【作者】 黄贞益；

【导师】 陈光；

【作者基本信息】 南京理工大学 ， 材料科学与工程， 2012， 博士

【摘要】 针对近年发展起来的V-N微合金化铁素体-珠光体型热轧低合金高强度H型钢、Nb-V-Ti-Mo微合金化针状铁素体型低合金高强度深海管线钢和Nb-Ti-Cr-Mo微合金化贝氏体型低合金高强度耐磨钢存在的问题,分别研究了合金的成分和塑性变形机制、组织性能控制与预报、修复再制造,得到如下主要结论：(1)V/N质量比为3.64,强度值最高,塑性最低。碳含量为0.19 wt%且V/N比为7.14时综合性能最好。(2)V-N微合金化铁素体-珠光体型低合金高强度钢的高温塑性变形行为符合幂指数关系。在900-1150℃及0.001-15s-1下,塑性变形由位错芯区扩散的幂律蠕变所控制,不存在塑性失稳区域。建立的塑性变形机制图,可有效指导该钢生产工艺的制定。(3)V-N微合金化铁素体-珠光体型低合金高强度钢在热变形过程中,α相与V(C,N)及γ相之间分别存在(010)V(C,N)//(011)α和[110]γ//[111]。关系。铁素体易在V(C,N)上形核生成晶内铁素体；随相变温度的降低、形变量的增加、轧后等温温度的降低及保温时间的延长,晶内铁素体含量增加,在650℃时大量生成。热轧H型钢的冷却速率和等效应变由翼缘边部到翼缘与腹板交界的R处逐渐降低。铁素体晶粒尺寸在翼缘1/4和1/2处没有明显差别,均小于R处。截面不同部位珠光体含量差别不大,但珠光体片层间距由翼缘1/4到R处逐渐增大。V(C,N)以球状或块状分布在铁素体中,其含量由翼缘1/4到R处逐渐增加。大角度晶界在翼缘1/4和翼缘1/2处所占比例大致相等,R处小约15%。采用在线控制冷却技术,成功实现了热轧H型钢截面温差的降低,最高可达80%,晶粒尺寸波动降低64%,屈服强度波动值和残余应力显著降低,消除了轧后腹板冷却波浪。(4)数值模拟和有限元模拟相结合的Nb-V-Ti-Mo微合金化针状铁素体型低合金高强度深海管线钢的组织和性能预报结果表明,屈服强度和抗拉强度预报值与实测值最大偏差分别为8.72%和9.43%,但80%样本的偏差均在6.80%之内,可以指导深海管线钢生产工艺的优化。(5)等离子堆焊镍基合金涂层主要由γ(Ni, Fe)、(Fe, Cr)7C3和(Fe, Cr)2B相构成,亚结构主要为位错,具有亚共晶的组织特征,存在明显的成分偏析。30wt.%Cr3C2的加入,增加了涂层中的富(Fe, Cr)化合物的相对含量,出现了Cr3C2和Ni4B3相,具有过共晶的组织特征。0.8wt.%纳米α-Al2O3的加入,没有改变镍基合金涂层的亚共晶组织特征及γ(Ni, Fe)固溶体与富(Fe,Cr)相的相对含量,但降低了(Fe, Cr)7C3相的相对含量,增加了(Fe, Cr)2B相的相对含量,出现了四方结构的纳米y-A1203,有形成堆垛层错亚结构的趋势。Cr3C2和纳米A1203的加入,均降低成分偏析程度。等离子堆焊镍基合金涂层和添加30wt.%Cr3C2或0.8wt.%纳米Al2O3的镍基合金涂层的冲击磨损性能分别是Nb-Ti-Cr-Mo微合金化高强度NM450耐磨钢的1.3倍和2.2倍或6倍。综合经济因素,采用等离子堆焊添加0.8wt.%纳米Al2O3的镍基合金涂层来修复NM450耐磨钢进行再制造是合适的。更多还原

