Microstructure,Mechanical and Abrasive Wear Behavior of 8.0 wt pct Cr White Iron Subjected to Continuous and Cyclic Annealing Treatment

Continuous annealing treatment (austenitization for 4 hours followed by furnace cooling) and cyclic annealing treatment (four cycles of austenitization, each of 0.66 hours duration followed by forced air cooling) of 8.0 wt pct Cr white iron samples are undertaken at 1173 K, 1223 K, 1273 K, 1323 K, and 1373 K (900 °C, 950 °C, 1000 °C, 1050 °C, and 1100 °C) as steps of destabilizing the as-cast structure. Continuous annealing results in precipitation of secondary carbides on a matrix containing mainly pearlite, while cyclic annealing treatment causes similar precipitation of secondary carbides on a matrix containing martensite plus retained austenite. On continuous annealing, the hardness falls below the as-cast value (HV 556), while after cyclic annealing treatment there is about 70 pct increase in hardness, i.e., up to HV 960. Decrease in hardness with increasing annealing temperature is quite common after both heat treatments. The as-cast notched impact toughness (4.0 J) is nearly doubled by increasing to 7.0 J after both continuous and cyclic annealing treatment at 1173 K and 1223 K (900 °C and 950 °C). Cyclic annealing treatment gives rise to a maximum notched impact toughness of 10.0 J at 1373 K (1100 °C). Abrasive wear resistance after continuous annealing treatment degrades exhibiting wear loss greater than that of the as-cast alloy. In contrast, samples with cyclic annealing treatment show reasonably good wear resistance, thereby superseding the wear performance of Ni-Hard IV.

     

Wear Resistant Steels and Casting Alloys containing Niobium Carbide

Niobium, like titanium and vanadium, forms superhard MC carbides that remain relatively pure in technical alloys on account of their low solubility for other metallic alloying elements. However, because they have a greater hardness than the precipitated chromium carbides commonly used in wear‐resistant alloys, they are suitable as alternative hard phases. This contribution deals with new wear‐resistant steels and casting alloys containing niobium carbide. These include a secondary hardening hardfacing alloy, a composite casting alloy for wear applications at elevated temperatures, a white cast iron as well as two variants of a corrosion‐resistant cold‐work tool steel produced by melt metallurgy and by powder metallurgy. A heat‐resistant casting alloy is also discussed. Based on equilibrium calculations the microstructures developing during production of the alloys are analysed, and the results are discussed with respect to important properties such as abrasive wear and corrosion resistance.     

Microstructure and Abrasive Wear Behavior of Medium Carbon Low Alloy Martensitic Abrasion Resistant Steel

The effect of processing parameters such as hot rolling and heat treatment on microstructure and mechanical properties was investigated for a new 0.27mass% C and Ni,Mo-free low alloy martensitic abrasion resistant steel.The three-body impact abrasive wear behavior was also analyzed.The results showed that two-step controlled rolling besides quenching at 880℃and tempering at 170℃could result in optimal mechanical property:the Brinell hardness,tensile strength,elongation and-40 ℃impact toughness were 531,1 530 MPa,11.8% and 58J,respectively.The microstructure was of fine lath martensite with little retained austenite.Three-body impact abrasive wear results showed that wear mechanism was mainly of plastic deformation fatigue when the impact energy was 2J, and the relative wear resistance was 1.04times higher than that of the same grade compared steel under the same working condition.The optimal hardness and toughness match was the main reason of higher wear resistance.     

Correlation between Microstructure and Mechanical Properties of High C‐Cr Cast Steel

The effect of carbide morphology and matrix structure on abrasion resistance of cast alloyed steel with 2.57% C, 16.2% Cr and 0.78% Mo was studied in the as‐cast and heat treated conditions. Samples were austenitized at three different temperatures of 980, 1050 and 1250 °C for 15 minutes and followed by tempering at 540 °C for 3 hours. The austenitizing temperature of 980 °C revealed fully martensitic structure with little amount of retained austenite, while at 1050 °C the matrix was austenitic with massive amount of coarse secondary carbides. The austenitic matrix with very fine secondary carbides was developed at 1250 °C. The maximum abrasion resistance was obtained at 1050 °C due to the highest structure hardness and existence of both eutectic and secondary carbides in larger size than the formed groove by the abrasive particles during the wear test. On the other hand, the as‐cast pearlitic structure showed high wear rate by an applied load of up to 0.2 bar, followed by very rapid increase in wear rate with higher applied loads. It could be considered that the austenitizing temperature of 1050 °C showed better combination of abrasion resistance and toughness in comparison with other heat treatment cycles.     

