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New Mold Materials in Chinese Injection Industry

With the sustained and rapid development of Chinese economy in recent years, China's plastic injection industry has achieved a leapfrog development and made remarkable achievements. According to the requirements of plastic products and the specific properties of the mold steel, the rational selection of plastic mold steel is a very important task. How to choose plastic injection mold steel?
1. New Cold Working Die Steel 
The main performance requirements for the cold work injection mold steel materials are: good wear resistance, sufficient strength and toughness, high fatigue life, good scratch resistance, and good process performance. In recent years, In the field of cold-working die steel, the following new types of cold-working die steel have appeared.
  • Low-alloy cold working die steel. In the past, cold work die steels commonly used in China were low alloy steels and high carbon and high chromium tool steels. In recent years, some new low-alloy cold working die steels have been developed in China. The main characteristics of these steels are good processability, low quenching temperature, small heat treatment distortion, good toughness, and appropriate wear resistance.
  • High-carbon high-alloy wear-resistant cold working die steels. High-carbon high-alloy wear cold work die steels commonly used are Crl2, Crl2MoV steels, etc., they are all of the ledeburitic steel, and there are a large number of eutectic carbides in the structure. Many retained austenite after quenching, small deformation, high wear resistance, bearing capacity. It has been widely used in large and medium cold working dies in China.
  • Matrix steel, the main characteristic of the matrix steel is that its carbon content is slightly higher than that of the high speed matrix steel, to increase primary carbonization quality and improve wear resistance. After the quenching of such steel, the amount of surplus carbides is small and uniform, which makes the toughness and cold-heat fatigue resistance of the steel further improved.
Plastic injection mold steel
2.2 New plastic mold steel
In recent years, while introducing foreign plastic mold steel, China has also developed a number of new types of special plastic mold steel to meet the increasing demand of plastic injection mold development. This type of steel can be roughly divided into the following four categories,
  • Pre-hardened plastic mold steel. The United States P20 (3Cr2Mo) and Sweden 718 (3Cr2N iMo) are the most widely used pre-hardened plastic mold steels in the world. They are currently listed in China's alloy tool steel standards (GB/T1299-2000) and have been widely used in china, mold processing quality and life expectancy has improved.
  • Free-cutting pre-hardened steels. In order to improve the machinability of pre-hardened plastic mold steels, pre-hardened steels are often added with free-cutting elements such as S, Pb, and Ca. Recently, some newly developed sulfur-containing and free-cutting pre-hardened plastic mold steels such as 8Cr2S (8Cr2MnWMoVS) steel, SM1 (Y55CrN iMnVS) steel and S-Ca composite free-cutting pre-hardened plastic mold steel 5N iSCa (5CrN iMnVSCa) steel, etc. have been significantly developed in workability.
  • Age-hardening plastic mold steels, as for complex, precise, long-life plastic molds, a series of age-hardening steels have been developed to avoid deformation during quenching heat treatment. The hardness of these steels after solution treatment is very low (generally ≤ HRC30), and they can be easily machined. After processing, the steels are subjected to low-temperature age hardening to obtain the required comprehensive mechanical properties and wear resistance. Due to the small deformation during aging treatment, after the aging treatment, no need for cutting processing, you can get high precision mold products, the service life is higher than pre-hardened plastic mold steel.
  • Cold Extrusion Molding Plastic Mold Steel, Some plastic molds with complex cavities adopt cold extrusion method to directly press out the cavity on the hardened products, eliminating the need for cutting and processing of the cavity, which is one very economical method for mass production molds. After the cavity is processed, various molds requiring good wear resistance and good heart toughness can be manufactured.
  • Hot rolled high strength plastic mold steel, this type of steel doesn’t need tempering treatment, and it can reach pre-hardness after forging and rolling, which is beneficial to energy conservation, production cost reduction, and shortening the production cycle. The type of steel developed in China includes medium-carbon manganese boron-based air-cooled bainite steel, which can be used to make plastic molds and rubber molds.
  • Corrosion-resisting plastic mold steel, When mass production of polyvinyl chloride, fluorinated plastics, flame-retardant plastics and other plastic products, the mold needs to be resistant to corrosion of halogen element gases such as fluorine, chlorine, etc., and this requires chrome plating on the mold surface, or directly using corrosion-resistant steel, usually martensite stainless steel and PH stainless steel, such as: 3Cr13, 4Cr13 (420), 9Cr18 and 0Crl7N i4CuNb and so on.

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