Method for improving hardness of martensitic stainless steel after heat treatment

Abstract

The method for improving the hardness of the martensitic stainless steel after heat treatment is suitable for heat treatment in the quenching stage, and comprises the steps that the martensitic stainless steel is subjected to heat treatment at the temperature of 1120 DEG C in the quenching process stage, the hardness of 1Cr12Ni2WMoVNbN after heat treatment can be stabilized by adjusting the quenching temperature, and the cutting efficiency of products in the cutting stage is improved; and the situation that cutting is not easy due to high hardness is avoided.

Description

Technical Field

[0001] This invention belongs to the technical field of martensitic stainless steel processing methods, and particularly relates to a method for hardening martensitic stainless steel after heat treatment. Background Technology

[0002] 1Cr12Ni2WMoVNbN is a Cr-Ni series martensitic stainless steel. It is an advanced structural steel developed from traditional 12% Cr type martensitic stainless steels (such as 1Cr13 and 2Cr13) through multi-element composite alloying design. It possesses high strength, high toughness, good corrosion resistance, and excellent heat resistance, and is widely used in the manufacture of key hot-end components for high-end equipment such as aero-engines and gas turbines. The design aims to maintain sufficient corrosion resistance and fatigue resistance while meeting high strength and toughness requirements to cope with the high-temperature, high-stress, and corrosive environments of components such as aero-engine compressor blades and discs.

[0003] However, in the existing heat treatment process, quenching at 1130±10℃ and tempering at 570-610℃ and 670-720℃ in two stages results in high hardness of 1Cr12Ni2WMoVNbN. This leads to difficulties in subsequent processing (such as cutting and drilling), rapid tool wear, increased processing costs, and reduced production efficiency, limiting its application in the production of aerospace parts where high processing accuracy and cost are required. Summary of the Invention

[0004] The present invention provides a method for hardening martensitic stainless steel after heat treatment, which solves the technical problem of low processing efficiency in existing methods. The technical solution of this invention has many beneficial effects, as described below: A method for hardening martensitic stainless steel after heat treatment, applicable to heat treatment during the quenching stage, the method comprising: heat treatment of martensitic stainless steel at 1120℃ during the quenching process stage, preferably, the quenching temperature is 1120±10℃.

[0005] Compared with the prior art, the technical solution provided by the present invention has the following beneficial effects: During the hardness check after heat treatment (quenching), the hardness of the 1Cr12Ni2WMoVNbN part was found to be too high, failing to meet the design requirement of d3.5-3.3 (HB302-341). The hardness of this product after heat treatment is higher than the design requirement of d3.5-3.3 (HB302-341). Adjusting the quenching temperature can stabilize the hardness of 1Cr12Ni2WMoVNbN after heat treatment, improve the cutting efficiency of the product during the cutting stage, and avoid the situation where the high hardness makes it difficult to cut. Attached Figure Description

[0006] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0007] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0008] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that, in the absence of conflict, the following embodiments and features in the embodiments can be combined with each other. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0009] It should be noted that various aspects of embodiments within the scope of the appended claims are described below. It will be apparent that the aspects described herein can be embodied in a wide variety of forms, and any particular structure and / or function described herein is merely illustrative. Based on this invention, those skilled in the art will understand that one aspect described herein can be implemented independently of any other aspect, and two or more of these aspects can be combined in various ways. For example, any number of aspects set forth herein can be used to implement the device and / or practice the method. Additionally, this device and / or method can be implemented using structures and / or functionalities other than one or more of the aspects set forth herein.

[0010] It should also be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. The drawings only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0011] Furthermore, specific details are provided in the following description to facilitate a thorough understanding of the examples. However, those skilled in the art will understand that aspects can be practiced without these specific details. To enable those skilled in the art to better understand the invention, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined as "first" and "second" may explicitly or implicitly include one or more of that feature. In the description of the invention, unless otherwise stated, "a plurality of" means two or more.

[0012] like Figure 1 The method described herein relates to the hardening of martensitic stainless steel after heat treatment. The martensitic stainless steel is 1Cr12Ni2WmoVNbN, and is suitable for heat treatment during the quenching stage. Traditional processes include multiple steps such as initial selection of the blank, grinding, quenching, and tempering. This invention modifies the process temperature during quenching and tempering to reduce the hardness of the product after heat treatment. Specifically, it appropriately reduces the hardness while still meeting national standard hardness requirements, facilitating subsequent cutting processes. The method includes... Martensitic stainless steel is heat-treated at 1120±10℃ during the quenching process. Preferably, the quenching temperature is 1120±10℃.

