大型环坯近固态压力成形理论与实验研究

During the manufacture of steel ring billet by using sand casting process, there have some problems, such as the waste of materials and energy. And the same time, coarse grains and prominent shrinkage porosity and cavity result in worse mechanical properties of cast-steel ring billet. Therefore, in order to save materials and energy, and decrease environmental pollution, and provide ring billet with good microstructure and mechanical properties for the following rolling process, a new preparation process for ring billet, near-solid press forming process, was offered by our research team. The process and theory of the near-solid press forming will be investigated by theory analysis, numerical simulation and experiment research in this project. In order to supply the theoretic proof for the parameters design of near-solid press forming process, the influences of process parameters on the microstructure and properties of metallic materials will be analyzed. The procedure of the near-solid press forming will be simulated by use of finite element analysis software, and the optimal technological parameters and quality control scheme will be obtained primarily. The near-solid press forming experiments will be carried out, and the effects of different of technological parameters on the microstructure, properties, flaw formation and distribution of steel ring billet will be studied. Based on the above investigation, the near-solid press forming process and theory of large-sized steel ring billet for the casting-rolling forming technology will be established.

采用砂型铸造工艺生产环形钢坯存在浪费材料、浪费能源等问题，并且环坯晶粒粗大、缩松缩孔难以去除、力学性能较差。因此，为了节约材料和能源，减小环境污染，并为后续辗扩工艺提供优质的环形钢坯，本研究团队提出了一种制备环坯的新工艺——近固态压力成形工艺。本项目将采用理论分析、数值模拟与实验研究相结合的方法，对近固态压力成形工艺和理论进行研究。分析工艺参数对金属材料组织、性能的影响规律，为环坯的近固态成形工艺参数设计提供理论依据；利用有限元软件对近固态压力成形过程进行数值模拟，初步确定最佳的工艺参数和质量控制方案；开展环坯近固态压力成形的现场实验，研究不同工艺参数对环坯组织、性能、缺陷形成及分布规律的影响，建立基于短流程铸辗复合成形的大型环坯近固态压力成形工艺和理论。

近固态压力成形工艺是为铸辗复合成形工艺提供优质性能环坯的一种新工艺。本项目利用ProCAST软件对Q235B近固态压力成形过程进行数值模拟，得到了近固态压力成形主要工艺参数压力、浇注温度、模具预热温度对金属液压力成形过程中的凝固过程及凝固时间的影响规律，其中冲头压力、模具预热温度、浇注温度对其的影响程度依次减小。采用正交试验法对工艺参数压力、浇注温度、模具预热温度进行优化，得到了环坯液态压力成形过程中的最优的工艺参数组合：冲头压力为150-200MPa，浇注温度为1560℃，模具预热温度为350℃以及保压时间为25s。环件液态成形过程中，合理的固相分数决定着环件的微观组织细化的程度。不同压力值作用可以得到不同的固液相比。采用数值模拟方法，得出了金属液的固相分数在30%范围时，初生枝晶半径和二次枝晶臂间距都较小。此时对应于凹模与环件接触的中间部分位置的温度为1445℃，借助于测温仪间接来控制固相分数，从而可以控制加压开始时间以及压力值。与国家标准GBT700-2006 《碳素结构钢》中规定的Q235B板坯的力学性能相比，采用近固态压力成形法生产的Q235B铸坯的性能明显较高，屈服强度提高了10.7%，断后伸长率提高了18%，且整个铸坯的力学性能良好。所以，近固态压力成形法生产的Q235B坯料不需经过锻造和热处理即可进入辗环工艺，进行辗扩成形。综合理论分析、数值模拟及实验研究的结果，确定一条近固态压力成形的最佳质量控制方案，生产出优质的环形钢坯，为后续辗扩工艺创造良好条件。