Grain boundary engineering to overcome temper embrittlement in martensitic steel
Introduction
GBE concept has been introduced in various polycrystalline materials and their alloys to improve strength, ductility, stress corrosion resistance, creep and intergranular damage resistance [1], [2], [3], [4], [5]. This technique has been successfully employed in many iron based austenitic stainless steel and nickel base alloys having low stacking fault energy, favoring the formation of twins during deformation followed by annealing or TMT (thermo-mechanical treatment) [6], [7], [8], [9]. GBE is less popular in iron based body centered cubic system due to its high stacking fault energy (SFE). It is difficult to implement GBE concept in martensitic steel due to its complex microstructure having precipitates at different boundaries and within lath [10]. These precipitates pin the boundaries and restrict their migration during tempering. Grain boundary character distributions (GBCD) in 9-12Cr ferritic steels have been used to characterize microstructure [11]. But, till today no effort has been made to overcome temper embrittlement in martensitic steels through GBE approach. In GBE approach, generations of low energy CSL boundary will reduce segregation of tramp elements. In martensitic steel, CSL boundary are related to the martensitic phase transformation. Hence, for a given composition CSL boundary fraction is fixed. If martensitic transformation can be performed in different stages of cooling by modifying composition of austenite, fraction of CSL boundary will increase. This is possible if carbon can be partitioned between martensite and austenite while cooling. Q&P process is established based on partitioning of elements from martensite to austenite [12]. Therefore, the objective of the present investigation is to overcome temper embrittlement in martensitic steel using this concept [13].
Section snippets
Experimental procedure
12Cr martensitic steel plate of 12 mm thick was used and cut into sizes of 12 × 12 × 57 mm3 and 122 × 12 × 12 mm3. One set of specimen were solutionised at 980 °C for 30 min, followed by quenching and partitioned at 150, 175, 200, 225, 250 and 275 °C for 2 h in a salt bath furnace. This set of heat treatment is defined as Q&P. Austenite and martensite phases were stable in these temperature ranges as Ms (Martensite start) and Mf (Martensite finish) temperatures of the steel are 316 and 130 °C
Results and discussion
Toughness value of N and N&T specimens were found to be 5 and 7 J respectively. It increases monotonically from 36 to 76 J for Q&P specimens, with increasing Q&P temperature from 150 to 225 °C, but decreases to 27 J at 250 °C from the peak value. XRD peak analysis reveals the presence of austenite phase in addition to martensite phase only in those specimens which were Q&P at 200, 225 and 250 °C and the volume fractions of austenite is 1.3, 4 and 9.8% respectively. Austenite was absent in
Conclusions
Q&P heat treatment between Ms and Mf temperature stabilizes austenite. Heat treatment at higher temperature increases the volume fraction of austenite but reduces toughness of the steel. Q&P and Q&P-tempered heat treatment significantly modify GBCD in martensitic steel. Presence of lower fraction of retained austenite reduces fraction of Σ3 boundary but increases grain boundary line length per unit area. Tempering of Q&P steel increases fraction of Σ3 boundaries. Low energy boundary reduces
CRediT authorship contribution statement
Kirtiratan Godbole: Investigation. C.R. Das: Conceptualization, Writing - original draft. Bharat B. Panigrahi: Project administration and Writing - review editing. S.K. Albert: Supervision.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
Authors acknowledge the support and encouragement received from Director, IGCAR for this work. Authors also acknowledge the TEM facility of NIT Surathkal and DST (Govt. of India) for FIST Project for SEM at IIT Hyderabad.
References: (18)
- et al.
Acta Mater.
(1999) - et al.
Mater. Sci. Eng. A
(2003) - et al.
Acta Mater.
(2002) - et al.
Acta Mater.
(1997) - et al.
Scripta Materialia
(2006) - et al.
Procedia Eng.
(2014) - et al.
Mater. Sci. Eng. A
(2007) - et al.
Acta Mater.
(2003) Mater. Sci. Eng. A
(2003)
Cited by (16)
Hydrogen embrittlement and failure mechanisms of multi-principal element alloys: A review
2022, Journal of Materials Science and TechnologyCitation Excerpt :It should be pointed out that the microscopic hydrogen-induced failure mechanisms mentioned above are proposed based on the ex-situ microstructural characterization of tensile fracture specimens, and their reliability needs to be validated via in-situ tensile tests. For traditional alloys, the damage caused by HE [97–100], liquid metal embrittlement [101], temper embrittlement [102], high-cycle fatigue [103] and stress corrosion cracking [104], can be limited by controlling the type of grain boundaries. Similarly, a grain boundary engineering design concept is also applicable to novel HEAs for overcoming the typical inverse relationship between strength and HE resistance.
Grain boundary evolution during low-strain grain boundary engineering achieved by strain-induced boundary migration in pure copper
2022, Materials Science and Engineering: ACitation Excerpt :GBE usually involves specific thermomechanical processing (TMP) to enhance the fraction of low-Σ CSL boundaries and interrupt the random boundary connectivity [7]. Therefore, GBE was widely used to improve grain boundary-related properties, such as corrosion [8–10], embrittlement [11–13] and radiation damage [14], in face-centered cubic metals with low to medium stacking fault energy. Various TMP routes have been proposed to produce optimized GBE microstructures and they can be roughly classified into strain annealing and strain recrystallization approaches based on the degree of deformation [15].
Synergy of strengthening and toughening of a Cu-rich precipitate-strengthened steel
2022, Materials Science and Engineering: ACitation Excerpt :Temper-embrittlement is one of the main reasons for reduction of the impact toughness in martensitic and ferritic steels, which is caused by the segregation of impurities along the prior austenite grain boundaries [11,17,19]. These impurities will weaken the grain boundaries and lead to an intergranular fracture, resulting a significantly reduction of the impact toughness [63]. As we can see from Fig. 3, only ductile fracture and transgranular cleavage fracture occurred in AG525 at various temperatures.
Assessing the potential of sparsely nucleated recrystallized grains to lead grain boundary engineering during extending annealing in Alloy 600H
2020, Materials CharacterizationCitation Excerpt :Grain boundary engineering (GBE) stands out as one of the most feasible microstructural approaches in alleviating material's susceptibility against various intergranular related degradation phenomena like fracture [1], corrosion [2–6], segregation [7,8], precipitation [9], embrittlement [10–13], weld cracking [14], etc.