高碳高钼高速钢导辊的研究与应用

导辊是高速线材轧机上的主要消耗工具 ,要求高耐磨性、抗粘钢性和热疲劳抗力。普通奥氏体耐热钢 ,马氏体耐磨钢或耐磨铸铁导辊满足不了上述要求 ,使用寿命短 ,降低了轧机作业率。硬质合金导辊具有良好的耐磨性和高温稳定性 ,使用效果好 ,但生产成本高。高碳高钼高速钢具有硬度高、红硬性和耐磨性好等特点 ,但铸造高速钢脆性大 ,采用RE -Mg -Ti复合变质处理 ,可以改变共晶碳化物的形态和分布 ,使铸造高速钢冲击韧性提高 86 .2 % ,热疲劳抗力和耐磨性也明显改善。变质处理高速钢导辊使用中不粘钢、不破碎、不剥落 ,使用寿命比高Ni-Cr合金铸钢导辊提高 3倍以上 ,接近硬质合金导辊     

Influence of matrix structure on the abrasion wear resistance and toughness of a hot isostatic pressed white iron matrix composite

The influence of the matrix structure on the mechanical properties of a hot isostatic pressed (hipped) white iron matrix composite containing 10 vol pct TiC is investigated. The matrix structure was systematically varied by heat treating at different austenitizing temperatures. Various subsequent treatments were also employed. It was found that an austenitizing treatment at higher temperatures increases the hardness, wear resistance, and impact toughness of the composite. Although after every different heat treatment procedure the matrix structure of the composite was predominantly martensitic, with very low contents of retained austenite, some other microstructural features affected the mechanical properties to a great extent. Abrasion resistance and hardness increased with the austenitizing temperature because of the higher carbon content in martensite in the structure of the composite. Optimum impact energy values were obtained with structures containing a low amount of M (M₇C₃+M₂₃C₆) carbides in combination with a decreased carbon content martensite. Structure austenitized at higher temperatures showed the best tempering response. A refrigerating treatment was proven beneficial after austenitizing the composite at the lower temperature. The greatest portion in the increased martensitic transformation in comparison to the unreinforced alloy, which was observed particularly after austenitizing the composite at higher temperatures,^[1] was confirmed to be mechanically induced. The tempering cycle might have caused some additional chemically induced transformation. The newly examined iron-based composite was found to have higher wear resistance than the most abrasion-resistant ferroalloy material (white cast iron).     

Effects of a Destabilization Heat Treatment on the Microstructure and Abrasive Wear Behavior of High-Chromium White Cast Iron Investigated Using Different Characterization Techniques

The hypoeutectic white cast iron was subjected to various destabilization heat treatment temperatures of 1173 K, 1273 K, and 1373 K (900 °C, 1000 °C, and 1100 °C) for 2 hours. The as-cast and destabilized specimens were characterized by optical metallography, classical direct comparison, and the Rietveld method. The volume fractions of carbides were measured by optical metallography. Moreover, the volume fractions of retained austenite and martensite were measured by the classical direct comparison method. Despite the limitations of optical metallography and the classical direct comparison method, the Rietveld method was successively and accurately applied to determine the volume fractions of all phases. In addition, the Rietveld analysis yielded certain results, such as the crystallographic properties of the phases that can be used to explain the relationship between the microstructural parameters and the wear behavior. Abrasive wear tests with different sliding speeds were carried out on the as-cast and destabilized alloys to identify the effect of microstructural parameters on the wear behavior. The results indicated that the morphologies of secondary carbides, the crystallographic properties of the phases, and the proper combination of the amount of martensite, retained austenite, and carbides were the principle parameters that affect the hardness and wear behavior of the alloy.     

