冷卻速度對(duì)Ti-V-Mo復(fù)合微合金鋼組織轉(zhuǎn)變及力學(xué)性能的影響

冷卻速度對(duì)Ti-V-Mo復(fù)合微合金鋼組織轉(zhuǎn)變及力學(xué)性能的影響EFFECT OF COOLING RATE ON MICROSTRUCTURE EVOLUTION AND MECHANICAL PROPERTIES OF Ti-V-Mo COMPLEX MICROALLOYED STEEL

利用OM、EBSD、HRTEM和Vickers硬度計(jì)等手段研究了冷卻速率對(duì)Ti-V-Mo復(fù)合微合金鋼組織轉(zhuǎn)變、析出相及硬度的影響，闡明了(Ti, V, Mo)C在不同冷卻速率下的析出規(guī)律及其對(duì)顯微組織、硬度的作用機(jī)理。結(jié)果表明，當(dāng)冷卻速率低于20 ℃/s時(shí)，隨著冷卻速率的增加，析出相平均尺寸由13.2 nm逐漸減小至6.9 nm，鐵素體平均晶粒尺寸由5.06 μm逐漸細(xì)化至2.97 μm，硬度呈先快速增大而后緩慢增大的趨勢(shì)，鐵素體的細(xì)晶強(qiáng)化和(Ti, V, Mo)C的沉淀強(qiáng)化是硬度升高的主要因素；冷卻速率為20~30 ℃/s，其對(duì)晶粒細(xì)化和沉淀強(qiáng)化的影響效果已趨于飽和，硬度基本保持不變，此時(shí)Ti-V-Mo復(fù)合微合金鋼的硬度具有最大值410 HV，屈服強(qiáng)度高達(dá)1090 MPa。Ti-V-Mo復(fù)合微合金鋼的硬度y與冷卻速率x符合指數(shù)衰減關(guān)系：y=-229exp(-x/5)+412。

Nanoscale co-precipitation strengthening in steels has received increasing attention in recent yearsand has become a new cornerstone for the development of advanced high performance steels with superiorcombination of strength and ductility. Rolling process, finishing temperature, cooling rate and coiling temperatureare the main factors which affect mechanical properties of microalloyed steels by changing the volume fraction and particle size of precipitates. Nevertheless, the influence of cooling rate on microstructural evolution,precipitates and mechanical properties of complex microalloyed ferritic Ti-V-Mo steel has been rarely reported. Inthis work, the precipitation law of (Ti, V, Mo)C carbides at different cooling rates and its effect on microstructueevolution and mechanical properties of Ti-V-Mo complex miroalloyed steel were studied by OM, EBSD, HRTEMand Vickers-hardness test. The results indicate that the hardness first increases quickly and then increases slowlyas the cooling rate increased (lower than 20 ℃/s). The mean size of (Ti, V, Mo)C particles decreased from 13.2nm to 6.4 nm and the average size of ferrite grain reduced from 5.06 μm to 2.97 μm. The hardness of Ti-V-Mosteel was improved by the means of grain refinement hardening and precipitation hardening. However, when thecooling rate increased from 20 ℃/s to 30 ℃/s, its effects on grain refinement hardening and precipitationhardening has become saturated, so the hardness was kept flat and achieved a maximum vlaue of 410 HV, and theyield strength reached as high as 1090 MPa. The hardness y of Ti-V-Mo microalloyed steel and cooling rates xaccord with a exponential decay relationship: y=-229exp(-/5)+412.

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