Carbon quenched and tempered steel and alloy quenched and tempered steel are traditional connecting rod steels. Generally, carbon quenched and tempered steel is used for low-power engines, and alloy quenched and tempered steel is used for high-power engines.
The quenched and tempered hardness of carbon steel is generally 229~269HBS, and that of alloy steel can reach 300HBS, but the maximum is not more than 330HBS. The tensile strength of carbon steel can reach above 800MPa, and the impact toughness is above 60J/cm2. The tensile strength of alloy quenched and tempered steel can reach above 900MPa, and the impact toughness is above 80J/cm2. Quenched and tempered steel connecting rods are used in high-power diesel engines that require connecting rods with high strength and toughness.
2. Non-tempered steel
Non-quenched and tempered steel is strengthened by adding microalloyed elements such as vanadium, titanium and niobium on the basis of medium carbon steel, and dispersing carbon and nitrogen compounds in the matrix structure by controlling the cooling rate during rolling or forging. Heat treatment is omitted after forging of non-quenched and tempered steel. According to its strength and toughness, it can be divided into four categories, among which basic type and high strength type are suitable for engine connecting rods.
The non-quenched and tempered steels studied in China are mainly vanadium series, manganese vanadium series and manganese vanadium nitrogen series. Each series has developed steel grades with free-cutting elements. The steels used for engine connecting rods are 35 mnv, 35MnVN, 40MnV and 48MnV. , the strength is below 900MPa. The fatigue test shows that the fatigue strength of non-quenched and tempered steel connecting rod is equivalent to that of quenched and tempered steel of the same brand.
With the requirement of engine lightweight and the improvement of connecting rod design stress, the application of steel grades of C70S6 series will be more and more. On the basis of this steel grade, Germany has developed a steel grade with higher strength.
3, powder metallurgy connecting rod
Britain, Switzerland and Germany cooperate, and the selected ingredient is Pe? The engine connecting rod was trial-produced with 1.5Cr-0.5C alloy powder, and passed the fatigue performance test of parts in tension and compression and the engine bench test. Germany also uses Fe? (0.35-0.45)C？ (0.3-0.4)Mn？ (0. 1-0.25)Cr-(0.2-0.3)Ni powder metallurgy connecting rod for Porsche 928 engine.
By forging, the strength and toughness of powder metallurgy connecting rod are improved, the density of powder blank is improved, and alloying elements are added, so that the powder forging connecting rod has enough hardenability and reaches the level of forged steel connecting rod. Fe-0.5C-2.0Cu-0.09S and Pe-0.55C made in Japan? The density of 2.0Cu-0.2S powder sintered forging connecting rod reaches 7.82z/cm3 (99.8% of theoretical density). The test shows that reaching the fatigue performance of forged steel connecting rod can save 40% of materials, reduce the cost 10% and save 50% of energy. The density of titanium alloy connecting rod metal titanium is 4.5g/cm3, which is only 58% of steel. The tensile strength of titanium is low, only 250-300MPa. In production, alloying elements are added to strengthen the matrix, usually aluminum and alum. From the test results, the fatigue strength of titanium alloy with yield strength below 850MPa is directly proportional to the yield strength;
However, the fatigue strength and yield strength of titanium alloy with yield strength above 850MPa become the limit state. Free-cutting elements such as sulfur and rare earth are usually added to titanium alloy, but when the yield strength is above 850MPa, the fatigue performance of the alloy under high load will be reduced. Japan uses Ti-3A 1-2V titanium alloy to produce connecting rods, and the tensile strength can be
The yield strength can reach 800MPa and 600MPa, which is equivalent to the strength level of 45 quenched and tempered steel.
The mass of titanium alloy connecting rod can be reduced by 30% compared with steel connecting rod, which greatly reduces the reciprocating inertia force of connecting rod. The rotating speed of titanium alloy connecting rod engine is 700r/m in higher than that of steel connecting rod engine, which greatly improves the output power, significantly reduces the engine noise and is beneficial to environmental protection.