With the hot sales of Huawei P20 Pro, its excellent camera effect has won the attention of consumers. A new material has entered everyone’s attention. This is the high nitrogen non-magnetic austenitic stainless steel used to make the P20 Pro mobile phone camera decoration (HNSS).
How did HNSS emerge as a popular material for camera decoration circles? We have to start with the special material requirements of this part for mobile phones.
First of all, the autofocus of a smart phone is achieved by a voice coil motor. This requires that the surrounding materials of the camera module have a low magnetic permeability (that is, non-magnetic), otherwise it will affect the magnetic field of the focus motor. This affects the photographing effect; secondly, it is required that the material of the camera decoration ring has high strength to provide protection for the lens; at the same time, as the appearance part of the mobile phone, it also needs to have good corrosion resistance.
From the perspective of material selection, rolled 316L stainless steel profiles meet the above requirements, but because of the complex structure of the camera’s decorative ring, the use of rolled profiles + CNC machining processes is relatively inefficient, requires a long CNC machining time, and is costly. The efficiency of the aluminum alloy profile + CNC machining process is slightly higher than 316L, but it also requires longer CNC machining time, higher cost, poor strength, and poor ID realization. Aluminum alloy die-casting has inherent defects caused by its inclusions, shrinkage holes, pores, etc., and it is difficult to achieve better ID appearance requirements …
The metal powder injection molding (MIM) technology, which has been widely used in the manufacture of mobile phone parts in recent years, is a highly efficient near-net forming process for metal parts, which is very suitable for mass production of complex metal parts, which can greatly reduce processing costs, and Can achieve better ID effect. With regard to the selection of MIM process materials, Shanghai-based Fuchi High-Tech Co., Ltd. has carried out a large number of theoretical research, analysis and material selection. Based on independent research and development, breaking through technical barriers, it analyzed MIM316L, MIM17-4PH and other MIM materials The advantages and disadvantages of the process and the degree of performance matching are summarized. The MIM HNSS material and independent feeding technology that are suitable for the performance requirements of the mobile phone camera decorative ring are summarized and developed, which strongly supports the application of the MIM process in the mobile phone camera decorative ring.
For stainless steel to be non-magnetic, the key is to ensure that the interior is an austenite structure, which requires adding a large amount of austenite-stabilizing alloying elements to the material composition to achieve it. The 18-8 type stainless steel that we are familiar with, by adding Ni to form an austenitic structure (304L, 316L), is the most widely used austenitic stainless steel, but the strength of MIM316L stainless steel is relatively low, which meets the strength of 3 camera decorative rings Poor performance when requested.
In addition to Ni, Mn and N are also elements that stabilize austenite, especially N, which has an austenite stabilizing capacity almost 20 times that of Ni. Due to the high price of Ni, research on the preparation of austenitic stainless steel with N-generation Ni has been carried out for a long time, and many grades of HNSS high nitrogen stainless steel have been developed (such as Armtronic’s Nitronic series). However, although the solubility of element N in solid austenite is high, the solubility in ferrite and molten steel is low. The production of high nitrogen stainless steel by the melting-casting method requires very special processes and expensive equipment. Although types of stainless steel have been around for a long time, they are not widely used.
MIM technology provides new opportunities for the application of HNSS. The raw material of the MIM process is very fine metal powder (particle diameter <30 microns). The final product is obtained by high-temperature solid-phase sintering. If a suitable high-purity nitrogen atmosphere is used in the sintering process, the N element can be diffused. Permeate into the stainless steel metal matrix (the diffusion distance is only half of the particle diameter, which is easy to complete), so that austenitic non-magnetic stainless steel products with high nitrogen content are easily obtained. At the same time, a large number of dissolved nitrogen atoms fill the octahedral gap in the austenite fcc lattice, resulting in a strong lattice distortion, which brings a significant solid solution strengthening effect, so the strength of MIM HNSS is much higher than that of MIM316L stainless steel.
The successful use of SHFC’s MIM HNSS material on the mobile phone’s 3-camera decoration ring has once again proved the advantages of deep cultivation in the industry. Shanghai Fuchi insists on focusing on the development of independent MIM technology and materials for 20 years. Its products are used in consumer electronics, automotive, medical, tools Locks, communications (5G) and other fields have blossomed in full force, contributing to the advancement of China’s MIM industry.