烧结钢烧结过程中的气氛控制及其对性能的影响(1)

烧结气氛的正确选择及其控制对烧结后部件的性能至关重要。这里所谓的控制主要是指对气氛中氧及碳浓度（含量的）控制，因为两者均对烧结的质量及其后部件的力学性能，烧结表面质量等具有决定性的作用。本文综述了PM钢烧结过程中所用的不同的烧结气氛，阐述了不同气氛的作用及其影响，着重分析了不同气氛中碳势及氧浓度的控制，并举例说明。     

N2—H2系氮基烧结气氛的研究

研究作介绍了粉末冶金氮基烧结气氛的制备原理和流程设计，氮基气氛中各组份的作用，铁碳材料和零件在氮基气氛中烧结后的性能及其应用效果和经济意义。     

烧结气氛对注射成形Fe/2Ni合金性能的影响

在H_2,H_2+N_2及真空气氛下对Fe/2Ni合金进行了烧结,讨论了烧结气氛对合金碳含量以及合金力学性能的影响;指出烧结气氛是通过H_2+N_2混合气氛中H_2脱出合金中的碳,从而影响合金的最终组织来影响合金力学性能的,因此可以通过控制烧结气氛的H_2与N_2体积比来控制合金中的碳含量,以得到所需的力学性能;并对合金脱碳机理作了初步探讨。     

烧结气氛对Mo_2FeB_2金属陶瓷组织与性能的影响

以钼粉、铁粉、硼铁合金粉为原料,采用粉末冶金的方法,分别在真空、N2和Ar气氛下制备Mo2FeB2金属陶瓷材料。研究了烧结气氛对Mo2FeB2金属陶瓷密度、成分、力学性能以及显微组织的影响。研究结果表明,在同样烧结温度下,试样在真空气氛下的烧结密度为8.23g/cm3,硬度为75.3HRA,抗弯强度为1246.38MPa,优于在N2和Ar气氛下烧结制备的试样的密度、硬度和抗弯强度。金属陶瓷在N2和Ar中烧结后,碳含量比在真空中烧结的碳含量低1.0%～1.2%,而氧、氮含量均高于真空中烧结的含量。论文还通过对材料的显微组织的分析,发现真空气氛下制备的试样组织发育良好,结构致密,并阐述了不同烧结气氛对该材料组织结构影响的原因。     

配碳量对烧结烟气排放规律的影响

为了更好地对烧结烟气进行协同治理,建立一体化控制技术,对不同配碳量混合料进行烧结实验。通过德国testo350烟气分析仪实时在线测得烧结烟气中CO、SO_2、NO_x、O_2等成分数据,分析烧结过程中CO、SO_2、NO_x形成的机理及主要影响因素。结果表明:烧结过程中,烟气CO平均质量浓度随配碳量增加而上升;SO_2的排放在烧结终点前始终存在一个排放质量浓度峰值区间,并且配碳过高造成的还原性气氛不利于脱硫;烟气中的NO_x主要来自于燃料燃烧产生的燃料型NO_x,应使烧结燃料引入的N最小化;建议分级治理烟气,将SO_2质量浓度高的区域烟气引入点火区域实现热风烧结,并且利用自反应、自催化作用协同富集降低其污染物的质量浓度。     

粉末冶金钢烧结过程控制和分析

烧结过程控制对粉末冶金整个工艺过程起着至关重要的作用,控制不好,将导致烧结后的零件在尺寸和性能上不稳定或达不到产品设计要求,并可能还会出现氧化、脱碳、渗碳、崩裂和积碳等工业中常见的问题。随着对粉末冶金产品的性能和成本控制要求不断提高,金属Cr因其价格低并具有很好的强化效果,成为粉末冶金工业开拓的重点方向。但是金属Cr容易氧化,对烧结气氛要求较高,因此对烧结工艺提出了挑战。随着烧结炉技术的发展和氮基保护气体广泛使用,在网带炉中烧结含Cr成分的零件已经成为现实。利用热电偶、氧分压和CO分析仪等设备组成的分析系统,评估了以氮氢混合气体作为保护气氛的网带烧结炉的实际烧结情况,分析了几种烧结过程中常见的缺陷及其原因,并提出了相应的改善措施,同时也总结了含Cr材料所需的烧结条件及其控制。     

烧结碳气氛对CVD涂层刀片基体脱β层厚度的影响

为了研究烧结气氛对硬质合金脱β层厚度的影响，本研究以WC、Co、Ti(C,N)、(Ti,W)C和(Ta,Nb)C粉末为原料，通过脱氮气氛烧结制备了WC-(Ti,W)C-Ti(C,N)-(Ta,Nb)C-Co梯度硬质合金，并分析了Ti(C,N)含量和烧结碳气氛对合金微观组织与性能的影响规律。结果表明，添加Ti(C,N)将促进立方相向合金内部扩散，钴往外的扩散驱动力增强，在合金表面形成岛状或层状覆钴现象。烧结气氛主要是通过合金表面的碳含量来影响液相和立方相的迁移来影响脱β层的形成，随烧结炉碳气氛升高，脱β层厚度减少，添加0.9%Ti(C,N)制备的梯度硬质合金在低、中、高3种碳浓度气氛中脱β层厚度分别为20.2μm、10.7μm、0μm，因此，碳浓度气氛是影响脱β层厚度的一个重要因素。     

