4Cr5MoSiV1 steel is an air-cooling hardened hot work die steel and one of the most widely used steel grades among all hot work die steels. Compared with 4Cr5MoSiV steel, this steel has higher thermal strength and hardness; it has good toughness, thermal fatigue performance and certain wear resistance under medium temperature conditions, and it can be air quenched under lower austenitizing temperature conditions. The heat treatment deformation is small, the tendency to produce iron oxide scale during air quenching is small, and it can resist the erosion of molten aluminum.
Comply with the standard GB/T1299-2000.
Unified digital code A20502
Grade 4Cr5MoSiV1 Carbon C: 0.32～0.45 Its density is 7.8t/m3; elastic modulus E is 210000MPa.
Heat treatment: (delivery status: Brinell hardness HBW10/3000 (less than or equal to 235)),
Quenching: 790 degrees +-15 degrees preheating, 1000 degrees (salt bath) or 1010 degrees (furnace controlled atmosphere) +-6 degrees heating,
Insulation, air cooling for 5~15 minutes, tempering at 550 degrees +-6 degrees; annealing, hot processing;
It is imported H13 air-hardened hot work die steel from the United States. The long-term performance and use are basically the same as 4Cr5MoSiV steel, but because of its higher vanadium content, the medium temperature (600 degrees) performance is better than 4Cr5MoSiV steel. It is a representative steel grade with a wide range of uses among hot work die steels.
4Cr5MoSiV1 steel is C-Cr-Mo-Si-V steel, which is widely used in the world. At the same time, many scholars from various countries have conducted extensive research on it and are exploring improvements in its chemical composition. Steel’s wide range of applications and excellent properties are mainly determined by its chemical composition. Of course, impurity elements in steel must be reduced. Some data show that when Rm is 1550MPa, the sulfur content of the material is reduced from 0.005% to 0.003%, which will increase the impact toughness by about 13J. It is very obvious that the NADCA 207-2003 standard stipulates that the sulfur content of premium H13 steel should be less than 0.005%, while the sulfur content of superior should be less than 0.003% S and 0.015% P. The composition of 4Cr5MoSiV1 steel is analyzed below. Carbon: The carbon content of American AISI H13, UNS T20813, ASTM (latest version) H13 and FED QQ-T-570 4Cr5MoSiV1 steel is specified as (0.32~0.45)%, which is the highest carbon content range among all 4Cr5MoSiV1 steels. Wide.
The carbon content of German X40CrMoV5-1 and 1.2344 is (0.37~0.43)%, and the carbon content range is narrow. The carbon content of X38CrMoV5-1 in German DIN17350 is (0.36~0.42)%. The carbon content of Japanese SKD 61 is (0.32~0.42)%. The carbon content of 4Cr5MoSiV1 and SM 4Cr5MoSiV1 in my country’s GB/T 1299 and YB/T 094 is (0.32~0.42)% and (0.32~0.45)%, which are the same as SKD61 and AISI H13 respectively. It should be pointed out in particular that the carbon content of H13 steel is specified as (0.37~0.42)% in the North American Die Casting Association NADCA 207-90, 207-97 and 207-2003 standards. The carbon content in the steel determines the matrix hardness of the quenched steel. According to the relationship curve between the carbon content in the steel and the hardness of the quenched steel, we can know that the quenching hardness of H13 steel is around 55HRC. For tool steel, part of the carbon in the steel enters the matrix of the steel to cause solid solution strengthening. Another part of the carbon will combine with the carbide-forming elements in the alloy steel disc springs elements to form alloy carbides. For hot work die steel, in addition to a small amount of residual alloy carbides, it is also required to disperse and precipitate on the quenched martensite matrix during the tempering process to produce a double hardening phenomenon. Therefore, the properties of hot work die steel are determined by the uniform distribution of residual alloy carbon compounds and the structure of tempered martensite.
