铬对锰硅硼铸造耐磨钢组织和性能的影响

研究了铬对锰硅硼低合金耐磨钢组织及性能的影响,结果表明：加入铬合金化后,组织仍然以马氏体和贝氏体为主,存在少量残余奥氏体。随着铬含量增加,马氏体数量增加,贝氏体数量减少。加入铬对钢的硬度基本没有影响,但加入铬明显提高冲击韧性,比相同成分和热处理条件下不加铬钢的冲击韧性提高10J／cm^2左右;还对比了铬对常温及低温冲击韧性影响。     

耐磨材料中残余奥氏体在磨损中的结构变化及其影响

通过x衍射分析、薄膜透射电镜分析和亚表层硬度分析,研究了GCr15和高铬铸铁两类耐磨材料中残余奥氏体在磨料磨损中的结构变化及其影响。试验结果表明,磨损中相当数量的残余奥氏体发生马氏体转变,形成密排六方ε型马氏体,提高表面硬化程度,改善一定磨损条件下材料的耐磨性。     

Comparison of mechanical properties of martensite/ferrite and bainite/ferrite dual phase 4340 steels

Different microstructures were produced by heat treatment of 4340 steel. These microstructures are bainite, martensite, ferrite–martensite and ferrite–bainite. Mechanical tests were carried out at room temperature. The results showed that steel with bainite–ferrite microstructure has better ductility and charpy impact energy than steels with martensite–ferrite and full bainite microstructures. But yield and tensile strengths of this steel are less than the yield and tensile strengths of the other two steels. Hardness measurements showed that their hardness is the same. Fracture surface observations of tensile specimens showed increase in toughness of bainite–ferrite in comparison to martensite–ferrite and full bainite microstructures.     

Study on carbide-bearing and carbide-free bainitic steels and their wear resistance

Carbide-free and carbide-bearing bainitic steels have been obtained. The relationship between the bainitic microstructure and wear resistance has been studied. Results show that carbide-free upper and lower bainitic microstructures obtained in the steel with Si?+?Al mainly consist of bainitic ferrite and retained austenite. Carbide-bearing upper and lower bainitic microstructures obtained in the steel without Si?+?Al consist of bainitic ferrite, carbide and trace amounts of retained austenite. The carbide-free bainite exhibits higher strength and toughness than carbide-bearing bainite, especially the toughness. Under lower wear loading, carbide-bearing lower bainite (LB) exhibits higher wear resistance. Under higher wear loading, carbide-free LB exhibits higher wear resistance, which results from the improved surface hardness due to strain-induced martensitic transformation from the retained austenite.     

Austempering of spheroidal graphite cast iron

We study gray spherulitic cast iron, its microstructure, hardness ultimate strength in tension, elongation, and impact toughness as functions of the duration of isothermal austenitizing in the bainite region at 350 and 400°C after austenitizing at 900°C. As the temperature of quenching increases from 350 to 400°C, the microstructure of the analyzed cast iron changes from lower to higher bainite and the amount of retained austenite increases (its maximum is attained after 1 h). At the same time, the ultimate strength in tension and hardness decrease, whereas the elongation and fracture toughness increase.Published in Fizyko-Khimichna Mekhanika Materialiv, Vol. 40, No. 4, pp. 79–83, July–August, 2004.     

Wear perfornance of 0·6%Cr alloyed cast and heat treated steels with carbon contents of 0·7, 1·0, and 1·3%

Abstract

The effect of carbon content and heat treatment on the abrasive wear performance of three 0·6%Cr alloyed cast steels with carbon contents near the eutectoid composition (0·7, 1·0 and, 1·3%) were investigated using a pin on drum abrasion tester. Specimens were austenitised at 870,970, or 1070°C for 1 h and quenched. Additionally, a 1·3%C specimen was spheroidised, then austenitised at 870°C and quenched. The microstructure, which was dependent on heat treatment and carbon content, significantly influenced the wear rate. The wear rate is related non-linearly to hardness. The lowest wear rate was obtained for the 1·3%C alloy austenitised at 1070°C producing a quenched microstructure of 40% retained austenite and 60% martensite. This specimen also exhibited the lowest quenched hardness. However, for a practical industrial heat treatment, the 1·0 %C alloy austenitised at 970°C provides the best wear performance.

