steel Weldments

2005

View full text Add to dashboard Cite

In the present study, creep flow and damage behaviour of modified P91 steel weldments are investigated. Premature creep failure of weldments (with respect to base metal) occurs in the intercritical heat affected zone (ICHAZ). This microstructure is reproduced by thermal simulation applied to blanks cut from the base metal. Metallurgical investigations of what happens during the welding cycle show that the weakest part of the heat affected zone is heated slightly below complete austenitisation, with little (if any) carbide dissolution. During the post-weld heat treatment, extensive recovery is allowed by carbide coarsening. The intrinsic creep behaviour of the resulting microstructure is experimentally determined under controlled constraint conditions. The welding cycle strongly decreases the creep strength by increasing the creep strain rate, but not necessarily by decreasing the ductility, at least for lifetimes up to 3 500 h.KEY WORDS: 9Cr1Mo-NbV martensitic steel; intercritical heat affected zone; Gleeble 1 500 thermalmechanical simulator; High temperature creep flow and damage.in the microstructure of interest was not known, just as for cross-weld specimens. The key point of the present study is thus to determine the properties of the weakest HAZ while eliminating, as much as possible, the constraint effects due to the surrounding materials. Material and Experimental Procedures MaterialsThe study focuses on a V-shaped, circumferentially welded joint of two pipes of 295 mm in outer diameter and 55 mm in thickness. It was fabricated by submerged metal arc welding in seventeen runs followed by a post weld heat treatment (PWHT) of 2 h at 760°C. The base metal is a tempered, modified P91 martensitic steel (see Table 1 for chemical composition). Its microstructure consists of lath martensite packets with M 23 C 6 (100 nm in mean size) and MX precipitates. The filler metal has nearly the same chemical composition as the base metal (Table 1). Simulation of Welding Thermal CyclesWelding thermal cycles were applied by using a Gleeble 1 500 thermal-mechanical simulator capable of heating specimens by Joule effect at very high heating rates, corresponding to those encountered in welding conditions (i.e. 100 to 250°C · s Ϫ1). The temperature is controlled by a thermocouple spot welded onto the specimen surface. Round bars of 5 mm in diameter were used to optimise the thermal cycle and 12 mm round blanks were treated and used to machine mechanical testing specimens respectively. For each of these two geometries, the closed-loop parameters of the Gleeble 1 500 simulator were carefully adjusted in order to ensure an uncertainty lower than 2°C for the value of T peak and smaller than 1 s for the value of the cooling parameter Dt 800→500 . For specimens of 5 mm in diameter, phase transformations were continuously monitored using in-situ dilatometric measurement of the specimen diameter. To prevent from extensive oxidation of the specimen, heat treatments were performed under primary vacuum (0.1 Pa). Phase transformations moni...

show abstract

Section: )supporting

confidence: 93%

Section: Microstructure Of the Matrix After The Simulatedmentioning

confidence: 86%

High Temperature Creep Flow and Damage Properties of the Weakest Area of 9Cr1Mo-NbV Martensitic Steel Weldments

2005

View full text Add to dashboard Cite

show abstract

“…As previously reported, 9) even the low C-9Cr-3Co-3W-V, Nb-N-B steel 18) showed the same formation behavior under the same heat treatment condition and the same contents of boron and nitrogen as the ones in this study. In other words, the formation of boron nitride inclusions is assumed to be affected mainly by the added contents of boron and nitrogen and the condition of heat treatments, and is hardly influenced by the steel structure.…”

Section: Influence Of Alloy Composition and The Structure On Boron Nisupporting

confidence: 87%

Influence of Heat Treatment on Formation Behavior of Boron Nitride Inclusions in P122 Heat Resistant Steel

