scholarly journals Effect of Fire Temperature and Exposure Time on High-Strength Steel Bolts Microstructure and Residual Mechanical Properties

Materials ◽  
2021 ◽  
Vol 14 (11) ◽  
pp. 3116
Author(s):  
Paweł Artur Król ◽  
Marcin Wachowski
Keyword(s):  
Mechanical Properties ◽  
High Strength ◽  
Heating Time ◽  
Heat Treatments ◽  
Initial State ◽  
Natural Fire ◽  
Xrd Phase Analysis ◽  
Steel Bolts ◽  
Cooling Methods ◽  
Fire Conditions

In this study, the influence of different fire conditions on tempered 32CrB3 steel bolts of Grade 8.8 was investigated. In this research different temperatures, heating time, and cooling methods were correlated with the microstructure, hardness, and residual strength of the bolts. Chosen parameters of heat treatments correspond to simulated natural fire conditions that may occur in public facilities. Heat treated and unheated samples cut out from a series of tested bolts were subjected to microstructural tests using light microscopy (LM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), XRD phase analysis, and the quantitative analysis of the microstructure. The results of the microstructure tests were compared with the results of strength tests, including hardness and the ultimate residual tensile strength of the material (UTS) in the initial state and after the heat treatments. Results of the investigations revealed considerable microstructural changes in the bolt material as a result of exposing it to different fire conditions and cooling methods. A conducted comparative analysis also showed a significant effect of all such factors as the temperature level of the simulated fire, its duration, and the fire-fighting method on the mechanical properties of the bolts.

scholarly journals Effect of Fire Temperature and Exposure Time on High-strength Steel Bolts Microstructure and Residual Mechanical Properties

2021 ◽  
Author(s):  
Paweł Artur Król ◽  
Marcin Wachowski
Keyword(s):  
Mechanical Properties ◽  
Steel Structures ◽  
High Strength ◽  
Strength Properties ◽  
Heating Time ◽  
Point Of View ◽  
Structural Safety ◽  
Equivalent Diameter ◽  
Natural Fire ◽  
Steel Bolts

The article presents results of research consisting in an attempt to assess the influence of temperature, heating time and cooling method on microstructure and residual strength properties of steel previously tempered during the production process. Simulated environmental conditions to which high-strength bolts, commonly used in steel construction, were subjected, were intended to reflect conditions of a natural fire that may occur in public facilities where the obligation to ensure safety of users and rescue teams is of key importance, also required by law. Furthermore, the tests carried out also comprised a simulated effect of a rescue and firefighting operation using shock, rapid cooling of some of the heated bolts. Samples cut out from the tested bolts, after they were properly prepared, were subjected to microstructural tests using light microscopy, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), phase analysis with the use of an X-ray diffractometer (XRD) and quantitative analysis of the microstructure involving, inter alia, measuring the surface area of grains, their equivalent diameter and mean diameter. As a result of the tests, considerable microstructure changes were identified occurring in the bolt material as a result of exposing it to fire conditions, leading to a change in key, from the point of view of structural safety, mechanical properties. The results of the microstructure tests were compared with the results of previous strength tests, including hardness of the material after the heat treatment and the residual tensile strength of the material Rm. A conducted comparative analysis showed a significant effect of all such factors as the temperature level of the simulated fire, its duration and the fire-fighting method on the mechanical properties of bolts. Results obtained were provided with required comments and the concept of using the microstructure for the post-fire assessment of steel structures was referred to.

scholarly journals Post-Fire Susceptibility to Brittle Fracture of Selected Steel Grades Used in Construction Industry—Assessment Based on the Instrumented Impact Test

Materials ◽  
2021 ◽  
Vol 14 (14) ◽  
pp. 3922
Author(s):  
Mariusz Maslak ◽  
Michal Pazdanowski ◽  
Marek Stankiewicz ◽  
Paulina Zajdel
Keyword(s):  
Charpy Impact ◽  
Water Mist ◽  
Heating Regime ◽  
Building Structures ◽  
Initial State ◽  
Slow Cooling ◽  
Natural Fire ◽  
Development Scenarios ◽  
Steel Grades ◽  
Fire Conditions