[0013] The process parameters were compiled according to Q / S12.2003-2016[E] "Technical Conditions for Forgings of 1Cr12Ni2WMoVNbN Steel". The quenching temperature was selected as 1130±10℃, resulting in a relatively high hardness after tempering. 1Cr12Ni2WMoVNbN contains a large amount of strong carbide-forming elements such as Cr, W, Mo, V, and Nb. At lower quenching temperatures, these elements form stable carbides (such as MC-type VC and NbC, and M23C6-type Cr23C6). These undissolved carbides are "pinned" to grain boundaries and within grains, preventing austenite grain growth, but their direct contribution to martensitic hardness is limited. As the quenching temperature increases, these carbides gradually dissolve into the austenite. The solubility of carbon and alloying elements (especially carbon) in austenite increases. At a temperature of 1120℃, most carbides (especially V and Nb carbides that provide secondary hardening effect) are fully dissolved, and the carbon and alloying element content in austenite reaches saturation or near saturation. When the quenching temperature exceeds 1120℃, which is above the temperature at which carbides are completely dissolved, the "pinning" effect of carbides on grain boundaries is lost, and austenite grains will grow rapidly. The coarse austenite grains will transform into coarse martensite, which will affect the hardness of the material. Excessively high quenching temperatures macroscopically make austenite overly stable, lowering its martensitic transformation initiation temperature (Ms point) and transformation completion temperature (Mf point). This results in a large amount of retained austenite in the microstructure after quenching to room temperature, which also affects the material's hardness. However, a quenching temperature of 1120±10℃ can achieve a balance between "grain refinement" and "full austenite transformation." Refined grains increase grain boundary area, hindering dislocation movement and dispersing stress concentration, allowing the steel to maintain good impact toughness (αk≥40J / cm²) while achieving high strength (tensile strength ≥1000MPa), avoiding a "strong but brittle" structure. The purpose of this method is to lay a uniform grain foundation for subsequent tempering precipitation. The uniform and fine austenite grains are transformed into a uniform martensite structure after quenching. During the subsequent tempering process, carbides (such as NbC and Mo2C) will precipitate uniformly at the martensite lath boundaries and dislocations, forming "precipitation strengthening" to further improve strength. Moreover, it will not cause the precipitates to aggregate due to uneven grains, as aggregation would reduce the strengthening effect and toughness.

[0014] In one embodiment, a tempering process is also included after the quenching stage. The tempering process adopts a one-stage heat treatment, replacing the multi-stage heat treatment. Preferably, the process temperature of the one-stage heat treatment is 670°C or 670±10°C.

[0015] Traditional tempering processes employ a two-stage tempering heat treatment with stepped temperature changes of 670 to 720℃ and 570 to 610℃, following the AETM900A-1Cr12Ni2WMoVNbN stainless steel hot-rolled and forged bar specifications. The tempering temperature parameters are (670-720℃) ±10℃ + air cooling. The corresponding hardness is d3.5-3.3 (HB302-341). When tempering at 570-610℃, a large number of extremely fine alloy carbides (such as V, Nb, Mo, and W carbides) precipitate from the supersaturated martensite, causing the hardness to increase instead of decrease, reaching the peak hardness. Tempering at 610℃ will exceed the design requirements. It is necessary to further increase the tempering temperature to 620-670℃. Tempering within this temperature range allows the material to completely surpass the secondary hardening peak and enter the "over-tempered" softening stage, where these fine carbides will begin to aggregate and grow.

[0016] This invention employs a single-stage heat treatment at 630℃, which significantly improves the product's plasticity, toughness, and high-temperature creep resistance during tempering. Within a controllable strength loss range, it achieves precise optimization of toughness, stress release, and process adaptability, avoiding second-type temper brittleness and achieving stable toughness. It also prevents intergranular brittle fracture caused by the segregation of impurity elements (P, Sn, Sb) at grain boundaries. Simultaneously, it alleviates stress concentration in the microstructure. At 630℃, the quenched martensite microstructure undergoes a full "recovery transformation," reducing dislocation density and softening martensite lath boundaries. At the same time, the residual austenite (≤5%) generated during quenching is partially stabilized (avoiding stress caused by secondary transformation after cooling). The residual stress can be reduced to 80-120 MPa. This low-stress, homogenized microstructure significantly reduces the risk of stress concentration, increases fatigue life (σ-1) by 20-30%, and effectively reduces product hardness.

[0017] To address the issue of excessively high hardness in 1Cr12Ni2WMoVNbN samples after heat treatment, tests were conducted on samples of the same material and in the same condition using the following process parameters: quenching temperature 1130℃, tempering temperature 610℃; quenching temperature 1130℃, tempering temperature 670℃; quenching temperature 1120℃, tempering temperature 610℃; and quenching temperature 1120℃, tempering temperature 630℃. The differences in hardness after heat treatment caused by four different process parameter control methods were verified, as shown in Table 1. Table 1 shows the experimental results data.

[0018] The product provided by this invention has been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this invention. The descriptions of the embodiments above are merely for the purpose of helping to understand the core ideas of this invention. It should be noted that those skilled in the art can make various improvements and modifications to the invention without departing from the principles of the invention, and these improvements and modifications also fall within the protection scope of the invention claims.

Claims

1. A method for the heat treatment of a martensitic stainless steel after hardening, suitable for the quenching phase, characterised in that, The method comprises, The martensitic stainless steel is heat treated at 1120℃ during the quenching process.

2. The method of claim 1, wherein, The quenching process temperature is 1120±10℃.

3. The method of claim 2, wherein, It also includes a tempering process after the quenching stage, which uses a one-stage heat treatment.

4. The method of claim 3, wherein, The one-stage heat treatment process temperature is 630℃.

5. The method of claim 4, wherein, The one-stage heat treatment replaces the multi-stage heat treatment.

6. The method of claim 4, wherein, The one-stage heat treatment process temperature is 630±10℃.

7. The method of claim 1, wherein, The martensitic stainless steel is 1Cr12Ni2WmoVNbN.

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