An experimental study on the ballistic impact behavior of some metallic armour materials against 7.62 mm deformable projectile

The investigation describes and analyses the ballistic impact behavior of a high strength armour steel and Al-7017 alloy under 7.62 mm deformable projectiles at a velocity of 830 ± 10 m/s at normal angle of attack. The high strength armour steel is subjected to two different heat treatments to see the effect of different mechanical properties on the ballistic behavior. The ballistic result of the Al-7017 alloy is compared with that of the steel. Some observations relating to the adiabatic shear bands formation have also been presented. Experimental results showed that among the investigated materials, the best ballistic performance was attained with the armour steel at 910 °C austenitisation followed by 200 °C tempering condition.     

The effects of heat treatment variables on the microstructure and properties of ultra-high strength steels differing in titanium content

The influences of different austenitizing and tempering temperatures on the microstructure and properties of three experimental ultra-high strength steels (UHS) have been investigated. The steels had different Ti content and were subjected to austenitizing treatment at 900, 1000, 1100 and 1200°C followed by oil quench and tempering at 200, 300, 450 and 600 °C. It has been found that the high temperature (1100 and 1200 °C) austenitizing treatments, alter both microstructure and properties, and depending on the subsequent tempering temperature, may have a beneficial or detrimental influence upon the mechanical properties. Addition of up to 0.011 wt% Ti to the steel composition improves hardness, toughness and tensile strength. This improvement in mechanical properties is obtainable with any subsequent heat treatment. For higher Ti content (0.089 wt%), although some further improvement in hardness and tensile strength was obtained, significant degradation in toughness was achieved, particularly when the steel was subjected to high temperature austenitizing and tempering treatment.     

Effect of chemical composition, martensite volume fraction and tempering on tensile behaviour of dual phase steels

In this work an investigation was conducted into the tempering effects on mechanical properties of a carbon steel and a microalloyed steel, both with dual phase microstructure. The UTS and YS decreased and elongations increased with an increase of tempering temperature. However, the loss in UTS and YS at tempering temperatures of 100, 200, 300, 400, 500 and 600 °C was a minimum for microalloyed dual phase steel. This is thought to be due to tempering of the martensite and precipitation in the ferrite.     

The effect of heat treatment on the toughness, hardness and microstructure of low carbon white cast irons

The effect of destabilisation and subcritical heat treatment on the impact toughness, hardness, and the amount and mechanical stability of retained austenite in a low carbon white cast iron have been investigated. The experimental results show that the impact energy constantly increases when the destabilisation temperature is raised from 950°C to 1200°C. Although the hardness decreases, the heat-treated hardness is still greater than the as-cast state. After destabilisation treatment at 1130°C, tempering at 200 to 250°C for 3 hours leads to the highest impact toughness, and secondary hardening was observed when tempering over 400°C. The amount of retained austenite increased with the increase in the destabilisation temperature, and the treatment significantly improves the mechanical stability of the retained austenite compared with the as-cast state. Tempering below 400°C does not affect the amount of retained austenite and its mechanical stability. But the amount of retained austenite is dramatically reduced when tempered above 400°C. The relationship between the mechanical properties and the microstructure changes was discussed.     

An investigation on the microstructure and mechanical properties of direct-quenched and tempered AISI 4140 steel

Direct quenching (DQ) process is an appropriate method in steels heat treatment field. This method enhances production rate, reduces energy consumption and decreases environment contamination. In this study hot-rolled AISI 4140 steel billets with different diameters (75, 80, 85, 100, 105 and 115 mm) and 20 m length were quenched directly in a water tank. Also some samples with similar size and composition were provided by conventional reheating, quenching and tempering (RQ) heat treatment process. The quenched samples were tempered at the temperature of 630 °C for 2 h. Mechanical properties of heat treated samples including tensile strength, yield strength, elongation, hardness and impact toughness were measured. Also, the microstructure and harden-ability of this steel were investigated under various conditions and the results were compared to RQ heat treated products. The results showed that direct quenching and tempering processes (DQ–T) is due to enhance of mechanical properties such as tensile strength and harden-ability of AISI 4140 and it is affected by various parameters such as steel temperature before quenching, water temperature, quenching time and also billet size.     

