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CN-122013051-A - 33CrNiMo steel and heat treatment process thereof

CN122013051ACN 122013051 ACN122013051 ACN 122013051ACN-122013051-A

Abstract

The invention relates to the technical field of metal materials, in particular to 33CrNiMo steel and a heat treatment process thereof. The 33CrNiMo steel is designed by specific components, adopts a complete heat treatment process comprising 650 ℃ preheating, 880 ℃ long-time normalizing, 890 ℃ quenching and 575 ℃ high-temperature tempering, and realizes grain ultra-refinement, full martensitic structure and nano precipitation strengthening by controlling the residue and secondary precipitation of AlN and V (C, N) precipitation phases. The invention provides 33CrNiMo steel and a heat treatment process thereof, and aims to solve the problems of coarse grains and insufficient strength and toughness matching of a shell of a traction box of a traditional 33CrNiMo steel coal mining machine.

Inventors

  • LI YANG
  • MENG FANXI
  • WEI JIANHUA
  • SU HUI
  • Xie Kangqing
  • LIU PEIFANG
  • SONG MINGJUAN
  • DU XUESHAN

Assignees

  • 郑州煤机格林材料科技有限公司

Dates

Publication Date
20260512
Application Date
20260327

Claims (8)

  1. 1. A33 CrNiMo steel is characterized by comprising the following chemical components, by mass, 0.29-0.37% of carbon, 0.30-0.60% of silicon, 0.60-1.00% of manganese, 0.45-0.65% of chromium, 0.70-0.90% of nickel, 0.22-0.27% of molybdenum, not more than 0.50% of copper, not more than 0.10% of vanadium, not more than 0.40% of aluminum, not more than 0.015% of sulfur, not more than 0.020% of phosphorus and the balance of iron.
  2. 2. A heat treatment process for 33CrNiMo steel as claimed in claim 1, characterized by comprising the steps of: Placing the 33CrNiMo steel casting in a resistance furnace, heating to 650 ℃ and preserving heat for 1-2 hours, wherein the temperature fluctuation range is +/-5 ℃, then continuously heating to 880 ℃ and preserving heat for 12-13 hours, wherein the temperature fluctuation range is +/-10 ℃, and completing normalizing heat treatment; closing a power supply after heat preservation is finished, opening a furnace door for air cooling, and finishing normalizing cooling treatment; placing the workpiece subjected to normalizing treatment in a resistance furnace again, heating to 650 ℃, preserving heat for 1-2 hours, wherein the temperature fluctuation range is +/-5 ℃, and then heating to 890 ℃, preserving heat for 3.0-4.5 hours, wherein the temperature fluctuation range is +/-5 ℃; Rapidly transferring the heat-preserving workpiece to a quenching medium with the temperature not higher than 45 ℃ to finish the medium quenching treatment; And (3) placing the quenched workpiece in a resistance furnace, heating to 575 ℃, preserving heat for 6-7 hours, enabling the temperature fluctuation range to be +/-10 ℃, and then cooling or air-cooling to room temperature along with the furnace to finish high-temperature tempering treatment.
  3. 3. The heat treatment process according to claim 2, wherein during the normalizing at 880 ℃ for 12 hours, the austenitic structure is sufficiently homogenized while retaining a residual ratio of aluminum nitride to vanadium carbonitride precipitated phases of greater than 60%.
  4. 4. The heat treatment process according to claim 2, wherein during the quenching heat treatment at 890 ℃ for 3.0 hours, the austenitizing temperature is lower than the vanadium carbide complete dissolution temperature, so that part of the vanadium carbide particles are undissolved, the volume fraction thereof is 0.05% to 0.10%, and the average size thereof is 10 to 20 nm.
  5. 5. The heat treatment process according to claim 2, wherein the quenching time of the medium is 30 to 50 minutes, the workpiece is taken out and air-cooled to room temperature after the surface temperature of the workpiece is reduced to 50 to 90 ℃, the flow rate of the medium is 1.0 to 1.5m/s, and the average cooling rate of the workpiece in the medium is 50 to 55 ℃.
  6. 6. The heat treatment process according to claim 2, wherein after the medium quenching treatment, the martensite content in the work piece structure exceeds 99%, the retained austenite content is less than 1%, and the average width of the lath martensite bundles is 0.12 to 0.15 μm.
  7. 7. The heat treatment process according to claim 2, wherein the dispersed nano-sized vanadium carbide particles are precipitated during a high temperature tempering treatment at a temperature of 575 ℃ for 6.0 hours.
  8. 8. The heat treatment process according to claim 2, wherein aluminum element is segregated to the prior austenite grain boundaries during tempering, grain boundary segregation of phosphorus and sulfur elements is suppressed, and spheroidization of residual carbide is promoted.