2006

Self Cite

View full text Add to dashboard Cite

a cast structure or a forged and rolled structure, by assuming the same heat treatment condition and also by the appearance of the d-phase. As previously reported, 9) even the low C-9Cr-3Co-3W-V, Nb-N-B steel 18) showed the same formation behavior under the same heat treatment condition and the same contents of boron and nitrogen as the ones in this study. In other words, the formation of boron nitride inclusions is assumed to be affected mainly by the added contents of boron and nitrogen and the condition of heat treatments, and is hardly influenced by the steel structure. The Methods to Avoid the Formation of CoarseSize Boron Nitride Inclusions Boron and nitrogen that would help improve the creep strength of newly developed high Cr heat resistant steels would not perform efficiently if a large number of coarse boron nitride inclusions form. The growth of boron nitride inclusions of 20 to 30 mm are assumed to have undesirable influences on the mechanical properties of steel such as fatigue, thermal fatigue and impact. Therefore, the cooling rates after the hot working process should be controlled to avoid the formation of these inclusions. They can be avoided by adapting fast cooling rates or by controlling the heat treatments of normalizing or tempering to relatively thin and small size products such as heat exchange tubes.However, it will be difficult to employ fast cooling rates to thick and large size products such as main steam pipes that are produced from several ton steel ingots. The amount of boron and nitrogen concentrations which do not form boron nitride inclusions and the minimum adequate nitrogen contents that is needed to precipitate vanadium and niobium nitrides will have to be determined. Figure 12 shows the relation between boron and nitrogen in high Cr heat resistant steels that is necessary to form coarse size boron nitride inclusions 9) and the limits of boron and nitrogen concentrations in P122 and P92 steels by the ASME code.3) As shown in Fig. 12, boron and nitrogen concentrations are include in the area of boron nitride formation for both P122 and P92 steels. Therefore, we should try to obtain the boron and nitrogen concentration limit at the left side of the plot and the lowest point in the concentration limit area, to avoid the formation of coarse size boron nitride inclusions as much as possible. ConclusionsThe influences of remelting, forging, rolling and heat treatment on the boron nitride inclusion that were formed in P122 heat resistant steel containing 0.003 mass% boron and 0.06 mass% nitrogen were investigated by the SEM observation of the fractured surface. The following conclusions were drawn from this investigation.(1) The temperature where the boron nitride inclusion formation in P122 steel begins is between 1 150 to 1 200°C.(2) After forging and rolling, boron nitride inclusions form agglomerated groups of 20 to 30 mm during very slow cooling or of 10 to 20 mm during medium slow cooling.(3) Re-dissolution of boron nitride inclusions into the steel matrix begins above 1 200°...

show abstract

“…The small particles (<60 nm) in as-TMT and TMT + temper were assumed to be MX as they were enriched in Nb and V, and the larger particles (>60 nm) in TMT + temper were assumed to be M 23 C 6 as they were enriched in Cr, which is consistent with literature. [19][20][21] Micro-Vickers hardness measurements were conducted on cross-sections of the GTAW + PWHT samples, using a 300 g load for 12 seconds and automated stage motion, measuring hardness in 50-100 lm steps across the base metal, heat-affected zone, and weld metal. For creep-rupture testing, standard cross-weld tensile specimens with a cylindrical gage section (ASTM E8) with 6.4 mm diameter and 31.8 mm length were machined from the GTAW + PWHT samples, and then tested at 873 K (600°C) and 100 MPa in laboratory air.…”

Section: Methodsmentioning

confidence: 99%

Toward Improving the Type IV Cracking Resistance in Cr-Mo Steel Weld Through Thermo-Mechanical Processing

Shassere

Yamamoto

Babu

2016

Metall Mater Trans A

View full text Add to dashboard Cite

Detailed microstructure characterization of Grade 91 (Modified 9Cr-1Mo, ASTM A387) steel subjected to a thermo-mechanical treatment process was performed to rationalize the cross-weld creep properties. A series of thermo-mechanical processing in the austenite phase region, followed by isothermal aging at temperatures at 973 K to 1173 K (700°C to 900°C), was applied to the Grade 91 steel to promote precipitation kinetics of MX (M: Nb and V, X: C and N) in the austenite matrix. Detailed characterization of the base metals after standard tempering confirmed the presence of fine MX dispersion within the tempered martensitic microstructure in steels processed at/and above 1073 K (800°C). Relatively low volume fraction of M 23 C 6 precipitates was observed after processing at 1073 K (800°C). The cross-weld creep strength after processing was increased with respect to the increase of MX dispersion, indicating that these MX precipitates maintained during weld thermal cycles in the fine-grained heat-affected zone region and thereby contribute to improved creep resistant of welds in comparison to the welds made with the standard ''normalization and tempering'' processes. The steels processed in this specific processing condition showed improved cross-weld creep resistance and sufficient room temperature toughness. The above data are also analyzed based on existing theories of creep deformation based on dislocation climb mechanism.

show abstract

Effect of carbon concentration on precipitation behavior of M23C6 carbides and MX carbonitrides in martensitic 9Cr steel during heat treatment

Cited by 217 publications

References 8 publications

High Temperature Creep Flow and Damage Properties of the Weakest Area of 9Cr1Mo-NbV Martensitic Steel Weldments

High Temperature Creep Flow and Damage Properties of the Weakest Area of 9Cr1Mo-NbV Martensitic Steel Weldments

Influence of Heat Treatment on Formation Behavior of Boron Nitride Inclusions in P122 Heat Resistant Steel

Toward Improving the Type IV Cracking Resistance in Cr-Mo Steel Weld Through Thermo-Mechanical Processing

Contact Info

Product

Resources

About