Heat Treatment Effect on Microstructure, Hardness and Wear Resistance of Cr26 White Cast Iron

High chromium cast iron（HCCI） is taken as material of coal water slurry pump impeller, but it is susceptible to produce serious abrasive wear and erosion wear because of souring of hard coal particles. The research on optimization of heat treatments to improve abrasive wear properties of HCCI is insufficient, so effect of heat treatments on the microstructure, hardness, toughness, and wear resistance of Cr26 HCCI is investigated to determine the optimal heat treatment process for HCCI. A series of heat treatments are employed. The microstructures of HCCI specimens are examined by using optical microscopy and scanning electron microscopy. The hardness and impact fracture toughness of as-cast and heat treated specimens are measured. The wear tests are assessed by a Type M200 ring-on block wear tester. The results show the following： With increase of the quenching temperature from 950 ℃ to 1050 ℃, the hardness of Cr26 HCCI increased to a certain value, kept for a time and then decreased. The optimal heat treatment process is 2 h quenching treatment at 1000 ℃, followed by a subsequent 2 h tempering at 400 ℃. The hardness of HCCI is related to the precipitation and redissolution of secondary carbides in the process of heat treatment. The subsequent tempering treatment would result in a slight decrease of hardness but increase of toughness. The wear resistance is much related to the ＂supporting＂ effect of the matrix and the ＂protective＂ effect of the hard carbide embedded in the matrix, and the wear resistance is further dependent on the hardness and the toughness of the matrix. This research can provide an important insight on developing an optimized heat treatment method to improve the wear resistance of HCCI.

Effects of Heat Treatment on Hardness and Dry Wear Properties of a Semi-Solid Processed Fe-27 wt pct Cr-2.9 wt pct C Cast Iron

EfFects of heat treatments on hardness and dry wear properties of a semi-solid processed Fe-26.96 wt pct Cr- 2.91 wt pct C cast iron were studied. Heat treatments included tempering at 500℃, destabilisation at 1075℃ and destabilisation at 1075℃ plus tempering at 500℃, all followed by air cooling. Electron microscopy revealed that, in the as-cast condition, the primary proeutectic austenite was round in shape while the eutectic M7C3 carbide was found as radiating clusters mixed with directional clusters. Tempering did not change the microstructure significantly when observed by scanning or transmission electron microscopy. Destabilisation followed by air cooling led to a precipitation of secondary M23C6 carbide and a transformation of the primary austenite to martensite. Precipitation behaviour is comparable to that observed in the conventionally cast iron. Tempering after destabilisation resulted in a higher amount of secondary carbide precipitation within the tempered martensite in the eutectic structure. Vickers macrohardness and microhardness in the proeutectic zones were measured. Dry wear properties were tested by using a pin-on-disc method. The maximum hardness and the lowest dry wear rate were obtained from the destabilisation-plus-tempering heat treatment due to the precipitation of secondary carbides within the martensite matrix and a possible reduction in the retained austenite.

Calculation of carbon content of austenite during heat treatment of cast irons

The austenitizing temperature controls the carbon content of the austenite which,in turn,influences the structure and properties of cast irons after subsequent cooling to room temperature.In this paper,for a cast iron with known silicon content,a formula of calculating austenite carbon content at a certain austenitizing temperature was developed.This relationship can be used to more accurately select carbon content of austenite or austenitizing temperature to produce desired properties after subsequent cooling to room temperature.

Effect of Heat Treatment on Mechanical Property of High Cr-W Cast Iron

The microstructure of high Cr-W cast iron after heat treatment were analyzed, and the effect of various heat treatment temperature and time on mechanical properties of high Cr-W cast iron were studied, and the best process parameter of heat treatment was provided in this paper. The results show that the heat treatment can improve the mechanical property of high Cr-W cast iron, and higher synthetic mechanical property of high Cr-W cast iron can be obtained when treated with normalization at 980 ℃ for 2 h and tempered at 400 ℃ for 2 h.

