共查询到20条相似文献,搜索用时 343 毫秒
1.
W. Solano-Alvarez H. K. D. H. Bhadeshia 《Metallurgical and Materials Transactions A》2014,45(11):4916-4931
The premature failure of large bearings of the type used in wind turbines, possibly through a mechanism called “white-structure flaking”, has triggered many studies of microstructural damage associated with “white-etching areas” created during rolling contact fatigue, although whether they are symptoms or causes of failure is less clear. Therefore, some special experiments have been conducted to prove that white-etching areas are the consequence, and not the cause, of damage. By artificially introducing a fine dispersion of microcracks in the steel through heat treatment and then subjecting the sample to rolling contact fatigue, manifestations of hard white-etching matter have been created to a much greater extent than samples similarly tested without initial cracks. A wide variety of characterization tools has been used to corroborate that the white areas thus created have the same properties as reported observations on real bearings. Evidence suggests that the formation mechanism of the white-etching regions involves the rubbing and beating of the free surfaces of cracks, debonded inclusions, and voids under repeated rolling contact. It follows that the focus in avoiding early failure should be in enhancing the toughness of the bearing steel in order to avoid the initial microscopic feature event. 相似文献
2.
Mostafa Omar El-Bealy 《Metallurgical and Materials Transactions B》2014,45(3):988-1017
The aim of the current article is to elucidate the significant effects of macrosegregation distribution and its level on the different stages of interdendritic crack formation during dendritic solidification in continuously cast steel slabs. Couple formations of macrosegregation and interdendritic crack phenomena during dendritic solidification of peritectic carbon steels have been investigated by metallographic study of collected slab samples and by performing a set of mathematical analyses. The metallographic study involved plant trails to measure slab surface temperature of different secondary spray cooling conditions. Also, macro–microexaminations, measurements of dendrite arm spacing, macrosegregation analysis, and interdendritic distance between the dendrites of collected samples from plant trials have been performed. The experimental results show a fluctuation of carbon segregation with respect to distance from slab surface. These results also reveal that the interdendritic cracks vary with this fluctuation in various nano, macro, and microscales based on the cooling conditions. A mathematical model of heat transfer, solidification, structure evolution, interdendritic strain, macrosegregation, and elementary interdendritic area “EIA” has been developed. This model takes also into account the calculating of interdendritic distance between the dendrites “IDD” to evaluate the interdendritic crack width. The model predictions of different thermal and solidification phenomena show a good agreement with measurements. The results pointed out also that the coupled effect of interdendritic strain and macrosegregation phenomena and their distributions can be considered as the most important tools to evaluate the surface and internal interdendritic cracks in continuously cast steel slabs. The formation mechanisms of different types of interdendritic crack with interdendritic strain patterns and fluctuation of macrosegregation levels during various cooling zones have been explained, and the possible solutions to these problems have been discussed. 相似文献
3.
4.
5.
Conny Eriksson 《国际钢铁研究》2004,75(12):818-828
Surface defects in wire rod and bar rolling are common and well‐known to mill people. Nowadays, surface defects are not accepted on high‐alloyed steel wire rods. The steel making, casting and rolling processes give rise to defects. Also, the final handling of the wire and bar can destroy the surface. In this work, artificial V‐shaped cracks in the longitudinal direction were investigated for different reduction series. The false round‐oval series are known as a series for high quality steels and are usually better than square–oval series. Experiments confirmed that in the false round‐oval sequences a surface crack in the groove bottom may open up during rolling at the same time as its depth is reduced, which is a beneficial situation. Surface cracks found at 45° to the rolling direction, at groove “corners” and on free surfaces will be closed or reduced in depth. The closing of cracks is detrimental since the cracks usually hide rolled‐in oxides beneath the bar surface. The experiments showed that for the subsequent oval–false round sequence the visible crack at the groove bottom will be closed and become shallower. The cracks at 45° and on the free sides will also be closed, but deeper causing a serious surface defect. An FE‐analysis was carried out, explaining the experimental results. Flat oval grooves are better than round ovals and false rounds are superior to square for opening and decreasing the depth of a longitudinal crack. It is difficult to eliminate a surface defect constituting a closed crack. 相似文献
6.
7.
连铸中碳钢用CK—2保护渣的研制 总被引:4,自引:1,他引:3
中碳钢亦称裂纹敏感性钢,在加铸过程中容易产生铸坯表面纵裂纹等缺陷,使用性能合适的保护渣可以改善结晶器内初始坯壳的传热条件,控制表面裂纹的产生,介绍了研制武钢三炼钢厂中碳钢用保护渣的过程及裂纹控制效果,分析了保护渣使用过程的性能变化和渣膜微观结构。 相似文献
8.
9.
10.
11.
《Acta Metallurgica Materialia》1995,43(3):965-972
Depending on the conditions under which an indentation is performed or indented specimen stored, different crack configurations can be obtained. In this work, the influence of these different configurations on the failure process, strength and fatigue behaviour of soda-lime silicate glass, was investigated. To obtain the different crack geometries, indentations were performed in moist air and deionized water with two different dwell times. In this way, typical “half-penny” and deeper “circular” cracks were obtained. Both as-indented and annealed samples were studied. An extensive fractographical analysis revealed a strong “pinning” effect of lateral cracks on the radial crack propagation for indentations obtained in air with short dwell times. Strength measured both in inert and active environments was shown to be lower for indentations obtained in water with longer dwell times. An analogous trend was observed for the lifetime results obtained in static fatigue. Some discrepancies were observed in time-to-failure predictions for “half-penny” indentation cracks and these were related to the interaction between the lateral and radial cracks. 相似文献
12.
