Optimising heat treatment requirements for improved toughness of V containing 3%NiCrMo steel

Abstract

One major field of application of medium carbon low alloy steels is military hardware, especially the production of mortars. In manufacturing, it is usually necessary to adhere to specific standards; however, since economic and technological requirements depend on using scrap extensively, it can be difficult to keep minor additions within the specification. Heat treatment will therefore play an important role in obtaining the required mechanical properties. The combined effect of vanadium level and heat treatment cycles on strength and toughness of type 4337V (3%NiCrMo) 'gun steel' has been investigated. Vanadium is added mainly as a grain refiner, but it is also a strong carbide former, and therefore likely to reduce toughness. Conventional heat treatment (normalising at 900°C followed by quenching from 850°C), a modified heat treatment (double normalising at 900 and 800°C, successively, before the conventional treatment), and thermomechanical treatment (quenching in oil directly from the forging temperature at about 800–850°C), were applied. All specimens were tempered at 600°C for 3 h. For all heat treatments, it was concluded that for maximum toughness, a marginal content of 0·08–0·14%V should not be exceeded. Using heat treatment cycles other than the conventional one made it possible to accommodate V at the upper end of the range. Thermomechanical processing increased strength but only increased toughness slightly, whereas double normalising improved both strength and toughness compared with conventional heat treatment.     

Effect of industrial surface finishes on heat treatment and surface engineering of steel

Abstract

The surface state of industrial parts is complex and effective heat treatment or surface engineering of such parts requires a precise knowledge of how the steel was produced and manufactured. During manufacturing a mechanical part will be subject to the actions of various tools, mechanical constraints and diverse: solids, liquids or gases. Current highly automated processes have introduced new materials and chemicals which change the characteristics of the surface and may generate defects or even scrap. A series of case studies is presented illustrating the problems arising from industrial processes and their solutions.     

Computation of isothermal transformation diagrams of 42CrMo4 steel from dilatometer measurements with continuous cooling

Abstract

To generally predict the mechanical properties of steels following heat treatment, the isothermal time–temperature–transformation (TTT) diagrams must be known. The isothermal kinetics of the phase transformation is influenced by the austenitisation conditions and the deformation processes. Owing to the requirements of the process chain 'integrated heat treatment following hot-forging', the steels are austenitised at a comparatively high temperature and deformed before quenching. The TTT diagrams found in the literature only treat limited austenitisation temperatures and do not generally consider different deformation levels. However, the measurements of the corresponding TTT diagrams are both costly and time consuming. In addition to this, the isothermal transformations of low alloyed steels, which transform very quickly, cannot be measured using those dilatometers which are readily available.¹ In this paper, the TTT diagrams of the 42CrMo4 steel austenitised at 1200^°C and deformed at different levels are computed from the dilatometer measurements with continuous cooling using the methods developed by Buza et al.² and Rios.³     

Pitting corrosion of thixoformed,rheocast and gravity cast A356-T6 alloy in chloride media

Abstract

In the research work presented here, the pitting behaviour of thixoformed A356-T6 alloy, with different reheating temperatures, was evaluated and compared with the pitting behaviour of rheocast and gravity cast A356-T6 alloys with the same composition. To study the pitting behaviour, linear sweep voltammetric tests were performed on thixoformed, rheocast and gravity cast A356-T6 alloys in a 3·5%NaCl solution. A simulation method was also used to identify local galvanic corrosion current density between local galvanic couples. Results obtained show that the resistance to pitting corrosion of thixoformed samples formed at 590°C was higher than that of the samples formed at 600°C as well as rheocast and gravity cast samples. The improvement in the pitting corrosion resistance due to the thixoforming process is attributed to morphological aspects of the silicon phase as well as the area effect as related to galvanic corrosion between the silicon particles and the eutectic aluminium phase.     

Effect of residual austenite on properties of tool steel following shortened treatments in lower bainitic phase

Abstract

Recent investigations show the possibility of shortened low-cost treatment of chromium alloyed tool steels in the lower bainitic state. But with these treatments just above the martensite start temperature remains still an amount of residual austenite. For better understanding of the reactions due to the transformation of austenite into lower bainite metallographic, studies completed by dilatometric tests have been carried out. Structural characteristics due to applied heat treatment processes are discussed and special changes of specific properties are discussed by example of the steel 100Cr6 (SAE 52100).     

