CN102534419A - Super-martensitic stainless steel and preparation method thereof - Google Patents

Abstract

The invention relates to super-martensitic stainless steel and a preparation method thereof, and belongs to the field of steel materials. The super-martensitic stainless steel comprises the following chemical components in percentage by mass: 0 to 0.03 percent of C, 0 to 0.03 percent of N, less than 0.015 percent of S, less than 0.020 percent of P, less than 1 percent of Si, less than 1 percent of Mn, 13 to 16 percent of Cr, 4 to 6 percent of Ni, 1 to 2 percent of Mo, 0.05 to 0.15 percent of Nb, 0.001 to 0.01 percent of Ti and the balance of Fe. The preparation method comprises the following steps of: smelting by using a vacuum induction furnace to obtain a casting blank which meets the requirements of chemical component ranges, performing hot forging at the temperature of 1,200 DEG C, performing hot rolling at the temperature of between 1,100 and 1,200 DEG C, performing solid solution treatment at the temperature of between 1,050 and 1,100 DEG C for 0.5 to 1 hour, performing air cooling and normalizing treatment, tempering at the temperature of between 550 and 700 DEG C for 2 to 4 hours, and performing oil cooling to room temperature. The super-martensitic stainless steel has high strength and toughness and high local corrosion resistance.

Description

A kind of super martensitic stainless steel and preparation method thereof

technical field

The invention belongs to the field of iron and steel materials, and in particular relates to a super martensitic stainless steel and a preparation method thereof.

Background technique

Super martensitic stainless steel is an ultra-low carbon soft martensitic stainless steel developed on the basis of traditional martensitic stainless steels such as 1Cr13 and 2Cr13 by reducing carbon content and increasing nickel and molybdenum content. This type of stainless steel has good hardenability, excellent room temperature and low temperature mechanical properties, corrosion fatigue strength and dynamic and static fracture toughness, good casting, forging, welding and machining and other cold and hot process performance, widely used in nuclear power engineering construction, Construction of large water turbines and high-pressure water pumps, oil extraction and other energy fields. The good performance of this type of steel is not only due to its improved chemical composition, but also to its special heat treatment system. After solution treatment and normalizing, it becomes a lath martensite structure. When it is tempered at a temperature above A _c1 , part of the martensite undergoes reverse transformation to form austenite that can be partially stable during subsequent cooling to room temperature. Finally, Lath martensite + reversed austenite dispersed between and inside martensite laths is obtained. Although the existence of reversed austenite is the key to the good ductility, fatigue performance and weldability of this type of stainless steel, it also greatly reduces the strength of this type of stainless steel. At the same time, although the carbon content of this type of martensitic stainless steel is low, there are still Cr carbides precipitated at the boundaries and inside of the martensitic lath during tempering, resulting in the depletion of Cr around the precipitates and destroying the stainless steel. corrosion performance.

In recent years, nitrogen, as an austenite forming element, has been widely used in austenitic stainless steel and duplex stainless steel, which not only improves the strength of stainless steel but also significantly improves the corrosion resistance of stainless steel. There are also patents and some domestic manufacturers use nitrogen alloying to improve the strength and corrosion resistance of super martensitic stainless steel. However, due to the extremely low solubility of nitrogen in martensitic stainless steel, N and Cr combine to form Cr during heat treatment. The nitrides also cause the depletion of Cr around the precipitates and damage the corrosion resistance of martensitic stainless steel. For this reason, some manufacturers use microalloying elements Nb, V and N to compound microalloying, aiming to rely on the stronger combination of microalloying elements Nb and V with C and N than Cr and C and N to make the microalloying elements In the heat treatment process, it is the first to combine with C and N in the steel to form microalloying element carbonitride to improve the strength, and inhibit the precipitation of Cr carbonitride to improve the corrosion resistance of stainless steel. However, high nitrogen content often leads to the appearance of coarse microalloying element carbonitrides. At the same time, due to the low thermodynamic stability of microalloying element V carbonitrides, it is easy to coarsen during heat treatment, which not only cannot effectively improve stainless steel. In addition, these designs do not consider the ratio between nitrogen and microalloying elements, and the added microalloying elements cannot completely inhibit the precipitation of Cr nitrides during heat treatment, so they cannot effectively improve stainless steel. corrosion resistance.