Effect of variable heat treatment modes on microstructures of Fe-Cr-Bcast iron alloy

The effect of heat treatment mode on the microstructure of Fe-Cr-B cast iron alloys was investigated inthis paper by comparing the difference of precipitation patterns of secondary particles after thermal cycling treatment(TCT) with those after normal heat treatment (NHT). No obvious differences were found in precipitation patterns ofsecondary particles between TCT and NHT when experimental temperature was below Ar1. However, whentemperature was over Ar1, there were significant differences, with secondary particles prominently segregated at thegrain boundaries under TCT, while the particles evenly distributed in the matrix under NHT. The reason for themicrostructure differences could be associated with the development of non-equilibrium segregation of boron duringTCT.

Influence of Semi-Solid Isothermal Heat Treatment on Microstructure of Gray Cast Iron

Materials serve as an enabling technology contributing to solutions in problems of concern to society. In this research, the effect of semi-solid isothermal heat treatment on graphite morphologies and matrix structure for gray cast iron were studied. Microstructure observations and measurements of flaky graphite morphology are reported as a function of isothermal heating time range of 5 to 25 minutes after isothermal heating temperature at 1163℃. The effect heating time, on the semisolid microstructures during partial re-melting was investigated. Flack graphite morphology was changed significantly by isothermal heating of gray cast iron at 1163℃ for heating time above 15 min resulting fine graphite morphology in matrix structure. Hardness increases with increasing heating time due to the amount of cementite and fine pearlite matrix for air cooled gray cast iron. The optimum heating treatment condition was achieved at the temperature of 1163℃ for the range of 15 to 20 min.

Influence of Heating Temperature on Property of Low Chromium Wear Resistant Cast Iron Containing Rare Earth

The influence of heating temperature on mechanical properties of low chromium wear resistant cast iron containing rare earth elements was studied by means of metallographic examination, scanning electron microscopic examination and mechanical property test. The experimental results show that heating temperature has great effect on impact toughness (α_k), bending fatigue (σ_(bb)) and relative toughness (σ_(bb)×f), but little effect on hardness (HRC). When the specimen was held at 960 ℃ for 3 h, it has better comprehensive mechanical properties, and the reason and regularity of the change for mechanical properties of the cast iron were reviewed.

Effects of Rare Earths and Al on Structure and Performance of High Chromium Cast Iron Containing Wolfram

Effects of RE and Al on the structure, impact toughness, hardness, and wear resistance of high chromium cast iron containing wolfram were investigated. The results show that without modification the volume fraction of austenite is high and the carbide appears to be thick lath and the grain size is relatively large; proper modification using RE combined with Al can reduce volume fraction of residual austenite in the as-cast structure obviously, refine grain size of primary austenite notably, and make the morphology of carbide changing from thick lath to thin lath, rosette, and feather-like modification can also increase hardness, wear resistance and impact toughness of cast iron.

Surface and Bulk Defects in Cr-Mn Iron Alloy Cast in Metal and Sand Moulds: Characterization by Positron Annihilation Techniques

High chromium (Cr: 16% - 19%) iron alloy with 5% and 10% manganese (Mn) fabricated in metal and sand moulds by induction melting technique were investigated for defects microstructure both in the as-cast and heat treated conditions. Non-destructive techniques namely Positron Lifetime Spectroscopy and slow positron Doppler Broadening studies were employed to characterize the defects in the bulk as well as surface of the alloy and their influence of metallurgical parameters. The Positron Lifetime Spectroscopy data reveals that the defect concentration is higher for sand mould alloy samples compared to metal mould ones. The reasons for fewer defects in metal mould are attributed to faster heat transfer in the metal mould. Further, heat treatment yielded spherodization of carbides in the matrix resulting in reduced defects concentration. The S-parameter profiles from Doppler Broadening studies suggest defect concentration at the surface is less in 5% Manganese and near absence of any modification of defect structure following heat treatment in 10% Manganese sample closer to surface.