It can be seen that the C content in steel cannot be too low. 4Cr5MoSiV1 steel containing 5% Cr should have high toughness, so its C content should be maintained at a level that forms a small amount of alloy C compounds. Woodyatt and Krauss pointed out that on the Fe-Cr-C ternary phase diagram at 870°C, the position of H13 steel is better at the junction of the austenite A and (A+M3C+M7C3) three-phase regions. The corresponding C content is about 0.4%. The figure also shows A2 and D2 steels with higher wear resistance by increasing the amount of C or Cr to increase the amount of M7C3 for comparison. It is also important to keep the C content relatively low so that the Ms point of the steel is at a relatively high temperature level (general information on Ms of H13 steel is about 340°C), so that when the steel is quenched to room temperature An alloy C compound structure composed mainly of martensite with a small amount of residual A and uniformly distributed residues is obtained, and a uniform tempered martensite structure is obtained after tempering. Avoid causing excessive residual austenite to transform at the working temperature and affect the working performance or deformation of the workpiece. These small amounts of retained austenite should be completely transformed during the two or three tempering processes after quenching. By the way, it is pointed out here that the martensite structure obtained after quenching H13 steel is lath M + a small amount of flaky M + a small amount of residual A. Domestic scholars have also done some work on the very fine alloy carbides that precipitate on the lath-shaped M after tempering.
As we all know, increasing the carbon content in steel will increase the strength of the steel. For hot work die steel, it will increase the high-temperature strength, hot hardness and wear resistance, but will lead to a decrease in toughness. Scholars clearly proved this point by comparing the performance of various H-shaped steels in the tool steel product manual literature. It is generally believed that the carbon content limit that reduces the plasticity and toughness of steel is 0.4%. For this reason, people are required to follow the following principles when designing steel alloy machining: the carbon content of steel should be reduced as much as possible while maintaining strength. Some data have proposed that when the tensile strength of steel reaches more than 1550MPa, the C content should be 0.3 %-0.4% is appropriate. The strength Rm of H13 steel is 1503.1MPa (at 46HRC) and 1937.5MPa (at 51HRC). The C content in steels such as TQ-1, DIEVAR and ADC3 recommended by FORD and GM companies are 0.39% and 0.38%. The corresponding toughness indicators are listed in Table 1. The reasons can be understood from this. For hot work die steels that require higher strength, the method used is to increase the Mo content or increase the carbon content based on the composition of H13 steel. This will be discussed later. Of course, a slight reduction in toughness and plasticity is possible. expected.
2.2 Chromium: Chromium is the most commonly contained and cheap alloying element in alloy tool steel. In the United States, the Cr content in H-type hot work die steel ranges from 2% to 12%. Among the 37 steel grades of my country’s alloy tool steel (GB/T1299), all except 8CrSi and 9Mn2V contain Cr. Chromium has a beneficial impact on the wear resistance, high temperature strength, hot hardness, toughness and hardenability of steel. At the same time, its dissolution into the matrix will significantly improve the corrosion resistance of steel. H13 steel contains Cr and Si will make the oxide film dense to improve the oxidation resistance of steel. Furthermore, based on the analysis of the effect of Cr on the tempering performance of 0.3C-1Mn steel, adding <6% Cr is beneficial to improving the tempering resistance of the steel, but it does not constitute secondary hardening; when the steel containing Cr >6% is quenched After tempering at 550℃, a secondary hardening effect will occur. People generally choose 5% chromium for hot work steel mold steel.
Part of the chromium in tool steel dissolves into the steel for solid solution strengthening, and the other part combines with carbon and exists in the form of (FeCr)3C, (FeCr)7C3 and M23C6 according to the chromium content, thereby affecting the performance of the steel. In addition, the interaction effect of alloy elements must also be considered. For example, when steel contains chromium, molybdenum and vanadium, Cr can prevent the formation of V4C3 when Cr>3%<sup>[14]</sup> and delay the coherent precipitation of Mo2C. V4C3 and Mo2C are strengthening phases that improve the high-temperature strength and tempering resistance of steel <sup>[14]</sup>. This interaction improves the heat resistance of the steel. Deformation performance. Chromium dissolves into the austenite of the steel to increase the hardenability of the steel. Cr, Mn, Mo, Si and Ni, like Cr, are alloy elements that increase the hardenability of steel. People are accustomed to use the hardenability factor to characterize it. Generally, the existing domestic data “15” only use the data of Grossmann et al. Later, the further work of Moser and Legat “16,22” proposed that the The C content and austenite grain size determine the basic hardenability diameter Dic and the hardenability factor determined by the alloy element content (shown in Figure 3) to calculate the ideal critical diameter Di of alloy steel, which can also be calculated from the following formula Approximate calculation: Di=Dic2.21Mn1.40Si2.13Cr3.275Mo1.47Ni (1) (1) Each alloy element in the formula is expressed in mass percentage. From this formula, people have a fairly clear semi-quantitative understanding of the effects of Cr, Mn, Mo, Si and Ni elements on the hardenability of steel. The effect of Cr on the eutectoid point of steel is roughly similar to that of Mn. When the chromium content is about 5%, the C content of the eutectoid point drops to about 0.5%. In addition, the addition of Si, W, Mo, V, and Ti can significantly reduce the C content of the eutectoid point.