X70管线钢DWTT试样的分层裂纹及其断口评价 总被引:3,自引:0,他引:3
通过对管线钢不同温度的落锤撕裂试验和微观断口分析,研究了DWTT试样断口的分层裂纹及其对断裂的影响.结果表明,分层裂纹是受力变形时管线钢内部的薄弱界面受到三维应力作用的结果.分层裂纹出现于主裂纹起裂或加速之前,裂纹稳定扩展或减速时不会产生新的分层裂纹.分层裂纹的数量、张开程度和分层裂纹间距与主裂纹起裂或加速时的应力状态有关,而分层裂纹的长度与裂纹扩展时裂尖的应力状态有关.分层裂纹表面为解理形貌,解理面较大.韧脆转变温度以下的脆性断裂断口或韧脆转变温度附近混合型断口的脆性断裂区,不出现分层裂纹,仅在韧性断口或断口的韧性区出现宏观分层裂纹.研究表明,产生分层裂纹处的断口,分层裂纹无论是三角形分布或是其它形状分布,该区域均应评价为韧性. 相似文献
13.
To improve the current grinding procedure of the back-up roll of CVC hot rolling mills so that the back-up roll service life can be extended, the crack initiation and propagation behavior of medium carbon bainitic back-up roll steel was investigated, a kind of asperity-scale, surface originated vertical short cracks occurred at 5 × 10^2 -1 × 10^4 cycles. Theoretical analysis indicated that the maximum tensile stress occurring at the back edge of the contact of asperities keeps at above 1 347. 97 MPa, and ratcheting and cyclic plastic deformation take place at such sites within 1 × 10^4 cycles. The early initiation of the vertical short cracks is caused by the asperity contact. According to the crack initiation mechanism, short crack behavior and preventive grinding strategy, steel consumption can be reduced considerably by decreasing the surface roughness and removing the asperity influenced surface thin layer at about 70%-80% of the surface distress life. 相似文献
14.
Sarmishtha Palit Sagar G. V. S. Murthy Tarun Kumar Das Amit Prakash Uday Shankar Goel T. Venugopalan 《国际钢铁研究》2013,84(2):163-168
Over the last few years, the use of work rolls for hot rolling of flat steel has been changed from clear chill rolls to indefinite chill, then high chrome steel and now high speed tool steel (HSS). HSS rolls are highly crack‐sensitive because of its high surface hardness. The crack propagation develops within the working surface of the roll, gradually increases in depth and width followed by a large “cats‐tongue” band type spalls of the overlying barrel surface and that leads to abnormal roll failure. This paper presents the development of surface wave based ultrasonic technique to optimize the grinding procedure for having crack free roll surface. 相似文献
15.
针对12Cr1MoV钢在生产过程中出现不同程度的表面裂纹,采用金相显微镜以及扫描电镜检测确认,轧材裂纹是由铸坯裂纹导致。对裂纹的形成原因进行了分析,得出钢水洁净度,钢水氮含量以及结晶器保护渣是导致铸坯裂纹的主要原因,通过控制电弧炉终点碳、优化精炼渣系以及钙化处理脱氧产物提升钢水洁净度,控制圆坯表面氮化物析出,保证钢中N含量 < 0.007%,同时使用管坯钢保护渣,使得12Cr1MoV钢表面裂纹缺陷率由1.6%下降到0.3%。 相似文献
16.
17.
18.
The fracture behavior of cold sprayed 304 stainless steel coating in cold rolling process was studied. The 304 stainless steel coatings were deposited on low carbon steel substrate by cold gas dynamic spray (CGDS) and then cold rolled, respectively. The fracture morphology of the coatings was observed and analyzed, and the crack distributions along the longitudinal rolling direction of the coatings were also investigated and discussed. The results showed that the cohesive strength of the cold sprayed 304 stainless steel coating was too low to be cold rolled. Microcracks were formed in the as-sprayed coatings and ran perpendicularly to the rolling direction. The spacing distance between these cracks decreased with the increase of the cold rolling reduction. In addition, it was also found that the initial crack generated at the surface of the coating and propagated from the surface to the interface along the weakly bonded particles. A theoretical analysis was developed for the coating fracture. It gave a critical minimum cohesive bonding strength of the coating for non-breaking in cold rolling process. The crack propagation manner of the cold rolled coatings was also discussed. 相似文献
19.
In thin strip casting of steel surface cracks may occur; it was analysed which influencing parameters are important and how the cracks can be avoided. The studies, mainly with C60‐steel, lead to the following results: the cracks are formed during the casting process under high temperatures; on the strip surface hot and colder areas occur, and the cracks have to be studied in both areas separately; mostly transverse cracks are formed; the crack density depends on roll material, ‐ force, ‐ roughness, ‐ surface layers; the cracks are initiated by a temperature break down and by rolling within the pool range. 相似文献