高性能气缸套材料及其热处理工艺研究

为了满足气缸套的高爆发压力,对材料的强度和弹性模量有了更高的要求,因此进行了灰铸铁的合金化及热处理试验研究,获得了合适的化学成分和热处理工艺;使灰铸铁的抗拉强度超过600 MPa,弹性模量大于140 GPa。

基于文献计量学的高铬铸铁组织及性能研究进展

耐磨材料在工业发展中起到关键作用,其中高铬铸铁因其耐磨性能优异、成本较低得到了快速发展。高铬铸铁的研究主要集中在制备工艺、组织与性能调控、耐磨性等几个方面。本研究借助文献计量学方法对近年来的研究进行了梳理,介绍了研究的侧重点,并从耐磨性研究的最新进展、合金成分和热处理对组织及性能的影响,总结了近年来的研究现状。研究表明,M_(7)C_(3)型碳化物是高铬铸铁组织中最重要的强化相,能够显著提高基体的强度和耐磨性能。对高铬铸铁进行热处理,能够细化晶粒,提高硬度和耐磨性。另外,通过添加合金元素或者加入强化相也能提高高铬铸铁的性能,例如,添加Ti_(2)AlC后材料的力学性能明显提高。总之,对高铬铸铁的制备工艺、组织与性能调控、耐磨性等方面进行研究,有助于优化其性能并扩大其应用领域。

Cementites decomposition of a pearlitic ductile cast iron during graphitization annealing heat treatment

Cementites decomposition of a pearlitic ductile cast iron during graphitization annealing heat treatment was investigated.Fractographies and microstructures of heat treated samples were observed using a scanning electron microscope and mechanical properties were measured by a universal tensile test machine.The results indicated that during isothermal annealing at 750°C,the tensile strength of pearlitic ductile cast iron was increased to a peak value at 0.5h,and decreased gradually thereafter but the elongation was enhanced with the increase of annealing time.Moreover,the diffusion coefficient of carbon atoms could be approximately calculated as 0.56μm2/s that could be regarded as the shortrange diffusion.As the holding time was short（0.5h）,diffusion of carbon atoms was incomplete and mainly occurred around the graphites where the morphology of cementites changed from fragmentized shape to granular shape.In addition,the ductile cast iron with tensile strength of 740MPa and elongation of 7% could be achieved after graphitization annealing heat treatment for 0.5h.Two principal factors should be taken into account.First,the decomposition of a small amount of cementites was beneficial for increasing the ductility up to elongation of 7%.Second,the diffusion of carbon atoms from cementites to graphites could improve the binding force between graphites and matrix,enhancing the tensile strength to 740 MPa.

化学成分及热处理工艺对高铬铸铁力学性能的影响

为了得到综合性能优秀的双金属耐磨锤头耐磨端材料,利用正交实验法研究了成分(碳含量和铬含量)和热处理工艺(淬火温度和回火温度)对高铬铸铁力学性能的影响,具有一定的工程应用价值。实验结果表明,各因素对热处理后高铬铸铁力学性能影响关系为w(Cr)/%>回火温度>淬火温度>w(C)/%,优化后的高铬铸铁成分及热处理工艺为2.8%C,20%Cr(质量分数),淬火温度1040℃,保温2 h,空冷,回火温度250℃,保温2 h,空冷。硬度为60.17 HRC,冲击韧性αk为9.88 J/cm^(2)。

高强韧性球墨铸铁轮盘铸件的试制

根据球墨铸铁轮盘铸件的结构特点,进行了铸造工艺设计。采用顶冒口和热侧冒口相结合实现顺序凝固,对铸件进行有效补缩。针对材质技术要求,对熔炼和浇注工艺、热处理工艺进行了研究。结果表明,采用设计的铸造工艺和热处理工艺批量试生产的轮盘铸件没有出现缩孔、缩松、夹渣和气孔等缺陷,材质性能满足客户要求。

