With the improvement of domestic engine emission standards and the demand of high-power engines, the traditional gray cast iron cylinder block can no longer meet the use requirements. Compared with gray iron, vermicular graphite cast iron has a shorter and thicker graphite length, a rounder end, a length-thickness ratio of less than 10 and a rough surface. The rounder end can inhibit the occurrence and propagation of cracks, and the rough surface can limit the separation of graphite. The tensile strength is increased by at least 70%, the elastic modulus is increased by 35%, and the fatigue strength is nearly doubled. At the same time, vermicular cast iron engine can reduce the weight of the engine by 10% – 15%, up to 29.4%. Therefore, vermicular graphite cast iron will become an important choice of engine v-block material because of its excellent mechanical properties and thermal fatigue resistance.
At present, the majority of cylinder block castings are still made of high-strength gray iron. With the improvement of gray iron grade, there are many problems in the products, such as leakage, unstable performance, and increased cost. As early as the 1970s, foreign countries have used vermicular graphite cast iron to manufacture engines. Ford, Opel, BMW, Chrysler and other famous automobile manufacturers have used vermicular graphite cast iron cylinder blocks in automobile engines. Domestic main engine manufacturers such as FAW and CNHTC have begun to produce v-cylinder blocks in large quantities and have been well applied in engines. It is reported that FAW has provided more than 200000 vermicular graphite cast iron cylinder blocks every year since 2020.
The material test is mainly carried out for a non-road diesel engine to find the amount of vermicular agent that can reach the vermicular rate of vermicular graphite cast iron cylinder block under certain S content, and the appropriate amount of alloy to meet the mechanical property requirements of vermicular graphite cast iron cylinder block. At the same time, the vermicular graphite cast iron is trial-produced on the cylinder block in the way of rapid casting.
During the trial production of vermicular cast iron cylinder block, when the sulfur content is about 0.03%, the reasonable adding range of vermicular agent should be 0.55%~0.65%, the tensile strength of vermicular cast iron cylinder block can reach 450 MPa, the vermicular rate of the thick part of the vermicular cast iron cylinder block can reach 90%, and the vermicular rate of the thinner part of the cylinder block can reach 80%. The success of the trial production of the cylinder block provides certain technical support for the mass production of the vermicular graphite cast iron cylinder block.