Influences of post-weld heat treatment on fatigue crack growth behaviour of strength mismatched HSLA steel welds

Abstract

Welding of high strength low alloy steels (HSLA) involves usage of low, even and high strength filler materials (electrodes) compared with the parent material depending on the application of the welded structures and the availability of the filler material. In the present investigation, the influences of post-weld heat treatment (PWHT) on fatigue crack growth behaviour of under matched (UM), equal matched (EM) and over matched (OM) weld metals has been studied. The base material used in this investigation is HSLA-80 steel of weldable grade. The Shielded Metal Arc Welding (SMAW) process has been used to fabricate the single 'V' butt joints. Centre Cracked Tension (CCT) specimens have been used to evaluate the fatigue crack growth behaviour of the welded joints. Fatigue crack growth experiments have been conducted using servo hydraulic controlled fatigue testing machine at constant amplitude loading (R = 0). From this investigation, it has been found that the fatigue performance of over matched joints is superior compared to under matched and equal matched joints. Moreover, PWHT reduced the magnitude of the tensile residual stress field in the weld region and subsequently enhanced the fatigue performance of the joints irrespective of weld metal strength mismatch.     

喂线增硫法生产42CrMoS4V钢

生产42CrMoS4V钢时经常出现硫的回收率和硫成分不稳定问题，采用喂线增硫法替代包中加FeS后硫的收得率由35％提高到75％以上，硫成分稳定，钢的纯净度高，力学性能、超声波探伤全部满足顾客要求。     

Hardness and microstructural developments of spray formed aluminium alloys with high Mg2Si content during hot extrusion and heat treatment

Abstract

Spray forming offers the possibility of producing alloys with very fine, homogeneous microstructures. Even materials with high contents of intermetallic precipitates, which cannot be produced by casting because of the high solidification rates required, can be distributed homogeneously. Alloying aluminium with high contents of Mg and Si (>20 wt-%Mg₂Si) gives an increase in stiffness plus a significant reduction in density, but a very fine distribution of the Mg₂Si particles in the aluminium matrix is required. Therefore, such alloys are commonly produced by spray forming. Post-spraying processes such as forming and heat treatment are generally carried out to optimise properties. To examine the microstructure and hardness as a result of subsequent processing, aluminium alloys with high Mg₂Si content (22–30 wt-%) have been produced under a variety of spray forming conditions. The duration and temperature of heating before extrusion were varied. In addition, some specimens were preheated without extrusion. The influence of subsequent heat treatment was investigated by varying the age hardening parameters. Hardness measurements were conducted and the distribution and size of the precipitates were evaluated by light microscopy. Image analysis was used to study the coarsening behaviour of primary Mg₂Si. The results indicate that the subsequent processing conditions have a strong influence on the microstructure and hardness of the material. Further, a significant dependence of coarsening rate during subsequent processing on the initial state of the material after spray forming was observed. Knowledge of correlations between process parameters and microstructural development offers the possibility of optimising the hot extrusion and heat treatment parameters for high Mg₂Si containing aluminium alloys.     

Compression behaviour of semisolid YL112 die casting aluminium alloy following isothermal heat treatment

Abstract

The semisolid compression deformation behaviour of YL112 die casting aluminium alloy with the non-dendritic and dendritic structures has been compared in tests using a Gleeble-1500 thermomechanical simulator. The non-dendritic structure was obtained by isothermal treatment at 570°C for 120 min. In tests up to compressive strains of 0·8, the semisolid compression stress of the alloy with non-dendritic structure initially increases rapidly with increasing strain, then decreases, before reaching a plateau value. Under different deformation temperatures and deformation rates, the maximum compressive stresses are obtained in all cases at strain values of ～0·07. The semisolid deformation stress decreases with increasing deformation temperature and increases with increasing deformation rate. The compression behaviour of the two types of alloy differs. The semisolid compression stress of the alloy with dendritic structure is higher than that of the alloy with non-dendritic structure; and for strains >0·07, the semisolid compression stress increases and decreases with increasing strain for alloys with dendritic and non-dendritic structures respectively.     

