CN103966523B - A kind of superfine two-phase stainless cast steel QPQ treatment process - Google Patents

Abstract

The invention provides a kind of super duplex stainless cast steel and QPQ (Quench-thereof? Polish-Quench) treatment process, superfine two-phase stainless steel contains the composition of following weight percents: C≤0.03%, Si≤1.0%, Mn≤1.0%, Ni:5.0% ~ 7.0%, Cr:28.5% ~ 30.5%, Mo:1.7% ~ 2.5%, S, P:& lt; 0.03%, N:0.2% ~ 0.4%, remainder is iron.Material first carries out solution treatment and carries out QPQ process again.QPQ process is mainly two portions, and first part carries out Nitrizing Treatment, adopts cyanic acid root type base salt.Second section is oxide treatment.Material after QPQ process is ensureing, under conventional mechanical property, corrosion resisting property, can significantly improve wear resistance, extends material or part work-ing life, has significant economic benefit.

Description

A QPQ treatment method for super duplex stainless cast steel

technical field

The invention belongs to the technical field of duplex stainless cast steel materials, and in particular relates to a special-grade duplex stainless cast steel and a QPQ treatment method thereof.

Background technique

Duplex stainless steel refers to the type of stainless steel whose microstructure is composed of ferrite (α) and austenite (γ). Environment, such as marine, petroleum, chemical, shipbuilding and other industries. When the pitting resistance equivalent value of duplex stainless steel is PREN (pitting resistance equivalent number) ≥ 42, it belongs to super duplex stainless steel. Compared with the third-generation duplex stainless steel, it has higher strength and corrosion resistance. It is an ideal material for deep water or sea water, and it generally has no intermetallic phase in the temperature range of 500~650 °C. Precipitate. But it still has the same shortcomings as other duplex stainless steels, such as low hardness and poor wear resistance. Especially under the conditions of corrosion, wear and heavy load, etc., the service life will be significantly shortened. Therefore, it is particularly important to improve its wear resistance, which not only prolongs the service life of parts and improves resource utilization, but also has good social value and economic benefits.

QPQ (Quench-Polish-Quench) is a metal surface heat treatment technology, which is generally called QPQ salt bath composite treatment technology in China. It is a new type of salt bath composite treatment technology improved on the basis of the new pollution-free TF1 salt bath infiltration method, that is, the technology of polishing the surface of the material that has been infiltrated in the salt bath and then performing oxidation treatment. The core of QPQ technology can be said to be a low-temperature nitriding technology. At the same time, as a comprehensive metal surface strengthening method, its essence is the combination of nitriding and oxidation processes. The obtained nitriding layer structure is also a composite of nitrides and oxides. . After the material is infiltrated and oxidized, a hard and dense infiltrated layer will be formed on the surface of the material, which can significantly improve the wear resistance of the material, thereby improving the overall performance of the material. At the same time, this technology uses a green salt bath formula, which will not pollute the environment and consumes less energy. In addition, the materials processed by this technology have the advantages of beautiful appearance, small deformation, and good performance. Based on this, the technology has been widely used in automobiles, moulds, cutting tools, petroleum machinery, engineering machinery and other industries since its development. With the improvement of people's awareness of environmental protection and the goal of "building a conservation-oriented society", energy-saving, environmentally friendly, and efficient QPQ technology has attracted extensive attention from material researchers.

At present, in industrial production, some enterprises have adopted QPQ technology to improve the wear resistance of stainless steel. For example, Cummins of the United States uses QPQ technology to process engine valve material 5Cr21Mn9Ni4N (austenitic stainless steel) to increase its wear resistance under high temperature conditions. The German stretch wire machine manufacturer also uses QPQ technology to treat the hot rail material 0Cr18N12Mo2Ti (austenitic stainless steel) to improve its high temperature wear resistance. However, at present, the application reports of QPQ technology in stainless steel are mainly aimed at single-phase stainless steels such as austenitic and martensitic, and there are few reports on its application in super duplex stainless steel. Therefore, QPQ treatment on special-grade duplex stainless steel improves its wear resistance, which can not only prolong the service life of the material, reduce costs, but also further expand the application range of QPQ technology.

