Mr. Lin, whom I haven’t been in touch with for many years, reached out to ask: He currently has a part that’s injection-molded from nylon, and the mold contains multiple cores—four of which are relatively thin. He’s currently using H13 mold steel, but the cores keep breaking after producing only a few parts—sometimes one breaks, then another; sometimes they break shortly after being installed, and other times they break after running for a short while. He’s wondering if there’s a mold steel with higher hardness, better toughness, and greater resistance to breakage.
After discussing the matter with him in detail, I learned that he is injection molding nylon. Each mold has multiple interlocking cores, and each core consists of four thin plates. The current H13 steel is unreliable—sometimes it breaks as soon as it’s installed, and one core breaks after another, which is causing a lot of trouble. The cores are machined using slow-wire EDM, which is very expensive. With cores breaking one after another, he’s wasting a lot on machining costs. Constantly replacing them also prevents him from achieving the desired production volume. He’s looking for a mold steel that’s less prone to breaking while also offering higher hardness to improve strength.
During the injection molding process, the thin-plate cores are subjected to compression forces from multiple directions. The mold steel must therefore possess both high toughness and high strength; if the toughness is insufficient, it is prone to brittle fracture, and if the strength is too low, it is prone to tearing.
H13, S136, 2344, 8407, and even 8418 are all medium-carbon steels with a carbon content of 0.38% and a hardness of 50 HRC. and while they offer good toughness, their strength is too low. When subjected to external compressive forces, they are prone to failure by tearing or shearing. Currently, using H13 results in very few successful products—one part breaks here, another there; some fail after only a short time in production. This consistent instability further confirms that H13 simply lacks the necessary strength for thin-walled cores.
With this type of thin-sheet core, whether you use H13, 2344, SKD61, or even S136 and 8418, they are all prone to breaking—there’s no way to solve this issue. I recommend using high-toughness LG mold steel.
LG is a proprietary high-toughness die steel developed by Yuhui Company. LG’s toughness is 8 to 9 times that of DC53, with a hardness of HRC 54–58. It’s so tough that it won’t break even if you bend it by hand.
Mr. Yu took a 60mm-high scrap piece of hard LG material left over from wire cutting, bent it 180°, and it didn’t break. After the force was released, it even sprang back. Mr. Yu said: “LG has both rigidity and toughness. The scraps left over from wire cutting were snapped up by a group of friends to cut small cores on the spot, and they worked very well.”
With a hardness of 54–58 HRC, LG offers significantly higher strength than medium-carbon steels such as H13, S136, and 8407, ensuring high strength. Furthermore, its toughness is 8–9 times that of DC53—so tough that it won’t break even if you bend it with a hammer. When making thin, interlocking cores or connector pins, materials like H13, 8407, 8418, and S136 are prone to breaking—problems you simply can’t solve. Try LG mold steel instead—it won’t break even if you bend it.
LG is a high-toughness mold steel exclusive to Yuhui Mold Steel. However, due to its high market visibility, strong sales, and customers specifically requesting it, it has attracted widespread imitation across the industry. When purchasing, please pay close attention to the source of the material.
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Wu Dejian’s tool steel, the chief of staff of the user, bought everything he had used.