CN110205543B

CN110205543B - Casting method of high-strength austenitic stainless steel cast

Info

Publication number: CN110205543B
Application number: CN201910450466.4A
Authority: CN
Inventors: 李永新; 马进; 冯周荣; 纳学洋; 赵建东; 李阳
Original assignee: Kocel Steel Foundry Co Ltd
Current assignee: Kocel Steel Foundry Co Ltd
Priority date: 2019-05-28
Filing date: 2019-05-28
Publication date: 2021-08-24
Anticipated expiration: 2039-05-28
Also published as: CN110205543A

Abstract

The invention relates to a casting method of a high-strength austenitic stainless steel casting for a large steel casting, which comprises the following steps of firstly, carrying out optimal design on a steel casting material according to standard components of the steel casting, and finally, carrying out optimal design on alloy components of stainless steel according to the mass percentage: 0.045-0.07 percent of C, 0.8-1.2 percent of Si, 0.8-1.2 percent of Mn, less than or equal to 0.025 percent of P, less than or equal to 0.015 percent of S, 18.5-19.5 percent of CrN, 9.2-10.8 percent of Ni9, 0-0.07 percent of N, 0.1-0.5 percent of Mo, and the balance of inevitable impurity elements and Fe, wherein the total percentage of all elements is 100; smelting materials and sand casting of the steel casting according to the optimized alloy components, performing high-temperature boxing after the materials are solidified and cooled to 1000-800 ℃, performing primary sand cleaning treatment, performing rapid circulating water cooling when the temperature of the steel casting is higher than 800 ℃, transferring the steel casting into a heating furnace, heating to 1040-1060 ℃, preserving heat for 10-30 min, and discharging and quenching. The casting method improves the strength and the plasticity and toughness of the casting through the optimized design of the alloy elements of the casting and the improvement of the casting after pouring and the heat treatment process.

Description

Casting method of high-strength austenitic stainless steel cast

Technical Field

The invention relates to the technical field of high-strength alloy steel casting production, in particular to a casting method of a high-strength austenitic stainless steel casting for a large steel casting.

Background

In the prior art, an austenitic stainless steel casting product with a material mark ZG08Cr18Ni9 comprises the following alloy element components in percentage by mass according to the mark in the national standard GB/T2100: c is less than or equal to 0.08, Si is less than or equal to 1.5, Mn = 0.8-2.0, P is less than or equal to 0.040, S is less than or equal to 0.030, Cr: 17.0 to 20.0, Ni: 8.0-11.0, and the balance of iron (Fe) and inevitable impurities. At the same time, the tensile strength is required according to the national standardRm is more than or equal to 441MPa, and yield strength Rp_0.2196MPa or more, the elongation A is 25% or more, the reduction of area Z is 32% or more, and the room temperature impact toughness value akv is 98J/cm or more²The impact energy AKV2 is about 200J. The prior requirement of a large-scale steel casting is that the austenitic stainless steel casting is delivered after quenching and solid solution, the tensile strength Rm is more than or equal to 485MPa, and the yield strength Rp_0.2205MPa or more, the elongation A is more than or equal to 25 percent, the reduction of area Z is more than or equal to 32 percent, and the impact AKV2 at the temperature of minus 150 ℃ is more than or equal to 78J. Compared with the national standard, the tensile strength requirement of the product is improved by 44 MPa, and the yield strength is improved by 9 MPa. The test detection temperature of the impact energy is adjusted by more than one hundred degrees, and other mechanical properties are not changed greatly.

And (3) casting the alloy components, cooling the whole casting after casting, pre-cleaning, and carrying out quenching and solution treatment. In the actual production process, through the adjustment production of components and a heat treatment process, the index that the tensile strength of the cast steel product is required to be more than or equal to 485MPa after solid solution is difficult to realize, even though the test improvement is carried out by adopting different quenching media (tap water and saline water), stirring and cooling speeds and heat preservation time, although the strength is improved, the tensile strength is basically 440-475 MPa, the yield strength is 185-240 MPa (under the condition of 80 percent, the yield strength can meet more than or equal to 205MPa, 20 percent of the product yield strength can still reach not 205 MPa), the elongation is 50-65 percent, the reduction of area is 64-85 percent, the room-temperature AKV2 can reach 160-180J, and the temperature AKV2 at-150 ℃ can reach 100-120J. Therefore, the tensile strength is an index that needs to be improved by taking relevant measures urgently.

