CN110586851A

CN110586851A - Cast steel coating

Info

Publication number: CN110586851A
Application number: CN201910839651.2A
Authority: CN
Inventors: 李慧; 蔡帅; 张松灿; 申德彪; 孙定云; 陈艳萍
Original assignee: Shanghai Zhuoran Engineering Ltd By Share Ltd; ZHUORAN (JINGJIANG) EQUIPMENT MANUFACTURING Co Ltd
Current assignee: Shanghai Zhuoran Engineering Ltd By Share Ltd; ZHUORAN (JINGJIANG) EQUIPMENT MANUFACTURING Co Ltd
Priority date: 2019-09-06
Filing date: 2019-09-06
Publication date: 2019-12-20

Abstract

The invention discloses a cast steel coating for a stainless steel centrifugal cast steel pipe, which can increase the thickness of a stainless steel equiaxial crystal extremely-cold layer, wherein the aggregate of the coating is zircon powder and quartz powder, and the zircon powder accounts for 20-50% of the weight of the quartz powder. Calculated by the weight of the aggregate, the solvent water accounts for 30-50%, the suspending agent CMC accounts for 1-4%, the sodium bentonite accounts for 2-5%, the inorganic adhesive silica sol accounts for 2-5%, the preservative accounts for no more than 0.1%, the defoaming agent accounts for no more than 0.01%, the tellurium powder accounts for 1.5-10%, the stainless steel powder accounts for 1-4%, and the rare earth modifier accounts for 1-3%. The coating increases the thickness of the cast steel pipe equiaxial crystal extremely-cold layer, so that part of equiaxial crystal is still remained after the extrusion blank is processed, and the qualification rate of the stainless steel extrusion pipe is greatly increased.

Description

Cast steel coating

Technical Field

The invention is applied to the field of centrifugal casting, in particular to centrifugal casting of stainless steel cast steel pipes, and relates to cast steel paint sprayed on the inner surface of a centrifugal pipe die.

Background

With the continuous progress of the technology, the production of the stainless steel seamless tube starts to perform trial production along the process route of centrifugal steel tube casting, processing, extrusion and cold rolling, and the process route is short, the metal yield is high and the production cost is low. However, in the case of austenitic stainless steel, grain size improvement cannot be performed by heat treatment, and only by hot working or cold working, the grains are deformed, thereby reducing the grain size, improving the grain size, and improving the overall properties of the stainless steel material. However, for the stainless steel centrifugal casting tube, the thickness of the extremely cold layer of the isometric crystal of the outer surface layer is thinner, the extremely cold layer is removed before extrusion, and the cast coarse dendrite is easy to crack during extrusion, so that more waste products are generated.

Disclosure of Invention

The technical problem solved by the invention is as follows: provides a cast steel coating which can improve the supercooling degree of molten steel of stainless steel, increase the thickness of an isometric crystal electrode cold layer of a cast steel pipe and avoid the generation of extrusion cracks.

The technical scheme adopted by the invention is as follows: the aggregate of the cast steel coating is zircon powder and quartz powder, and the zircon powder accounts for 20-50% of the quartz powder by weight. Calculated by the weight of the aggregate, the solvent water accounts for 30-50%, the suspending agent CMC accounts for 1-4%, the sodium bentonite accounts for 2-5%, the inorganic adhesive silica sol accounts for 2-5%, the preservative butyl p-hydroxybenzoate accounts for no more than 0.1%, the defoaming agent dimethicone accounts for no more than 0.01%, the tellurium powder accounts for 1.5-10%, the stainless steel powder accounts for 1-4%, and the rare earth modifier accounts for 1-3%.

Further, the tellurium powder accounts for 1.5-6% preferably.

The invention has the beneficial effects that: the thickness of the extremely-cold layer on the outer surface of the stainless steel cast steel pipe is increased, and a part of the isometric crystal extremely-cold layer is still remained after the stainless steel cast steel pipe is processed, so that the qualification rate of the stainless steel extruded pipe is greatly increased.

Detailed Description

When the process of 'centrifugal steel pipe casting-processing-extrusion-cold rolling' is adopted to manufacture the stainless steel seamless steel pipe, the centrifugal steel pipe needs to be processed on the inner surface and the outer surface, firstly, the surface casting defects such as slag inclusion, air holes, shrinkage cavities and the like are removed, and secondly, the requirement of the surface roughness of an extrusion blank is met. The existing coating for the cast steel pipe has the advantages that the service life of a pipe die is protected, the heat preservation performance is good, the cooling speed of stainless steel water is low, the supercooling degree of molten steel is low, an extremely cold layer on the outer surface of the cast steel pipe is thin, the extremely cold layer is completely processed and removed in the processing before extrusion, and therefore cast dendritic crystals of the stainless steel are exposed, and the dendritic crystals have directional orientation and are easy to generate deformation cracks in the subsequent extrusion process, so that the extruded pipe is scrapped.