Contents of the invention

Aiming at the problems existing in the prior art, the present invention provides a super martensitic stainless steel and a preparation method thereof. This method prepares a super martensitic stainless steel material with high strength, high toughness and good resistance to localized corrosion by controlling the content of C and N in the steel and adding microalloying elements Nb and Ti.

The chemical composition of the super martensitic stainless steel of the present invention is: C: 0~0.03%, N: 0~0.03%, S<0.015%, P<0.020%, Si<1%, Mn<1% , Cr: 13~16%, Ni: 4~6%, Mo: 1~2%, Nb: 0.05~0.15%, Ti: 0.001~0.01%, and the balance is Fe.

The preparation method of super martensitic stainless steel of the present invention, carries out according to the following steps:

(1) Vacuum induction furnace is used to melt the super martensitic stainless steel billet meeting the requirements of the above chemical composition range, the martensitic stainless steel billet is hot forged at 1200°C, and then hot rolled at 1100°C~1200°C;

(2) Perform solution treatment on the hot-rolled super martensitic stainless steel plate, the solution treatment temperature is 1050 ° C ~ 1100 ° C, the treatment time is 0.5 ~ 1h, normalize after solution treatment, and air cool to room temperature;

(3) Temper the solid-solution super martensitic stainless steel plate at 550°C~700°C for 2~4h in a box-type resistance furnace, and cool it to room temperature with oil to obtain tempered super martensitic stainless steel.

The invention relates to a super martensitic stainless steel and a preparation method thereof. By controlling the content of C and N in the steel, a certain mass fraction of Nb, a microalloying element capable of forming carbonitrides with high thermodynamic stability with C and N, is added at the same time. Ti, so that it is the first to combine with residual C and N in the steel during heat treatment to form nano-scale microalloying element carbonitrides in a diffuse distribution, which can not only effectively improve the strength of super martensitic stainless steel, but also effectively inhibit the corrosion caused by Cr The precipitation of carbonitrides leads to the generation of Cr-depleted areas around the precipitates, thereby improving the pitting corrosion resistance of super martensitic stainless steel. After the super martensitic stainless steel of the present invention is processed by the above scheme, the yield strength at room temperature is in the range of 700~1000MPa, the tensile strength is in the range of 900~1050MPa, and the elongation at break is in the range of 17~21%. The corrosion potential is in the range of 90~260mV, with high strength, high toughness, and good resistance to localized corrosion.

Detailed ways

The present invention will be described below through different embodiments. The present invention is not limited to these embodiments, and can be implemented with adjustments within the scope of the aforementioned chemical components and manufacturing methods.

Example 1

The chemical composition obtained by melting in a vacuum induction furnace is C: 0.008%, N: 0.009%, S: 0.007%, P: 0.010%, Si: 0.39%, Mn: 0.63%, Cr: 13.35%, Ni: 4.35%, Mo : 1.08%, Nb: 0.11%, Ti: 0.008%, super martensitic stainless steel billet with Fe balance. After hot forging at 1200°C, and then hot rolling at 1200°C. In the heat treatment furnace, the hot-rolled super martensitic stainless steel plate is subjected to solution treatment. The solution treatment temperature is 1100°C, and the treatment time is 0.5h. After tempering at 550°C for 2 hours in oil-cooled type resistance furnace, the yield strength at room temperature is 920MPa, the tensile strength is 1030MPa, the elongation is 17.22%, and the Charpy V-shaped notch impact absorption energy is 145J. The pitting potential is 125mV; after tempering at 700°C for 2h oil cooling, the yield strength at room temperature is 700MPa, the tensile strength is 900MPa, the elongation is 17.44%, and the Charpy V-notch impact absorption energy is 150J. The pitting potential in 3.5% NaCl brine is 80mV; after tempering at 600°C for 2 hours, the best comprehensive strength, toughness and corrosion resistance can be obtained, the yield strength is 930MPa, the tensile strength is 980 MPa, and the elongation is 19.68 %, the Charpy V-notch impact absorption energy is 160J, and the pitting potential in 3.5%NaCl brine reaches 90mV.