MST/3130     

Austempered ductile iron: an alternative material for earth moving components

Traditionally steels have enjoyed some kind of monopoly in earth movement applications like ripper tips and grader blades. Earth movement demands that the material possesses both wear resistance and toughness. Ironically, the limitation of steels is that it is difficult to get a good combination of these properties. Recent research efforts in earth movement have focused on austempered ductile iron (ADI) as an alternative material, which exhibits both these properties. ADI is obtained when ductile cast iron is accorded a special heat treatment known as austempering. Before the usage of ADI can flourish, there is a need to thoroughly understand its mechanical and tribological behaviour. This paper details the heat treatment of ductile iron to yield ADI and also examines its mechanical and abrasive wear properties. These properties are compared with those of a proprietary quenched and tempered (Q&T) steel used in applications requiring wear resistance. Typically, when a load of 0.25 N mm⁻² is used, the relative abrasion resistance (RAR) of ADI austempered at 375 °C with an initial hardness of 315 Hv is 2.01, while that of a Q&T steel, of hardness 635 Hv is 2.02. The good wear resistance exhibited by ADI despite the low initial hardness can be attributed to the surface transformation of retained austenite to martensite during abrasion. This phenomenon has been positively confirmed by XRD.     

Mn-Si-Cr系无碳化物贝氏体/马氏体复相高强钢的研究进展

无碳化物贝氏体/马氏体复相高强钢具有比同等强度马氏体钢更优异的韧性和塑性,被广泛应用到轨道交通、机械、建筑等领域。文章概述了低成本Mn-Si-Cr系无碳化物贝氏体/马氏体复相钢近年来在合金化设计、工艺设计、微观组织、强韧化机理、强塑化机理、延迟断裂及疲劳性能等方面取得的研究成果。特别介绍了近年来笔者在BQP工艺处理CFB/M复相钢方面的工作进展,经过BQP处理之后,CFB/M复相钢显示了更优异的强度、塑性、韧性和疲劳性能的匹配。最后简单介绍了Mn-Si-Cr系无碳化物贝氏体/马氏体复相钢在不同领域的应用情况,特别是其在重载高速铁路领域的应用现状和前景。     

Effects of heat input on microstructure and mechanical properties of Fe–2Cr–Mo–0.12C steel

ABSTRACT

Thermal simulated specimens with the heat inputs of 20, 50 and 80?kJ/cm were used to investigate the effects of heat input on the microstructure and mechanical properties of the Fe–2Cr–Mo–0.12C pressure-vessel steel. The results indicated that the microstructures in the coarse-grained heat affected zone of tested steels with various heat inputs were mainly consisted of lath martensite and bainite ferrite. As the heat input increased, the fraction of martensite decreased and the bainite ferrite fraction increased. The toughness (tested at ?40°C) and hardness for the heat input of 50?kJ/cm were 102?J and 346?HV, respectively, which was attributed to the high-volume fraction (60%) of the high-angle grain-boundary and the fine bainite lath.

This paper is part of a thematic issue on Nuclear Materials.     

Improving impact toughness of high-C–Cr bearing steel by Si–Mo alloying and low-temperature austempering

Nanostructured bainite and dispersed carbide particles were formed in Si–Mo-alloyed high-C–Cr bearing steels by low-temperature austempering after partial austenitizing in the intercritical gamma + carbide region. Comparing with conventional quenched and tempered high-C–Cr bearing steel, the impact toughness is remarkably enhanced; the hardness is still adequate for the bearings even though it is slightly decreased.     

Development of mechanical properties of structural high-carbon low-alloy steels through modified heat treatment

The modified heat treatment, which produces a mixed structure of martensite and lower bainite through short-term isothermal transformation at just above the martensitic transformation temperature,M _s temperature, followed by oil quenching (after conventional austenitization), has been applied to three high-carbon low-alloy steels with different levels of nickel and chromium contents at similar molybdenum levels, in which carbon was allowed to replace relatively expensive additions of nickel and chromium, for their ultra-high strength application. The significant conclusions are as follows: an ultra-high strength steel of 1900 M Pa yieldstress grade with a high toughness level can be obtained when about 60 vol % lower bainite is associated with 473 K tempered martensite of 0.60% C-1.80% Ni-0.80% Cr-0.25% Mo steel. If approximately 25 vol % lower bainite appears in 673 K tempered martensite of the steel, a 1700 M Pa yield-stress grade steel with high toughness and moderate ductility levels can be attained. However, alloying nickel is essential to some extent for development of the mechanical properties with the modified heat treatment suggested in the present work.     

