Abstract:The correlation between the impact toughness and microstructural characteristics of a large bainitic steel bloom has been investigated. The study focuses on microcrack nucleation and propagation in the basic cleavage plane. To analyze the phase transformation during the wind-cooling process, the temperature field of the bloom was acquired by computer simulation, and a continuous cooling transformation experiment was conducted. The results show that compared with the surface of the bloom, the toughness of the b… Show more
“…In the production process of DST bainitic steel, spray cooling is adopted after forging instead of water or oil cooling to avoid quenching cracks, which may be caused by thermal stress or phase transformation stress. 2 Compared with conventional QT steel, the DST bainitic steel with low carbon content has good weldability and hardness uniformity, and the production process is significantly shortened by reducing the reheating process. Moreover, it does not require the addition of expensive alloying elements like Ni.…”
Section: Introductionmentioning
confidence: 99%
“…Later, a non-quenched prehardened (NQP) bainitic steel has also been developed, whose microstructures consist of bainite throughout the whole section, and it has a good hardness uniformity and mechanical properties. Zhang et al 2 developed a direct-cooled and tempered (DT) bainitic steel, and investigated the correlation between the impact toughness and microstructural characteristics. The composition design of DST bainitic steel aims at good bainitic hardenability and delaying ferrite and pearlite area to very low cooling rates, which is based on the composition design of FT, NQP and DT bainitic steel.…”
In order to avoid the appearance of soft particles composed of ferrite or pearlite in the actual production of new bainitic steel, the phase transformation behaviour and bainite formation kinetics were investigated by DIL805A dilatometer, optical microscopy, scanning electron microscopy and Vickers-durometer. The results show that the soft particles cannot appear when the cooling rate exceeds 0.025 K s −1 , and this condition can be ensured by direct spray cooling in production. The local activation energy decreases with increasing transformed bainite volume fraction ( f b ), and the average energy is about 136.7 kJ mol −1 . The local Avrami exponent mainly lies between 0.5 and 3 in a wide f b range, indicating that the dominating mechanism of bainite formation is two-dimensional and one-dimensional growth.
“…In the production process of DST bainitic steel, spray cooling is adopted after forging instead of water or oil cooling to avoid quenching cracks, which may be caused by thermal stress or phase transformation stress. 2 Compared with conventional QT steel, the DST bainitic steel with low carbon content has good weldability and hardness uniformity, and the production process is significantly shortened by reducing the reheating process. Moreover, it does not require the addition of expensive alloying elements like Ni.…”
Section: Introductionmentioning
confidence: 99%
“…Later, a non-quenched prehardened (NQP) bainitic steel has also been developed, whose microstructures consist of bainite throughout the whole section, and it has a good hardness uniformity and mechanical properties. Zhang et al 2 developed a direct-cooled and tempered (DT) bainitic steel, and investigated the correlation between the impact toughness and microstructural characteristics. The composition design of DST bainitic steel aims at good bainitic hardenability and delaying ferrite and pearlite area to very low cooling rates, which is based on the composition design of FT, NQP and DT bainitic steel.…”
In order to avoid the appearance of soft particles composed of ferrite or pearlite in the actual production of new bainitic steel, the phase transformation behaviour and bainite formation kinetics were investigated by DIL805A dilatometer, optical microscopy, scanning electron microscopy and Vickers-durometer. The results show that the soft particles cannot appear when the cooling rate exceeds 0.025 K s −1 , and this condition can be ensured by direct spray cooling in production. The local activation energy decreases with increasing transformed bainite volume fraction ( f b ), and the average energy is about 136.7 kJ mol −1 . The local Avrami exponent mainly lies between 0.5 and 3 in a wide f b range, indicating that the dominating mechanism of bainite formation is two-dimensional and one-dimensional growth.
“…6 The results by Zhang et al . 11 also show that as compared with the surface of the bloom, the toughness of the bloom's core was decreased by the increase in proeutectoid ferrite. 10Proeutectoid ferrite in NQT steel…”
Section: Resultsmentioning
confidence: 72%
“…8,9 In response to the intense competition on technique and cost, and also to avoid the above-mentioned technical and economical drawbacks, 10 low cost prehardened mould steels with good qualities are becoming the focus of factories and researchers. 11,12 Direct air cooling after forging or hot rolling, in place of quenching, was proved to have realised cost savings to a large scale. 13 The direct cooling product after forging (Fig.…”
Two non-quenched and tempered (NQT) prehardened plastic mould steels, differing by titanium content, were produced to have good hardness uniformity in large sections (485 × 970 and 465 × 1325 mm 2 ). The effect of titanium on continuous cooling transformation curves, hardness uniformity and microstructure (grain size, phase constituents) were studied. It was found titanium had refined the grain size of NQT steel by the pinning effect of Ti (C, N) at grain boundaries, and titanium also effectively postponed the nucleation of proeutectoid ferrite in intercritical region. Using finite element method, the cooling rate from core to surface along longitude direction of the steels was predicted. The results indicated that the NQT steel with titanium had better process adaptability than that of NQT steel without titanium. Compared with production of NQT steel without titanium, production for NQT steel with titanium can largely save the production cost by shortening the production cycle and reducing the resources.
“…Three‐dimensional (3D) printing is a new manufacturing technology that has recently gained attention in the field of energetic materials [1–3]. Direct writing is a type of 3D printing that can be used to create energetic materials by adding appropriate binders and solvents to the material, forming a direct ink and molding it through direct printing.…”
In order to solve the short stabilization time of the water‐in‐oil emulsion binder system and the shortcomings of the critical blast size of the explosive ink molding sample, a water‐in‐oil emulsion binder was designed with polyvinyl alcohol (PVA) aqueous solution as the aqueous phase, fluorocarbon resin (FEVE) ethyl acetate solution as the oil phase, and toluene diisocyanate (TDI) added to modify the water‐in‐oil emulsion binder. The hexanitrohexaazaisowurtzitane(CL‐20)based explosive ink was made by incorporating submicron CL‐20 into the binder system, and the print‐formed samples were tested for microscopic morphology, crystallographic analysis, mechanical susceptibility, and detonation transmission performance. The results showed that the explosive ink‘s viscosity was moderate and suitable for direct printing, and the formed sample‘s surface particles were uniformly dispersed and had a honeycomb structure. The crystal form of CL‐20 explosive in the explosive ink did not change, the molded sample‘s impact and frictional sensitivities were 1 J and 32 N lower than those of submicron CL‐20, respectively, and the detonation velocity of the molded sample was 6655 m/s. The critical detonation size and critical detonation thickness were 1×0.0078 mm and 0.1 mm, respectively, and a critical detonation corner turning of 90°–160° could be achieved. The results show that the prepared binder system is stable for a long time, and the explosive ink molding samples have excellent blast transmission performance.
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