Description

33CrNiMo steel and heat treatment process thereof Technical Field The invention relates to the technical field of metal materials, in particular to 33CrNiMo steel and a heat treatment process thereof. Background The traction box shell of the coal mining machine is used as a core bearing component in high-end heavy mining equipment, the service environment is extremely harsh, and long-term stable operation under high load, strong impact and complex alternating stress conditions is required. For this reason, the components are usually manufactured by large cast steel with complex structure, and extremely high requirements are imposed on the comprehensive mechanical properties (especially high strength, high toughness and dimensional stability) of the materials. 33CrNiMo alloy steel is the preferred base material for the key castings due to the excellent hardenability, good welding performance and moderate cost. However, to fully exert the potential of the steel grade, not only is the reasonable chemical composition design relied on, but also whether the heat treatment process can accurately regulate and control the microstructure evolution path is more critical, so that the cooperative optimization of grain ultra-refinement, phase-change structure homogenization and precipitation strengthening mechanism is realized. In the research of the performance of the steel for the high-end coal mining equipment, how to effectively activate the multi-scale strengthening effect of the micro-alloy elements through the design of a heat treatment system is a scientific difficulty of restricting the performance breakthrough of metallurgy. For alloy steel heat treatment systems under similar working conditions, a certain technical deposition is formed, but the microstructure control is still limited. For example, the heat treatment system of the patent with publication number CN108842042B adopts stepped heat preservation to promote the precipitation of carbide or pearlite in austenite grain boundaries, and then utilizes the corrosion resistant grain boundaries of the structure to display after quenching, and further utilizes the grain boundary morphology to represent the uniformity of austenite grains under similar working conditions. The heat treatment logic is not aimed at metallurgy of microalloy elements in the high-temperature phase transformation process, namely, dynamic behaviors such as a precipitated phase retention strategy are regulated and controlled through tissue design logic so as to activate a Zener pinning effect and prevent austenite grains from growing. For the traction box shell casting with the wall thickness of more than 200 mm, the support of a low-temperature long-time normalizing process is lacking, austenite grains cannot be refined to be 9 grades, the yield strength and the impact toughness are limited, and the strict requirement of tough matching under working conditions cannot be met. In another patent with publication No. CN118745498A, the steel is used for large-scale low alloy steel Q460D forgings, austenite is obtained by single-stage temperature rise to 900 ℃, then water quenching is carried out, and tempering is carried out at 520-540 ℃. The scheme is suitable for common structural steel, but is directly applied to 33CrNiMo cast steel containing vanadium and aluminum, and a deeper metallurgical contradiction is exposed. Because the austenitizing temperature of 900 ℃ is far lower than the dissolution temperature of AlN (> 1100 ℃) so that AlN can still be retained, but the temperature is close to the dissolution temperature of VCN (about 950 ℃), partial undissolved phases can be dissolved in the process of preserving heat, the effects of pinning grain boundaries and inhibiting the growth of austenite grains are weakened, and in 33CrNiMo steel, the temperature can cause excessive dissolution of VCN due to local component fluctuation, and the grain boundary control is ineffective. Furthermore, the tempering temperature is 520-540 ℃, which is lower than the peak temperature range (about 550-600 ℃) of the secondary precipitation of vanadium carbide, so that the nano-grade VC precipitation phase can not be completely dispersed and precipitated, and the opportunity of secondary hardening and simultaneous strength and toughness improvement is lost. In addition, normal-temperature water without temperature control is used as a quenching medium, the fluctuation of cooling speed is large, non-martensitic transformation (such as bainite) is induced in a thick and large section, uneven hardness and structural heterogeneity are caused, and the overall service reliability of the component is greatly reduced. The key point for improving the quality of steel is heat treatment, but the existing heat treatment process cannot establish dynamic relations among chemical components, heat treatment, tissues and performances, namely the existing heat treatment process cannot grasp multiple functions of dissolution an