Integrated small-scale gold steel integrated steel integration

The main driving force for converting quenched and tempered steel into air-cooled non-quenched and tempered steel is to reduce costs. The total manufacturing cost can be reduced by following all or part of the following process routes: eliminating the need for heat treatment; no need for correction; shortening order-to-delivery time; reducing rework.

The advantages of the non-quenched and tempered steel parts in terms of performance over ordinary heat-treated quenched and tempered steels are: reduced deformation; reduced mechanical performance deviations; uniform performance across the entire section; improved machining performance. In the early 1970s, Germany developed the forged microalloyed medium-carbon steel 49MnVS3, which was mainly used as crankshaft for automobile engines. In the 1980s, non-quenched and tempered steels developed rapidly. Crankshaft with the traditional quenched and tempered steel CK45 (equivalent to SAE1045, C0142% 0145%, Mn015%018%, ie 45 steel) need to be quenched, and high energy consumption, quenching during quenching, the risk of deformation, but a large degree; When the non-tempered steel 49MnVS3 is used (C0147%, Mn0175%, V0110%, S0105%), the cost for the heat treatment equipment and related heat treatment process is not required, and the risk of cracks and deformation of the workpiece is eliminated.

The Japanese auto industry also accepted the steel and developed it in the late 1970s. By the mid-1980s, 75% of Japanese forged connecting rods and 55% of forged crankshafts were made of microalloyed non-quenched and tempered steels; at that time, 30% 35% of European forged connecting rods, crankshafts and front axle beams were made of non-quenched and tempered steel. Manufacturing, then the scope of non-tempered applications has expanded to the United States.

The Vanard series of non-quenched and tempered steel jointly developed by the UK Engineering Steel Company and Swedish laboratories in the 1970s covers a strength range of 7001000 MPa and is mainly used to make crankshafts, connecting rods, axles and hubs. 1 is the comparison of mechanical properties of Vanard non-tempered and tempered steel, tempered alloy steel and SG ductile iron. The economics of non-quenched and tempered steels have been demonstrated in applications. Rover Group claims that the use of microalloyed non-quenched and tempered steel in the crankshafts of Series A 1131 engines has saved 500,000 pounds per year at 1982 prices. 90% of the crankshafts of Nissan Motor Co. in Japan have been manufactured with non-quenched and tempered steel. The use of non-quenched and tempered steel for the manufacture of front wheel hubs has reduced the production cost by 45%. The air-cooled ferrite 2 pearlite is not adjusted. Through the proper selection of carbon, manganese, silicon and vanadium content in steel, the strength of air-cooled ferrite 2 pearlitic non-quenched and tempered steel can reach 7501150 MPa, which is mainly used to manufacture crankshafts, connecting rods, axles and wheels. . Although ferrite 2 pearlitic non-quenched and tempered steels have lower impact toughness than quenched and tempered steels of equal strength, they can still meet the requirements of various forging products, and their impact toughness is higher than that of cast iron. In order to improve the toughness, one method is to add a trace amount of titanium to form titanium nitride to refine the grains; another method is to form a large amount of intragranular ferrite in the prior austenite grains even though the austenite structure is coarse. Core, produces fine ferrite 2 pearlite structure. VC and VN are used as the cores for forming the intragranular ferrite, and the intragranular ferritic steel has a finer structure than the ferrite 2 pearlite of the titanium microalloyed steel.

Strength and toughness The German DIN 49 MnVS has an ultimate strength limit of more than 850 MPa in the air-cooled state, which is achieved by high volume percentage of relative/dilutive pearlite (low average carbon content) and in ferrite and pearlite ferrite (eutectoid The precipitation of V(C,N) in ferrite is enhanced to replace the Mn and Mn2Cr quenched and tempered steels. The strength of the part can be increased by increasing the cooling rate after the steel has been forged, since the increase in cooling rate (from natural cooling to air cooling) can result in a large amount of fine pearlite and smaller V(C,N) precipitates. It should be noted that the addition of 011% V can effectively shift the pearlite to bainite transformation to a faster cooling rate on a continuous cooling transformation (CCT) map, thereby reducing the latter transition to a normal process later. .

