CN107245555A - Improve the double tempering method of 30CrNi2MoV steel forgings low-temperature impact toughness - Google Patents

Abstract

A secondary tempering method for improving the low-temperature impact toughness of 30CrNi2MoV steel forgings, which is characterized in that the forged steel forgings are first subjected to a conventional quenching austenitization process, and then cooled to room temperature after the conventional tempering process, followed by Heat to 350°C~580°C and keep it warm for 16h, then cool it by air cooling. Compared with the conventional tempering process (600°C×16h), the grain size refinement of the present invention can greatly improve the low-temperature impact toughness of 30CrNi2MoV steel, which increases by about 40.9% from 31.7J to 43.67J. The tensile strength and elongation have little effect. The invention has a short technological process, is beneficial to reduce production costs, and can meet the manufacturing requirements of large-scale load-bearing and transmission structural components in thermal power, nuclear power and other power station equipment and large-scale metallurgy, mining and transportation equipment in China.

Description

Second Tempering Method for Improving Low Temperature Impact Toughness of 30CrNi2MoV Steel Forgings

technical field

The invention relates to a metal heat treatment method, in particular to a 30CrNi2MoV steel heat treatment method, in particular to a secondary tempering method for improving the low-temperature impact toughness of a 30CrNi2MoV steel forging.

Background technique

30CrNi2MoV steel is a medium-carbon medium-alloy steel with high hardenability and good comprehensive mechanical properties. It is often used to manufacture large forgings with high strength and toughness. It is widely used in the manufacture of thermal power, nuclear power and other power station equipment and large-scale metallurgy, mining and transportation. Load-bearing and transmission structural components in equipment.

30CrNi2MoV steel often works at lower temperatures, and has higher requirements for its low-temperature impact toughness. Generally, the austenitization process of steel materials is an important factor affecting their properties after quenching and tempering. Sub-temperature quenching can improve the low-temperature impact toughness of steel materials, but sub-temperature quenching to improve low-temperature impact toughness is usually carried out after conventional quenching, but this method of normal quenching + sub-temperature quenching to improve low-temperature impact toughness of materials involves two Independent quenching, the process is relatively complicated, and the cost is relatively high. If the low-temperature impact toughness of steel materials can be improved by cooling down to room temperature after the conventional tempering process, then heating to 350°C and holding for 16 hours in air, it undoubtedly has the advantages of relatively simple process and relatively low cost. The purpose of normal tempering here is to eliminate the internal stress of quenching, reduce brittleness, stabilize the size of forgings, adjust hardness, improve plasticity and toughness, and obtain the final mechanical properties required for forgings. Subsequent medium-temperature tempering can obtain tempered troostite, which has high elastic limit, yield strength and yield ratio, and has certain plasticity and toughness.

So far, there is no suitable method for 30CrNi2MoV steel to improve the low-temperature impact toughness of 30CrNi2MoV steel based on the conventional tempering and continuing to increase the medium temperature tempering process, which limits the improvement of the quality of 30CrNi2MoV steel and the reduction of manufacturing costs to a certain extent. .

Contents of the invention

The purpose of the present invention is to solve the problem that the present 30CrNi2MoV steel forging post-forging heat treatment has complicated technology, high cost, and unreasonable technology that affects the crystal phase structure of the finished product, and to invent a kind of slow cooling after forging, isothermal annealing, quenching and tempering. On the basis of the process, add medium temperature tempering to improve the heat treatment method of large forgings of 30CrNi2MoV steel. This method suppresses the formation of flaky retained austenite in large forgings through slow cooling after forging and isothermal annealing after forging, so as to cut off and eliminate tissue inheritance. The grains are uniformly refined by quenching, and good comprehensive mechanical properties are obtained by adding secondary medium temperature tempering and air cooling after conventional tempering.

Technical scheme of the present invention is:

A secondary tempering method for improving the low-temperature impact toughness of 30CrNi2MoV steel forgings, which is characterized in that: firstly, the forged steel forgings are subjected to a conventional quenching austenitization process, and then cooled to room temperature after the conventional tempering process is completed, followed by Second heating to 350°C~580°C and holding for 16h.

The process parameter of the conventional quenching and austenitizing treatment is 860°C×6h, which is cooled by oil cooling; the characteristic of the conventional tempering process is that the tempering process is 600°C×16h, and then the oil cooling method is adopted Allow to cool.