The change in the value of the breaking energy is discussed here for selected steel grades used in building structures after subjecting the samples made of them to episodes of heating in the steady-state heating regime and then cooling in simulated fire conditions. These changes were recorded based on the instrumented Charpy impact tests, in relation to the material initial state. The S355J2+N, 1H18N9T steels and also X2CrNiMoN22-5-3 duplex steel were selected for detailed analysis. The fire conditions were modelled experimentally by heating the samples and then keeping them for a specified time at a constant temperature of: 600 °C (first series) and 800 °C (second series), respectively. Two alternative cooling variants were investigated in the experiment: slow cooling of the samples in the furnace, simulating the natural fire progress, without any external extinguishing action and cooling in water mist simulating an extinguishing action by a fire brigade. The temperature of the tested samples was set at the level of −20 °C and alternatively at the level of +20 °C. The conducted analysis is aimed at assessing the risk of sudden, catastrophic fracture of load-bearing structure made of steel degraded as a result of a fire that occurred previously with different development scenarios.

Mechanical Properties of a Novel High-Strength Aluminum-Lithium Alloy

2011 ◽  
Vol 689 ◽  
pp. 385-389 ◽  
Author(s):  
Zhi Shan Yuan ◽  
Zheng Lu ◽  
You Hua Xie ◽  
Xiu Liang Wu ◽  
Sheng Long Dai ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Fracture Toughness ◽  
Tensile Test ◽  
High Strength ◽  
Heat Treatments ◽  
Fracture Toughness Test ◽  
Aluminum Lithium Alloy ◽  
Toughness Test ◽  
Aluminum Lithium ◽  
Strength And Ductility

As a heat treatable aluminum alloy to be used in T6 and T8 temper, belongs to Al-Cu-Li system, a novel high-strength aluminum-lithium alloy 2A97 was developed. In order to improve the relationships of strength and ductility and fracture toughness, and to urge the applications in the aeronautical and aerospace industries, the effects of normal heat treatments and thermomechanical heat treatments on the mechanical properties and fracture toughness were investigated by Transmission Electron Microscope(TEM), Scanning Electronic Microscope (SEM), tensile test, and fracture toughness test. The results show that for the alloy aged at 135 °C for 24 h after quenching and 4 percent plastic deformation, its microstructures are strengthened by strain hardening and precipitation hardening, consisting of fine T1phase, θ″/θ′ phase and δ′ phase densely and homogeneously distributed in the matrix. It yields optimum relationship of strength and ductility, fracture toughness, its σ0.2, σband δ5are 454 MPa, 536 MPa, and 11.8%, respectively. It yields 43.5 MPa·m1/2of Kqvalues higher than that of 42.5 MPa·m1/2 in T6 temper. The fracture morphologies of impact tensile samples of fracture toughness test and normal tensile test were observed, indicating the dominance of intergranular failure and subintergranular failure with some dimples and trangranular failure.

The Effect of Microalloying of Nickel, RRA Treatment on Microstructure and Mechanical Properties for High Strength Aluminum Alloy

2014 ◽  
Vol 925 ◽  
pp. 253-257 ◽  
Author(s):  
Haider T. Naeem ◽  
Kahtan S. Mohammad ◽  
Khairel R. Ahmad
Keyword(s):  
Mechanical Properties ◽  
Aluminum Alloys ◽  
High Strength ◽  
Casting Process ◽  
Direct Chill ◽  
Heat Treatments ◽  
Alloy Sample ◽  
Retrogression And Reaging ◽  
High Strength Aluminum Alloys ◽  
Direct Chill Casting Process

High strength aluminum alloys Al-Zn-Mg-Cu-(0.1) Ni produced by semi-direct chill casting process were homogenized at different conditions then conducted heat treatment process which comprised pre-aging at 120°C for 24 h, retrogression at 180°C for 30 min, and then re-aging at 120°C for 24 h. Microstructural studies showed that add Ni (0.1 wt %) to the alloy will be forming Ni-rich phases such as AlCuNi, AlNi, AlNiFe and AlMgNi which provide a dispersive strengthening affected in the solid-solution and the subsequent heat treatments. The results showed that by this three-step process of heat treatments, the mechanical properties of aluminum alloys Al-Zn-Mg-Cu-(0.1) Ni were substantially improved. The highest attain for the ultimate tensile strength and Vickers hardness for the alloy sample after applied the retrogression and reaging process is about 545 MPa and 237 HV respectively.

