It can be seen that the main differences between the quenched and tempered steel connecting rod and the non quenched and tempered steel connecting rod are as follows:
1) Microalloyed non quenched and tempered steel is to add V, Nb, Ti, B, N and other strengthening and refining ferrite elements to carbon structural steel, control the cooling rate after steel rolling or forging, and microalloyed carbides and carbon nitrogen compounds are highly dispersed and precipitated in the controlled cooling process, which plays the role of precipitation strengthening and fine grain strengthening. It can achieve the comprehensive mechanical property index of quenched and tempered steel, omit the quenching and tempering process, and save 2500-3500kw/h electricity per ton of steel. It is an intermediate chemical process, Save electricity and time, reduce costs and increase benefits; Non quenched and tempered steel has better cold cutting performance than quenched and tempered steel, and the tool life is doubled.
2) As microalloyed non quenched and tempered steel does not need the second stage of heat treatment process, it has high social and economic benefits. The economic benefits of forging connecting rod with microalloyed non quenched and tempered steel include canceling the quenching and tempering treatment of forgings, reducing the scrap rate, simplifying the process, shortening the production cycle and reducing the production cost. According to rough calculation, the cost of a single connecting rod can be reduced by 8-11 yuan. Its social benefits mainly include reducing environmental pollution, improving working conditions, and eliminating the need for investment in new heat treatment plants.
3) The forging process of non quenched and tempered steel connecting rod is to control the forging heating temperature at 1200 ℃± 10 ℃ and the final forging temperature at 950 ℃ -1000 ℃. After forging, a single piece of air blowing cooling is adopted. When it is cooled to below 500 ℃, it can be heap cooled. The results of metallography and properties test of connecting rod show that the size effect of non quenched and tempered steel is small, which is consistent with the properties measured by small samples. The overall tensile test of connecting rod shows that the strength of non quenched and tempered steel connecting rod is greater than that of quenched and tempered steel connecting rod, and the air cooling strength of V-Ti steel is close to 42CrMo, about 40kN. The cutting performance of non quenched and tempered steel is better than that of quenched and tempered steel, and its machined surface roughness is equivalent to that of quenched and tempered steel.
4) The forging process of microalloyed non quenched and tempered steel is different from that of quenched and tempered steel. For Quenched and tempered steel, forging is only a means of preliminary forming of parts, and it is not required to ensure the mechanical properties, which are affected by the chemical composition of the steel and subsequent heat treatment; The forging process of microalloyed non quenched and tempered steel is not only a means of forging, but also an important process for parts to achieve mechanical properties. In addition to chemical composition, forging process parameters will have an important impact on the properties of non quenched and tempered steel. The effects of a series of process parameters such as heating temperature, final forging temperature and cooling rate after forging on the microstructure and properties of non quenched and tempered steel are discussed, which is very important for the application of microalloyed non quenched and tempered steel for hot forging.