A critical assessment of the microstructure and mechanical properties of friction stir welded reduced activation ferritic–martensitic steel

Investigation into the viability of K-TIG for joining armour grade quenched and tempered steel

“…In full austenitic region which is composed of CGHAZ and FGHAZ, all of the tempered martensite has transformed to austenite which decomposes upon cooling and different kinds of products are formed, depending on the cooling rate and chemical composition of steels in question, or hardenability. In CGHAZ the temperature experienced is relatively high so that the redissolution of large amount of stable carbides reduce the pinning effect of the second phase on dislocation movement and grain growth, leading to an increase in size of austenite grain [36,37]. High carbon concentration and addition of austenite stablizers significantly increase the hardenability, with the results being that large amount of martensite and small amount of bainite are present in this region even with air cooling as indicated in Fig.…”

“…One comes from the nucleation of austenite at 'α' grain boundaries when being reheated to the intercritical temperature regime that lies between Ac1 to Ac3 and transformation to martensite, bainite and polygonal ferrite upon cooling [37]. The other is a result of elimination of the fine martensitic crystals, say laths, and formation of equiaxed ferritic grains during high temperature tempering, a variation in microstructure ascribed to recovery and recrystallization mechanisms associated with the migration of the low angle boundaries that separated parallel martensite crystals with the same orientation as well as the rearrangement of the large angle parallel boundaries to form equiaxed ferritic grains in order to minimize grain boundary energy [32,39].…”

“…In terms of grain size, it is known that increased number of grain boundaries helps to block crack propagation and increase the energy required for crack to propagate as a result [57]. It was also reported that finer grain size is conductive to minimizing stress resulting from dislocation pile-up and raise the resistance to cleavage fracture [37]. Therefore, The larger prior austenite grain size in weld metal and inherited larger packet size associated with high heat input compared with those in base metal increases the possibility of initiated cleavage crack propagation and deteriorate the toughness as a result.…”

Understanding the mechanical properties of reduced activation steels

“…RAFM steels are essentially modifications of the body-centered cubic (bcc), Fe-rich, Fe-Cr binary alloys and contain minor concentrations of low-activation elements, such as manganese to improve the abrasion and wear resistance as well as tensile properties [11], tungsten and vanadium to maintain a low activation level and to resist irradiation embrittlement [12,13]. The composition of the main alloying elements lies in the range (wt.%) Fe-(7.5-12)Cr-(1.0-2.2)W-(0.15-0.25)V-(0.05-0.6)Mn [14,15].Recent experimental progress has mainly focused on the fabrication, manufacturing, mechanical properties (precipitation behavior, fracture toughness, creep, fatigue, and thermal aging), effects of irradiation, and corrosion analysis of RAFM steels [14,[16][17][18][19][20]. Irradiation damage on the microstructure and mechanical properties, including irradiation hardening and embrittlement by neutrons and helium, fatigue and creep after irradiation, were intensively investigated [14,17,19,21].…”

“…Recent experimental progress has mainly focused on the fabrication, manufacturing, mechanical properties (precipitation behavior, fracture toughness, creep, fatigue, and thermal aging), effects of irradiation, and corrosion analysis of RAFM steels [14,[16][17][18][19][20]. Irradiation damage on the microstructure and mechanical properties, including irradiation hardening and embrittlement by neutrons and helium, fatigue and creep after irradiation, were intensively investigated [14,17,19,21].…”