超高强钛合金油井管固溶时效工艺探索

Study on Solution and Aging Treatment Process of Ultra-high Strength Titanium Alloy Taken as Oil Country Tubular Goods

为了探索开发高强度钛合金油井管产品的可行性,开展了不同时效温度、时间的固溶时效热处理工艺试验,利用拉伸试验机、金相显微镜等对材料强韧性、塑性、显微组织变化情况进行检测分析,采用扫描电镜分析了-10℃下冲击断口微观形貌,研究了超高强状态下钛合金微观韧化机制。试验结果显示,经910℃固溶1 h后水冷,再540℃时效处理4 h后空冷,可使试验钛合金材料屈服强度大于1100 MPa,拉伸强度高达1360 MPa,延伸率最高14.5%,冲击功达到18~20 J,且可获得较好的强度、塑性和韧性的配合。研究表明,时效温度和时间对钛合金的强度和塑性影响明显,对韧性影响较小,其原因在于强度变化主要受钛合金β相基体上析出针状等次生α相的强化作用的影响,塑性降低则因初生α相球化或粗化及次生α相含量升高影响,韧性变化则源自微观韧化机制上的差异,即二次裂纹易于在次生α相形成,有韧窝的撕裂棱易于在局部粗化的初生α相形成。

In order to explore the feasibility of developing titanium alloy oil country tubular goods with ultra-high strength products,the experiments of solution and aging heat treatment with different aging temperatures and times were carried out.The changes of strength,toughness,plasticity and microstructure of the materials were tested and analyzed by tensile testing machine and metallographic microscope.The fractography of Charpy impact specimen at-10℃was analyzed by scanning electron microscope.The toughening mechanism of titanium alloy with ultra-high strength was studied.The results show that the performances of the tested titanium alloy treated by water cooling after holding 1 hour at 910℃and air cooling after aging 4 hours at 540℃is over 1100 MPa in yield strength,up to 1360 MPa in tensile strength,up to 14.5%in elongation and up to 18~20 J in impact energy to obtain a good combination of strength,plasticity and toughness.The results show that aging temperature and time have obvious effects on the strength and plasticity of titanium alloy,but have little effect on the toughness.The reason for the change of strength is mainly affected by the strengthening effect of precipitated acicular and other secondaryαphases on the matrixβphase for titanium alloy.The decrease in plasticity is due to the spheroidization or coarsening of the primaryαphase and the increased content of the secondaryαphase.The change of toughness comes from the difference of microscopic toughening mechanism that the secondary cracks is apt to form in secondaryαphase and the formation of tearing edge with dimple is easily in locally coarsened primaryαphase.