As for the austenitic stainless steel cast piece, because the cast structure is mainly austenite, and the structure is also austenite after cooling to the room temperature after quenching and solution dissolving, the austenitic stainless steel cast piece cannot be strengthened by heat treatment phase transformation, and the strength of the cast piece is improved. Generally, austenitic stainless steels are strengthened by cold working alone, i.e., strain hardened, to improve strength. For austenitic stainless steel with the same grade, the strength values of the materials such as bars, wires, plates, strips, wires and forgings after deformation hardening are obviously higher than those of castings. However, for large steel castings, it is impossible to achieve strengthening by cold work deformation hardening and also impossible to achieve strengthening by phase transformation. Therefore, how to obtain high strength and ensure higher ductility and toughness of the austenitic stainless steel castings with larger tonnage in the component range required by the standards becomes a key for influencing the quality of the large-scale steel castings.

Disclosure of Invention

The invention provides a casting method of a high-strength austenitic stainless steel casting aiming at the requirements of high strength and high toughness of a medium-sized steel casting in the prior art, and the casting strength and the plastic toughness are improved through the optimized design of alloy elements of the steel casting and the improvement of a casting after pouring and a heat treatment process.

The invention aims to realize the purpose, and the casting method of the high-strength austenitic stainless steel casting comprises the following steps of firstly, optimally designing the material of the casting, wherein the material of the casting is optimally designed by the following alloy components in percentage: c is less than or equal to 0.08, Si is less than or equal to 1.5, Mn0.8-2.0, P is less than or equal to 0.040, S is less than or equal to 0.030, Cr: 17.0 to 20.0, Ni: 8.0-11.0, and the balance of Fe and inevitable impurities, wherein the total amount of each element is 100; the method is characterized in that the optimization design process of the steel casting material is as follows: the content of ferrite in an alloy structure is 0-5%, the ratio Nieq/Creq of nickel equivalent Nieq to chromium equivalent Creq is = 0.62-0.68, and the alloy components of the stainless steel after the final optimized design comprise the following components in percentage by mass: 0.045-0.07 percent of C, 0.8-1.2 percent of Si, 0.8-1.2 percent of Mn, less than or equal to 0.025 percent of P, less than or equal to 0.015 percent of S, 18.5-19.5 percent of CrN, 9.2-10.0 percent of Ni9, 0-0.07 percent of N, 0.1-0.5 percent of Mo, and the balance of inevitable impurity elements and Fe, wherein the total percentage of all elements is 100; smelting materials and sand casting of the steel casting according to the optimized alloy components, performing high-temperature boxing when the temperature is reduced to 1000-800 ℃ after solidification, hanging the steel casting out of a sand box, performing primary sand cleaning treatment, performing water cooling when the temperature of the steel casting is ensured to be higher than 800 ℃, transferring the steel casting into a heating furnace, heating to 1040-1060 ℃, preserving the temperature for 10-30 min, and discharging and quenching.

The casting method of the high-strength austenitic stainless steel cast steel piece of the invention adaptively controls the ferrite content to be 0-5% in the austenitic stainless steel structure under the condition of ensuring the mechanical property and the service property of the material, utilizes the stainless steel structure diagram and the values of nickel equivalent Nieq and chromium equivalent Creq to optimally design the content of each relevant alloy element, simultaneously appropriately controls the content of Mn and Si to reduce the non-metal inclusion characteristics, reasonably adjusts the nickel-chromium equivalent ratio, finally optimally designs the alloy elements, avoids the coarse grains of the cast steel piece and prevents the precipitation of harmful phases such as carbide and the like through high-temperature flask beating and rapid circulating water cooling after pouring and condensing, prevents the cracking of the later-stage cast piece, lays the foundation for preventing the coarse grains of the later-stage cast piece from solid solution, controls the quenching solid solution bonding temperature of the cast piece to be in the middle-lower limit of 1040 ℃ -1060 ℃, and keeps the temperature for short time to prevent the growth of the grains from quenching and solid solution, can effectively improve the strength of the casting and keep higher plastic toughness. The tensile strength of the large steel casting is basically 490-535 MPa, the yield strength is 210-240 MPa, the elongation is 50-65%, the reduction of area is 64-75%, the room temperature AKv2 can reach 160-180J, and the temperature AKv2 at-150 ℃ can reach 100-120J. Completely meets various performance requirements of large austenitic stainless steel castings with higher strength.