【Abstract】 Considering the insufficiency in the recent developed V-N microalloyed ferrite-pearlite hot rolled high-strength low-alloy steel (HSLA) H-shape steel, Nb-V-Ti-Mo microalloyed acicular ferrite HSLA pipeline steel, and Nb-Ti-Cr-Mo microalloyed bainite HSLA abrasion resistance steel, the compositions and plastic deformation mechanisms, the prediction of the microstructure and property, the repairing and remanufactuering were investigated, respectively. The primary conclusions are shown following:(1) The highest strength and lowest plasticity can be obtained in the V-N microsalloyed steel with 3.64 of V/N ratio in weight percentage. The better overall properies can be received in the steel with 0.19 wt.%C and V/N ratio being 7.14 in the range of 0.06-0.19 wt. %C.(2) The plastic deformation behavior under high temperatures of the high strength low alloy steel with ferrite-pearlite microstructure microalloyed by V and N elements is power-law creep. The plastic deformation mechanism at temperatures of 900-1150℃and shear strain rates of 0.001-15 s"1 is power-law creep by dislocation core diffusion and the plastic instabilities cannot be obtained. Under the above deformation conditions, the plastic deformation mechanism of the observed steel can be studied by plastic deformation mechanism map built based on the strain rate constitutive equations for the Fe-C alloys. The dynamic recrystallization (DRX) microstructure can be obtained at a low strain rate and temperatures of 900-1033℃. Increasing temperature to 1033℃, the DRX microstructure can be obtained at 0.1-100 s-1.(3) During the hot deformation of the high strength low alloy steel with ferrite-pearlite microstructure microalloyed by V and N elements, the relationship between a and V(C,N) being(010)V(C,N)//(011)α,αandγbeing [110]γ//[111]αcan be obtained. The IGF can be easily obtained by nucleating the ferrite on the V(C, N) particles. The contents of IGF increase with decreasing the phase transformation temperature, increasing the deformation degree, decreasing the soaking temperature or increasing the soaking time, and the peak values can be obtained when the temperatures are 650℃. The cooling rate and the equivalent strain of the hot rolled H-beam steel decrease gradually from the edge of the flange to the boundary between the flange and the wave (R). The obvious difference in the grain size of the ferrite in the flange 1/4 and 1/2 cannot be found, where the grain size of the ferrite is lower than that of the R. Little difference about the contents of pearlite in the different sections of the H-beam can be obtained, though the lamellar distance of pearlite increases from flange 1/4 to R. The V(C, N) particles in the morphology of spherical or block distributes on the ferrite. The content of V(C, N) particles increases from flange 1/4 to R. The proportion of the high-angle boundary in flange 1/4 and 1/2 is almost the same, where the proportion of the high-angle boundary is higher than R by 15%. Using on-line controlled cooling technique, the decreasing of the temperature difference and the grain size fluctuating on the different cross-section of the hot rolled H-beam steel is obtained successfully. Under such condition, the highest temperature difference by 80% and the grain size fluctuating by 64% can be received. Besides, the yield strength fluctuating and the residual stress decrease significantly. And the waves on the web can be removed.(4) The results about the prediction of the microstructure and properties of the submarine pipe steel with acicular ferrite microstructure microalloyed by Nb, Ti and Mo elements invesitigated by numerical simulation companied by finite element simulation show that the maximum difference of the yield strength and the yield strength between the predication and the measurement values are about 8.72% and 9.43%, respectively. Nevertheless, for the 80% sample, the maxiumum difference is lower than 6.80%. Therefore, the production process of submarine pipe line steel can be improved.(5) The nickel-based alloy coating deposited by plasma surfacing is consisted of y (Ni, Fe)、(Fe, Cr)7C3 and (Fe, Cr)2B phases. The substructure is mainly dislocation. The hypoeutectic microstructure and the obvious component segregation can be seen in the deposited coating. Adding 30 wt.%Cr3C2 leads to increase the relative contents of (Fe, Cr)-rich phases and the occurrence of Cr3C2 and Ni4B3 phases. The hypereutectic microstructure can be obtained in the Cr3C2-strengthen nickel-based alloy coating. Adding 0.8 wt.% nanometerα-Al2O3 with rhombohedral lattice structure does not change the hypoeutectic microstructure and the relative contents between y (Ni, Fe) and (Fe, Cr)-rich phases in the nickel-based alloy coating, but decreases the relative content of (Fe, Cr)7C3 phase and increases that of (Fe, Cr)2B phase. Besides, adding 0.8 wt.% namometerα-Al2O3 with rhombohedral lattice structure leads to the occurrence of nanometerγ-Al2O3 with tetragonal lattice structure and promote the formation of the stacking fault. Adding Cr3C2 and nano-Al2O3 can decrease the component segregation in the nickel-based alloy coating. The impact abrasion resistance of the nickel-based alloy,30 wt.% Cr3C2 and 0.8 wt.% nano-Al2O3 strengthen nickel-based alloy coatings is 1.3,2.2 and 6 times to that of the Nb-Ti-Cr-Mo microalloyed NM450 high strength low alloy abrasion resistance steel, respectively. Considerating the economic fator further, it is suitable to use 0.8% nano-Al2O3-strengthen nickel-based alloy coating deposited by plasma surfacing to repair NM450 steel to reach the purpose to remanufacture.更多还原