Alloy and structure design of austenitic cast Cr-Ni-Cu-N steel exhibiting TRIP/TWIP properties for cold massive forming

该项目的目的是设计、加工和研究一种具有TRIP/TWIP性能的铜合金、奥氏体、不锈钢Cr-Ni-Cu-N铸钢，用于通过交叉轧制成测试样品，减少工艺步骤的冷块状成形（不含热成形）。铜的加入降低了应变诱发马氏体的形成能力，提高了奥氏体的层错能，提高了奥氏体的冷成形能力。此外，使用奥氏体稳定元素铜和氮可以通过部分节省昂贵的镍来降低合金化成本。进一步的目标是产生有助于奥氏体沉淀硬化的含铜析出物，并确定可以部分或完全抑制ε-铜相形成的热处理参数。借助量身定制的合金设计，可以有目的地触发奥氏体在冷成形过程中的变形机制（TRIP/TWIP效应、平面滑动），以保证最佳的冷成形性。此外，在冷成形操作后，计划对马氏体形成能力和显微组织进行相应的表征。进一步重点研究了Cr-Ni-Cu-N铸钢冷成形和再结晶试样的加工和研究。通过在700℃温度范围内的还原退火，使先前粗晶奥氏体铸造组织转变为(n)（超）细晶（FG， UFG）组织，而无需热成形。进一步的研究重点是温度和应变率相关的变形行为以及循环变形行为的广泛表征。铸钢材料的冷成形具有较短工艺链的显著优势，从而大大节约了能源，提高了生产率和经济效益。

The aim of the project is the conception, processing and research of a copper-alloyed, austenitic, stainless Cr-Ni-Cu-N cast steel with TRIP/TWIP properties used for process step reduced cold massive forming (without hot forming) by cross rolling into test samples. The addition of copper increases the stacking fault energy and improves the cold formability of austenite due to a decrease of the strain-induced martensite formation capability. Moreover, using the austenite stabilizing elements copper and nitrogen the alloying costs can be reduced by partial saving of expensive nickel. A further aim is to produce copper-containing precipitates which contribute to the precipitation hardening of the austenite and to define heat treatment parameters at which the formation of the ε-copper phase can be partially or completely suppressed. With the aid of tailored alloy design, the deformation mechanisms (TRIP/TWIP effect, planar glide) running in the austenite during cold forming can be triggered purposefully to guarantee an optimal cold formability. Furthermore, after cold forming operation an accompanying characterization of martensite formation capability and microstructure is planned. A further focus is placed on the processing and research of cold formed and recrystallized test samples made of Cr-Ni-Cu-N cast steel. By means of reversion annealing in the temperature range of 700 °C the previously coarse grained austenitic cast microstructure should be transferred in a(n) (ultra) fine-grained (FG, UFG) microstructure without hot forming. A further research focus is the extensive characterization of the temperature and strain rate dependent deformation behaviour as well as the cyclic deformation behaviour.Cold forming of cast steel material possesses the substantial advantage of a shorter process chain, which leads to a considerable energy saving, and the increase of productivity and economic efficiency.