From the results of computer simulation and actual experiments, the cooling speed of the molten steel in the pipe die is reduced, and the pipe die is protected mainly because the heat conduction capability of the coating is not the clearance between the inner surface of the pipe die and the coating in the solidification process of the molten steel, and the heat resistance generated by the clearance plays a role in protecting the pipe die. Based on the principle, the invention provides a cast steel coating which is mainly used for centrifugal casting of stainless steel cast steel pipes and can extremely chill the surface layers of the steel pipes and increase the cores of equiaxial crystal nuclei, thereby increasing the thickness of equiaxial crystal extremely cold layers. In the subsequent processing process, isometric crystals with certain thickness exist on the outer surface of the extrusion blank, so that when the stainless steel cast steel pipe is extruded, a protective layer is equivalently added on the outer surface of the stainless steel cast steel pipe, and the rejection rate of the stainless steel extrusion pipe is greatly reduced.

The aggregate of the coating adopts zircon powder and quartz powder, the lower the zircon powder is, the better the coating is from the cost perspective, stainless steel belongs to high alloy steel, the pouring temperature of the coating is 100-200 ℃ lower than that of low alloy steel and plain carbon steel, and the lower zircon powder content can also meet the requirement of refractoriness, so that the weight of the zircon powder accounts for 20-50% of the weight of the quartz powder.

In a coating configuration, solvents, suspending agents, binders, preservatives, defoamers, and the like, should also typically be included in the coating. The solvent is water or alcohol, and the safety and the economical efficiency of alcohol are different from those of water, so that the coating solvent is water. The suspending agent adopts sodium bentonite and CMC (carboxymethyl cellulose), CMC is directly mixed with water to prepare pasty glue solution for standby. CMC is used with bentonite, and the suspension property is better. In order to prevent the gas generated by the organic adhesive from causing harm to the centrifugal cast steel pipe, the adhesive is mostly inorganic adhesive, such as silica sol, glass water and the like. The preservative is a measure for preventing the paint from deteriorating at high temperature in summer, and butyl p-hydroxybenzoate is generally adopted instead of the necessity of proportioning the paint. The defoaming agent is usually dimethyl silicone oil, is used only when foams are more, and is not necessary to be compounded. Calculated according to the weight of the aggregate, the proportion of water is 30-50%, the proportion of CMC is 1-4%, the proportion of sodium bentonite is 2-5%, the proportion of silica sol is 2-5%, and the amount of preservative and defoamer is proper, and is generally not more than 0.01%.

On the basis of the above-mentioned compounding and proportioning, the tellurium powder, stainless steel powder or rare earth alterant powder are added. Tellurium is the strongest in all non-metals, has good electrical conductivity and thermal conductivity, and can extremely cool molten steel on the surface layer of stainless steel, thereby playing a role in increasing the thickness of an extremely cold layer. As the specific gravity of the tellurium powder is large, the coating added with the tellurium powder is required to be in the stirring process from the beginning of the addition until the coating is sprayed on the surface of the pipe die. The added amount of tellurium powder is 1.5-10% of the weight of the aggregate. The stainless steel powder or the rare earth alterant powder is added to increase nucleation cores, which is beneficial to the nucleation of the extremely cold layer, thereby increasing the thickness of the isometric crystal extremely cold layer. The addition amount of the stainless steel powder or the rare earth alterant powder is 1 to 4 percent of the weight of the aggregate. The content of the rare earth modifier is lower than that of the tellurium powder, because the stainless steel powder or the rare earth modifier powder plays a role in promoting the thickening of the extremely cold layer, is not a decisive role, and the cost is relatively higher.

Centrifugal casting experiments were conducted according to the coating formulations in Table 1 below, with the cast steels being 304L and 316L stainless steel, the centrifugally cast steel tubes having an outer diameter of 375mm, a thickness of 70mm, and a length of 1850 mm. The thickness of the extremely cold layer of the equiaxial crystal is measured after the macroscopic corrosion, after the macroscopic corrosion of the section of the stainless steel cast steel pipe, the equiaxial crystal on the outer layer and the columnar dendritic crystal in the equiaxial crystal have obvious boundary lines, and the thickness of the extremely cold layer can be measured.

TABLE 1 coating formulation and very Cold layer thickness

It can be seen that the key factor determining the thickness of the ultra-cold layer is the content of tellurium powder. Generally, the outer surface of the stainless steel cast steel pipe is processed by about 3mm, and casting defects can be completely removed. In rare cases, the steel needs to be processed by 5-6mm, such as eccentricity caused by poor centering on a cast steel tube lathe, poor molten steel smelting quality, poor parameter control in the pouring process and the like. Therefore, the extremely cold layer is controlled to be more than 4mm, the processing requirement of the extrusion billet can be basically met, and the processing requirement of all the extrusion billets can be met when the extremely cold layer is more than 6 mm. Therefore, the tellurium powder is preferably 1.5 to 6%.

Claims

1. The cast steel coating is characterized in that the aggregate is zircon powder and quartz powder, and the cast steel coating is prepared from the following raw materials in parts by weight: the zircon powder accounts for 20-50% of the quartz powder by weight; calculated by the weight of the aggregate, the proportion of water is 30-50%, the proportion of CMC is 1-4%, the proportion of sodium bentonite is 2-5%, the proportion of silica sol is 2-5%, the proportion of preservative is not more than 0.01%, the proportion of defoaming agent is not more than 0.01%, the proportion of tellurium powder is 1.5-10%, the proportion of stainless steel powder is 1-4%, and the proportion of rare earth modifier is 1-3%.

2. The cast steel coating of claim 1, wherein: the tellurium powder accounts for 1.5-6%.