Selection of Heat Treatment Process and Wear Mechanism of High Wear Resistant Cast Hot-Forging Die Steel

Dry sliding wear tests of a Cr-Mo-V cast hot-forging die steel was carried out within a load range of 50--300 N at 400℃ by a pin-on-disc high temperature wear machine. The effect of heat treatment process on wear resistance was systematically studied in order to select heat treatment processes of the steel with high wear resistance. The morphology, structure and composition were analyzed using scanning electron microscopy （SEM）, X-ray diffraction （XRD） and energy dispersive spectroscopy （EDS） ; wear mechanism was also discussed. Tribo-oxide layer was found to form on worn surfaces to reduce wear under low loads, but appear inside the matrix to increase wear under high loads. The tribo-oxides were mainly consisted of Fe3O4 and Fe2O3, FeO only appeared under a high load. Oxidative mild wear, transition of mild-severe wear in oxidative wear and extrusive wear took turns to operate with increasing the load. The wear resistance strongly depended on the selection of heat treatment processes or microstructures. It was found that bainite presented a better wear resistance than martensite plus bainite duplex structure, martensite structure was of the poorest wear resistance. The wear resistance increased with increasing austenizing temperature in the range of 920 to 1 120 ℃, then decreased at up to 1 220 ℃. As for tempering temperature and microstructure, the wear resistance increased in following order： 700℃ （tempered sorbite）, 200 ℃ （tempered martensite）, 440 to 650 ℃ （tempered troostite）. An appropriate combination of hardness, toughness, microstructural thermal stability was re- quired for a good wear resistance in high-temperature wear. The optimized heat treatment process was suggested for the cast hot-forging steel to be austenized at 1020 to 1 120 ℃, quenched in oil, then tempered at 440 to 650℃ for 2 h.

Reducing Efficiencies of the Commonly Used Heat Treatment Methods and Fermentation Processes on Aflatoxin M1 in Naturally Contaminated Fresh Cow Milk

The reducing efficiencies of the commonly used heat treatment methods and fermentation processes on aflatoxin M1 (AFM1) in Nigeria were investigated. Seventy samples of fresh cow milk from both conventional and traditional dairy cattle herds were collected and analyzed for the determination of AFM1 using Cobra-cell incorporated high performance liquid chromatography. Of these analyzed samples, 56 (80.0%) tested positive for AFM1 out of which 3 milk samples with high AFM1 concentrations were selectively pooled and subjected to varied conditions of heat treatments and fermentation processes using both indigenized and exotic strains of lactic acid bacteria (Lactobacillus bulgaricus + Streptococcus thermophilus and L. rhamnosus and L. plantarum) as starter cultures respectively. Both processes used either singly or combined, demonstrated high degrees of reducing effects on AFM1 levels. Sterilization of the milk at 121?C and 80?C under the same condition of time (15 - 20) min showed significant reduction of up to 58.8% (p 0.05) in the level of AFM1 when compared with the initial mean AFM1 concentration of the untreated fresh milk. The situation was however different around the boiling temperature of 100?C at which point the level of AFM1 reduction was found to be inconsistent. The indigenized combined strains showed some slight margins of AFM1 reduction in the proportions of (20.5, 30.8 and 43.9)% over and above that of the exotic strains (17.4, 30.0 and 41.1)% in 12 h, 48 h and 72 h of fermentation respectively. Generally, fermentation alone showed lower reduction of AFM1 in milk from 24.5% to 43.9% compared with the reducing activities of (35.4 to 58.8)% when heat-treated milk samples were subsequently subjected to varied fermentation conditions.

A NEW HEAT-TREATMENT PROCESS FOR 2014 ALUMINUM ALLOY AND ITS MECHANISM

The plan of heat-treatment process for 2014Al alloy is designed using orthogonal method, the heat-treatment experiments are made and the mechanical properties are tested according to the designed plan. The effect of solid solution temperature, ageing temperature, ageing time on microscopic mechanism of the mechanical properties of the 2014Al alloy is studied using microscope, transmission electron microscope. The best heat treatment process of the 2014Al alloy is developed. The experimental results indicate that the strength σb, yield stress σ0.2, percentage elongation δ of the alloy reach separately 490～500 MPa, 450～490 MPa, 10～12％ adopting the new heat treatment process. Compared with GB, the strength increases 20～30％, the percentage elongation increases 30～40％. The mechanism of the new heat-treatment process is also discussed.