热处理工艺对1Cr15Ni4Mo3N钢组织和性能的影响

通过力学性能测试和显微组织观察,研究了热处理工艺对1Cr15Ni4M03N钢显微组织和力学性能的影响。结果表明：该钢经780℃×5h空冷和590℃×4h空冷二级退火处理后具有良好的切削性能,适合进行机加工;再经过1070℃×1h油淬、-70℃冷处理和200-470℃回火处理后,可获得较好的综合力学性能。     

Finite Element simulation coupled to optimisation stochastic process to assess the effect of heat treatment on the mechanical properties of 42CrMo4 steel

The present study aims at studying the influence of heat treatment on the mechanical performance of 42CrM04 steel. Heat treatment is conduced in a way to affect significantly the microstructure, more precisely the tempered martensite structure. Tempering temperature is varied between 200 and 600° C. Experimental testing includes the determination of tensile properties and hardness scores. The identification of the mechanical parameters associated to elastic–plastic behaviour is undertaken using Finite Element computation to quantify the effect of heat treatment. The predictions show that characterisation of the material behaviour can be approached using a bilinear hardening model. The tempering temperature has a significant effect on the yield stress and tangent modulus.     

热处理工艺对压裂泵阀体用钢4330MOD组织及性能的影响

为提高压裂泵阀体的强度和韧性,研究了不同热处理工艺对改进型4330钢组织及力学性能的影响。结果表明:4330MOD钢通过添加微合金元素及调质工艺优化能够提高强度和韧性。微合金元素Nb、V,正火+调质工艺能够降低晶粒尺寸,提高强韧性。4330MOD钢在550℃～700℃回火时,组织为回火索氏体组织,随回火温度的升高强度降低,韧性先升高后降低,在600℃～650℃回火强韧性匹配较好。4330MOD钢通过微合金元素添加及热处理工艺优化使晶粒尺寸及板条块宽度细小,大角度晶界比例高,从而提高了钢的强韧性。      

Evaluation of the structure and properties of steel 35KhN2MFA under static and dynamic loading

We investigated the effect of the structure of heat-treated steel 35KhN2MFA on the mechanical properties under static and dynamic loading; the conditions of heat treatment were: hardening from 740–1100°C, isothermal quenching from 360°C, tempering at 300–550°C, heat cycling. It was established that a higher hardening temperature entails greater endurance: from 5700 cycles (T_h=740°C) to 10,100 cycles (T_h=1100°C), yet the required strength (_u=1740 MPa) is retained, and ductility and impact toughness are somewhat reduced. Isothermally quenched and high-tempered specimens have high endurance (N=12,000–13,500 cycles) but a low level of strength (_u=1330 MPa). Specimens subjected to heat cycling under the conditions hardening from 860°C and tempering at 650°C have the best complex of mechanical properties under static and cyclic loading.Translated from Problemy Prochnosti, No. 1, pp. 17–20, January, 1992.     

Microstructure,mechanical properties and high stress abrasive wear behavior of air-cooled MnCrB cast steels

Three medium carbon low alloyed MnCrB cast steels containing different Cr contents (0.3%, 0.6%, and 1.2%) were designed and the effect of Cr contents on the microstructure, mechanical properties and high stress abrasive wear behavior of the cast steels after 850 °C air-cooling and 220 °C tempering was studied. The results show that the hardenability of the MnCrB cast steels was excellent. The microstructure of the cast steels with low Cr contents (0.3% or 0.6%) consists of granular bainite and lower bainite/martensite multiphase. With increasing of Cr content, the formability of martensite was improved, the hardness and wear-resistance increased, but the impact toughness decreased in that more bainite was replaced by martensite. The air-cooled MnCrB cast steel containing 0.6% Cr, with granular bainite and lower bainite/martensite multiphase, exhibited excellent combination of strength, hardness, ductility, and impact toughness. In addition, its abrasive wear-resistance was 30% more than that of Hadfield cast steel in the high stress abrasive wear condition. This air-cooled MnCrB cast steel by simple alloying scheme and heat treatment has the advantages of high-performance, low cost, and environmentally friendly. It is a potential advanced wear-resistant cast steel for low- or even medium-impact abrasive conditions.     

