Microalloyed non quenched and tempered steel was developed in the 1970s with the international energy shortage. It is a special steel that can achieve the mechanical properties of quenched and tempered steel and fully meet the service performance of parts by adding trace alloying elements (V, Ti, Nb, N, Mn, Si, s, Al, etc.) to carbon steel and eliminating the quenching and tempering treatment process through temperature controlled rolling (forging), temperature controlled cooling and other strengthening and toughening methods. This kind of steel has been successfully developed by Germany thyssente Steel Company since 1972. The representative steel is 49mnvs3. Due to its remarkable energy-saving effect, it can simplify the production process, avoid cracks and deformation of general steel parts during quenching, and has good social and economic benefits. It is known as “green steel”. Therefore, non quenched and tempered steel is widely valued in the machinery (mainly automobile and tractor) manufacturing industry, and is used to manufacture automobile connecting rod, crankshaft, camshaft, gear and other parts.
At present, non quenched and tempered steel is developing rapidly, and a variety of steel grades suitable for different purposes have been developed at home and abroad. Non quenched and tempered steel can be divided into: non quenched and tempered steel for forging, free cutting non quenched and tempered steel, cold work strengthening non quenched and tempered steel; According to the structure characteristics, it can be divided into ferrite pearlite type non quenched and tempered steel, intragranular ferrite type non quenched and tempered steel, bainitic type non quenched and tempered steel and martensitic type non quenched and tempered steel. It is also a ferritic pearlitic non quenched and tempered steel used to manufacture automobile connecting rods.
Microalloyed non quenched and tempered steel for automobile connecting rod was used earlier abroad. For example, the German Volkswagen plant uses non quenched and tempered steel 27mnsivs6 to manufacture car connecting rods with an annual output of 2.5 million pieces, reducing the total cost by about 10%; At Volvo automobile factory in Sweden, at the end of 1980s, more than 50% of forgings were made of non quenched and tempered steel, including crankshaft, connecting rod, steering knuckle, gear, hook and other parts; At present, 75% of automobile connecting rods forged in Japan have been made of non quenched and tempered steel. For example, s43cv, s45cv and s50cv of Sumitomo Metal are used for automobile connecting rod manufacturing; The development of non quenched and tempered steel in the United States and Russia started late, but gradually began to pay attention to it in recent years, with rapid development.
China has also included the research and development of non quenched and tempered steel in the “Seventh Five Year Plan” and achieved results. By the eighth five year plan, it has been gradually popularized and applied in some manufacturers. In the process of developing microalloyed non quenched and tempered steels, China has successively developed a variety of non quenched and tempered steels, such as F40MnV, f35mnvn, yf35v and 35mnvnbs, which are used to make connecting rods for various automotive engines and air compressors. For example, since 1985, FAW has successively applied non quenched and tempered yf35v instead of quenched and tempered 35 steel to manufacture air compressor connecting rod; The connecting rod of CA15 engine is made of non quenched and tempered yf35mnv instead of quenched and tempered 40 steel; The connecting rod of CA6102 engine is made of non quenched and tempered yf35mnv steel instead of quenched and tempered 55 steel; Since 1993, the non quenched and tempered steel automobile connecting rod has basically replaced the quenched and tempered steel connecting rod, and its annual consumption has reached 2500t. The connecting rod of EQ6100 engine of second automobile was changed from 40MnB to f35mnvn, and 400000 vehicles were loaded; The connecting rod of Cummins 6BT engine of the company is made of F40MnV steel. By June, 1998, more than 9000 vehicles had been loaded, and the same material was used to manufacture EQ6102 engine connecting rod. NAC uses non quenched and tempered f35mnvn steel instead of quenched and tempered 40Cr and 45 steel to manufacture D433 engine connecting rod and nj70 engine connecting rod. Volkswagen in Shanghai uses 30mn2vs non quenched and tempered steel to make connecting rod; Tianjin Xiali Dafa tj370q and Tj376Q engine connecting rods are made of imported non quenched and tempered steel s43cvs1; Guangzhou Peugeot introduced 45m5ua2 steel from France to make automobile connecting rods. The factory also cooperated with the iron and Steel Research Institute and Dalian steel plant to carry out the test of using yf45mnv steel to replace 45m5ua2 steel to process Peugeot car connecting rods; Jiangling Automobile Co., Ltd. has started the application research of non quenched and tempered steel auto parts since 1995. So far, it has used non quenched and tempered steel to produce 40000 4J series diesel engine crankshafts and 120000 connecting rods; Some achievements have been made in the localization application, and the economic benefits are remarkable. The table shows the properties of several domestic non quenched and tempered steel automobile connecting rods.
| Steel grade | Use | Strength σb(MPa) | αk(J/cm2） | HB |
| 35MnVS | CA6102 connecting rod | 930 | 120 | 240 |
| S43CVS1 | TJ370Q connecting rod | 900 | 56 | 240 |
| 45M5UA2 | Peugeot connecting rod | 800 | 80 | 217-225 |
| YF45MnV | Peugeot connecting rod | 825 | 85 | 240 |