18CrNi8油泵用钢的试制

本文主要介绍了油泵针阀体用钢18CrNi8冷拔棒材，在冶炼轧制中需要解决的一些技术难题及所采用的生产工艺。     

潜孔钻头用钢18CrNi3MoA锻制圆棒的生产实践

根据潜孔钻头用钢18CrNi3MoA技术要求及钢种特性,通过40t电弧炉(终点[C]≥0.05％、P≤0.003％,出钢温度≥1 630℃)-LF(精炼渣碱度3.0～4.5)-VD(≤70 Pa时间≥25 min)-氩气保护1.52 t铸锭-钢锭(1250±10)℃15 h均质化处理-锻坯Φ140 mm,780～810...     

焊接速度对18-8不锈钢接头组织形态的影响

以18-8不锈钢为研究材料,采用TIG焊方法,仅改变焊接速度来观察接头组织形态的变化。研究发现：在固态相变区中,焊接速度越大,该区残留的δ-铁素体愈多且在晶内按一定方向平行分布。在1150℃以下接近1150℃的热影响区中,仅在晶界出现δ-铁素体,焊接速度越大,该区晶粒越小,晶界δ-铁素体数量愈多。焊接速度对焊缝中δ-铁素体形态有影响,但不太明显。     

18-8型纯净不锈钢生产工艺优化及其效果

太原钢铁集团公司第二炼钢厂引进的以预处理后铁水、合金为主要原料的不锈钢新生产线,在开发18-8型纯净不锈钢中,发挥主原料铁水Cu、P、S、等五害元素很低和VOD真空冶金的优势,对LF精炼不锈钢工艺进行优化;并采取措施优化中间包流体流场等,使得18-8纯净不锈钢铸坯O、Al2O3质量分数分别在30×10-6、5×10-6以下,金相法观察到50mm2铸坯内夹杂物总量降低幅度在40%左右,大于20μm的夹杂物控制在5%以下.     

H13挤压模具失效分析

采用直读光谱仪、光学显微镜、显微维氏硬度计,对一种早期失效的H13钢铝型材挤压模具试样开展化学成分和金相、硬度检测,经分析,模具早期失效的主要原因是渗氮层硬度偏高、厚度偏薄,导致了疲劳磨损.     

Cr12MoV与65Cr4W3Mo2VNb钢制冲齿模的失效分析

由自行车飞轮冲齿模的失效分析结果表明,Cr12MoV钢中所存在的严重碳化物不均匀性诱发了裂纹的产生,导致了模具多在低周疲劳状态下发生断裂失效;而65Cr4W3Mo2VNb钢中的碳化物呈弥散分布,模具主要呈磨损失效,所以,使用寿命较高。     

大容量火电机组奥氏体钢管材失效分析及预防对策

30 4奥氏体不锈钢管材是 2 0 0MW以上火电机组近年来使用较多的受热面材料 ,由于该材料失效而引发的停机事故也时有发生 ,特别是在沿海地区具有一定的普遍性 .通过对某厂机组的失效分析 ,表明应力高低是造成失效的主要原因 ,并提出了预防对策 .     

Φ160 mm 42CrMoA钢内部裂纹失效分析

采用电子显微分析及微区成分分析等检测方法,φ160mm42CrMoA钢内部裂纹产生的原因进行了分析。结果表明,氢原子在该钢产生的中心疏松及夹杂物聚集区富集产生氢致裂纹,在矫直外力作用下裂纹得到了进一步扩展。     

热处理过程中氢致滚子开裂失效分析

通过体视显微镜、光学显微镜、扫描电镜及X射线能谱仪对一批送检失效滚子进行分析,滚子基体材料为20Cr钢。结果表明,滚子宏观失效形式分为三类,失效原因均为氢致脆断,沿晶断口平滑,呈冰糖块状,断面上有典型的“鸡爪形”发纹。氢脆失效主要是由滚子渗碳工艺后的直接淬火导致的,镀锌工艺也部分提供了氢的来源。     

The influence of solidification morphology on the high-temperature mechanical properties of an 18–10CrNi steel

Cylindrical specimens of the grade X4CrNi18-10 (material no 1.4301) having diameters of 10, 15 and 20 mm were examined on a hot tensile testing unit after partial melting and cooling at different rates. Experiments were performed at temperatures between solidification and 1000°C. As a comparison non-melted specimens taken from a continuously cast slab were investigated. In the experiments in which specimens were partially melted the radially solidified area increases with enhancing cooling rate. At cooling rates ≥ 3 K/s it accounts for more than 80 % of the specimen cross-section. The secondary dendrite arm spacings λ₂ range between approx. 30 and 50 μm at these cooling rates. As the radially solidified area increases, strength at zero-toughness temperature decreases. At lower temperatures, on the other hand, the solidification morphology of these samples had no effect on the mechanical properties. Unlike the results achieved with partially melted specimens, with specimens taken from a continuously cast slab the solidification morphology was found to have a distinct effect. Between 1350 and 1100°C toughness is around 20 % points lower when tensile loading acts transversely to the direction of crystal growth in comparison with axial loading. On the contrary strength is slightly higher. These results show that when investigating the causes of fracture initiation and propagation during and after solidification, the solidification morphology is of prime concern.     