Further, the optimization design method of the alloy components comprises the following steps: according to the formulas of nickel equivalent Nieq and chromium equivalent Creq given in a stainless steel organizational chart, Nieq = Ni +30(C + N) +0.5Mn, Creq = Cr + Mo +1.5Si +0.5Nb, respectively substituting the upper limit value and the lower limit value of the percentage content of each corresponding alloy element into the formulas of nickel equivalent Nieq and chromium equivalent Creq to obtain a marking point a corresponding to the nickel equivalent Nieq and chromium equivalent Creq of each upper limit value and a marking point C corresponding to the nickel equivalent Nieq and chromium equivalent Creq of each lower limit value, framing a Creq region abcd by taking the point a and the point C as two opposite corner points of a cabinet shape in the stainless steel organizational chart, further selecting a Creeq region and a Creq region corresponding to the ferrite content of 0-5%, wherein the Nieq value range corresponding to the region is 12.8-14.0, the q range is 20.0-21.0, and the Nieq/0.68 percent of the non-metal inclusions and the non-metal inclusions are reduced by 1.8-1 percent, finally, the mass percentage content of the optimized austenitic non-cast steel piece is confirmed.

Further, the temperature rising process of the cast steel in the heating furnace comprises the following steps: heating to 800-850 ℃ at a heating rate of 60-80 ℃/h, heating to 1040-1060 ℃ at a long heating rate of 100-120 ℃/h, keeping the temperature for 10-30 min, and discharging for quenching.

Further, the quenching method comprises the steps of cooling the steel casting by circulating water, wherein the circulating water temperature is 10-30 ℃, the quenching intensity H of water is 1.5-2.0, and after the steel casting is cooled to be less than 200 ℃, the casting is lifted out of the water surface and is naturally cooled to the normal temperature.

In order to ensure the uniformity of the temperature in the furnace in the heating process, the deviation between the highest value and the lowest value in the heating furnace and the average temperature value is less than 14 ℃ at the same time in the temperature rising process of the steel casting.

In order to facilitate the monitoring of the surface temperature of the steel casting, at least two thermocouples for detecting the temperature of the steel casting are arranged on the surface of the steel casting.

Drawings

FIG. 1 is a structural diagram of stainless steel involved in the casting method of a high-strength austenitic stainless steel cast piece according to the present invention.

Detailed Description

According to the stainless steel structure diagram shown in fig. 1, the requirement that the Nieq range corresponding to the ferrite content of about 0-5% is 12.8-14.0, the Creq range is 20.0-21.0, Nieq/Creq = 0.62-0.68 is met, meanwhile, the content of Mn and Si is controlled within 0.8-1.2, the content of nonmetallic inclusions is reduced, and the chemical composition (mass percentage) of the casting is finally adjusted to be as follows: 0.045-0.07 of C, 0.8-1.2 of Si, 0.8-1.2 of Mn, less than or equal to 0.025 of P, less than or equal to 0.015 of S, 18.5-19.5 of Cr and 9.2-10.0 of Ni, and in order to adjust the equivalence ratio and increase the strength of the material, the N content is properly added and controlled to be 0.015-0.07 to homogenize the components of molten steel, 0.1-0.5 of Mo, and the balance of impurity elements and Fe, and the total amount is 10O.

On the basis of the finally optimized alloy element range, a large-scale steel casting product is smelted and poured for many times according to the element content described in the examples 1-5 and the comparative examples 6-9 of the table 1, a casting test block is attached, high-temperature boxing is carried out when the temperature is reduced to 1000-800 ℃ after solidification, preliminary sand removal treatment is carried out, the steel casting is immersed in a tap water tank when the temperature of the steel casting is ensured to be higher than 800 ℃, rapid circulating stirring and water cooling are carried out, the steel casting is cooled to be lower than 100 ℃, then further sand removal treatment is carried out, a runner and a core bone notification paving auxiliary component are cut off, the steel casting is transferred into a heating furnace to be heated to 1040-1060 ℃ and is kept warm for 10-30 min, and then the steel casting is taken out of the furnace for quenching. The specific boxing and heat treatment processes for each example are described in table 2.

In order to ensure that at least two thermocouples are attached to the surface of a casting for temperature measurement in the processes of temperature reduction and heat treatment, the steel casting is immersed into a tap water tank for continuous cooling in the process of temperature reduction and quenching cooling after boxing, the temperature of the tap water is controlled to be between 10 and 30 ℃, and the quenching intensity H of water is 1.5 to 2.0. (the quenching intensity H is a relative value, the cooling capacity of static water at 18 ℃ is taken as a standard, H =1.0, when H is more than 1, the cooling capacity of the medium is larger than that of water or faster than that of static water, for example, H = 1.4-1.5 under good stirring) after the casting is cooled to the temperature of less than 100 ℃, the casting is lifted out of the water surface for natural cooling. And then carrying out metallographic structure detection and mechanical property detection on the casting attached casting test block. The test results are shown in the following table 3, wherein the quality percentage ratios of the alloy elements determined according to the requirements of the method of the invention in examples 1-5 and the properties of the final castings meet the requirements after heat treatment, and the properties of the final castings do not meet the structure and performance indexes required by the invention due to the overrun of the ratio of the individual key alloy elements in the comparative examples 6-9.