The Integration of Vacuum Brazing into Heat Treatment - A Progressive Combined Process

The continuous constructive challenge to improve the functionality and efficiency of components always results in higher demands on production engineering, against the background of the generally increasing cost pressure. In many cases, you will just succeed in producing competitive and innovative products by combining and coupling of different procedures to an independent (hybrid) technology. The use of hybrid procedures for metal joining and heat treatment of metallic materials finds more and more industrial fields of application. Modern vacuum lines with integrated pressurized gas quenching are considered high-performance and flexible means of production for brazing and heat treatment tasks as well in the turbine industry as in the mould making and tool manufacturing industry. In doing so, the heat treatment is coupled with the brazing cycle in a combined process so that the brazing temperatures and soak times are adapted to the necessary temperatures and times for solution heat treatment and austeniting. This user-oriented article describes on the one hand examples of brazing of turbine components, but above all the practical experience from the plastics processing industry, where the requirement for a high-efficient cooling of injection moulding dies gains more and more importance. The combined procedure "Vacuum Brazing and Hardening" offers plenty of possibilities to produce mould inserts with an efficient tempering system in an economic way.

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.

Effects of Fillerwire Composition along with Different Pre- and Post-Heat Treatment on Mechanical Properties of AISI 4130 Welded by the GTAW Process

This research intends to find out the optimal mechanical properties of AISI 4130 steel welded by the GTAW process. Six test plates were joined by two types of filler wire with similar chemical composition to the base metal, and with lower carbon content and slightly higher alloy elements content compared to the first one. Test plates then exerted three different pre-heat and post-heat treatments on both groups. The three types of heat treatments were alternatively without pre-heat and post-heat, with pre-heat only, and finally with pre-heat and post-heat. Tensile, side bends and impact tests (for weld zone and HAZ) have been conducted. Results show that using low-carbon filler wire along with pre- and post-heat resulted in outstanding mechanical properties.

Recent process in special steel,heat treatment and surface modification of automotive components

Demand of improving the mechanical properties and productivity of automotive components while minimizing environmental impact makes the development of special steel combined with advance heat treatment and surface modification technologies become an important research area. Recently,to reduce CO_2 emissions by saving the manufacturing time,the following new special steel and advance heat treatment methods were developed: (1 ) An anti-coarsening extra-fine case hardening steel for automobile gear was developed,whose carburizing temperature can be improved for conventional 930 - 950℃to 1 050℃without coarsening,and the carburizing time can be reduced by maximum 75%. (2) Various microalloyed steels for fracture splitting connecting rod were developed.By using the above-mentioned steel combined with Thermo Mechanical Control Process(TMCP) method,the manufacturing time can be reduced by 30%-40%. (3) Vacuum carburizing and mild carburizing combined with induction quenching are being developed to replace the traditional gas carburizing,and the CO_2 emissions can be reduced by 20%-40%. (4) Intensive quenching is another new quenching technology which can be defined as cooling usually with pure water quenchant or low concentration water/salt solutions at a rate several times higher than the rate of ' normal' or conventional quenching,and the conventional effective case hardening depth can be reduce greatly and carburizing time can reduced. In addition,the high pressure gas quenching for reducing the quenching distortion and dual shot-peening for improving fatigue strength of gear will also be discussed. In a word,the present paper will focus on how to use the interaction among the development of special steel, advance heat treatment and surface modification to improve the strength of automotive components while reducing the manufacturing cost and impact to environment.

State of the Art Treatment of Non-Ferrous Castings 3-in-l Heat Treatment Systems Combine Foundry Processes

The interior of a high-pressure die-casting is of an unsatisfactory quality. Engine blocks made with this die casting process show lower specific engine performance. Pressure die-casting can hardly be heat treated for obvious reasons. PSM (Precision Sand Molds) process uses sand and organic binder to generate a mold and even allows the manufacturing of complex diesel engine blocks in aluminum alloys. Combined technologies are available for semi-permanent mold castings with cores and castings made in Precision Sand Molds with organic binders. Castings are placed into the special heat treatment furnace immediately after pouring without the operations in stand alone machinery. This patented Sand Lion 3- in-1 technology processes hot castings and carries out three (3) foundry processes simultaneously in one (1) automated machine: 1) De-coring and sand removal; 2) Thermal sand reclamation; 3) Solution heat treatment of castings. The combination of several main casting processes is reflected in significant reductions of energy consumption, of production costs, and improving the quality of the castings. Audits in foundries using the 3-in-l process showed an average reduction in production costs of more than 30%.

Air cushion furnace technology for heat treatment of high quality aluminum alloy auto body sheet

The process characteristics of heat treatment of aluminum alloy auto body sheet and the working principle of air cushion furnace were introduced.The process position and irreplaceable role of air cushion furnace in the aluminum alloy auto body sheet production was pointed out after the difficulty and key points in the whole production process of auto body sheet were studied.Then the development process of air cushion furnace line of aluminum alloy sheet was reviewed,summarized and divided to two stages.Based on the research of air cushion furnace,the key technology of it was analyzed,then the key points on process,equipment and control models of air cushion furnace for aluminum alloy auto body sheet in future were put forward.With the rapid development of automotive industry,there will be certainly a new upsurge of research and application of air cushion furnace for heat treatment of aluminum alloy auto body sheet.

