1.Materials and technical requirements of quenched and tempered steel connecting rod
Jb3764-84 stipulates that the following materials shall be used for common connecting rod materials: 40, 50 (selected carbon content), 45MN, 40Cr, 35CrMo, 42CrMo. Jb/nq64.1 stipulates that the connecting rod shall be 45 (the selected carbon content is 0.42 ω%- zero point four seven ω%) Or 10Cr, 35CrMo and other materials.
Common materials and technical requirements of quenched and tempered steel connecting rod are listed in the table.
| Material Science | Heat treatment | JB/NQ 64.1 hardness | JB3764 hardness |
| 45 | Conditioning | 217-293 | 217-293 |
| 40Cr | Conditioning | 223-280 | 217-293 |
| 35CrMo | Conditioning | 250-320 | 217-293 |
| 40MnB | Conditioning | 229-269 | 229-269 |
| 55 | Quenching and tempering by forging waste heat | 229-269 | 229-269 |
| 18Cr2Ni4W | Conditioning | 321-363 | 321-363 |
The microstructure of the rod after quenching and tempering treatment should be uniform fine grain sorbite. No sheet ferrite and non-metallic inclusions are allowed, and the depth of decarburization layer on the I-shaped surface shall not be greater than 0.01mm.
JD / NQ 64.1 stipulates that the mechanical properties of connecting rod after heat treatment are: tensile strength σ b≥735MPa； yield strength σ s≥539MPa； impact toughness α k≥58.8J/cm2。
2.Non quenched and tempered steel
The use of ferritic pearlitic non quenched and tempered steel to manufacture automobile connecting rods can eliminate the quenching and tempering process and improve the cutting performance. Compared with quenched and tempered steel, it has the advantages of simplifying the process, improving the material utilization, improving the quality of parts, reducing energy consumption and low manufacturing cost. Therefore, good economic and social benefits can be achieved. The chemical composition of this kind of steel is characterized by appropriately increasing the silicon Manganese content (silicon content is generally ω (SI) 0.2%-0.5%, manganese content is generally ω (MN) less than 1.5%) and adding trace vanadium, niobium, titanium and other elements to improve the strength and toughness of the steel through interphase precipitation, grain refinement and promoting the formation of intragranular ferrite (IGF) structure. In addition, in order to improve the machinability of steel, 0.035%-0.08% sulfur (mass fraction) is usually added. Since the Seventh Five Year Plan, China has made certain achievements in the development and localization of non quenched and tempered steel.
In order to ensure the stability of the performance and quality of non quenched and tempered steel parts under the condition of mass continuous production, it is required not only to strictly control the chemical composition (including the control of residual elements) and metallurgical quality (such as the purity and grain size of the steel), but also to strictly control the heating temperature, final forging temperature and other hot processing parameters of the forging stock and the controlled cooling after forging, so as to obtain the required pearlite ferrite structure and properties.