工业烧结矿矿相形成的模拟烧结条件

在烧结矿工业生产中,原料在还原气氛下加热,然后在氧化气氛下冷却。为了研究气氛在烧结工艺中的作用,试验选用含工业铁矿粉、石灰石、石英及高岭土的小压块作为试样,在控制气氛的条件下,观察气氛,加热温度及冷却条件对于烧结矿中矿物生成的影响。试验结果概述如下: 在烧结试验加热阶段,氧从分压下降时,磁铁矿含量增加,赤铁矿含量减少。铁酸钙含量在低烧结温度(1210℃)下也会减少。但是,在较高烧结温度(1255℃)和中等氧位(5×10~(-3)大气压)条件下,可生成最大数量的铁酸钙。在用空气冷却阶段,磁铁矿可与熔态硅酸盐及氧发生反应,生成大量柱状铁酸钙。试样在混合气体(CO=1％,CP_2=24％,N_2=75％)中加热4分钟至1255℃,然后在空气中缓慢冷却,能很好地模拟生成普通工业烧结矿中由柱状铁酸钙、粒状磁铁矿晶粒和玻璃硅酸盐组成粘结相的典型显微结构。     

有关烧结部件表面问题的几个案例

烧结钢部件在生产过程中，尤其是烧结之后其表面有时会出现针孔、孔洞及斑痕等缺陷。本文结合PM生产的实际过程，总结了影响部件表面问题的各种因素，并举例分析如何诊断各种不同的表面问题及其解决方案。     

分层供热富氢烧结关键技术探索与研究

 中国提出2030年碳达峰、2060年碳中和的“双碳”战略以缓解温室效应带来的环境问题。钢铁是仅次于火电的国内第二碳排放大户,作为钢铁行业中的核心环节,烧结工序的碳减排已是必然趋势。常规烧结工艺中,料层中固体颗粒燃料难准确满足“自蓄热效应”要求的“上多下少”的分布要求,导致料层内部供热不均、成矿质量差、能效低下,且易出现微观局部还原性气氛,对烧结成矿和烟气中CO增多造成负面影响,制约了烧结节能减碳水平的提升。对此,作者研究了燃料形态、燃料分布对烧结的影响规律,提出了“分层供热富氢烧结”理念,阐述了厚料层烧结条件下料层上、中、下各层不同的气固组合供热方法,即顶层依靠富氧点火耦合固体燃料供热、上中层依靠富氢燃气喷加耦合固体燃料供热,下层依靠水蒸气喷加耦合固体燃料供热,同时探明了对应该方法的分层供热低碳烧结机理,详细阐述了富氧点火耦合固体燃料顶层供热、富氢燃气喷加耦合固体燃料中上层供热、水蒸气喷加耦合固体燃料下层供热等关键技术及其技术效果,并对应用上述技术可能出现的烧结过湿层恶化问题提出了解决办法。通过这些技术的集成应用,可以大幅降低烧结工序能耗,减少烧结工序碳消耗、碳排放及其他污染物排放,并改善烧结矿质量。     

Sintering of transparent Nd:YAG ceramics in oxygen atmosphere

Yttrium aluminum garnet (YAG) transparent ceramics were fabricated by sintering at oxygen atmosphere. Tetraethyl orthosilicate (TEOS) was added as the sintering additive to control the grain growth and densification. Pores were eliminated clearly at temperature lower than 1700oC, while grain size was around 3 μm. The in-line transmittance was 80% at 1064 nm when samples were sintered at 1710oC. The effect of TEOS was studied in oxygen atmosphere sintering for Nd:YAG transparent ceramics. At higher temperature like 1710oC, the grain growth mechanism was solute drag, while at 1630 and 1550 oC the grain growth was controlled by liquid phase sintering mechanism. And 0.5 wt.% TEOS was the best adding content for Nd:YAG sintered in oxygen atmosphere.     

烧结气氛对铜基粉末冶金摩擦材料性能的影响

本文分别在N2、H2和N2+H2:混合气三种气氛下,采用热压烧结法制备了合金强化铜基粉末冶金摩擦材料,并观察了微观形貌,测试了物理力学性能和摩擦磨损性能.结果表明:不同烧结气氛下制备的材料的显微组织相似,但抗压强度和摩擦磨损性能有显著区别:H2气氛烧结的材料挤压强度最低,摩擦系数随转速和制动压力的增加波动较大,且磨损严...     