Effect of isothermal heat treatment on semi-solid microstructure of AZ91D magnesium alloy containing rare earth Gd

The AZ91 D magnesium alloy containing rare earth Gd was prepared in this study, and the effect of semi-solid isothermal heat treatment on the microstructure of the alloy was investigated to obtain an optimum semi-solid structure. Results show that Gd can refine the microstructure of AZ91 D magnesium alloy, and the optimum semi-solid AZ91 D microstructure can be achieved by adding 1.5wt.% Gd. After treated at 585 °C for 30 min, the well distributed rose-shaped and near-spherical semi-solid microstructures of AZ91D+1.5wt.%Gd alloy can be obtained. The liquid phase of the semi-solid alloy consists of three components, namely, the molten pool, the "entrapped liquid" pool and the liner liquid film which separates two neighbor particles. The solid phase is composed of two phases, the primary α-Mg particles and the α-Mg phase formed in the second stage of solidification. With the increase of holding time, melting which causes the decrease of the primary α-Mg particle size is the dominant mechanism in the initial stage while coalescence and Ostwald ripening tend to be the principles later.

Microstructure evolution and mechanical properties of rheo-squeeze casting AZ91-Ca alloy during heat treatment

The rheo-squeeze casting(RSC)process is a newly-developed casting process for high-performance components.In order to further improve the mechanical properties of magnesium alloys,AZ91-2wt.%Ca(AZX912)alloy was prepared by the RSC process and then subjected to heat treatment.The microstructure evolution and mechanical properties of AZX912 alloy during heat treatment were investigated.It was found that during solid solution treatment at 410°C,β-Mg_(17)Al_(12) phase with low melting point dissolves intoα-Mg matrix,while the connected network-like Al_2Ca phase with high melting point tends to separate gradually,and the tips of Al_2Ca phase is partially spheroidized.With the increase of solid solution time,the yield strength(YS)of AZX912 alloy decreases gradually while the ultimate tensile strength(UTS)and elongation to failure(E_f)increase continuously.Isothermal ageing at 225°C promotes the precipitation ofβ-Mg_(17)Al_(12) phase in the matrix of AZX912 alloy.The hardness reaches the peak after ageing for 96 h and the increase in hardness is about 24.8%.The precipitation ofβ-Mg_(17)Al_(12) phase during ageing treatment is beneficial to YS but harmful to E_f.The mechanism of microstructure evolution during heat treatment and its effect on mechanical properties are discussed.

Effect of rolling and heat treatment on microstructure and properties of Ti-26 sheet

The effect of heat treatment and rolling process on the properties and microstructures of Ti-26(Ti-15V-3Al-3Cr-3Sn-Forming) sheet was studied. The results show that the best rolling temperature for Ti-26 alloy is in the temperature range from 900 ℃ to 950℃. Under this condition,the resistance of deformation and yield ratio are low and the alloy has better hot work ability. The alloy will achieve better mechanical properties and completely recrystallized β microstructure when the deformation ratio is not less than 60% and the solution temperature is 30 ℃ above the phase transformation temperature. The best heat treatment conditions are recommended as:790℃,30 min,AC or WQ followed by 510 ℃,10 h,AC. Under this heat treatment condition the strength of the Ti-26 alloy is 1 230 MPa and the elongation is 15%.

热处理工艺对大规格TC17钛合金棒材组织与力学性能的影响

研究了固溶温度、冷却方式、保温时间及取样方向对两相区锻造的大规格TC17钛合金棒材显微组织和力学性能的影响,并根据实验结果选择最佳热处理制度。结果表明:TC17钛合金棒材的最佳热处理工艺为800℃/2h/WQ+630℃/8h/AC;固溶温度在两相区时,随着固溶温度的升高,合金强度升高,塑性降低;固溶空冷+时效的合金较相同温度固溶水冷+时效的合金强度高、塑性低;在相同温度固溶水冷条件下,缩短固溶保温时间,可改善合金的塑性;锻造后的TC17钛合金大规格棒材存在各向异性。

2种热处理工艺对N07718镍基合金力学及耐蚀性能的影响

为探明不同热处理工艺对镍基合金力学及耐蚀性能的影响,利用万能拉伸试验机、摆锤冲击试验机对2种不同固溶时效保温时间的N07718材料进行了拉伸、低温冲击等力学性能对比测试,同时利用高温高压H_(2)S/CO_(2)腐蚀电化学试验装置对2种热处理工艺的材料进行高温高压电化学测试。结果表明,固溶保温时间对N07718材料的韧塑性影响较大,对耐蚀性影响较小。利用热场发射扫描电镜(SEM)、X射线能谱仪(EDS)等对比分析了2种N07718材料韧塑性差异的原因。研究发现固溶时效保温时间的延长使N07718合金材料晶界位置析出大量棒状δ相,且部分连接成串,导致材料塑韧性降低。针对N07718镍基合金推荐使用1 029.4℃固溶保温1.5 h后水冷+779.4℃保温时效6.5 h,空冷的热处理工艺,其综合性能更优。

