Preparation and warm compaction behavior of the ho

Warm compaction powder preparation and its warm compaction behavior

powder metallurgy is a new technology integrating material metallurgy and mechanical manufacturing. It has significant advantages such as material saving and low energy consumption, and provides a large number of high-quality and low-cost p/m parts for mechanical manufacturing, especially the automotive industry. However, the pores determine that the parts have low mechanical properties, which limits the scope of use of p/m parts, resulting in the potential of powder metallurgy technology to compete with other parts manufacturing technologies under the weak national billet price on the 10th. In order to expand the application scope of p/m parts, we must improve the density of p/m parts. At present, the common methods to improve the density of p/m parts are: the preparation and application of high compressibility iron powder; Re pressing and re firing; Copper dipping process; Powder forging; Liquid phase sintering; High temperature sintering. Because these processes have technical problems such as varying degrees of cost and difficult to ensure the accuracy of parts, it is necessary to find new technical ways to improve the density of p/m parts

warm compaction is a new process for preparing high-density p/m parts developed by hogenas company of the United States on the basis of diffusion bonded iron powder in 1994. So far, more than 20 patents related to warm compaction have been applied, including the preparation of warm compaction powder, new lubricants, heating devices and related preparation processes. At present, more than 30 warm pressed parts production lines have been established worldwide, which can produce dozens of warm pressed parts. The key to the rapid development of warm compaction technology lies in its low-cost manufacturing of high-density p/m structural parts. A better combination between performance and cost is found for high-density parts. It is reported that the relative cost of warm pressing process is 20%, 30% and 80% lower than that of copper dipping process, re pressing and re firing process and powder forging process respectively. Due to the high strength, low demoulding pressure and low elastic aftereffect of the blank prepared by warm pressing process, it is convenient to manufacture p/m structural parts with complex shape and high precision. Thus, powder metallurgy technology is endowed with strong competitiveness over other parts manufacturing technologies

warm pressed powder is the technical core and foundation for obtaining high-density iron-based p/m parts. In order to promote the development of China's powder metallurgy technology and reduce the dependence of China's p/m parts manufacturing enterprises on imported warm pressed powder, the State Key Laboratory of powder metallurgy of Central South University of technology, in cooperation with Dongfeng Motor Corporation and Panzhihua Iron and steel company, with the assistance of the national "863" plan, focuses on the preparation of warm pressed powder and the development of high-density iron-based p/m structural parts, in order to establish a set of self owned Warm pressed parts manufacturing technology system in line with China's national conditions

1fe-1.5ni-0.5mo warm pressed powder preparation

ni, Mo is a common alloy element to improve the mechanical properties of iron-based p/m parts, especially after subsequent heat treatment. Nickel and molybdenum in simple form have high diffusion excitation energy in the "made in China 2025" iron. During the sintering process, they can be alloyed with iron base to form nickel and molybdenum enrichment areas, which cannot achieve the purpose of improving mechanical properties. In order to alloying Ni and Mo alloy elements with iron, the sintering temperature must be increased. In the sintering process, due to the diffusion of Ni and Mo and the excessive sintering shrinkage, the accuracy of the parts is difficult to control. The main reason for the unqualified hard quality of fully alloyed powder is that the polymer content is low, and the high speed and compressibility create conditions for sintering diffusion and dimensional stability control of parts. At present, China has not mastered this technology

generally, the basic raw material of warm pressed powder is atomized iron powder, and its market price is generally 6000 to 8000 yuan/T. with the alloy elements Ni, Mo and polymer lubricant in it, the operating principle of raw material search engine alone is as high as 9000 to 11000 yuan/T. Therefore, the price of warm pressed powder is close to the lower limit price of imported powder. This is unacceptable to domestic p/m parts manufacturers, which is not conducive to the development of powder metallurgy warm compaction technology in China, and other basic raw materials must be found

the smoke and dust produced by the converter during the blowing process contains about 20% iron powder. In terms of particle shape, it is similar to atomized iron powder. However, due to the high impurity content and poor formability, this iron powder cannot be directly used as the raw material of iron powder for powder metallurgy. Because the recovery cost of this iron powder is only about 800 yuan/t, it has unique advantages in cost. After a series of treatment, the main chemical components of the recovered converter dust iron powder are as follows: w (FE) ≥ 98.4%, w (s) =0.036%, w (c) =0.014%, w (P) =0.169%

1.1fe-1.5ni-0.5mo diffusion bonding powder preparation process flow

fe-1.5ni-0.5mo warm pressed powder preparation process flow is as follows: after proper particle selection, the -100 mesh converter dust iron powder treated in the early stage is evenly mixed with -200 mesh nickel, molybdenum powder and a small amount of binder. Activation treatment plays a key role in this process, that is, to create conditions for alloying Ni, Mo alloy elements with iron and moderate roughening of the surface of iron particles. Subsequent annealing has the functions of diffusion alloying and stabilizing the surface roughness of existing iron particles

the bulk density of diffusion bonded iron powder is 3.13g/cm3, and the flow property is 27s/50g. The powder added with 0.6% zinc stearate is pressed at room temperature under the pressure of 588mpa, and the density of the compacted blank is 7.16g/cm2

1.2 development of new lubricants

for lubricants such as zinc stearate under room temperature pressing, it mainly plays the role of lubricating the mold wall, that is, reducing the friction between powder particles and the mold wall, reducing the external pressure loss, effectively improving the density of compacts and improving the density distribution. The function of lubricant for warm compaction is different. In addition to reducing the friction between powder particles and mold wall, it can also effectively reduce the friction between powder particles, which is conducive to the rotation and sliding of powder particles in the compaction process, and create conditions for the mutual filling between particles and the maximum densification of powder. However, zinc stearate has melted at the general warm pressing temperature, which not only greatly reduces the fluidity of the powder, but also degrades the lubrication effect due to the change of the structure of zinc stearate. Therefore, new polymer lubricant systems must be developed

1.2.1 effect of polymer A and its addition on the warm compaction behavior of powder

in the initial warm compaction experiment, the effect of powder heating temperature on the warm compaction behavior of powder with 0.6% addition of polymer a was investigated, and the results are shown in Table 1. Table 2 shows the effect of polymer addition on the warm compaction behavior of powder. It can be seen from the table that the density of warm compaction is lower than that of ordinary room temperature compaction, and the demoulding pressure is large. Although the compacts density increases when the addition amount is 0.7%, the elastic aftereffect (0.23%, while the elastic aftereffect in other cases is 0.15%) increases