Hardness and Conductivity of Die Forged ZYK530 Magnesium Alloy

The relationship among the microstructure, hardness and electrical conductivity of the as-forged ZYK530 Mg alloy after heat treatment was analyzed and studied using a microscope, X-Ray Diffractometer, eddy current conductivity meter, and Vickers microhardness tester, to explore optimum heat treatment process of ZYK530 Mg alloy. The results show that: with the prolongation of holding time, the electrical conductivity and microhardness show the same change trend, both of which show an oscillatory upward trend, and then decrease in an oscillatory downward trend after reaching the peak value. There is a linear positive correlation between the conductivity and the hardness, and the fitting results of the conductivity and hardness are in good agreement with the measured results; combined with the actual production, when the heat-treatment is 480 ℃ × 8 h + 220 ℃ × 3 h, the highest hardness is 79.2 HV, the electroconductivity is 36.2%IACS, and the comprehensive performance is the best, which is the best heat treatment process.

A Low-Cost and Highly Efficient Method of Reducing Coolant Leakage for Direct Metal Printed Injection mold with Cooling Channels Using Optimum Heat Treatment Process Procedures

Metal additive manufacturing (MAM) provides lots of benefits and potentials in manufacturing molds or dies with sophisticated conformal cooling channels. It is known that the conformal cooling technology provides effective cooling to reduce cycle time for increasing productivity. Ordinarily, mold inserts fabricated by general printing procedures will result in coolant leakage in the injection molding process. The yield in the manufacturing of fully dense injection molding tools was limited to the very narrow working widow. In addition, high costs of fully dense injection mold fabricated by MAM constitute the major obstacle to its application in the mold or die industry. In general, the high cost of MAM is approximately 50-70% more expensive than conventional computer numerical control machining. In this study, a low-cost and highly efficient method of reducing coolant leakage for direct metal printed injection mold with cooling channels was proposed. This new method employs general process parameters to manufacture the green injection mold rapidly and then uses optimum heat treatment (HT) procedures to improve microstructure of the green injection mold. The results of this study revealed that optimum HT procedures can prevent coolant leakage and save manufacturing time of the injection mold fabricated by direct metal laser sintering. The evolution mechanisms of microstructure were investigated experimentally. The save in the injection mold manufacture time about 67% can be obtained.

Effect of Heat Treatments on Microstructural Evolution and Tensile Properties of 15Cr12MoVWN Ferritic/Martensitic Steel

In this study, the phase transformation temperature of 15Cr12MoVWN ferritic/martensitic steel was determined by differential scanning calorimetry to provide a theoretical basis for the design of a heat treatment process. An orthogonal design experiment was performed to investigate the relationship between microstructure and heat treatment parameters, i.e., normalizing temperature, cooling method and tempering temperature by evaluating the room-temperature and elevated-temperature tensile properties, and the optimum heat treatment parameters were determined. It is shown that the optimized heat treatment process was composed of normalizing at 1050 °C followed by air cooling to room temperature and tempering at 700 °C. Under the optimum heat treatment condition, the room-temperature tensile properties were 1014 MPa (UTS), 810.5 MPa (YS) and 18.8% (elongation), while the values are 577.5 MPa (UTS), 469 MPa (YS) and 39.8% (elongation) tested at 550 °C. The microstructural examination shows that the strengthening contributions from microstructural factors were the martensitic lath width, dislocations, M23C6, MX and grain boundaries of prior austenite grain (PAG) in a descending order. The main factors influencing the tensile strength of 15Cr12MoVWN steel were the martensitic lath width and dislocations.

The spheroidizing tendency and spheroidization mechanism of 75Cr1 steel

Spheroidization annealing process was carried out on 75Cr1 steel after cold rolling. Using TEM, SEM and image analysis software Image-Pro Plus 6.0, the effects of cold rolling and spheroidization processes on microstructure and mechanical properties were analyzed. The result shows that the cold rolling leads to fragmentation of the cementite and formation of the defects, which induces faster lamellae break-up and accelerates the annealing process. With the increase of isothermal temperature and holding time, the dimension of the spheroidized carbides increase as driven by Ostwald ripening mechanism, whereas the hardness of the steel decreases. The prior cold rolling before annealing process causes the yield strength improve slightly, however shows little effect on the cold formability. The optimum heat treatment process is, holding the samples at 705oC for 6 hours with cold deformation ratio (ε) of 0.6.

Effect of Heat Treatment on Microstructural Evolution of 13Cr Martensitic Stainless Steel

13Cr martensitic stainless steels are widely used in gas industry, which are usually manufactured by quenching-tempering treatment. Microstructural study of 13Cr steel through various heat treatments was carried out for determining the optimum parameters for industry manufacture. After quenching treatment at 975 °C for 20 min, precipitation-free martensitic structures were formed. During tempering, recovery of martensite through grain boundaries migration and dislocations annihilation was found to soften the steel. In addition, transformation of needle-like Cr7C3 carbides to the irregular shaped Cr23C6 carbides was observed when tempering temperature is above 710 °C. The phase transformation induced precipitation strengthening is discussed. The optimum heat treatment parameters of 13Cr steel for avoiding over tempering and the precipitation hardening are found.

Optimization of Heat Treatment of Castings

The use of various types of software for rapid identification of potential problems in manufacturing processes is becoming ever more popular. One of such programs is DEFORM, simulation software for forming and heat treatment processes. The purpose of this study was to construct a 3D model of a specific casting, to identify its critical locations and then select the optimum heat treatment procedure preventing cracking. Results of this work include a detailed analysis of stress and temperature fields in the cast part.