Investigations on intercrystalline creep crack growth of the austenitic steels X 6 CrNi 18 11 and X 8 CrNiMoNb 16 16

The aim of the investigations was to get information about the behaviour of intercrystalline creep cracks during creep deformation from the evaluation of metallographic micrographs and finite element calculations. Two austenitic steels, X 8 CrNiMoNb 16 16 and X 6 CrNi 18 11, were investigated by carrying out creep tests at a temperature of 973 K with varying nominal stresses leading to times of failure from 1 to 3 783 h, as well as to certain creep strains in the tertiary creep stage. These creep tests were followed by analyzing metallographic micrographs of the creep tested specimens and by carrying out finite element calculations, which simulated creep crack growth. It was found that intercrystalline creep cracks in austenitic steel grow independently from momentary crack length but dependent on applied nominal stress and time. Finite element calculations show that local creep strain is a criterion for intercrystalline creep crack growth, contrary to stress-dependent fracture mechanical results.     

连铸生产60CrNi工具钢的研制

通过优化连铸工艺参数，成功地用140mm^2连铸机生产了60CrNi马氏体工具钢，各项性能指标优于模注材，满足用户特殊要求。     

Oxidation behavior of a fine-grained rapidly solidified 18-8 stainless steel

The cyclic oxidation behavior of a fine-grained, rapidly solidified 303 stainless steel was determined at 900 °C in pure oxygen. The rapidly solidified alloy exhibited superior resistance to oxidation compared with that of a wrought 304 stainless steel; its oxidation resistance was as good as that of a wrought 310 stainless steel, even though the latter alloy contained more Cr and Ni. The matrix of the rapidly solidified steel contained a uniform dispersion of fine MnS precipitates (0.2 to 0.5 μm), which were effective in inhibiting grain growth at elevated temperatures. The enhanced resistance to oxidation of the rapidly solidified alloy is attributed to two factors: (1) the formation and growth of protective Cr₂O₃ and SiO₂ scales were promoted by the fine alloy grain size (5 to 8 =gmm) and by the presence of the MnS dispersion, and (2) the adherence of the scale was increased by the formation of intrusions of SiO₂ from the external scale into the alloy, which formed around MnS precipitates and along closely-spaced alloy grain boundaries, and which acted to key the scale mechanically to the alloy.     

热处理工艺对10CrNi3Mo钢板性能及尺寸的影响

采用万能拉伸试验机、示波冲击能量测试仪、光学显微镜和X射线分析仪对不同热处理工艺后的10CrNi3Mo钢板的力学性能、组织形貌、尺寸变化以及残余奥氏体含量进行研究。结果表明：与传统调质工艺相比,经过二次淬火处理后10CrNi3Mo钢的综合力学性能明显改善,屈强比由0.90以上下降到0.85左右,-84℃冲击功及断口纤维率也得到较大提高;同时,试样的尺寸发生了较明显的变化,试样在厚度方向减小,而在宽度和长度方向上增加,经分析这与试样中残余奥氏体的含量有较大关系。     

20CrNi3H钢裂纹倾向的分析

20CrNi3H钢是一种高级齿轮钢。由于该钢种的金相组织结构特性．生产中常常出现因各种原因产生的裂纹而导致产品成批报废的质量事故。是困扰许多生产厂家的老大难问题。故从成材轧制前的钢锭二次加热曲线入手,根据金属学的相变原理,着重分析了产生表面裂纹的工艺操作原因,并提出了相应的解决措施。     

Risk of reoperative valve replacement for failed mitral and aortic bioprostheses

BACKGROUND: One factor influencing the choice of mechanical versus bioprosthetic valves is reoperation for bioprosthetic valve failure. To define its operative risk, we reviewed our results with valve reoperation for bioprosthetic valve failure. METHODS: Records of 400 consecutive patients having reoperative mitral, aortic, or mitral and aortic bioprosthetic valve replacement from January 1985 to March 1997 were reviewed. RESULTS: Reoperations were for failed bioprosthetic mitral valves in 219 patients, failed aortic valves in 153 patients, and failed aortic and mitral valves in 28 patients. Including 26 operations (6%) for acute endocarditis, 153 operations (38%) were nonelective. One hundred nine patients (27%) had other valves repaired or replaced, and 72 (18%) had coronary bypass grafting. The incidence of death in the mitral, aortic, and double-valve groups was respectively, 15 (6.8%), 12 (7.8%), and 4 (14.3%); and the incidence of prolonged postoperative hospital stay (>14 days) was, respectively, 57 (26.0%), 41 (26.8%), and 8 (28.6%). Only 7 of 147 patients (4.8%) having elective, isolated, first-time valve reoperation died. Multivariable predictors (p < 0.05) of hospital death were age greater than 65 years, male sex, renal insufficiency, and nonelective operation; and predictors of prolonged stay were acute endocarditis, renal insufficiency, any concurrent cardiac operation, and elevated pulmonary artery systolic pressure. CONCLUSIONS: Reoperative bioprosthetic valve replacement can be performed with acceptable mortality and hospital stay. The best results are achieved with elective valve replacement, without concurrent cardiac procedures.