不同碳含量高硬度共晶高铬铸铁的微观组织与力学性能

通过控制不同元素含量制备出含有2.9%碳和3.1%碳(质量百分比)的两种共晶高铬铸铁,并讨论了碳元素对共晶高铬铸铁微观组织与力学性能的影响。研究结果表明,两种高铬铸铁微观组织和力学性能存在显著差异。Ni、Mo、Mn、Cu和稀土元素的复合合金化以及优化热处理工艺可以控制碳化物的分布和数量,从而进一步提高样品硬度。此外通过弯曲和冲击测试,证实了两种不同碳含量的共晶高铬铸铁合金都具有优秀的硬度(65HRC)、抗弯强度(≥1160 MPa)和冲击韧性(≥2.88 J)。3.1%的较高碳含量导致铸态样品具有更高硬度,但抗弯强度明显降低。

高铬铸铁耐磨性研究的进展

高铬铸铁是一种耐磨材料,广泛应用于建筑、电力和矿山等领域。概述了进一步改善高铬铸铁耐磨性的途径,包括以稀土元素、钼、镍、铌、钨、硼等合金化,淬火、回火、渗碳、渗铬等热处理,以及以陶瓷颗粒增强等。

高硬度过共晶高铬铸铁的合金化与热处理工艺研究

通过Nb、W、V和B合金化,使过共晶高铬铸铁的铸态硬度得到显著提高。高硬度主要来源于碳、硼化物比例的显著提高和碳、硼化物尺寸的明显细化。大尺寸的碳化物明显消失,微观组织更加均匀,使合金化铸态硬度达到了未合金化样品热处理态的硬度水平。将过共晶高铬铸铁在不同热处理方案下的硬度值进行对比,结果表明,快速冷却相比缓慢冷却会使过共晶高铬铸铁的硬度增加,较低的温度、较长的加热时间以及较长的固溶时间会产生更高的硬度值,炉冷或空冷等回火冷却方式对硬度值影响较小。这为过共晶高铬铸铁提高硬度值、简化热处理流程以及优化生产工艺提供了理论借鉴。

热处理对含钨高铬铸铁组织及性能的影响

采用金相显微镜、扫描电镜观察微观组织，X射线衍射仪分析相组成，并测定洛氏硬度、冲击韧性及耐磨性，研究了热处理对含钨高铬铸铁组织及性能的影响。结果表明，钨在高铬铸铁基体和碳化物中均匀分布，热处理对钨的分布影响不大，钨能显著提高高铬铸铁的性能。含钨高铬铸铁合理热处理工艺是1050℃奥氏体化淬火，250～350℃回火，在该热处理条件下的组织为马氏体＋碳化物＋少量残留奥氏体，铬的碳化物类型为Cr7C3、Cr23C6，钨的碳化物有WC1-x、W6C2.54、W3C，硬度为62～63HRC，冲击韧度为7～8J／cm^2，耐磨性比不含钨高铬铸铁显著提高。

Cr20高铬白口铸铁磨片的热处理工艺

研制了Cr20高铬白口铸铁磨片,设计正交试验方案研究了不同热处理参数对应试样的硬度和冲击韧性。结果表明,以硬度为试验指标的热处理工艺参数中,回火温度最重要,其次为淬火保温时间,再次为淬火温度及回火保温时间;在本热处理试验范围内,Cr20铸铁试样的硬度均达到了57·5HRC以上,以960℃×2·5h空冷淬火+450℃×3·5h回火的优方案热处理可获得最高硬度61·6HRC、冲击韧度2·31J/cm2。Cr20铸铁的铸后热处理能在保持冲击韧性基本不变的同时有效提高Cr20铸铁的硬度,其金相组织主要由坚硬的条状共晶碳化物(Fe,Cr)7C3和马氏体基体组成。