A perspective in the understanding of strength–toughness combination during processing of engineering ferrous alloys

Figures & data

Figure 1. Effect of heat treatment temperature (time 1 h) on K_IC and grain size of maraging steel (250) (Bars indicate the range over which K_IC and grain size values were measured at a particular temperature (adapted from reference [10,11]).

Figure 2. Variation of K_IC and atomic% titanium on fracture surface with heat treatment temperature (adapted from reference [10,11]).

Figure 3. Schematic representation of fracture process in steel with grain boundary TiC carbides (adapted from reference [10]).

Figure 4. Effect of anneal sequence on grain boundary precipitates (adapted from reference [12]).

Figure 5. Effect of anneal sequence on martensite lath size (adapted from reference [12]).

Figure 6. Summary of the effect of heat treatment on microstructure based on transmission electron microscopy studies (adapted from reference [12]).

Figure 7. Impact toughness, and intergranular atomic % C and P and ΔG^o [P] and ΔG^o [C] as a function of bulk weight % C (also Nb/C ratio) in 17–4 precipitation hardened stainless steel [10,13,14].

Figure 8. Significance of Nb/C ratio in 17–4 precipitation hardened stainless steel to obtain desired toughness (adapted from reference [10]).

Figure 9. The effect of post-aging quenching treatment on impact toughness of 17Cr-4Ni precipitation hardened stainless steels (adapted from reference [16]).

Figure 10. Inverse of the product of impact toughness and atomic % segregant (C or P) as a function of ∆G° _b - ∆G° _S in 17–4 PH stainless steel (adapted from reference [17]).

Figure 11. (A) grain boundary segregation isotherms recorded at 823 K for 2.6Ni-0.4Cr-0.28Mo-0.10V steel. Bars indicated on the figure represent the range over which the values were measured. (b) ratio of grain boundary [(θ_N+ θ_C)/(θ_Cr+ θ_V)] as a function of isothermal heat treatment time at 823 K for 2.6Ni-0.4Cr-0.28Mo-0.10V steel. Bars indicated on the figure represent the range over which the values were measured (adapted from reference [21]).

Figure 12. Grain boundary interactions (interaction maps) occurring amongst trace and alloying elements in 2.6 Ni-0.4Cr-0.28Mo-0.10V steel (adapted from reference [22]).

Figure 13. Time-temperature diagrams of grain boundary segregation of P in 0.05 wt.%P interstitial-free steel, numbers labeling each curve are levels of P segregation in monolayers; computed horizontal lines denote equilibrium concentration of P (adapted from references [28–30]).

Figure 14. (a) temperature dependence of batch annealing cycle (heating rate 15 K h⁻¹ to 973 K, holding for 2 h at 973 K, cooling at 15 K h⁻¹) and (b) associated grain boundary P concentration as function of time in the absence and presence of P-C site competitive process (adapted from references [28–30]).

Figure 15. Schematic diagram showing role of B in retarding ferrite nucleation and promoting bainite formation in HSLA steels (adapted from reference [31]).

Figure 16. Skeletal ε fibre plot for indicated depths below surface in ultrahigh strength hot rolled microalloyed steel [34].

Figure 17. Room temperature charpy v-notch impact toughness (adapted from reference [37]).

Figure 18. (a) Bright field TEM micrograph of Nb-microalloyed steels processed at (a) low (or normal) cooling rate showing polygonal ferrite structure, (b) intermediate cooling rate showing elongated ferrite structure and (c) high cooling rate showing bainitic/lath-type ferrite structure (adapted from reference [37]).

Figure 19. Bright field TEM micrograph of Nb-microalloyed steels processed at (a) low (or normal) cooling rate showing lamellar pearlite structure and (b) intermediate cooling rate showing degenerate pearlite structure (adapted from reference [37]).

Figure 20. A schematic illustration of formation of degenerate pearlite and its influence on toughness (adapted from reference [37]). When cementite is distributed in pearlite with a fine rod or platelet phase, it is referred as”degenerate pearlite” or sometimes as “nodular bainite”..

Figure 21. Bright field TEM micrographs illustrating the general microstructure of the 700 MPa pipeline steel with lean chemistry. (a) non-equiaxed or quasi-polygonal ferrite, (b) precipitate–dislocation interaction in the ferrite matrix, (c) upper bainite and (d) obtained from carbon extraction replica showing fine scale precipitation (adapted from reference [43]).

Figure 22. (a) Bright field image showing ferrite grain with array of fine precipitate inside the grain and (b) dark field image taken using NbC (−13–1) diffraction spot (adapted from reference [43]).

Figure 23. Bright field images (left) and corresponding dark field images (right) of medium-carbon silicon-containing steels quenched at 150°C for 20 s and partitioned for 30 s at 200°C. Dark field images were taken using 220 austenite reflection (adapted from reference [45]).

Figure 24. Bright field (left) and corresponding dark field image (right) of medium-carbon steel quenched to 100°C for 20 s and partitioned at 350°C for 10–30 s. Dark field images were taken using 020 ε-carbide reflection (adapted from reference [45]).

Figure 25. A schematic representation of phase reversion concept to obtain nanograined structure (adapted from references [50,51]). Similar approach was proven in microalloyed steels.

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Data availability statement

Given that it is an overview article, data availability is not relevant. The author has done his best in citing the relevant articles. However, inadvertently there may be a situation where an article has not been appropriately cited. All figures adapted from references and reference numbers are indicated in the figure caption.