Effect of processing parameters on the evolution of dislocation density and sub-grain size of a 12%Cr heat resistant steel during creep at 650 °C

The influence of hot-deformation and tempering temperature on the microstructure evolution of a 12%Cr heat resistant steel during short-term creep at 80-250 MPa and 650 °C was investigated. Quantitative determination of dislocation density and sub-grain size in the initial microstructure and after creep was investigated by STEM-HAADF. A correlation between microstructure evolution and creep response is established. All crept samples showed a significant increase of sub-grain size and a reduction of dislocation density. Hot-deformed samples showed better creep strength than non hot-deformed samples due to homogenization of the microstructure. The tempering temperature affected the dislocation density and the sub-grain size evolution, influencing the creep behavior.     

热处理对C12A耐热钢的组织与性能影响

通过对铸造C12A耐热钢进行热处理,观察其微观组织,测定其力学性能。试验结果表明：正（淬）火组织为板条马氏体＋部分针状马氏体＋少量残余奥氏体,其硬度比较高,塑性和韧性不是很好;正（淬）火＋回火组织为回火马氏体,其硬度不是很高,塑性和韧性比较好,具有良好的综合性能;退火组织为铁素体,其硬度低,塑性和韧性高;通过正火＋回火,研究回火温度对其微观组织和力学性能的影响。试验结果表明：回火温度对C12A钢的组织和性能有较大影响,其硬度随回火温度的升高呈先降后升趋势。     

Enhancement of the mechanical properties of EN52CrMoV4 spring steel by deep cryogenic treatment

The effect of the deep cryogenic treatment on the micro-structure and mechanical properties (tensile strength, toughness, residual stress and fatigue strength) of the medium carbon spring steel, which is subjected to different heat treatment steps, is investigated. Deep cryogenic treatment causes spring steel to keep compressive residual stress more efficiently due to an increase in the density of the crystalline defects, retardation in the stress relief after the phase transformations and nano-cluster carbide formations. If deep cryogenic treatment is applied before the tempering then the homogeneously distributed fine carbides form after the tempering and the grains remain relatively fine. The microstructure with homogeneously distributed fine carbides and fine grains cause spring steels to have simultaneously enhanced tensile strength, ductility and fatigue strength. If deep cryogenic treatment is applied after the conventional heat treatment (quenching+tempering), however, the coarse carbides form in the micro-structure and the improvement in the mechanical properties of the spring steel is limited.     

热处理工艺对连铸10CrNi3MoV钢性能的影响

针对高温热成型及正常调质处理后连铸10CrNi3MoV钢性能恶化这一问题,研究了循环/亚温淬火热处理工艺,进行了力学性能测试、显微组织观察及晶粒度评定.结果表明,采用亚温淬火( 835℃×2h+ 820℃×2h)+高温回火(630℃×3h)热处理工艺,可有效细化连铸10CrNi3MoV钢的晶粒,显著改善其低温韧性,使其...     

循环淬火工艺对连铸10CrNi3MoV钢组织与性能的影响

针对高温热成型及正常调质处理后结构件用连铸10CrNi3MoV钢性能恶化这一问题,采用循环淬火热处理工艺研究了力学性能、显微组织及晶粒度。结果表明,采用860℃三次循环淬火+高温回火(630℃×3 h)热处理工艺,能够有效细化连铸10CrNi3MoV钢的晶粒,改善其低温韧性,使其力学性能满足使用要求。     

Effect of tempering temperature on microstructure and properties of aluminium-bearing high boron high speed steel