For this reason, we can know that hot work die steel and high-speed steel are both hypereutectoid steels. The decrease in the eutectoid C content will increase the casting alloy parts carbide content in the structure after austenitization and in the final structure. The behavior of alloy C compounds in steel is related to its own stability. In fact, the structure and stability of alloy C compounds are related to the electron deficiency degree of the d electron shell and S electron shell of the corresponding C compound forming element[ 17]. As the degree of electron deficiency decreases, the atomic radius of the metal decreases, the atomic radius ratio rc/rm of carbon and metal elements increases, the alloy C compound changes from an interstitial phase to an interstitial compound, the stability of the C compound weakens, and its corresponding melting temperature and As the dissolution temperature in A decreases, the absolute value of its free energy of formation decreases, and the corresponding hardness value decreases. VC carbide with face-centered cubic lattice has high stability. It begins to dissolve at a temperature of about 900~950°C and begins to dissolve in large quantities above 1100°C (the end temperature of dissolution is 1413°C)[17]It It precipitates during the tempering process at 500~700°C and is not easy to aggregate and grow. It can be used as a strengthening phase in steel. M2C and MC carbides formed by the medium carbide-forming elements W and Mo have close-packed and simple hexagonal lattice. They are less stable and have higher hardness, melting point and dissolution temperature. They can still be used as 500~ The strengthened phase of steel is used in the 650°C range. M23C6 (such as Cr23C6, etc.) has a complex cubic lattice, worse stability, weaker bonding strength, lower melting point and dissolution temperature (dissolved in A at 1090°C), and is only found in a few heat-resistant steels after comprehensive alloying Only with higher stability (such as (CrFeMoW) 23C6, can it be used as a strengthening phase.
M7C3 with a complex hexagonal structure (such as Cr7C3, Fe4Cr3C3 or Fe2Cr5C3) is even worse in stability. Like Fe3C carbides, it is easy to dissolve and precipitate, has a large aggregation and growth rate, and generally cannot be used as a high-temperature strengthening phase&# 91;17]. We can still easily understand the alloy carbide phase in H13 steel from the Fe-Cr-C ternary phase diagram. According to the phase diagrams of the Fe-Cr-C series ternary isothermal sections at 700℃-18~20] and 870℃-9], for steel containing 0.4% C, as the amount of Cr increases (FeCr)3C (M3C) and (CrFe)7C3 (M7C3) type alloy carbides will appear. Note that on the 870°C chart, M23C6 will appear only if the Cr content is greater than 11%).
In addition, according to the vertical section of the Fe-Cr-C ternary system at 5% Cr, the steel containing 0.40% C in the annealed state is α phase (approximately 1% Cr in solid solution) and (CrFe) 7C3 alloy carbides. When heated to above 791°C, austenite A forms and enters the (α+A+M7C3) three-phase region. It enters the (A+M7C3) two-phase region at about 795°C. At about 970°C, (CrFe)7C3 disappears. Enter single-phase A zone. When the matrix contains C < 0.33%, the three-phase region (M7C3 + M23C6 and A) only exists at around 793°C, enters the (A + M7C3) region at 796°C (at 0.30%C), and then remains until the liquid Mutually. The remaining M7C3 in the steel prevents the growth of A grains. Nilson proposed that for alloys with a composition of 1.5% C-13% Cr, unstable (CrFe) 23C6 does not form “20”. Of course, there will be some deviations in the analysis of the Fe-Cr-C ternary system alone, and the influence of adding alloy elements must be considered.
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