深冷处理对NM500耐磨钢性能与磨损行为的影响

以一种自行设计的NM500级别耐磨钢为研究对象,利用冲击磨损试验,分析了深冷处理对其组织性能和磨损行为的影响。结果表明,NM500耐磨钢经深冷处理后,抗拉强度、硬度和冲击韧性均有提高,在淬火+深冷+回火处理后,最佳的综合力学性能可达抗拉强度1 910 MPa、硬度523HB、冲击韧性24.3 J/cm2,此时试验钢组织主要为马氏体,有Nb和Ti的碳化物析出。深冷处理通过残余奥氏体向马氏体转变,减少了不稳定相的含量,提升了试验钢的力学性能,从而使淬火+深冷+回火处理后的试验钢具有更高的耐磨性,此时的磨损机制以磨粒磨损为主,磨损形貌主要为犁沟、犁皱。而未经深冷处理的淬火+回火处理试验钢磨损机制以黏着磨损为主,磨损形貌主要为剥落坑和切削。     

磁场对离心铸造高碳高速钢组织和性能的影响

 用自制的电磁离心铸造机,在离心机转速为960r/min,磁场强度分别为005、010、015、020T的条件下,制备了高碳高速钢,试验研究了不同磁场强度下的高碳高速钢的铸态组织和热处理后的组织与性能。结果表明：随着磁场强度的增加,高碳高速钢的铸态组织中角状、点状碳化物的分布逐渐趋于均匀、弥散,共晶碳化物呈现出先减少、变短,后增加、变长的趋势;热处理后组织中的共晶碳化物变细、变短,且在磁场强度为015T的试样中硬度、冲击韧度和耐磨性能达到最佳。     

Influence of Tempering Time on the Microstructure and Mechanical Properties of AISI M42 High-Speed Steel

AISI M42 high-speed steel is prone to fracture as a result of its brittle martensitic microstructure together with abundant carbides located at the grain boundaries. In this study, a series of property tests including hardness, impact toughness, and wear loss were performed to study the effect of tempering conditions on the mechanical properties of AISI M42 high-speed steel over holding time ranging from 1 to 20 hours. The effects of the tempering time on the characteristics and growth of carbides were also investigated. The results indicated that carbides in the experimental steels were obviously coarsened when the tempering time exceeded 4 hours. The dimension of the carbides increased, while the volume fraction decreased with the increasing tempering time, and the grain sizes were significantly augmented due to the reducing of small carbides. Moreover, the dislocation density decreased with the increasing tempering time, which led to the reducing of the yield stress of high-speed steel. An appropriate holding time (4 hours) resulted in fine-scale secondary carbides and a smaller grain size, which efficiently improved the impact toughness and wear resistance simultaneously. Nevertheless, a prolonged tempering time (>?4 hours) promoted the coarsening and coalescence of carbides, which were detrimental to the impact toughness and wear resistance. Consequently, the formation of fine-scale secondary carbides is the major influential factor to improve both the wear resistance and impact toughness.     

钼对等离子堆焊钴基合金组织结构及性能的影响

采用光学显微镜，扫描电镜（SEM），X射线衍射（XRD），透射电镜（TEM）和磨粒磨损试验，研究了8％Mo对等离子堆焊钴基合金组织结构和性能的影响。结果表明，堆焊合金层主要是由面心立方的γ（Co）和六方结构的M7C3构成，并且在钴基固溶体中存在着许多堆垛层错。8％Mo的加入，没有改变合金层的相结构，但其亚结构却发生了变化，堆垛层错消失，在钴基固溶体中出现了大量的位错。8％Mo的加入，不但可以细化钴基固溶体和共晶体组织，还可以提高合金层中富Cr碳化物相的相对含量，有助于提高合金层的硬度和耐磨性能。     

B含量对PTA铁基耐磨熔覆层组织与性能的影响研究

采用等离子熔覆（PTA）在Q235上制备出含有细小碳化铌的Fe-Cr-B-C-Nb熔覆层,设计了B含量分别为0,2.2％,3.2％,4.0％的四组合金,通过SEM,XRD,MLS-225型湿式橡胶轮磨粒磨损试验机,自制落锤冲击试验机研究了B含量对Fe-Cr-B-C-Nb熔覆层组织与性能的影响.结果表明B含量对熔覆层组织与性能有显著的影响,随B含量的增加,合金硬度不断增加,耐磨性逐渐增加,合金的耐冲击性逐渐变差,当B含量为2.2％时,合金具有良好的综合性能.     