激光增材制造与连接GH4169合金的热处理工艺研究

采用激光增材制造技术制备了GH4169合金母材样品,并采用相同的工艺参数实现了母材的激光增材连接,检测了不同热处理状态下合金的拉伸性能,分析了性能改变的内在机理。结果表明:凭借激光增材制造技术热影响区小的优势,热处理前后母材与连接区域处微观组织的演变基本一致。沉积态合金呈典型的柱状晶组织,且二次枝晶并不发达,γ+Laves共晶相呈条带状和岛链状沿晶界分布;均匀化+固溶处理后Laves相发生分解并回溶入基体,并伴随着柱晶的粗化;当进行双重时效处理时Laves相的分布状态发生改变。不同热处理工艺试样的拉伸性能均高于同合金铸态指标,热处理对Laves相的含量和分布状态的改变是影响其强度和塑性的主要因素。

某跨声速风洞用980 高强度钢的去应力热处理工艺研究

热处理是结构件制造的重要环节,与结构件的制造质量和使用性能紧密相关。对某型号跨声速风洞用980高强度钢去应力热处理工艺进行了研究,采用拉伸试验和-20℃低温冲击试验,对比分析了一次、二次去应力退火试验后980高强度钢的强度和韧性。结果表明,当去应力热处理工艺为去应力退火温度为(450±10)℃,保温时间为10~12 h时,跨声速风洞用980高强度钢材料可获得最优的强度和韧性。试验结果对同类材料的去应力热处理具有一定的借鉴意义。

基于热处理工艺的拖拉机发动机铝合金组织性能研究

采用不同时长的热处理工艺,对拖拉机发动机铝合金组织性能进行了对比分析。结果表明:热处理后,铝合金性能得到了较大程度的提高,若优先考虑材料性能,则应该采用180℃×4 h的单级热处理时效;若优先考虑工艺效率和成本,则可以采用150℃×1 h+170℃×1 h的双级热处理时效。

关于钢质无缝气瓶热处理工艺评定规范性的思考

在钢质无缝气瓶的制造工序中,热处理工序对产品的安全性能起着至关重要的作用。TSG 23—2021《气瓶安全技术规程》和钢质无缝气瓶的制造标准均明确提出气瓶的热处理应按评定合格的热处理工艺进行。目前,国内还没有相应的规范或标准能够明确指导钢质无缝气瓶热处理工艺评定的制定过程,各制造厂在生产中的热处理工艺评定制定标准和水平也参差不齐。提出了钢质无缝气瓶的热处理工艺评定涵盖的内容及相应要求,并通过试验进行了举例。

热处理工艺对Al-Si-Mg-Cu合金微观组织和力学性能的影响

采用扫描电镜(SEM)、透射电镜(TEM)和万能拉伸试验机等研究了固溶温度、固溶时间、时效温度以及时效时间等工艺参数对Al-Si-Mg-Cu合金微观组织与力学性能的影响。结果表明,固溶温度由500℃升高至545℃时,合金的共晶硅尺寸逐渐减小,545℃时共晶硅平均尺寸达到最小,超过550℃合金会发生部分过烧现象;固溶温度为545℃时,固溶时间由2 h增加至16 h,共晶硅尺寸随着固溶时间增加先减小后增大,固溶时间为12 h时,共晶硅的平均尺寸最小;时效处理后合金的硬度显著提升,时效温度由155℃升高至185℃时,峰值时效时间从8 h减少至4 h,在175℃时效时合金的峰值硬度最高;155℃时效时合金的组织中仅观察到β″相,在高于155℃峰值时效时组织中均观察到β″相与θ′相,实现了双析出相强化,175℃峰值时效时合金的抗拉强度可达365 MPa,但断后伸长率下降至2.1%。综合考虑合金的强度和韧性,合适的热处理工艺为545℃×12 h+165℃×8 h。

强化知识应用能力的教学探讨——以《热处理原理与工艺》课程为例

工程教育专业认证的目标是从知识、能力和素质三维度提升学生解决复杂工程问题的技能,打造新时代所需的全面型工程应用人才。在分析学生对《热处理原理与工艺》课程学习难点的基础上,针对综合性和应用性强的热处理工艺制定内容,提出了知识条件化和结构化的教学方法。近几年的教学效果分析和总结表明,采用知识条件化和结构化教学后,对应的课程目标达成度有了明显的提升,证明了针对该课程不同内容采用不同教学方法的策略可行、有效。