Contents of the invention

The purpose of the present invention is to provide a special-grade duplex stainless steel and its surface QPQ treatment method. After the special-grade duplex stainless steel material is subjected to QPQ treatment, the matrix will not precipitate harmful phases and maintain good mechanical properties and corrosion resistance. It greatly improves its wear resistance and enhances its service life in special environments, which has significant economic and social benefits.

To achieve the above object, the present invention adopts the following technical solutions:

The element composition and mass percentage of a super duplex stainless cast steel are: C≤0.03%, Si≤1.0%, Mn≤1.0%, Ni: 5.0%~7.0%, Cr: 28.5%~30.5%, Mo : 1.7%~2.5%, S, P: <0.03%, N: 0.2%~0.4%, the rest is iron.

The preparation method comprises the following steps:

(1) Pre-treatment of raw materials: All raw materials must be degreased, derusted and degassed before entering the furnace;

The raw materials and their mass fractions are: 316L stainless steel ingot or scrap 40%-50%, ferromolybdenum with molybdenum content greater than 60% 1.0%-1.3%, chromium metal with chromium content greater than 99% 18%-22% 2%-3% of electrolytic copper with a copper content greater than 99%, 3.0%-5.0% of chromium nitride with a nitrogen content greater than 9%, and the rest being industrial pure iron; the sum of the mass fractions of the raw materials is 100%;

(2) Melting in a conventional induction furnace: first add 316L stainless steel ingots or scraps for melting, then add industrial pure iron, ferromolybdenum, metallic chromium and electrolytic copper in sequence; when the temperature reaches 1600-1610°C, add 0.2% of the total mass Silicon calcium manganese for deoxidation, then add chromium nitride, then add 0.2% of the total mass of silicon calcium manganese for deoxidation, then remove impurities and measure temperature and pour, the pouring temperature does not exceed 1620 °C; the cast castings are air-cooled and then undergo solid solution treatment at 1050 °C 2h, water quenching.

The QPQ processing method of described super duplex stainless cast steel comprises the following steps:

(1) After cleaning the solid solution material with acetone and alcohol, preheat the furnace at 400°C for 0.5 hours;

(2) Next, the material is subjected to N infiltration treatment in the cyanate-type base salt in the N-infiltration furnace: the cyanate-type base salt is sodium cyanate or potassium cyanate, sodium carbonate or potassium carbonate, and sodium chloride or potassium chloride , wherein the mass content of cyanate is 33%~39%, [Na ⁺ ]/[K ⁺ ]=1:1~1:1.5, the temperature is 550-590°C, and the time is 90min-150min;

(3) After the nitrogen infiltration is completed, put the material in an oxidation furnace for oxidation treatment: the oxidized salt is a mixture of sodium nitrate and potassium nitrate, the mass ratio of the two is 1:1~1:2, the oxidation temperature is 400°C, and the time is less than 30min;

(4) Polish the oxidized material.

The remarkable advantage of the present invention is that: after the super-grade duplex stainless steel material prepared by the present invention is treated with QPQ, the matrix will not precipitate harmful phases and maintain good mechanical properties and corrosion resistance, and can also greatly improve its wear resistance and enhance Its service life under special environment has significant economic and social benefits.

Description of drawings

Fig. 1 is the metallographic diagram after the QPQ process of embodiment 1 is processed.

Fig. 2 is the metallographic diagram after being processed by the QPQ process of embodiment 2.

Fig. 3 is the metallographic diagram after being processed by the QPQ process of embodiment 3.

Fig. 4 is the metallographic diagram after being processed by the QPQ process of embodiment 4.

Fig. 5 is the metallographic diagram after being processed by the QPQ process of embodiment 5.

detailed description

The following examples describe the present invention in more detail, and these examples are only descriptions of the best implementation modes of the present invention, and do not limit the scope of the present invention in any way.

Embodiment: Molten steel is smelted in an induction furnace, poured into a melting mold shell, cleaned and processed into a test rod with a diameter of φ 22mm×220mm after cooling.