In the secondary tempering process, after the conventional tempering process is completed, the temperature is lowered to room temperature, and then heated to 350° C. to 580° C. and kept for 16 hours, and cooled by air cooling.

The secondary heating temperature is characterized in that the optimal temperature is 350°C.

Beneficial effects of the present invention:

(1) The present invention can significantly improve the low-temperature impact toughness of the 30CrNi2MoV steel forging while maintaining little change in its tensile strength. Compared with Example 1 and Comparative Example 1, the low-temperature impact toughness increased by 40.9%, the tensile strength decreased by only 2.7%, and the elongation increased by 3.9%.

(2) The present invention has obtained an ideal secondary tempering method for improving the low-temperature impact toughness of 30CrNi2MoV steel forgings through a large number of tests, especially obtained the best low-temperature tempering temperature of 350°C through a large number of tests, and the process according to the present invention can It is easy to improve the low temperature impact toughness of 30CrNi3MoV steel forgings.

(3) To a certain extent, the invention breaks the technical blockade of foreign countries on the heat treatment process of large-scale forgings, and can meet the manufacturing needs of large-scale load-bearing and transmission structural components in thermal power, nuclear power and other power station equipment and large-scale metallurgy, mining and transportation equipment in China .

Description of drawings

Figure 1 Example 1: 860°C×16h oil quenching, 600°C×16h oil cooling and tempering to room temperature, then heating up to 350°C for 16 hours and the metallographic structure after air cooling and tempering.

Figure 2 Comparative Example 1: Metallographic structure after oil quenching at 860°C×16h and oil cooling and tempering at 600°C×16h.

detailed description

The following is a detailed description of the embodiments of the present invention. This embodiment is implemented on the premise of the technical solution of the present invention, and detailed implementation methods and specific operating procedures are provided, but the protection scope of the present invention is not limited to the following implementation example.

Embodiment one

Heat the 30CrNi2MoV steel forging to 860°C for 6 hours, then take out the forging for oil quenching; heat the forging after oil quenching from room temperature to 600°C for 16 hours, take out the forging and cool it to room temperature, and then heat the forging again from room temperature Heat it at 350°C for 16 hours, take out the forging and cool it to room temperature in air (the grain size is shown in Figure 1, which is smaller than the grain size of the comparative example shown in Figure 2).

The 30CrNi2MoV steel forging that has been so heat-treated has a low-temperature impact toughness A _KV (-40°C) of 43.67J at -40°C, a room temperature tensile strength _Rm of _986.3MPa , and a room temperature elongation A5 of 39.1%.

Comparative example one

Heat the 30CrNi2MoV steel forgings to 860°C for 6 hours, then take out the forgings for oil quenching; heat the forgings after oil quenching from room temperature to 600°C for 16 hours, take out the forgings and cool them to room temperature (the grain size is shown in Figure 2 Shown, larger than the grain size of the embodiment shown in Figure 1).

The 30CrNi2MoV steel forging that has been so heat-treated has a low-temperature impact toughness A _KV (-40°C) of 31.7J at -40°C, a room temperature tensile strength _Rm of _1014.1MPa , and a room temperature elongation A5 of 37.63%.

The parts not involved in the present invention are the same as the prior art or can be realized by adopting the prior art.

Claims (4)

1. a kind of double tempering method of raising 30CrNi2MoV steel forgings low-temperature impact toughness, it is characterized in that first by after forging Steel forgings carry out conventional quenching austenitizing PROCESS FOR TREATMENT, are then cooled to room temperature after conventional tempering process terminates, then enter Row reheating is to 350 DEG C ~ 580 DEG C and is incubated 16h.

2. according to the method described in claim 1, it is characterized in that the technological parameter of conventional quenching austenitizing processing is 860 DEG C × 6h, cooled down by the way of oil cooling；Described conventional tempering process it is characterized in that tempering process is 600 DEG C × 16h, Then cooled down using oil cooling mode.

3. the double tempering technique described in claim 1, it is characterized in that：Room temperature is down to after the end of conventional tempering process, is connect And be heated to 350 DEG C ~ 580 DEG C and be incubated 16h, cooled down using air cooling mode.

4. the double tempering technique described in claim 1, it is characterized in that described reheating optimum temperature is 350 DEG C.