Evaluation of effect of chromium on wear performance of high manganese steel

Abstract

The effects of elements such as Ni, Mo, Cr, Cu, and V on the wear behaviour of high manganese steels have been reported extensively. Most researchers agree on the influence of many of the elements but disagree on the effect of Cr. A study has been conducted to evaluate the effect of 1.7 and 2.3 wt-Cr on high manganese steel when subjected to various wear conditions: impact loading, abrasion, combined impact-abrasion, and combined abrasion-corrosion. The study has revealed that adding Cr to high manganese steel resulted in an increase in hardness and hardenability, and a decrease in toughness. The effect on wear resistance was found to depend on the wear conditions. Chromium alloyed high manganese steels showed superior wear resistance compared with plain Hadfield steels where corrosion, abrasion, and combined impact-abrasion conditions prevailed. Such conditions required a high surface hardness. Plain Hadfield steel showed superior wear resistance in conditions where pure impact wear is encountered. Such conditions required an increase in toughness rather than surface hardness.     

Microstructural evolution and tensile behaviour of medium carbon microalloyed steel processed through two thermomechanical routes

Abstract

A multiphase microstructure was obtained in a medium carbon microalloyed steel using two step cooling (TSC) from a lower than usual finish forging/rolling temperature (800–850°C). A low temperature anneal was then used to optimise the tensile properties. A multiphase microstructure (ferrite–bainite–martensite) resulted from forging as well as rolling. These were characterised using optical and scanning and transmission electron microscopy. X-ray diffraction, transmission electron microscopy and hardness measurements were used for phase identification. Tensile properties and work hardening curves were obtained for both the forged and the rolled multiphase variants. A Jaoul–Crussard (J–C) analysis was carried out on the tensile data to understand the basic mode of deformation behaviour. Rolling followed by the TSC process produced a uniform microstructure with a very fine grain boundary allotriomorphic ferrite, in contrast to the forged variety, which contained in addition coarse idiomorphic ferrite. The volume fraction of ferrite and its contiguity ratio in the rolled microstructure were greater than in the forged grade. The rolled microstructure exhibited a better combination of strength and toughness than that of the forged material. The rolled steel work hardened more than the forged variety owing to its fine, uniform (bainite–martensite and ferrite) microstructure. Retained austenite present in these steels underwent a strain induced transformation to martensite during tensile deformation. The J–C analysis of the work hardening rates revealed typical three stage behaviour in both varieties during tensile deformation.     

Development of carbon—Low alloy steel grades for low temperature applications

Low alloy steels are processed to fulfill the requirements of low temperature applications. Besides the chemical composition, the steel should receive a suitable heat treatment to ensure the targeted mechanical properties at low temperature. In other words, the steels are designed to delay the ductile to brittle transition temperature to resist dynamic loading at subzero temperatures. Steel alloys processed for liquefied gas pipeline fittings are examples for applications that need deep subzero impact transition temperature (ITT).The main purpose of the present work was to find a suitable heat treatment sequence for alloys LC2 and LC2-1. Further, it aimed to correlate the impact toughness with the microstructure and the fracture surface at different sub-zero temperatures.The steels under investigation are carbon-low alloy grades alloyed with Ni, Cr and Mo. LC2 steel alloy has been successfully processed and then modified to LC2-1 alloy by addition of Cr and Mo. Oil quenching from 900 °C followed by tempering at 595 °C was used for toughness improvements. Hardness, tensile and impact tests at room temperature have been carried out. Further impact tests at subzero temperatures were conducted to characterize alloys behavior. Metallographic as well as SEM fractographic coupled with XRD qualitative analysis are also carried out.Non-homogenous martensite-ferrite cast structure in LC2 was altered to homogeneous tempered martensite structure using quenching-tempering treatment, which is leading to shift the ITT down to −73 °C. Addition of Cr and Mo creates a very fine martensitic structure in LC2-1 alloy. Quenching-tempering of LC2-1 accelerates ITT to −30 °C. It is expected that the steel was subjected to temper embrittlement as a result of phosphorus segregation on the grain boundary due to Cr and Mo alloying, as it was concluded in reference no. [6].     

