CN101851699A

CN101851699A - Method for manufacturing carbide-free bainite low-temperature cast steel

Info

Publication number: CN101851699A
Application number: CN 201010203003
Authority: CN
Inventors: 黄岩
Original assignee: Dalian Maritime University
Current assignee: Dalian Maritime University
Priority date: 2010-06-12
Filing date: 2010-06-12
Publication date: 2010-10-06
Anticipated expiration: 2030-06-12
Also published as: CN101851699B

Abstract

The invention provides a method for manufacturing carbide-free bainite low-temperature cast steel. The cast steel is prepared by the steps of performing medium-temperature quenching and high-temperature tempering on the following materials in weight percentage: 0.03 to 0.05 percent of carbon, 0.1 to 0.5 percent of silicon, 0.4 to 0.6 percent of manganese, less than 0.03 percent of sulfur, less than 0.03 percent of phosphor, 5.0 to 6.0 percent of nickel, 0.1 to 0.2 percent of molybdenum and the balance of iron. In medium-temperature quenching, the rest austenite is completely converted into martensite without residual austenite, so that the bainite tissue with excellent comprehensive mechanical properties is obtained, and the reliability for the steel when being used at low temperature is fundamentally determined.

Description

The manufacture method of carbide-free bainite low-temperature cast steel

Technical field

The present invention relates to the manufacture method of Cryogenic Steel, in particular, the present invention relates to have the manufacture method of the low-temperature cast steel of carbide-free Bainite.

Background technology

Both at home and abroad to low-temperature steel research more be stocking, study lessly to the casting material.Compare with the casting material with regard to stocking, under same chemical ingredients and heat treated condition, the performance of casting material is lower than stocking.The crystal grain of as cast condition steel is thicker, and its as-cast structure often occurs as casting flaws such as shrinkage cavity, shrinkage porosite, tiny cracks, and these factors all can make the mechanical property reduction of steel.This phenomenon not only exists at normal temperatures, exists equally under cold condition.Be applied to many low temperature mechanical means of industrial sectors such as oil, chemical industry, metallurgy, have the parts of special shape, can only could prepare by Foundry Production as pump, valve, pipeline and container etc.Used casting low-temperature steel generally adopts Chromiumnickel Austenite Stainless Steel both at home and abroad.Such steel grade has good low-temperature toughness, but yield strength is low.Bainite with the tough and soft ferrite matrix of hard phase martensite strengthening has the excellent comprehensive performance, becomes the potential alternative steel grade of austenite low-temperature cast steel.Yet carbide in the bainitic steel and residual austenite can reduce the low-temperature performance of low-temperature steel greatly under the low-temperature working condition.

Huangyan, black ancestral elder brother is in the 29th volume the 2nd phase Dalian Maritime University's journal (article numbering: delivered the paper of " non-carbide bainitic steel low-temperature flexibility " by name 1006-7736 (2003) 02-0075-03), wherein disclose a kind of residual austenite and carbide, obdurability overall target bainite structure preferably that do not have.Yet its manufacture method but is not disclosed so far as know-how.

Summary of the invention

The present invention aims to provide the manufacture method of the bainite low-temperature cast steel of the good comprehensive low temperature mechanical property of having of carbides-free and residual austenite.

Technical scheme of the present invention is as follows:

The manufacture method of the carbide-free bainite low-temperature cast steel that the contriver provides is to have the material of following compositions, and the mode of temperature quenching+high tempering is carried out the cast steel manufacturing in the employing,

Carbon 0.03%～0.05%

Silicon 0.1%～0.5%

Manganese 0.4%～0.6%

Sulphur is less than 0.03%

Phosphorus is less than 0.03%

Nickel 5.0%～6.0%

Molybdenum 0.1%～0.2%

Iron all the other

The above per-cent all is weight percentage;

Its gordian technique is:

1. warm quenching temperature is 850 ℃ in described, and medium is a water, 25 ℃～65 ℃ of water temperatures;

2. described high tempering temperature is 700 ℃.

Adopt the low-temperature cast steel of aforesaid method gained to see Table 1 in the data of normal temperature and low temperature impact test,

Table 1 normal temperature and low-temperature impact toughness

Temperature/℃	Room temperature	??-12	??-25	??-35	??-50	??-80
Temperature/℃	Room temperature	??-12	??-25	??-35	??-50	??-80	Impact toughness/J	??10.60	??10.48	??10.15	??9.36	??7.35	??5.66

Can be drawn by the test-results in the table 1, under the low-temperature working condition, the impact toughness of carbide-free bainite low-temperature cast steel is greater than the index of the impact toughness 2.07J of general in the world charpyV type notched impact specimen.In the time of-80 ℃, the impact toughness of carbide-free bainite low-temperature cast steel is greater than 2 times of the minimum requirements impact toughness.The steel that are used for low temperature machinery, most important mechanical performance index is an impact toughness.The impact toughness of carbide-free bainite low-temperature cast steel is fit to be applied in the toughness index with steel of low temperature range more than-80 ℃.

