Thermophysical property measurements on low alloy high strength carbon steels

The solidus/liquidus temperatures, heat of fusion, specific heat capacity, and thermal expansion for AISI 43 10 and 4320 steels were measured in this study. Both steels have similar heat of fusion values and solidification temperature ranges but differ in the absolute solidus/liquidus temperatures. The specific heat capacity vs. temperature curves for both steels show similar trends with difference in the peak value at austenite phase transformation temperatures.

Both steels demonstrate similar thermal expansion trends and absolute values. The thermal expansion vs. temperature curve shows considerable difference between the heating part and the subsequent cooling part which reflects the different solid state phase changes experienced during the heating and cooling of these two heat-treatable steels. This phenomenon should be taken into account during the modeling of welding, casting and other processing of these steels. The relative density as a function of temperature for these steels can be estimated based on the thermal expansion values.     

Detection of spring steel surface decarburization by magnetic hysteresis measurements

Surface decarburization of steel was non-destructively and quantitatively investigated by magnetic hysteresis. Flat samples were prepared from spring steel 54SiCr6 and decarburized layers of different thickness were produced on their surfaces by annealing at 800 °C in air for 1, 4, 8 and 20 h. Three types of treatment were applied on different samples in order to remove the simultaneously appearing surface oxides. The decarburized layers were examined magnetically by hysteresis loops measurements and the results were related to their optically determined depths. The magnetic measurements showed high sensitivity with respect to free ferrite and mixed ferrite/pearlite layers detection even without removal of the oxide layer. The free ferrite layers were easily and quantitatively detected by minor loops measurements with low field amplitude.     

热作模具钢热疲劳性能的研究现状与发展趋势

针对热作模具钢(各种热锻模、热压模、热挤压模和压铸模)的工作型腔表面高于600℃时易产生热疲劳裂纹和热疲劳失效问题,综合分析了国内外热疲劳的研究现状及其发展,重点讨论热疲劳试验方法、影响热疲劳的因素、热疲劳性能的评价方法以及热疲劳裂纹萌生和扩展机理,提出一些提高热作模具钢热疲劳性能的措施,以及今后热疲劳性能研究和发展趋势.     

Evaluation of residual stress in ferromagnetic steels based on residual magnetic field measurements

The paper presents a residual stress evaluation method using the gradients of the residual magnetic field (RMF) components. Distributions of the RMF components were measured on the surface of samples with a various degree of plastic strain. The finite element method was used to model residual stress in samples. The impact of residual stress on changes in the residual magnetic field was shown. A very good qualitative correlation was found between places with residual stress and areas with increased values of the gradients of the RMF components. An algorithm was developed and verified for steel T/P24 to make a quantitative evaluation of residual equivalent (von Mises) stress based on the gradients of tangential component dH_T,Y/dx and field gradient dH/dx. Directions of further research were formulated, which included the validation of the method and which took into consideration the factors affecting its accuracy. The developed algorithm can be a significant complement to the Metal Magnetic Memory (MMM) method.     

Analysis of mechanical property distribution in multiphase ultra-fine-grained steels by nanoindentation

The strength characteristics of microphases in ultra-fine-grained steels were analyzed using nanoindentation and AFM. It was found that there were fine ferrite grains (1–2 μm) formed by a strain-induced dynamic transformation in ultra-fine-grained steels. They had equiaxed and polygonal grain shape, and higher hardness and elastic modulus than coarse ferrite transformed statically. Strengthening factors of strain-induced dynamic transformation ferrite were analyzed in terms of cementite particles and dislocation density.     

Predicting the fatigue limit of steels hardened by chemical-thermal treatment

ÉNIMS, MAMI. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 8, pp. 37–41, August, 1989.     

Effects of Mn addition on the magnetic property and corrosion resistance of bulk amorphous steels

We aim to obtain bulk amorphous steels (BASs) with low magnetic permeability and high corrosion resistance by designing the compositions of (Fe₄₄Cr₁₀Mo_12.5Mn₁₁C₁₅B₆Y_1.5)_100−xMn_x (x = 0, 2, 4, 8). The vibrating sample magnetometer (VSM) tests show that the magnetization of the BASs exhibits linear relationship to applied magnetic field, indicating the BASs are paramagnetic at room temperature. It is measured that by increasing Mn content from x = 0 to 8, the magnetic permeability can be decreased from 1.0036 to 1.0025. The potentiodynamic polarization experiments show that the BASs have a high corrosion resistance in 3.5% NaCl and 1.0 mol/L HCl solutions. Increasing Mn content can improve corrosion resistance of the BASs in 1.0 mol/L HCl solution to a large degree, while it does not take much effect in 3.5% NaCl solution.