Three Point Bend Performance of Solutionized, Die Quenched and Heat Treated AA7075 Beam Members

2014 ◽  
Vol 794-796 ◽  
pp. 431-436 ◽  
Author(s):  
Alexander Bardelcik ◽  
Alexandre Bouhier ◽  
Michael J. Worswick
Keyword(s):  
Mechanical Properties ◽  
Peak Load ◽  
Natural Aging ◽  
High Strength ◽  
Total Elongation ◽  
Strength Properties ◽  
Heat Treatments ◽  
Forming Process ◽  
Heat Treated ◽  
Point Bend

To overcome the low room temperature formability of AA7075-T6 aluminum sheet, without sacrificing the high strength properties of this alloy, a hat section beam member was formed and quenched within a cold die immediately after a 20 minute solutionizing treatment. Natural aging for 24 hours followed the forming process which was then followed by various heat treatments that included a typical precipitation hardening (PH) and industrial paint bake (PB) temperature-time treatment. Tensile specimens were extracted from the beams to evaluate their mechanical properties. When compared to the as-received AA7075-T6 mechanical properties, the beams heat treated with the PH, PHPB and PB treatment resulted in a 5%, 13% and 20% reduction in ultimate tensile strength respectively. A similar trend was shown for the yield strength measurements. There was little effect of the heat treatments on the total elongation, with the PH condition showing a slight improvement. A backing plate was riveted to the beams and a quasi-static 3 point bend test was conducted to evaluate the crush performance. The peak load for the PH, PHPB and PB beams was 9.2, 8.5 and 7.3 kN respectively, but the calculated energy-displacement (or energy absorption) curves were similar for the PH and PHPB parts due to a more ductile fracture behavior for the PHPB material condition.

Distribution of Mechanical Properties by Volume in Titanium Billets Processed by Twist Extrusion

2010 ◽  
Vol 667-669 ◽  
pp. 851-856 ◽  
Author(s):  
Alexey Reshetov ◽  
Alexander Korshunov ◽  
A. Smolyakov ◽  
Yan Beygelzimer ◽  
Viktor Varyukhin ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
High Strength ◽  
Strength Properties ◽  
High Plasticity ◽  
Initial Value ◽  
Initial State ◽  
Twist Extrusion ◽  
Billet Cross Section ◽  
Reduction In Area ◽  
Forming Methods

The influence of multipass processing by Twist Extrusion (TE) on distribution of mechanical properties by volume in commercially pure (CP) titanium billets is investigated. Experiments show that the mechanical properties are almost homogeneous in the billet cross-section already after the second pass of TE. This can be explained by mixing effect and saturation of properties as well. Warm TE leads to the formation of high strength properties in combination with high plasticity. Ultimate and yield stresses of the billet processed by two cycles of TE increased, in comparison with initial state, by 30% and 60% respectively. The value of the reduction in area remained at the initial value. This fact is indicating a high technological plasticity of the material, i.e. its ability for further shaping by metal forming methods.

Residual mechanical properties of high strength steel bolts subjected to heating-cooling cycle

2017 ◽  
Vol 131 ◽  
pp. 122-131 ◽  
Author(s):  
Venkatesh Kodur ◽  
Mahmood Yahyai ◽  
Abbas Rezaeian ◽  
Mohamadreza Eslami ◽  
Alireza Poormohamadi
Keyword(s):  
Mechanical Properties ◽  
High Strength Steel ◽  
High Strength ◽  
Cooling Cycle ◽  
Residual Mechanical Properties ◽  
Steel Bolts

Influence of Heat Treatments on the Microstructure and Mechanical Properties in Ti-10V-2Fe-3Al Alloy

2015 ◽  
Vol 750 ◽  
pp. 160-165
Author(s):  
Cong Li ◽  
Jian Chen ◽  
Wei Li ◽  
Wei Qiu ◽  
Jian Jun He
Keyword(s):  
Mechanical Properties ◽  
Phase Field ◽  
Solution Treatment ◽  
Heating Time ◽  
Heat Treatments ◽  
Ongoing Research ◽  
Field Solution ◽  
Β Phase ◽  
Α Phase ◽  
Treatment Conditions

This paper reports the results of an ongoing research which was set up to investigate the effect of microstructures on the activity of different deformation mechanisms and the resulting mechanical behavior of the Ti-10V-2Fe-3Al alloy. Various microstructures were established by different heat treatments. Depending on the microstructures, obvious differences in the mechanical properties of this alloy were obtained. It is shown that in α+β phase field solution treatment conditions, with the increase of heating time, the fraction of globular α phase decreases, the compression strength increases. In β+(α+β) phase field solution treatment conditions, with the increase of heating time, alloys have opposite trends. In aging conditions, the microstructure and mechanical property do not change apparently with the aging time. The microstructure of the α phase and β phase has a great influence on the fractographic morphology.

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