纯钼烧结规律研究

系统研究了在1 000～1 900℃温度范围采用H2气氛中频感应加热烧结纯钼坯过程中不同温度阶段O含量、微观形貌、孔隙、密度、抗弯强度的变化规律。结果表明:随烧结温度提高钼坯O含量逐渐降低,最终降至30mg/kg左右。钼坯密度随温度升高呈增大趋势,致密化的本质是微观形态烧结变化的结果。致密进程可分为4个阶段,各阶段微观晶粒及孔隙作用机制不一致。抗弯强度与致密进程紧密联系但两者随温度变化趋势有所不同。     

Effect of carbon content,sintering temperature,density, and cooling rate upon properties of prealloyed Fe–1·5Mo powder

Abstract

Mixtures of prealloyed Fe–1·5Mo (Astaloy Mo) with and without additions of 0·5–1·2 wt-%C were prepared and their sintering, as well as their mechanical, properties investigated under different process conditions. It was found that carbon content, sintering temperature, and cooling rate had marked effect on physical and mechanical properties. Sintered density decreased with increase in carbon content and sintering temperature. On the other hand, UTS, TRS, and hardness values improved with up to 0·8 wt-%C addition, sintering temperature, and cooling rate. Percentage elongation decreased with increase in carbon content and cooling rate, but was higher for specimens sintered at higher temperatures. The as sintered microstructures consisted of either fine or coarse pearlite, upper or lower bainite, and their mixture depending on the carbon content and cooling rate. The heat treated mechanical properties showed some improvement for the specimens containing 0·5 and 0·8 wt-%C. It became evident that a variety of ternary low alloy steels consisting of Fe + 1·5Mo + 0·5–0·8 wt-%C can be produced and used in the as sintered or heat treated conditions for PM structural parts having good physical and mechanical properties as well as high dimensional accuracy with acceptable microstructures.     

Mechanical properties of fully densified injection-molded carbonyl iron powder

The mechanical properties of carbonyl iron powder shaped by injection molding techniques are affected by the grain size, sintered density, and carbon content. Control of the carbon level depends on several factors, including the binder composition, debinding approach, and sintering conditions (atmosphere, temperature, time, and furnace design). Sintered compacts were densified by containerless hot isostatic pressing, giving smaller grain sizes and superior properties than were possible by pressureless sintering at a high temperature. A quick hot isostatic pressing route (gas forging) with a peak pressure higher than 500 MPa for 1 minute helps retain carbon and results in excellent properties due to a high final density and small grain size. This approach resulted in a final strength of 732 MPa with extensive ductility (23 pct reduction of area) for injection-molded carbonyl iron.     

感应烧结工艺对Fe基粉末冶金材料组织与性能的影响

采用感应加热对不同密度和不同C含量的压坯在不同温度下进行烧结,通过金相观察和力学性能测试分析感应烧结技术对Fe基粉末冶金材料组织和性能的影响.研究结果表明:感应加热会使粉末颗粒在界面处产生较高的温度,促进了C向Fe中的溶解与扩散,有利于Fe、C的化合;当C含量较多时,经感应烧结后的试样珠光体含量明显多于普通电阻炉烧结后...     

JPMA development awards

Abstract

The challenges in controlling carbon potential during sintering of steel powder have been discussed in many experimental and theoretical studies. The main issues lie within the complex thermodynamics and kinetics of processing atmosphere chemistry in continuous sintering furnaces. Although many models have been proposed to address the problem, these have rarely come to reality and entered industry practice. The purpose of this article is to summarise these discussions and investigate the interaction of the atmosphere constituents with the sintered compact within a sintering furnace. An important aim is to provide the PM industry with a fresh understanding of furnace operations and to provide recommendations to improve the control of furnace conditions. A case study is given of an existing furnace installation using Sinterflex technology which allows continuous monitoring and/or control of the furnace atmosphere. The reduction of oxides and carbon potentials to optimise the production parameters is described.     

铝基烧结含油轴承研究现状

综述了铝基烧结含油轴承的发展与研究现状, 讨论了铝基烧结含油轴承制备的难点以及优化措施, 展望了铝基烧结含油轴承的发展方向。研究表明, 采用适当的烧结工艺, 可以促使铝合金粉末的烧结成形, 同时, 添加适量的合金化元素形成强化相, 能够有效提高铝基烧结含油轴承的强度, 制备的铝基烧结含油轴承具有工程实用价值。可按需制备不同组元的铝基烧结含油轴承, 通过优化烧结工艺参数, 选择适当的烧结气氛, 得到符合实际工程需要的铝基烧结含油轴承。此外, 提高烧结含油轴承的耐磨性, 开发轻质烧结含油轴承也是未来烧结含油轴承的重要发展方向。