Non-national standard plastic mold steel sold in the domestic market
Non-GBP plastic mold steel circulating in the domestic market refers to steel products that fail to meet national standards (such as GB/T 1299-2014 “Tool and Die Steel”). These products exhibit significant fluctuations in composition, mechanical properties, and processing performance, posing numerous risks to injection mold manufacturing. This type of steel is often produced by small steel companies. To reduce costs, they often reduce the addition of alloying elements (such as chromium, nickel, and molybdenum) or use inferior scrap steel as raw material. This results in insufficient steel purity, numerous non-metallic impurities, and pores. For example, one batch of non-GBP P20 mold steel had a chromium content of only 0.8%, far below the national standard requirement of 1.4%-2.0%. This significantly reduced its hardenability and wear resistance. Molds made with this steel exhibited severe wear on the cavity surface after only 10,000 cycles, rendering them unusable.
While the appearance of non-GBS plastic mold steel may differ slightly from GBS steel, the inherent quality differs significantly. The carbon content of non-GBS steel typically fluctuates by more than ±0.05%, while GBS steel’s carbon content tolerance is limited to ±0.02%. Excessively high carbon content increases the steel’s brittleness, making it prone to cracking during mold processing; too low a carbon content results in insufficient hardness, shortening the mold’s lifespan. Furthermore, non-GBS steel often contains excessive sulfur and phosphorus. Excessive sulfur content impairs the steel’s hot working properties, making it prone to cracking during forging; excessive phosphorus content increases the steel’s cold brittleness and reduces the mold’s impact resistance. A testing agency examined 10 batches of non-GBS 718H mold steel on the market and found that six contained sulfur contents exceeding 0.03%, with the highest reaching 0.08%, far exceeding the GBS upper limit of 0.015%.
The mechanical properties of non-GBS plastic mold steel are extremely unstable, creating significant challenges in mold design and use. GBS plastic mold steel specifications for hardness, tensile strength, and impact toughness are clearly defined, with relatively narrow fluctuations. For example, the hardness of P20 mold steel is controlled between 28-32 HRC , while the hardness of non-GBS steel can fluctuate between 20-35 HRC, with hardness variations of up to 10 HRC within the same batch. This instability in properties makes molds prone to deformation or cracking during heat treatment. For example, a mold manufacturer fabricated a cavity using non-GBS NAK80 mold steel, which developed multiple cracks after quenching. Analysis revealed that the steel’s impact toughness was only 15 J/cm², far below the GBS requirement of 30 J/cm². Furthermore, non-GBS steel exhibits poor machinability, prone to tool sticking during milling and surface burns during grinding. This results in excessive mold surface roughness, impacting the appearance quality of the plastic part.
Using non-GBS plastic mold steel significantly increases mold production costs and risks. While non-GBS steel is typically 10%-30% cheaper than GBS steel, its inconsistent performance leads to a high mold scrap rate, which in turn increases production costs. For example, a small appliance company, to reduce costs, used non-GBS P20 mold steel for its housing molds. This saved 20,000 yuan in initial procurement costs, but after 5,000 cycles, the mold became severely worn, necessitating a remake at an additional cost of 80,000 yuan and impacting production schedules. Furthermore, the quality of plastic parts produced using molds made with non-GBS steel is difficult to guarantee. Dimensional instability and surface defects are common, potentially leading to customer complaints and order losses. An automotive parts supplier suffered a batch of product returns due to dimensional deviations in plastic clips produced using molds made with non-GBS steel, resulting in direct losses of 500,000 yuan.
It’s imperative to regulate the domestic plastic mold steel market and crack down on non-national standard products. Relevant departments should strengthen market oversight, increase penalties for companies producing and selling non-national standard steel, and establish a steel quality traceability system to ensure that every batch of steel can be traced back to the manufacturer. Mold companies should also enhance quality awareness, establish strict raw material inspection procedures, conduct composition analysis, mechanical property testing, and flaw detection on purchased steel, and eliminate the use of non-national standard steel. Furthermore, industry associations should strengthen publicity and guidance, promote the use of national standard steel, organize technical training for companies, and raise awareness of the hazards of non-national standard steel. Only by regulating and controlling every aspect of production, sales, and use can we curb the circulation of non-national standard plastic mold steel and promote the healthy development of the mold industry.
