铸辗成形大口径25Mn钢环件微织构及力学性能

Micro-texture and Mechanical Properties of 25Mn Large-scale Ring Based on Casting-rolling Forming Technology

根据铸辗复合成形工艺对大口径25Mn钢环件进行离心铸造和热辗扩工业试验以及对其调质处理,运用金相显微镜、扫描电镜和电子背散射衍射技术分析组织与织构,并采用拉伸与冲击试验等手段检测其力学性能。结果表明,辗扩件外形尺寸精确,组织相对均匀,个别区域伴有不规则晶粒;微观织构组态主要为沿着<111>//ND取向线分布的黄铜R织构{111}<112>和取向密度为6.0的高斯织构{110}<001>,力学性能较好,但塑性稍微偏低;揭示拉伸和冲击断裂机理为解理与韧窝共存形式。调质后回火析出弥散分布的细小碳化物颗粒,晶粒更加细小均匀,大角度晶界所占比例为3/4;揭示织构演化表现为高斯织构沿着?-取向线逐渐向旋转立方织构{110}<110>聚集转变,塑性性能得到明显提高,呈现典型的韧窝断裂。研究揭示通过离心铸造25Mn钢环坯直接热辗扩成形大口径环件是切实可行的,达到了环件成形/成性的双重目的。

The centrifugal casting and hot rolling for large-scale 25Mn ring in industries are performed based on casting-rolling forming technology, and then hardening and tempering is conducted. By means of optical microscope, scanning electron microscope and electron backscatter diffraction technique, the microstructure and micro-texture are analyzed. The mechanical properties are also examined by tensile and Charpy impact tests. The results show that the rolled ring possesses precise geometrical dimension and uniform microstructure, but with a few irregularity grains in several areas. The textures are mainly brass-R {111}〈112〉 along 〈110〉//ND and Goss{110}〈001〉 with orientation density of 6.0, leading to sound mechanical properties except for lower plasticity. The mechanisms of tensile and impact fracture are the coexistence of cleavage and dimple. After heat treatment, the comprehensive mechanical properties are enhanced due to fine and dispersed carbide particle precipitated during tempering. The proportion of high-angle boundary is 3/4 in fine and uniform grains. The textural development indicate Goss texture gradually gather and transform towards to {110}〈110〉 alongξ-orientation, resulting to evidently enhance in plasticity. The dimple fracture plays a dominant role during tensile and impact. This investigation reveal it is feasible to fabricate 25Mn large-scale ring directly from centrifugal casting blank by hot ring rolling, and achieve the dual-purpose of forming and modification for ring components.