激光冲击对海洋工程用E690钢微观组织及性能的影响

Effect of Laser Peening on the Microstructure and Properties of E690 Offshore Steel

目的 提高E690钢的耐磨损性能。方法 将E690钢基体经磨床打磨后进行超声清洗,利用PROCUDO?200激光冲击系统,对其表面施加冲击强化处理。利用光学显微镜、扫描电子显微镜和X射线衍射仪分析激光冲击(LSP)对E690钢微观组织结构的影响。通过显微硬度测试、纳米压痕测试、干滑动摩擦磨损试验,评价未冲击处理和LSP处理E690钢试样的硬度、弹塑性性质和耐磨损性能。结果 LSP作用下,E690钢基体表层晶粒尺寸细化,形成明显的梯度结构,试样的相组成仍然为α相和γ相,但α相最强衍射峰的半高宽由0.218°增大到0.266°。LSP处理后,E690钢基体表层残余应力转变为较大的残余压应力,最大残余应力达到–268 MPa。LSP处理E690钢的影响层深度约为700μm,表面硬度为(302.5±12.2)HV100,与未冲击处理试样相比,提高了8.7%。LSP处理E690钢试样的弹性模量为(419.80±8.79) GPa,提高了21.4%,弹性恢复功略有提高。LSP处理使得E690钢的摩擦系数由0.59±0.03减小为0.55±0.03,同时使其磨损率降低了32%。未冲击处理和LSP处理E690钢试样的磨损机制为黏着磨损、氧化磨损和磨粒磨损。结论 LSP处理可有效改善E690钢基体表层的微观组织,形成明显的冲击影响层深度,有效提高E690钢基体的硬度和弹性模量,降低其滑动摩擦系数。此外,LSP处理有效提高了E690钢的耐干滑动磨损性能。

It is an advanced surface strengthening method to construct gradient structure by laser shock peening,which can improve the performances of metallic materials without changing their internal microstructure,such as fatigue strength,corrosion resistance,wear resistance and other properties.The gradient structure and residual stress have an obvious effect on the failure mechanism of the materials.The refined grain and high residual compressive stress are favorable to the improvement of mechanical properties,which affects the friction and wear behavior of the matrix.The work aims to study the microstructure,mechanical properties and wear behavior of E690 steel treated with and without LSP.The commercial E690 steel plate was cut into long squares of 75 mm×75 mm×15 mm as the base materials and polished by milling and cleaned ultrasonically.Black 3M tape was pasted on the surface of the base materials to absorb laser power.Flowing deionized water was used as confinement layer.A PROCUDO®200 laser peening system was used to perform the LSP treatment.The spot size was 2 mm.The pulse width was 20 ns.The frequency was 5 Hz.The laser pulse energy was fixed as 6 J.Both of the overlap rates of the scanning paths along X and Y axes were 30%.The specimens used for microstructure observation were ground with sandpaper,polished with diamond polishing agent and etched with 4%natal.An optical microscope and a scanning electron microscope(SU8010)were used to observe the microstructure.The phase of the specimens was studied by an X-ray diffractometer(D8 ADVANCE).The residual stress was measured by an X-ray stress analyzer(XL-640).The mechanical properties were measured by a micro-hardness tester(HV-1000)and a nano-indenter(TI 950).The friction and wear tests were performed on a ball-on-disc tribometer(MFT-3000).The cross-sectional area of wear tracks was measured with a laser confocal microscope(OLS4100)to calculate the wear volume loss.The morphology of wear tracks was observed to reveal the wear mechanism.The superficial layer of E690 steel matrix is refined obviously to form gradient structure.The E690 steel specimens treated with and without LSP are composed ofαandγphases.The full width at half maximum of the highest peak ofαphase of the specimen after LSP treatment increases from 0.218°to 0.266°.Besides,relatively large residual stress forms in the E690 steel specimen surface after LSP treatment,the highest value of which is-268 MPa.The influence depth of LSP is about 700μm.The surface micro-hardness and Young's modulus of the E690 steel specimen after LSP treatment are 302.5±12.2HV100 and 419.80±8.79 GPa,which increase by 8.7%and 21.4%compared with those of the specimen without LSP treatment.The elastic recovery ratio of the E690 steel specimen after LSP treatment increases slightly.The coefficient of friction of the untreated and LSP treated E690 steel specimens are 0.59±0.03 and 0.55±0.03.The wear rate of the E690 steel specimen after LSP treatment decreases by 32%compared with that of the E690 steel specimen without LSP treatment.The wear mechanisms of the untreated and LSP treated specimens are adhesion wear,abrasion wear and oxidation wear.LSP treatment can improve the mechanical properties and wear resistance of E690 steel.The improved hardness,Young's modulus and high compressive stress are the important factors leading to the improvement of dry sliding wear resistance and decrease of coefficient of friction for E690 steel after LSP treatment.Besides,the lubrication role played by oxidative layer is also an important reason.