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As a new grade in stainless steel family, duplex stainless steels (DSSs) have an excellent combination of mechanical properties and corrosion resistance due to their duplex microstructure. Thermomechanical processing (TMP) is as one of the most common manufacturing methods of such steel, concerning its hot ductility and precipitation behaviour. The microstructural development during serval different TMP procedures was investigated in this thesis. The hot tensile behaviour of as-cast DSS S32750 was investigated in the temperature range of 1000-1200 ℃. The results show that the optimal ductile temperature range of S32750 is limited within ~1050-1150 ℃, and typical ductile fracture surface with a uniform distribution of micro-voids can be observed. However, at 1000 ℃ and 1200 ℃, the reduced hot ductility is related to the quasi-cleavage fracture and intergranular fracture respectively. Multi-pass hot compression testing was carried out in Gleeble 3500. It is shown that the dynamic recovery (DRV) and discontinuous dynamic recrystallization (dDRX) are the primary softening mechanisms of ferrite and austenite respectively. The presence of interphase interfaces and the lack of grain boundaries in DSS castings can impact the microstructural evolution of the constituent phases and their restoration mechanisms in some local regions. DSS was annealed after multi-pass hot compression to study the post-dynamic restoration of the constituent phases. The occurrence of post-dynamic recovery (post-DRV) after DRV in ferrite and metadynamic recrystallization (mDRX) after DRX can cause partial softening when the prior strain exceeds a critical level. Continuous static recrystallization (cSRX) in ferrite occurred through a gradual transformation from low-angle grain boundaries (LABs) to high-angle grain boundaries (HABs). And complete softening can be achieved within 30s with the accomplishment of SRX in both phases.

To investigate the transformation behavior of TRIP steel retained austenite under cyclic load, cyclic V-bending deformation of low carbon Si-Mn TRIP600 was studied by experiment and finite element in this paper. The results showed that, under cyclic V-bending deformation, retained austenite in TRIP steel transformed into martensite gradually with the increasing of bending times, and for the symmetrical characteristic, upper surface and lower surface presented the same transformation tendency. From the first to the fourth V-bending deformation, retained austenite volume fraction decreased nearly linearly and then attained saturation step by step. Compressive stress state was helpful for martensite transformation than tension stress state with V-bending deformation, and strain magnitude was the determining factor for retaining austenite martensitic transformation. With the increasing of bending times effective stress increased and the relationship between maximum effective stress and bending times was nearly linear. Effective stress and effective strain distribution were non-uniform, the maximum effective stress and effective strain were present in the center of the samples. The relationships between retained austenite and V-bending times, and retained austenite with effective strain were set up as Eqs.(1)–(5). The relationship was typical quadric function, decreased linearly for the initial deformation and attained saturation finally.

The influence of diversity in agricultural landscapes on pest abundance remains controversial despite several studies on the subject.For example,the ecological role of crop diversity in determining the source-sink dynamics of populations of polyphagous Heliothis spp.is complex,and varies at field,farm,region and national scales.Recently,the cropping structures within farms in Xinjiang,China,were adjusted due to changes in market conditions.The effects of these rapid changes in cropping structure at the landscape scale on the dynamics of Helicoverpa armigera have,however,not been well studied.This is particularly so for intensive agriculture in isolated oasis ecosystems,such as the irrigated cropping regions within the deserts of northern Xinjiang.The influence of a mosaic landscape on the population dynamics of H.armigera was measured using light traps in 16—17 farms covering 240 km2 in 2007—2009.Light traps were placed in clusters on commercial farms which varied in the relative amounts of cotton,tomatoes,sugar beet,corn and wheat that they grew.Moths were collected and identified every morning from the beginning of May to the middle of August in each of the three years of the study.The average number of moths caught each day / trap and each month/ trap were calculated for individual farms for each year.Farms were classified according to whether they used complex or simple cropping systems.For the purposes of this study,farms wherein the acreage of conventional cotton constituted 50% of the cropping area were arbitrarily classed as complex,whilst farms where cotton made up 50% of the cropped area were classed as simple(i.e.with a more homogeneous pattern of crops compared to complex farms). There were at least 3 generations of H.armigera per year,and as moth abundance was highest in the 3rd generation,there appeared to be a progressive build up in numbers through the season.The abundance of H.armigera moths was strongly correlated to the complexity of the agricultural landscape which influenced the source-sink dynamics of these pests amongst the different farms.The abundance of moths in complex cropping landscapes was 2—8 times larger than that in simple cropping landscapes. The area of cotton(as a proportion of arable area) within the study region overall was 88% in 2007,56% in 2008,and 35% in 2009.A consistent difference in Simpson′s Reciprocal Index remained between the complex and simple agricultural systems throughout the 3 years.Furthermore,the numbers of moths captured annually per trap was correlated positively with Simpson′s reciprocal diversity for three consecutive years.The annual abundance of H.armigera per trap had a positive relationship with the percentage of corn,processing tomato and wheat grown,and a negative relationship with the percentage of conventional cotton grown.Our study demonstrates that complex landscapes,with a variety of alternative plant hosts provided for H.armigera can support larger numbers of moths,compared with simpler(conventional cotton mostly) systems.These findings imply that diverse landscapes could increase the risk of a pest outbreak in non-Bt cropping regions,and delay the evolution of H.armigera resistant to Bt-crops in the Bt-crop belt.This study also suggests that an agricultural diversity index should be used for improving predictive modeling of pest abundance.