Microstructure Aspects of a Newly Developed, Low Cost, Corrosion-Resistant White Cast Iron

The purpose of this work is to study the influence of heat treatment on the corrosion resistance of a newly developed white cast iron, basically suitable for corrosion- and wear-resistant applications, and to attain a microstructure that is most suitable from the corrosion resistance point of view. The composition was selected with an aim to have austenitic matrix both in as-cast and heat-treated conditions. The difference in electrochemical potential between austenite and carbide is less in comparison to that between austenite and graphite. Additionally, graphitic corrosion which is frequently encountered in gray cast irons is absent in white cast irons. These basic facts encouraged us to undertake this work. Optical metallography, hardness testing, X-ray diffractometry, and SEM–EDX techniques were employed to identify the phases present in the as-cast and heat-treated specimens of the investigated alloy and to correlate microstructure with corrosion resistance and hardness. Corrosion testing was carried out in 5 pct NaCl solution (approximate chloride content of sea water) using the weight loss method. In the investigated alloy, austenite was retained the in as-cast and heat-treated conditions. The same was confirmed by X-ray and EDX analysis. The stability and volume fraction of austenite increased with an increase of heat-treated temperature/time with a simultaneous decrease in the volume fraction of massive carbides. The decrease in volume fraction of massive carbides resulted in the availability of alloying elements. These alloying elements, on increasing the heat treatment temperature or increasing the soaking period at certain temperatures, get dissolved in austenite. As a consequence, austenite gets enriched as well as becomes more stable. On cooling from lower soaking period/temperature, enriched austenite decomposes to lesser enriched austenite and to a dispersed phase due to decreasing solid solubility of alloying elements with decreasing temperature. The dispersed second phase precipitated from the austenite adversely influenced corrosion resistance due to unfavorable morphology and enhanced galvanic action. Corrosion rate and hardness were found to decrease with an increase in heat treatment temperatures/soaking periods. It was essentially due to the increase in the volume fraction and stability of the austenitic matrix and favorable morphology of the second phase (carbides). The corrosion resistance of the investigated alloy, heat treated at 1223 K (950 °C) for 8 hours, was comparable to that of Ni-Resist iron. Thus, a microstructure comprising austenite and nearly spherical and finer carbides is the most appropriate from a corrosion point of view. Fortunately, the literature reveals that the same microstructure is also well suited from a wear point of view. It confirms that this investigated alloy will be suitable for corrosive-wear applications.     

热处理对钢结硬质合金TLMW50中复式碳化物形态与分布的影响

利用SEM对烧结态和热处理态钢结硬质合金TWLM50微观组织中复式碳化物形态与分布进行研究。结果表明：烧结态钢结硬质合金TLMW50微观组织中主要复式碳化物Fe3W3C、Fe2W2C相形状基本呈现长条状,宽约10—20μm之间,颗粒长度可达10～60μm之间,且复式碳化物的晶粒上还有细小的三角状二次碳化物析出。经过1050℃淬火,250℃回火复式碳化物颗粒的棱角有所钝化,条形颗粒明显减少。二次碳化物析出数量明显减少,大部分二次碳化物溶于或与初生复式碳化物发生反应,形成复式碳化物,且随机分布在初生复式碳化物上。热处理导致钢结硬质合金TWLM50硬度提高到65HRC,耐磨性显著提高。     

以紫钨为原料制备超细WC-Co硬质合金

超细硬质合金具有高硬度、高耐磨性等优异性能,保证超细硬质合金的晶粒度小而且均匀的一个关键因素就是以粒度细小、分布均匀的超细WC粉末为原料。超细WC粉末的制备过程中,常用的氧化物原料为蓝钨,以紫钨为原料的制备工艺报道较少。采用相同的工艺,分别以蓝钨和紫钨为原料制备出超细WC粉末,并采用相同工艺制备出超细硬质合金,对两种产品性能进行对比,发现以紫钨为原料制备出的超细硬质合金晶粒度小,强度和硬度高,具有较好综合性能。     

Effects of heat treatment on wear resistance and fracture toughness of duo-cast materials composed of high-chromium white cast iron and low-chromium steel

The objective of this study is to investigate effects of heat treatment on wear resistance and fracture toughness in duo-cast materials composed of a high-chromium white cast iron and a low-chromium steel as a wear-resistant part and a ductile part, respectively. Different size, volume fraction, and distribution of M₇C₃ carbides were employed in the wear-resistant part by changing the amount of chromium, and the volume fraction of martensite in the austenitic matrix was varied by the heat treatment. In the alloys containing a small amount of chromium, an interdendritic structure of eutectic M₇C₃ carbides was formed, and led to the improvement of wear resistance and fracture toughness. After the heat treatment, the selective wear of the matrix and the cracking or spalled-off carbides were considerably reduced since the hardness difference between carbides and matrix decreased by the increase in the matrix hardness, thereby leading to the improvement of the wear resistance. However, the fracture toughness of the heat-treated alloys was lower than that of the as-cast alloys because the matrix containing a considerable amount of martensite did not effectively prevent the crack propagation.     