The general air-cooled non-quenched and tempered steel is based on carbon steel with a small amount of Nb, V, Ti or Mo added. (In practice, it is shown that lowering the carbon content and increasing the Mn or Cr content can improve the toughness of non-quenched and tempered steels and reduce the carbon content. The strength loss of the steel is greater, but the impact toughness is significantly improved, mainly due to the reduction of the amount of pearlite in the steel, and the Mn content in the steel is appropriately increased, when the Mn content increases from 0185% to 1115% 1130%, then The toughness of the non-quenched and tempered steel at the same strength increased by 30JPcm2, which was comparable to that of tempered carbon steel.

Austenite grains are usually refined by adding a small amount of titanium so as to form very fine proeutectoid ferrite grains and pearlite, thereby improving the toughness of the steel. Although reducing rolling and forging temperatures are also beneficial to improving the toughness of non-quenched and tempered steels, they will increase the energy consumption for forging and rolling and reduce the production capacity of the rolling and rolling mills. The strength and toughness of non-quenched and tempered steel generally increase with the increase of the cooling rate after hot working, and the toughness increases more significantly.

However, if the cooling rate is higher than 65ePmin, although the finer grains can be obtained, the toughness is significantly reduced. In order to obtain fine grains, after forging, the temperature should be rapidly cooled above 700e, and then slowly cooled to below 600e. The 600700e interval is equivalent to the phase transition temperature. The cooling rate affects the morphology of the transformed ferrite and pearlite, and the relative phases of the two phases. Quantity has an important influence. If the non-quenched and tempered steel after heating is cooled to about 800e and then deformed by appropriate amount of heat, or the final processing temperature is reduced to 800e or less, the toughness of the non-quenched and tempered steel can be significantly improved.

The development of high toughness non-quenched and tempered steel ferrite 2 pearlite non-quenched and tempered steel is usually medium carbon steel, adding trace elements such as vanadium, by increasing the amount of pearlite and vanadium carbide precipitation strengthening to increase the strength of the steel, such as composition and The thermal processing technology is reasonable and can completely reach the strength level of 9001000 MPa for tempered and tempered steel. However, the non-quenched and tempered steel is a ferrite 2 pearlite structure, its toughness is generally lower than the tempered sorbite structure of the quenched and tempered steel, together with precipitation strengthening of the co-precipitate, it further reduces the toughness of the steel. The application of non-quenched and tempered steels to components subject to impact loading is limited. In order to overcome the lack of toughness of non-quenched and tempered steel, the development of high toughness non-quenched and tempered steel was promoted.

The toughness of quenched and tempered steel is mainly affected by chemical composition and heat treatment process. In addition to the influence of chemical composition, the toughness of non-tempered steel is affected by the heating temperature, heat processing and cooling rate. The amount of strain required for hot working affects the precipitation of carbides, which in turn affects the recrystallization process. With a large amount of strain, the gestation period and completion period of the precipitate are shorter. Microalloyed non-quenched and tempered steels refine the grain size of ferrite and reduce the thickness and spacing of Fe3C in pearlite, which can increase the strength of steel and increase the toughness of steel. Therefore, for non-quenched and tempered steel, in addition to reasonable selection and precise control of the composition of the steel, the strict forging and rolling process is a necessary condition for the steel to obtain high strength and toughness.