Heat treatment is of great significance to the performance improvement of high speed steel. Via heat treatment, the microstructure of high speed steel can be improved, thus greatly improving the material performance. The effect of tempering temperature on the microstructure of aluminium-bearing high boron high speed steel (AB-HSS) was investigated by optical microscope (OM), scanning electron microscope (SEM) and x-ray diffraction (XRD). The hardness and wear resistance of the alloy at different tempering temperatures were tested by Rockwell hardness tester, micro-hardness tester and wear tester. The experimental results indicate that the tempering microstructure of aluminium-bearing high boron high speed steel consists of α-Fe, M₂B and a few of M₂₃(C, B)₆. Tempering temperature could greatly affect the wear resistance of materials. With the increase of tempering temperature, the wear resistance of aluminium-bearing high boron high speed steel firstly increase and then decrease. The alloy tempered at 450 °C has the best wear resistance and minimum wear weight loss. This study provides a reference for the formulation of heat treatment process of aluminium-bearing high boron high speed steel.     

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].     

Study on dislocation density,microstructure, and mechanical properties of P92 steel for different heat treatment conditions

The impact of various heat treatment procedures on microstructure, dislocation density, hardness, tensile characteristics, and impact toughness of P92 steel was examined in the current experiment. The martensitic microstructure and average microhardness of 463 HV 0.2±8 HV 0.2 of the normalized steel were prevalent. A tempering procedure was carried out at 760 °C for a range of 2 hours to 6 hours. Additionally, an X-ray diffraction examination was carried out, and the results were used to determine the dislocation density. The normalized sample was characterized by a high dislocation density. The dislocation density was decreased by tempering of normalized samples. With an increase in tempering time, the effect of the treatment coarsened the grains, precipitates, and decreased the area fraction of precipitates. After tempering, MX, M₂₃C₆, and M₇C₃ types precipitates were found to have precipitated, according to energy dispersive spectroscopy and x-ray diffraction research. The ideal tempering period was determined to be 4 hours at a tempering temperature of 760 °C based on the microstructure and mechanical characteristics. Steel that was tempered at 760 °C for 4 hours had a yield strength of 472 MPa, an ultimate tensile strength of 668.02 MPa, and an elongation of 26.05 %, respectively.     

Effect of tube spinning and subsequent heat treatments on strength,microstructure and residual stress state of AISI/SAE type 4140 steel

Abstract

In the present study, the effects of deformation percentage (23, 30, 50 and 66%) and subsequent stress relief and tempering heat treatments on the mechanical properties, residual stress state and microstructure of AISI/SAE type 4140 steel tubes manufactured by forward spinning were evaluated. Mechanical properties were determined by means of hardness and tensile tests. The tangential component of the surface residual stresses was determined by a slitting method. Plastic deformation of the metal during spinning refined and elongated the grains in the direction of metal flow, following a spiral path, resulting in improved mechanical properties. Tensile and yield strengths, as well as hardness, were all increased as a function of increasing percentage deformation. With stress relieving, the strength values were enhanced, whereas a slight decrease in hardness took place. Stress relieving did not change the microstructure considerably, whereas tempering resulted in a partially recrystallised microstructure, removing the effect of plastic deformation. The tangential residual stresses were tensile, and those of the as deformed tubes increased with an increasing amount of deformation up to 50%, then tended to decrease. The magnitude of the residual stresses decreased with stress relieving heat treatment, while tempering reduced the residual stresses to negligible levels.     

Microstructure effect on the properties of a commercial low-fusing dental porcelain

The aim of this study was to investigate the effect of firing cycle on a dental porcelain microstructure in order to correlate microstructure changes with mechanical and thermal properties. A commercial low-fusing dental porcelain powder (Omega 900, Vita) was investigated for this purpose. The powder was treated at different temperatures in the range 750–1000 °C. The fired samples were characterized in terms of their morphology and microstructure, and their mechanical and thermal properties were evaluated. The results showed that firing temperature affects porcelain microstructure influencing significantly in this way both the mechanical properties and the thermal expansion coefficient of the fired objects. Firing at 800 °C led to a homogeneous structure. After treatment at this temperature, the leucite crystals exhibit their maximum concentration and they are well dispersed into the glassy phase. As a consequence the optimum mechanical strength and the maximum thermal expansion coefficient are observed in these samples.