Example 2

The chemical composition obtained by melting in a vacuum induction furnace is C: 0.016%, N: 0.025%, S: 0.012%, P: 0.009%, Si: 0.34%, Mn: 0.78%, Cr: 14.86%, Ni: 5.35%, Mo : 1.55%, Nb: 0.080%, Ti: 0.0065%, super martensitic stainless steel billet with Fe balance. After hot forging at 1200°C, and then hot rolling at 1150°C. In the heat treatment furnace, the hot-rolled super martensitic stainless steel plate is subjected to solution treatment. The solution treatment temperature is 1050°C, and the treatment time is 0.8h. After tempering in a box-type resistance furnace at 550°C for 4 hours and oil cooling, the yield strength at room temperature is 940 MPa, the tensile strength is 1040 MPa, the elongation is 18.62%, and the Charpy V-notch impact absorption energy is 150J. The pitting potential in salt water is 190mV; after tempering at 700°C for 2h oil cooling, the yield strength at room temperature is 720MPa, the tensile strength is 920MPa, the elongation is 17.11%, and the Charpy V-notch impact absorption energy is 155J. The pitting potential in 3.5% NaCl brine is 170mV; after tempering at 600°C for 2 hours, the best comprehensive strength, toughness and corrosion resistance can be obtained, the yield strength is 940MPa, the tensile strength is 1000MPa, and the elongation is 19.40%. , Charpy V-shaped notch impact absorption energy is 160J, and the pitting potential in 3.5%NaCl brine is 175mV.

Example 3

The chemical composition obtained by melting in a vacuum induction furnace is C 0.028%, N: 0.015%, S: 0.004%, P: 0.018%, Si: 0.68%, Mn: 0.48%, Cr: 12.91%, Ni: 5.65%, Mo: 2.05%, Nb: 0.075%, Ti: 0.0043%, super martensitic stainless steel billet with Fe balance. After hot forging at 1200°C, and then hot rolling at 1100°C. In the heat treatment furnace, the hot-rolled super martensitic stainless steel plate is subjected to solution treatment. The solution treatment temperature is 1050°C, and the treatment time is 1h. After tempering at 575°C for 2 hours in an electric resistance furnace, the yield strength at room temperature is 980 MPa, the tensile strength is 1030 MPa, the elongation is 19.65%, and the Charpy V-shaped notch impact absorption energy is 165J. The pitting potential is 240mV; after tempering at 650°C for 2h oil cooling, the yield strength at room temperature is 720MPa, the tensile strength is 950MPa, the elongation is 21.05%, and the Charpy V-notch impact absorption energy is 190J. The pitting potential in 3.5% NaCl brine is 250mV; after tempering at 600°C for 2 hours, the best comprehensive strength, toughness and corrosion resistance can be obtained, the yield strength is 960MPa, the tensile strength is 1010 MPa, and the elongation is 19.38 %, the Charpy V-notch impact absorption energy is 160J, and the pitting potential in 3.5%NaCl brine reaches 260mV.

Claims (2)

1. super martensitic stainless steel is characterized in that said stainless chemical constitution is by mass percentage: C:0 ~ 0.03%, and N:0 ~ 0.03%, S < 0.015%; < 0.020%, < 1%, Mn < 1% for Si for P; Cr:13 ~ 16%, Ni:4 ~ 6%, Mo:1 ~ 2%; Nb:0.05 ~ 0.15%, Ti:0.001 ~ 0.01%, surplus is Fe.

2. the preparation method of super martensitic stainless steel as claimed in claim 1 is characterized in that carrying out according to following steps:

(1) adopt vacuum induction melting to be met the super martensitic stainless steel strand of above-mentioned chemical ingredients area requirement, with the Martensite Stainless Steel strand 1200 ℃ of forge hots, hot rolling in 1100 ℃ ~ 1200 ℃ scopes again;

(2) the super martensitic stainless steel plate after the hot rolling is carried out solution treatment, solid solution temperature is 1050 ℃ ~ 1100 ℃, and the treatment time is 0.5 ~ 1h, carries out normalizing treatment after the solution treatment, and air cooling is to room temperature;

(3) the super martensitic stainless steel plate of the solid solution attitude after utilizing chamber type electric resistance furnace with normalizing treatment is at 550 ℃ ~ 700 ℃ scope tempering 2 ~ 4h, and oil cooling is to room temperature, obtains the super martensitic stainless steel after the temper.