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Claims

1. A casting method of a high-strength austenitic stainless steel cast steel piece comprises the following steps of firstly, optimally designing the material of the cast steel piece, wherein the material of the cast steel piece is optimally designed by the following alloy components in percentage: c is less than or equal to 0.08, Si is less than or equal to 1.5, Mn0.8-2.0, P is less than or equal to 0.040, S is less than or equal to 0.030, Cr: 17.0 to 20.0, Ni: 8.0-11.0, and the balance of Fe and inevitable impurities, wherein the total amount of each element is 100; the method is characterized in that the optimization design process of the steel casting material is as follows: the content of ferrite in an alloy structure is 0-5%, the ratio Nieq/Creq of nickel equivalent Nieq to chromium equivalent Creq is = 0.62-0.68, and the alloy components of the stainless steel after the final optimized design comprise the following components in percentage by mass: 0.045-0.07 percent of C, 0.8-1.2 percent of Si, 0.8-1.2 percent of Mn, less than or equal to 0.025 percent of P, less than or equal to 0.015 percent of S, 18.5-19.5 percent of CrN, 9.2-10.8 percent of Ni9, 0.015-0.07 percent of N, 0.1-0.5 percent of Mo, and the balance of inevitable impurity elements and Fe, wherein the sum of the percentage of the elements is 100; smelting materials and sand casting of the steel casting according to the optimized alloy components, performing high-temperature boxing after the materials are solidified and cooled to 1000-800 ℃, performing primary sand cleaning treatment, performing rapid circulating water cooling when the temperature of the steel casting is higher than 800 ℃, transferring the steel casting into a heating furnace, heating to 1040-1060 ℃, preserving heat for 10-30 min, and discharging and quenching.

2. The method of casting a high strength austenitic stainless steel cast according to claim 1, wherein the optimal design method of the alloy composition is: according to the formulas of nickel equivalent Nieq and chromium equivalent Creq given in the stainless steel texture map, Nieq = Ni +30(C + N) +0.5Mn, Creq = Cr + Mo +1.5Si +0.5Nb, the upper limit value and the lower limit value of the percentage content of each corresponding alloying element are respectively substituted into the formulas of nickel equivalent Nieq and chromium equivalent Creq, obtaining a marking point a corresponding to the nickel equivalent Nieq and the chromium equivalent Creq of each upper limit value and a marking point c corresponding to the nickel equivalent Nieq and the chromium equivalent Creq of each lower limit value, a cabinet-shaped area abcd is outlined by two diagonal points which take a point a and a point c as a cabinet shape in the stainless steel structural diagram, further selecting a Nieq area and a Creq area corresponding to the area with the ferrite content of 0-5%, the value range of Nieq corresponding to the area is 12.8-14.0, the value range of Creq is 20.0-21.0, and meanwhile, the percentage content of Mn and Si is adjusted to 0.8-1.2 to reduce nonmetallic inclusions, and finally, the mass percentage content of the optimized austenite non-cast steel piece is determined.

3. The method for casting a high-strength austenitic stainless steel cast according to claim 1, wherein the cast is rapidly cooled to room temperature by circulating water, and then each part of the cast is cleaned again and the casting system is cut off.

4. The method of casting a high strength austenitic stainless steel cast according to claim 1, wherein the temperature raising process of the cast in the heating furnace is: heating to 800-850 ℃ at a heating rate of 60-85 ℃/h, heating to 1040-1060 ℃ at a long heating rate of 100-120 ℃/h, keeping the temperature for 10-30 min, and discharging for quenching.

5. The casting method of the high-strength austenitic stainless steel cast steel according to claim 1, wherein the quenching method comprises the steps of cooling the cast steel by circulating water, wherein the circulating water temperature is 10-30 ℃, the quenching intensity H of the water is 1.5-2.0, and after the cast steel is cooled to be less than 100 ℃, lifting the cast steel out of a water surface and naturally cooling to normal temperature.

6. The method of casting a high strength austenitic stainless steel cast according to claim 3, wherein the deviation of the highest and lowest values from the average temperature value in the furnace at the same time is less than 14 ℃ during the temperature rise of the cast in the furnace.

7. The method of casting a high strength austenitic stainless steel cast according to claim 3, wherein the surface of the cast is provided with at least two thermocouples for detecting the temperature of the cast.