Effect of alloying on the wear resistance of cast steel

We study the influence of rare-earth metals on physicomechanical properties and wear resistance of cast tool steel and establish the optimal content of carbon (0.55–0.65%) which guarantees sufficiently high abrasive wear resistance of steel. Alloying with titanium, niobium, and rare-earth metals improves wear resistance of steels, especially with elevated contents of carbon.Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences. L'viv. Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 31, No. 3, pp. 103–106, May–June, 1995.     

Mechanical properties and hot-rolled microstructures of a low carbon bainitic steel with Cu-P alloying

A low carbon bainitic steel with Cu-P alloying was developed. The new steel aims to meet the demand of high strength, high toughness and resistance to chloride ion corrosion for the components used in the environment of sea water and oceanic atmosphere. Mechanical properties of the steel were tested and strengthening and toughening mechanisms were analyzed by comparing hot-rolled microstructures of the low carbon bainitic steels with and without Cu-P alloying. The results show that Cu-P alloying provided strong solution strengthening with weak effect on ductility. The toughness loss caused by Cu-P alloying could be balanced by increasing the amount of martensite/remained austenite (M/A island) at lower finishing temperature. The static recovery process during rolling interval was delayed by the interaction of phosphorous, copper atoms with dislocations, which was favorable to the formation of bainitic plates. Super-fine Nb(C, N) particles precipitated on dislocations had coherency with bainite ferrite at 830 °C finishing temperature. Raising finishing temperature to 880 °C, Nb(C, N) particles were prone to coarsening and losing coherency. It was also found that no accurate lattice match relationship among retained austenite, martensite and bainite in granular bainitic microstructure.     

The influence of copper addition on microstructure and mechanical properties of thermomechanically processed microalloyed steels

The present study concerns the influence of Cu addition on the microstructural evolution and mechanical properties of directly air-cooled microalloyed thin-gauge steel. For this purpose, 1.5 wt% Cu was added to a Ti–B microalloyed steel. It is known that Ni addition to Cu-containing steel is beneficial to eliminate hot shortness caused by Cu. Therefore, the effect of Ni addition (half that of Cu in wt%) on the microstructure formation and mechanical properties has also been studied. Microstructures and mechanical properties of the directly air-cooled steels have demonstrated that addition of 1.5 wt% Cu along with 0.8 wt% Ni in Ti–B microalloyed steel results in a dual phase-like microstructure, which yielded attractive tensile strength (746 MPa) and ductility (31%). However, Cu addition deteriorated the impact toughness of the directly air-cooled Ti–B microalloyed steels.     

Effect of quenching temperature on structure and abrasive wear resistance of boron‐containing medium carbon steel

Under the condition of oil cooling, the effect of quenching temperatures on the structure and abrasive wear resistance of medium carbon steel containing 2% B has been studied. The results show that the metallic matrix of Boron‐containing Medium Carbon Steel (BMCS) transforms into the martensite from the mixture of martensite, pearlite and ferrite while quenching at 900°C – 1050°C. The change of boron carbide existing in BMCS is few in different quenching temperature. After quenching the hardness of BMCS excels 56 HRC, and the change of quenching temperature has no obvious effect on the hardness of BMCS. The increase of quenching temperature leads to the increase of impact toughness, and impact toughness has no obvious change when quenching temperature exceeds 1000°C. Moreover, the increase of quenching temperature leads to a slight decrease of weight loss and the abrasive wear resistance of BMCS has a slight increase while increasing quenching temperature. Quenching at 1000°C–1050°C BMCS has excellent comprehensive property.     

Laser Surface Hardening of 9CrSi Steel

The effects of laser hardening parameters such as beam power,beam diameter and scanning rate on microstructure and mardness of 9CrSi steel were investigated.The microstructure of the surface layer of 9CiSi steel was changed from pearlite to martensite,retained austenite and carbide by laser hardening .The depth of the hardened layer increased with increasing laser energy density and the surface hardeness increased by 3-5times as high as the untreated steel.The laser hardened surface had good wear resistance due to martensite and carbide in the surface layer.The wear mode at low speed was abrasive,while the wear mode at high speed was adhesive.