The chemical composition of the super duplex stainless steel of the present invention is shown in Table 1. Solution treatment process: heat preservation at 1050°C for 2 hours and then water quenching. The QPQ treatment process is shown in Table 2. (The example is a super duplex stainless cast steel with QPQ treatment after solution treatment, and the comparison material is a material only after solution treatment, which is called the base material). Performance comparison is shown in Table 3 (hardness is measured by microhardness tester; 1h wear is measured by ring-block wear tester; corrosion current density is measured by Tafel extrapolation method; tensile strength is measured by standard GBT228- 2002 (Metal material room temperature tensile test method) for measurement). Fig. 1-5 is the metallographic diagram after being processed by the QPQ process of embodiment 1-5.

Table 1 Material chemical composition and solid solution treatment process

According to the formula of PREN=Cr%+3.3×Mo%+30×N%, its calculated value is 43.9, which belongs to super duplex stainless steel.

Table 2 QPQ treatment process comparison table

Table 3 Performance comparison table

It can be seen from Figures 1-5 that the sample after QPQ treatment has a certain thickness of the infiltrated layer, and there is no intermetallic phase precipitation on the substrate, which will not cause deterioration of mechanical properties and corrosion resistance. It can be seen from Table 3 that although they have strong wear resistance compared with the base metal, their mechanical properties and corrosion resistance are equivalent. Therefore, the base metal can be used in strong wear and corrosion conditions after QPQ treatment.

The above descriptions are only preferred embodiments of the present invention, and all equivalent changes and modifications made according to the scope of the patent application of the present invention shall fall within the scope of the present invention.

Claims (1)

1. A special-grade duplex stainless cast steel, characterized in that: the element composition and its mass percentage are: C=0.03%, Si=0.72%, Mn=0.81%, P=0.02%, S=0.02%, Ni =6.61%, Cr=29.19%, Mo=2.11%, Cu=0.79%, N=0.26%, and the rest is iron; raw materials are firstly solid solution treated and then QPQ treated; Solution treatment includes the following steps: (1) Pre-treatment of raw materials: All raw materials must be degreased, derusted and degassed before entering the furnace; The raw materials and their mass fractions are: 316L stainless steel ingot or scrap 40%-50%, ferromolybdenum with molybdenum content greater than 60% 1.0%-1.3%, chromium metal with chromium content greater than 99% 18%-22% 2%-3% of electrolytic copper with a copper content greater than 99%, 3.0%-5.0% of chromium nitride with a nitrogen content greater than 9%, and the rest being industrial pure iron; the sum of the mass fractions of the raw materials is 100%; (2) Melting in a conventional induction furnace: first add 316L stainless steel ingots or scraps for melting, then add industrial pure iron, ferromolybdenum, metallic chromium and electrolytic copper in sequence; when the temperature reaches 1600-1610°C, add 0.2% of the total mass Silicon calcium manganese for deoxidation, then add chromium nitride, then add 0.2% of the total mass of silicon calcium manganese for deoxidation, then remove impurities and measure temperature and pour, the pouring temperature does not exceed 1620 °C; the cast castings are air-cooled and then undergo solid solution treatment at 1050 °C 2h, water quenching; QPQ processing consists of the following steps: (1) Clean the solid solution material with acetone and alcohol in sequence, and then preheat the furnace at 400°C for 0.5 hours; (2) Next, the material is subjected to N infiltration treatment in the cyanate-based salt in the N-infiltrated furnace: the cyanate-based salt is a mixture of cyanate, carbonate and chloride, and the salt is sodium salt or potassium salt, wherein the mass content of cyanate is 33%~39%, [Na ⁺ ]/[K ⁺ ]=1:1~1:1.5, the temperature is 550-590°C, and the time is 90min-150min; (3) After the nitrogen infiltration is completed, put the material in an oxidation furnace for oxidation treatment: the oxidized salt is a mixture of sodium nitrate and potassium nitrate, the mass ratio of the two is 1:1~1:2, the oxidation temperature is 400°C, and the time is less than 30min; (4) Polish the oxidized material.