Deformation and fracture behaviour of P91 steel weldments at high temperatures

Abstract

Microtensile specimen tests are conducted across similar welds of a P91 steel at 873 K. Specimens of different surface conditions are tested at two different loading rates, 0·2 and 0·5 mm min^?1, in order to study the effects of surface finish and loading rate on mechanical properties of P91 steel. Deformation behaviour is studied with an SEM on specimen side surfaces. Correlation between microstructural behaviour and mechanical properties is studied both in microtensile and standard tensile tests.     

Microstructure and strength of a squeeze cast aluminium piston alloy composite reinforced with alumina short fibre using Al2O3 binder

Abstract

Alumina short fibre preforms were fabricated using an Al₂O₃ binder and infiltrated with aluminium piston alloy melt by squeeze casting. Al₂O₃ binder is thermodynamically more stable than the conventional SiO₂ binder and reduces the fibre/matrix interfacial reaction. The effects of fibre volume fraction, temperature and heat treatment on the yield strength and tensile strength of the composite were investigated. The Al₂O₃ binder provided a satisfactory interfacial bond between the fibre and the matrix without any interfacial reaction or fibre damage. Aging behaviour was not changed by reinforcement. At every temperature, the composites showed the highest strength with a fibre volume fraction of 18%. The strength of the composite was improved by T6 heat treatment. Examination of the fracture surfaces and calculation of the tensile strength using the rule of mixtures indicated that the 18% fibre reinforced composite had a strong interfacial bond even at high temperatures.     

Development of steel grades for heat treated power train components: a review

Abstract

The development of new carburising steel grades by Daido Steel for heat treated transmission parts is reviewed. These developments are driven by the need for cost reduction, weight saving, fuel economy and higher mechanical performance in new car models under development in response to environmental and economic demands. The next generation of gears will be peened, then vacuum carburised to improve fatigue and impact strength in lighter components designed with smaller tooth cross-sections, and new steels giving improved performance have been developed. Case studies of new steels for pulleys (allowing shorter carburising times) and constant velocity joints are also described.     

Effect of post-weld heat treatment on joint properties of friction welded joint between brass and low carbon steel

Abstract

This paper describes the effect of post-weld heat treatment (PWHT) on joint properties of copper–zinc alloy (brass) and low carbon steel friction welded joints. The as-welded joint obtained 100% joint efficiency and the brass base metal fracture without cracking at the weld interface, and had no intermetallic compound layer. The joint efficiency with PWHT decreased with increasing heating temperature and its holding time, and its scatter increased with those increasing parameters. When the joint was heat treated at 823 K for 360 ks, it did not achieve 100% joint efficiency and fractured between the weld interface and the brass base metal although it had no intermetallic compound. The cracking at the peripheral portion of the weld interface was generated through PWHT. The cracking was due to the dezincification and the embrittlement of the brass side during PWHT.     

Effect of post-weld heat treatments on microstructure and mechanical properties of electron beam welded flow formed maraging steel weldment

Abstract

Seamless tubing of C-250 maraging steel manufactured by the flow forming technique was joined by the electron beam welding process. Various post-welding heat treatments were conducted to improve the overall mechanical properties of the welded tubing. For the 480°C/6 h/air cooling post-weld aging treated maraging steel, a significant increment of 11% reversion austenite was present in the weld metal. Only the tensile strength of this aging treated metal met the required specification while its percentage elongation reached only 50% of the specification, attaining only 35% of the strength of the parent metal. For the post-welded solution + aging treated maraging steel, only the yield strength met the specification. Moreover, a significant amount of reversion austenite pools was also present at the grain boundaries of the material located at the weld metal. Although the homogenisation treatment could improve the hardness of the weld metal, it failed to have the tensile strength of the steel met the specification.     

