【摘要】：H13熱作模具鋼（國際牌號40CrMoV5，國內(nèi)牌號4Cr5MoSiV1）是目前應用最廣泛的熱作模具鋼之一，被廣泛應用于鋁、銅、鎂及其合金的熱擠壓模、熱鍛模和鋁、鎂及其合金的壓鑄模等。由于模具的工作環(huán)境惡劣、成本高，對其進行強化與修復存在實際意義。激光淬火技術(shù)是現(xiàn)有各種激光表面處理技術(shù)中研究和應用最多的方法之一，具有變形小、硬度高等優(yōu)點。激光熔覆技術(shù)是近年來發(fā)展比較迅速的一種表面改性技術(shù)，在激光作用下，基材表面形成良好冶金結(jié)合的熔覆層，從而改善或修復零部件，，延長其使用壽命。 本文采用FL-DLS21-Dlight4kW半導體激光器對H13模具鋼表面進行激光淬火強化和Ni基粉末激光熔覆修復。通過X-射線衍射儀（XRD）、光學顯微鏡（OM）和掃描電鏡（SEM）等手段分析硬化層和熔覆層組織結(jié)構(gòu)、物相組成，解釋組織形態(tài)的形成機理及物相分布區(qū)域；采用HVS-1000A數(shù)顯維氏硬度計對硬化層和熔覆層進行顯微硬度測量；利用MG-2000型摩擦磨損試驗機對基體、硬化層和熔覆層的耐磨性進行測試，并分析耐磨機理。同時本文還分析了熔覆層的裂紋和氣孔的形成機理，并給出改進方法。 組織分析表明，激光淬火后組織由表及里分為硬化區(qū)、熱影響區(qū)和基體，硬化區(qū)主要由針狀馬氏體和少量殘余奧氏體組成。激光熔覆后組織由表及里依次是熔覆區(qū)、結(jié)合區(qū)、熱影響區(qū)和基體，組織形狀依次為等軸晶、樹枝晶、胞狀晶和平面晶，Ni/SiC-Y2O3熔覆層由γ-(Ni,Fe)、Ni31Si12、M23C6、Ni3B組成， Y元素可能以Cr2Si2Y形式存在，同時還存在FeNi3化合物。 硬化層與熔覆層硬度都得到明顯提高。優(yōu)化后的激光淬火硬化層最大硬度達到達到792.1Hv0.2，較基體提高58.4%，搭接區(qū)硬度較非搭接區(qū)有所下降，是由后續(xù)激光的回火作用導致。添加1.0wt.%Y2O3得到的激光熔覆層硬度最高，達867.4Hv0.2，較基體硬度提升73.5%。 摩擦磨損實驗表明，各試樣磨損初期均表現(xiàn)為氧化磨損，H13基體主要表現(xiàn)為粘著磨損，激光淬火后硬化層與基體相比相對磨損性達到2.5，磨損機理表現(xiàn)為磨粒磨損。Ni/SiC-1.0wt.%Y2O3熔覆層耐磨性較基體提高1倍多，磨損機理以磨粒磨損和粘著磨損為主。 裂紋形成的主要形式有：基體與結(jié)合區(qū)的界面產(chǎn)生的彌散裂紋；熔覆層頂部萌生的粗大裂紋；碳化物顆粒上的裂紋。氣孔主要產(chǎn)生的原因：熔覆過程中熔池內(nèi)的反應生成氣體；粉末潮濕高溫下產(chǎn)生氣體。改善裂紋的主要方法：減少殘余內(nèi)應力；不使開裂的傾向性成為現(xiàn)實。改善氣孔的主要方法：改進工藝參數(shù)與熔覆粉末配方；熔覆前對粉末進行預熱。
[Abstract]:H13 hot work die steel (international grade 40CrMoV5, domestic grade 4Cr5MoSiV1) is one of the most widely used hot work die steels at present. It is widely used in hot extrusion dies of aluminum, copper, magnesium and its alloys, hot forging dies and die casting dies of aluminum, magnesium and its alloys. Because of the bad working environment and high cost, it has practical significance to strengthen and repair the mould. Laser quenching is one of the most studied and applied methods of laser surface treatment, which has the advantages of small deformation and high hardness. Laser cladding is a kind of surface modification technology which has been developed rapidly in recent years. Under the action of laser, a good metallurgical cladding layer is formed on the substrate surface, which can improve or repair parts and prolong their service life. In this paper, the surface of H13 die steel is strengthened by laser quenching with FL-DLS21-Dlight4kW semiconductor laser and repaired by laser cladding of Ni based powder. By means of X-ray diffractometer (XRD),) optical microscope (OM) and scanning electron microscopy (SEM), the microstructure and phase composition of hardened and cladding layers were analyzed, and the formation mechanism and phase distribution region of microstructure were explained. The microhardness of hardened layer and cladding layer was measured by HVS-1000A digital display Vickers hardness tester, the wear resistance of substrate, hardened layer and cladding layer was tested by MG-2000 friction and wear tester, and the wear resistance mechanism was analyzed. At the same time, the formation mechanism of cracks and pores in the cladding is analyzed, and the improvement method is given. The microstructure analysis shows that the microstructure can be divided into hardening zone, heat affected zone and matrix from outside to inside after laser quenching. The hardening zone is mainly composed of acicular martensite and a small amount of residual austenite. After laser cladding, the microstructure was in turn cladding zone, binding zone, heat affected zone and matrix. The microstructure shape was equiaxed crystal, dendrite, cellular crystal and plane crystal in turn. The Ni/SiC-Y2O3 cladding layer consisted of 緯-(Ni,Fe), Ni31Si12,M23C6,Ni3B, and Y element might exist in the form of Cr2Si2Y. There are also FeNi3 compounds. The hardness of hardened layer and cladding layer are improved obviously. The maximum hardness of the hardened layer after laser quenching is 792.1 Hv0.2, which is 58.4% higher than that of the matrix, and the hardness of the lap zone is lower than that of the non-lap zone, which is caused by the subsequent laser tempering. The hardness of laser cladding coating obtained by adding 1.0wt.%Y2O3 is the highest, reaching 867.4Hv0.2, which is 73.555% higher than that of matrix. The results of friction and wear experiments show that all the specimens exhibit oxidation wear at the beginning of wear, while the H13 matrix mainly exhibits adhesive wear. The relative wear resistance of the hardened layer after laser quenching is 2.5, and the wear mechanism is abrasive wear. The wear resistance of the Ni/SiC-1.0wt.%Y2O3 cladding layer is more than twice that of the substrate. The wear mechanism of the Ni/SiC-1.0wt.%Y2O3 cladding layer is mainly abrasive wear and adhesive wear. The main forms of crack formation are: dispersion crack at the interface between matrix and bonding zone; coarse crack at the top of the cladding layer; crack on carbide particle. The main reasons for the formation of porosity are the reaction gas in the melting pool during cladding, and the gas produced in the powder under moist and high temperature. The main ways to improve the crack are to reduce the residual internal stress and not to make the crack tendency come true. The main methods to improve the porosity are to improve the technological parameters and the formula of cladding powder, and preheat the powder before cladding.
【學位授予單位】：吉林大學
【學位級別】：碩士
【學位授予年份】：2015
【分類號】：TG174.4

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