镍磷合金碳化硅复合镀层的制备与磨损性能研究

采取化学沉积方法，获得镍磷合金碳化硅复合材料镀层，研究了复合镀层的构成与磨损性能。研究结果表明，镍磷合金中加入碳化硅，不会影响其组织结构，但会显著地提高硬度和耐磨性；复合镀层经过热处理，组织结构发生变化；６７３Ｋ／１ｈ处理后，硬度与耐磨性最高，较镍磷合金镀层具有更高的硬化性能。     

The postweld heat-treatment response of simulated coarse-grained heat-affected zones in a new ferritic steel

The tempering behavior of simulated coarse-grained (CG) heat-affected zones (HAZs) in two ferritic alloy steels, 2.25Cr-1Mo and HCM2S, was investigated. The hardness of HCM2S was found to be stable at longer times and higher temperatures than the 2.25Cr-1Mo steel, even though the “as-welded” hardnesses were approximately equal. Both materials reached a peak secondary hardness after tempering for 5 hours at 575 °C. The increase in hardness of the 2.25Cr-1Mo steel was due to precipitation of Fe-rich M₃C carbides within the prior-austenite grains, whereas the secondary hardening in HCM2S was due to a fine dispersion of intragranular, W-rich carbides. The HCM2S steel retained its hardness at longer times and higher temperatures than 2.25Cr-1Mo steel, because of the precipitation of intragranular, W-rich carbides and V-rich MC carbides that stabilized the lath structure. This study shows that HCM2S should not be heat treated in the same way as 2.25Cr-1Mo steel and also provides a basis for defining the postweld heat treatment (PWHT) of HCM2S.     

The influence of heat treatment on the high-stress abrasion resistance and fracture toughness of alloy white cast irons

The influence of a range of austenitizing and subcritical (tempering) heat treatments on the high-stress abrasion resistance and fracture toughness of four commercially significant grades of alloy white cast iron was investigated. Complementing an earlier study^[1] on the influence of a more limited range of heat treatments on the gouging abrasion performance of the same alloys, the results showed that the effect of austenitizing temperature on high-stress abrasion pin test weight loss differed for each alloy. With increasing austenitizing temperature, these results ranged from a substantial improvement in wear performance and retention of hardness through to vir-tually no change in wear performance and substantial falls in hardness. Fracture toughness, however, increased markedly in all alloys with increasing austenitizing temperature. Tempering treatments in the range 400 °C to 600 °C, following hardening at the austenitizing temperature used commonly in industrial practice for each alloy, produced significant changes in both hard-ness and wear performance, but negligible changes in fracture toughness. Most importantly, the data showed that selection of the correct temperature for subcritical heat treatment to reduce the retained austenite content for applications involving repeated impact loading is critical if abrasion resistance is not to suffer.     

Composition, microstructure, hardness, and wear properties of high-speed steel rolls

The effects of alloying elements on the microstructural factors, hardness, and wear properties of four high-speed steel (HSS) rolls fabricated by centrifugal casting were investigated. A hot-rolling simulation test was carried out using a high-temperature wear tester capable of controlling speed, load, and temperature. The test results revealed that the HSS roll containing a larger amount of vanadium showed the best wear resistance because it contained a number of hard MC-type carbides. However, it showed a very rough roll surface because of cracking along cell boundaries, the preferential removal of the matrix, and the sticking of the rolled material onto the roll surface during the wear process, thereby leading to an increase in the friction coefficient and rolling force. In order to improve wear resistance with consideration to surface roughness, it is suggested that a reduction in the vanadium content, an increase in solid-solution hardening by adding alloying elements, an increase in secondary hardening by precipitation of fine carbides in the matrix, and formation of refined prior austenite grains by preaustenitization treatment be employed to strengthen the matrix, which can hold hard carbides in it.