Optimal heat treatment conditions and properties of bimetal (high Cr cast iron/alloyed steel) hammers

Abstract

This study intended to establish the optimal heat treatment conditions for the desired hardness and wear resistance property for the bimetal hammers developed by the authors. The objective of this study is to attain bimetal hammers that have a tough Cr–Ni alloyed steel shank and a high wear resistant high Cr cast iron head to replace conventional single alloy (high Mn steel) hammers. The results show that the optimal heat treatment condition obtained for the bimetal hammers is: destabilisation: 1000–1050°C for 2 h, quench: FAC and tempering: 480–500°C for 6 h. By employing this optimal heat treatment condition, the highest hardness value can be attained along with the best wear resistance property for the head portion and acceptable toughness for the shank portion. The microstructure of the head portion that corresponds to the optimal properties consists of eutectic M₇C₃ carbides, secondary M₇C₃ carbides, tempered martensite and almost nil retained austenite.     

Trends in automotive materials: state of steel and processing technologies and future tasks

Abstract

The average fuel consumption of Japanese vehicles is improving constantly and the material share of non-ferrous and non-metal materials is constantly evolving. There is too little general understanding of the role advanced steel products are playing in power train systems to improve fuel mileage. Future developments in automotive materials, and steel in particular, are considered.     

Effect of minor change in composition on toughness of weldmetal for repair of turbine blades made of martensitic stainless steel

Abstract

Repair welding procedure for cracked turbine blades, made of 13Cr–2˙6Ni–1˙1Mo martensitic stainless steel, has been developed using gas tungsten arc welding process and a twin wire filler metal. The twin wire consists of a 1˙5 mm diameter ER 16-8-2 and a 2˙0 mm diameter ER 410 filler wires tack welded along the length of the two filler wires. A two stage post-weld heat treatment at 675°C for 2 h and 615°C for 4 h, such that the first heat treatments is above the Ac ₁ temperatures of the weld metal and the second is just below its Ac ₁ temperature; has been found to be suitable for obtaining good mechanical properties for the weldment. The weldment has a good combination of transverse weldment strength and weldmetal toughness, with its room temperature yield strength and Charpy V notch impact toughness being similar to that of the turbine blade material.     

Fracture resistance of simulated heat affected zone areas in HSLA structural steel

Abstract

The fracture toughness of some areas in the multi-pass heat affected zone (HAZ) of a high strength low alloy (HSLA) structural steel was analysed in a straightforward way using precracked, cylindrical specimens tested on a conventional tensile machine. The specimens were made from samples with a simulated HAZ microstructure; however, the size of the samples was restricted by the limitations of the Gleeble machine. The brittleness of the samples was an indication of the detrimental effect of welding on their toughness. The specimens were not large enough for a direct K_Ic measurement over a wide testing temperature range; it was necessary to modify the results. The low fracture toughness and the substantial shift of fracture transition temperatures suggest that welding of the investigated steel could be a delicate procedure.     

42CrMo4钢风电主轴的热处理工艺

某公司生产的42CrMo4钢风电空心主轴产品某一型号出现淬火开裂的比例较高,报废率近20％.用ARL8860直读光谱仪、MTS万能试验机、SANS冲击试验机、徕卡光学显微镜等对该产品进行一系列理化检验,并结合相关理论基础分析发现,将原淬火工艺优化为860℃加热后预冷至820℃浸水淬火,淬火水冷20 min,极大降低了产...     

Thermomechanical coupling simulation and experimental study in the isothermal ECAP processing of Ti-6Al-4V alloy

The thermomechanical coupling simulation of the isothermal equal channel angular pressing(ECAP) of Ti-6Al-4V alloy was conducted.The effect of processing parameters,ECAP pass number and the residual billet on the effective strain,stress and temperature distribution was investigated.Based on the coupling simulation results,it is found that the shear factor,ram speed,deformation temperature,channel intersection angle and residual billet significantly affect the ECAP deformation behaviors.Meanwhile,the experimental study of the isothermal ECAP process of Ti-6Al-4V alloy using route C,in which the repeated rotation angle around the longitudinal billet axis before reinsertion in the die was 180°,were conducted at a deformation temperature of 750°C,a ram speed of 0.3 mm·s-1,an outer arc of curvature of 60° and a channel intersection angle of 120°.Furthermore,a large amount of recrystallization occurs and some prior α phase grains grow in the post-ECAP process of Ti-6Al-4V alloy.The yield strength of post-ECAP Ti-6Al-4V alloy increases compared with that of as-received Ti-6Al-4V alloy.