Table 2 is the tension test data that adopt the low-temperature cast steel of aforesaid method gained,

Table 2 tensile property

Tensile strength б _b/MPa	Elongation δ/%	Relative reduction in area ψ/%
Tensile strength б _b/MPa	Elongation δ/%	Relative reduction in area ψ/%	??750	??17.4	??63.8

By the test-results in the table 2 as can be known, this carbide-free bainite low-temperature cast steel at normal temperatures, its intensity index (б _b) reached the index (б of the highest casting carbon steel ZG55 of intensity _b〉=650MPa), and its plasticity index (δ ψ) then reaches or near the index (δ of the best casting carbon steel ZG15 of plasticity ₅〉=25%, ψ 〉=40%).

In the foundry goods, though the few stable residual austenite have an impact toughness that helps improve low-temperature cast steel, in case can under the worst cold case condition, change into martensite by this part residual austenite, will produce tiny crack in its vicinity, these tiny cracks will reduce the impact toughness of steel greatly.Can draw the low-temperature cast steel X-ray diffraction analysis that adopts the aforesaid method gained, not have residual austenite to exist in the carbide-free bainite low-temperature cast steel.Temperature was quenched during the thermal treatment process of carbide-free bainite low-temperature cast steel of the present invention adopted 850 ℃, and medium is a water, 25 ℃～65 ℃ of water temperatures; 700 ℃ of high temperings, and when alloy designs, the content of carbon is controlled at 0.03%～0.05% scope, obtained the ideal tissue of no residual austenite after Overheating Treatment.Fundamentally determined the reliability that this steel grade uses at low temperatures.

Description of drawings

Fig. 1 is the microstructure of the carbide-free bainite low-temperature cast steel that makes of the method for the invention.

Wherein the secret note piece is martensite, and the informal voucher piece is ferrite, and this is typical bainite structure, does not find the existence of carbide. Bainite is a kind of more special microscopic structure. Carbide-free bainite low-temperature cast steel is crossed and is chilled to middle temperature area in heat treatment process, and this process can be to occur with the isothermal form, also can adopt the mode of continuous cooling. Can see that from the microscopic structure of carbide-free bainite low-temperature cast steel the bainite of carbide-free bainite low-temperature steel forms with diffusion way, has incoherent interface. The quench hot temperature has guaranteed carbon atom when diffusion coefficient is very large, from α mutually precipitation, the boundary by ferrite Ovshinsky body spreads to austenite, has formed by lath ferrite folder to be changed the martensite that forms by rich carbon austenitic. Austenite all is transformed into martensite, has guaranteed that fundamentally microscopic structure is stable when the low-temperature working state.

Embodiment

The manufacture method of carbide-free bainite low-temperature cast steel is to have the material of following compositions, and the mode of temperature quenching+high tempering is carried out the cast steel manufacturing in the employing,

Carbon 0.03%～0.05%

Silicon 0.1%～0.5%

Manganese 0.4%～0.6%

Sulphur is less than 0.03%

Phosphorus is less than 0.03%

Nickel 5.0%～6.0%

Molybdenum 0.1%～0.2%

Iron all the other

The above per-cent all is weight percentage; Warm quenching temperature is 850 ℃ in described, and medium is a water, 25 ℃～65 ℃ of water temperatures; Described high tempering temperature is 700 ℃.

Claims

1. the manufacture method of carbide-free bainite low-temperature cast steel is to have the material of following compositions, and the mode of temperature quenching+high tempering is carried out the cast steel manufacturing in the employing,

Carbon 0.03%～0.05%

Silicon 0.1%～0.5%

Manganese 0.4%～0.6%

Sulphur is less than 0.03%

Phosphorus is less than 0.03%

Nickel 5.0%～6.0%

Molybdenum 0.1%～0.2%

Iron all the other

The above per-cent all is weight percentage;

It is characterized in that:

Warm quenching temperature is 850 ℃ in described, and medium is a water, 25 ℃～65 ℃ of water temperatures;

Described high tempering temperature is 700 ℃.