The influence of chemical composition on toughness and toughness of non-quenched and tempered steels The effects of chemical composition on the strength and toughness of non-quenched and tempered steels can be summarized as follows: (1) Elements that increase strength and reduce toughness include C, N, V, Nb, and P. ( 2) Mn, Cr, Cu + Ni, and Mo are the elements that increase the strength while improving the toughness. In the 1980s, medium-carbon manganese chromium non-quenched and tempered steels were developed: 0145C21Mn2015Cr2011V, which is called IVA1000. Its tensile strength and Fatigue strength is better than that of quenched and tempered steel, and impact toughness can be improved by hot working and low temperature normalizing. (3) Solid Al has little effect on strength and toughness, but existence in the form of AlN can refine the grain and improve the toughness of the steel. (4) The role of Ti in non-quenched and tempered steel is to reduce strength and improve toughness. When Mn content is 110% 215%, adding 0101% 0105% Ti can effectively improve the toughness of the steel.

Using the regression analysis method, the effect of each element on the V2 notch impact value and hardness can be obtained. In order to obtain high quality and stable performance of non-quenched and tempered steel, some use ultra-pure steel smelting technology, so that the chemical composition control in a very narrow range, such as non-quenched and tempered steel crankshaft, the required component fluctuation range: C0103%, Mn0110%, V0103%, while limiting the Cr, Mo content.

Effect of grain refinement on the toughness of non-quenched and tempered steels In addition to the above-mentioned addition of appropriate Ti, Al, N to refine the austenite grains of the steel, the machining process is also an important factor affecting the austenite grains. The processing temperature is high, the recrystallization speed is fast, the austenite grains are large, the amount of pearlite in the steel after cooling increases, the strength increases, and the toughness decreases. When the processing temperature is low, precipitation is induced by deformation, the recrystallization core is increased, the driving force for grain growth after recrystallization is small, the grain size is refined, and the strength of the steel is not greatly changed, but the toughness can be greatly improved. Studies have shown that as the temperature of the finish rolling decreases, the impact value increases. At the same temperature, the amount of processing increases, and the strength and toughness can be increased at the same time.

The cooling rate after thermal processing also affects the grain size of the steel. For example, the thermal deformation is above the transformation temperature of the pearlite. After the deformation, the cooling rate of the larger steel or forging part should be accelerated to prevent grain growth. If the cooling rate is too slow, the particles of the precipitates will become coarser and the toughness will not be improved. For small-size steel or forgings, excessive cooling after machining must be avoided. Otherwise, residual stresses may occur, and bainite structure may be formed, which may affect the room temperature toughness of the steel.

The formation of intragranular ferrite improves the toughness of non-quenched and tempered steels. Although the addition of titanium to form dispersed TiN particles can effectively prevent austenite grain coarsening, compared with quenched and tempered quenched and tempered steel, non-quenched Ti containing The toughness of quenched and tempered steel is still insufficient. Because in this case, when the steel is heated to 1250e, it is difficult to keep the austenite grain of the steel thinner than the 7th grade.

In the cooling process of non-quenched and tempered steel after hot working, ferrite first nucleates along the austenite grain boundary, and the remaining austenite transforms into a pearlite cluster. This pearlite, which is surrounded by a ferrite mesh, has poor toughness.

On the other hand, if a large number of ferrite nuclei can be produced in the prior austenite grains, a fine ferrite 2 pearlite structure can be obtained even if the austenite grains are coarse. VC and VN can be used as the core of intragranular ferrite, and vanadium and nitrogen must be added simultaneously in order to generate intragranular ferrite. It was found that when the sulfur content in the steel increases, the amount of intragranular ferrite increases, which can significantly increase the toughness of hot forging materials.

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(1) Since the 1970s, due to the advantages of non-tempered steel, such as energy conservation, reduction of workpiece deformation and cracking, and reduction of environmental pollution, it has received widespread attention from major industrial countries in the world, especially the improvement of the toughness of non-quenched and tempered steels. The adoption of technology has improved the series of non-quenched and tempered steel products, expanded the use of non-quenched and tempered steel, and has been used on a large scale in machinery manufacturing, especially in the automotive industry. (2) China's non-quenched and tempered steels have made progress in application, standard level and stability of physical quality, but high-performance non-quenched and tempered steels should be developed.